[Influence of sequential breath-holding on the slope of phase III (author's transl)]

Many factors contribute to the slope of phase III of the single-breath nitrogen test (SB-N2). By its effect of nitrogen concentrations, alveolar oxygen exchange may be responsible for a fraction of this slope. In fact, the slope of phase III is steeper when expiratory time is prolonged. We studied the effect of two sequential breath-holding periods of 20 seconds each with ten healthy young male volunteers, by SB-N2 and a reverse technique (SB-R). We observed a sudden increase (mean 1.27%) in the expired nitrogen concentration after each breath-holding period. Closing volume remained the same in all tests, but the slope of phase IV decreased by 44% in SB-N2A (SB-N2 with breath-holding) and increased by 55% in SB-RA. Expiratory vital capacity was significantly less after breath-holding. These data suggest that gas exchange during expiration is partly responsible for the slope of phase III.