Abstract
Introduction: The NETT noted that baseline exercise tolerance may influence long-term outcomes following lung volume reduction. The association of baseline six minute walk distance (6MWD) to outcomes was examined in a study of endoscopic thermal vapor ablation in patients with heterogeneous emphysema.
Methods: Post hoc subgroup analysis from the Vapor trial, a multicenter single-arm trial of InterVapor (single upper lobe treatment at 10 cal/g) in patients with upper lobe emphysema. Inclusion: FEV1 15%-45% predicted, RV>150%, TLC>100%, 6MWD>140 m, DLCO>20%, prior pulmonary rehabilitation. Outcomes included spirometry, body plethysmography, lobar volume reduction (LoVR) by HRCT, SGRQ, mMRC dyspnea, and 6MWD. Endpoints were dichotomized based on two thresholds for baseline 6MWD.
Results: 44 patients received InterVapor. Demographics: 50% men, age 63 years, FEV1 0.86 L (31% predicted), SGRQ 59 units, 6MWD 300 m. Results at 6 and 12 months (mean change from baseline):

 FEV1 (%)LoVR (%)6MWD (m)SGRQ (units)RV (L)
 6 / 12 mo6 / 12 mo6 / 12 mo6 / 12 mo6 / 12 mo
<300 (n=22)14.3 / 8.8-54.0 / -51.631.7 / 26.7-13.7 / -11.6-0.413 / -0.330
≥300 (n=22)18.8 / 11.4-42.2 / -39.258.6 / 9.7-15.7 / -9.6-0.400 / -0.281
<350 (n=31)16.5 / 12.6-45.1 / -46.740.6 / 28.6-14.0 / -11.0-0.383 / -0.351
≥350 (n=13)17.5 / 5.5-51.9 / -41.658.7 / -12.7-16.3 / -9.6-0.453 / -0.193


Conclusion: Baseline 6MWD was associated with differences that were most prominent with the subsequent 6MWD and SGRQ at 12 months. Other outcomes showed no consistent pattern of association. A bias such as regression to the mean cannot be ruled out in this analysis.