title: The Effect of Body Position on Physiological Factors that Contribute to Obstructive Sleep Apnea.
abstract: OBJECTIVE
  Obstructive sleep apnea (OSA) resolves in lateral sleep in 20% of patients. However, the effect of lateral positioning on factors contributing to OSA has not been studied. We aimed to measure the effect of lateral positioning on the key pathophysiological contributors to OSA including lung volume, passive airway anatomy/collapsibility, the ability of the airway to stiffen and dilate, ventilatory control instability (loop gain), and arousal threshold.
  
  
  METHODS
  Non-randomized single arm observational study.
  
  
  METHODS
  Sleep laboratory.
  
  
  METHODS
  20 (15M, 5F) continuous positive airway pressure (CPAP)-treated severe OSA patients.
  
  
  METHODS
  Supine vs. lateral position.
  
  
  METHODS
  CPAP dial-downs performed during sleep to measure: (i) Veupnea: asleep ventilatory requirement, (ii) passive V0: ventilation off CPAP when airway dilator muscles are quiescent, (iii) Varousal: ventilation at which respiratory arousals occur, (iv) active V0: ventilation off CPAP when airway dilator muscles are activated during sleep, (v) loop gain: the ratio of the ventilatory drive response to a disturbance in ventilation, (vi) arousal threshold: level of ventilatory drive which leads to arousal, (vii) upper airway gain (UAG): ability of airway muscles to restore ventilation in response to increases in ventilatory drive, and (viii) pharyngeal critical closing pressure (Pcrit). Awake functional residual capacity (FRC) was also recorded.
  
  
  RESULTS
  Lateral positioning significantly increased passive V0 (0.33 ± 0.76L/min vs. 3.56 ± 2.94L/min, P < 0.001), active V0 (1.10 ± 1.97L/min vs. 4.71 ± 3.08L/min, P < 0.001), and FRC (1.31 ± 0.56 L vs. 1.42 ± 0.62 L, P = 0.046), and significantly decreased Pcrit (2.02 ± 2.55 cm H2O vs. -1.92 ± 3.87 cm H2O, P < 0.001). Loop gain, arousal threshold, Varousal, and UAG were not significantly altered.
  
  
  CONCLUSIONS
  Lateral positioning significantly improves passive airway anatomy/collapsibility (passive V0, pharyngeal critical closing pressure), the ability of the airway to stiffen and dilate (active V0), and the awake functional residual capacity without improving loop gain or arousal threshold.
authors.affiliation: Monash Lung and Sleep, Monash Health, Clayton, Victoria, Australia.|Ritchie Centre, Monash Institute of Medical Research/Prince Henry Institute, Monash University, Clayton, Victoria, Australia.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Joosten
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Edwards
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Wellman
authors.affiliation: Monash Lung and Sleep, Monash Health, Clayton, Victoria, Australia.
authors.forename: Anthony
authors.initials: A
authors.lastname: Turton
authors.affiliation: Ritchie Centre, Monash Institute of Medical Research/Prince Henry Institute, Monash University, Clayton, Victoria, Australia.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Skuza
authors.affiliation: Ritchie Centre, Monash Institute of Medical Research/Prince Henry Institute, Monash University, Clayton, Victoria, Australia.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Berger
authors.affiliation: Monash Lung and Sleep, Monash Health, Clayton, Victoria, Australia.|School of Clinical Sciences, Monash University, Clayton, Victoria, Australia.
authors.forename: Garun S
authors.initials: GS
authors.lastname: Hamilton
mesh_terms: D001143:Arousal / Q000502:physiology; D045422:Continuous Positive Airway Pressure; D005260:Female; D006801:Humans; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D008875:Middle Aged; D010614:Pharynx / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011312:Pressure; D012119:Respiration; D012129:Respiratory Function Tests; D012137:Respiratory System / Q000033:anatomy & histology / Q000503:physiopathology*; D012890:Sleep / Q000502:physiology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology* / Q000628:therapy; D016683:Supine Position / Q000502:physiology; D014851:Wakefulness / Q000502:physiology
keywords: airway obstruction; functional residual capacity; lung volume measurements; obstructive; sleep apnea; supine position