"Intrinsic" positive end-expiratory pressure in stable patients with chronic obstructive pulmonary disease

We have assessed "intrinsic" positive end-expiratory pressure (PEEPi), during quiet breathing in 18 patients with chronic obstructive pulmonary disease (COPD) in stable condition. Ventilatory flow, lung volume, oesophageal (Poes), gastric (Pga), and transdiaphragmatic pressure (Pdi) were measured. PEEPi was measured as the pressure difference (delta Poes) between the onset of the inspiratory effort, indicated by the start of the Pdi swing, and the point corresponding to zero flow. PEEPi was present in all of the 18 COPD patients, and averaged 2.4 +/- 1.6 cmH2O. The maximum transdiaphragmatic pressure (Pdi,max) was also measured and averaged 81.5 +/- 17.4 cmH2O. Following a randomized sequence, ten patients then inhaled an adrenergic agonist (fenoterol 1.6 mg), and eight patients the corresponding placebo. Fenoterol, but not placebo, caused a significant increase in forced expiratory volume in one second (FEV1) (+34%, on average), associated with a significant decrease in PEEPi (-63%, on average) and a significant improvement in Pdi,max (+19%, on average). We conclude that: 1) intrinsic PEEP can be present in stable COPD patients due to increased airflow resistance; 2) fenoterol improved diaphragmatic strength (Pdi,max) in our COPD patients, possibly due to a decrease in lung volume.