WO1997048335A1

WO1997048335A1 - An apparatus for the detection and determination of the magnitude of the regurgitant flow of blood across a heart valve

Info

Publication number: WO1997048335A1
Application number: PCT/IB1997/000752
Authority: WO
Inventors: Jiri Endrys
Original assignee: Jiri Endrys
Priority date: 1996-06-17
Filing date: 1997-06-16
Publication date: 1997-12-24
Also published as: JP2000512865A; SE9602389D0

Abstract

The present invention relates to an apparatus (10) for the detection and determination of the magnitude of the regurgitant flow of blood across a heart valve by the use of thermodilution. Two thermodilution curves are measured from different parts of the heart, i.e. upstream and downstream the valve. The presence of valvular regurgitation is indicated by detection (18) of the presence of a temprature decrease upstream the valve. The areas below the thermodilution curves are calculated (20) in the first place, and this area information is used for the calculation (20) of the cardiac output and then the magnitude of the regurgitant flow.

Description

AN APPARATUS FOR THE DETECTION AND DETERMINATION OF THE MAGNITUDE OF THE REGURGITANT FLOW OF BLOOD ACROSS A HEART VALVE

Technical field of the invention

The present invention relates to an apparatus for the detection and determination of the magnitude of the regurgitant flow of blood across a heart valve by the use of thermodilution.

Description of related art

Defects on heart valves are today normally detect¬ ed m the first place by auscultation, i.e. by using a stethoscope. This method is not quantitative, is prone to errors, and it is not possible to determine the magnitude of the regurgitant flow of blood across the heart valve.

To make a more thorough examination of defects on heart valves, one often uses angiocardiography, which is semiquantitative only. It is not providing data of regur- gitant flow m 1/mm.

Summary of the invention

The present invention solves the problems noted above and provides an apparatus for the detection and de- termination of the magnitude of the regurgitant flow of the blood across a heart valve by the use of thermodilution. By using the known thermodilution technique, two thermodilu¬ tion curves are established through measurements from dif¬ ferent parts of the heart, i.e upstream and downstream of the valve. The presence of a defect of a heart valve, i.e. a regurgitant flow of blood, is detected by the presence of a temperature decrease upstream of the valve, which indi¬ cates valvular regurgitation. In order to determine the magnitude of the regurgitant flow of blood across a heart valve, the areas below the measured thermodilution curves are calculated This area information is used for the calculation of the cardiac output, i.e the volume of blood pumped by the heart per time unit, and then the magnitude of the regurgitant flow. Thermodilution is one of several different techniques to determine cardiac output, but the advantage of thermodilution lies m its simplicity. Thermodilution is one common form of indicator dilution used to obtain carciac output . With this tech¬ nique, a thermodilution catheter is placed in e.g. the left half of the heart so that an injection part of the catheter is in the left ventricle and the catheter's two sensors are located upstream and downstream of the valve respectively. A bolus dose of cold saline is injected into the left ventricle through the injection part where it mixes with the blood and produces a temperature change which is de¬ tected by the sensors. From this, two thermodilution curves can be plotted and the presence of a measurable cardiac output, or temperature decrease, upstream of the valve indicates valvular regurgitation.

The apparatus for the detection and determination of the magnitude of the regurgitant flow of blood across a heart valve by the use of thermodilution according to the present invention comprises means for measuring the tempe¬ rature of the blood as a function of time for establishing two different thermodilution curves obtained by measure¬ ments from different parts of the heart. Then the thermo- dilution curves are digitized by a digitizing means, e.g. an A/D-converter. The digitized thermodilution curves are then stored in a memory unit connected Lo the digitizing means. The apparatus according to the invention also com¬ prises a dectection unit connected to the memory unit for detecting the presence of a temperature decrease upstream of the valve, which indicates valvular regurgitation. The apparatus according to the invention also comprises a cal¬ culation means connected to the detection unit for calcula¬ tion ιr the first place of the areas below the thermodilu- tion cirves. In the second place, the calculation means calculates the cardiac output and the magnitude of the regurgitant flow. By using the apparatus according to the present invention, an accurate and reliable way to detect and determine the magnitude of the regurgitant flow of blood across a heart valve is provided. The magnitude of the regurgitant flow of blood across a heart valve is one important parameter in determining if e.g. a valve opera¬ tion is needed on a patient.

The invention, together with additional features and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing.

Brief description of the drawings

Fig. 1 is a schematic sectional view of a human heart and

Fig. 2 is a schematic block diagram of an apparatus according to the present invention.

