Physiologic Evidence for the Efficacy of Positive Expiratory Pressure as an Airway Clearance Technique in Patients With Cystic Fibrosis

Abstract

Background and Purpose. Individuals with cystic fibrosis (CF) have large amounts of infected mucus in their lungs, which causes irreversible lung tissue damage. Although patient-administered positive expiratory pressure (PEP) breathing has been promoted as an effective therapeutic modality for removing mucus and improving ventilation distribution in these patients, the effects of PEP on ventilation distribution and gas mixing have not been documented. Therefore, this preliminary investigation described responses in distribution of ventilation and gas mixing to PEP breathing for patients with moderate to severe CF lung disease. Subjects and Methods. The effects of PEP breathing on ventilation distribution, gas mixing, lung volumes, expiratory airflow, percentage of arterial blood oxyhemoglobin saturation (Spo 2 ), and sputum volume were studied in 5 patients with CF (mean ageϭ18 years, SDϭ4, rangeϭ13-22) after no-PEP, low-PEP (10 -20 cm H 2 O), and high-PEP (Ͼ20 cm H 2 O) breathing conditions. Single-breath inert gas studies and lung function tests were performed before, immediately after, and 45 minutes after intervention. Single-breath tests assess ventilation distribution homogeneity and gas mixing by observing the extent to which an inspired test gas mixes with gas already residing in the lung. Results. Improvements in gas mixing were observed in all PEP conditions. By 45 minutes after intervention, the no-PEP group improved by 5%, the low-PEP group improved by 15%, and the high-PEP group improved by 23%. Slow vital capacity increased by 1% for no PEP, by 9% for low PEP, and by 13% for high PEP 45 minutes after intervention. Residual volume decreased by 13% after no PEP, by 20% after low PEP, and by 30% after high PEP. Immediate improvements in forced expiratory flow during the middle half of the forced vital capacity maneuver (FEF 25%-75% ) were sustained following high PEP but not following low PEP. Discussion and Conclusion. This study demonstrated the physiologic basis for the efficacy of PEP therapy. The results confirm that low PEP and high PEP improve gas mixing in individuals with CF, and these improvements were associated with increased lung function, sputum expectoration, and Spo 2 . The authors propose that improvements in gas mixing may lead to increases in oxygenation and thus functional exercise capacity. [Darbee JC, Ohtake PJ, Grant BJB, Cerny FJ. Physiologic evidence for the efficacy of positive expiratory pressure as an airway clearance technique in patients with cystic fibrosis. Phys Ther. 2004;84:524 -537.]

The Clinical Significance of Collateral Ventilation

“…They have shown in surgical patients that periodic continuous positive airway pressure by mask was superior to standard postoperative conventional therapy in decreasing atelectasis and improving gas exchange (87). The use of positive end-expiratory pressure maneuvers in patients with cystic fibrosis has been shown to increase lung volumes and promote peripheral collateral air movement distal to bronchi obstructed with mucus (88). Taken together, a reasonable conclusion is that chest physical therapy that includes maneuvers that increase lung volume works because enhanced collateral ventilation at higher lung volumes allows air to accumulate distal to airways narrowed or obstructed by inflammation and secretions, and that, during coughing and expiration, the resultant higher lung volumes and increased air pressure in alveoli distal to the airways obstruction promotes mucus movement to the more proximal, larger airways (89).…”

Positive expiratory pressure – Common clinical applications and physiological effects

“…to temporarily increase FRC and VT in combination with techniques to mobilize and evacuate secretions, Fig. 3 [5,6,14,19,21,59]. The latter is performed by the forced expiration technique (FET), huffing and/or coughing while the expiratory resistor is temporarily put aside [1,2,60e63].…”

“…The latter is performed by the forced expiration technique (FET), huffing and/or coughing while the expiratory resistor is temporarily put aside [1,2,60e63]. PEP with FET has been shown to be an effective airway clearance technique [5,6,14,64,65] and better maintenance of lung function over time and improved physical function in patients with cystic fibrosis [6,22,66,67]. Several studies have reported its effect to be equal to other airway clearance techniques such as positioning and postural drainage [5,59,64,68e77] or superior to chest wall oscillation, postural draining with percussions and OscPEP [22,66,67].…”

“…Patients are instructed to take eight to ten breaths with slightly active expiration against the resistance, and then perform two to three single FVC manoeuvres against the resistance in the mask, interspersed with some rest with VT breaths outside the mask [7,14,21,81]. Each cycle is to be completed with directed coughing outside the mask to evacuate the mobilized secretion [7,14,21,81]. The treatment frequency and the number of cycles included in each treatment session are individualized [7,14,21,81].…”

“…Each cycle is to be completed with directed coughing outside the mask to evacuate the mobilized secretion [7,14,21,81]. The treatment frequency and the number of cycles included in each treatment session are individualized [7,14,21,81].…”