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Excerpt
Conflicting studies of erythropoiesis have often used either carbon monoxide to estimate hemoglobin mass (HbmassCO) or Evans blue (EB) dye to estimate plasma volume (PVEB). Measuring hemoglobin concentration [Hb] and hematocrit (Hct) allows calculation of blood volume (BVCO = HbmassCO/[Hb] and BVEB = PVEB/(1-Hct)). PURPOSE: To measure HbmassCO and PVEB contiguously on athletes exposed to 4 wks of intermittent hypoxia (3h/day, 5d/wk at 4000–5500m) or double-blind placebo. METHODS: 48 pairs of BVCO and BVEB measurements were taken on 24 well-trained athletes (13 men, 11 women, 23 ± 8yrs, 174 ± 9cms, 68 ± 12kg; mean ± SD). HbmassCO was determined semi-supine from Δ%COHb after two doses of 99.9% CO; Dose1 = 20 or 15 ml, Dose2 = 1.5ml/kg or 1.25ml/kg for men and women, respectively. Samples were analysed (Radiometer OSM-3) in sextuplicate for %COHB and [Hb]. PVEB fully supine was determined without delay after CO-rebreathing. After an initial blood sample, ∼2.5 ml of EB was injected intravenously and blood re-sampled ∼10, 20 and 30 min later. The exact dye volume was determined as initial minus final syringe mass. After centrifugation, PVEB was calculated from time zero extrapolation of the regression derived from the 3 post-injection absorbances at 620 and 740 nm. The typical error (TE) of duplicate CO-rebreathing measures taken prior to treatment (= SD of difference scores/√2) was expressed as a percentage of the mean. RESULTS: BVCO = 5814 ± 1102 ml and BVEB = 6354 ± 1233 ml, respectively, and on average BVEB was 10 ± 8% higher. The linear regression between methods was BVEBD = 1.04 BVCO +320, r2 = 0.86, SEE = 465 ml. There was no change in BV in the hypoxic or placebo group for either method (F(1,21) = 0.27, p = 0.61). The TE for BVCO and HbmassCO before the intervention was 3.4% (95%CI = 2.7–4.8%) and 2.0% (95%CI = 1.6–2.7%), respectively. CONCLUSIONS: Our results do not support the assertion that CO may be distributed beyond the circulation to non-blood iron porphyrin molecules such as in muscle (myoglobin) and liver; CO did not overestimate BV. When carefully performed, both methods are suitable to measure blood volume and associated variables in athletes undergoing intermittent hypobaric hypoxia.
Supported by USOC, AIS & ACSM* (2003 International & Visiting Scholar Award Programs).
