title: Heart rate variability is augmented in patients with positional obstructive sleep apnea, but only supine LF/HF index correlates with its severity.
abstract: OBJECTIVE
  Data on cardiac autonomic functioning, as expressed by heart rate variability (HRV), in patients with positional obstructive sleep apnea (p-OSA) disorder are lacking. The purpose of the study was to compare HRV indices between sleep segments derived from supine body position and another body position with and without apneic events, respectively. Our intention was to find some correlation between HRV indices and the pathophysiological characteristics of the corresponding temporal period.
  
  
  METHODS
  Nocturnal polysomnograms derived from twenty-seven patients (22 men) with documented positional apnea were retrospectively reviewed. Patients never treated for OSA and free from diseases/drugs altering HRV were examined. Data from total sleep studies were collected. Two N2 sleep segments, from supine body position with sleep-disordered breathing (SDB) and another body position without SDB were analyzed. Apneic events (namely, apneas, hypopneas, and respiratory effort-related arousals (RERAs)), arousals, number of desaturations, minimum pulse oximetry (SaO2min), time domain variables (average RR, SDNN, SDSD, RMSSD, pNN50, and HRV triangular index) and frequency domain variables (VLF, LF, HF, TP, LF/HF) were recorded for both temporal periods.
  
  
  RESULTS
  With the exception of average RR and HF, all other variables were significantly higher in segments with SDB. Only LF/HF_supine ratio was positively correlated with the apneic_supine_index (t = 3.13, p < 0.01) and negatively correlated with SaO2min (t = -2.9, p < 0.01) and the desaturation_supine_index (t = -2.5, p = 0.02). Arousals were negatively correlated with SaO2min (t = -2.8, p < 0.01).
  
  
  CONCLUSIONS
  SDB augments autonomic tone in patients with p-OSA, but only LF/HF correlates with its severity and might be used as a screening tool in the future. On the contrary, parasympathetic tone, as reflected by HF, remains constant in both periods.
authors.affiliation: First University Department of Critical Care and Pulmonary Services, Center of Sleep Disorders, Medical School of Athens University, Evangelismos General Hospital, 45-47 Ipsilantou str., 10676, Athens, Greece, kflevari@gmail.com.
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Flevari
authors.forename: Emmanouil
authors.initials: E
authors.lastname: Vagiakis
authors.forename: Spyridon
authors.initials: S
authors.lastname: Zakynthinos
mesh_terms: D000328:Adult; D000368:Aged; D001341:Autonomic Nervous System / Q000503:physiopathology*; D015331:Cohort Studies; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012189:Retrospective Studies; D020181:Sleep Apnea, Obstructive / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology*; D013223:Statistics as Topic; D016683:Supine Position / Q000502:physiology*