A novel work-loop calorimeter successfully measured the simultaneous rate of heat production and force-length work output of mammalian cardiac trabeculae, showing a maximum mechanical efficiency near 12%.
The development of a novel work-loop calorimeter allows for the simultaneous measurement of heat production and work output in isolated cardiac trabeculae, providing the first estimation of their net mechanical efficiency.
We describe a unique work-loop calorimeter with which we can measure, simultaneously, the rate of heat production and force-length work output of isolated cardiac trabeculae. The mechanics of the force-length work-loop contraction mimic those of the pressure-volume work-loops experienced by the heart. Within the measurement chamber of a flow-through microcalorimeter, a trabecula is electrically stimulated to respond, under software control, in one of three modes: fixed-end, isometric, or isotonic. In each mode, software controls the position of a linear motor, with feedback from muscle force, to adjust muscle length in the desired temporal sequence. In the case of a work-loop contraction, the software achieves seamless transitions between phases of length control (isometric contraction, isometric relaxation, and restoration of resting muscle length) and force control (isotonic shortening). The area enclosed by the resulting force-length loop represents the work done by the trabecula. The change of enthalpy expended by the muscle is given by the sum of the work term and the associated amount of evolved heat. With these simultaneous measurements, we provide the first estimation of suprabasal, net mechanical efficiency (ratio of work to change of enthalpy) of mammalian cardiac trabeculae. The maximum efficiency is at the vicinity of 12%.
Taberner et al. (2011) studied this question. Work-loop calorimeter was evaluated on Measurement of the rate of heat production and force-length work output. A novel work-loop calorimeter successfully measured the simultaneous rate of heat production and force-length work output of mammalian cardiac trabeculae, showing a maximum mechanical efficiency near 12%.