Sodium chloride-citrate beverages attenuate hypovolemia in men resting 12 h at 2800 m altitude.
BACKGROUND
The mechanism for reduction and restoration of total body water and plasma volume (PV) during initial exposure to acute altitude (ALT) is not clear but may involve involuntary dehydration; i.e., delayed voluntary fluid intake.


METHODS
Ten men (24 +/- SD 3 yr, 180.8 +/- 8.1 cm height, 78.8 +/- 12.8 kg weight, 1.99 +/- 0.19 m2 surface area, and 12.2 +/- 4.0% body fat) were in a semi-reclining position for 12 h in a chamber at 2800 m (539 mmHg) ALT or at 321 m (732 mmHg; ground). They ate a controlled breakfast (450 kcal + 3 ml x kg(-1) H2O) on the ground, and lunch and dinner at ALT (or on the ground) for a total daily intake of 2850 kcal (14% PRO, 67% CHO, 16% fat, 2.6g NaCl). At hour 10 they consumed fluid-electrolyte beverages or water (12 ml x kg(-1), 948 ml x d(-1)) in 4 sessions at weekly intervals. Beverage compositions were: a) 185 mEq x L(-1) Na+, 283 mOsm x kg(-1); b) 21.6 mEq x L(-1) Na+, 365 mOsm x kg(-1); c) water at ALT; and d) water on the ground.


RESULTS
After 10 h at ALT % deltaPV (Hb-Hct) decreased (p < 0.05) by: a) 9.0 +/- SE 1.5%; b) 6.2 +/- 1.7%; c) 7.4 +/- 2.2%; and d) by 9.0 +/- 2.4%, respectively. After drinking from 1000-1030 h, PV at 1200 h changed by: a) +8.3 +/- SE 2.0% (p < 0.05); b) +2.8 +/- 2.7% (NS); c) -0.9 +/- 1.5% (NS); and d) by +0.8 +/- 3.5% (NS), respectively. The similar ground-induced hypovolemia suggests a response to confinement rather than an ALT effect and involuntary dehydration does not appear to be implicated.


CONCLUSIONS
The significant increase in PV after consuming the (a) NaCl-NaCitrate beverage indicates that drink ionic composition appears to be more important than its osmolality for restoring PV in these conditions. Practical considerations: Because this hypovolemia was probably due to the confinement rather that reduced ambient pressure, appropriate countermeasures could be consumption of isotonic beverages, elastic stockings, leg exercise, and leg elevation.
Greenleaf
J E
JE
Laboratory for Human Environmental Physiology, NASA-Ames Research Center, Moffett Field 94035-1000 CA, USA.
Farrell
P A
PA
Loomis
J L
JL
Fedele
M J
MJ
West
J
J
Rössler
A
A
Hinghofer-Szalkay
H
H
D000328:Adult; D000337:Aerospace Medicine; D000531:Altitude; D001628:Beverages; D001834:Body Water / Q000187:drug effects; D002626:Chemistry, Pharmaceutical; D002940:Circadian Rhythm; D019343:Citric Acid / Q000627:therapeutic use*; D003681:Dehydration / Q000188:drug therapy* / Q000209:etiology* / Q000378:metabolism; D004311:Double-Blind Method; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D010953:Plasma Volume / Q000187:drug effects; D015532:Rehydration Solutions / Q000032:analysis / Q000627:therapeutic use*; D012146:Rest / Q000502:physiology*; D012965:Sodium Chloride / Q000627:therapeutic use*; D013997:Time Factors; D014195:Travel
D015532:Rehydration Solutions; D019343:Citric Acid; D012965:Sodium Chloride