title: Time and sample site dependency of the optimized co-rebreathing method.
abstract: OBJECTIVE
  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%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Physiology, Australian Institute of Sport, Canberra, AUSTRALIA. chris.gore@ausort.gov.au
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gore
authors.forename: Pitre C
authors.initials: PC
authors.lastname: Bourdon
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Woolford
authors.forename: Laura M
authors.initials: LM
authors.lastname: Ostler
authors.forename: Annette
authors.initials: A
authors.lastname: Eastwood
authors.forename: Garry C
authors.initials: GC
authors.lastname: Scroop
mesh_terms: D000328:Adult; D001775:Blood Circulation / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002196:Capillaries; D002248:Carbon Monoxide / Q000008:administration & dosage; D002263:Carboxyhemoglobin / Q000032:analysis; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008297:Male; D018962:Phlebotomy / Q000379:methods*; D015203:Reproducibility of Results; D013997:Time Factors; D014680:Veins
chemical_list: D006454:Hemoglobins; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin