Respiratory-related leg movements: what is the evidence behind the rules?

Abstract

Current sleep scoring rules exclude leg movements that occur near respiratory events from the scoring of periodic leg movements during sleep. While the AASM rules exclude leg movements that occur during a period of 0.5 s preceding to 0.5 s following an apnea or hypopnea, the WASM/IRLSSG rules consider only leg movements during 0.5 s before to 0.5 s after the end of an apnea or hypopnea. So far, the distribution of leg movements in relation to respiratory events is unknown and the aim of the present study was therefore to describe this distribution and contribute to the question whether there is evidence that favors one over the other of the two scoring rules Retrospective chart review and analysis of polysomnographic recordings. We included all patients with polysomnographic recordings between January 2010 and July 2011, aged 18 to 75 years, and AHI > 20, ODI > 10, more than 50% of apneas being obstructive, more than 15 leg movements/hour of sleep, no more than 20% of total sleep time with artifacts and no medical condition or medication that could influence leg movements or respiratory disturbances. Onset and duration of all leg movements (0.5–10 s), apneas, and hypopneas during sleep were extracted from the polysomnographic recordings. Polysomnographic recordings of 64 patients (55 male, 56 Â ± 11 years) were included in the analysis. Back-averaging of leg movement activity (LMA) with respect to the beginning, the middle, and the end of respiratory events revealed no indication that LMA was increased in the middle of respiratory events. Increased LMA before the beginning of the respiratory event consisted mainly of the longer tail of LMA after the end of the previous respiratory event. Importantly, LMA increased shortly before the end of the respiratory events, with peak onset of LMA 2.5 s after the end of the respiratory event. Our results showed that leg movements are not augmented at the beginning or middle of respiratory events but are increased around the end of respiratory events over a period significantly longer than specified in the AASM and the WASM/IRLSSG rules. Both rules therefore underestimate the number of respiratory leg movements in patients with obstructive sleep apnea.