WO2000035513A2

WO2000035513A2 - Neonatal blood pump

Info

Publication number: WO2000035513A2
Application number: PCT/IB1999/002120
Authority: WO
Inventors: Claude F. Mondiere
Original assignee: Mondiere Claude F
Priority date: 1998-12-17
Filing date: 1999-12-17
Publication date: 2000-06-22
Also published as: EP1141547A1; CA2312298A1; AU4255100A; WO2000035513A3

Abstract

A peristaltic pump employs a tensioner to add additional stretch to a distensible, compliant segment of tubing stretched around pin rollers mounted (120) degrees apart on a rotating wheel just before stretch is released on the segment as the wheel rotates. The release creates a pressure wave giving a pulsatile flow. The tubing is not compressed against a raceway, but is tensioned against rollers restricting the lumen of the tubing where it is stretched across the rollers. This feature allows the stretched tubing to function as a capacitance reservoir, eliminating the need for upstream and downstream reservoirs. The volume of blood in the header tubing varies according to available venous return. When outflow obstruction occurs, blood accumulates in the header tubing. As the tubing distends, it becomes progressively less occlusive, so that over pressure is avoided. When the obstruction is released, blood flows downstream rapidly propelled by the large stroke volume of the distended header tubing. The tubing is never totally occlusive, so that negative pressure, blood cell lysis and degassing do not occur.

Description

NEONATAL BLOOD PUMP

Field of the Invention

This invention relates to pumps used in the circulation of blood from the body for treatment and return back into the body, a process called extracorporeal perfusion, and more particularly, relates to peristaltic pumps for extracorporeal perfusion that are characterized by non-occlusion of the blood flow path by the pump.

Background of the Invention

Extracorporeal perfusion is used for the most part in cardiac bypass surgery. In a total bypass, all the patient's systemic venous return blood is diverted from the right side of the heart into an extracorporeal circuit, emptying the chambers of the heart. The circuit includes a heart-lung machine that comprises a pumping function and an oxygenation function, completely taking over cardiopulmonary function for the patient, returning oxygenated blood to the aorta. In a partial bypass only a portion of the blood is diverted to the extracorporeal circuit, the remaining flow passing to the lungs and from the lungs through the coronary and systemic arterial circulation. Partial bypass usually is temporarily used following total bypass surgery to slowly give the heart work to do, measurely decreasing flow through the heart-lung machine, until the heart is weaned from assist and can fully take over its pumping role.

Some procedures using blood pumps in extracorporeal circulation do not include an oxygenation function. These include cardiac assist procedures. In these, the blood pump provides higher systemic blood pressure and more blood flow than can be provided by a failing heart. A "fem-fem" (femoral vein to femoral artery) circuit is commonly used. Cardiac assist is also sometimes used if, after open heart surgery, the left side of the heart — responsible for pumping to the body oxygenated blood returned from the lungs — does not resume its pumping role despite attempts at weaning. If other assist circulatory devices (such as an intra-aortic balloon) are unsuccessful, the left heart may be bypassed to the aorta by cannulation of the left atrium, with the blood that has been oxygenated by the lungs being withdrawn through the cannula and pumped to the aorta extracorporeally without extracorporeal oxygenation. Another use of extracorporeal circulation is for "extracorporeal membrane oxygenation" known by its acronym "ECMO." As opposed to the more conventional extracorporeal circulation in substitution or assist of the cardiac function, ECMO connotates the application of such support to supply oxygenation where the native lungs are compromised. This is especially useful for neonates or premature birth babies whose life is threatened because their immature lungs cannot provide adequate gas exchange. The extracorporeal circulation provides oxygenated blood to the infant lungs under the impetus of the infant's native heart and gives time to allow healing of the lungs to occur until the lungs can take over oxygenation. In excess of 1,000 ECMO procedures are conducted annually in the United States.

The basic components of the extracorporeal circuit for a conventional heart-lung machine are one or more venous cannulas, a venous reservoir, an oxygenator and heat exchanger, a pump, an arterial line filter, an arterial cannula, and a control module. The ECMO system includes a blood pump, a membrane oxygenator, a countercurrent heat exchanger to warm the blood, and a control module. In the typical extracorporeal circuit, deoxygenated blood drains by gravity into the circuit and flows into the venous reservoir, usually placed 25 to 30 inches below the plane of the great veins. If the oxygenator is a bubble type, the reservoir is incorporated into a oxygen-blood mixing chamber. In any case, the reservoir is placed upstream to the pump, for reasons amplified below, to prevent negative pressure in the inlet line. A water heat exchanger is used for the perfusate to control body temperature. Blood filters are used to trap particulate and gaseous emboli.

The arterial cannula is usually placed in the ascending aorta but can be placed downstream in the arterial system where the vessel is large enough to accommodate the necessary flow.

About 2 liters of priming solution are required to prime the extracorporeal system for adults. Priming solution usually consists of a balanced saline solution. Blood is not added to the system unless the patient is anemic. The normal adult has about a gallon of blood (3.785 L) in systemic circulation. Dilution from the priming solution reduces the patient's hematocrit (a measure of the content of red blood cells) from the normal 40-45% range to 20-25%. Red blood cells are the respiratory messengers of the blood circulatory system, carrying oxygen to cells and CO₂ from cells. Thus respiratory capacity is reduced about 50%) in the adult during an extracorporeal circulation procedure, and hematocrit has to be watched carefully.

The blood pump is the "heart" of the extracorporeal perfusion circuit. In general, extracorporeal circulation systems use two either an occlusive compression roller pump or a noncompressive centrifugal pump. Both produce continuous flow rates on the order of several liters per minute, thus apply well to adult usage requirements.

