Apparatus For Applying Hydraulic Pulsation

Abstract

An improved external pressure circulatory assist device of the type comprising a mechanical means for transmitting a pressure pulse to a liquid-filled blanket wrapped about a patient's legs, the pulse being in synchronization with the heartbeat of the patient. A novel feature of the invention is that wherein air disturbed by the pulsing mechanism is isolated from the gas atmosphere in the vicinity of the aforesaid blanket and is vented to atmosphere, thereby improving the control of the pressure wave imparted by the circulatory assist action when negative pressure is being used in the immediate environment of the blanket.

Description

BACKGROUND OF THE INVENTION

This invention relates to a novel apparatus for assisting blood flow through the circulatory system by the use of external pressure on a patient's body. The invention particularly relates to a means for obtaining optimum control of the pulsing action when a negative pressure is used adjacent the hydraulic reservoir to which the pulsing action is transmitted.

Methods for atraumatically assisting blood circulation of patients have been described in the art. In U.S. Pat. No. 3,303,841 to Dennis, a process is described whereby an external compressing of the lower part of the body expresses a volume of blood larger than the volume of blood pumped in a single stroke of the heart. The blood so expressed is forced back into the aorta and greater arterial vessels, thereby allowing a reduction in ventricular work load while maintaining a satisfactory perfusion during ventricular diastole. This general type of process is elaborated upon in an article entitled "Synchronous Assisted Circulation," by Birtwell et al appearing in The Canadian Medical Association Journal (vol. 95, pages 652 to 664 on Sept. 24, 1966). In general, synchronous external pressure assist processes are distinguishable and advantageous over preexisting counterpulsation processes because the latter kind of procedures involve the cannulation of a major artery, use of an extra corporeal blood-handling device, the use of stringent sterile techniques and the necessity of administering anti-coagulants to the patient. Moreover, the blood trauma or hemolysis produced by extra corporeal pumping devices limits the permissible duration of the assist procedure and compromises the condition of the patient. Finally, these trauma-requiring procedures are time-consuming and can present a very significant hazard to many patients. They increase the risk factor in treating all patients.

In U.S. Pat. No. 3,654,919, filed by William C. Birtwell, an improved external assist apparatus was described wherein the effective pressure on the circulatory passages of the legs could be cycles to valves at or below ambient pressure. This apparatus, a major advance of the art, has been extensively used as a vehicle for evaluating the therapeutic potential of externally assisted circulation. At the present time, the external counterpulsation method, e.g. as is generally described in the Birtwell application, is the only controlled method which requires no surgical intervention or sterile procedures, no use of anti-coagulants or anesthesia, and produces no significant trauma. These factors are most important because they usually allow for much earlier use of the apparatus on the patient, in say, a state of circulatory show than could be justified if another type of assist apparatus had to be used.

Further advances in the development of this type of apparatus are described in U.S. Ser. No. 197,824, filed Nov. 11, 1971 by Harold S. Sauer et al and now U.S. Pat. No. 3,734,087. That application disclosed a platen mounted beneath the bladder enclosing the legs to provide a reciprocal vertical motion which controlled the magnitude of the positive pressure on the bladder. A novel mechanical linkage arrangement was used with the apparatus described in that invention. That mechanical linkage helped to minimize the input power requirements of the apparatus. This was achieved by providing a mechanism that provided relatively large displacement in the lower portion of the stroke where the reaction action pressure of the bladder against the platen is relatively low, but which at the upper portion of the stroke where the bladder reaction pressure materially increases, provided a displacement which was markedly reduced. In that manner, the stroke required of the hydraulic cylinder which operated the platen, and, consequently the power losses from pressure drop in a servo valve were held to a minimum.

Although the mechanism described on that application has been used successfully in a number of circumstances, it has been discovered that when negative pressure is used during the operation of such an external assist device, an undesirable difficulty was experienced in the obtaining and keeping of the optimum counterpulsation waveform.

SUMMARY OF THE INVENTION

Therefore it is the principal object of this invention to provide an apparatus for external pressure circulatory assist which apparatus may be operated at subatmospheric pressures with improved control of the pulsing cycle.

Another object of the invention is to provide a circulatory assist apparatus which has an improved mechanical pulsating means incorporated therein.

A further object of the invention is to provide a novel means for exerting pulsing action on the hydraulic blanket of an external circulatory assist device.

Still another object of the invention is to provide a novel means for operating a circulatory assist device.

