IL102360A - Cardiac assist device with counterpulsation balloon and coronary squeezer - Google Patents

Description

CARDIAC ASSIST DEVICE WITH COUNTERPULSATION BALLOON AND CORONARY SQUEEZER ABSTRACT The present invention relates to a cardiac assist device (CAD) intended for improving, by mechanical means, the pumping function of a failing human heart.

According to this invention, the assist device comprises an intraaortal counterpulsation balloon and a coronary squeezer which is attached to the balloon in order to increase the diastolic blood pressure at the aorta root, promote the coronary blood flow and thus improve the pumping capacity of the heart.

BACKGROUND OF THE INVENTION The limited coronary blood flow through a failing heart restricts the oxygen supply to myocardium and, therefore, the letter's capacity of providing the pumping function of the heart. In order to overcome such a limitation, one has to considerably increase the coronary blood flow by means of a mechanical device capable of elevating the blood pressure in coronary arteries.

One of the most common CADs used as a mechanical aid for a failing human heart is an intraaortal counterpulsation balloon (IABP) which is supposed to improve the pumping capacity of the heart. However, the volume of this balloon may not exceed 50 ml; it means that, at the elasticity coefficient of the aorta Ca = 0.3 mm Hg/ml, the resulting rise in diastolic pressure will not exceed 15 mm Hg, yielding the maximum increase in circulation capacity of 20-25%.

The overcoming of this limitation represents a major problem in the development of efficient mechanical blood circulation systems.

Many other CADs have been proposed, including those using intraaortal balloons, e.g., the CAD described in U.S. Patent 4,785,795 (two balloons enclosed into aorta are pulsating in a counter-phase manner with a rate exceeding that of pulse beats by a number of times), or the CAD described in U.S. Patent 4,771,765 (one balloon placed into left ventricle of the heart is pulsating in a counter-phase manner with regard to another balloon contained within aorta, the rate of pulsation being synchronized with that of heart beats). However, these CADs are unable to considerably promote the pumping capacity of the heart, since their operation is aimed at increasing the systemic blood flow by actions whose magnitude is less than required by at least one order, because these devices are operating in an open vascular bed.

The only known attempt to solve this problem in an adequate way relates to device described in the Soviet patent 921,569. This invention supposes complementing the IABP with an auxiliary balloon adjoining the main balloon at the latter's distal end facing the descending aorta, so that it locks the aorta for the duration of diastole. However, this device should not considered a satisfactory solution for increasing the coronary blood flow, since (a) it does not assure a required rise in diastolic pressure because it operates in an open vascular bed. Since the IABP volume is less than 60 ml, the elasticity coefficient of aorta is K ~ 0.5 mm Hg / ml and taking into account large arteries branching from the aortal arc, the attainable rise in aortal pressure during diastole may not exceed 5 - 6 mm Hg, with resulting increase in the efficiency of IABP to just 25 - 30% - not a considerable figure when compared to 20 - 25% without this measure; (b) it does not include means of control capable of establishing due correspondence between the pressure rise in aorta during diastole and the intensity of metabolism.

The assist device proposed in this present invention solves the above problem in a radical way and using rather simple techniques, increasing the efficiency of IABP by a number of times, because it is functioning operating in a vascular bed which is closed during diastole.

The device may be also used for introducing drugs directly into coronary vessels.

SUMMARY OF THE INVENTION The main idea of this invention is the possibility of a substantial rise in the aorta root pressure due to the fact that the aorta root is closed during diastole. Such an increase of the blood pressure in the aorta root is achieved by means of an elastic balloon - coronary squeezer - attached to the head (distal) end of the IABP counterpulsation balloon. The squeezer is made of the same material as the IABP balloon, i.e. material suitable for a long-time operation within flow of blood. The inner cavity of the squeezer is connected with the inner cavity of the IABP balloon so that both these balloons are expanded or constricted almost simultaneously due to, correspondingly, incoming or outgoing stream of a working medium through a catheter connecting the balloons to a source of such medium.

