Oxygen Cycles and Metabolic Autoregulation

Rhythmical three to eight per minute cycles in oxygen availability are characteristic of recordings from chronically implanted open tip polarographic electrodes. These were demonstrated to be progressively decreased in amplitude as mean arterial blood pressure was raised from 75 mm Hg to 160 mm Hg, at which level they were abolished. Amplitude of these cycles also decreased as BP was reduced below 75 mm Hg and they again disappeared at an iverage of 60 mm Hg. Oscillation frequency appeared to be a function of rate of metabolism, oeing reduced by anesthesia, hypothermia, and ischemia. An hypothesis is proposed which relates these oscillations to the feedback delay between metabolic generation of CO2 and the appropriate adjustment in tension of the pH sensitive muscle of the precapillary arteriole which in turn determines rate of local CO2 clearance. The changes in amplitude of the oxygen cycles may indicate alteration in pH reactivity of precapillary smooth muscle as a function of BP.