US 3303841 A
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Description (OCR text may contain errors)
Feb. 14, 1967 c. DENNIS 3,303,841
PROCESS AND APPARATUS FOR PRESSURIZING LOWER EXTREMITIES OF A PATIENT DURING VENTRICULAR DIASTOLE Filed June 18, 1964 IZ HINT CLARENCE DENNIS 4 4 United States Patent 3,303,841 PROCESS AND APPARATUS FOR PRESSURIZING LOWER EXTREMTHES OF A PATENT DURHNG VENTRICULAR DIASTGLE Clarence Dennis, Pelharn Manor, N.Y., assignor to the United States of America as represented by the Secretary, Department of Health, Education and Welfare Filed June 18, 1964, Ser. No. 377,178 9 Claims. (Cl. 128--24) My invention relates to the process of and apparatus for reducing the work of the left ventricle of the heart by forcing blood back into the aorta and great arterial vessels through external compression of the body during ventricular diastole and relieving this back pressure when the left ventricle is emptying to the aorta.
External compression of a part of the body will express a volume of blood larger than the volume of blood pumped in one stroke of the heart, this expressed blood being forced back into the aorta and great arterial vessels to reduce ventricular work while maintaining satisfactory body perfusion during ventricular diastole.
The principle of counterpulsation for support of the failing heart is known. Large cannulas are placed in the femoral vessels directed proximally and blood is removed from the aorta while the ventricle is ejecting blood into the aorta, thus permitting contraction of the left ventricle against a lower than normal pressure and thereby reducing the work of the left ventricle. An external pump is used to return blood to the aorta as soon as the end of the ventricular contraction has occurred and the aortic valve is closed. During the period in which the left ventricle is filling from the left atrium and lungs with the aortic valve closed, blood is returned to the aorta in suflicient volume to raise the pressure to a level equivalent to the peak pressure observed under control circumstances. In this manner, the amount of work required of the left ventricle is reduced while maintaining a satisfactory perfusion pressure in the arterial tree to take care of the needs of the entire body.
My invention avoids the necessity for the trauma of making incisions and putting cannulas into blood vessels and avoids the necessity of administering heparin to prevent clotting. A particularly effective technique involves squeezing blood out of the caudal arterial tree to produce a rise in aortic pressure during ventricular diastole and relieving the caudal arterial tree when the left ventricle is emptying to the aorta. A surveillance means, such as an electrocardiograph, can through a synchronizing means operate a compression means to compress and release the hind quarters and pelvis and thereby cyclically squeeze blood from the arterial tree in the desired synchronization with the cardiac cycle.
Other objects and advantages will become apparent in the course of the following detailed description, wherein:
FIG. 1 is a diagrammatic view of the human body and the apparatus of my invention;
FIG. 2 is a graphical showing from top to bottom of pressures in the left ventricle, aortic arch, and compression means, and also of the cardiac cycle as shown on the electrocardiograph; and
FIG. 3 is a perspective View of a flexible envelope used in my invention.
