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An experimental animal preparation is described which has allowed us to determine coronary haemodynamics and the overall myocardial metabolic rate of the disease-free, beating, normothermic heart during total cardiopulmonary bypass. We have confirmed that under these conditions the required coronary blood flow is about 50ml/min/100g myocardium, which can be achieved at a low perfusion pressure (60 mm Hg or 8 kPa), and that overall myocardial metabolism is represented by an oxygen utilization of just over 2 ml/min/100g. We have also defined the associated dynamic parameters which characterize oxygen transport in the coronary circulation during bypass. By controlling coronary perfusion, analogous in a clinical setting to selective coronary perfusion, we have demonstrated a simple linear correlation between perfusion pressure and coronary flow, indicating a "fixed" coronary vascular resistance. Under these conditions the myocardial oxygen uptake rises towards a maximum of 4ml/min/100g with the expected associated changes in the parameters characterizing oxygen transport in the coronary circulation. These trends are postulated as being a reflection of alterations in regional myocardial perfusion. By extrapolating to the clinical situation, these data have appeared to give valid information concerning the adequacy of coronary perfusion.
Richardson et al. (1979) studied this question.
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