CA1324556C

CA1324556C - Endotracheal tube with asymmetric balloon

Info

Publication number: CA1324556C
Application number: CA000599689A
Authority: CA
Inventors: Roland E. Weber
Original assignee: Applied Biometrics Inc
Current assignee: Applied Biometrics Inc
Priority date: 1988-06-23
Filing date: 1989-05-15
Publication date: 1993-11-23
Anticipated expiration: 2010-11-23
Also published as: EP0420854A1; JPH04502562A; US4886059A; US4913642A; EP0420854A4; WO1989012425A1; US5076268A

Abstract

ABSTRACT OF THE DISCLOSURE
Blood flow in the aorta and pulmonary artery of a mammal, most typically a human, is measured volumetrically by a non-invasive, ultrasound apparatus. The apparatus (10) comprises a tracheal tube or probe with of flexible tubing (11) having a transducer assembly (21) mounted at one end the tube. The transducer assembly (21) is disposed to transmit ultrasound in selected directions. Electrical conductors (24) extend the length of the probe from the transducer assembly. Improved means is provided to positively locate the probe in the trachea and to urge the ultrasound transducer assembly (21) into intimate contact with the inner wall of the trachea. The improved location and urging means comprises a single inflatable asymmetric balloon cuff member (29) mounted on the tube (11) in proximity to and above the transducer assembly (21) and extending around the entire periphery of the tube, the balloon being mounted on the tube such that when inflated the balloon sealingly engages the tracheal wall while urging the transducer assembly into contact with the inner wall of the trachea.
The asymmetric balloon cuff is conveniently formed in a mold prepared by angularily sectioning the conical portion of a pair of funnel shaped mold forms at equal angles relative to the central axis thereof, rotating one of the sectioned funnel forms 180° about the axis and then joining the two forms at the section plane to form the balloon cuff mold form.

Description

~32~56 ; 3 Background of Invention 4 Field of Invention Measurement of cardiac output is crucial in the care of 6 critically ~ll patients such as patients with multiple trauma, 7 patients in overwhelming sepsis, and patients with acute myocardial 8 infarction. In the ease of patients with acute myocard;al 9 infarction, there is a worsening prognosis with decrease in cardiac output. Knowledge of the cardiac output provides information useful 11 in determining the clinical state of a given patient and in 12 rationally planning therapy for the patient. Such information is not ~; 13 contained in the usually measured vital signs. For example, a low14 mean arterial pressure with elevated pulse does not adequately distinguish between cardiogenic and septic shock, the treatments for 16 which are quite different. Consequently, a method that distinguishes 17 between cardiogenic and septic shock would be ;mportant in planning 18 appropriate therapy. The measurement of cardiac output, in this 19 case, would provide valuable information that would allow an appropriate diagnosis to be made.
21 Prior Art 22 ~he importance of knowing cardiac output has led to many 23 methods for its determination. The most commonly used method in 24 widespread clin;cal use is thermodilution. In the thermodilution i 25 method a catheter is placed into the central venous circulation, .

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1 usually by percutaneous entry into the internal jugular or 2 subclavian vein. A balloon at the end of the catheter is inflated, 3 and the normal flow of blood is employed to direct the tip of the ~` 4 catheter into the pulmonary artery. Measurement of cardiac output is made by observing the dissipation of a temperature pulse, usually a 6 bolus of iced sterile water or saline solution. As is evident, the 7 method cannot be used without invasion of the vascular tree. Indeed, " 8 the catheter is threaded through the heart and the heart valves.
9 Flow direction is not entirely reliable. In certain patients access to the pulmonary artery is impossible. During placement of the 11 catheter cardiac arrhythmias are not uncommon. Other complications , 12 include sepsis, thrombosis of the central veins, emboli, and fatal 13 rupture of the pulmonary artery. Other disadvantages of the 14 technigue include lack of continuous information about the cardiac output and chance location of the catheter, such as in an 16 unfavorable pulmonary artery branch, with erroneous values for the 17 cardiac output. Analysis of the error inherent in the measurement of 18 blood flow by thermodilution has revealed a standard deviation of 19 2~-30%.
Measurement of cardiac output has also been done by the 21 indocyanine green dye technique, which suffers from sevcral 22 disadvantages. The technique is cumbersome, it requires the 23 placement of an arterial catheter, is not accurate at low levels of 24 cardiac output and is difficult to use for repeated measurements in the same patient. Complications include catheter site hematoma, . ~ - -,.

