Pulmonary function tests and thyroid hormone concentrations in patients with chronic obstructive pulmonary disease.

OBJECTIVE To evaluate the relationship between pulmonary function tests, arterial blood gases, and thyroid gland functions in patients with chronic obstructive pulmonary disease (COPD). SUBJECTS AND METHODS Thirty-two patients (mean age 64.1 +/- 7.3 years, range 53-84 years) with stable COPD (mean duration of disease 11.1 +/- 9.1 years, range 1-30 years) and 15 healthy control cases participated in the study. Pulmonary function, arterial blood gas, and thyroid hormone concentration were measured, and thyroid ultrasonography and scintigraphy were also performed. RESULTS The values of the pulmonary function tests (vital capacity, forced vital capacity, forced expiratory volume in 1 s and peak expiratory flow) and PaO2 were lower in the study than control group (p < 0.001), but the values of PaCO2 and concentration of free 3,5,3'-triiodothyronine (fT3) were higher in the study than control group (p < 0.01) although thyroid hormone concentrations were within normal limits in all cases. However, there was no difference between the values of thyroid-stimulating hormone and free thyroxine in both the study and control groups and therefore association could not be established between them on the one hand and pulmonary function test and arterial blood gases on the other hand. Only the values of PaCO2 and fT3 were positively associated; all other values were negatively associated with fT3. CONCLUSION Changes in pulmonary function tests and arterial blood gases seem to be associated with fT3 concentrations in patients with COPD. Increased respiratory workload could affect thyroid functions.