An evidence-based recommendation for a new definition of respiratory-related leg movements

Abstract

Study objectives: Current sleep scoring rules exclude leg movements that occur near respiratory events from being scored as periodic leg movements during sleep (PLMS) but differ in whether they exclude leg movements occurring at the end (WASM/ IRLSSG) or during a respiratory event (AASM). The aim of the present study was to describe the distribution of leg movements in relation to respiratory events and to contribute to an evidence-based rule for the identification and scoring of respiratory-related leg movements (RRLMs).

Design: Retrospective chart review and analysis of polysomnographic recordings.

Setting: Clinical sleep laboratory.

Participants: 64 patients with polysomnographic recordings between January 2010 and July 2011, aged 18 to 75 years, with AHI >20, ODI >10, more than 50% of apneas being obstructive, >15 leg movements of any type per 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.

Interventions: None.

Measurements and results: Back-averaging of leg movement activity (LMA) with respect to respiratory events revealed that LMA was present shortly before the end of the respiratory events, but occurred mostly following respiratory events with peak onset of LMA 2.5 s after respiratory event termination. Increased LMA before the beginning of the respiratory event consisted mainly of the tail of LMA after the end of the previous respiratory event. Change-point analysis indicated that LMA was increased over an interval of -2.0 s to +10.25 s around the end of respiratory events. Changing the definition of RRLMs had a significant influence on PLMS counts. The number of patients with obstructive sleep apnea (OSA) with PLMS index >15 was 80% when considering the WASM/ IRLSSG definition, 67% for the AASM criteria, and 41% when based on the interval identified by change-point analysis (-2.0 to 10.25 s).

Conclusions: 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 underestimate the number of RRLMs and thus overestimate the number of PLMS in patients with OSA.

Keywords: Respiratory-related leg movements; periodic leg movements; sleep apnea.

Figure 1

Distribution of leg movement activity (LMA) ± 30 s around the beginning, middle, and end of respiratory events. The distribution of LMA was constructed based on the information (in ms) about the onset and duration of LMs that occurred within the depicted interval (for details see Methods). Upper panel: Distribution of respiratory-related LMA according to the WASM/IRLSSG criteria, which consider only the interval ± 0.5 s around the end of the respiratory event. Middle panel: respiratory-related LMA according to the AASM criteria, which consider an interval of −0.5 s before the beginning to +0.5 s after the end of respiratory events. Lower panel: All LMA observed around the beginning, middle, and end of respiratory events.

Figure 2

Upper panel: Distribution of the duration of respiratory events. Middle panels: Distribution of leg movement activity (LMA) around the middle of respiratory events, for all events and events with a minimum duration of 20 s, 30 s, and 40 s. The distribution of LMA was constructed based on the information (in ms) about the onset and duration of LMs that occurred within the depicted interval. Lower panel: Distribution of all LMA relative to the duration of the respiratory event. In addition, we constructed the relative distribution of LMs was obtained by setting the respiratory event duration to 100%, where 0% is the onset of the event, 50% the middle, and 100% is the end of the event. The occurrence of LMA was then transformed to this common relative metric.

Figure 3

Upper panel: Distribution of the intervals between respiratory events measured from the end of the first respiratory event to the beginning of the subsequent respiratory event. Middle panel: Distribution of leg movement activity (LMA) around the end (−10 s to +30 s, left middle panel) and the beginning of respiratory events (−30 s to +10 s, right middle panel). The dark parts refer to overlapping LMA, i.e., leg movements that occurred in both intervals, the light gray parts refer to remaining, unique leg movements not contained in the other interval. Of all LMs, 77.2% occurred in either one or both of these intervals. Of these, 69.5% occurred in both intervals, which represents 79.3% of all LMs around the end and 84.8% of all LMs around the onset of respiratory events. Lower panel: Distribution of LMA relative to the duration of the interval between respiratory events. Here, 0% denotes the end of the first event and 100% the start of the subsequent event.

Figure 4

Upper panel: Results of the change point analyses (see Methods). Change point analyses identified time points where a significant change in the statistical properties of the sequence occurs. The analyses identified 5 change points both for leg movement activity (LMA, left panel) and the onsets of leg movements (right panels). Middle panel: Distribution of the number of leg movements within the intervals identified by change point analysis. The dark parts show the distribution of the first leg movement in this interval, the light gray parts show the distribution of the 2^nd to 4^th leg movements during that interval. Lower panel: Frequency of multiple leg movements in the identified intervals. In the vast majority of cases (∼87%) only one leg movement was observed around the end of respiratory events.