title: Model-based assessment of autonomic control in obstructive sleep apnea syndrome.
abstract: OBJECTIVE
  To quantitatively assess autonomic cardiovascular control in patients with obstructive sleep apnea syndrome (OSAS) using a mathematical model that relates changes in R-R interval (RRI) to respiration and changes in systolic blood pressure (SBP), and to compare the results obtained with conventional techniques.
  
  
  METHODS
  Respiration, RRI, and arterial blood pressure were monitored noninvasively in awake subjects in the supine and standing postures. A mathematical model was used to partition the fluctuations in RRI into a component ("RSA") correlated with respiration and a component ("baroreflex") correlated with fluctuations in SBP.
  
  
  METHODS
  Sleep disorders laboratory in a hospital setting.
  
  
  METHODS
  11 middle-aged male patients with untreated OSAS (apnea-hypopnea index = 75.9 +/- 11.1 (SE) events h-1) and 11 age-matched normal controls (10 males + 1 female).
  
  
  METHODS
  The subjects were monitored while breathing spontaneously in both supine and standing postures. Each subject also had to perform a battery of 5 standard autonomic stress tests (AST).
  
  
  RESULTS
  Four of the 5 ASTs did not indicate any difference between controls and OSAS subjects. There were also no differences in the indices derived from power spectral analysis of RRI and blood pressure variability; however, these spectral indices were sensitive to postural changes (orthostatic stress). Both RSA and baroreflex gains estimated from the model were substantially depressed in OSAS (P < 0.02) Changes in posture affected RSA gain but not baroreflex gain. The time-courses of the dynamics of these model components were not significantly different between subject groups.
  
  
  CONCLUSIONS
  OSAS leads to abnormal parasympathetic and sympathetic control of heart rate, as reflected in depressed RSA and baroreflex gains. Model-based assessment was more sensitive in detecting abnormal autonomic function, compared to standard autonomic testing and power spectral analysis. The model-based approach represents a relatively simple and nonintrusive means of quantifying the key aspects of autonomic control in spontaneously breathing OSAS patients during wakefulness.
authors.affiliation: Biomedical Engineering Department, University of Southern California, Los Angeles, California 90089, USA.
authors.forename: Vasily
authors.initials: V
authors.lastname: Belozeroff
authors.forename: Richard B
authors.initials: RB
authors.lastname: Berry
authors.forename: Michael C K
authors.initials: MC
authors.lastname: Khoo
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006973:Hypertension / Q000209:etiology; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D010275:Parasympathetic Nervous System / Q000503:physiopathology; D011187:Posture; D012119:Respiration; D020181:Sleep Apnea, Obstructive / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000503:physiopathology; D014851:Wakefulness / Q000502:physiology