title: Caffeine levels following treatment of obstructive sleep apnoea.
abstract: BACKGROUND
  Randomised trials show that treatment of obstructive sleep apnoea (OSA) with nasal continuous positive airway pressure (CPAP) greatly improves sleepiness and also lowers diurnal systemic blood pressures (BP). Such patients consume more coffee than controls (presumably to combat their sleepiness) and might reduce their consumption following effective treatment, thus lowering BP by this mechanism rather than via a direct effect of alleviating OSA.
  
  
  METHODS
  Plasma caffeine levels before and after treatment with either therapeutic (n=52) or subtherapeutic (control, n=49) CPAP were measured in stored blood samples from a previous randomised controlled trial of CPAP for 4 weeks in patients with OSA.
  
  
  RESULTS
  There was a small significant rise in caffeine levels when the two groups were analysed as a whole (p=0.02), but not individually. Despite the fall in sleepiness measured objectively in the therapeutic CPAP group, there was no difference in absolute (or change in) caffeine levels between the two groups (mean (SE) micro mol/l; therapeutic CPAP 9.2 (1.2), 10.2 (1.0), subtherapeutic 6.7 (0.9), 8.6 (0.9) before and after treatment, respectively).
  
  
  CONCLUSIONS
  Reduced coffee consumption is unlikely to be the explanation for the falls in BP following treatment of OSA.
authors.affiliation: Oxford Centre for Respiratory Medicine, Churchill Hospital, Oxford OX3 7LJ, UK.
authors.forename: G V
authors.initials: GV
authors.lastname: Robinson
authors.forename: J C
authors.initials: JC
authors.lastname: Pepperell
authors.forename: R J O
authors.initials: RJ
authors.lastname: Davies
authors.forename: J R
authors.initials: JR
authors.lastname: Stradling
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D002110:Caffeine / Q000097:blood*; D000697:Central Nervous System Stimulants / Q000097:blood*; D006801:Humans; D011175:Positive-Pressure Respiration / Q000379:methods*; D020181:Sleep Apnea, Obstructive / Q000097:blood / Q000628:therapy*
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine