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.
Laboratory for Human Environmental Physiology, NASA-Ames Research Center, Moffett Field 94035-1000 CA, USA.
J E
JE
Greenleaf
P A
PA
Farrell
J L
JL
Loomis
M J
MJ
Fedele
J
J
West
A
A
Rössler
H
H
Hinghofer-Szalkay
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