title: Initial mechanical efficiency of isolated cardiac muscle.
abstract: The aim of this study was to determine whether the initial mechanical efficiency (ratio of work output to initial metabolic cost) of isolated cardiac muscle is over 60%, as has been reported previously, or whether it is approximately 30%, as suggested by an estimate based on the well-established net mechanical efficiency (ratio of work output to total, suprabasal energy cost) of 15%. Determination of initial efficiency required separation of the enthalpy output (i.e. heat + work) into initial and recovery components. The former corresponds to energy produced by reactions that use high-energy phosphates and the latter to energy produced in the regeneration of high-energy phosphates. The two components were separated mathematically. Experiments were performed in vitro (30 degrees C) using preparations dissected from rat left ventricular papillary muscles (N=13). Muscle work output and heat production were measured during a series of 40 contractions using a contraction protocol designed to mimic in vivo papillary muscle activity. Net mechanical efficiency was 13.3+/-0.7%. The total enthalpy output was 2.16 times greater than the initial enthalpy output, so that initial mechanical efficiency was 28.1+/-1.2%.
authors.affiliation: Department of Physiology, Monash University, Clayton, Victoria 3800, Australia. c.barclay@griffith.edu.au
authors.forename: C J
authors.initials: CJ
authors.lastname: Barclay
authors.forename: C
authors.initials: C
authors.lastname: Widén
authors.forename: L J
authors.initials: LJ
authors.lastname: Mellors
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004734:Energy Metabolism / Q000502:physiology*; D006358:Hot Temperature; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D013816:Thermodynamics