Optimization of pulse train duration for the electrical stimulation of a skeletal muscle ventricle in the dog

The optimal means of electrically stimulating a skeletal muscle to contract around a fluid-filled pouch (i.e., a skeletal muscle ventricle [SMV]) has not been determined. A SMV was made from the latissimus dorsi muscle in five dogs and the rectus abdominis muscle in five dogs, and each SMV was electrically stimulated via the motor nerve(s) to contract around a fluid-filled pouch, which was connected to a mock circulatory system. The pulse train duration (PTD) was varied from 100 ms to 800 ms in 100 ms increments to determine the effect of this variable upon SMV output. The pulse width of the electrical stimulus was kept constant at 100 microseconds and the pulse frequency was maintained at 50 s-1. For SMV contraction rates of 20, 30, and 40 min-1, the optimal PTD was 400 ms for both muscles. The peak output was 710 ml min-1 for the rectus SMV and 556 ml min-1 for the latissimus SMV. For an SMV contraction rate of 10 min-1, the optimal PTD was 800 ms for the rectus SMV and 600 ms for the latissimus SMV. Use of less than an optimal PTD caused reductions in SMV output of 25-50%. Although SMVs made from rectus abdominis and latissimus dorsi had similar values for the optimal PTD, the maximum SMV output was usually greater with the rectus abdominis in this acute study with untrained muscles. We conclude that PTD is an important variable to control, which can markedly affect results when studying the potential use of skeletal muscle power for cardiac assistance.