Effect of adaptive pulse train duration on latissimus dorsi blood flow

Blood flow, intramuscular pressure, and stroke work of the trained latissimus dorsi muscle (LD) were measured during electrical stimulation at contraction rates between 20 and 160/min using pulse trains of 2 to 6 pulses in length. Epimysial electrodes and intramuscular pressure sensors were implanted in the LD of 5 dogs. The muscle remained in situ. After 12 weeks of a progressive training protocol, LD blood flow (BF) was measured using an ultrasonic flow probe and work (SW) was determined from the measured force and shortening. For pulse trains of 2 or 3 pulses, BF increased with rate, and SW was maintained at all rates. For 4 pulses, BF and SW decreased when the contraction rate exceeded 120/min. SW decreased above 100/min and 80/min for 5 and 6 pulses, respectively. An upper rate limit dependent upon the pulse train duration exists above which BF and SW decline. Exceeding these upper rate limits should be avoided in cardiomyoplasty. Excessive stimulation rates could be detrimental to the muscle by creating a metabolic insufficiency or ischemia. The cardiac assistance benefit is compromised as SW declines during high contraction rates of long pulse train duration.