Detailed description of the preferred embodiment In figure 1, there is disclosed a schematic sec¬ tional view of a human heart. The heart is partitioned in a right half and a left half. The right half of the heart comprises the right ventricle RV and the right atrium RA. Correspondingly, the left half of the heart comprises the left ventricle LV and the left atrium LA. In figure 1, there is also disclosed the inferior vena cava IVC, which leads to the right atrium RA and the pulmonary artery PA, which leads to the lungs. The pulmonary vein PV leads to the left atrium LA and the aorta AO leads the blood to the rest of the body. In figure 1, there is also disclosed the pulmonary valve PV, i.e. the valve between the right ven¬ tricle RV and the pulmonary artery PA, as well as the aortic valve AV, i.e. the valve between the left ventricle LV and the aorta AO. The valve between the left atrium LA and the left ventricle LV is called the mitral valve MV, and the valve between the right atrium RA and the right ventricle RV is called the tricuspid valve TV. Different defects of the valves can cause a regurgitant flow of blood across a heart valve. The regurgitant flow, i.e. the back¬ wards leakage, causes the measured cardiac output to appear higher than it actually should be. In figure 1, arrows ln- dicate the situation with a defect on the mitral valve MV. The mitral valve flow MVF is the sum of the cardiac output CO and the mitral regurgitation MR.

MVF = CO + MR The priciple upon which the themodilution tech- nique . s based is that the change of heat m a substance is related to its mass and specific heat for a given change in temperature. For a static system, where two substances of different temperatures are mixed, the resulting temperature of the mixture will fall between the starting temperatures of the two substances. If the mass of one substance is unknown, it can be determined by equating at equilibrium the change m heat of the two substances and calculating the unknown mass from the resulting equation.

When this principle is applied to a system of contmous flow, as in the heart and vasculature, a small amount of relatively cool substance, e.g. saline, is injected into and mixed with the blood, thereby yielding a time-temperature curve which may be sensed slightly down¬ stream of the point at which the saline is injected into the system. The curve is referred to as the thermodilution curve, and the area below the thermodilution curve repre¬ sents the sum of the instantaneously mixed temperatures at the sensing point. Normally, the resulting time-temperature curve is reversed, so the curve is displayed as positive values .

To be able to record a thermodilution curve, a catheter is inserted, e.g. into a large vein and passed along the vein towards and through e.g. the right half of the heart to a point a short distance beyond. The catheter has an orifice to the outside of the catheter and liquid is injected through this orifice into the bloodstream from the far end of the catheter. One or two sensors for measuring the temperature are disposed in the catheter, which sensors are located at different places along the catheter. These catheters are well-known in the medical field and accordingly not shown or described in detail . To be able to detect and determine the magnitude of the regurgitant flow of blood across a heart valve with the apparatus according to the present invention, two dif¬ ferent thermodilution curves have to be recorded. Depending on the type of valve defect, the catheter has to be placed in different locations within the heart, i.e. cold saline is injected into different places and the sensor (s) is/are measuring the temperature at different sites within the heart. A list of where to inject cold soline and where to place the sensor (s) in order to provide the necessary information for the apparatus according to the present invention is given below:

Measurement of mitral regurgitation

A) Simultaneous: Injection of cold saline into the left preferabl e ventricle LV

Thermo-probe :

1st in the aorta AO - measures cardiac output CO

2nd in the left atrium LA - measures mitral regurgitation

B) Successive: 1. Injection of cold saline into the right atrium RA

Thermo-probe: in pulmonary artery PA - measures cardiac output CO 2. Injection of cole saline into the left ventricle LV

Thermo-probe: in the left atrium LA - measures mitral regurgitation Measurement of aortic regurgitation A) Simultaneous: Injection of cold saline into the ascending aorta AA

Thermo-probe : 1st in the descending aorta - measures cardiac output CO

2nd in the left ventricle - measures aortic regurgitation

B) Successive 1. Injection of cold saline into the preferable right atrium RA

Thermo-probe: m pulmonary artery PA - measures cardiac output CO

2. Injection of cold saline into the ascending aorta AA

Thermo-probe: in the left ventricle LV - measures aortic regurgitation Measurement of tricuspid regurgitation

Successive- 1. Injection of cold saline into the right atrium RA

Thermo-probe: in pulmonary artery PA - measures cardiac output 2. Injection of cold saline into the right ventricle RV Thermo-probe : m the right atrium RA - measures tricuspid regurgitation.

The magnitude of the regurgitation flow is calculated according to the following formulas. RF = Areg/Aco = REG ( 1/mιn) /VF

REG(% of VF) = Areg/Aco x 100

REG(l/mιn) =RF/(1-RF) x COU/min)

VF = REG + CO(all in 1/rtun) , where RF = regurgitant fraction VF = valvular flow

Aco = Area below 1st curve

Areg = Area below 2nd curve (regurg curve!

If two thermodilution curves are available for simultaneous registration, both the CO curve and the regurgitation curve can be recorded and calculated after a single injection of cold saline into the left ventricle m patients with mitral regurgitation.