Referring now to FIG. 1, it will be seen that the body 15 is placed in a container 17 having an opening 18 therein which closely conforms to the lower torso of the body, the legs, hind quarters and pelvis of the body being housed within the container. The container 17 includes a two-piece cover 16 which forms opening 18 and which is tightly clamped to the walls of the container by swing clamps 19. The container includes an envelope 2%) of flexible material, such as mil polypropylene, which 33%,841 Patented Feb. 14, 1967 has peripheral outer walls 22 which conform to the inner confines of the container, the envelope 20 also having inner walls 24 which define a cavity for the part of the body within the container. As shown, the envelope 20 takes the form of what might be considered a pantaloon type garment, the material of the envelope completely contacting and engirdling the legs and lower torso of the body. A filling connection 26 is provided for filling the envelope with water, a suitable vent 28 being provided for exhausting air from the envelope as the envelope is filled. A flexible air bladder 30 is suitably positioned within the container 17 and connected through a solenoid air control valve 32 to a pressured air source such as tank and supply line 34, these elements making up a pressure means. The solenoid air control valve 32 is electrically connected to a synchronizing means 36 which in turn is connected to a surveillance means 38. When the surveillance means 38, which is electrically connected to the body, indicates the closing of the aortic valve, the synchronizing means 36 responds to this signal and actuates the solenoid valve 32 to admit air to the bladder 30 and to inflate the bladder and thereby increase the pressure in the bladder to a predetermined pressure as determined by the pressure setting and relief valve unit such as the pressure controller 40. When the bladder 3% is inflated as shown in FIG. 1, the pressure within the container is increased due to the incompressibility of the water in the envelope 20 and the legs and lower torso of the body part are compressed, thereby squeezing blood from the caudal arterial tree 42 back into the aorta 44 to establish a satisfactory perfusion pressure in the arterial tree. It will be understood that an electrocardiograph with voltage taps 39 can serve as the surveillance means 38 and that the synchronizing means 36 can take the form of an electronic timing device which will synchronize the compression means 46 with the cardiac cycle. It has been found that with a human being in a half pressure suit engirdling the lower torso and legs, approximately 7.5 gm./kg. of body Weight can be expressed from the legs and pelvis at a pressure of mm. Hg. The synchronizing means 36 in response to a signal from the surveillance means 38 identifying the opening of the aortic valve will cause the opening of the solenoid valve 32 and thereby exhaust the high pressure air from the bladder 30 to relieve the pressure in the container and relieve the pressure in the caudal arterial tree and the aorta to enable emptying of the ventricle against a lower aortic pressure.
It has been found that the use of an incompressible fluid to transmit the pressure developed by a compression means provides a fast and sound technique for accomplishing compression of the body part within the short time period afforded by the cardiac cycle. Suitably sized air fittings and air volumes are required to substantially instantaneously produce the required predetermined pressure in the bladder and to accomplish relief of this pressure in synchronism with the cardiac cycle. Fluids employed have been air and water although other gases and liquids may be substituted. The liquid should have a specific gravity equal to or greater than the blood when the body part is in the somewhat vertical position to prevent a top to bottom closing of the arteries in the body part.
It will be understood that the flexible polypropylene envelope 20 of FIG. 3 provides a feasible method of enveloping the body; a simple pant garment might also be used with the container 17 being made fluid tight and equipped with the necessary connections.
The air-liquid combination provides a fluid system capable of substantially instantaneous response to signals from the surveillance means 38 and synchronizing means 36.
An application of my process and apparatus to an 11 kg. dog involved a rigid container somewhat similar to that shown in FIG. 1 and having the opening 18 at one end precisely formed to fit the contour of the dog just above the pelvis. The envelope pressure was produced by a -14 p.s.i. pressure line with an air reservoir tank and a /4 inch solenoid communicating through a 1 inch iron pipe connection to a heavy rubber bladder in the bottom of the encasing box. The solenoid was activated through an electronic circuit so as to provide external pressure of predetermined duration, pressure level, or lag after initiation of ventricular contraction. The electronic circuit was triggered by the R wave of the QRS complex of the electrocardiograph; the beginning rise in the left ventricular pressure may also be used for triggering the electronic circuit. A tracheal tube was routinely placed for utilization of a Jefferson respiration and the left chest was opened for direct placement of polyethylene catheters (0.054 inch in external diameter) into the left ventricle and into the aorta. The electrocardiograph and pressures in the left ventricle, the aortic arch, and the compression envelope were recorded on a 4-channel Sanborn recorder, the recordings being shown in FIG. 2. Intra-abdominal pressure and venous pressure may also be recorded where desired. FIG. 2 shows typical recordings identifying changes in left ventricular and aortic pulse waves with external counterpulsation applied to the hind quarters. The left ventricular component of the aortic pressure curve is reduced from 112 mm. Hg to 90 mm. Hg. The left ventricular peak pressure is lowered from 112 mm. Hg to 100 mm. Hg. The imposed aortic peak pressure is 114 mm. Hg. Paper speeds: slow-O.25 mm./sec.; fast mm./sec. Use of a slow paper speed permits perspective as to relatively slow responses. For 5 to 6 seconds there was a rise in left ventricular and aortic arch pressure, followed by a mm. Hg drop, with resumption in about 30 seconds of a peak pressure in diastole slightly greater than the control systolic pressure. The left ventricular pressure rose late in the first 30 seconds of external counterpulsation to a level 12 to 15 mm. Hg below the control left ventricular systolic pressure. At the end of periods of external counterpulsation, the changes in left ventricular pressure were essentially mirror images of those at the beginning. The aortic arch pressure changes were slower to revert to control levels, but did so in 1% min.
