Plethysmographic measurement of intrinsic PEEP in stable COPD patients at rest

Background: In stable chronic obstructive pulmonary disease (COPD), intrinsic positive end-expiratory pressure (PEEPi) due to tidal expiratory flow-limitation (FL) is responsible for the increase in work of breathing and for adverse haemodynamic effects. PEEPi during spontaneous breathing can be only measured invasively with the esophageal balloon technique (ES). Aims: To obtain a non-invasive estimation of PEEPi in stable COPD patients using a commercially available plethysmograph (PEEPipl) and to compare it with existing data on PEEPi obtained with ES (PEEPies) [Haluszka, J. et al. Am Rev Respir Dis 1990; 141:1194-97;Dal Vecchio, L. et al. Eur Respir J 1990; 3:74-80]. Methods: Stable mild to very severe COPD patients performed body-plethysmography before and after bronchodilation (BD) according to current guidelines. PEEPipl was calculated by converting into alveolar pressure the shift volume measured at the end of a spontaneous tidal expiration. FL was assessed with the negative expiratory pressure method. Results: 62 COPD patients were enrolled (mean±SD 72±7 years; 40 males). At baseline patients with FL (N=35) exhibited a higher PEEPipl than those with no FL (0.8±0.4 vs 0.3±0.2 cmH2O, P<0.01). After BD PEEPipl decreased (P=0.01) similarly in both groups (-12% vs -15%). As previously documented for PEEPies, PEEPipl was correlated with FEV1 (R=-0.597), vital capacity (R=-0.541), inspiratory capacity (R=-0.521) and residual volume (R=0.489), all P<0.01. However, PEEPipl and changes post-BD were lower than previously reported for PEEPies (2.4±1.5 cmH2O and -60%). Conclusions: Although further implementations are necessary, the non invasive assessment of PEEPi by means of plethismography appears achievable.