title: Treatment of Sleep Apnea With CPAP Lowers Central and Peripheral Blood Pressure Independent of the Time-of-Day: A Randomized Controlled Study.
abstract: BACKGROUND
  Obstructive sleep apnea (OSA) is a risk factor for hypertension and randomized controlled trials have shown that OSA treatment with continuous positive airway pressure (CPAP) reduces peripheral blood pressure and arterial stiffness. Arterial stiffness is known to augment central aortic blood pressure independent of peripheral brachial blood pressure. Currently, it is unclear whether the reduction in blood pressure with CPAP is similar between central and peripheral sites. It is also unknown whether there are any time-of-day influences on central blood pressure changes after CPAP.
  
  
  METHODS
  Thirty-eight patients received therapeutic and sham CPAP in random order for 8 weeks each with an intervening 1-month washout. Peripheral and central blood pressure and arterial stiffness (augmentation index and time to reflection) were measured by pulse wave analysis at end-of-treatment visits. Measurements were taken in the afternoon (~2 pm) and the next morning (~9 am).
  
  
  RESULTS
  Compared to sham, CPAP significantly reduced central systolic (mean difference: -4.1 mm Hg; P = 0.003), central diastolic (-3.9 mm Hg; P = 0.0009), peripheral systolic (-4.1mm Hg; P = 0.004), and peripheral diastolic (-3.8 mm Hg; P = 0.001) blood pressure. These effects were not influenced by time-of-day. Time to reflection was improved with CPAP compared to sham (3.7 ms; P = 0.01). There was no overall difference in augmentation index however when examined by time-of-day, a modest reduction with CPAP was observed in the morning (-2.5%; P = 0.03) but not in the evening (0.12%; P = 0.91).
  
  
  CONCLUSIONS
  CPAP reduces both central and peripheral blood pressure independent of the time-of-day. In contrast, modest improvements in conduit arterial stiffness after CPAP may only occur in the morning.
authors.affiliation: Sleep and Circadian Group, Centre for Integrated Research and Understanding of Sleep, Woolcock Institute of Medical Research, University of Sydney, Sydney, New South Wales, Australia; Discipline of Sleep Medicine, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia; camilla.hoyos@sydney.edu.au.
authors.forename: Camilla M
authors.initials: CM
authors.lastname: Hoyos
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Yee
authors.forename: Keith K
authors.initials: KK
authors.lastname: Wong
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Grunstein
authors.affiliation: Sleep and Circadian Group, Centre for Integrated Research and Understanding of Sleep, Woolcock Institute of Medical Research, University of Sydney, Sydney, New South Wales, Australia; Discipline of Sleep Medicine, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia; Department of Respiratory and Sleep Medicine, Royal North Shore Hospital, Sydney, New South Wales, Australia.
authors.forename: Craig L
authors.initials: CL
authors.lastname: Phillips
mesh_terms: D000328:Adult; D001794:Blood Pressure; D045422:Continuous Positive Airway Pressure; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology / Q000628:therapy*; D013997:Time Factors; D059289:Vascular Stiffness
keywords: arterial stiffness; blood pressure; central aortic pressure; continuous positive airway pressure; hypertension; obstructive sleep apnea; pulse wave analysis.