TNF and pulmonary arterial hypertension: It can’t be concluded that the results of this study are against previous studies that state that TNFα expression in patients with COPD may be higher[15] nor are they against the study by Chung[4] that stated that overexpression of TNFα resulted in severe pulmonary hypertension.[16] The control group values in our study could have been raised close to the values of the other groups as smoking in subjects in the control group might have worked as a confounding factor.