The significantly fewer symptoms, the significantly smaller number of acute exacerbations, and the rate of exacerbations in the PEP group showed that the use of PEP by PEP-mask relieved the symptoms and had a prophylactic effect on acute exacerbations in patients with chronic bronchitis. In this respect, PEP treatment was superior to conventional chest physiotherapy with diaphragmatic breathing and forced expiration technique. The reduced rate of acute exacerbations in the PEP group was reflected in a reduced use of antibiotics and mucolytics compared to the control group.
The conclusions may be limited by the fact that the study was not double blind. It is not possible to design this kind of study in a double blind manner. It could be argued that the control group should use a mask without expiratory resistance, but an expiratory resistance will be felt by the patient using it. Furthermore, we found that breathing through the mask without expiratory resistance could give a positive airway pressure of less than 5 cm HaO (unpublished). We were very anxious to attend the control group as carefully as the PEP group, giving repeated instructions, etc. The control group, in fact, found the treatment useful by the final assessment, which was not supported by the other results of the study.
The use of the patient s assessment from diary cards as the main effect parameter might be another limitation. Chronic bronchitis and chronic airflow limitation are regarded as independent diseases. Chronic bronchitis, although associated with morbidity, it is not always associated with chronic airflow limitation. Most patients in the present study had normal or moderately reduced lung function, and their morbidity was caused by the symptoms and acute exacerbations. Several studies, recently reviewed by Sutton et al and Demedts, show that changes in lung function indices after various regimens of chest physiotherapy are minor and mostly found as an immediate and short- term effect after the therapy. On this background, we did not expect significant changes in lung function as a long-term effect and chose the major effect parameters to be the symptomatic relief and the number of acute exacerbations.
Because of the inability to perform a double blind study and the subjective effect parameters, we found it particularly important to use an assessment independent of the investigators. The method of calculating the number of acute exacerbations by standardized diary cards was described by Boman et al who used this method in a multicenter trial and found that the inevitable differences in assessment of acute exacerbations by the investigators in this way could be ruled out. This method of assessment of acute exacerbations was recommended for future studies. The randomization of the patients turned out with a tendency towards less disease severity in the control group, but no statistically significant differences were found. However, this supports our findings of fewer symptoms and acute exacerbations in the PEP group. Only four patients, all in the PEP group, had severe pulmonary obstruction (FEV1<l.O L). This partly explains the difference concerning baseline lung function in the two groups. The small increase in FEVb FVC, and VC in the PEP group compared to the decrease in the same parameters in the control group is remarkable because the FEVb FVC, and VC usually declines over time, especially in patients with chronic bronchitis. The variation of the measured values were large and to ascertain an influence of PEP treatment on lung function, more patients or a longer study period is required.