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1 sepsis from the catheter, thromboses of the artery contain;ng the 2 indwelling catheter,and pseudoaneurysm formation at the site of ` 3 arterial puncture.

4 The Fick method is based on the measurement of oxygen consumption. It is best used in awake, alert, stable patients not 6 requiring respiratory support on a ventilator. The method requires 7 invasion of the pulmonary artery in order to obtain samples of mixed 8 venous blood for determination of the oxygen content. Like the 9 indocyanine green dye technique, an arterial catheter must be placed ~or sampling of arterial blood for oxygen content with the 11 disadvantages mentioned above.
12 Transcutaneous ultrasound has also been used.
13 Ultrasound transducers are placed externally on the body at ~he 14 suprasternal notch. Under the most sanguine circumstances, at least 10% of patients cannot have their cardiac outputs measured in this 16 way. Many difficulties with this approach have been reported:
17 repeated measurements may lead to varying location of the sample 18 volume that is scanned, there are changes in the angle of 19 intersection of the ultrasound beam with the axis of the vessel, capability for contlnuous measurement of the cardiac output is not 21 available, and other major thoracic vessels may interfere with the 22 Doppler ultrasound signals. Further, the method is not feasible in 23 many ~mportant clinical settings in which the patients are not ,~ 24 cooperative or are in the operating room, where the suprasternal notch may not be accessible.

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1 ~ 5 6 :' 1 Because of these difflculties, an implantable, removable 2 Doppler ultrasoun~ dev;ce for measurement of the cardiac output has 3 been developed for direct attachment to the aorta. The device 4 requires a major, operative, invasive intervention, such as splitting the sternum on removal of a rib to enter the chest cavity, 6 for placement of the device directly on the wall of the aorta.
7 Removal of the device also requires surgical intervention. If the 8 device were to be lost in a major body cavity, a major surgical 9 procedure would be required.
Measurement of cardiac output by continuous or single 11 breath, gas-washout has been attempted, but is not used in standard 12 clinical medicine. Such methods require many approximations of lung 13 function in modeliny the system. Time cunsuming numerical analysis 14 is required. In one study, measurement of cardiac output in anesthetized patients using argon and freon during passive 16 rebreathing was shown to provide lower cardiac outputs than a 17 simultaneously performed Fick determination. The authors concluded 18 that the method caused significant disturbances of hem~dynamics and 19 was therefore not suitable for widespread use.
Indirect measurements include the pulse, blood pressure, 21 and urine output, but these measurements are not specific for 22 cardiac output. For example, in the presence of acute renal fa;lure, 23 urine output cannot be correlated w;th perfusion of major organs.

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~32~6 1 In the patent art, Tickner, U.S. Patent No. 4,316,391 2 discloses an ultrasound technique for measur;ng blood flow rate.
3 Colley et al., ~.S. Patent No. 4,354,501, discloses an ultrasound 4 technique for detecting air emboli in blood vessels. Numerous patents disclose catheters or probes, including Calinog, U.S. Patent 6 No. 3,734,094, Wall, U.S. Patent No. 3,951,136, Mylrea et al., U.S.
7 Patent No. Re. 31,377, Perlin, U.S. Patent Nos. 4,304~239; 4,304,240 8 and 4,349,031, Colley et al., U.S. Patent No. 4,354,501 and Furler, 9 U.S. Patent No. 4,369,794.
U.S. Patent No. 4,331,156 discloses an esophageal 11 cardiac pulse probe wh;ch utilizes a closed end lumen with a 12 pressure transmitting fluid therein to transmit sounds from the 13 heart and lungs to an external transducer.
` 1~ In U.S. 4,671,295 and 4,722,347 there is described a : 15 method and apparatus for measuring cardiac output which comprises , 16 placing an ultrasound transducer in great proximity to the ascending t~, 17 aorta of the heart of the mammal by pass;ng a probe carrying the ~i~ 18 transducer into the trachea and transmitting ultrasound waves from 19 the transducer toward the path of flow of blood in the ascending 20 aorta. The probe can be passed through the nasal or oral cavity, ~ 21 past the epiglottis into the trachea or, in the case of patients who L 22 have had a tracheostomy, directly into the trachea through the 23 surgical opening. The reflected ultrasound waves are received by 24 the transducer and the average Doppler frequency difference between ~5 the transmitted waves and the reflected waves is measured. The ':
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- 13~4~6 1 cross-sectional size or area of the ascending aorta at the po;nt of 2 ultrasound reflection is calculated and the volumetric blood flow 3 rate is determined from such measurements. The method and apparatus 4 for measuring cardiac output described in U.S. Patents 4,671,295 and 4,722,347 provides for the determination of the cardiac output in a 6 way that is accurate, noninvasive, continuous, inexpensive and 7 suitable for use in those patients whose cardiac output measurement , 8 is most critical.
9 SummarY of the Invention The present invention comprises an improvement ;n the 11 apparatus of U.S. 4,671,295 and 4,7?2,347. In one embodiment the 12 invention comprises an improved tracheal probe for use in - 13 determining blood flow in a major discharge artery, including the 14 pulmonary artery and the aorta, of a mammalian heart, which :15 comprises:
16 a. a flexible tube having a length sufficient to 17 extend from the oral or nasal cavity of the mammal or from the 18 surgical tracheal opening through the trachea to the bifurcation 19 thereof, b. an ultrasound transducer assembly mounted to the 21 tube in proximity to the distal end thereof, and 22 c. means mounted on the tube for urging the 23 transducer into contact with the inner wall of the trachea, the 24 improvement comprising that said urging means comprises a single 25 asymmetric inflatable balloon cuff member in proximity to and above . 26 "

132~6 1 the transducer assembly and extending around the entire periphery of 2 the tube, said single asymmetric balloon being mounted on the tube 3 such that when ;nflated the balloon sealingly engages the tracheal 4 wall while urging the transducer into contact with the inner wall of the trachea.
6 In another aspect of the invention the inventive balloon 7 cuff may be used with any device, mounted on a catheter or flexible 8 tube which is ;nserted into a mammalian body passageway and threaded 9 through the passageway to a point in the body where it is desired that the device mounted on the cathcter or flexible tube contact the 11 side wall of the body passageway.
12 A still further aspect of the invention compr;ses a 13 method for manufacturing the balloon cuff mold by angularly 14 sectioning the conical portion of a pair of funnel shaped mold forms at equal angles relative to the central axis thereof, rotating one 16 of the sectioned funnel forms 180 about the axis and then joining 17 the two forms at the section plane to produce the balloon cuff mold 18 form.
19 The asymmetric balloon mold and the balloon molded therefrom are further aspects of the invention.
21 Brl~f Description of the Drawinas 22 FIG. 1 is a front-to-back vertical sectional view of the 23 upper portion of the human body showing the oral cavity and the 24 pathway through the trachea to the bifurcation thereof. The heart is shown in lateral or side view. The tracheal probe of the ..

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A 1 lnvention is shown in position in the trachea with the transducer 2 assembly contacting the tracheal wall in proximity to the ascending 3 aorta.
4 FIG. 2 is a front view of the ascending aorta, the 5 trachea, including the bifurcation thereof, and the esophagus and 6 shows the close relationship between the tracheal and the ascending d, 7 aorta.
8 FIG. 3 is a horizontal sectional view of the trunk of a 9 human taken at the level of the tracheal bifurcation and shows the 10 close relationship between the trachea and the ascending and 11 descending aorta and the pulmonary arter;es.

12 FIG. 4 is a perspective view from the left side of the 13 tracheal probe of the present invention with the balloon inflated.

14 FIG. 5 is a front view of the preferred balloon cuff of 15 the invention.

16 FIG. 6 is a left side view of the preferred balloon cuff ; 17 of the invention.
18 Descr~tion of Preferred E~bodiment 19 Reference is made to the disclosure of U.S. Patents 20 4,671,295 and 4,722,347 for a detailed description of the theory and ;.
21 operation of the tracheal probe and for modifications9 not relevant 22 to the present invention, which may be employed. The present 23 disclosure should be considered in conjunction with those two 24 patents to the extent necessary to fully understand the invention.
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-. . - - . . . ~ ~ -132~5~6 1 The apparatus of the preferred emhodiment consists of a 2 probe with a piezoelectric transducer mounted at one end and 3 electrical conductors extending the length of the probe for 4 connection to conventional directional pulsed or continuous wave Doppler ultrasound hardware, such as that described by Hartley et 6 al. in the Journal of Applied Physiology, October 1974, and by Keagy 7 et al. in the Journal of Ultrasound Medicine, August 1983.
8 Modifications to the signal output can be made to display blood flow 9 volume rate, aorta or other vessel diameter, blood velocity and other selected displays.
11 The probe 10 is shown in Figures 1 and 6. Probe 10 12 conslsts of flexible plastic tubing 11. The length must be 13 sufficient to extend from outs;de the bo~y to the vicinity of the 14 heart through the trachea, entering either through the nasal or oral cavity or through a surgical opening in the case of patients who 16 have had a tracheotomy. The particular probe shown in Fig. 1 is 17 adapted for oral insertion.

18 Near the distal end of the probe a transducer assembly 19 21, suitably comprising one or more pie oelectric transducers and associated lenses~ is mounted on the exterior of tubing 11.
21 Transducer assembly 21 is used to collect Doppler data for 22 velocity calculation and to collect data for calculation of the 23 d;ameter of the artery at the point of velocity measurement.

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132~6 1 Electrical conductors 24, extend the length of tube 11 for 2 connection of transducer assembly 21 to conventional Doppler 3 ultrasnund hardware.
4 An acoustical gel, such as Aquasonic 100, a krademark of and available from Park Laboratories, Orange, New Jersey, may be 6 placed on the surface of the transducer assembly to fill in the 7 small, irregular space or spaces between the transducer lens and the 8 trachea that remain because of the irregularly shaped and relatively 9 non-deformable cartilaginous inn~r surface of the trachea when the lens engages the trachea. Alternatively, a generous appl;cation of 11 a conventional lubricant, such as a anesthetic lubricant, commonly ~, 12 used when inserting a tracheal tube can be relyed upon to provide 13 whatever gap filling is necessary.
~ 14 An understanding of the use of the present invention r'~ 15 requires some understanding of mammalian anatomy and in particular 6 16 an understanding of the human anatomy, which ;s shown in pertinent . 17 portion in Figures 1, 2 and 3. The apparatus is used by placing the ,~?, 18 ultrasound transducer assembly 21 in great proximity to the arterial !? ~ 19 vessel in which blood flow is to be measured, most typically the ascending aorta of a human, without surgery or other invasive 21 techniques. The method relies on the anatomical discovery or fact 22 that the ascending aorta is located adjacent the trachea just above !j 23 the bifurcation thereof, and that a transducer placed in the trachea i` 24 can be directed toward the ascending aorta and accurate blood flow measurements made without sign;ficant interference~ With reference ,s /, 1S~ 6 1 to Figures 1, 2 and 3, access to the trachea, T, of a human, H, can 2 be had in accordance with standard medical practice through the 3 nasal cavity, N, or the oral cavity, O, past the epiglottis, E, and 4 into the trachea, T. Access can also be had through a suryical S opening at the suprasternal notch, S, in the case of patients who 6 have had a tracheotomy. The ascend;ng aorta, A, and the pulmonary 7 aSrtery, PA, are located in great proximity to the trachea, T, just 8 above the bifurcation, as best seen ;n Figures 2 and 3.
9 Consequently, a transducer or transducers placed in the 10 trachea as shown ;n Figure l can be directed to transm;t and receive 11 ultrasound waves through the wall of the trachea and through the 12 wall of the ascending aorta or the pulmonary artery to be reflected 13 by the blood flowing in the selected artery and, due to ~he movement 14 of the blood, cause a Doppler sh~ft in the frequency o~ the reflected waves as compared to the frequency of the transmitted 16 waves. The ultrasound waves are also reflected by the near and far 17 walls of the artery and such reflection can be used for diameter 18 measurement of the artery.
l9 Means is provided to positively locate probe 10 in trachea, T, and to urge transducer assembly 21 into intimate contact 21 with the inner wall of the trachea.
22 The disclosed dev;ce of U.~. 4,671,295 and 4,722,347 23 utilizes a pair of inflatable balloons to properly position the 24 transducer asssembly 21 against the wall of the trachea in proximity to the ascending aorta. One such balloon is a donut shaped cuff .

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1 which positions the probe in the center of the trachea and seals the 2 trachea. A second balloon, located on the back s;de of the probe 3 behind the transducer assembly, is inflated to urge the transducer 4 assembly against the tracheal wall. This is a complicated construction and it is an object of the invention to simplify the 6 construction by utilizing a single balloon cuff, asymmetrically 7 disposed about the axis of the tube 11 when viewed from the side, to 8 simultaneously seal the trachea, securely position probe 10 in the 9 trachea and urge the transducer assembly 21 against the tracheal wall in proximity to the selected artery.
11 The asymmetric balloon is designated by the numeral 29 12 and is shown in detail in figures 4-6. The balloon is made of 13 conventional materials. Suitably it is dip or blow molded. The 14 mold is formed by sectioning a pair of cones, suitably funnel shaped cones, at an acute angle relative to the central axis thereof, 16 rotating nne of the cones 180 relative to the other and 30ining the 17 two cones alone the section line. The resulting mold form has the 18 shape of the balloon, shown in figures 4 and 5. The balloon has a 19 pair of sleeves 30 formed by the funnel shaft for mating the cuff to tubing 11 over an opening to an inflation lumen 31 which runs along 21 tube 11. Circumferential line 32 defines the mat;ng edges of the 22 two cones. The angle of the conical section relative to the central 23 axis of the cone is designated ~ in figure 6. The angle of the 24 conical surfaces relative to the central axis of the cone is designated ~ in ~igure 5. Neither angle ~ nor angle ~ are critical `" ~ ,, " ' ' ' 1324~6 :
1 and the seleotion of angle will generally be determined by the `A, 2 desirability of complying with industry standards regarding the 3 overall dimensions of trachea sealing balloons. Without limitation, 4 however, angle ~ may suitably be in the range of 50-75, preferably 60-65~ and angle ~ may suitably be in the range of 10-30, 6 preferably about 15-20.
7 As shown in figure 5, the preferred balloon when vie~ed 8 from the front is symmetric about the plane the passing through axis 9 line 40 and perpendicular to the page. Preferably when the balloon is mounted on tube 11 this line of symmetry is aligned with the 11 plane which passes through the cen~ral axis of tube 11 and the , 12 center of transducer assembly 21. However, the two planes may be 13 offset slighty without departing from the invention hereof.
14 The asymmetry of the balloon when viewed from the side is such that when inflated the balloon has a bulge 42 on the back i~ 16 side thereof on the portion of the cuff closest to the transducer .
~, 17 and a second bulge 43 on the front side of the probe of the portion ~ 18 of the cuff furthest from the transducer.
,; l9 The structure of balloon 29 allows a single balloon to accomplish the functions of the dual balloon system disclosed in 21 U.S. Patents 4,671,295 and 4,722,347. The use of mated angularly ` 22 sectioned cones ko provide a mold configuration conPerring the 23 desired asymmetry in the balloon allows the mold to be prepared very 24 inexpensively. These features provide significant advantages over , 25 the dual balloon system of U.S. Patents 4,671,295 and 4,722,347.
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1 In use probe 10 is placed to locate transducer assembly 2 21 in the trachea, T, pointing toward the selected artery, suitably 3 as the ascending aorta. The position of probe 10 and transducer 4 assembly 21 can be adjusted until the maximum Doppler shift is obtained and the position can also be checked or confirmed by X-rays 6 to insure placement for optimum data collection. In general, 7 transducer assembly 21 should be located just above the tracheal 8 bifurcation and directed toward the selected artery.
9 For ventilation purposes it is necessary to seal the trachea. It is also important that the ~ransducer assembly 21 be 11 held in position so that it is not moving about within the trachea 12 while measurements of cardiac output are being taken. Use of a 13 traditional symmetric balloon will force the distal end of the probe 14 away from the wall of the trachea and toward the center thereof, thus requiring a second means for urging the transducer assembly 16 against the tracheal wall. The asymmetric balloon 29, however, 17 complements the natural curvature of tube 10, shown in Fig. 4, so 18 that it effectively seals the trachea and holds the tube in place 19 while simultaneously urging the transducer assembly 21 ;nto acoustic contact with the tracheal wall. Inflation of asymmetric balloon 29 21 is accomplished with using conventional procedures for inflating an 22 endotracheal tube balloon.

