title: Direct and indirect methods for determining plasma volume during thermoneutral and cold-water immersion.
abstract: Plasma volume (PV), determined indirectly from changes in haematocrit (Hct) and haemoglobin concentration ([Hb]), underestimates the absolute PV change (Evans blue dye) during thermoneutral immersion. Since PV changes during cold-water immersion have only been determined indirectly, we hypothesised that a similar underestimation may occur. Therefore, we compared the indirectly-measured PV with a direct-tracer dilution method (Evans blue dye column elution) in seven healthy males, during three, 60-min exposures: air (control; 21.2 degrees C), thermoneutral immersion (34.5 degrees C) and cold-water immersion (18.6 degrees C). During thermoneutral immersion, the directly-measured PV increased by 16.2 (1.4)% (P<0.05) and the indirectly-measured by 8.5 (0.8)% (P<0.05), with the latter underestimating the former by 43 (9.1)% (P<0.05). During cold immersion, the direct PV decreased by 17.9 (3.0)% (P<0.05) and the indirect by 8.0 (1.2)% (P<0.05), with the latter representing a 52 (6.8)% (P<0.05) underestimation of the direct PV change. Directionally-equivalent underestimations of PV change occur when using the indirect method during both thermoneutral and cold-water immersion. The assumptions inherent in the indirect method (constant F-cell ratio) appear to be violated during water immersion.
authors.affiliation: Faculty of Health Science, Australian Catholic University, Sydney, Australia.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gordon
authors.forename: Alison L
authors.initials: AL
authors.lastname: Fogarty
authors.forename: John E
authors.initials: JE
authors.lastname: Greenleaf
authors.forename: Nigel A S
authors.initials: NA
authors.lastname: Taylor
authors.forename: Jodie M
authors.initials: JM
authors.lastname: Stocks
mesh_terms: D000328:Adult; D001833:Body Temperature Regulation / Q000502:physiology*; D003080:Cold Temperature; D005070:Evans Blue; D006400:Hematocrit / Q000379:methods*; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D007101:Immersion; D007201:Indicator Dilution Techniques; D008297:Male; D010953:Plasma Volume / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic
chemical_list: D006454:Hemoglobins; D005070:Evans Blue