LUNG AND CHEST-WALL MECHANICS IN NORMAL ANESTHETIZED SUBJECTS AND IN PATIENTS WITH COPD AT DIFFERENT PEEP LEVELS

In order to assess the relative contribution of the lung and the chest wall to the derangements of respiratory mechanics in chronic obstruct ive pulmonary disease (COPD) patients with acute ventilatory failure ( AVF), we studied eight COPD patients undergoing controlled mechanical ventilation for AVF and nine normal subjects anaesthetized for surgery as a control group, With the use of the interrupter technique togethe r with the oesophageal balloon technique we measured: static lung and chest wall elastances (Est,L and Est,w, respectively), maximum (RL,max ), minimum (RL,min) and additional (Delta RL) lung resistances, additi onal chest wall resistance (Delta Rw) and, in the COPD group, total in trinsic positive end-expiratory pressure (PEEPtot). Measurements were repeated at 0, 5, 10 and 15 cmH(2)O of applied positive end-expiratory pressure (PEEP), We found that, in the COPD group: 1) both Est,w and Delta Rw were higher than in the normal group; 2) RL,max was markedly increased due to an increase of both RL,min and Delta RL; 3) even low levels of PEEP increased PEEPtot; 4) PEEP did not reduce elastance or total resistance of either the lung or the chest wall, We conclude tha t chest wall mechanics are abnormal in chronic obstructive pulmonary d isease patients with acute ventilatory failure undergoing controlled m echanical ventilation and that positive end-expiratory pressure does n ot seem to be effective in reducing either elastance or resistance of the lung or chest wall.