RESUMO
Studies were undertaken for a mathematical analysis of reactive hyperaemia in the isolated rat heart with and without electrical pacing and the introduction of a new parameter i.e., rate of reactive hyperaemia, to evaluate reactive hyperaemia. Rate of reactive hyperaemia is represented as a change of coronary perfusion pressure in function with duration of reactive hyperaemia (delta P/DRH). The experiments were performed on the isolated rat heart using constant flow Langendorff's technique. Reactive hyperaemia was induced by interruption of coronary inflow for 30, 60, 120 sec. The electrical pacing produced two-phasic changes in the coronary perfusion pressure (CPP). Restoration of CPP (a long lasting gradual increase of coronary perfusion pressure after the period of ischaemia) correlated well with time following the logistic function. Correlation coefficient was 0.9485 (P < 0.05) with electrical pacing and 0.9892 (P < 0.05) for CPP restoration without electrical pacing. Duration of reactive hyperaemia was significantly (P < 0.05) shorter with electrical pacing than without it. However, the rate of reactive hyperaemia was not significantly different with or without electrical pacing. Fitting of the experimental results as well as the rate of reactive hyperaemia suggest the same mechanism of CPP restoration during the reactive hyperaemia with or without pacing. However, the extent of the phenomenon is significantly affected by pacing.