Journal of Applied Physiology, Vol 53, Issue 4 1034-1038, Copyright © 1982 by American Physiological Society
Evaluation of a method for estimating cardiac output from a single breath in humans
H. Chen, N. P. Silverton and R. Hainsworth
We have modified the single-breath method of Kim et al. (J. Appl. Physiol.
21: 1338-1344, 1966) for estimating cardiac output and arterial and mixed
venous carbon dioxide tensions (PCO2). We assessed this using 30 normal
subjects and 23 cardiac patients. The procedure was performed
satisfactorily in all but two patients. The random errors, from 60 pairs of
estimates of cardiac output in normal subjects and 50 pairs in patients,
were +/- 12.8 and +/- 19.6% (95% tolerance limits; i.e., coefficient of
variation multiplied by 2 for n greater than 50). The systematic error was
assessed in 15 patients from comparisons with results obtained by the
direct Fick method. There was no significant difference except in two
patients with large intracardiac shunts. Mean values of cardiac output by
single-breath and direct Fick estimates were 3.80 and 3.83 l/min. Arterial
and mixed venous PCO2 were estimated by the single-breath method with
random errors of +/- 1.5 and +/- 1.4 Torr, respectively, and no significant
systematic errors. We conclude that our modification of the single-breath
method is reliable in humans at rest, although the procedures for
delivering the breath and processing the data are of critical importance.
