Plasma volume by Evans blue: effects of eating and comparison with other methods at altitude.
OBJECTIVE
Measurements of plasma volume (PV) and its changes (delta%PV) by Evans blue (EB) dye are presumed to be valid only in fasting subjects. In addition, delta%PVEB with acute altitude exposure has not been compared with other methods employing the concentration or dilution of naturally occurring blood (hematocrit (Hct), hemoglobin (Hb)) and plasma (density, proteins) components, but should be similar if capillary permeability and the sampled vein/whole body Hct ratio remain unchanged.


METHODS
PVEB was determined in six subjects while fasting or eating on different days, with injection and sampling in the same arm, 4-h extrapolation to time zero and correcting readings with the 620-740 A method. For 93 experiments at altitude, delta%PVEB was obtained similarly from a 3-h extrapolation near the end of a 12-h chamber exposure to 426 mm Hg (-4,880 m =16,000 ft) and at the same time on the preceding control day.


RESULTS
Mean PVEB with and without eating was not significantly different (SE of absolute difference = +/- 2.8%). The EB decay curves had significantly more scatter with eating than fasting. The fasting vs. non-fasting values for the single 20-min post-injection point also gave a close comparison (r = +0.97). At altitude the loss in PV measured with EB was significantly greater (delta%PVEB = -6.3%) than losses estimated from Hct-Hb (-2.9%), plasma protein (-3.7%), and plasma density (-3.9%). The expected larger PV loss in subjects tolerant to altitude sickness compared with intolerant ones was most clearly shown by delta%PVEB (8.8%).


CONCLUSIONS
Obtaining more samples can offset reproducibility lost by eating. The delta%PVEB were largest and nearest to values previously reported at altitude, perhaps because the single baseline and altitude samples utilized by the other methods are more sensitive to subtle, transient fluctuations in body water and vasomotor tone associated with apprehension, vomiting, fluid intake, and regional vasodilation and constriction.
Loeppky
Jack A
JA
New Mexico Resonance, Albuquerque 87106, USA. Loeppky@unm.edu
Luther
Deborah K
DK
Maes
Damon
D
Riboni
Katrina
K
Hinghofer-Szalkay
Helmut
H
Charlton
Gerald A
GA
Icenogle
Milton V
MV
D000328:Adult; D000531:Altitude; D004396:Coloring Agents; D004395:Dye Dilution Technique / Q000592:standards; D004435:Eating; D005070:Evans Blue; D005260:Female; D006801:Humans; D008297:Male; D010953:Plasma Volume
D004396:Coloring Agents; D005070:Evans Blue