The extracorporeal circuit pump most used is the occlusive compression roller pump. The roller pump consists of two rollers, 180 degrees apart, that rotate in a circle through a half circular raceway. A length of tubing between 1/4 and 5/8 inch inner diameter is placed between the rollers and the raceway. The rollers rotating in a circular movement compress the tubing against the raceway, squeezing the blood ahead of the rollers. The rollers are set to almost completely occlude the tubing, and operate essentially as a positive displacement pump, each passage of a roller through the raceway pumping the entire volume of the fluid contained in the tubing segment between the rollers. As a positive displacement pump, high positive pressures can be generated at the pump outlet and high suction (negative) pressures at the pump inlet. The inlet suction initiates the filling of the extracorporeal circuit but presents a hazard — fluid degassing, rupture of blood cells and collapse of the thin-walled great veins around the cannula, thereby obstructing flow —that is avoided through the use of the venous reservoir. The venous reservoir gives capacitance to the suction line and prevents the risk of imbalance between suction and discharge volumes, but at a cost of additional priming volume.

The high outlet positive pressures caused by occlusive compression of the tubing present the risk of sudden excessive downstream pressure if a restriction occurs in the circuit tubing downstream from the pump as can happen if the line is stepped on in the operation room. This has the potential for rupture of the tubing or separation of connectors from the tubing, producing a "blowout", perfusate loss from the circuit, and cessation of blood flow to the patient, with fatal implications. Another risk with the occlusive compression pump is that the work applied on the tubing creates a friction that causes the abrasion and wear of the tube. This wear also can cause accidental rupture. The abrasion can cause "spallation" or interior shedding of small particles that if returned to the native circulatory system can cause emboli formation.

Numerous surgical services limit the complications derived from occlusive compression pumps by using a non-compressive pump of the centrifugal type. Centrifugal pumps rapidly rotate an impeller in a stationary blood compartment. The impeller may be a series of blades that push the blood forward, or it may be nested concentric cones of increasing diameter to propel the blood forward by centrifugal force. Flow is a function of outflow line pressure in nested concentric cone centrifugal pumps, so these pumps have advantage over the bladed impeller centrifugal pumps and the roller pumps, namely, the nested concentric cone centrifugal pumps do not produce high back pressures when the downstream tubing is temporarily obstructed. But, both bladed impeller and nested concentric cone centrifugal pumps can produce negative pressure when inflow is impeded. All centrifugal pumps require a significant acceleration of blood flow to maintain a constant flow as outlet pressure is increased. The liquid circulation rate in the heads of centrifugal pumps range from 2000 to 4000 revolutions per minute.

Centrifugal pumps represent most of the market for non-occlusive pumps. These pumps require the blood of the patients to have an ideal viscosity. The flowing of the fluids at 3,000 rpm through the head of the pump can produce the formation of aggregates, especially in the case of hyperinosemia. The interventions can only be for a short period of time and it is difficult to adapt them to low volume requirements. Furthermore, the cost of pump heads is very high, which limits their use to high budget services. As in the case of compression pumps, they require constant monitoring in order to avoid the complications of the venous return flow, and they must be fitted with a safety reservoir and a filter to prevent reinjection complications. As mentioned above, the total volume of foreign fluid required for extracorporeal circulation with included venous reservoirs is high, reducing respiratory capacity about 50% in an adult during an procedure. This is exacerbated by hemolysis that occurs with the use of either compression occlusive pumps or centrifugal pumps. The occlusion in compression roller pumps and the centrifugal forces imparted by centrifugal pumps hemolyzes blood cells, which is reflected by a depression of the hematocrit already lowered by dilution, as described above. This effect, if material, has to be corrected by infusion of foreign packed blood cells or blood transfusions to maintain physiological respiration as safe levels.

At least partially because of the inherent limitations of these continuous flow systems, current guidelines in the United States do not allo continued use of extracorporeal circulation for more than 6 to 10 hours. This eliminates the employment of these systems for sustained blood oxygenation and/or pumping to allow damaged or compromised lung and cardiac tissues to have enough time to heal and regain their physiological power.

The continous flow systems described above were designed for open heart surgery on adults. There is a critical need for improvement of extracorporeal circulation systems for non-adults, who are a large part of the cardiac surgery population . Some form of congenital heart disease occurs in about one in 100 new born, amounting to about 30,000 annually in the United States. Defects can include incorrectly formed valves, septal defects, and abnormal connections of the arteries and veins. Correction of these defects requires open heart surgery. Correction of congential heart defects is the third most common open heart surgery procedure, amounting to about 5% of the approximately 700,000 open-heart surgeries performed worldwide each year, slightly more than half of which are in the United States.

The above described continuous flow systems produce continuous flow rates in the order of several liters per minute, responding to requirements of adult usage and older pediatric children. These systems are applied for children through the miniaturization of the same designs. They respond to downsizing less well for the youngest pediatric children and older babies, poorly for infants, and not at all for the prematurely born neonates ("premies") of low and very low birthweight. This is partially a matter of patient blood volume available for dilution and circulation extracorporeally and partially a matter of the inherent limitations and risk factors implicit in these continuous flow systems. Whereas a normal adult has about a gallon of blood (about 3875 ml blood) with which to afford a 50% dilution of oxygen carrying capacity caused by the priming volume needed with the continuous flow extracorporeal circuit, infants that weigh about 3 kg (6-8 pound range) have only about 1 kg or 1000 ml of blood volume. The high total volume of liquid required for the continuous flow extracorporeal circulation that requires admixing with fluids foreign to the patient, especially where blood transfusions are needed, is especially dangerous in the new born, who have little or no developed immunities. Downsizing of the adult continuous flow extracorporeal circuitry designs runs into critical limits for neonates of low body weight nearer 2 kg (4.4 pounds), and is not feasible for neonates that have a birthweights as small as 1 kg (2.2 pounds). These latter premies have a blood volume of only about 300 ml. All the systems in use in the United States and Europe require a priming volume that exceeds 300 ml to such an extent that the requisite dilution for an extracorporeal circulation system for a premie would be fatal.

In consequence, numerous heart surgery procedures are delayed until the child is capable of withstanding the extracorporeal circulation. This delay can be fatal but if not it can also cause irreversible brain damage. The sooner heart or lung malformation corrections are performed, the more efficient they are. In the case of fetal distress or of an accident during the birthing delivery, the early administration of cardiorespiratory assistance can allow for a treatment without after-effects. Premies and neonates need the time for lung development that can be afforded by ECMO extracorporeal circulation lung assist techniques. But by the time premies of this size reach the weight (at least 2 Kg or 4.4 pounds) when they can be put on an ECMO assist, if they have survived that long, the artificial forced ventilation imposed on them in the meantime often has damaged the lung tissue past restorative healing.

