Non-invasive semi-quantitative measurements of tidal pressure-volume and flow relations of lung in COPD patients.

Movement of the suprasternal fossa as detected by surface inductive plethysmography (SIP) has been utilized as a non-invasive means for estimation of intrapleural pressure in the calculation of lung compliance. The purpose of the present study was to ascertain whether pulmonary resistance and work of breathing could also be obtained with SIP. A new calibration procedure based upon substituting values for inspiratory total respiratory resistance measured by forced oscillations into an uncalibrated SIP deflection-flow loop was utilized to convert the SIP waveform to a pressure recording. This permitted estimation of lung compliance, expiratory pulmonary resistance and work of breathing which were then compared to simultaneously measured intraesophageal pressure derived values. Nine seated patients with varying degrees of obstructive airways disease were studied. No differences were found between the SIP and intraesophageal derived group mean values for any parameters, viz inspiratory and expiratory pulmonary resistance, lung compliance and work of breathing. The least variable measurement between the two methods was the work of breathing in which eight of the nine patients had values deviating less than 25% from unity. Values for lung compliance were slightly more divergent and expiratory pulmonary resistance showed large variation. The present investigation indicates that surface inductive plethysmographic detection of suprasternal fossa movement reflects intrapleural pressure swings in a semiquantitative manner; it serves as a non-invasive research technique for estimation of lung compliance, pulmonary resistance and work of breathing.