The value of a study based on reports from the patients will be dependent on the cooperation of the patients. We found good cooperation in filling out the diaries; only seven patients discontinued the study for this reason. They should use the treatments every morning and evening, but most patients used the treatments more often. This indicates that they felt an immediate benefit from the maneuvers.
The physiologic effects of PEP cannot be explained by our study. It is possible that PEP worked by loosening secretions, improving ventilation, and/or dilating airways. To our knowledge, the present study is the first concerning long-term treatment of chronic bronchitis with PEP. The acute effect of PEP has been studied in the treatment of cystic fibrosis. These studies compared more vigorous regimens including postural drainage with percussion, and the effect parameters were the amount of expectoration and oxygen saturation during and after the treatment. Furthermore, the studied regimens were different, which make comparison difficult. Falk et al found PEP to be most effective concerning the amount mucus expectorated, whereas Hofmeyr et al found postural drainage with breathing exercises and forced expiration technique to be the most effective regimen. The PEP might enhance the effect of forced expiration by moving the equal pressure point of dynamic compression peripherally, thereby removing mucus from smaller bronchi.
Studies have shown that both expiratory positive airway pressure (equal to PEP) and CPAP increase functional residual capacity in healthy subjects and in diseases accompanied by reduced resting lung volume. This was supported by a study of patients undergoing abdominal surgery where the use of PEP- mask was found to be as effective as CPAP in reducing the incidence of atelectasis and in restoring pulmonary function. This effect is probably explained by an increase in closing capacity, thus improving the ability to mobilize secretions from the peripheral airways.
Similarly, the study of Groth et al confirmed the increase in FRC with positive expiratory pressure by PEP-mask in patients with cystic fibrosis, and this study also showed improvement in ventilation and reduction in volume of trapped gas. The mechanism of PEP might be a redistribution of the ventilation and airflow, thus loosening secretions and dilating obstructed airways. The possibility of a bronchodila- ting effect of positive airway pressure was recently supported by the finding of decrease in airway resistance during application of CPAP in induced asthma.
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It would be interesting to contrast our results with the results of one of the most important long-term studies of patients with chronic obstructive pulmonary disease, the multicenter trial of the IPPB-group, where no significant changes in pulmonary function, mortality, rate, and duration of hospitalizations and life quality indices were found. A comparison is difficult because the patients in the IPPB study had significantly more airways obstruction with predicted FEVt of mean 36 percent. The treatments in the IPPB study were quite different from ours and consisted of nebulized bronchodilator with or without IPPB applied by a Bennett ventilator giving a standardized tidal volume, thus giving inspiratory assistance instead of expiratory resistance as PEP
Though the physiologic effects of positive expiratory pressure are still not clearly understood, new clinical applications are found. The present study shows that treatment with a simple and inexpensive PEP device without side effects can reduce morbidity in patients with chronic bronchitis and may preserve lung function from a more rapid decline.