Physiological basis of improvement after lung volume reduction surgery forsevere emphysema: where are we?

Lung volume reduction surgery has become an accepted therapeutic option to relieve the symptoms of selected patients with severe emphysema, in a major ity of these patients, it causes objective as well as subjective functional improvement. A proper understanding of the physiological determinants unde rlying these beneficial effects appears very important in order to better s elect patients for the procedure that is currently largely carried out on a n empirical basis. Lung volume reduction surgery has two distinct effects, Firstly, it causes an increased elastic recoil, which at least partially explains the enhanced maximal expiratory flow. Secondly, it is associated with a reduction of hy perinflation which allows for an increase in global inspiratory muscle stre ngth and in diaphragmatic contribution to tidal volume as well as a decreas e in the inspiratory elastic load imposed by the chest wail, Taken together , these effects result in a reduced work of breathing and in an enhanced ma ximal ventilation which both contribute to the increased exercise capacity and reduced dyspnoea after surgery. The improved lung recoil and the reduce d hyperinflation after volume reduction surgery were the primary postulates upon which the usual selection criteria for the procedure were based, It i s now likely that these are correct. Nevertheless, some patients do not ben efit from lung volume reduction surgery and the current Literature does not allow for a refinement of the selection process from a physiological point of view, The exact mechanisms underlying the improvement in lung recoil, lung mechan ics, and respiratory muscle function remain incompletely understood, Moreov er, the effects of lung volume reduction surgery on gas exchange and pulmon ary haemodynamics still need to be more fully investigated. An analysis of the characteristics of patients who do not benefit from the procedure and t he development of an animal model for lung volume reduction surgery would p robably help address these important issues.