[Chemoreflex modification of the myocardial contractility of rabbits]

The effects of arterial hypoxia on the minute ventilation (AMV), the heart interval (HI), the contractility index (KI = (P/P) max., the left ventricular systolic pressure (LVSP), and the pressure-increase-time RP were tested before and after infusion of a selective stimulator of the arterial chemoreceptors (0.5 mg/kg Almitrine-Bismesylate). The arterial blood-pH and the paO2 were increased by Almitrine whereas the paCO2 was decreased significantly. The AMV is elevated, the heart interval and the RP-interval are reduced, KI and LVSP increase after Almitrine. The hypoxia-effects after changing the paO2 from 19 to 9 kPa are an increase of AMV, KI, LVSP and a shortening of HI and RP. These effects were intensified by Almitrine. The hypoxia effects were not changed by vagotomy. A correlation between the increase of the respiration and the appertaining cardiac effects was not discovered.