In patients with spinal muscular atrophy (SMA), obstructive sleep apnea syndrome (OSAS) constitutes an important cause of cardiovascular morbidity and mortality. We investigated heart rate variability (HRV) to evaluate the effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in patients with SMA and OSAS. Six patients with SMA (type 1 and 2) and six age- and sex-matched healthy children were consecutively enrolled. A whole-night diagnostic polysomnography was performed, and SMA patients with OSAS were given non-invasive mechanical ventilation therapy. HRV analysis was performed on the basis of whole-night electrocardiography recordings via a computer-base program. Apnea-hypopnea index (AHI) was 9.2 +/- 6.2/hr in SMA patients, while it was 0.4 +/- 0.5/hr in controls (p = 0.036). All SMA patients had OSAS, while none of the controls had OSAS (p = 0.012). Mean percentage of successive R wave of QRS complex (R-R) intervals > 50 ms was significantly lower in SMA patients than those in controls (p = 0.031). Significant correlations were found between AHI and high-frequency power, low/high-frequency ratio in wakefulness and in sleep (p <0.05). Repeated HRV analysis in SMA patients following OSAS therapy showed significant reductions in average R-R duration (p = 0.028) and percentage of successive R-R intervals >50 ms (p = 0.043). Our study demonstrates the beneficial effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in SMA patients with OSAS. (C) 2020 Elsevier B.V. All rights reserved.