Performance of Dynamic and Isovolumetric Trained Skeletal Muscle Ventricles 1

BackgroundDynamic training and maintaining muscle tension are important factors during skeletal muscle ventricle (SMV) conditioning that may improve SMV performance. This study sought to determine the effects of dynamic muscle training and progressive SMV resting pressure expansion on SMV pumping capability.Materials and methodsSMVs were constructed in 14 goats using the left latissimus dorsi muscle. SMVs were conditioned with a 40 ml constant-volume isovolumetric implant (n = 5, IsoVol group) or a compliant, pneumatic system that allowed dynamic shortening and direct exposure to resting pressures. Dynamic SMV resting pressure was either progressively increased from 40 to 100 to 120 mmHg (n = 5, HiP group) or maintained at 40 mmHg (n = 4, LowP group) during conditioning. After 8 to 10 weeks of electrical stimulation conditioning, SMVs were connected to a counterpulsation mock circulation system and SMV pumping performance evaluated across a range of pressures and stimulation parameters.ResultsSMV pumping performance was similar in each group. Stroke works generally increased with pressure and reached a plateau in all groups above 80 mmHg (120 msec contraction ∼80 mJ/stroke; 480 msec contraction ∼180 mJ/stroke). Stroke volumes decreased with pressure except at high stimulation levels where loading effects were observed. Chronic changes in SMV volume significantly effected pumping performance.ConclusionsThese data suggest that acute pumping performance is not different between 8 to 10 weeks of dynamic or isovolumetric training if SMV volume is not constrained. A potentially improved SMV conditioning protocol is proposed that determines, positions, and maintains SMV volume near the initial volume for maximal isovolumetric pressure during conditioning.