Currently there is a demand for a blood pump that is capable of treating newborn in order to repair congenital malformations and to treat accidents that require short or long term cardiopulmonary assistance. Not mentioned above, because it does not fall into the categories of continuous flow characteristic of the pumps used in the United States, is the peristaltic pump. One such pump, originally designed for use in hemodialysis, is a pump invented by A. Sausse, described in U.S. Patent 3,748,323, incorporated herein by reference.

In U.S. Patent 5,069,661, the Sausse pump is combined in a circuit with a membrane oxygenator of particular degassing design. U.S. Patents 5,222,880, 5,281,112 and 5,342.182 describe peristaltic pumps in an extracorporeal circuit that do not adhere to the principles of the Sausse pump, using instead a naturally occluded or collapsed line. U.S. Patent 5,486,099 uses a peristaltic pump preceded by a normally collapsed line that functions as a capacitance reservoir. Use of the Sausse type pump for ECMO in normal birthweight infants and babies is described by Chevalier, J.Y., Durandy Y.. Batisse A. et al., Preliminary Report: Extracorporeal Lung Support for Neonatal Acute Respiratory Failure." Lancet 1990. vol. 335, pp 1364-1366; and by Trittenwein, G.. Furst, G.. Golej et al. Preoperative ECMO in Congenital Cyanotic Heart Disease Using the AREC System,'^'' Ann. Thorac Surg 1997, vol. 63, pp 1298-1302.

Lastly, it is to be noted that the natural circulation in newborn is driven by a wave- motion. This motion is created by the transmission of the systolic discharge through the arterial walls. This pulse wave is necessary to ensure the secretion of endothelial cells to prevent thrombogenesis and ensure the proper oxygenation of the tissue. The continuous flow systems and the Suisse type pump do not furnish the needed pulsewave needed for the newborn.

There are a few prototypes of pulsed flow pumps which achieve said flow through a flap or valve that is often of porcine origin. The results are satisfactory but their use is very delicate and requires specialized personnel. These pumps cannot be used outside of services that have a significant monitoring structure in place.

Summary of the Invention

This invention provides a method and a pump for providing pulsatile flow in a return line of an extracorporeal circuit. The method comprises

(a) stretching a portion of a distensible shape compliant first tubing around pin rollers mounted 120 degrees apart on a rotating wheel to restrict the lumen of the tubing where it is stretched across the rollers,

(b) restraining the first tubing at a proximal end thereof and at a distal end thereof to maintain a selected degree of tension for the compliance of the first tubing, the proximal end having an inlet and the distal end having an outlet, (c) connecting the inlet of the proximal end of the first tubing to second tubing that comprises the receiving line of the extracorporeal circuit at the distal end of the second tubing and connecting the outlet of the distal end of the first tubing to third tubing that comprises a return line of the extracorporeal circuit at the proximal end of the third tubing,

(d) receiving extracorporeal fluid in circuit to fill the circuit with the fluid,

(e) rotating the wheel to advance the rollers in a circular direction proceeding from near the proximal end of the first tubing to near the distal end of the first tubing, thereby defining successively segments of the first tubing between leading and trailing pairs of the rollers, each leading roller forming the trailing roller of the rotationally preceding segment, each segment containing a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of the first tubing, and

(f) imparting additional stretch to the distal end of the first tubing to narrow the passageway therethrough when the leading roller of a segment is near the point of release of contact with the first tubing before the contact is released, whereby upon the release of the contact the bolus in the segment released by the leading roller is driven through the narrowed passageway, thereby accelerating flow of the released bolus through the passageway and creating a pulsatile wave in the return line greater than afforded by the first tubing upon the release absent the additional stretch. The stretched first tubing functions as a capacitance reservoir, eliminating the need for upstream and downstream reservoirs as used in occlusive and centrifugal pumps. This allows use of a very small volume of fluid in an extracorporeal circuit, making it a useful pump in an extracorporeal circuit suitable for neonates. The stretched tubing is never totally occlusive, so that negative pressure and degassing do not occur. Accordingly, the pump is self-regulating and is remarkably safe.

The magnitude of the pulse wave of the pulsatile flow is managed by controlling the amount of additional stretch imparted to the distal end of the first tubing. The stroke volume of each the bolus is controlled by selecting the diameter of the wheel and the radial distance of the pin rollers from the axis of the wheel, by selecting the first tubing according to the size of its relaxed cross section and the compliance of the tubing, by adjusting the restraint imposed on the first tubing to increase or decrease the stretch tension across the portion of tubing, by adjusting the restraint imposed on the first tubing to increase or decrease the stretch tension across the portion of tubing. The flow rate of the extracorporeal circulation is controlling by regulating the speed of rotation of the wheel relative to the stroke volume. By selecting the appropriate wheel diameter, roller pin radial distance, compliance and relaxed cross section of the first tubing, and by adjustment of restraint of the tubing a stroke volume of 1 to 5 ml with a flow rate of 50 to 750 ml at an RPM up to 50 is afforded by the invention.

This invention creates the conditions of the blood circulation in the newborn through the generation of a pulsed flow rate. The unique nature of this invention is derived from the fact that, on one hand, the desired flow rate is produced by adjusting the tension of the line, among other factors as above described, and, on the other hand, the ejection volume is propelled so as to have the required force to transmit a pulse wave during the reinjection of the fluid into the receiving vessel of the neonate patient.

