Effect of lung volume reduction surgery on diaphragm length in severe chronic obstructive pulmonary disease

Lung volume reduction surgery (LVRS) has been suggested as improving respir atory mechanics in patients with severe chronic obstructive pulmonary disea se (COPD). We hypothesized that LVRS might lengthen the diaphragm, increase its area of apposition with the chest wall, and thereby improve its mechan ical function. To determine the effect of bilateral LVRS on diaphragm lengt h, we measured diaphragm length at TLC, using plain chest roentgenograms (C XRs), in 25 patients (11 males and 14 females) before LVRS and 3 to 6 mo af ter LVRS, a subgroup of seven patients (reference data) also had diaphragm length measurements made with CXRs, using films made within a year before t heir presurgical evaluation. Right hemidiaphragm silhouette length (PADL) a nd the length of the most vertically oriented portion of the right hemidiap hragm muscle (VDML) were measured. Diaphragm dome height was determined fro m the: (1) distance between the dome and transverse diameter at the manubri um; and (2) highest point of the dome referenced horizontally to the verteb ral column. Patients also underwent spirometry, measurements of lung volume s and diffusion capacity, an Incremental symptom-limited maximum exercise t est, and measurements of 6 min walk distance (6MWD) and transdiaphragmatic pressures during maximum static Inspiratory efforts (Pdi(max) (sniff)) and bilateral supramaximal electrophrenic twitch stimulation (Pdi(twitch)) both before and 3 mo after LVRS. Patients were 58 +/- 8 yr of age, with severe COPD and hyperinflation (FEV1 = 0.68 +/- 0.23 L, FVC = 2.56 +/- 7.3 L, and TLC = 143 +/- 22% predicted). Following LVRS, PADL increased by 4% (from 13 .9 +/- 1.9 cm to 14.5 +/- 1.7 cm; p = 0.02), VDML increased by 44% (from 2. 08 +/- 1.5 cm to 3.00 +/- 1.6 cm, p = 0.01), and diaphragm dome height incr eased by more than 10%. In contrast, diaphragm lengths were similar in subj ects with CXRs made before LVRS and within 1 yr before evaluation. The Incr ease in diaphragm length correlated directly with postoperative reductions In TLC and RV, and also with increases In transdiaphragmatic pressure with maximal sniff (Pdi(max) (sniff)), maximal oxygen consumption (V (over dot)( O2)max), maximal minute ventilation (V (over dot)E-max), and maximum volunt ary ventilation following LVRS. We conclude that LVRS leads to a significan t increase in diaphragm length, especially in the area of apposition of the diaphragm with the rib cage. Diaphragm lengthening after LVRS is most like ly the result of a reduction In lung volume. increases in diaphragm length after LVRS correlate with postoperative improvements in diaphragm strength, exercise capacity, and maximum voluntary ventilation.