PURPOSE: Dynamic hyperinflation is an important mechanism of exercise limitation in COPD but its measurement by conventional equipment is technically demanding and depends on optimal patient cooperation. We therefore evaluated whether hyperinflation can be detected without airway instrumentation in ambulatory patients during natural breathing by a portable respiratory inductive plethysmograph.
METHODS: Five patients with COPD (age 62-71y, FEV1 21-74 %pred, RV/TLC ratio 0.43-0.72) underwent progressive treadmill exercise while their breathing pattern was continuously monitored by a calibrated respiratory inductive plethymsograph that monitors lung volume by sensors built into an elastic body garment. Data are recored by a device of the size of a palmtop computer (LifeShirt, VivoMetrics, CA; Chest 2005;128:1282). Lung volume changes were simultaneously derived by opto-electronic plethysmography, a technique that continuously measures chest wall dimensions by means of several video cameras (OEP System, BTS, Milano, Italy; Thorax 2004;59:210). No special breathing maneuvers were required. Mean values of end-expiratory lung volume during 30sec-epochs were computed and changes during successive epochs compared between methods.
RESULTS: Mean individual exercise duration was 13.7 min (8.7-20.5min) and a total of 140 epochs of 30 sec duration were available for comparison between methods. Mean tidal volume was 1.03L (0.59-1.63L). All patients had dynamic hyperinflation as estimated by both methods (mean increase in end-expiratory lung volume of 0.87L, range 0.38 to 1.16L). Epoch to epoch changes in end-expiratory lung volume over the course of exercise tests comprised a range from -0.55 to +0.40L. Agreement between inductance plethysmograph and opto-electronic plethysmograph in estimation of changes in end-expiratory lung volume was close with a bias of -0.05L and a 95% confidence interval of the difference between methods of ±0.20L.
CONCLUSION: The portable respiratory inductive plethysmograph accurately tracked changes in end-expiratory lung volume during exercise in COPD patients.
CLINICAL IMPLICATIONS: The LifeShirt monitor holds promise as a convenient tool to monitor dynamic hyperinflation in unrestrained COPD patients without requirement for specialized breathing maneuvers.
DISCLOSURE: Konrad Bloch, No Financial Disclosure Information; No Product/Research Disclosure Information