It is a further object of the invention to provide a simple mechanical pressuring means which has relatively few bearing surfaces and has an improved life because of the incorporation therein of rotary bearing surfaces rather than linear bearing surfaces.

Still another object of the invention is to provide an improved mechanical pressurizing means which is advantageously enclosed within a rigid housing for an external circulatory assist apparatus. The mechanical forces exerted thereby have a minimum tendency to distort the leg unit in such a way as to either require relatively heavy construction techniques or have an undesirable effect on the control of the pressure pulse transmitted to the legs of a patient.

Other objects will be apparent to those skilled in the art on their reading of the instant application.

ILLUSTRATIVE EXAMPLE OF THE INVENTION

In this application and accompanying drawings there is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it in a variety of forms, each as may be best suited in the condition of a particular case.

IN THE DRAWINGS

FIG. 1 is a plan view of a mechanical actuating device constructed according to the invention with the top bearing part removed therefrom to better show the structural parts of the apparatus.

FIG. 2 is a side elevation of the apparatus shown in FIG. 1 with the device in the upward or expanded position.

FIG. 3 is a side elevation of the apparatus shown in FIG. 2 with the device in a contracted position.

FIG. 4 is a perspective view of a leg unit of the type in which the mechanical actuating unit of the type shown in FIGS. 1 through 3 is normally contained.

FIG. 5 is a section of the leg unit of FIG. 4, is somewhat schematic, has the bellows cut away and shows the mechanical actuating unit in place.

Referring to FIGS. 1 through 3, it is seen that a mechanical actuating means 10 comprises a platen 12 which is pivotally mounted at 14 on one end thereof and is connected to a mechanical linkage system 16 at the other end thereof. This platen 12 is actuated by a hydraulic cylinder 18 pivotally anchored at 20 to the frame 22 of the mechanism. Cylinder 18 is also fixed by bolt 24 and yoke 26 to operating shaft 28 of linkage system 16 at the other end thereof. Operating shaft 28 is in turn linked to two generally triangular cam bearings 30. Cam 30 is mounted for pivotal movement about shaft 32. And thus when the plunger 34 on hydraulic cylinder 18 exerts force on operating shaft 28 the triangular cam is forced to rotate in a clockwise direction about shaft 32. This causes arm 38 of cam 30 to be raised. Concurrently lever arms 39, pivotally mounted at each side of platen 12 and to cam bearings 30, are caused to raise platen 12. The surface of platen 12 has been partly omitted from FIG. 1 so that one can see the means by which diaphragm or bellows 41 is attached between frame 22 and platen 12.

In FIG. 1 is seen a flange 44 to which the lower section 42 of bellows 41 is attached. Flange 44 is the upper part of a bellows support structure 43 which is mounted on bottom plate 46 and with which bellows 41 forms a means to totally enclose the major portion of the volume between bottom of plate 46 and plate 12, thereby forming a housing for linkage system 16. A seal 47 is provided about the aperture through which cylinder 18 passes through bellows mount 43.

An exit path for gas expelled by the bellows is provided by vent 50.

In operation, when plunger 34 is caused to bear against operating rod 28 and thereby to rotate triangular cams 30 in the clockwise direction, the platen 12 rises pivoting about 14. Air is then sucked from the atmosphere into bellows 41. Conversely, when the platen is brought down by the retraction of the plunger, and there is a consequent compression of the volume enclosed by bellows 41, air is expelled through vent 50.

This arrangement has allowed an improved control to be achieved, especially when the apparatus is operated at subatmospheric pressure, i.e. when it is enclosed within a bag, such as shown at 57 in FIG. 5 on which a vacuum is drawn. Moreover, the linkage also has been found to be particularly advantageous because it minimizes stresses on the inside of housing leg housing 54 as seen in FIG. 5.

