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Analysis of the interbeat interval increment to detect obstructive sleep apnoea/hypopnoea

¹ Dept of Clinical Physiology and Exercise, Faculty of Medicine, Jacques Lisfranc University Jean Monnet, Saint-Etienne, France. ² Sleep Laboratory, Dept of Psychiatry, University Hospital, Geneva, Switzerland.

CORRESPONDENCE: F. Roche, Physiology laboratory, EFCR, CHU Nord - Niveau 6, F - 42055 Saint-Etienne Cedex 2, France. Fax: 33 477828447. E-mail: Frederic.Roche{at}univ-st-etienne.fr

Keywords: Autonomic nervous system activity, ECG Holter, heart rate variability, sleep apnoea/hypopnoea syndrome, sleep fragmentation

Received: March 25, 2006
Accepted January 16, 2007

The prevalence of obstructive sleep apnoea/hypopnoea syndrome (OSAHS) is underestimated and its diagnosis is costly and restricted to specialised sleep laboratories. The frequency component of interbeat interval increment (III) has been proposed as a simple and inexpensive diagnostic tool in OSAHS.

In a set of 150 patients with clinically suspected sleep-related breathing disorder, the actual predictive accuracy of the power spectral density of the III of the very low frequencies (%VLFI) was analysed by comparing with the apnoea/hypopnoea index (AHI), as assessed by synchronised polysomnography.

OSAHS was defined in 100 patients according to an AHI 15 events·h^–1. Receiver operator characteristic curves built for %VLFI confirmed that this variable was able to separate OSAHS positive from OSAHS negative with statistical significance. Using an appropriate threshold (>4%), %VLFI demonstrated a positive predictive value of 80%. Misclassification of false-positive subjects occurred when the patient presented significant sleep discontinuity and sleep fragmentation (sleep fragmentation index 50 events·h^–1) related to insomnia or periodic limb movements.

A power spectral density of the interbeat interval increment of very low frequencies >4% allowed correct classification of obstructive sleep apnoea/hypopnoea syndrome when the clinical history suggested sleep-related breathing disorders and when moderate-to-severe cases are considered. Higher power spectral density of the interbeat interval increment of very low frequencies may also indicate disrupted sleep in the absence of clear clinical symptoms of sleep apnoea/hypopnoea syndrome.