Nocturnal pulse oxygen saturation dynamics at simulated high altitude: Predictive value for acute mountain sickness in healthy men born pre-term

The physiological sequelae of pre-term birth might influence the responses of this population to hypoxia. Moreover, identifying variables associated with development of acute mountain sickness (AMS) remains a key practically significant area of altitude research. We investigated the effects of pre-term birth on nocturnal oxygen saturation ( $S_{p{O}_2}$ ) dynamics and assessed the predictive potential of nocturnal $S_{p{O}_2}$ -related metrics for morning AMS in 12 healthy adults with gestational age < 32 weeks (pre-term) and 12 term-born control participants. Participants spent one night at a simulated altitude of ∼4200 m (normobaric hypoxia; fraction of inspired O₂ = 0.141), with nocturnal $S_{p{O}_2}$ and heart rate recorded continuously at the fingertip using pulse oximetry and with morning AMS assessed using the Lake Louise scale. Pre-term and term-born participants had similar nocturnal mean $S_{p{O}_2}$ (mean ± SD; 77% ± 3% vs. 77% ± 4%; P = 0.661), minimum $S_{p{O}_2}$ (median[IQR]; 67[4]% vs. 69[5]%; P = 0.223), relative time spent with $S_{p{O}_2}$ < 80% (72% ± 29% vs. 70% ± 27%; P = 0.879) and mean heart rate (79 ± 12 vs. 71 ± 7 beats/min; P = 0.053). However, the increase in $S_{p{O}_2}$ between the two halves of the night was blunted with prematurity (-0.12% ± 1.51% vs. 1.11% ± 0.78%; P = 0.021). Moreover, the cumulative relative desaturation-based hypoxic 'load' was higher with prematurity (32[26]%min/h vs. 7[25]%min/h; P = 0.039), underpinned by increased desaturation frequency (69[49] vs. 21[35] counts/h; P = 0.009). Mean $S_{p{O}_2}$ , minimum $S_{p{O}_2}$ , morning $S_{p{O}_2}$ and relative time spent with $S_{p{O}_2}$ < 80% predicted AMS incidence better than a random classifier exclusively in the pre-term group, with no other variables predictive of AMS in the two groups separately or combined. Overall, pre-term birth might alter nocturnal $S_{p{O}_2}$ dynamics and influence AMS prediction in severe hypoxia.