title: Pulse wave analysis in a pilot randomised controlled trial of auto-adjusting and continuous positive airway pressure for obstructive sleep apnoea.
abstract: OBJECTIVE
  Non-invasive measurements of arterial stiffness including the augmentation index (AIx) and central blood pressure (BP) have been used to assess the cardiovascular health of patients with obstructive sleep apnoea (OSA), a well-established independent risk factor of cardiovascular disease. Continuous positive airway pressure (CPAP) can significantly reduce the AIx, but no studies have analysed the effect of auto-adjusting PAP (APAP) or studied morbidly obese patients with severe OSA at higher risk of cardiovascular disease. In this randomised, single-blinded crossover pilot trial, we aimed to compare the efficacy of CPAP with APAP (ResMed S8 Autoset II) in improving peripheral BP, central BP and the AIx, using SphygmoCor technology.
  
  
  METHODS
  Twelve severe OSA patients (mean±SD; apnoea-hypopnoea index, 75.8 ± 32.7; BMI, 49.9 ± 5.2 kg/m(2)) were consecutively recruited and received CPAP (mean pressure, 16.4 cm H(2)O) or APAP in random order for four nights at home, separated by a four-night washout. Cardiovascular measurements were taken at baseline, post-washout and following each treatment arm.
  
  
  RESULTS
  The polysomnographically recorded residual apnoea-hypopnoea index and compliance to treatment were not significantly different between arms (p > 0.05). There were no significant differences in peripheral or central BP between arms (p > 0.05). The AIx was lower with CPAP than APAP (by 5.8%), with a large effect size not reaching statistical significance (r = 0.61, p = 0.14).
  
  
  CONCLUSIONS
  The large effect size evident when comparing the AIx following CPAP and APAP indicates the need to perform an adequately powered trial in order to determine if APAP improves arterial stiffness to the same extent as CPAP.
authors.affiliation: WellSleep Sleep Investigation Centre, Department of Medicine, University of Otago, Wellington, New Zealand. jessie.bakker@otago.ac.nz
authors.forename: Jessie P
authors.initials: JP
authors.lastname: Bakker
authors.forename: Angela J
authors.initials: AJ
authors.lastname: Campbell
authors.forename: Alister M
authors.initials: AM
authors.lastname: Neill
mesh_terms: D000328:Adult; D000399:Air Pressure; D001794:Blood Pressure; D015992:Body Mass Index; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000150:complications*; D010865:Pilot Projects; D017286:Polysomnography / Q000295:instrumentation*; D011674:Pulse; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D016037:Single-Blind Method; D020181:Sleep Apnea, Obstructive / Q000628:therapy*; D013813:Therapy, Computer-Assisted / Q000295:instrumentation*; D014655:Vascular Resistance; D055815:Young Adult