The Ventricular‐Synchronous, Skeletal‐Muscle Ventricle: Preliminary Feasibility Studies

The two requirements for the optimal use of skeletal muscle wrapped around a pouch used to pump blood are.(1) a low poucli diastolic pressure (to assure a iiigh musde capillary blood flow; and (2) a high pouch precontraction pressure (PCP) (to assure a forceful muscle contraction). Both requirements are satisfied with the pumping method described herein. This new type of skeletal‐muscle ventricle (SMV) consists of a rectus abdominis muscle wrapped around a pouch connected to the left ventricular apex (with no valve) and to the aorta via a one‐way valve. Consequently, the pressure in the SMV pouch is always equal to left ventricular pressure. The high PCP is obtained by stimulating the rectus muscle to contract tt the desired left ventricular pressure. The R (or P) wave of the cardiac electrogram initiates a delayed train of stimuli to cause the rectus muscle to contract tetanically and expel Wood from the pouch. We have designated this pumping configuration the ventricular‐synchronous SMV (VS‐SMV). In this study, eight ucute anesthetized dogs were used. The muscles were unconditioned and among the items investigated were the importance of the delay (d) between the R (or P) wave and the onset of the stimulus train, the optimal stimulus frequency and train duration, the VS‐SMV output with different ratios of VS‐SMV to left ventricular contractions, unloading of the left ventricle, Frank‐Starling curves for the VS‐SMV, pressure‐volume loopsforthe VS‐SMV with and without contraction of the rectus muscle, and washout characteristics of the VS‐SMV. It was found that a stimulus frequency of 40/sec. and a train duration of 250 msec is optimal. It was also found that choice of the proper delay from the R or P wave provided maximal augmentation in stroke volume, typically 20 to 40 mL. Pumping with a ratio of 1:2 provided VS‐SMV outputs ranging from 20 to 140 mL/min per kg of body weight. With this same pumping ratio, cardiac output increased by 28% and the post‐VS‐SMV contraction, left ventricular stroke volume was reduced. The Frank‐Starling curves showed that PCPs on the order of aortic pressure are needed for the most forceful muscle contraction. With this new pumping configuration, the left ventricle resembles an atrium which delivers blood to the VS‐SMV that is stimulated to contract when the desired PCP is reached. Studies were also conducted in which the VS‐SMV outlet (valve end) was closed and filling and emptying occurred through the left ventricle. Saline washout studies were performed to determine the emptying characteristics with and without pumping using the closed‐end pouch. A typical emptying was 50% for five VS‐SMV contractions with the muscle contracting. However, even without the muscle contracting, there was washout due to the compliant recoil of the pouch which was stretched during ventricular systole. Essentially the same pumping performance was obtained with the closed‐end mode of operation.