Nocturnal hypoxaemia in PAH patients living at high altitude relocated to low altitude

BACKGROUND: Patients with pulmonary arterial hypertension (PAH) living at high altitudes experience exacerbated hypoxaemia. This study aimed to assess the effects of relocating PAH patients from high altitude (2850 m) to sea level on nocturnal hypoxaemia, sleep-disordered breathing, and autonomic cardiovascular function. METHODS: In a repeated measures design, PAH patients underwent evaluations near their living altitude at 2850m and at sea level. The primary outcome was the change in mean nocturnal SpO2, while secondary outcomes included changes in time spent with SpO2 <90% (t<90), apnoea-hypopnoea index (AHI), heart rate variability (HRV), and blood pressure. Measurements were taken using cardio-respiratory polygraphy at 2850m and during the first two nights following relocation f to sea level. RESULTS: 28 patients (86% women) with a mean mPAP of 52±17 mmHg and PVR of 16.6±8.8 Wood units were included. Relocation to sea level resulted in significant improvements in nocturnal hypoxaemia, with mean SpO2 increasing by 6.9% (95% CI 5.9 to 7.9) and t<90 decreasing by -53% (95% CI -67.1 to -39.0). AHI and supine AHI decreased, and sleep quality significantly improved. HRV analysis showed increased parasympathetic activity, with RMSSD, pRR50, LF, and HF rising, and the LF/HF ratio decreasing. Morning PaO2 increased by 3.0 kPa (95% CI 2.3 to 3.7), and blood pressure significantly decreased. CONCLUSIONS: Relocation of PAH-patients from high to low altitude led to significant improvements in nocturnal oxygenation and SDB, and enhanced parasympathetic activity, suggesting that short-term exposure to sea level may offer benefits for PAH-patients living at high altitude.