RELATION BETWEEN MUSCLE-CONTRACTION SPEED AND HYDRAULIC PERFORMANCE IN SKELETAL-MUSCLE VENTRICLES

Background The fatigue resistance and power-to-weight ratio of skeleta l muscle that has been conditioned by electrical stimulation makes car diac assistance from a graft of such muscle a realistic prospect. A sk eletal muscle must be surgically reconfigured to act on the circulatin g blood, but little is known about the power losses that accompany suc h interventions. We investigated in acute experiments the hydraulic pe rformance of approximately cylindrical pumps made from sheep latissimu s dorsi (LD) muscles, having first characterized the performance of ea ch muscle in situ. Methods and Results Force-length and force-velocity relations were measured in situ for LD that had received either 8 wee ks of stimulation at 2 Hz or no chronic stimulation. Two sizes of skel etal muscle ventricle (SMV) were formed from the same muscles, and the ir hydraulic performance was measured. The hydraulic performance was a lso calculated from the linear data, models of the force-length and fo rce-velocity curves, and a description of the stress distribution with in the SMV wall. The model predicted well the isovolumetric function o f the ventricles and the optimum afterload but overestimated the flow and therefore the power. In conditioned ventricles the performance was particularly poor because of the slow contractile properties of the m uscles. Conclusions If SMVs are to pump effectively against the arteri al impedance, the pressure drop caused by flow (or the internal resist ance) should be lower than that of the ventricles we constructed. Prog ress can be made through refinement of surgical technique and stimulat ion protocols that generate faster fatigue-resistant muscles.