Global and regional function in the regionally ischaemic left ventricle related to plasma ionised calcium

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Abstract
To study the response of function in the regionally ischaemic left ventricle to increased and decreased concentrations of plasma ionised calcium, twenty-two anaesthetised dogs were placed on right heart bypass with constant mean aortic pressure and heart rate. Regional (sonomicrometry) and global left ventricular function were assessed before coronary artery ligation. Then, following ligation, function after 45 min stable ionised hypercalcaemia ([Ca2+]=1.68±0.01 mmol·litre−1) and hypocalcaemia ([Ca2+]=0.73±0.02 mmol·litre−1) were each compared to function during an immediately preceding normocalcaemic period. Control of cardiac output enabled paired comparisons to be made at matched preloads: systolic shortening from common end-diastolic chord lengths (n=10), and stroke work at common left ventricular end-diastolic pressures (n=22). With hypercalcaemia, systolic shortening in the ischaemic region (2.11±0.39 mm preligation) increased from −0.62±0.17 to −0.04±0.20 mm (P−1, P−1). Hypercalcaemia also increased myocardial oxygen consumption (by 1.0±0.3 cm3·min−1·100 g−1, P<0.005) but not coronary blood flow. With hypocalcaemia, systolic shortening decreased in ischaemic and control regions, global function curves were markedly depressed, and myocardial oxygen consumption did not change but coronary blood flow increased. Thus hypercalcaemia improved function in ischaemic and control regions but improvement in the ischaemic region was small compared with the depression associated with ischaemia itself. Hypercalcaemia also improved global function, but not to preischaemic levels, at an increased oxygen cost.