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

¹ Service de Physiologie Clinique et de l'Exercice, Faculté de Médecine Jacques Lisfranc Université Jean Monnet, Saint-Etienne, France
² Sleep Laboratory, Dept of Psychiatry, University Hospital, Geneva, Switzerland

	Abstract

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

We analysed on 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) by comparing with apnoea plus hypopnoea index (AHI) assessed by synchronised polysomnography.

OSAS was defined in 100 patients according to an apnoea plus hypopnoea index 15·h^-1. Receiver-operator characteristic curve built for %VLFI confirmed that this variable was able to separate OSAS+ from OSAS- with statistical significance (W value: 0.70±0.05). 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·h^-1) related to insomnia or periodic limb movements.

A %VLFI>4 allows correct classification of OSAS when the clinical history suggested sleep-related breathing disorders and when moderate-severe cases are considered. Higher %VLFI may also indicate disrupted sleep in the absence of clear clinical symptoms of OSAS.