The pump of this invention for non-occlusively pumping perfusion fluids in an extracorporeal circuit, comprises: (a) at least one pair of stacked discs each on the same axis, each disc axially separated to form a carrier wheel ,

(b) at least three pin rollers rotatably mounted between a first and second disc of the carrier wheel, each pin roller being mounted on a roller axis parallel to and equidistant from the carrier wheel axis, spaced 120 degrees apart, for rotation both about the axis of the carrier wheels and the axis of the individual roller,

(c) a flexible distensible compliant first tube of selected relaxed cross section and having a proximal with an inlet and distal end with an outlet,

(d) flexible second and third tubing each of a relaxed cross section smaller than the relaxed cross section of the first tubing, the second tubing having a distal end with an outlet and the third tubing having a proximal end with an inlet,

(e) a first tubing connector having a central bore for connecting the inlet in the proximal end of the first tubing to the outlet in the distal end of the second tubing,

(f) a second tubing connector having a central bore for connecting the outlet in the distal end of the first tubing to the inlet in the proximal end of the third tubing,

(g) a yoke including at least a pair of openings for receiving and holding the first and second connectors below the carrier wheel and between each disc of the wheel, (h) an adjuster for vertically adjusting the yoke relative to the axis of the wheel for retaining the first tubing in tension with a portion of the first tubing stretched around the pin rollers, restricting the lumen of the first tubing where it is stretched across the rollers,

(i) a rotator for rotating the carrier wheel about the carrier wheel axis to cause the rollers to advance in a circular direction proceeding from near the proximal end of the first tubing to near the distal end of the first tubing, thereby defining successively segments of the first tubing between leading and trailing pairs of the rollers, each leading roller forming the trailing roller of the rotationally preceding segment, whereby each segment can contain a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of the first tubing on filling of the extracorporeal circuit with fluid, (j) an indicator on the wheel and an indication receptor spaced from the indicator and responsive to the indicator to signal when the indicator is at a position indicating that the leading roller of a segment of the first tubing is near the point of release of contact with the first tubing before the contact is released, and (k) a tensioner responsive to the signal for imparting additional stretch to the distal end of the first tubing to narrow the passageway therethrough when the leading roller of the segment is near the point of release of contact with the first tubing before the contact is released, whereby upon the release of the contact the bolus in the segment released by the leading roller is driven through the narrowed passageway, thereby accelerating flow of the released bolus through the passageway and creating a pulsatile wave in the third tubing line greater than afforded upon the release absent the additional stretch. In accordance with the invention, the roller is longitudinally arcuate in the direction of the roller axis, with a larger diameter intermediate opposite ends of the roller than the diameter of the roller at the ends of the roller. The roller pins are stainless steel and have a surface polished to a mirror finish, and are supported on sealed ball bearings. The polishing reduces contact friction with the first tubing, diminishing greatly wear that could lead to accidental rupture of the tubing. The first tubing preferably is ovoid in relaxed state and radially and longitudinally shape memory compliant. This shape of the first tubing makes it possible to apply a maximum effort on the center of such tubing, thus creating, from the tubing-roller contact, a restriction that is capable of segmenting the first tubing into separate fluid filled compartments without full compression of the tubing as in a roller pump, yet at the edges of the roller, where diameter of the roller is smaller than intermediate the ends of the roller, leaving channels allowing blood cells to be centrifugally displaced from the center of the tubing to the channels without lyotic compression of the cell membranes by the contact impress of the roller on the tubing at the restriction. The channels also provide fluid communication with adjacent segments of the first tubing.

The bore of the second connector increases in diameter smoothly in a manner to avoid eddying and provide laminar flow from the second tubing into the first tubing, and the bore of the third tubing connector decreases in diameter smoothly in a manner to avoid eddying and provide laminar flow from the first tubing into the third tubing. The connectors suitably and preferably each include an external circumferential rigid flange intermediate its their ends. The yoke cooperates with the flanges for holding the first tubing in tension with the portion of the first tubing stretched around the pin rollers according to the adjustment of the adjuster.

The rotator of the pump includes a drive shaft connectable with the carrier wheels and a motor for rotationally driving the drive shaft, and further comprises a controller operatively associated with the motor for controlling the rotational speed of the motor, and a speed selector operatively associated with the controller for generating a selected speed signal signifying a selected rotational speed for the carrier wheels.

The pump suitably has a cover for the carrier wheels supported by the frame, and .comprising a power source to the rotator and circuitry including a switch connection of the power source to the rotator, a sensor for determining presence of an electically conductive fluid on the yoke, and circuitry connecting the sensor to the switch, to disconnect the power source from the rotator when an electrically conductive fluid is sensed on the yoke by the sensor. Suitably for use in a biventricular extracorporeal flow circuit and other uses as as later described herein, the pump of this invention also may comprise a third disc on the same axis as the first carrier wheel axially spaced from the first disk, thereby providing a second carrier wheel on the same axis, the second carrier wheel having at least three pin rollers rotatably mounted between the third disc and the first disc of the first wheel, each pin roller being mounted on a roller axis parallel to and equidistant from the carrier wheel axis and spaced 120 degrees apart and 60 degrees apart from the pin rollers in the first carrier wheel, for rotation both about the axis of the carrier wheels and the axis of the individual second wheel roller, for rotation both about the axis of the carrier wheels and the axis of the individual roller. The pump further accordingly includes: a flexible distensible compliant fourth tubing of selected relaxed cross section and having a proximal with an inlet and distal end with an outlet: flexible fifth and sixth tubing of smaller cross section than the cross section of the fourth tubing, the fifth tubing having a distal end with an outlet and the sixth tubing having a proximal end with an inlet, a third tubing connector having a central bore for connecting the inlet in the proximal end of the fourth tubing to the outlet in the distal end of the fifth tubing, and a fourth tubing connector having a central bore for connecting the outlet in the distal end of the fourth tubing to the inlet in the proximal end of the sixth tubing. The yoke of the pump relatedly will then include at least a pair of openings for receiving and holding the third and fourth connectors below the carrier wheel and between each disc of the second wheel, and the adjuster will vertically adjust the yoke relative to the axis of the wheel for retaining the fourth tubing in tension with a portion of the fourth tubing stretched around the pin rollers of the second wheel, restricting the lumen of the fourth tubing where it is stretched across the rollers. The rotator will also rotate the second carrier wheel about the carrier wheel axis to cause the rollers on the second wheel to advance in a circular direction proceeding from near the proximal end of the fourth tubing to near the distal end of the fourth tubing, thereby defining successively segments of the fourth tubing between leading and trailing pairs of the rollers with 60 degrees of separation from the segments of the first tubing, each leading roller forming the trailing roller of the rotationally preceding segment of the fourth tubing, whereby each segment can contain a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of the fourth tubing on introduction of extracorporeal fluid into the fifth tubing.

