Exercise performance in young and middle-aged female patients with subclinical hyperthyroidism

Subclinical hyperthyroidism (SH) may be responsible for many cardiovascular changes, including an impaired exercise performance. The aim of our study was to evaluate the response to the treadmill cardiopulmonary test in patients with SH. We studied 14 female patients from our endocrine clinic with exogenous SH, free from cardiovascular diseases, with mean age of 38.6 +/- 10.2 years, body mass index (BMI) of 24.4 +/- 4.0 kg/m(2), and disease duration of 4.9 +/- 4.9 years. The mean serum thyrotropin (TSH) was 0.03 +/- 0.03 mU/L, serum free thyroxine (FT(4)), 1.72 +/- 0.21 ng/dL, and serum triiodothyronine level, 137 +/- 32 ng/dL. The control group comprised 15 euthyroid, healthy women, with mean age of 35.4 +/- 7.4 years and BMI of 27.3 +/- 5.9 kg/m(2). Both groups had a sedentary lifestyle and underwent the cardiopulmonary test using a treadmill with the Balke protocol. Gas concentrations and the respiratory outflow were measured and the electrocardiogram (ECG) was registered in real time. We calculated the minute ventilation (V(E)), the oxygen consumption (peak VO(2)), the carbonic gas exhalation (peak VCO(2)) and the anaerobic threshold (AT). The heart rate (HR) at rest (90.9 +/- 15.7 versus 78.9 +/- 8.7 beats per minute; p = 0.03) was higher in the patients from our clinic. There was no difference between groups regarding age, BMI, fat percentage, blood pressure, peak HR, exercise duration, mean treadmill peak inclination, V(E), peak VO(2), peak VCO(2), and AT. There was no correlation between peak VO(2) and FT(4), TSH, or disease duration. Our results show that exercise capacity in young and middle-aged female patients is not significantly affected by exogenous SH.