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Objectives: The Sherpa ethnic group living at altitude in Nepal may have experienced natural selection in response to chronic hypoxia. We have previously shown that Sherpa in Kathmandu (1400 m) possess larger spleens and a greater apnea-induced splenic contraction compared to lowland Nepalis. This may be significant for exercise capacity at altitude as the human spleen responds to stress-induced catecholamine secretion by an immediate contraction, which results in transiently elevated hemoglobin concentration ([Hb])., Methods: To investigate splenic contraction in response to exercise at high-altitude (4300 m; P b  = ~450 Torr), we recruited 63 acclimatized Sherpa (29F) and 14 Nepali non-Sherpa (7F). Spleen volume was measured before and after maximal exercise on a cycle ergometer by ultrasonography, along with [Hb] and oxygen saturation (SpO 2 )., Results: Resting spleen volume was larger in the Sherpa compared with Nepali non-Sherpa (237 ± 62 vs. 165 ± 34 mL, p < .001), as was the exercise-induced splenic contraction (Δspleen volume, 91 ± 40 vs. 38 ± 32 mL, p < .001). From rest to exercise, [Hb] increased (1.2 to 1.4 g.dl -1 ), SpO 2 decreased (~9%) and calculated arterial oxygen content (CaO 2 ) remained stable, but there were no significant differences between groups. In Sherpa, both resting spleen volume and the Δspleen volume were modest positive predictors of the change (Δ) in [Hb] and CaO 2 with exercise (p-values from .026 to .037 and R 2 values from 0.059 to 0.067 for the predictor variable)., Conclusions: Larger spleens and greater splenic contraction may be an adaptive characteristic of Nepali Sherpa to increase CaO 2 during exercise at altitude, but the direct link between spleen size/function and hypoxia tolerance remains unclear., (© 2024 The Authors. American Journal of Human Biology published by Wiley Periodicals LLC.)

Sonographic B-lines can indicate pulmonary interstitial edema. We sought to determine the incidence of subclinical pulmonary edema measured by sonographic B-lines among lowland trekkers ascending to high altitude in the Nepal Himalaya. Twenty healthy trekkers underwent portable sonographic examinations and arterial blood draws during ascent to 5160 m over ten days. B-lines were identified in twelve participants and more frequent at 4240 m and 5160 m compared to lower altitudes (P < 0.03). There was a strong negative correlation between arterial oxygen saturation and the number of B-lines at 5160 m (ρ = -0.75, P = 0.008). Our study contributes to the growing body of literature demonstrating the development of asymptomatic pulmonary edema during ascent to high altitude. Portable lung sonography may have utility in fieldwork contexts such as trekking at altitude, but further research is needed in order to clarify its potential clinical applicability., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Many physiological and anthropological studies have investigated the unique Andean and Himalayan populations that have resided for many hundreds of generations at high altitude (HA). A nonscientific survey of the extant literature reveals a relatively liberal tradition of inferring genetic (evolutionary) adaptation to HA in these groups, often based on limited evidence and/or based on study designs insufficient to fully address the issue. In order to provide some perspective, I review relevant methodological issues that should be considered before evolutionary inference is made. On the whole, this paper takes a conservative stance and cautions against evolutionary inference based on the serious limitations of currently applied research approaches.