A new noninvasive method for measurement of dynamic lung compliance from fluctuations on photoplethysmography in respiration.

Lung compliance is important in interstitial lung disease (ILD) as a marker of lung sclerosis. However, the measurement requires placement of an esophageal pressure probe, and is therefore not done routinely in clinic. This study was performed to develop and verify a new noninvasive method for estimation of dynamic lung compliance (Cdyn) using a photoplethysmograph (PPG), and to examine its usefulness. A system for measuring Cdyn in combination with changes in estimated pleural pressure (Ppl) from the fluctuations on PPG with respiration and lung volume measured simultaneously by spirometry was developed, and verified to show correspondence with the estimated Ppl and the esophageal pressure (Pes) (healthy adult volunteers (HS); n = 3), and estimated Cdyn and Cdyn measured using an esophageal balloon (HS; n = 28, COPD; n = 14, ILD; n = 10). Further, the estimated Cdyn was compared among HS (n = 33), COPD (n = 31), and ILD (n = 30). Both the estimated Ppl and Cdyn were significantly correlated with the Pes (r = 0.89) and measured Cdyn (r = 0.63), respectively. The estimated Cdyn in ILD showed significant lower values than those in HS and COPD. The estimated Cdyn was significantly related to %VC (r = 0.56, P < 0.01) and %DLCO (r = 0.52, P < 0.01) in patients with ILD. These findings suggested that the newly developed noninvasive and convenient method for estimation of Cdyn using a combination of PPG and spirometry may be useful for the assessment of lung sclerosis in ILD.