Polysomnography underestimates altered cardiac autonomic control in patients with obstructive sleep apnea.

Background: Repetitive nocturnal sympathetic activation during episodes of apnea and postapneic hyperventilation increases cardiovascular risk. The effects of hypopnea and non-apneic, non-hypopneic intervals before and after hypopnea/apnea on sympathico-vagal balance have not been assessed yet.

Hypothesis: Hypopnea and non-apneic, non-hypopneic intervals before and after hypopnea/apnea cause increased sympathetic activity when compared to normal respiration in nonREM stages 2–4.

Methods: A total of 34 patients were studied using in-laboratory polysomnography including continuous ECG recording. Absolute spectral power of heart rate variability in the very low (VLF), low (LF), and high frequency (HF) bands and low frequency to high frequency power ratio (LF/HF ratio) were analyzed during apnea, hypopnea, and during the pre- and post-phases of such respiratory episodes and compared to spectral powers during normal respiration in nonREM sleep 2–4.

Results: Patients with hypopnea and/or obstructive apnea showed higher power of VLF and the LF/HF ratio in intervals of hypopnea/apnea and in non-apneic, non-hypopneic intervals before and after hypopnea/apnea compared to normal respiration in nonREM stages 2–4.

Conclusion: The effect of sleep-disordered breathing on alteration of autonomic tone in patients with hypopnea and obstructive apnea is more severe than estimated by conventional polysomnographic assessment of apnea and hypopnea. Patients with sleep apnea show a sympathetic overdrive not only during phases of hypopnea and obstructive apnea but also in non-apnea, non-hypopnea intervals before and after hypopnea, and obstructive apnea.