title: Mechanisms of gas exchange response to lung volume reduction surgery in severe emphysema.
abstract: Lung volume reduction surgery (LVRS) improves lung function, respiratory symptoms, and exercise tolerance in selected patients with chronic obstructive pulmonary disease, who have heterogeneous emphysema. However, the reported effects of LVRS on gas exchange are variable, even when lung function is improved. To clarify how LVRS affects gas exchange in chronic obstructive pulmonary disease, 23 patients were studied before LVRS, 14 of whom were again studied afterwards. We performed measurements of lung mechanics, pulmonary hemodynamics, and ventilation-perfusion (Va/Q) inequality using the multiple inert-gas elimination technique. LVRS improved arterial Po₂ (Pa(O₂)) by a mean of 6 Torr (P = 0.04), with no significant effect on arterial Pco₂ (Pa(CO₂)), but with great variability in both. Lung mechanical properties improved considerably more than did gas exchange. Post-LVRS Pa(O₂) depended mostly on its pre-LVRS value, whereas improvement in Pa(O(2)) was explained mostly by improved Va/Q inequality, with lesser contributions from both increased ventilation and higher mixed venous Po(2). However, no index of lung mechanical properties correlated with Pa(O₂). Conversely, post-LVRS Pa(CO₂) bore no relationship to its pre-LVRS value, whereas changes in Pa(CO₂) were tightly related (r² = 0.96) to variables, reflecting decrease in static lung hyperinflation (intrinsic positive end-expiratory pressure and residual volume/total lung capacity) and increase in airflow potential (tidal volume and maximal inspiratory pressure), but not to Va/Q distribution changes. Individual gas exchange responses to LVRS vary greatly, but can be explained by changes in combinations of determining variables that are different for oxygen and carbon dioxide.
authors.affiliation: Unità di Pneumologia, Istituto Scientifico San Raffaele, Via Olgettina 60, 20132 Milano, Italy. george.cremona@hsr.it
authors.forename: George
authors.initials: G
authors.lastname: Cremona
authors.forename: Joan A
authors.initials: JA
authors.lastname: Barberà
authors.forename: Joan A
authors.initials: JA
authors.lastname: Barbara
authors.forename: Teresa
authors.initials: T
authors.lastname: Melgosa
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Appendini
authors.forename: Josep
authors.initials: J
authors.lastname: Roca
authors.forename: Caterina
authors.initials: C
authors.lastname: Casadio
authors.forename: Claudio F
authors.initials: CF
authors.lastname: Donner
authors.forename: Roberto
authors.initials: R
authors.lastname: Rodriguez-Roisin
authors.forename: Peter D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000503:physiopathology / Q000601:surgery*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011013:Pneumonectomy; D011656:Pulmonary Emphysema / Q000503:physiopathology / Q000601:surgery*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology