Changes in Pulmonary Mechanics after Lung Volume Reduction Surgery

Lung volume reduction surgery (LVRS) is a promising new treatment for emphysema and leads to increased flow rates. We investigated the mechanisms by which flow rates could increase and the correlates of lessened dyspnea in patients undergoing LVRS before and 3 months after LVRS in patients with severe emphysema. The following were done: routine pulmonary function testing, measurements of elastic recoil (Pel), tidal breathing patterns, inspiratory work of breathing (Winsp), construction of static recoil-maximum flow curves, and measurement of baseline and transitional dyspnea index (TDI). There were increases in forced vital capacity (FVC: 2.24 ± 0.71 to 2.92 ± 0.63 liters; p < 0.05), forced expired volume in 1 (FEV1: 0.64 ± .16 to 1.03 ± 0.28 liters; p < 0.01), and decreases in all divisions of lung volume, e.g. total lung capacity (TLC: 6.86 ± 1.41 to 5.96 ± 1.49 liters; p < 0.01). Maximum Pel increased (11.7 ± 3.7 to 19.8 ± 7.8 cmH2O; p < 0.02) as did the coefficient of retraction (CR= Pel/TLC: 1.8 ± 0.7 to 3.6 ± 3.6 ± 2.2 cmH2O/liter). However, the individual responses in other parameters were markedly different among patients. There was no consistent trend in changes in the slope or position of the static recoil-maximum flow curve or Winsp. The only positive correlate of improved dyspnea (TDI = 3.22 ± 2.22; p < 0.01) was improvement in CR, FEV1 being a weak negative correlate and change in lung volume not being a correlate at all. We conclude that there is a heterogeneous response of the airways to LVRS. Increased elastic recoil was the primary determinant of improved flow rates after LVRS and is the only positive correlate for improvement in dyspnea.