Leg unit inserts

[57] ABSTRACT

In an external pressure circulatory assist apparatus of the kind wherein hydraulic pressure is cycled against a patient’s legs usually in synchronization with the patient’s heartbeat, means to improve the performance of the apparatus on smaller patients by providing rigid leg inserts adapted to fit between the upper portion of a supine patient’s legs and a rigid shell for enclosing both the inserts and a hydraulic blanket. The inserts provide means to improve pressure cycle control on a patient’s legs.

Claims, 4 Drawing Figures

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PATENTED JAH 22 1974

SHEET 1 HF 2

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PATENTED JAN 2 2 1974

SHEET 2 OF 2

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FIG. 4

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LEG UNIT INSERTS used with a hollow or foam- or honeycomb-supported core to reduce the overall weight of the inserts and the

BACKGROUND OF THE INVENTION

This invention relates to improved external pressure circulatory assist apparatus of the kind wherein hydraulic pressure is cycled against a patient’s legs, usually in synchronization with the patient’s heartbeat cycle.

There has been a considerable effort in recent years in developing external pressure assist apparatus to exploit the potential of the process generally discussed in U.S. Pat Nos. 3,303,841 to Dennis and 3,654,919 to Birtwell. The more advanced of this work has utilized a liquid-filled blanket wrapped about the legs of a patient and enclosed in a strain-resistant housing that assures pressure is transmitted directly from a pressurecycling source (say, a reciprocating platen positioned between the legs as the patient lies supine) to the liquid-filled blanket wrapped about the leg. Such an arrangement is disclosed in commonly-owned and copending U.S. application Ser. No. 197,824 filed Nov. 11, 1971 by Sauer et al. and is embodied in apparatus commercially available from Medical Innovations, Inc. of Waltham, Mass, under the trademark Cardiassist.

It was noticed, however, that when smaller patients were treated with the above-described apparatus, it was difficult to maintain the desired pressure-time cycle with the apparatus even when adjustments were made in the stroke of the mechanically-actuated platen and in the amount of liquid used in the aforesaid blanket. This problem persisted even when the pressure apparatus was constructed to be substantially independent of pumping water in and out of the liquid-filled blanket and dependent primarily on the mechanical pulsation of liquid contained in a substantially non-extensible bladder.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide an improved leg housing for an external pres- ⁴⁰sure circulatory assist apparatus which provides improved pressure coupling between the legs of patients and mechanical pressurizing means.

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

The above objects have been substantially achieved by constructing a leg unit which reduces the amount of water required in the leg unit during treatment of the ₅θ patient and also reduces the potential of the occurrence of unsupported bladder area in the leg unit during operation. This apparatus comprises rigid, generally leg-conforming inserts of generally truncated conical shape and positioned between the liquid bladder in di- ₅₅rect contact with the inner wall of the rigid housing of the leg unit. These inserts must be formed of substantially non-deformable material; they may not be formed of deformable cushioning materials. Such inserts are advantageously fastened to the restraining housing of ₆θ the leg unit to prevent movement during use. This coupling can be achieved by use of mechanical fasteners of the conventional type, by providing a high-friction contact surface between the inserts and the housing or by any other means found suitable in a given situation. ₆₅

Fiberglass-reinforced polyester resin is one material suitable for construction of the leg insert members. Such a material is sufficiently rigid so that it can be unit.

Although not wishing to be bound by the theory, the 5 inventors believe that the particular advantage of the invention is primarily the result of avoiding so called end-effects, that is, small effects of pressure in the liquid blanket on the geometry of the blanket at the “ends” of the blanket, i.e. near the ankle and at the 10 upper thigh. Although with a non-extensible blanket these effects theoretically would be infinitely small, practical experience shows that a small amount of variation often occurs because of the hurried fit of the blanket when it is placed about the patient or some 15 other such practical consideration. It is the reduction of the annular volume at these end points which is the important aspect of the inserts.

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 25 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 ³⁰ 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 an exploded view of a leg unit useful in ex³⁵ temal pressure circulatory assist apparatus. The unit is shown with the control and mechanical-actuating modules removed.

FIG. 2 is an end view of an insert constructed for use in the invention, said view being taken from the ankle and of the insert.

FIG. 3 is a perspective view of the insert of FIG. 2.

FIG. 4 is a section of the apparatus shown in FIG. 1 showing the relationship of a liquid-containing, pressure-transmitting bladder, the rigid casing and the inserts of the invention.

Referring to FIG. 1, it is seen that a leg unit 10 adapted for use in external pressure circulatory assist treatment comprises an upper housing 12 and a lower housing 14. The upper and lower housings are connected one to the other by slide fasteners consisting of male members 16 mounted on housing 14 and female members 18 on housing 12. Three quick-connecting bolts 19 are utilized to connect the triangular lower housing reinforcing frame 20 to the upper housing reinforcing frame 22. This frame, combined with the hoopstress-resistant configuration of the leg unit provides excellent resistance to pressure-caused distortion of unit 10 by pressure created therein during treatment of a patient. The weight of unit 10 is minimized by providing a gloss-reinforced polyester shell reinforced in the triangular bracing area 24 by a honeycomb construction 26.

Within the housing is a liquid-filled blanket 28 which is adapted to enclose a patient’s legs. Only a fragment of blanket 28 is shown in FIG. 1. FIG. 4 shows a section of the entire blanket and also shows a mechanical actuator, i.e. a platen 30 mounted for reciprocating contact

3,786,802 ments of the scope of the invention which might be said to fall therebetween.