Linear performance characteristics of latissimus dorsi muscle: potential for cardiac assistance

Knowledge of the quantitative performance capabilities of skeletal muscle in a linear geometry is necessary to predict the performance and to optimize the design of linearly configured, skeletal muscle powered cardiac assist devices (MCADs). This study determined the performance characteristics of goat latissimus dorsi muscle (LDM) using a linear, ex vivo experimental apparatus. In five goats, the LDM (130.6 +/- 18.8 g) was dissected free of its distal attachments, connected to a series of weights (500 to 2250 g), and maximal tetanic contractions were elicited via thoracodorsal nerve stimulation. Second order polynomial equations were derived to represent each of the following variables versus load: muscle prestretch (range 1.5 to 5.4 cm), contraction duration (220 to 360 milliseconds), contraction shortening distance (13.5 to 10.9 cm), contraction velocity (60 to 31 cm/s), generated stroke power (3 to 7 W), and stroke work (0.7 to 2.4 J). Analysis of the potential stroke volumes obtained with a linearly configured, cylindrically shaped MCAD directly coupled to the circulation indicate that a feasible MCAD operating region exists based on the LDM performance data across a range of device geometries and mean ejection pressures.