The CAD proposed in this invention operates in the following manner: While expanding, the squeezer locks the lower part (root) of the aorta, and its continuing expansion produces a rise in blood pressure at the aorta root and at the inlets of coronary arteries, thus increasing the coronary blood flow and promoting the pumping function of the heart. Besides that, a pressure rise in coronary arteries produces forces capable of straightening these arteries and, therefore, relaxing the myocardium during diastole.

The rise in the aorta root blood pressure may also be achieved by injecting blood from an extracorporal source into the aorta root locked by an inflatable valve.

The control of the proposed CAD is effected by means of a command device which receives signals of the start of diastole from an analyzer of cardiac electric activity, and supplies the working medium to the balloons, thus making them expand for the duration of diastole and constrict for the duration of systole.

The length of interval Tc between the signals of the start of diastole may serve as an indirect indicator of the oxygen concentration in mixed venous blood. This allows one, by comparing the actual value of Tc with its prescribed value Tco , to change the intensity of CAD operation according to the Tc deviation from Tco. The intensity of CAD operation may affected by means of, e.g., valving the supply of the working medium. The prescribed value Tco may be set and adjusted by physician and/or by patient himself, according to his/her body feelings.

In order to introduce drugs into coronary vessels, the cardiac assist device is provided with an injector which, during diastole, pushes the drug via a drug catheter into the locked part of aorta, from which it is moved with the flow of blood into coronary arteries.

BRIEF DESCRIPTION OF THE DRAWINGS The further explication of the invention is made using its preferred embodiment and the attached drawings.

Fig. 1 — Schematic drawing of the squeezer placed into aorta and connected with the IABP balloon.

Fig. 2 - Schematic cut drawing of the squeezer in its (a) initial state, (b) state of being expanded up to touching the aorta walls, (c) final state.

Fig. 3 - Time diagrams of changes in the values: PA - blood pressure in aorta; PR - blood pressure in the aorta root; Ps - working medium pressure in the squeezer; Vs - volume of the squeezer.

Fig. 4 - Structural diagram of the system of coronary squeezer automatic control.

Fig. 5 - Schematic drawing of the coronary squeezer provided with the injector f or introducing drugs into coronary vessels.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to this invention, the cardiac assist device, as diagrammatically shown in Figure 1, consists of a coronary squeezer 1 and a counterpulsation balloon (IABP) 2. Said squeezer 1 is connected to the source of a working medium (e.g., helium or carbon dioxide) via the catheter 3, and to the IABP 2. The whole device is contained inside the aorta 4 in such a position, that the inlets of coronary vessels 5 are situated between the squeezer 1 and the aortal valve 6.

The coronary squeezer may be implemented either as a single elastic balloon or as a combination of an inflatable valve 1' and a balloon 1".

As shown in Figure 2, the squeezer 1 may also be implemented as a combination of an inflatable valve 1' and a balloon 1" separated by a valve. In this case, the closure of the aorta root is attained by inflating the valve, while blood is squeezed into coronary arteries by the balloon.

The squeezer 1 has three principal states. At the initial state la, the pressure inside the squeezer is equal to the blood pressure in aorta during systole; at the expanded state lb, the pressure inside the squeezer's valve 1' is increased to an extent enabling the said valve to completely lock the aorta root during diastole; at the state lc, the pressure in the balloon 1" is increased to an extent as to enable blood to enter the coronary arteries under the action of such pressure.

The diagrams shown in Figure 3 illustrate the processes occurring in the aorta root and in the squeezer during the proposed assist device operation.

The rise of pressure in the squeezer Ps at the starting phase of diastole results in its expansion, so that at the moment of time tc the squeezer volume Vs achieves the value Vsc sufficient for the squeezer to lock the aorta root, thus separating the latter from the other parts of aorta. Soon after that, owing to the continuing expansion of the squeezer, the pressure in the aorta root Pr rises to the prescribed value Pm and is maintained close to this value due to the further gradual expansion of the squeezer which compensates the outgoing flow of blood from the aorta root to coronary arteries.

At the end of diastole, the pressure Ps of the working medium falls to the value Pso, and the squeezer returns to its initial state la (Figure 2), in which state it remains during systole.

The force resulting from the difference in blood pressure in the aortal arc and in its root will be partially taken by the aortal walls, while a portion of this force will be conveyed by the catheter 3 to the IABP balloon 2 resting upon the walls of aortal arc or its descending part.

