The Use of Electrically Stimulated Skeletal Muscle to Pump Blood

Electrically stimulated skeletal muscle can be used in many ways to pump blood. The important physiological characteristics of skeletal muscle for use in a cardiac assist role are presented. The force developed by a twitch and tetanic contraction are quantilated and the considerations in the choice of the stimulus applied to the innervating motor nerve are discussed. The importance of stimulus frequency and duration of the stimulus train are presented in terms of the stroke volume produced by skeletal muscle contracting around a pouch. The effect that preload has on pouch stroke volume and muscle blood flow are demonstrated. Finally an example is given in which cardiac output is augmented by an untrained, electrically stimulated, canine rectusabdominis muscle wrapped around a pouch connected between the apex of the left ventricle and the aorta. In this study, the augmentation in cardiac output was measured when the skeletal muscle was contracted after each second, third, and fourth ventricular contraction. The augmentation was 46%± 4, 31%± 7, and 25%± 4, respectively, for the three contraction regimens. Although electrically stimulated skeletal muscle can be used as a power source to assist the failing heart, the optimum application is yet to be discovered. Important considerations in selecting the optimal application are preload, stimulus train duration, train rate, and muscle blood flow.