Respiratory-Related Leg Movement as a predictor of mortality: the Osteoporotic Fractures in Men (MrOS) sleep study.

Study objectives: Respiratory event-related leg movements (RRLMs) in obstructive sleep apnea (OSA) may reflect event severity and predict adverse outcomes. This study examines the association between RRLM frequency and mortality.

Methods: A sample of 571 men (median [IQR] age: 76.0 [72.0-81.0] years; BMI: 28.0 [25.0-30.0] kg/m2) with an apnea-hypopnea index (AHI, ≥3% desaturation) ≥10 events/hour was selected based on available incident data and annotations of RRLMs, from the Osteoporotic Fractures in Men (MrOS) studies. RRLMs were scored if they occurred within ±5 seconds of respiratory event termination lasting 0.5-10 seconds; the average number of RRLMs per hour of sleep (RRLMI) was measured. For comparison, the number of periodic leg movements (PLMS) per hour of sleep (PLMI) was also quantified. Cox regression models estimated the adjusted hazard ratios (aHR) for mortality per SD increase in RRLMI and PLMI. Secondary analyses assessed the relationship between RRLM duration (i.e. a measure of RRLM strength) and measures of event severity (i.e. desaturation area, arousal, heart rate response, and event duration).

Results: There were 287 all-cause deaths during 11.4[6.9;12.5] years of follow-up. RRLMI and PLMI were 6.0[3.4;9.3] and 22.0[2.0;54.0] events/hour, respectively. In an adjusted model, every 1SD increase in RRLMI was associated with all-cause mortality (aHR:1.17[95% CI:1.01-1.34], p-value=0.03). In contrast, PLMI was not associated with mortality (aHR:1.04[95% CI:0.92-1.17], p-value=0.5). Furthermore, RRLM duration was linked to measures of event severity.

Conclusions: In a sample of older men with OSA, RRLMI was independently associated with all-cause mortality, whereas PLMI was not, though confirmatory studies are needed.