It is reasonable to maintain the intensity of coronary blood flow on a level necessary and sufficient for proper oxygen supply of myocardium under varying load. This level may be adequately controlled by acting on the blood pressure at the inlets of coronary arteries, the latter being a function of the corresponding pressure in the squeezer.

The pulse rate, which rises on oxygen's deficiency in tissues and falls on its abundance, may serve as a signal for increasing or decreasing the intensity of coronary blood flow.

A possible way of implementation of this principle is structurally shown in Figure 4.

The desired duration of cycle TCQ is set by means of adjustment, while its actual value Tc is established by the discriminator according to the interval between the heart beats. The

Claims (10)

difference TCQ - Tc acts upon the pressure PS by valving the working medium in such a direction as to keep the value Tc on a level close to TCQ. It should be possible, by a proper adjustment of TCQ, to select a mode of the squeezer operation ensuring the optimal, with regard to patient's health and comfort, blood circulation. Figure 5 schematically shows the coronary squeezer provided with a device for introducing drugs into coronary vessels. This device consists of an injector bellows 51 connected with a reservoir 52 containing the drug to be introduced. The injector 51 is connected with an output valve 55 by means of a catheter 54. Whenever the working medium enters the coronary squeezer (which occurs at the beginning of diastole), the actuator bellows 56 expands and compresses the injector 51, so that a dose of drug is injected, via the catheter 54 and the output valve 55, into blood locked at the aortal root 4, from which this blood, together with the drug contained therein, enters coronary arteries. Upon the end of diastole, the pressure of the working medium falls, and the actuator 56 constricts which results in expansion of the injector 51, and a dose of drug is sucked in via the input valve 53, to be injected during the next diastole. The invention's description presented above has to be seen as merely one of the possible embodiments. The idea of this invention permits its different technical implementations while following the claims as listed below. What is claimed is:

1. A cardiac assist device with a counterpulsation balloon and a coronary squeezer, comprising: (a) main and auxiliary inflatable balloons connected, by means of a catheter, to each other and to a source of a working med um, (b) a source of a working medium used for inflating the said balloons, (c) means for monitoring the electric activity of the heart, (d) command means for controlling the letting of the working medium in and out of said main and auxiliary balloons in a manner synchronized with the heart beats, (e) a controller of the intensity of device operation in accordance with the patient's body demand in oxygen, (f) means for introducing drugs into coronary vessels.

2. A cardiac assist device according to claim 1, wherein the main balloon is a conventional IABP, with the catheter and the auxiliary balloon being attached to its outlying (distal) end.

3. A cardiac assist device according to claim 1, wherein said auxiliary balloon is an elastic shell which, while being inflated, takes a pear-like shape thus locking the aorta root, with resulting increase in blood pressure in the locked aorta root.

4. A cardiac assist device according to claim 1, wherein said auxiliary balloon has the walls of a variable thickness: thicker at its inlet adjoining the catheter, and gradually thinning towards its top (proximal) end.

5. A cardiac assist device according to claim 1, wherein said auxiliary balloon is supplemented with an inflatable valve.

6. A cardiac assist device according to claim 1, wherein said command device contains means for analyzing the electric activity of the heart and forming the signals of (a) the start of diastole and (b) the end of diastole, which determine the moments for the command device to let the working medium in and out of said main and auxiliary balloons.

7. A cardiac assist device according to claim 1, wherein said controller of the intensity of device operation changes the pressure of the working medium used for inflating said main and auxiliary balloons in a manner depending on the difference between the pulse rate and a certain prescribed value.

8. A cardiac assist device according to claims 1 to 7, which additionally comprises an injector actuated by the same working medium as used for actuating the device.

9. A cardiac assist device according to claim 1, wherein the squeezer is implemented as a combination of an inflatable valve and a balloon, the said valve and balloon being separated by a valve.

10. A cardiac assist device according to any of the claims 1-8, wherein the dimensions of the inflatable valve are chosen so that the difference between the blood pressures in the aorta's arc and root results in a thrust force applied to the aorta walls, thus enabling the squeezer retained by such a force to produce an increased aorta root pressure. Signature: Alexander Lerner