Frequency-domain analysis of oxygen stores during hypoxia in the goat.

Abstract

Sinusoidal variations of expired oxygen fraction (FEO2) and arterial blood oxygen saturation (S aO2) were measured in three paralyzed and anesthetized goats after producing sinusoidal changes in inspired oxygen fraction (FIO2) under controlled ventilation. These frequency-domain data were used to evaluate the quantitative dynamic relations amongFIO2,FEO2, oxygen uptake at the lung $$\dot VO_2 $$ andS aO2 using the material balance equation at the lung and the Fourier transform of this equation. The overall transfer function betweenFIO2 andFEO2 wasT(s)=0.07/(s+0.075) with a time constant of 13.3 sec, and $$\dot VO_2 $$ andS aO2(s) were related by a transfer function,G 1(s)=0.03/(s+0.008), with a time constant of 125 sec. The magnitude of the fundamental component ofS aO2(s), |S aO2(jw)|, was related to |FEO2(jw)| by a constant,K=0.607, asS aO2 remained near the linear portion of the O2-hemoglobin dissociation curve in moderate hypoxia. Based upon the present frequency-domain analysis, the slow time response ofS aO2 to the transient change of O2 concentration of the atmosphere is related to the homeostatic mechanism of the change of oxygen stores in the blood due to circulatory responses. The fast time response inFEO2 to the change ofFIO2 is produced by the tachometer feedback function of the oxygen stored in the functional residual capacity of the lung. The present analysis and experimental observation provide a new method of investigating oxygen uptake using frequency-domain analysis.