Study objective: To determine how the volume and
severity of emphysema measured by CT morphometry (CTM) before and after
lung volume reduction surgery (LVRS) relates to the functional status
of patients after LVRS.
Design: A histologically
validated CT algorithm was used to quantify the volume and severity of
emphysema in 35 patients before and after LVRS: total lung volume
(TLV), normal lung volume (< 6.0 mL gas per gram of tissue), volume
of mild/moderate emphysema (ME; 6.0 to 10.2 mL gas per gram of tissue),
volume of severe emphysema (> 10.2 mL gas per gram of tissue),
surface area/volume (SA/V; meters squared per milliliter), and surface
area (SA; meters squared). Outcome parameters included maximal
cardiopulmonary exercise (CPX) performance in 21 patients and routine
pulmonary function in all patients. We hypothesized that baseline CTM
parameters predict response to LVRS and that the change in these
parameters may offer insight into mechanisms of improvement.
Patients and intervention: Thirty-five patients with
severe emphysema who had successful LVRS.
significant decrease in TLV following LVRS was entirely accounted for
by a decrease in severe emphysema. The SA/V and the SA both increased
significantly following LVRS. The change in maximal CPX in watts
following surgery correlated significantly with baseline values of
severe emphysema (r = 0.60), which was collinear with
TLV, and SA/V. The change in diffusing capacity of the lung for carbon
monoxide revealed a significant positive linear relationship with
preoperative severe emphysema (r = 0.37) and a
negative relationship with ME (r = −0.37). Change in
watts revealed a strong relationship with changes in severe emphysema
(r = −0.75) and weaker but significant relationships
with change in TLV, ME, SA/V, and SA. Other measures of pulmonary
function revealed significant albeit less dominant relationships with
baseline CTM and change in these indexes.
Using CTM, we have identified a close relationship between baseline
severe emphysema, or change in severe emphysema, and the improvement in
CPX after LVRS. These observations support a potential role of CTM in
future clinical trials for predicting responders to LVRS and
identifying mechanisms of improvement.