In the biventricular mode for which the second carrier wheel is suitable, there is no need to increase the tension of the fourth tubing because pulsatile flow is no as important as in the arterial circuit. Optionally, however, the embodiment of the pump with the second wheel may include an indicator in relation to the second wheel and an indication receptor spaced from the indicator and responsive to the indicator to produce a second signal when the indicator is at a position indicating that the leading roller of a segment of the fourth tubing is near the point of release of contact with the fourth tubing before the contact is released, and a tensioner responsive to the second signal for imparting additional stretch to the distal end of the fourth tubing to narrow the passageway therethrough when the leading roller of the segment of the fourth tubing is near the point of release of contact with the fourth tubing before the contact is released, whereby upon the release of the contact the bolus in the segment of the fourth tubing released by the leading roller is driven through the narrows of the passageway by rebound compliance of the released segment, thereby accelerating flow of the released bolus through the passageway and creating a pulsatile wave in the sixth tubing line greater than afforded by the rebound compliance of the fourth tubing upon the release absent the additional stretch.

This invention is capable of being used for newborn extracorporeal circulation on a routine basis. It makes it possible to consider new therapies in diverse fields ranging from perinatology, such as for the treatment of fetal distress or the performance of bivalve heart interventions in newborn, to the treatment of refractory cardiac insufficiency or acute respiratory insufficiency.

Brief Description of the Drawings Fig. 1 is a perspective view of the pump of this invention.

Fig. 2 is a left side elevational view of the pump of Fig 1.

Fig. 3 is a side view in partial cross section of the adjuster depicted in Figs 1 and 2.

Fig. 4 is a cross sectional view of the roller and spacer of a carrier wheel seen in Fig. 2. Fig. 5 is a frontal elevation of the pump with the front carrier wheel seen in Figs 1 and 2 removed, showing a first position of the sole carriage wheel.

Fig. 6 is a frontal elevation of the pump as in Fig. 5, showing a second position of the sole carriage wheel.

Fig. 7 is a frontal elevation of the pump as in Fig. 5, showing a third position of the carriage wheel of this invention.

Fig. 8 is a frontal elevation of the pump as in Fig. 5, showing a fourth position of the carriage wheel of this invention.

Fig. 9 is a frontal elevation of the pump as in Fig. 5, showing a fifth position of the carriage wheel of this invention. Fig. 10 is a frontal elevation of the pump as in Fig. 5. showing a sixth position of the carriage wheel of this invention.

Fig. 1 1 is a cross section of the tubing depicted in Fig. 5 along the line 1 1-1 1.

Fig. 12 is a cross section of the tubing depicted in Fig. 5 along the line 1 1 -and a portion of a roller as seen along line 4-4. Fig. 13 is a larger view in partial section of a portion of the left end of the yoke seen in Fig. 5.

Fig. 14 is the same view as Fig. 13.

Detailed Description of the Preferred Embodiment

Referring to Fig. 1, the pump of this invention is indicated by the reference numeral 10 and comprises a shockproof sealed case 12 on a frame support (not shown).

Case 12 contains a geared motor (not shown) and pump regulation and control components. A shaft (not shown) of the motor projects along an axis 14 at the front face 16 of the case 12 supported by a sealed joint located between the inner face (not shown) and front outer face 16 of the case 12.

A power supply battery pack (not shown) auxiliary to line power for the pump unit is of the type that is used with any device that operates in a mobile vehicle, whether or not motorized, in a room, or outdoors, on land or in the air. This power supply must provide said device with sufficient independent power to allow its use in all emergency systems that may require the patient to be moved.

The shaft on axis 14 supports a single carrier wheel 18 and optional second carrier wheel 20. A pair of stacked discs 22 and 24 are axially spaced on shaft 14 by spacers 26 or keys (not shown) or any other device capable of maintaining an equal distance on the shaft between the opposing surfaces of the two discs 22 and 24. the separated discs forming the carrier wheel 18. The optional second carrier wheel 20 shown in Figs. 1 and 2 is formed in the same manner as with carrier wheel 18, with a third disc and spacers 30 The rotor is attached to the shaft by a locking mechanism not shown.

The diameter of the rotors when the pump suitably is in the range from about to about , if used for infants and neonates, suitably is from about to about cm. This latter diameter corresponds generally to about 25% of the average skull diameter of infants and neonates for which this invention may be used (these are neonates ranging in birth weight from about 1 Kg to about 5 Kg).

Each carrier wheel 18 and 20 has at least three rollers (indicated as rotors A. B and C in Figs. 5 et seq.) that move in a circle on the periphery of wheel. The rollers are mounted on an axis (indicated in all cases by the reference numeral 30) that moves in a rotary pattern generated by a set of ball bearings 32 running in a raceway case 34. The rollers A, B and C consist of a hard, preferable stainless steel, sleeve with a smooth, preferably mirror finish at the surfaces 36 thereof. The smooth finish prevents any friction produced by the contact with the first tube 38 and any abnormal wear that could cause the accidental rupture of said first tube 38. The rollers A, B and C are placed with a spacing of 120° on each wheel, and 60° from one wheel to the other. Rollers A. B and C are also characterized by an arcuate surface that makes it possible to separate a volume defined between two rollers. The central diameter 40 of each roller is greater than the diameter of the roller ends 42 and 44.

Each wheel supports a flexible first tube (38 on wheel 18) (46 on wheel 20) that is sometimes referred to herein as a pump body. Each pump body has a portion stretched over the pin rollers (see at Figs 5-10 and 12), restricting the lumen 50 of the first tubing pump body 38. 46 where it is stretched across the rollers (A, B C) when stretch is imposed as described hereinbelow.

