How hard is it to breathe? Quantification of lung elastance and inspiratory work of breathing in healthy and COPD patients.

Abstract

Chronic Obstructive Pulmonary Disease (COPD) covers a range of underlying lung conditions. Lung mechanics, particularly airway resistance, are altered, increasing the work of breathing (WOB). Model-based methods to estimate lung parameters may help reduce the clinical burden of diagnosis and monitoring. This analysis presents a modified single compartment model describing lung mechanics and WOB. Plethysmographic data, including derived alveolar pressure, is used to identify inspiratory airway resistance (Rinsp), lung elastance (E), and inspiratory effort (Peff, cmH2O). Four (n=10 each) clinical cohorts comprise subjects who are healthy (young and old) and with COPD (with (FL) and without (NFL) expiratory flow limitation). E and R are correlated (R2 = 0.73) and within the normal range in healthy cohorts (Rinsp <5 cmH2O/L/s, E = 0-6 cmH2O/L), but elevated to R = 5-15 cmH2O/L/s and E = 5 - 12 cmH2O/L in patients with COPD. The peak negative Peff was highest in FL COPD patients, reflecting higher WOB required to overcome E and Rinsp dynamics. Increased Rinsp was more dominant than changes in E in COPD patients. Overall, the modelled Peff match pleural and esophageal pressure measurements in literature. The model presented appears to capture key inspiratory effort dynamics, and is a first step towards a more generalised model for non-invasive clinical diagnosis and monitoring of COPD lung conditions.