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I have gotten behind on my reading. I know
there is alot more information on insensible fluid loss at altitude. I did
a quick search and I found a few things of interest. I do know there are
physiology texts out there that have this information in it. If I remember
right there is even equations out there to figure all this out.... I will
do some more research..
This furst url relates to Fluid loss in space lab
studies. Obviously we don't usually fly this high ;-) but I found it
interesting...
044 P12
Westerterp OPERATION EVEREST III: ENERGY AND WATER BALANCE@ Klaas R Westerterp, Mira Rubbens, Erwin Meijer, Paul Robach, and Jean-Paul Richalet. Maastricht University, The Netherlands and Association pour la Recherche en Physiologie de l'Environnement, France Energy and water balance was studied during progressive hypoxia from 422 to 253 Torr (5000 to 8848 m) over 30 days, after a 7-day acclimatisation at 4350 m, in a hypobaric chamber in COMEX, Marseille, France. Subjects were eight men, age 26+4 y, body mass index 22.4+1.4 kg/m2. Food and water intake were measured with weighed dietary record, energy expenditure and water loss with labeled water, food digestibility and protein balance from intake and fecal and urinary losses with bomb calorimetry and Kjeldahl. Energy intake over a 7-day normoxia interval was 13.6+1.8 MJ/d. Energy intake and expenditure decreased from 10.3+2.5 to 8.2+2.2 MJ/d (p<0.001) and from 13.3+1.6 to 12.2+1.7 MJ/d (p<0.001), respectively, over the first and second 15-day interval of the subsequent 30-day interval with progressive hypoxia. The resulting energy balance was -45+19 and -61+22 MJ, and body mass loss was 1.7 and 0.1 kg fat-free mass, and 0.9 and 1.1 kg fat mass, respectively, over the corresponding intervals. The loss of fat-free mass was confirmed by a negative protein balance of 15 to 25 g/d. Insensible water loss remained the same, i.e. 1.67+0.26 and 1.66+0.37 I/d. There was an increase in the heat of combustion of the feces from 22.4 kJ/g dry weight at normoxia to 23.7 kJ/g at day 23-25 (p<0.05), indicating a lower digestion efficiency. In conclusion, hypoxia induced a negative energy balance, mainly by a reduction of energy intake. Body mass loss was initially higher through a relatively larger loss of fat-free mass. The increase in insensible water loss by pressure reduction was compensated by a reduction in metabolic rate David Steele RN |