In order to fully understand the particular structural advantage of the linkage disclosed herein, it is necessary to refer to the apparatus disclosed in FIGS. 2 and 3 and 5. It is to be understood that any substantial deflection by the bladder 52 of the leg unit housing 54 must be avoided. Were housing 54 not rigid, distension thereof would make the desirable control of the counterpulsation cycle difficult or impossible. It is seen that the operation of the mechanical actuating unit is ideally adapted to minimize distending stresses on housing 54. For example, when the platen is being forced upward by the action of hydraulic cylinder and the mechanical linkage, forces 60 are exerted on the platen mechanism itself and consequently on the leg unit in which the platen mechanism is held. Using the mechanical actuating means of the invention bottom plate 46 can be much lighter since it only has to tolerate such tensile strength as, for example, that exerted by the vectors 60 shown in FIG. 2. These forces cause bottom plate 46 to be placed in tension but do not exert any significant bending stresses thereon. Moreover, when the two sections of the leg unit are held down by quick disconnect bolts 55 as seen in FIG. 4 and which screw into rods 56 and 58 as seen in FIG. 2, all the vertical forces tending to separate the top and lower segments of the leg unit are resisted as tensile stresses in rods 56 and 58. Again there is no moment which tends to impart a vertical bending movement at points 64 or 66. It will be noted that the leg sections of housing 54 are adapted to dissipate stresses therein as hoop stresses and thereby minimize any strain from said stresses.

As a consequence of the relative lack of a bending movement and the aforesaid distribution of forces in the structure of the invention, the housing unit can be made of much lighter material than had been the case with the earlier designs.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which might be said to fall therebetween.

Claims

What is claimed is:

1. In an external circulatory assist apparatus of the type comprising a reciprocating mechanical actuating means adapted to act, in synchronous relationship to the heartbeat of a patient, on a liquid-filled bladder confined in a rigid housing the improvement wherein said mechanical actuating means includes a means for mechanically isolating, and venting from said housing, gas which is displaced by said actuating means during its reciprocal movement.

2. Apparatus as defined in claim 1 wherein said isolation means comprises an enclosed chamber mounted between one side of a reciprocating platen which is acting on said liquid-filled bladder and means to discharge gas from said chamber to outside of said housing chamber.

3. Apparatus as defined in claim 2 wherein said chamber is formed of a bellows extending from said platen to a frame member within said housing.

4. Apparatus as defined in claim 3 wherein said bellows enclose mechanical linkage means to raise and lower said platen.

5. Apparatus as defined in claim 2 wherein said chamber encloses mechanical linkage means to raise and lower said platen.

6. Apparatus as defined in claim 5 wherein said external assist apparatus comprises means to affect subatmospheric pressure in the space within said housing but outside said enclosed chamber.

7. Apparatus as defined in claim 2 wherein said external assist apparatus comprises means to affect subatmospheric pressure in the space within said housing but outside said enclosed chamber.

8. Apparatus as defined in claim 3 wherein said external assist apparatus comprises means to affect subatmospheric pressure in the space within said housing but outside said enclosed chamber.

9. In a process for operating an external circulatory assist apparatus of the type wherein a first side reciprocating mechanical device is utilized to impart a pulsed pressure wave to limbs of a patient which limbs are wrapped in a liquid-containing bladder within a rigid housing, the improvement comprising the steps of

1. enclosing gas space between a second side of the reciprocating mechanical means and said housing of the apparatus, and

2. venting gas from said space to atmospheric pressure as said device reciprocates to alternately enlarge and decrease said enclosed space.

10. The process of claim 9 wherein a sub-atmospheric pressure is maintained in the environment of said bladder.

11. Apparatus as defined in claim 2 wherein said reciprocating platen is pivotally mounted

1. near a first end of a frame within said housing, and

2. also pivotally mounted to a mechanical linkage which connects the platen to the other end of said frame, and wherein a linkage-actuating means is mounted at said first end of said frame and formed means to actuate said mechanical linkage mounted at the other end of said frame thereby forming means to distribute stress as tensile stress applied to said frame and to minimize bending stresses on said frame and said housing.

12. In external pressure circulatory assist apparatus of the type comprising a reciprocating member bearing against a liquid-filled bladder adapted to enclose a patient's legs, said bladder and reciprocating member being enclosed in a rigid housing, the improvement wherein said reciprocating platen is pivotally mounted on a frame for said actuating means near a first end of said frame and pivotally mounted to a mechanical linkage positioned near the other end of said frame and wherein a piston-actuating cylinder is mounted at said first end of said frame, said cylinder forming means to actuate said mechanical linkage to actuate said reciprocating member and thereby dissipating mechanical stresses along the length of said frame and minimizing bending stresses therealong.

13. Apparatus as defined in claim 12 wherein said mechanical linkage comprises

1. a generally-triangular cam pivotally mounted to rotate in response to the movement of a piston-actuating cylinder, and

2. a lever arm attached between said cam and said mechanical means, said lever arm forming means to raise said mechanical actuating means upon the rotation of said cam.