CHANGES IN VENTILATORY MECHANICS AND DIAPHRAGMATIC FUNCTION AFTER LUNG-VOLUME REDUCTION SURGERY IN PATIENTS WITH COPD

Background - Lung volume reduction (LVR) has recently been used to tre at severe emphysema. About 25% of the volume of each lung is removed w ith this method. Little is known about the mechanism of functional imp rovement so a study was undertaken to investigate the changes in venti latory mechanics and diaphragmatic function in eight patients after LV R. Methods - Measurements of work of breathing (WOE), intrinsic positi ve end expiratory pressure (PEEPi), dynamic compliance (Cdyn), and art erial carbon dioxide tension (Paco(2)) were performed on the day befor e surgery and daily for seven days after surgery, as well as one, thre e, and six months after surgery. All measurements were performed on sp ontaneously breathing patients, simultaneously assessing oesophageal p ressure via an oesophageal balloon catheter and air flow via a tightly adjusted mask. Diaphragmatic function was evaluated by measuring oeso phageal and transdiaphragmatic pressure (Pdi) preoperatively and at on e, three, and six months postoperatively. Results - Mean forced expira tory volume in one second (FEV1) was 23 (3.6)% predicted, and all pati ents were oxygen dependent before the operation. One day after LVR the mean decrease in WOE was 0.93 (95% confidence interval (CI) 0.46 to 1 .40) joule/1, the mean decrease in PEEPi was 0.61 (95% CI 0.35 to 0.87 ) kPa, and the mean increase in Cdyn was 182.5 (95% CI 80.0 to 284.2) ml/kPa. Similar changes were found seven days and six months after sur gery. Pace, was higher on the day after the operation but was signific antly reduced six months later. Pdi was increased three and six months after surgery. Conclusions - Ventilatory mechanics improved immediate ly after LVR, probably by decompression of lung tissue and relief of t horacic distension. An improvement in diaphragmatic function three and six months postoperatively also contributes to improved respiratory f unction after LVR.