Foreign and soluble gas rebreathing methods are attractive for determining cardiac output (Q̇c) because they incur less risk than traditional invasive methods such as direct Fick and thermodilution. We compared simultaneously obtained Q̇c measurements during rest and exercise to assess the accuracy and precision of several rebreathing methods. Q̇c measurements were obtained during rest (supine and standing) and stationary cycling (submaximal and maximal) in 13 men and 1 woman (age: 24 ± 7 yr; height: 178 ± 5 cm; weight: 78 ± 13 kg; V̇O2max: 45.1 ± 9.4 ml·kg -1·min-1; mean ± SD) using one-N 2O, four-C2H2, one-CO2 (single-step) rebreathing technique, and two criterion methods (direct Fick and thermodilution). CO2 rebreathing overestimated Q̇c compared with the criterion methods (supine: 8.1 ± 2.0 vs. 6.4 ± 1.6 and 7.2 ± 1.2 l/min, respectively; maximal exercise: 27.0 ± 6.0 vs. 24.0 ± 3.9 and 23.3 ± 3.8 l/min). C2H 2 and N2O rebreathing techniques tended to underestimate Q̇c (range: 6.6-7.3 l/min for supine rest; range: 16.0-19.1 l/min for maximal exercise). Bartlett's test indicated variance heterogeneity among the methods (P < 0.05), where CO2 rebreathing consistently demonstrated larger variance. At rest, most means from the noninvasive techniques were ±10% of direct Fick and thermodilution. During exercise, all methods fell outside the ±10% range, except for CO2 rebreathing. Thus the CO2 rebreathing method was accurate over a wider range (rest through maximal exercise), but was less precise. We conclude that foreign gas rebreathing can provide reasonable Q̇c estimates with fewer repeat trials during resting conditions. During exercise, these methods remain precise but tend to underestimate Q̇c. Single-step CO2 rebreathing may be successfully employed over a wider range but with more measurements needed to overcome the larger variability.
All Science Journal Classification (ASJC) codes
- Physiology (medical)