Analysis of cable properties under hypoxia in cardiac muscles

This study was undertaken to determine the effect of hypoxia on the cable properties of the canine ventricular muscle, employing a single sucrose gap method. Hypoxia caused the internal longitudinal resistance, Ri, to increase by 25% (P smaller than 0.02) and the length constant, lambda, to decrease by 13% (P smaller than 0.05), significantly. The control values of Ri and lambda were 198 +/-76 omega cm and 0.81 +/- 0.15 mm (mean +/- SD, n=5, respectively. The membrane resistance, Rm, (control; 3026 +/- 581 omega cm2) decreased by 6%. The membrane capacitance and the time constant were not affected significantly. It was also examined whether the increase in Ri during hypoxia could be caused by hyperkalemia or acidosis, which are known to occur during hypoxia. The results showed that Ri was unchanged under acidosis (pH 6.1) to high K+ concentration (10.8 mM), thus suggesting the direct effect of hypoxia on Ri. These results suggest that the changes in the cable properties play important roles in the genesis of arrhythmias during hypoxia.