Journal of Applied Physiology, Vol 53, Issue 3 789-792, Copyright © 1982 by American Physiological Society
Metabolic gas effect on phase III slopes of single-breath nitrogen tests
Y. Cormier and J. Belanger
This study was designed to estimate the relative contribution of gas
exchange to the slope of phase III and the mean respiratory quotient (R)
during this maneuver. With eight normal volunteers, we studied
single-breath nitrogen tests and single-breath reversed tests (SB-N2, SB-R)
without and with CO2 added to the test inspiration (SB-N2CO2, SB-RCO2).
With an inspired CO2 of about 6% the slope of phase III in SB-N2 and
SB-N2CO2 increased from 0.87 +/- 0.24 (mean +/- SD) to 1.03 +/- 0.21%
N2.l-1 (P less than 0.01); however, in SB-R an SB-RCO2 the steepness of the
slope of phase III decreased from 0.65 +/- 0.13% to 0.50 +/- 0.14% N2.l-1
(P less than 0.01). From these data we can calculate that gas exchange
accounted for 13% of the slope of phase III in SB-N2 and SB-R. The mean R
value during the slope of phase III for this effect was between 0.6 and
0.7. R was further decreased when CO2 was added, and its influence was
increased to 26% of the slope of phase III.
