title: Characterization and work optimization of skeletal muscle as a VAD power source.
abstract: Powering a ventricular assist device (VAD) with skeletal muscle in a linear configuration will require the understanding of basic muscle mechanics and efficient use of available power. Accordingly, a mathematical model incorporating aspects of the Hill equation has been developed. This model relates whole muscle length, force, velocity, and time during cyclic contraction to investigate coupling with a hydraulically actuated VAD. Parameters of the model have been determined from in vivo isometric and isotonic measurements of electrically stimulated pig latissimus dorsi with the humerus insertion reattached to a hydraulic loading system. The in vivo results show an exponential passive force-length relationship and active isometric forces increasing from 2 to 8 kgf over a 5 cm change in length. The maximum shortening velocity extrapolated from isotonic data in 85 cm/sec. With the experimentally determined parameters, the model system of differential equations was optimized computationally. Predicted maximum cycle work and corresponding muscle force are nonlinear functions of contraction duration; an increase in duration yields little improvement in work output for longer contraction times. The model helps clarify VAD system design parameters for optimal muscle coupling; for example, the model predicts that operating at maximum instantaneous power does not optimize stroke work.
authors.affiliation: Department of Cardiac Surgery, California Pacific Medical Center Research Institute, San Francisco, USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Reichenbach
authors.forename: D J
authors.initials: DJ
authors.lastname: Farrar
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001698:Biomedical Engineering; D005069:Evaluation Studies as Topic; D006353:Heart-Assist Devices; D007537:Isometric Contraction / Q000502:physiology; D007551:Isotonic Contraction / Q000502:physiology; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology* / Q000601:surgery; D013552:Swine