Model-Based Assessment of Cardiovascular Autonomic Control in Children with Obstructive Sleep Apnea

Study Objectives: To quantitatively assess daytime autonomic cardiovascular control in pediatric subjects with and without obstructive sleep apnea syndrome (OSAS). Design: Respiration, R-R intervals, and noninvasive continuous blood pressure were monitored in awake subjects in the supine and standing postures, as well as during cold face stimulation. Setting: Sleep disorders laboratory in a hospital setting. Participants: Ten pediatric patients (age 11.4 +/- 3.6 years) with moderate to severe OSAS (obstructive apnea-hypopnea index = 21.0 +/- 6.6/h) before treatment and 10 age-matched normal control subjects (age 11.5 +/- 3.7 years). Measurements and Results: Spectral analysis of heart rate variability revealed that high-frequency power was similar and the ratio of low- to high-frequency power was lower in subjects with OSAS vs control subjects. The closed-loop minimal model allowed heart rate variability to be partitioned into a component mediated by respiratory-cardiac coupling and a baroreflex component, whereas blood pressure variability was assumed to result from the direct effects of respiration and fluctuations in cardiac output. Baroreflex gain was lower in subjects with OSAS vs control subjects. Under orthostatic stress, respiratory-cardiac coupling gain decreased in both subject groups, but baroreflex gain decreased only in controls. The model was extended to incorporate time-varying parameter changes for analysis of the data collected during cold face stimulation: cardiac output gain increased in controls but remained unchanged in OSAS. Conclusions: Our findings suggest that vagal modulation of the heart remains relatively normal in pediatric subjects with OSAS. However, baseline cardiovascular sympathetic activity is elevated, and reactivity to autonomic challenges is impaired.