Altitude-Induced Sleep Apnea Is Highly Dependent on Ethnic Background (Sherpa Vs. Tamang)

Abstract

Heiniger, Grégory, Simon Walbaum, Claudio Sartori, Alban Lovis, Marco Sazzini, Andrew Wellman, and Raphael Heinzer. Altitude-Induced Sleep Apnea Is Highly Dependent on Ethnic Background (Sherpa Vs. Tamang). High Alt Med Biol. 23:165–172, 2022.

Rationale:

High altitude-induced hypocapnic alkalosis generates central sleep apnea (CSA). In Nepal, two ethnic groups live at medium-to-high altitude: Tamangs originate from low-altitude Tibeto-Burman populations, whereas Sherpas descend from high-altitude Tibetans.

Objective:

To compare apnea severity at low and high altitude between Sherpas and Tamangs.

Methods:

Polygraphy recordings, including airflow and oxygen saturation, were performed in Nepal at “low” (2,030 m) and “high” (4,380 m) altitudes. Resting ventilation ( ${\dot{V}}_E$ ) and mixed-exhaled CO₂ (F_ECO₂) were also measured at the same altitudes. Differences in apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and % of nocturnal periodic breathing (NPB) at the two altitudes were compared between ethnicities.

Measurements and Main Results:

Twenty Sherpas and 20 Tamangs were included (males, median [interquartile range] age: 24.5 [21.5–27.8] years vs. 26.0 [21.5–39.8] years, body mass index: 23.9 [22.1–26.1] kg/m² vs. 25.21 [20.6–27.6] kg/m²). Compared with Tamangs, Sherpas showed a lower increase in AHI (+7.5 [2.6–17.2]/h vs. +31.5 [18.2–57.3]/h, p < 0.001), ODI (+13.8 [5.5–28.2]/h vs. +42.0 [22.6–77.6]/h, p < 0.001), and NPB proportion (+0.9 [0–3.5]% vs. +12.8 [3.1–27.4]%, p < 0.001) from low to high altitude. Resting ${\dot{V}}_E$ was higher in Sherpas versus Tamangs at both low (8.45 [6.89–10.70] l/min vs. 6.3 [4.9–8.3] l/min, p = 0.005) and high (9.7 [8.5–11] l/min vs. 8.74 [7.39–9.73] l/min, p = 0.020) altitudes, whereas the mean ± standard deviation F_ECO₂ decrease between low and high altitude was greater in Tamangs versus Sherpas (−0.50% ± 0.44% vs. −0.80% ± 0.33%, p < 0.023).

Conclusion:

Overall, altitude-adapted Sherpas showed a 3.2-times smaller increase in sleep-disordered breathing between low and high altitude compared with Tamangs, and higher ventilation and a smaller drop in F_ECO₂ at high altitude. These data suggest that genetic differences in breathing control can be protective against CSA.