Patients were subjected to high-kilovolt chest X-rays to confirm the diagnosis of coal worker's pneumoconiosis in accordance with the China National Diagnostic Criteria for Pneumoconiosis (GBZ 70-2002) , which is the same as the International Labor Organization Classification of Pneumoconiosis .
The relation of the prevalence and stage of coal worker's pneumoconiosis with the prevalence of pulmonary artery hypertension was estimated by computing odds ratio (OR) and 95% confidence interval (CI) by logistic regression analysis; values were adjusted for possible confounders.
The coal worker's pneumoconiosis stages I-III of the cases were 63.8%, 20.3%, and 15.9% respectively.
The PASP of patients with coal worker's pneumoconiosis was increased with the severity of the disease.
Patients with stage II and III coal worker's pneumoconiosis exhibited a significantly reduced Pa[O.sub.2], forced expiratory volume in 1 s/forced vital capacity ratio ([FEV.sub.1]/FVC), diffusion capacity of carbon monoxide (DLCO) and increased residual volume (RV), residual volume/total lung capacity ratio (RV/TLC), and total airway resistance (Rtot and Reff) compared with those in stage I and control subjects (p < 0.05).
The prevalence rates of pulmonary artery hypertension were 0%, 0%, 12.5%, 54.7%, and 68.2% in healthy, exposure, stage I, stage II, and stage III coal worker's pneumoconiosis groups, respectively ([p.sub.trend] < 0.001) (Figure 1, Table 2).
The exposure to dust and the prevalence of coal worker's pneumoconiosis were independently associated with the prevalence of pulmonary artery hypertension.
Table 5 shows the correlation coefficients between various variables of pulmonary function and indicators of PASP and right cardiac structure of patients with coal worker's pneumoconiosis. We found that Pa[O.sub.2] and [FEV.sub.1]/FVC were negatively correlated with PASP, whereas Pa[O.sub.2] and [FEV.sub.1] were negatively correlated with PA diameter.
In particular, the prevalence of pulmonary artery hypertension was increased with the onset and severity of coal worker's pneumoconiosis. Furthermore, the prevalence or the severity of coal worker's pneumoconiosis was an independent risk factor of pulmonary artery hypertension.
Considering a previous study , we found that patients with coal worker's pneumoconiosis exhibited significantly impaired pulmonary functions vs.
For example, the medical and legal criteria for coal worker's pneumoconiosis
are different.(5) Under the 1969 Federal Coal Mine Health and Safety Act,(6) many coal workers met criteria for compensation only because they smoked cigarettes or had non-respiratory disability such as heart disease, hypertension or obesity.(7) The result is that many ex-miners hospitalized for exacerbation of COPD - with clear lung fields on chest x-ray - are erroneously noted throughout the chart as having "coal worker's pneumoconiosis
." This type of ECHO diagnosis fosters confusion about terminology and clinical causation.