title: Sympathetic activity in obese subjects with and without obstructive sleep apnea.
abstract: BACKGROUND
  Obese humans are reported to have increased muscle sympathetic nerve activity (MSNA). Obstructive sleep apnea (OSA) may also be accompanied by increased MSNA. Because there is a high prevalence of OSA in obese humans, it is possible that high MSNA reported in obese subjects may in fact reflect the presence of OSA in these subjects. We tested the hypothesis that obesity, per se, in the absence of OSA, is not accompanied by increased MSNA.
  
  
  RESULTS
  We measured MSNA in 25 healthy normal-weight subjects and 30 healthy sedentary obese subjects. All subjects were screened by history and examination to exclude subjects with OSA or hypertension. OSA was further excluded by overnight polysomnographic studies. Despite careful screening, polysomnography revealed that 1 of 25 normal-weight subjects and 9 of 30 obese subjects had occult OSA (P=0.015). MSNA was similar in normal-weight subjects (41+/-3 bursts per 100 heartbeats) and obese subjects without sleep apnea (42+/-3 bursts per 100 heartbeats, P=0.99). MSNA in the 9 obese subjects with occult OSA was 61+/-8 bursts per 100 heartbeats, which was higher than MSNA in normal-weight subjects without sleep apnea (P=0.02) and higher than MSNA in obese subjects without sleep apnea (P=0.02).
  
  
  CONCLUSIONS
  Obesity alone, in the absence of OSA, is not accompanied by increased sympathetic activity to muscle blood vessels.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, USA.
authors.forename: K
authors.initials: K
authors.lastname: Narkiewicz
authors.forename: P J
authors.initials: PJ
authors.lastname: van de Borne
authors.forename: R L
authors.initials: RL
authors.lastname: Cooley
authors.forename: M E
authors.initials: ME
authors.lastname: Dyken
authors.forename: V K
authors.initials: VK
authors.lastname: Somers
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply*; D009765:Obesity / Q000503:physiopathology*; D017286:Polysomnography; D015995:Prevalence; D012016:Reference Values; D012891:Sleep Apnea Syndromes / Q000209:etiology / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000502:physiology*