Submitted on October 2, 2006
Accepted on May 30, 2007
Simultaneous Determination of the Accuracy and Precision of Closed-Circuit Cardiac Output Rebreathing Techniques
Sara S. Jarvis1, Benjamin D. Levine2, Gordon Kim Prisk3, Barbara E. Shykoff4, Ann R. Elliott5, Eric Rosow6, C Gunnar Blomqvist7, and James A. Pawelczyk1*
1 Kinesiology, Pennsylvania State University, University Park, Pennsylvania, United States
2 Medicine, University of Texas at Southwestern/IEEM, Dallas, Texas, United States
3 Medicine, University of California, San Diego, La Jolla, California, United States
4 Physiology, State University of New York at Buffalo, Buffalo, New York, United States
5 Medicine, University of California, San Diego, San Diego, California, United States
6 Premise Development Corporation, Hartford, Connecticut, United States
7 Internal Medicine, University of Texas at Southwestern Medical Center, Dallas, Texas, United States
* To whom correspondence should be addressed. E-mail: jap18{at}psu.edu.
Foreign and soluble gas rebreathing methods are attractive for determining cardiac output (Qc) because they incur less risk than traditional invasive methods such as direct Fick and thermodilution. We compared simultaneously obtained Qc measurements during rest and exercise to assess the accuracy and precision of several rebreathing methods. Qc measurements were obtained during rest (supine and standing) and stationary cycling (submaximal and maximal) in 13 males and 1 female (age: 24±7 yrs; height: 178±5 cm; weight: 78±13 kg; VO2max: 45.1±9.4 ml·kg-1·min-1; mean±SD) using one-N2O, four-C2H2, one-CO2 (single-step) rebreathing technique, and two criterion methods (direct Fick and thermodilution). CO2 rebreathing overestimated Qc compared to 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). C2H2 and N2O rebreathing techniques tended to underestimate Qc (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 non-invasive 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 Qc estimates with fewer repeat trials during resting conditions. During exercise these methods remain precise but tend to underestimate Qc. Single-step CO2 rebreathing may be successfully employed over a wider range but with more measurements
