title: Acute hypoxemia increases cardiovascular baroreceptor sensitivity in humans.
abstract: BACKGROUND
  We postulated that acute hypoxemia increases susceptibility to orthostatic hypotension by increasing the sensitivity of cardiovascular baroreceptors.
  
  
  METHODS
  Hemodynamics were measured noninvasively in 17 healthy, normotensive subjects while being subjected to decreasing venous return by exposure to lower body negative pressure (LBNP) and breathing either a normobaric normoxic (21% O2) or normobaric hypoxic (12% O2) gas mixture.
  
  
  RESULTS
  Hypoxia variably decreased hemoglobin saturation (in percent+/-SEM, from 99%+/-1% to 87%+/-2%, P<.01). Incremental increases in LBNP to -50 mm Hg significantly lowered systolic blood pressure (BP), pulse pressure (PP), forearm blood flow (FBF), and increased heart rate (HR). Hypoxia significantly increased baseline systolic BP, PP, and HR. The maximum change in HR in response to LBNP-induced reductions in PP increased during acute hypoxemia (maximum DeltaHR/DeltaPP, in +/-SEM) from 1.32+/-0.18 beats/min/mm Hg v 1.91+/-0.25 beats/min/mm Hg, P<.05. Those subjects who had the most hemoglobin desaturation during hypoxia, when compared to those subjects who desaturated minimally, had greater systolic BP at rest (128+/-3 mm Hg v 114+/-3 mm Hg, P=.05) and during LBNP (115+/-4 mm Hg v 100+/-1 mm Hg, P=.01).
  
  
  CONCLUSIONS
  Acute hypoxia increased compensatory HR responses to LBNP-dependent reductions in BP. Those normotensive individuals with higher BP at rest and during LBNP developed greater degrees of hypoxia-induced hemoglobin desaturation. Patients with sleep apnea with periods of hypoxemia are prone to hypertension; more important, patients with higher BPs also demonstrate greater degrees of hypoxia-induced desaturation of oxyhemoglobin.
authors.affiliation: Department of Neurosurgery, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: W Christopher
authors.initials: WC
authors.lastname: Fox
authors.forename: Rex
authors.initials: R
authors.lastname: Watson
authors.forename: Warren
authors.initials: W
authors.lastname: Lockette
mesh_terms: D000208:Acute Disease; D015415:Biomarkers / Q000097:blood; D001794:Blood Pressure; D002319:Cardiovascular System / Q000378:metabolism / Q000503:physiopathology*; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007024:Hypotension, Orthostatic / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D009318:Natriuresis; D010100:Oxygen / Q000032:analysis; D010101:Oxygen Consumption; D011311:Pressoreceptors / Q000503:physiopathology*; D012016:Reference Values; D012039:Regional Blood Flow; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D006454:Hemoglobins; D010100:Oxygen