The cardie output CO is given by the modified

Stewart-Hamilton equation as

CO = V x(T_B - T_j) / A) x (S_j x C_j) / (S_B x C_B) ) x 60 x C_τ where 60 = seconds/minute

V = injected volume (1)

A = Area of thermodilution curve (°C x s) T_B = Blood temperature (°C) T_j = Temperature of injected liquid ^ϋC) S_j = Specific gravity of injected liquid

C_j = Specific heat of injected liquid S_β = Specific gravity of blood C_B = Specific heat of blood C_τ = Correction factor for heating in the catheter of the injected liquid.

In figure 2, there is disclosed a schematic block diagram of an apparatus 10 according to the present inven¬ tion. The apparatus 10 comprises a means 12 for measuring the temperature of the blood as a function of time. The measuring means 12 rceives the thermo-probe-input from the thermo-probe (s) in the catheter. The measuring means 12 is arranged to receive two different thermo-probe-signals simultaneously if the catheter has two thermo-probes (sen- sors) . The measuring means 12 emits an analog signal (or two analog signals respectively) in the form of a thermo¬ dilution curve to a digitizing means 14 for digitizing the thermodilution curve (s) . The apparatus 10 also comprises a memory unit 16 connected to the digitizing means 14 for the storing of the digitized thermodilution curve. The memory unit 16 is disposed to store at least two digitized thermo¬ dilution curves, because the information contained in two thermodilution curves is needed in order to both detect and determine the magnitude of the regurgitant flow of blood across a heart valve. A detection unit 18 is connected to the memory unit 16 for detecting the presence of a tempera¬ ture decrease upstream of the valve, indicating valvular regurgitation. The apparatus 10 also comprises a calcula¬ tion means 20 connected to the detection unit 18 for calcu¬ lating in the first place the areas below the thermodilu¬ tion curves, and in the second place, calculating the car- diac output and the magnitude of the regurgitant flow of blood across a heart valve. The apparatus 10 also comprises a display unit 22 connected to the calculation means 20 and to the memory unit 16. The display unit 22 displays plots of the measured themodilution curves and the magnitude of the regurgitant flow. The digitizing means 14 can be a conventional A/D-converter.

Although a representative embodiment of the invention has been shown and described, many changes, modifications and substitutions may be made by a person having ordinary skill in the art without necessarily departing from the spirit and the scope of this invention.

Claims

1. An apparatus (10) for the detection and deter¬ mination of the magnitude of the regurgitant flow of blood across a heart valve by the use of thermodilution, wherein a cold liquid is injected downstream of the valve and the temperature of the blood is measured upstream and down¬ stream of the valve, (e.g.) by two sensors, said apparatus comprising: - means (12) for measuring the temperature of the blood as a function of time for providing two different thermodilu¬ tion curves obtained from different parts of the heart;

- a means (14) for digitizing the thermodilution curves connected to the measuring means (12) ; - a memory unit (16) connected to the digitizing means (14) for storing the digitized thermodilution curves;

- a detection unit (18) connected to the memory unit (16) for detecting the presence of a temperature decrease upstream of the valve indicating valvular regurgitation; - a means (20) connected to the detection unit (18) for calculation in the first place of the areas below the ther¬ modilution curves and in the second place of the cardiac output and of the magnitude of the regurgitant flow.

2. An apparatus (10) according to claim 1, characte¬ rized in that the calculating means (20) is arranged to use the modified Stewart-Hamilton equation for the calculation of the cardiac output (CO) : CO = V x(T_B - T_j) / A) x [ S_τ x C_j) / (S_B x C_B) ) x 60 x C_τ, where V = injected volume (1) ; A = Area of thermodilution curve (°C x s) ; T_B = Blood temperature (°C) ; T_χ = Temperature of injected liquid °C) ; S_τ = Specific gravity of injected liquid; C_j - Specific heat of injected liquid; S_B = Specific gravity of blood; C_B = Specific heat of blood and C_τ = Correction factor for heating in the catheter of the injected liquid.

3. An apparatus (10) according to claim 2, characte¬ rized in that the calculating means (20) for calculating the magnitude of the regurgitant flow makes use of the equations: RF = Areg/Aco = REG (1/min) /VF; REG(% of VF) = Areg/Aco x 100; REG(l/min) =RF/(1-RF) x CO(l/min) ; VF = REG + CO (all in 1/min) , where RF = regurgitant fraction; VF = valvular flow and A = different areas for different thermo¬ dilution curves.

4. An apparatus (10) according to claim 3, characte¬ rized in that the digitizing means (14) is an A/D-conver- ter.

5. An apparatus (10) according to any of the preced- ing claims, characterized in that the apparatus (10) also comprises a display unit (22) for displaying plots of the measured thermodilution curves and of the magnitude of the regurgitant flow.