Hypoxia briefly increases diuresis but reduces plasma volume by fluid redistribution in women

Abstract

We have recently reported that hypobaric hypoxia (HH) reduces plasma volume (PV) in men by decreasing total circulating plasma protein (TCPP). Here, we investigated whether this applies to women and whether an inflammatory response and/or endothelial glycocalyx shedding could facilitate the TCCP reduction. We further investigated whether acute HH induces a short-lived diuretic response that was overlooked in our recent study, where only 24-h urine volumes were evaluated. In a strictly controlled crossover protocol, twelve women underwent two 4-day sojourns in a hypobaric chamber: one in normoxia (NX) and one in HH equivalent to 3,500m altitude. PV, urine output, TCPP, and markers for inflammation and glycocalyx shedding were measured repeatedly. Total body water (TBW) was determined pre- and post-sojourns by deuterium dilution. PV was reduced after 12h of HH and thereafter remained 230-330ml lower than in NX (p<0.0001). Urine flow was 45% higher in HH than in NX throughout the first 6h (p=0.01), but lower during the second half of the first day (p<0.001). 24-h urine volumes (p≥0.37) and TBW (p≥0.14) were not different between the sojourns. TCPP was lower in HH than in NX at the same time points as PV (p<0.001) but inflammatory or glycocalyx shedding markers were not consistently increased. As in men, and despite initially increased diuresis, HH-induced PV contraction in women is driven by a loss of TCPP and ensuing fluid redistribution, rather than by fluid loss. The mechanism underlying the TCPP reduction remains unclear but does not seem to involve inflammation or glycocalyx shedding.

Changes in body mass, appetite-related hormones, and appetite sensation in women during 4 days of hypobaric hypoxic exposure equivalent to 3,500-m altitude

“… 37 ). Additionally, some of the body weight loss may have reflected the loss of fat-free mass (FFM) including body water, although the latter must have been minimal, given that as reported elsewhere ( 22 ), 24-h urine volumes were almost identical between sojourns (2,135 ± 142 vs. 2,130 ± 153 mL/day, for NX and HH, respectively P = 0.915), and changes in total body water throughout the sojourns were minimal (−0.108 liters vs. 0.003 liters in HH and NX, respectively; P = 0.347 n = 8) in our participants. Finally, intestinal malabsorption could have contributed to a negative energy balance in HH, although this seems unlikely as malabsorption is only described at much higher altitudes ( 7 ).…”

“…The experiments were conducted as part of a project investigating different physiological effects of 4 days of hypoxia in women ( 22 ). Participants completed two 4-day sojourns in a hypobaric chamber (terraXcube, Bolzano, Italy), with barometric pressure either unmodified [normoxia (NX), P B = 761 mmHg, 262 m] or reduced to the equivalent of ∼3,500-m altitude [hypobaric hypoxia (HH), P B = 493 mmHg).…”

Protective Effect of Modified Hemoglobin on Rabbits and Goats in High‐Altitude Sickness

“…Third, the protective effect of the administration of modified hemoglobin on altitude sickness at higher altitudes was not observed. Fourth, Siebermann [ 28 ] et al. demonstrated that modified hemoglobin in humans could lead to transient diuresis at high altitudes and further investigation in this regard is warranted.…”

24-hour urine volume and 24-hour urine creatinine excretion in general adult populations, a systematic review and meta-analysis.

“…Increased solar radiation places additional heat on the surface of the body, while wind increases heat transfer from the body surface, but also increases the insensible loss of water from exposed skin (88,90). Higher altitude corresponds to lower mean ambient temperature and lower atmospheric (barometric) pressure, possibly inducing a hypoxic-mediated increase in urine volume (89,91,92). The interplay between the different variables is extensive and we have not found any fully satisfying modelling of the effect of climate on human water loss in our literature review, the study of Yamada et al being the closest (87).…”