The electronically controlled external counterpulsator unit of my invention has proven capable of raising the envelope pressure to 150 mm. Hg in 0.04 second and of permitting it to drop to the atmospheric level in 0.06 second. It has been possible to lower the peak aortic pressure 5 to 10 mm. Hg, to raise the aortic pressure during left ventricular diastole to levels higher than the control systolic pressure, and to lower the timetension index 8 to 10 percent. The time-tension index is a chief determinant of the work of the heart as measured by oxygen consumption and is determined by securing the product of the pressure against which the left ventricle must eject blood into the aorta and the duration of that ejection. Pressure tracings in an 11 kg. dog with pulse rate of 111 were obtained with 10 p.s.i. air pressure, a lag after the R wave of 0.12 sec. and a duration of compression of 0.32 see. FIG. 2 indicates the results of the application of my method and process to such a dog. It also has been noted that some reduction in time-tension index was obtained even though the envelope pressure peak was less than the systolic blood pressure. External counterpulsation as above discussed indicates that the effect on intra-abdominal and central venous pressure was very small.
The above application of my invention to a dog demonstrates that sufficient blood can be expressed from the buttocks and hind legs of the dog to be effective in lessening the time-tension index of the left ventricle, while providing a peak aortic pressure during left ventricular diastole equal to the control systemic blood pressure. The arterial blood expressible from the caudal arterial tree of a dog is of the order of magnitude of 3 ml./kg. of body weight. At pressures below 50 mm. Hg, much larger extremity weight losses occurred, these being attributed to expression of venous blood and lymph.
The fluid pressure developed in my apparatus is preferably in the range of 2 to 5 p.s.i. It will be noted that the anatomical and physiological characteristics of the human arterial system and the arterial system of a dog are somewhat similar, even though the dog normally has a higher blood pressure and faster pulse than the human.
As noted in the drawing, the body is preferably placed at an inclination of about 20 from the horizontal with the heart approximately at a level at or above the highest level of the fluid in the container, the fluid being oriented by the container to transmit pressure to the buttocks and to the lower torso preferably at and below the upper margin of the bony pelvis thereby to minimize compression of the internal organs. The inclination of the body may vary from patient to patient, the degree of inclination being similar to that presently employed in treating patients with acute left heart failure, the inclination being advantageous in that it positions the heart and upper part of the body at a level which tends to compensate for the increased pressure in the blood system produced by the liquid in the container in unpressurized condition.
While in an emergency, water may be used, it is advantageous that the fluid have a higher specific gravity than blood, satisfactory fluids being, for example, salt solutions such as magnesium sulfate solutions which have a specific gravity slightly higher than blood.
It will be understood that similar apparatus may be applied to one or both of the arms for compressing more peripheral portions of the distal arterial tree and suitably synchronized with the cardiac cycle to replace or supplement back pressure produced through compression of the lower torso, the arms being particularly suitable in that they provide greater volume-per-weight percentage of blood as compared to the lower torso. As seen in FIG. 1, a suitable arm container 50 schematically shown may be employed, this container being interconnected with the control and power components similar to container 17.
