title: Effect of CPAP on intrinsic PEEP, inspiratory effort, and lung volume in severe stable COPD.
abstract: BACKGROUND
  Intrinsic positive end expiratory pressure (PEEPi) constitutes an inspiratory threshold load on the respiratory muscles, increasing work of breathing. The role of continuous positive airway pressure (CPAP) in alleviating PEEPi in patients with severe stable chronic obstructive pulmonary disease is uncertain. This study examined the effect of CPAP on the inspiratory threshold load, muscle effort, and lung volume in this patient group.
  
  
  METHODS
  Nine patients were studied at baseline and with CPAP increasing in increments of 1 cm H(2)O to a maximum of 10 cm H(2)O. Breathing pattern and minute ventilation (I), dynamic PEEPi, expiratory muscle activity, diaphragmatic (PTPdi/min) and oesophageal (PTPoes/min) pressure-time product per minute, integrated diaphragmatic (EMGdi) and intercostal EMG (EMGic) and end expiratory lung volume (EELV) were measured.
  
  
  RESULTS
  Expiratory muscle activity was present at baseline in one subject. In the remaining eight, PEEPi was reduced from a mean (SE) of 2.9 (0.6) cm H(2)O to 0.9 (0.1) cm H(2)O (p<0.05). In two subjects expiratory muscle activity contributed to PEEPi at higher pressures. There were no changes in respiratory pattern but I increased from 9.2 (0.6) l/min to 10.7 (1.1) l/min (p<0.05). EMGdi remained stable while EMGic increased significantly. PTPoes/min decreased, although this did not reach statistical significance. PTPdi/min decreased significantly from 242.1 (32.1) cm H(2)O.s/min to 112.9 (21.7) cm H(2)O.s/min). EELV increased by 1.1 (0.3) l (p<0.01).
  
  
  CONCLUSIONS
  High levels of CPAP reduce PEEPi and indices of muscle effort in patients with severe stable COPD, but only at the expense of substantial increases in lung volume.
authors.affiliation: Sleep Disorders Unit, Repatriation General Hospital, Daw Park, South Australia 5041. Fergal.O'Donoghue@armc.org.au
authors.forename: F J
authors.initials: FJ
authors.lastname: O'Donoghue
authors.forename: P G
authors.initials: PG
authors.lastname: Catcheside
authors.forename: A S
authors.initials: AS
authors.lastname: Jordan
authors.forename: A D
authors.initials: AD
authors.lastname: Bersten
authors.forename: R D
authors.initials: RD
authors.lastname: McEvoy
mesh_terms: D000368:Aged; D004562:Electrocardiography; D005540:Forced Expiratory Flow Rates / Q000502:physiology; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D018467:Positive-Pressure Respiration, Intrinsic / Q000503:physiopathology / Q000628:therapy*; D011312:Pressure; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D012132:Respiratory Muscles / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology