Early radiographic pneumoconiosis is associated with impaired exercise gas exchange among coal miners with normal resting spirometry

Abstract

Rationale We sought to determine if radiographic pneumoconiosis predicts abnormal gas exchange during exercise in coal mine workers with preserved resting lung function. Methods We analyzed data from former coal miners seen between 2006 and 2014 in a single clinic specializing in black lung evaluations. We limited the analysis to those with normal resting spirometry and an A‐a gradient at peak exercise ≥10 mmHg. We used multivariable logistic regression to estimate predictors of A‐a gradient widened to >150% of the reference value. We focused on chest radiographs consistent with pneumoconiosis, taking into account higher silica exposure mining activities and years underground, and adjusting for cigarette smoking, obesity, and coronary artery disease. Results Of 5507 miners, we analyzed data for 742 subjects with normal spirometry and all key clinical variables available, of whom 372 (50.1%) had radiographic evidence of pneumoconiosis. All but 21 had small opacity profusion of less than 2/1. The median A‐a gradient at peak exercise was 108% of reference value (interquartile range, 81%–141%). In the multivariable analysis, radiographic pneumoconiosis was associated with increased odds of widened A‐a gradient (odds ratio [OR], 2.47; 95% confidence interval [CI], 1.7–3.7). Limited to 660 subjects with normal diffusing capacity for carbon monoxide, the odds were similarly increased (OR, 3.20; 95% CI, 1.5–3.6). Discussion Among coal miners with preserved resting lung function, radiographic evidence of early pneumoconiosis more than doubled the odds of abnormal exercise physiology. Impairment in pneumoconiosis occurs in early disease and may only be evident on exercise testing.

Resting diffusing capacity and severity of radiographic disease predict gas exchange abnormalities with exercise in former US coal miners

“…[35][36][37] Prior analysis of a subset of our data examining miners with normal spirometry and diffusion capacity showed increased odds of abnormal A-a gradient associated with increasing severity of radiographic disease. 12 Our current study extends these findings to demonstrate significant exercise gas exchange abnormalities and declines in work capacity associated with increasing ILO subcategory of small opacity pneumoconiosis, and even greater increases associated with PMF. We found a doubling of the prevalence of an abnormal A-a gradient comparing miners with normal chest radiographs to those with small opacity pneumoconiosis (11% vs. 26%).…”

“…Prior work by our group evaluated the relationship between alveolar-arterial oxygen (A-a) gradient and chest radiograph findings in coal mine workers with normal spirometry and D LCO . 12 In this study we expand previous findings to evaluate associations between measures of resting lung function (forced expiratory volume in 1 s [FEV 1 ], and D LCO ), the continuum of chest radiograph abnormalities, and cardiopulmonary exercise test (CPET) measures of gas exchange including A-a gradient and dead space to tidal volume (VT) ratios (dead space fraction; Vd/Vt), and peak exercise oxygen uptake (VO 2 max). We sought to characterize factors associated with abnormal exercise physiology in a large population of primarily retired coal miners examined at a specialized black lung clinic.…”

“…Characteristics of the population and data abstraction have been described previously. 12 Briefly we obtained deidentified black lung disability examination findings from former coal miners with significant respiratory symptoms who underwent evaluation at a West Virginia black lung clinic between 2004 and 2015. This clinic was chosen because of the systematic collection of occupational and medical historical data as well as availability of complete resting pulmonary function and exercise testing with metabolic measurements.…”

“…We calculated the percent predicted measured maximal VO 2 (VO 2 Maxpp) using reference equations from Hansen et al 18 and the alveolar-arterial oxygen gradient (A-app) using the alveolar gas equation with measured barometric pressure; and RER. 17,19,20 As in our prior work, we calculated the prevalence of abnormal oxygen transfer (A-app > 150%) 12 ; the proportion of subjects with moderately impaired work capacity (VO 2 Maxpp < 60%); the proportion of subjects with elevated dead space at peak exercise (Vd/Vt > 0.33). 21 ; and disabling exercise PO 2 measurements (PO 2 based on altitude and PCO 2 ) that met US DOL criteria for total disability for coal miners.…”

“…The addition of resting single‐breath diffusing capacity for carbon monoxide (D LCO ) and metabolic measurements during exercise provides greater understanding of gas exchange impairments in this population. Prior work by our group evaluated the relationship between alveolar‐arterial oxygen (A‐a) gradient and chest radiograph findings in coal mine workers with normal spirometry and D LCO 12 . In this study we expand previous findings to evaluate associations between measures of resting lung function (forced expiratory volume in 1 s [FEV 1 ], and D LCO ), the continuum of chest radiograph abnormalities, and cardiopulmonary exercise test (CPET) measures of gas exchange including A‐a gradient and dead space to tidal volume (VT) ratios (dead space fraction; Vd/Vt), and peak exercise oxygen uptake (VO 2 max).…”