Effect of CPAP on intrinsic PEEP, inspiratory effort, and lung volume in severe stable COPD
- 1Sleep Disorders Unit, Repatriation General Hospital, Daw Park, South Australia 5041
- 2School of Medicine, Flinders University of South Australia, South Australia 5042
- 3Department of Critical Care Medicine, Flinders Medical Centre, South Australia 5042
- Correspondence to:
Dr F O'Donoghue, Institute for Breathing and Sleep, Austin and Repatriation Medical Centre, Heidelberg, Victoria 3084, Australia;
Fergal.O'Donoghue{at}armc.org.au
- Accepted 12 December 2001
- Revised 30 October 2001
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 H2O to a maximum of 10 cm H2O. Breathing pattern and minute ventilation (V̇i), 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 H2O to 0.9 (0.1) cm H2O (p<0.05). In two subjects expiratory muscle activity contributed to PEEPi at higher pressures. There were no changes in respiratory pattern but V̇i 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 H2O.s/min to 112.9 (21.7) cm H2O.s/min). EELV increased by 1.1 (0.3) l (p<0.01).
Conclusion: 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.
- chronic obstructive pulmonary disease
- continuous positive airway pressure
- positive end expiratory pressure
- Cdyn, dynamic lung compliance
- CPAP, continuous positive airway pressure
- EELV, end expiratory lung volume
- EMGdi
- diaphragmatic electromyography
- EMGic, intercostal electromyography
- PEEP, positive end expiratory pressure
- PEEPi, intrinsic PEEP
- PEEPe, extrinsic PEEP
- PTPdi, diaphragmatic pressure time product
- PTPoes, oesophageal pressure time product
- Poes, oesophageal pressure. Pga, gastric pressure
- Pao, airway opening pressure
- Pdi, transdiaphragmatic pressure
- Ptp, transpulmonary pressure
- Rrs, total lung resistance
- Ti, inspiratory time
- Te, expiratory time
- Ttot
- respiratory cycle time
- V̇i, minute ventilation
- Vt, tidal volume
- Vt/Ti, mean inspiratory flow
- Vt
- Te, mean expiratory flow
Footnotes
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This study was supported by the National Health and Medical Research Council of Australia and the Daw Park Research Foundation.
