Chest Wall Strapping dilates airways and increases airway homogeneity in COPD

Background: Chest wall strapping (CWS) is a technique that restricts the chest wall to induce breathing at lower lung volumes. CWS increases lung elastic recoil and expiratory airflows. In computer tomography imaging studies CWS dilates small airways in healthy and COPD-subjects. Dynamic-dysanapsis describes the concept of airway dilation via interdependence of airways and lung parenchyma from CWS induced increase in lung elastance. The time course of CWS induced dynamic-dysnapsis is not defined. Volumetric capnography and plethysmography allow for repeated measurements of the lung structure function relationship. We hypothesized that CWS causes an increase in dead space of COPD-subjects via CWS induced increase in airway dimensions. Secondly, we hypothesized that CWS increases airway homogeneity and that these effects last for a period after removal of CWS. Methods: After performing baseline measurements (ventilation parameters, plethysmography, and volumetric capnography) participants with COPD (n=5) and healthy, sex-matched controls (n=5) underwent CWS. Measurements were repeated every 15 minutes for one hour following CWS. After CWS-removal measurements were repeated every 15 minutes for an additional hour. We related anatomic dead space, alveolar dead space, V _D /V _T , and slope of the capnogram to lung volume and tracked their changes over time. Results: Moving from unstrapped to the CWS and to post-CWS condition, we saw an overall increase in the anatomic dead space (a surrogate with the size of the airway tree) for both groups with CWS and post-CWS (p=0.001). The capnographic slope is an indicator of airway uniformity. Post-CWS had a significant effect on both groups causing a decrease in the slope of the capnogram to lung volume ratio, showing a significant increase in airway homogeneity (p=0.03). Conclusion: CWS dilates airways quantified by the increase in dead space. The increase in airway homogeneity persists at least 45 minutes after strapping is removed. This indicates lasting benefits of CWS on airway function. The dilatation of airways and the improvement in airway homogeneity during and after CWS could facilitate enhanced delivery of inhaled therapies in COPD. CWS should be further investigated as a novel non-pharmacological treatment for COPD.