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1 In other respects the endotracheal tube 10 is 2 constructed in accordance with recognized standards for construction 3 of endotracheal tubes. In particular, the distal end su;tably is 4 provided with a standard bevel opening 33 and oppositely directed Murphy eye 34 manufactured in accordance with ANSI standards.
6 After proper placement of probe 10 and connection with 7 the electrical hardware, ultrasound signals are generated and the 8 Doppler shift is measured for velocity calculation and data for 9 calculating the diameter of the artery is also collected. These data are used to determine the volumetric rate of blood flow as set forth 11 in detail in US 4,671,295 and 4,722,347.
12 A large number of patients who require continuous 13 measurement of cardiac output have significant associated clinical 14 problems. Often such patients have multiple systems organ failure, overwhelming sepsis, significant trauma to many major organ systems, 16 decompensated congestive heart failure, or major myocardial 17 infarction. Sueh patients often have an endotracheal tube in place 18 because of such problems. For example, in patients having a major 19 surgical procedure, use of general anesthesia requires the presence o~ an endotracheal tube for the maintenance of the patient's airway.
21 In the case of patients having open heart surgery, an endotracheal 22 tube is often in place for the night following surgery. Patients 23 suffering major trauma are routinely intubated following significant 24 thoracic trauma, significant head injury, or multiple abdominal injuries. Patients in multiple systems organ failure, septic shock, .
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1 or hemorrhagic shock have endotracheal tubes in place to ass;st : 2 ventilation during acute decompensation and in the immediate 3 resuscitation phase. Patients with signiFicant burn injuries 4 frequently require endotracheal intubation during initial resuscitation~ for transportation to a burn center, and for thermal 6 injury to the respiratory system. Patients with decompensated 7 congestive heart failure leading to pulmonary decompensation with 8 pulmonary accumulat;on of fluid require endotracheal intubation.
9 Such patients may have underlying myocard;al infarction, card~omyopathy, cardiac valvular disease, or chronic congestive 11 heart failure. In many of these examples, stabilization of the ; 12 cardiovascular system is a prerequisite for removal of the tracheal 13 tube. &onsequently, use of an endotracheal probe in accordance with 14 the present invention represents no further invasion of any body cavity. Thus, in the case of patients already having a tracheal tube 16 in place, as well as in patients in which no tracheal tube has been 17 previously placed for other reasons, the present invention provides 18 for measurement of cardiac output at optimum locations without major 19 surgical procedure or invasion of a closed body system~ No invasion !'~ 20 of a major body cavity, not routinely in communication with the 21 external environment, is required. No major or minor surgical 22 procedure is required~ No indwelling foreign body is necessary in 23 the vascular system, a major body cavity, or in a major organ. No . ~
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132~56 1 dye or radioactive substance is necessary for the measurement to be 2 performed, and no air emboli are introduced. Continuous monitoring 3 is also possible.
4 While the foregoing description of applicants' invention is directed to measurement of cardiac output in the ascending aorta, 6 measurement of blood fluw in the descending aorta, the right 7 pulmonary artery and the left pulmonary artery can also be made with the applicants' apparatus. Moreover, the inventive balloon cuff can 9 also be usefully employed with other devices located on catheters or other flexible tubes and inserted through a tubular body passageway 11 to a point where it is desired that the device contact the wall of 12 the passageway to effectively operate the device. For instance, a 13 balloon cuff of the invention may be used to position the end of a 14 laser angioplasty device of the type disclosed in U.S. 49685,458 adjacent to a plaque deposit in an artery.

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Claims

1. In a tracheal probe for use in determining blood flow rate in a major discharge artery, including the pulmonary artery and the aorta of a mammalian heart, the probe comprising:
a. a flexible tube having a length sufficient to extend from the oral or nasal cavity of the mammal or from a surgical tracheal opening through the trachea to the bifurcation thereof, b. an ultrasound transducer assembly mounted to the tube in proximity to the distal end thereof and, c. means mounted on the tube for urging the transducer into acoustic contact with the inner wall of the trachea, the improvement comprising that said urging means comprises a single inflatable asymmetric balloon cuff member in proximity to and above the transducer assembly and extending around the entire periphery of the tube, said single asymmetric balloon being mounted on the tube such that when inflated the balloon sealingly engages the tracheal wall while urging the transducer assembly into acoustic contact with the inner wall of the trachea.

2. The tracheal probe of claim 1 wherein the distal end of the tube is open to provide for ventilation of the mammal through the tube.

3. The probe of claim 1 wherein the said cuff when inflated is generally symmetric about a first plane which passes through the axis of the tube and through said transducer and said cuff is asymmetric about a second plane generally perpendicular to said first plane, said second plane defining front and back sides of the probe, the side bearing the transducer being the front side, the asymmetry of the cuff causing the portion of the cuff closest to the transducer to be enlarged on the back side of the probe relative to the front side thereof and causing the portion of the cuff furthest from the transducer to be enlarged on the front side relative to the backside of the probe.

4. In a device mounted on a cathether or other elongated flexible member whereby the device may be inserted into a mammallian body and passed through a tubular passageway in the body to a point where it is desired that the device contact the wall of said passageway to effectively operate the device, the improvement comprising that the said elongated flexible member includes an inflatable asymmetric balloon cuff member in proximity to and above the said device extending around the entire periphery of the flexible member and means for inflating said asymmetric balloon, said balloon being mounted on the flexible member such that when inflated the balloon sealingly engages the wall of the passageway while urging the said device into contact with the inner wall of said passageway.

5. A mold form for an asymmetric balloon cuff, said form comprising a pair of mated angularily sectioned cones, the two cones being sectioned at equal acute angles relative to the central axis thereof, the cones being mated along the lines thereof with one cone rotated 180° about its axis relative to the other.

6. A mold form as in claim 5 in which both of said cone portions is derived from a conical funnel having a tubular shaft portion at the apex thereof, said shaft portion providing a form for forming a pair of sleeves on either end of the said balloon cuff.

7. An asymmetric balloon cuff formed in a mold form as in claim 5.