[Duration of inhalation and exhalation in increasing hypercapnia and the effect of additional resistive inspiratory resistance].

In healthy subjects, patterns of inhalation and exhalation durations during growing hypercapnia were studied in free breathing and under the effect of resistive inspiratory resistance 20 and 35 cm H2O/1/sec. Pattern of the inhalation duration was divided into two ranges: the inhalation elongated in the first range and shortened in the second one. The border between these ranges corresponded in free breathing to CO2 tension of exhalation terminal portion (PETCO2)--47.2 +/- 1.0 mm Hg (M +/- m). The 1st range was found in 2/3 of cases in the exhalation duration pattern. Under the effect of additional inspiratory resistance, the border between the two ranges of inhalation pattern shifted towards greater PETCO2 values and was 51.0 +/- 1.0 mm Hg for the greater resistance. The 1st range was found in 1/3 of cases in the exhalation duration dynamics. The shift of the border between the ranges of the inhalation duration pattern occurring in breathing with a resistive load in the course of growing hypercapnia seems to result from an augmentation of cortical effects upon breathing and/or weakening of afferent influences from the lung stretch receptors under these conditions.