Journal of Applied Physiology, Vol 68, Issue 4 1443-1452, Copyright © 1990 by American Physiological Society
Assessment of rebreathing O2 consumption in humans with normal and diseased lungs
M. C. Kallay, R. W. Hyde and R. J. Smith
Department of Medicine and Toxicology, School of Medicine and Dentistry, University of Rochester, New York 14642.
We investigated sources of error in estimating steady-state O2 consumption
(VO2ss) by calculating O2 uptake from an anesthesia bag containing O2, He,
and N2 during 10-20 s of rebreathing (VO2rb). In 11 normal resting
subjects, VO2rb calculated with end-tidal sampling overestimated VO2ss by
16 +/- 15% (SD) (P less than 0.003). This error was proportional to the
increase in pulse rate during rebreathing, so that pulse-corrected VO2rb
slightly underestimated VO2ss by 2.1 +/- 12.2% (P = 0.66) in the six
subjects who rebreathed 28% O2 in the rebreathing bag but significantly
underestimated VO2ss by 7.5 +/- 6.7% (P less than 0.04) in the six subjects
who rebreathed 21% O2 in the rebreathing bag. During exercise, VO2rb
underestimated VO2ss by 4 +/- 12% (P less than 0.001) and by 7 +/- 6% at O2
consumptions greater than 2,000 ml/min if O2 in the rebreathing bag was
kept above 20% throughout rebreathing. We found that VO2rb calculated with
end-tidal gas concentrations underestimated VO2ss by 1-43% in patients with
moderate-to-severe obstructive lung disease, with even greater errors when
mixed expired samples were used. The magnitude of the discrepancy
correlated poorly with abnormalities in standard pulmonary function tests.
Based on these data, VO2rb closely approximates VO2ss in normal subjects,
provided hypoxia during rebreathing is avoided and cardiac acceleration
from rebreathing is taken into account during resting measurement.