Flexible second and third tubing bodies 60, 62 for respecαvely admitting and receiving extracorporeal fluid to the first tubing or pump body 38, each of a relaxed cross section smaller than the relaxed cross section of first tubing or pump body 38, are connected to pump body 38. Second tubing body 60 has a distal end 61 with an oudet and diird tubing body 62 has a proximal end 63 with an inlet. A first tubing connector 66 has a central bore for connecting the inlet in the proximal end 68 of the first tubing 60 to the oudet in the distal end 61 of the second tubing 60. A second tubing connector 70 has a central bore for connecting the oudet in the distal end 72 of the first tubing to the inlet in the proximal end 74 of the third tubing, A yoke 50 includes at least a pair of openings 52, 54 (also 56, 58 as shown in

Fig.1 ) for receiving and holding first and second connectors 66 and 70 below the carrier wheel 18 and between each disc 22, 24 of the wheel. The connectors 66, 70 each includes an external circumferential rigid flange 80, 82 intermediate its their ends. The yoke 50 cooperates with the flanges 80, 82 (accepting them in a slot recessed in the openings 54, 56) to holding the first tubing 38 in tension with the portion of the first tubing stretched around the pin rollers. The pump body 18 and connectors 66. 70 may be made and used as a single unit or as an assembly of 3 pieces; in any case, the flange is included on the outer part of the connector. The pump bodies 38, 46 are made of a shape memory polymer that can be stretched on its length and width. The interior of the connectors 66, 70 is funnel-shaped to ensure the reduction of the size between the pump body section and the second and third tubing connected to the cannula.

The yoke is mounted through its central part on a rack-type notched rail or any other secure adjustment system moved by knurled know adjuster 90. The adjuster 90 allows vertical movements with jacks or any other system that is commonly used in mechanical applications for vertically adjusting yoke 50 relative to axis 14 of wheels 18, 20 for retaining the first tubing 38 (and as applicable second pump body tubing 46) in tension with a portion of the first tubing 38 (and second pump body 46) stretched around said pin rollers (A, B, C for wheel 18), restricting the lumen 51 of the first tubing where it is stretched across the rollers, as depicted in Fig. 12. The projection of the central axis of connectors 66, 70 is tangential to the rotor. The position of said yoke determines the distance that is required on the axis of the wheel in order to adjust the tension of the pump body 38 and obtain the desired flow rate.

In operation, the filling of the pumping bodies 38 and 46 is performed passively, through the venous return flow of the patient that is diverted into the tubing to the proximate end of the pump bodies 38, 46. The suction pressure is equal to that of the venous system plus the gravity pressure that must be at least equal to 20 mm Hg. The internal pressure of the tube 38, 46 increases during filling until it reaches a plateau. This plateau represents the equilibrium point between the centrifugal forces of the incoming flow and the centripetal forces of the tube wall of 38, 46. The plateau is maintained during the transition from the filling phase to the evacuation phase described below. When it rotates, the rotor creates a contact between the tube and a first roller. This contacts creates the first boundary of the incoming liquid volume, while the second roller closes the segment and thus determines the ejection volume of the pump. When an obstacle appears downstream from the pump, the volume of the tube increases, the tube becomes rounded overall, forming an arc. the rollers can no longer divide the tube, the liquid can no longer be evacuated, and the passive filling is stopped by the downstream load. An equilibrium is established without danger for the patient; at this point, the extracorporeal circulation is likened to a reservoir. When an obstacle appears upstream from the pump, the extracorporeal circulation is simply stopped, the body of the pump becomes flat without generating any negative pressure and creates a natural barrier.

The deformation of the tube that is caused when the tube is stretched by the roller forces the cells out to the periphery (Fig 12) and creates a flowing channel on the creases 90, 91 of the tube. In this case, the device is considered non-occlusive. With this type of movement, the circulating cells are displaced by the physiological pressures; they are deformed without being crushed. A very low rate of hemolysis occurs.

When the tube is stretched over the roller, the roller applies a pressure on the tube which causes the pump body to be pinched. The surface of the rollers is as already mentioned, curved. During the contact with the pump body 38, the central part of the roller applies a tension on the pump body 38 that is greater on the center than on the periphery. The external creases of the pump body 38 are no longer in contact with the surface of the roller. As a result, lateral channels are formed. This roller geometry generates a non- occlusive flow which, in the vertical position, constitutes a safety device against any presence of air.

In order to obtain the full occlusion, the surface of the roller must be flat. A full occlusion provides for a smooth suction. This geometry is used during operations to recover the blood of the patient and reinject it in the extracorporeal circulation. The suction without compression is efficient to preserve blood that has already been altered by the surgical procedure.

Referring now to Figs 2 and 13, an indicator 100 on disc 22 of wheel 18 and an indication receptor 102 spaced from indicator 100 and responsive to indicator 100 to signal when indicator 100 is at a position indicating that the leading roller A of a segment of first tubing 38 is near a point of release of contact with first tubing body 38 before the contact is released (Fig 10). A tensioner comprising a solenoid 1 10 or other suitable mover responsive to said signal passing by electrical line 1 12, extends a plunger (Figs 13. 14) to impart additional stretch to the distal end of the first tubing body 38 to narrow the passageway therethrough when said leading roller A of the lead segment is near the point of release of contact with such first tubing before said contact is released (Fig. A), whereby upon the release of the contact the bolus in the segment released by the leading roller is driven through the narrowed passageway, thereby accelerating flow of the released bolus through the passageway and creating a pulsatile wave in the third tubing line 63 greater than afforded upon the release absent the additional stretch.

Alternatively, not shown, the connector 70 for the discharge line 63 is held by a removable clip. This clip is maintained by its own control device. It is activated by a downward movement that causes the stretching of the tube. This stretching causes the volume of fluid to be ejected into the tube that is connected to the reinjection cannula. The lowering of the clip is determined by a signal such as described above or in another form when the roller passes through the upper left quarter of the circle traced by the roller assembly. Suitable the signal consists of a magnetic, optic or any other type of marker that is capable of indicating the position of the roller to the machine, which transmits the signal to the discharge connector assembly, causing the stretching of the end of the line and forcing out the volume that is contained between the roller and the discharge of said pump body. This stretching produces enough force to propel the discharge volume. The force of the ejection generates a pulse wave on the walls that is strong enough to be transmitted to the connection of the arterial system. This produces a pulsed flow rate that is particularly efficient with small volumes.

This invention produces a physiological pulsed flow rate without the use of valves. The rotation speed of the axis, the compliance of the tube, and the tension of said tube on the rollers determine the flow rate of the pump according to the filling volume, the size of the rotor and that of the tube. The effort applied to stretch the ends of the tube in order to accelerate the ejection of the reinjection volume, determines the amplitude of the pulse wave.

