Partitioning of lung and chest-wall mechanics before and after lung- volume-reduction surgery

In the study reported here, we partitioned the mechanics of the respiratory system into lung and chest-wall components, using the rapid occlusion technique in seven patients with severe emphysema before lung- volume-reduction surgery and 3 mo later. Patients showed improvements in 6- min walk (p < 0.01) and dyspnea (p < 0.05). The resistances of the respiratory system and chest wall were not altered by surgery. Ohmic airway resistance did not change, but the component of lung resistance (ΔRL) due to viscoelastic behavior (stress relaxation) and time-constant inhomogeneities (pendelluft) decreased in six patients (p < 0.03). Dynamic elastance of the lung (E(dyn,L)) decreased after surgery (p < 0.02), whereas dynamic elastance of the chest wall did not change. The ratio of dynamic intrinsic positive end-expiratory pressure (PEEP(i)) to static PEEP(i), which also reflects viscoelastic properties and time-constant inhomogeneities, increased after surgery (p < 0.05). The decrease in dyspnea was related to the decrease in E(dyn,L) (r = 0.81, p = 0.03), and tended to be related to the decrease in ΔRL (r = 0.71, p = 0.07). In conclusion, lung-volume-reduction surgery decreased dynamic pressure dissipations caused by stress relaxation and time- constant inhomogeneities within lung tissue, and it had no effect on the static mechanical properties of the chest wall.