Worsening hypoxic load impairs cardiorespiratory coupling

In obstructive sleep apnea (OSA), the hypoxic load is one of the key factors impairing cardiorespiratory coupling (CRC) but the acute effect of its severity on the degree of CRC has remained unknown. Our data comprised 603 clinical polysomnographies segmented into non-overlapping 5minute segments (n=36 926). We retrospectively studied the high-frequency ($\mathrm{HF}, \mathbf{0. 1 5 - 0. 4 0 \mathrm { Hz } \text {) coupling (} \mathrm { HFc } \text {) between }}$ heart rate variability (HRV) signal determined from electrocardiography and nasal pressure in these 5-minute segments, and compared the HFc in the groups divided by the severity of hypoxic load in the segments. We found that increasing hypoxic load gradually impairs the level of CRC in terms of HFc (decreased from 0.813 to $0.689, p{\lt}0.001$). Therefore, hypoxic load progressively weakens vagal modulation and could be utilized more thoroughly in conventional OSA diagnostics to better assess OSA-related cardiac stress.