Simultaneous measurement of the spontaneous eupneic pattern of breathing and pulmonary gas exchanges in normoxic and hypoxic subjects (author's transl)

Abstract

In 158 normoxic or hypoxic subjects suffering from different bronchopulmonary diseases, we studied relationships between eupneic respiratory frequency (fR) or tidal volume (VT) and (1) ductances of O2 (DuO2) or CO2 (DuCO2); (2) alveolar-arterial difference in PO2, measured from end-tidal value (ET-a) or calculated from mean alveolar gas (A-a). All these variables were simultaneously measured. The individual mean value of PO2 in arterial blood (Pao2) allowed us to separate our subjects in three groups of similar Pao2 ( ± 5%). Negative correlations were found in each group between DuO2 or DuCo2 and fR but the slope of the Duo2 vs. fR relationship decreased with Pao2. A positive correlation, unrelated to Pao2 value, exists between Duo2 and VT. D(ET-a)O2 and D(A-a)O2 were not correlated with fR or VT. A mathematical model was obtained using equations of ductances (Lacoste) and taking into account part of our results, i.e. independency between D(A-a)O2 and breathing pattern; this model allowed us to verify the experimental relationships obtained between Duo2 and fR or VT for different values of Pao2. Studying all the previous relationships in subjects classified by their VT or fR individual values, we showed that the effects of interindividual changes in fR on Duo2 and Duco2 were most potent. It was concluded that: (l)the interindividual variations of eupneic VT and fR were not related to the alveolar-arterial O2 difference; (2) the individual changes in breathing were correlated with Duco2 in all subjects but with Duco2 essentially in normoxic subjects. So the calculation of the theoretical value of Duco2 must consider both components of the individual breathing pattern and measured value of Pao2.