Skeletal muscle ventricle pressure-volume properties conform to dynamic and static conditioning

Chronic changes in skeletal muscle ventricle (SMV) size and strength can directly affect performance and stability. These changes may depend on the conditioning protocol or implant system. Therefore the effects of conditioning protocols on SMV geometry and contractility must be identified for optimal SMV design and application.

Skeletal muscle ventricles were constructed in 14 goats using the left latissimus dorsi muscle. The 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 mm Hg (n = 5, high pressure [HiP] group) or maintained at 40 mm Hg (n = 4, low pressure [LowP] group) during conditioning. The SMV pressure and volume characteristics were monitored daily.

All HiP SMVs expanded in volume during conditioning after exposure to physiologic pressures. Three of 4 LowP SMVs decreased in volume during conditioning. Skeletal muscle ventricle passive and active (isovolumetric evoked pressure) pressure-volume curves shifted toward the increasing, stable, and decreasing volumes in HiP, IsoVol, and LowP SMVs respectively.

Frequent monitoring of SMV characteristics during conditioning enabled progressive pressure training and is a valuable tool to evaluate SMV conformation. Chronic SMV adaptation is dependent on the conditioning protocol or implant system utilized. Demonstration of SMV expansion at physiologic pressures suggests that clinical sized SMVs may be chronically unstable unless a supporting implant system is utilized or SMV compliance is reduced. Therefore the mechanisms effecting chronic expansion should be further defined to optimally design SMVs for clinical implementation.