Altitude-induced sleep apnea is highly dependent on the ethnic (Sherpa vs Tamang) background

Abstract

High altitude-induced hypocapnic alkalosis generates central sleep apnea (CSA). In Nepal, inhabitants can be of different ethnic backgrounds: Sherpas descend from Tibetan ancestors whereas Tamangs originate from south-Asia. The aim of this study was to compare CSA severity at low and high altitude between these two Nepalese ethnic groups. Twenty Sherpas were compared to 20 Tamangs (all males, mean±SD age 26.6±9.7 vs 30.3±11.3 y.o., mean±SD BMI 23.9±3.00 vs 24.6±4.03 respectively). Polygraphic recordings with airflow, oxygen saturation and heart rate measurements were performed in Nepal at “low” (L) (29020m) and high (H) (49380m) altitudes. Ventilation (VE: L/min) and exhaled CO2 (PETCO2%) were also measured at rest at the same altitudes. Differences between H and L in apnea-hypopnea index (AHI), oxygen desaturation index (ODI) and % of nocturnal periodic breathing (NPB) were calculated. Compared to Tamangs, Sherpas showed a lower increase in AHI (+10.96±11.69/h vs +37.27±24.59/h, p<0.00012), in ODI (+17.9±14.3/h vs +46.7±29.1/h, p<0.004), and in NPB (3.3±6.9% vs 20.4±21.5%, p<0.002). Furthermore, Sherpas’ VE at rest was higher than in Tamangs at L (8.7±2.1 vs 6.6±2.1L/min, p < 0018) and H (10.1±2.1 vs 8.5±2.2L/min, p < 0,003) but FETCO2 dropped more in Tamangs between L and H (-0.8016±0.33% vs -0.504±0.44%, p<0.023). In conclusion, altitude-adapted Sherpas showed a 3.4 x lower increase in sleep breathing disorders between L and H compared to Tamangs as well as a higher respiratory drive and a lower drop in PETCO2 level at high altitude. These data suggest that genetic differences in breathing control can be protective from CSA.