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Time and Sample Site Dependency of the Optimized CO-Rebreathing Method


Medicine & Science in Sports & Exercise: June 2006 - Volume 38 - Issue 6 - p 1187-1193
doi: 10.1249/01.mss.0000222848.35004.41
SPECIAL COMMUNICATIONS: Methodological Advances

Purpose: A new method to estimate hemoglobin mass (Hbmass) requires capillary blood and rebreathing a carbon-monoxide (CO) bolus for 2 min. We hypothesized that incomplete circulatory mixing of CO could confound this method, so we compared capillary with venous blood to determine whether sampling site altered the percentage of carboxyhemoglobin (%HbCO) and the reliability and accuracy of the "2-min Hbmass." The conventional 20-min CO-rebreathing procedure was used as the Hbmass criterion.

Methods: In the first experiment (N = 12), both fingertip capillary and antecubital venous blood were sampled 4 and 6 min after commencing 2 min of CO-rebreathing. Within 8 d, these subjects completed two 2-min and one 20-min CO-rebreathing periods. For the latter, capillary and venous blood were collected simultaneously after two 10-min periods of rebreathing. In a second experiment (N = 6), both capillary and venous blood were sampled 4, 6, 8, 10, and 12 min after commencing 2 min of CO-rebreathing. A third experiment (N = 6) evaluated the reliability of a modified 2-min CO-rebreathing test with capillary blood sampled at minutes 8 and 10.

Results: Typical error (TE) for the first two 2-min tests was 1.1% (90% confidence limits 0.9-1.8%), but the average Hbmass from 2-min capillary blood was 4.8% lower than from venous blood for the 20-min procedure. In the second experiment, peak venous %HbCO occurred at minute 6, and the difference between capillary and venous values was minimal (mean ± SD; 0.08 ± 0.07, 0.01 ± 0.09) at minutes 8 and 10. TE for the third experiment was 1.2% (0.8-2.5%).

Conclusion: A modified 2-min CO-rebreathing procedure using capillary or venous blood sampled 8 and 10 min after starting CO-rebreathing allows complete circulatory mixing and provides an accurate and reliable estimate of Hbmass.

1Department of Physiology, Australian Institute of Sport, Canberra, AUSTRALIA; 2Sport Science Unit, South Australian Sports Institute, Adelaide, AUSTRALIA; and 3Departments of Clinical and Experimental Pharmacology and Thoracic Medicine, Royal Adelaide Hospital, Adelaide, AUSTRALIA

Address correspondence: C. J. Gore, Australian Institute of Sport, PO Box 176 Belconnen ACT 2616, Australia; E-mail:

Submitted for publication September 2005.

Accepted for publication January 2006.

©2006The American College of Sports Medicine