The impact of averaging window length on the "Desaturation" indexes obtained via overnight pulse oximetry at high altitude

Study Objectives: To determine the impact of averaging window-length on the "desaturation" indexes (DIs) obtained via overnight pulse oximetry (SpO₂) at high altitude. Design: Overnight SpO₂ data were collected during a 10-day sojourn at high altitude. SpO₂ was obtained using a commercial wrist-worn finger oximeter whose firmware was modified to store unaveraged beat-to-beat data. Simple moving averages of window lengths spanning 2 to 20 cardiac beats were retrospectively applied to beat-to-beat SpO₂ datasets. After SpO₂ artifacts were removed, the following DIs were then calculated for each of the averaged datasets: oxygen desaturation index (ODI); total sleep time with SpO₂ < 80% (TST < 80), and the lowest SpO₂ observed during sleep (SpO₂ low). Setting: South Base Camp, Mt. Everest (5,364 m elevation). Participants: Five healthy, adult males (35 ± 5 y; 180 ± 1 cm; 85 ± 4 kg). Interventions: N/A. Measurements and Results: 49 datasets were obtained from the 5 participants, totalling 239 hours of data. For all window lengths ≥ 2 beats, ODI and TST < 80 were lower, and SpO₂ low was higher than those values obtained from the beat-to-beat SpO₂ time series data (P < 0.05). Conclusions: Our findings indicate that increasing oximeter averaging window length progressively underestimates the frequency and magnitude of sleep disordered breathing events at high altitude, as indirectly assessed via the desaturation indexes.