A trial of the measurement of dynamic lung compliance by the new method using photoplethysmography in patients with COPD and pulmonary fibrosis

Objective: Currently, lung compliance has been measured by the method of esophageal balloon, however, scarcely measured in hospital and clinic because of invasive method. In this study, we have developed a new method for the measurement of lung dynamic compliance (Cdyn) using a finger photoplethysmography, and tried to measure Cdyn in patients with COPD and pulmonary fibrosis. Patients and Methods: 53 healthy non-smokers, 27 patients with COPD, 30 patients with pulmonary fibrosis were recruited, and examined pulmonary function testing. We applied the within-breath changes in pulse wave to measure the difference of intra-thoracic pressure (ΔPpl) in substitution for the measurement of intra-esophageal pressure. A photoplethysmography was attached to a finger and the changes of absorbance synchronized with tidal breath, which represent the changes of cardiac output and reflect the changes of pleural pressure (ΔPpl), were monitored. The ΔPpl was calibrated by loading already-known inspiratory resistance. The Cdyn was calculated from the slope of linear regression line made from 10∼15 different sets of Δtidal volume and ΔPpl. Results: We fond a significant correlation between Cdyn by the method of photoplethysmography and esophageal balloon. There were no significant differences in Cdyn among the healthy non-smokers and the patients with COPD. However, the patients with pulmonary fibrosis showed significantly lower values compared with the other groups. Conclusions: The Cdyn can be measured by the new non-invasive method using a photoplethysmography and may be useful for the assessment of lung recoil pressure in pulmonary fibrosis.