The Use of an Electrically Activated Valve to Control Preload and Provide Maximal Muscle Blood Flow with a Skeletal‐Muscle Ventricle

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Abstract
A new method for optimally loading a skeletal muscle-wrapped pouch to act as a Wood pump is described. The method takes advantage of the fact that the high preload pressure required for a forceful contraction needs to be present for only a short time. By using an electrically controlled valve to delay pouch filing until just be/ore muscle contraction, pouch diastolic pressure can be kept low, which in turn maintains a high muscle capillary blood flow. The intrapouch precontraction pressure can be controlled by selecting the appropriate valve-open time (VOT). The pumping capabilities of untrained rectus abdominis and latissimus dorsi muscles were evaluated using a hydraulic circulatory system in a ten dog study (weight range 20–32.7 kg). The afterload was constant at 100 mmHg, and the pouch precontraction pressure, selected by choice of the VOT, was the test variable. It was found that for maximum pouch output, a precontraction pressure of 60–100 mmHg was required, being attained in this hydraulic model with a VOT of 400–500 msec. Typical pouch outputs were 400–600 mL/min with a muscle contraction rate of/40/min. Muscle capillary blood flow, measured with a periarterial electromagnetic flowmeter, varied inversely with pouch diastolic pressure and was near zero during tetanic muscle contraction. In one animal, a pouch output of 200 mL/min or more was maintained for more than 20 hours of continuous pumping without fatigue. In a related experiment, the method was applied to pump blood in a 32.7 kg dog, in which the muscle-wrapped pouch was connected between the descending thoracic aorta and the abdominal aorta. A pouch output of about 400 mL/min was obtained when the muscle was contracted 30 times/min and the VOT was 400 msec. This flow represented about 20% of the animal's cardiac output. This study demonstrates that by delaying pouch filling until just be/ore the muscle is to be contracted, a low pouch diastolic pressure can be maintained, thereby maximizing muscle capillary blood flow and, in turn, providing the best opportunity for prolonged pumping.