Global REACH 2018: renal oxygen delivery is maintained during early acclimatization to 4,330 m

Early acclimatization to high altitude is characterized by various respiratory, hematological, and cardiovascular adaptations that serve to restore oxygen delivery to tissue. However, less is understood about renal function and the role of renal oxygen delivery (RDO₂) during high altitude acclimatization. We hypothesized that 1) RDO₂ would be reduced after 12 h of high altitude exposure (high altitude day 1) but restored to sea level values after 1 wk (high altitude day 7) and 2) RDO₂ would be associated with renal reactivity, an index of acid-base compensation at high altitude. Twenty-four healthy lowlander participants were tested at sea level (344 m, Kelowna, BC, Canada) and on day 1 and day 7 at high altitude (4,330 m, Cerro de Pasco, Peru). Cardiac output, renal blood flow, and arterial and venous blood sampling for renin-angiotensin-aldosterone system hormones and NH₂-terminal pro-B-type natriuretic peptides were collected at each time point. Renal reactivity was calculated as follows: (Δarterial bicarbonate)/(Δarterial Pco₂) between sea level and high altitude day 1 and sea level and high altitude day 7. The main findings were that 1) RDO₂ was initially decreased at high altitude compared with sea level (ΔRDO₂: -22 ± 17%, P < 0.001) but was restored to sea level values on high altitude day 7 (ΔRDO₂: -6 ± 14%, P = 0.36). The observed improvements in RDO₂ resulted from both changes in renal blood flow (Δ from high altitude day 1: +12 ± 11%, P = 0.008) and arterial oxygen content (Δ from high altitude day 1: +44.8 ± 17.7%, P = 0.006) and 2) renal reactivity was positively correlated with RDO₂ on high altitude day 7 (r = 0.70, P < 0.001) but not high altitude day 1 (r = 0.26, P = 0.29). These findings characterize the temporal responses of renal function during early high altitude acclimatization and the influence of RDO₂ in the regulation of acid-base balance.