Lessons from the World Trade Center disaster: airway disease presenting as restrictive dysfunction

Abstract

Background: The present study (1) characterizes a physiologic phenotype of restrictive dysfunction due to airway injury and (2) compares this phenotype to the phenotype of interstitial lung disease (ILD).

Methods: This is a retrospective study of 54 persistently symptomatic subjects following World Trade Center (WTC) dust exposure. Inclusion criteria were reduced vital capacity (VC), FEV1/VC>77%, and normal chest roentgenogram. Measurements included spirometry, plethysmography, diffusing capacity of lung for carbon monoxide (Dlco), impulse oscillometry (IOS), inspiratory/expiratory CT scan, and lung compliance (n=16).

Results: VC was reduced (46% to 83% predicted) because of the reduction of expiratory reserve volume (43%±26% predicted) with preservation of inspiratory capacity (IC) (85%±16% predicted). Total lung capacity (TLC) was reduced, confirming restriction (73%±8% predicted); however, elevated residual volume to TLC ratio (0.35±0.08) suggested air trapping (AT). Dlco was reduced (78%±15% predicted) with elevated Dlco/alveolar volume (5.3±0.8 [mL/mm Hg/min]/L). IOS demonstrated abnormalities in resistance and/or reactance in 50 of 54 subjects. CT scan demonstrated bronchial wall thickening and/or AT in 40 of 54 subjects; parenchymal disease was not evident in any subject. Specific compliance at functional residual capacity (FRC) (0.07±0.02 [L/cm H2O]/L) and recoil pressure (Pel) at TLC (27±7 cm H2O) were normal. In contrast to patients with ILD, lung expansion was not limited, since IC, Pel, and inspiratory muscle pressure were normal. Reduced TLC was attributable to reduced FRC, compatible with airway closure in the tidal range.

Conclusions: This study describes a distinct physiologic phenotype of restriction due to airway dysfunction. This pattern was observed following WTC dust exposure, has been reported in other clinical settings (eg, asthma), and should be incorporated into the definition of restrictive dysfunction.

Figures

Figure 1.

Mean values for measured lung volumes are illustrated (± SD). The shaded area represents normal range. Valid data for FRC, TLC, and RV were obtainable in 49 of 54 subjects. ERV = expiratory reserve volume; FRC = functional residual capacity; IC = inspiratory capacity; RV = residual volume; TLC = total lung capacity; VC = vital capacity.

Figure 2.

IOS parameters (R20, R5-20, resonant frequency, and AX) are illustrated. Mean values ± SE are plotted before (●) and after (○) bronchodilator administration. The dashed line represents the published upper limit of normal for each parameter. Data are shown for the 49 of 54 subjects with valid postbronchodilator data. AX = reactance area; BD = bronchodilator; IOS = impulse oscillometry; R20 = resistance at an oscillation frequency of 20 Hz; R5-20 = resistance at 5 Hz minus resistance at 20 Hz.

Figure 3.

Maximal expiratory flow-volume curves. A, A representative patient in the present study. B, A patient with known interstitial lung disease with similar vital capacity. Tidal loops are superimposed upon the maximal curves for both subjects.

Figure 4.

The measured DLCO is plotted as a function of TLC in each of the subjects. Data are plotted on the background of prior published observations in patients with confirmed interstitial lung disease (shaded area depicts mean ± 95% CI). DLCO = diffusion capacity of the lung for carbon monoxide. See Figure 1 legend for expansion of other abbreviation.

Figure 5.

Maximal Pel is plotted as a function of the measured TLC in each subject. Data are plotted on the background of prior published data obtained in patients with confirmed interstitial lung disease (shaded area depicts mean ± 95% CI). Pel = elastic recoil pressure of the lung. See Figure 1 legend for expansion of other abbreviation.