Operation Everest III: energy and water balance

Abstract

We hypothesized that hypoxia decreases energy intake and increases total energy requirement and, additionally, that decreased barometric pressure increases total water requirement. Energy and water balance was studied over 31 days in a hypobaric chamber at 452-253 Torr (corresponding to 4,500-8,848 m altitude), after 7 days acclimatization at 4,350 m. Subjects were eight men, age 27+/-4 years (mean+/-SD), body mass index 22.9+/-1.5 kg/m2. Food and water intake was measured with weighed dietary records, energy expenditure and water loss with labelled water. Insensible water loss was calculated as total water loss minus urinary and faecal water loss. Energy intake at normoxia was 13.6+/-1.8 MJ/d. Energy intake decreased from 10.4+/-2.1 to 8.3+/-1.9 MJ/d (P<0.001) and energy expenditure from 13.3+/-1.6 to 12.1+/-1.8 MJ/d (P<0.001) over the first and second 15-day intervals of progressive hypoxia. Absolute insensible water loss did not change (1.67+/-0.26 and 1.66+/-0.37 l/d), however, adjusted for energy expenditure it increased with ambient pressure reduction (P<0.05). In conclusion, hypoxia induced a negative energy balance, mainly by a reduction of energy intake. Overall insensible water loss was unchanged because the increase in respiratory evaporative water loss was counterbalanced by a decrease in metabolic rate that probably limited the hypoxia-induced increase in ventilation.

Persistent suppression of resting energy expenditure after acute hypoxia

“…Although the relationship between obesity and increased energy expenditure has been shown [6], the impact of hypoxia, independent from obesity, on energy expenditure is less clarified. In healthy lean subjects, studied over 31 days in a hypobaric chamber corresponding to 4500-to 8848-m altitude, energy expenditure was significantly diminished [7]. The authors attributed the shift toward a negative energy balance to reduced food intake and thereby decreased energy supply, known from previous studies at high altitude [8], rather than to effects of hypoxia itself.…”

Nutrição para os praticantes de exercício em grandes altitudes

“…Na prática, no entanto, a perda total de água na altitude não é maior que ao nível do mar 42,43 . Um estudo mostra, ainda, que a perda total de água em relação ao nível do mar pode até diminuir em uma altitude de 4.350m, de 4,5 para 3,5 litros/dia, respectivamente, devido à diminuição na temperatura ambiente e no consumo voluntário de líquidos 44 .…”

“…Recomenda-se o consumo em torno de 3 a 5 litros por dia 32 , já que a diurese é regulada em função da ingestão hídrica e a retenção de fluidos na altitude é uma das causas da DAM 44 . Uma forma prática de observar a hidratação é monitorar a urina.…”

Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a request from the Commission related to the welfare of animals during transport

“…A further issue associated with aircraft hold conditions is the reduced barometric pressure and the reduction in water vapour density observed in the recycled air. Thus, whilst barometric pressure on the ground for the above journeys averaged 100kPa, in flight the value fell to 84kPa which will promote water loss (and dehydration) by altering the gaseous diffusion coefficient (Birchard 2000;Westerterp et al 2000). This situation would be exacerbated by low ambient humidity or water vapour density.…”