Acid-base balance at high altitude in lowlanders and indigenous highlanders

Abstract

High-altitude exposure results in a hyperventilatory-induced respiratory alkalosis followed by renal compensation (bicarbonaturia) to return arterial blood pH(a) toward sea-level values. However, acid-base balance has not been comprehensively examined in both lowlanders and indigenous populations - where the latter are thought to be fully adapted to high-altitude. The purpose of this investigation was to compare acid-base balance between acclimatizing lowlanders, and Andean and Sherpa highlanders at various altitudes (~3,800, ~4,300, and ~5,000 m). We compiled data collected across five independent high-altitude expeditions and report the following novel findings: 1) at 3,800 m, Andeans (n=7) had elevated pHa compared to Sherpas (n=12; P<0.01), but not to lowlanders (n=16; nine days acclimatized; P=0.09); 2) at 4,300 m, lowlanders (n=16; 21 days acclimatized) had elevated pHa compared to Andeans (n=32) and Sherpas (n=11; both P<0.01), and Andeans had elevated pHa compared to Sherpas (P=0.01); and 3) at 5,000 m, lowlanders (n=16; 14 days acclimatized) had higher pHa compared to both Andeans (n=66) and Sherpas (n=18; P<0.01, and P=0.03, respectively), and Andean and Sherpa highlanders had similar blood pHa (P=0.65). These novel data characterize acid-base balance acclimatization and adaptation to various altitudes in lowlanders and indigenous highlanders.

Global REACH 2018: increased adrenergic restraint of blood flow preserves coupling of oxygen delivery and demand during exercise at high‐altitude

“…Second, we would like to acknowledge that there are physiological differences in the adaptative response to short versus long stays at HA, which have been well summarized elsewhere (Moore, 2017; Peacock, 1998). The current investigation took place after 21–28 days at HA, with blood work confirming the expansion of haemoglobin/haematocrit, and stabilization of $${P}_{{\rm{aO}}_{\rm{2}}}$$, $${P}_{{\rm{aCO}}_{\rm{2}}}$$, HCO 3 − (Tymko et al., 2022), and the expected persistent increase in muscle sympathetic nervous system activity (Tymko, Lawley et al., 2020). Third, we would like to acknowledge the relatively small sample size used during this investigation.…”

Thermodynamic limitations on brain oxygen metabolism: physiological implications*

“…For the Tymko et al. (2022) study the arterial state changes alone would reduce tissue O 2 /CO 2 to 52% of baseline, essentially at the critical level.…”

“…When a healthy subject living near sea level travels to high altitude and remains they exhibit a range of physiological changes as they acclimatize to the lower atmospheric P $$_{\text{O}_{2}}$$. Table 3 lists the measured changes in the physiological state for three studies of Lowlanders partially acclimatized to an elevation of ∼5000 m. The columns from left to right are arranged in decreasing order of the length of stay at altitude: 3 weeks at an altitude of 5260 m (Moller et al., 2002); 14–20 days at 5050 m (Caldwell et al., 2021); and 14 days at 5050 m (Tymko et al., 2022). In the first study (column 1) CBF and CMRO 2 also were measured and found to be unchanged from sea level.…”

“…Here we consider data reported by Tymko et al. (2022) (Table 4) for participants from these populations studied at ∼4300 m, and use the modelling to test how well tissue O 2 /CO 2 in the brain is being maintained. In this study, CBF and CMRO 2 were not measured.…”

“…Including these as assumed CBF changes, tissue O 2 /CO 2 is reduced to 64% of baseline for the Andean group, but increased to 57% for the Sherpa group. However, these results should be interpreted just as an illustration of the potential effect of CBF; we do not know if these changes apply to the subjects in theTymko et al (2022) study.…”