Stretch-induced increase in resting metabolism of isolated papillary muscle.

A mathematical model of oxygen diffusion into quiescent papillary muscles in vitro is developed. The model incorporates a continuous sigmoidal function relating the rate of oxygen consumption and the partial pressure of oxygen within the tissue. The behavior of the model is explored over a wide range of external oxygen partial pressures, oxygen consumption/partial pressure relations, oxygen diffusivities, muscle dimensions, and resting metabolic rates, while the muscle is subjected to stimulated stretches of various extents in order to test the assertion that the stretch-induced increase in basal metabolic rate observed experimentally implies the existence of an anoxic core region of papillary muscles in vitro. The model predicts the existence of an oxygen diffusion-mediated stretch response of resting papillary muscle metabolism, but one which is quantitatively insignificant compared with experimentally observed values. The classic Hill diffusion model which explicitly predicts an anoxic core, likewise predicts stretch effects of magnitudes smaller than those frequently observed. It is concluded that the increment in basal metabolism of papillary muscles subjected to stretch in vivo cannot be taken as evidence of oxygen diffusion limitation in unstretched preparations.