This device makes it possible to determine the type of flow profile of the ejection volume as continuous or pulsed. The flow rate of the pump may be considered as the substitute cardiac output and the pump suction volume as the diverted venous return. The compliance of the tube allows for its volume to increase under the action of the suction pressure. The volume is evacuated in the form of a bowl; its evacuation causes the tube to regain a flat shape capable of being refilled. This compliance provides a level of security that is similar to that of a reservoir. This system for the filling and evacuation of a defined volume makes it possible to reestablish a pulsed flow, which produces the pulse wave necessary to ensure the circulation of blood in the brain.

The stretched pump body concept allows for the use of a veno-venous type cannula, which produces a flow rate in an alternate stream. According to this, the concept is used in infants. It eliminates the need for a reservoir, which is a significant advantage in the case of long term respiratory assistance provided to newborn who suffer from respiratory distress. The blood flows at low speeds under the effect of physiological pressures, allowing the cells to follow a laminar stream without significant modifications of their membrane and without any mechanical destruction. Since the patient-machine suction and discharge equilibrium is passive, there are no complications in the venous return: there are no overload or drainage complications.

This invention may be used with a single pump supporting a single rotor, using a single veno-venous type cannula that allows for an alternate flow. The same single-rotor pump may use a double cannula, one being venous and the other arterial. This invention allows for a device with a double pump design, one being placed under the patient and providing a venous flow, while the second provides an arterial pulsed flow and is placed at the level of the patient in order to restore as much as possible the pulse wave. This invention may be integrated into a compact device that consists of a single pump fitted with a double rotor; this double rotor may be used as a reservoir, as a safety device, or, as in the case of the double pump, to simulate a venous circuit and an arterial circuit. This second wheel can also be occlusive and act as a suction pump. In this case, the pump body is connected to the reinjection circuit.

This pump is an efficient therapeutic tool for low-weight patients, intended for applications that may need to be sustained for hundreds of hours, such as the cardiopulmonary assistance provided to hypotrophic newborn that require this type of assistance either to undergo treatment or to allow for a surgical procedure.

Claims

1. A method of providing pulsatile flow in a return line of an extracorporeal circuit, comprising stretching a portion of a distensible shape compliant first tubing around pin rollers mounted 120 degrees apart on a rotating wheel to restrict the lumen of the tubing where it is stretched across the rollers, restraining said first tubing at a proximal end thereof and at a distal end thereof to maintain a selected degree of tension for the compliance of said first tubing, said proximal end having an inlet and said distal end having an outlet, connecting said inlet of said proximal end of said first tubing to second tubing that comprises the receiving line of said extracorporeal circuit at the distal end of the second tubing and connecting said outlet of said distal end of said first tubing to third tubing that comprises a return line of said extracorporeal circuit at the proximal end of said third tubing, receiving extracorporeal fluid in circuit to fill the circuit with said fluid, rotating said wheel to advance said rollers in a circular direction proceeding from near said proximal end of the first tubing to near said distal end of the first tubing, thereby defining successively segments of said first tubing between leading and trailing pairs of said rollers, each leading roller forming the trailing roller of the rotationally preceding segment, each segment containing a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of said first tubing, and imparting additional stretch to said distal end of said first tubing to narrow the passageway therethrough when the leading roller of a segment is near the point of release of contact with said first tubing before said contact is released, whereby upon said release of said contact the bolus in said segment released by said leading roller is driven through said narrowed passageway, thereby accelerating flow of the released bolus through said passageway and creating a pulsatile wave in said return line greater than afforded by said first tubing upon said release absent said additional stretch.

2. The method of claim 1 comprising controlling the stroke volume of each said bolus by selecting the diameter of said wheel and the radial distance of said pin rollers from the axis of said wheel.

3. The method of claim 1 comprising controlling the stroke volume of each said bolus by selecting said first tubing according to the size of its relaxed cross section and the compliance of the tubing.

4 The method of claim 1 comprising the additional step of controlling the stoke volume of each bolus by adjusting the restraint imposed on the first tubing to increase or decrease the stretch tension across said portion of tubing.

5. The method of claim 2 in which the stroke volume is also controlled by selecting said first tubing according to the size of its relaxed cross section and the compliance of the tubing in relation to the selection of said wheel diameter and roller radial distance.

6. The method of claim 5 in which the stroke volume is also controlled by adjusting the restraint imposed on the first tubing to increase or decrease the stretch tension across said portion of tubing.

7. The method of claim 1 comprising the additional step of controlling the flow rate of the extracorporeal circulation by controlling the speed of rotation of said wheel.

8. The method of claim 1 in which said wheel diameter, said roller pin radial distance, the compliance and relaxed cross section of said first tubing, and said adjustment of _ ..

24

restraint of said tubing are selected to afford a stroke volume of 1 to 5 ml with a flow rate of 50 to 750 ml at an RPM up to 50.

9. The method of claim 1 comprising the additional step of controlling the magnitude of the pulse wave of said pulsatile flow by controlling the amount of additional stretch imparted to said distal end of said first tubing.

10. A non-occlusive peristaltic pump for pumping perfusion fluids in an extracorporeal circuit, comprising: (a) at least one pair of stacked discs each on the same axis, each disc axially separated to form a carrier wheel ,

(b) at least three pin rollers rotatably mounted between a first and second disc of said carrier wheel, each pin roller being mounted on a roller axis parallel to and equidistant from said carrier wheel axis, spaced 120 degrees apart, for rotation both about the axis of said carrier wheels and the axis of the individual roller,

(d) flexible second and third tubing each of a relaxed cross section smaller than the relaxed cross section of said first tubing, said second tubing having a distal end with an outlet and said third tubing having a proximal end with an inlet,

(e) a second tubing connector having a central bore for connecting the inlet in the proximal end of said first tubing to the outlet in the distal end of the second tubing,

(f) a third tubing connector having a central bore for connecting the outlet in the distal end of said first tubing to the inlet in the proximal end of said third tubing, (g) a yoke including at least a pair of openings for receiving and holding said first and second connectors below said carrier wheel and between each disc of said wheel, (h) an adjuster for vertically adjusting said yoke relative to the axis of said wheel for retaining the first tubing in tension with a portion of the first tubing stretched around said pin rollers, restricting the lumen of the first tubing where it is stretched across the rollers,

