Estimation of cardiac output and stroke volume from thermal equilibration and heartbeat rates in fish

Abstract

Cardiac output and stroke volume were estimated for a 200 g largemouth blackbass (Micropterus salmoides) by a modified whole-body thermodilution method using the relation between thermal equilibration rates and heartbeat frequencies. The reciprocal of the thermal time constant, k (min−1), was related to the heartbeat frequency, F (beats min−1), by the equation k=0.00146 F + 0.309; the slope is the weight-specific stroke volume (ml g−1) and the intercept is the weight-specific heat transfer constant (cal °C−1 min−1 g−1). Stroke volume was 0.292 ml (0.00146 ml/g body weight), yielding cardiac output values ranging from 44 ml kg−1 min−1 (at 30 beats min) to 158 ml kg−1 min−1 (at 108 beats min−1), or 4.4 to 15.8% of body weight. Active (convective) heat transfer due to blood flow constituted an estimated 11 to 34% (mean 22.5%) of total heat transfer, depending on heartbeat frequency; this variability constitutes physiological thermoregulation.