The exact synchronization of the solenoid valve varies somewhat from individual to individual and is influenced by the flexibility of the walls of the arterial tree and by the length of the great arteries. In the laboratory the development of the pattern of synchronization has been based upon pressure tracings from the ascending aorta and the lag after the QRS complex of the electrocardiogram, and the electronic circuitry is designed to permit adjustment of the duration of this lag and the duration of compression to the characteristics of the individual. In the clinical case it is uncomplicated to pass a fine flexible catheter through a hypodermic needle passed into the brachial or other artery to the aortic arch for verification of the synchronization. This requires neither incision nor anticoagulants.
1. The process of reducing the work of the left ventricle in the heart comprising surveillance of the cardiac cycle to identify the opened condition and the closed condition of the aortic valve, externally compressing the body when the aortic valve is in the closed condition to force blood back into the aorta to establish a satisfactory perfusion pressure in the aorta and arterial tree, relieving the compression when the aortic valve is in the opened condition to permit contraction of the left ventricle against a lowered aortic pressure.
2. The process of reducing the work of the left ventricle in the heart comprising surveillance of the cardiac cycle to identify the opening and closing of the aortic valve, externally compressing the hind quarters and pelvis of the body when the aortic valve is closed to force the blood from the caudal arterial tree back into the aorta to establish a satisfactory perfusion pressure in the aorta and arterial tree, relieving the compression when the aortic valve is open to permit contraction of the left ven tricle against a lowered aortic pressure.
3. A device for reducing the Work of the left ven tricle in the hear comprising surveillance means for identifying the opening and closing of the aortic valve, compression means for compressing the body, synchronizing means operatively interconnecting said surveillance means and said compression means for causing the compression means to compress the body when the aortic valve is closed to force blood into the aorta to establish a satisfactory perfusion pressure in the aorta and arterial tree, and for causing the compression means to relieve the compression when the aortic valve is open to permit contraction of the left ventricle against a lowered aortic pressure.
4. A device as defined in claim 3 and wherein said compression means includes a container having an opening therein for admitting and housing a part of the body, fluid surrounding said part of the body and filling the container, and pressure means acting on said fluid to raise and lower the pressure of the fluid in the container in predetermined response to signals from said synchronizing means.
5. A device as defined in claim 3 and wherein said compression means includes a rigid container having an opening therein for admitting a part of the body, an envelope of flexible material positioned within said container and having peripheral outer walls conforming to said container and inner walls, said inner walls defining a cavity in said envelope for the body part, incompressible fluid filling said envelope thereby causing said outer walls to contact said rigid container and said inner walls to contact and engirdle the body part, pressure means acting on said incompressible fluid to raise and lower the pressure of the fluid in the container in predetermined response to signals from said synchronizing means.
6. A device as defined in claim 5 and wherein said pressure means includes an inflatable flexible bladder positioned within said envelope and gas means connected to said bladder to inflate and deflate said bladder with gas in predetermined response to signals from said synchronizing means.
7. The process of reducing the work of the left ventricle in the heart comprising surveillance of the cardiac cycle to identify the opening and closing of the aortic valve, externally compressing the caudal arterial tree when the aortic valve is closed to force blood back into the aorta to establish a satisfactory perfusion pressure in the aorta and arterial tree, relieving the compression when the aortic valve is open to permit contraction of the left ventricle against a lowered aortic pressure.
8. The process of reducing the Work of the left ventricle in the heart comprising surveillance of the cardiac cycle to identify the opening and closing of the aortic valve, externally compressing the distal arterial tree when the aortic valve is closed to force blood back into the aorta to establish a satisfactory perfusion pressure in the aorta and arterial tree, and relieving the compression when the aortic valve is open to permit contraction of the left ventricle against a lowered aortic pressure.
9. A device as defined in claim 3 and wherein said container is positioned at an inclination from the horizontal to place the heart at about the level of the highest level of liquid in the container.
References Cited by the Examiner UNITED STATES PATENTS 4/1954 Erickson 128-24 X 9/1954 Fuchs 128-44