Surgery – Cardiac augmentation
Patent
1996-12-23
1998-06-16
Kamm, William E.
Surgery
Cardiac augmentation
A61M 110
Patent
active
057662070
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to equipment for, and methods for, driving pneumatically-operated apparatus such as pneumatically-actuated ventricular assist devices (commonly known as, and hereinafter called "VADs").
VADs are fitted to patients either singly (in a majority of cases) or as a pair to help the natural heart perform its blood circulation functions. The VADs can be located either para-corporeally or they can be implanted within the body; in either case suitable connections are made to the circulatory system of the patient.
VADs are used typically to support a patient recovering after surgery, or, in the case of heart failure, for example, to provide support to patients to enable them to maintain health whilst they are awaiting transplant surgery. In the latter case in particular, the VAD may be fitted to a patient for weeks or even months, until a suitable donor becomes available.
A pneumatically-actuated VAD may comprise a diaphragm-type or sac-type blood pump which is powered by subjecting the membrane separating a blood space from a gas space alternately to a forward flow of pressurised gas, such as air, for emptying blood from the VAD (systole), and to a reverse flow of exhaust gas under suction or partial vacuum pressure for inducing blood back into the VAD (diastole) to fill it in preparation for the next emptying phase. Thus, the VAD can be used either to pump blood in parallel (synchronously) with the heart, or in counter pulsation with the heart.
The operation of the pneumatic VAD is controlled by gas flow to and from its gas space via a gas supply line to subject the membrane alternately to a positive pressure (blood-emptying) and then to a partial vacuum pressure or negative pressure (blood-filling). This is achieved by connecting the VAD by means of suitable valves and tubing alternately to a source of high pressure gas and to a partial vacuum with means for controlling the flow. The rate of switching between alternate connections and the duration of each connection is controlled by a suitable microprocessor to provide the required blood pumping operation.
In prior art systems, the sources of high pressure and the partial vacuum (negative pressure) are provided in the form of reservoir gas tanks at high pressure, and at partial vacuum, respectively. Most commonly two separate pumping systems are used, which respectively maintain each reservoir at the appropriate pressure. Further, back-up sources of pressure, such as compressed gas cylinders, may also be provided.
Each pumping system, which can comprise one or more pumps or compressors, may be electrically driven and requires a battery or mains power source. The inlet of one pumping system may be used to establish a partial vacuum to be communicated to the VAD with the outlet of that pumping system typically being vented to the atmosphere. The outlet of the other pumping system may be used to establish a high pressure to be communicated to the VAD, typically with its inlet being open to the atmosphere.
Common driving equipment for operating a VAD therefore includes at least two gas reservoirs, two pumping systems (one for each reservoir), a power source, and the appropriate controller (control electronics). This equipment is typically contained in a separate housing which may be positioned beside the patient, and is connected to the VAD by means of suitable gas supply lines.
However, it is in many cases desirable for a patient to be able to move around on their own as easily as possible. This is especially true of patients wearing VADs for long periods of time who may otherwise be fit enough to leave their beds, for example, but are hindered by the need to take with them at all times the driver equipment for the VAD. In view of this, attempts have been made to make VAD drivers portable, so as to improve the patient's quality of life. To this end, the driver consoles have been placed on wheels such that the patient, or a helper, can wheel the driver console around as the patient moves. However, the driver's portability is constrained
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McCarthy Terrence Michael
Potter Charles David Ogilvy
Potter David Stuart
Wheeldon Dereck Ronald
Kamm William E.
Thoratec Laboratories Corporation
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