Effect of Chronic Hyperinflation on Diaphragm Length and Surface Area

Abstract

We have used three-dimensional reconstructions obtained with spiral computed tomography to measure total diaphragm length (L di ) and surface area (A di ), the length (L do ) and surface area (A do ) of the dome, and the length (L ap ) and surface area (A ap ) of the zone of apposition in 10 hyperinflated patients with severe chronic obstructive pulmonary disease, or COPD (FEV 1 ϭ 27% predicted: FRC ϭ 225% predicted) and 10 normal subjects matched for age, sex, and height. Measures of L di , A di , L ap , and A ap decreased linearly between FRC and TLC in the two groups, but L do and A do did not change. On average, patients' A di and A ap at FRC were reduced to 73% and 54% of normal values, whereas A do was unaffected. When compared at similar absolute lung volumes, mean diaphragm dimensions were similar in patients with COPD and normal subjects, but individual values were very variable in both groups. This variability was partly accounted for by differences in body weight: i.e., the greater the weight, the longer the diaphragm. We conclude that ( 1 ) patients with COPD have marked reductions in A di and A ap at FRC but have diaphragm dimensions similar to those of normal subjects when compared at similar absolute lung volumes, and ( 2 ) normal subjects and patients with COPD show substantial intersubject variability in diaphragm dimensions that is partly explained by differences in body weight. In patients with chronic obstructive pulmonary disease (COPD), hyperinflation of the lungs decreases the operating length of the diaphragm. As a result, the inspiratory function of the muscle is impaired. The magnitude of diaphragm shortening increases with the degree of hyperinflation, and it is generally assumed that, at a given absolute lung volume, diaphragm length and surface area are similar in patients with COPD and normal subjects.However, very few studies have investigated the effect of chronic hyperinflation on diaphragm dimensions. In two early studies using chest radiographs, Sharp and colleagues (1) reported that the diaphragm was 40% shorter at FRC in patients with COPD than in normal subjects, and Rochester and Braun (2) showed that diaphragm length was reduced by 28% in patients with COPD at residual volume (RV) compared with normal subjects at their RV; this difference, however, disappeared when diaphragm lengths were compared at similar absolute lung volumes. Interpretation of these results is difficult because measurements of diaphragm dimensions were obtained from two-dimensional analysis of chest radiographs, were generally performed at a single lung volume, and were not always compared with measurements obtained in adequately matched controls.In a previous study (3), we have described a technique of three-dimensional (3D) diaphragm imaging using spiral computed tomography (CT) that allowed accurate measurements of diaphragm length and surface area. In the present work, we have used this technique to compare diaphragm dimensions at different lung volumes in 10 hyperinflated patients with severe COPD...

Dynamic echo-planar MR imaging of the diaphragm for a 3D dynamic analysis

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Respiratory muscle fiber remodeling in chronic hyperinflation: dysfunction or adaptation?

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