Nocturnal short-term heart rate variability reflects impaired daytime vigilance better than overnight heart rate variability in suspected obstructive sleep apnea patients.

In obstructive sleep apnea (OSA), heart rate variability (HRV) decreases and performance in psychomotor vigilance task (PVT) worsens with more severe hypoxic load. Nevertheless, the association between HRV and PVT performance is poorly understood. Thus, we hypothesize that nocturnal short-term HRV is better related to daytime psychomotor vigilance compared with overnight HRV. To investigate this hypothesis, we retrospectively analyzed the electrocardiograms from polysomnographies of 546 consecutive patients with suspected OSA. We determined overnight HRV and short-term HRV in nonoverlapping 5-min segments and performed stepwise linear regression analyses to associate HRV with the median reaction time (RT) in the PVT. The short-term decrease in the median interval between two successive normal R peaks (NN interval), root mean square of successive NNs, and normalized high-frequency band power were all significant (p < 0.001) indicators of longer median RTs. However, the overnight HRV parameters did not indicate worsening median RT. Instead, increased hypoxic load and N3 duration were associated with longer median RT in men but not in women. The association of HRV and cardiorespiratory coupling with PVT performance was generally weak. Nocturnal short-term HRV evaluation reflected a state of vigilance better than the average overnight HRV. Thus, the overnight HRV analysis might not be optimal for patients with OSA. Utilizing the HRV analysis in a time-series manner and combined with the hypoxic load and sleep stages could bring new aspects to the health assessment of patients with OSA.