(i) a rotator for rotating said carrier wheel about said carrier wheel axis to cause said rollers to advance in a circular direction proceeding from near said proximal end of the first tubing to near said distal end of the first tubing, thereby defining successively segments of said first tubing between leading and trailing pairs of said rollers, each leading roller forming the trailing roller of the rotationally preceding segment, whereby each segment can contain a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of said first tubing on filling of said extracorporeal circuit with fluid,

(j) an indicator on said wheel and an indication receptor spaced from said indicator and responsive to said indicator to signal when said indicator is at a position indicating that the leading roller of a segment of said first tubing is near the point of release of contact with said first tubing before said contact is released, and (k) a tensioner responsive to said signal for imparting additional stretch to said distal end of said first tubing to narrow the passageway therethrough when said leading roller of said segment is near the point of release of contact with said first tubing before said contact is released, whereby upon said release of said contact the bolus in said segment released by said leading roller is driven through said narrowed passageway, thereby accelerating flow of the released bolus through said passageway and creating a pulsatile wave in said third tubing line greater than afforded upon said release absent said additional stretch.

11. The pump of claim 10 in which each roller is longitudinally arcuate in the direction of the roller axis, with a larger diameter intermediate opposite ends of the roller than the diameter of the roller at the ends of the roller.

12. The pump of claim 11 in which said roller pins are stainless steel and have a surface polished to a mirror finish.

13. The pump of claim 1 1 in which said roller pins are supported on sealed ball bearings.

14. The pump of claim 10 in which said first tubing is ovoid in relaxed state and radially and longitudinally shape memory compliant.

15. The pump of claim 10 in which said bore of said second connector increases in diameter smoothly in a manner to avoid eddying and provide laminar flow from the second tubing into said first tubing.

16. The pump of claim 10 in which said bore of said third tubing connector decreases in diameter smoothly in a manner to avoid eddying and provide laminar flow from the first tubing into said third tubing.

17. The pump of claim 10 in which each of said connectors includes an external circumferential rigid flange intermediate its ends and in which said yoke cooperates with said flanges for holding said first tubing in tension with said portion of the first tubing stretched around said pin rollers according to the adjustment of said adjuster.

18. The pump of claim 10, in which said said rotator includes a drive shaft connectable with said carrier wheels and a motor for rotationally driving the drive shaft, and further comprises: a controller operatively associated with said motor for controlling the rotational speed of said motor, and speed selector means operatively associated with said controller for generating a selected speed signal signifying a selected rotational speed for said carrier wheels.

19. The pump of claim 10 further comprising a cover for said carrier wheels, said cover being supported by said frame.

20. The pump of claim 1 further comprising a power source to said rotator and circuitry including

(a) a switch connection of said power source to said rotator,

(b) a sensor for determining presence of an electically conductive fluid on said yoke, and

(c) circuitry connecting said sensor to said switch, to disconnect said power source from said rotator when an electrically conductive fluid is sensed on said yoke by said sensor.

21. The pump of claim 10 in which said rotator includes a gear reducer to slow said motor speed to at least 1 rpm.

22. The pump of claim 1 comprising a third disc on the same axis as said first carrier wheel axially spaced from said first disk, thereby providing a second carrier wheel on the same axis, said second carrier wheel having at least three pin rollers rotatably mounted between said third disc and said first disc of the first wheel, each pin roller being mounted on a roller axis parallel to and equidistant from said carrier wheel axis and spaced 120 degrees apart and 60 degrees apart from the pin rollers in the first carrier wheel, for rotation both about the axis of said carrier wheels and the axis of the individual second wheel roller, for rotation both about the axis of said carrier wheels and the axis of the individual roller, a flexible distensible compliant fourth tubing of selected relaxed cross section and having a proximal with an inlet and distal end with an outlet, flexible fifth and sixth tubing of smaller cross section than the cross section of said fourth tubing, said fifth tubing having a distal end with an outlet and said sixth tubing having a proximal end with an inlet, a third tubing connector having a central bore for connecting the inlet in the proximal end of said fourth tubing to the outlet in the distal end of the fifth tubing, a fourth tubing connector having a central bore for connecting the outlet in the distal end of said fourth tubing to the inlet in the proximal end of said sixth tubing, said yoke including at least a pair of openings for receiving and holding said third and fourth connectors below said carrier wheel and between each disc of said second wheel said adjuster vertically adjusting said yoke relative to the axis of said wheel for retaining the fourth tubing in tension with a portion of the fourth tubing stretched around said pin rollers of said second wheel, restricting the lumen of the fourth tubing where it is stretched across the rollers, said rotator also rotating said second carrier wheel about said carrier wheel axis to cause said rollers on said second wheel to advance in a circular direction proceeding from near said proximal end of the fourth tubing to near said distal end of the fourth tubing, thereby defining successively segments of said fourth tubing between leading and trailing pairs of said rollers with 60 degrees of separation from the segments of said first tubing, each leading roller forming the trailing roller of the rotationally preceding segment of the fourth tubing, whereby each segment can contain a bolus of extracorporeal fluid in fluid communication with a bolus in an adjacent segment of said fourth tubing on introduction of extracorporeal fluid into said fifth tubing.

23. The pump of claim 22 further including: an indicator in relation to said second wheel and an indication receptor spaced from said indicator and responsive to said indicator to produce a second signal when said indicator is at a position indicating that the leading roller of a segment of said fourth tubing is near the point of release of contact with said fourth tubing before said contact is released, and a tensioner responsive to said second signal for imparting additional stretch to said distal end of said fourth tubing to narrow the passageway therethrough when said leading roller of said segment of said fourth tubing is near the point of release of contact with said fourth tubing before said contact is released, whereby upon said release of said contact the bolus in said segment of said fourth tubing released by said leading roller is driven through the narrows of said passageway by rebound compliance of the released segment, thereby accelerating flow of the released bolus through said passageway and creating a pulsatile wave in said sixth tubing line greater than afforded by the rebound compliance of the fourth tubing upon said release absent said additional stretch.