The present study aimed to investigate whether cardiac autonomic dysfunction in aging human might be related to an underlying thyroid disturbance. ageing has been associated with hypothyroidism and cardiac autonomic dysfunction. On the basis of body mass index (BMI), 150 patients were grouped into three groups (n = 50) 48 years ± 2, 55 years ± 2 and 63 years ± 2. Electrocardiogram was recorded using PowerLab system and the time and frequency domain measures of heart rate variability (HRV) were calculated. Fasting blood samples were drawn for measurement of serum thyroid stimulating hormone (TSH), total thyroxin (T4) and total triiodothyronine (T3) concentrations. The levels of TSH, T4 and T3 were not significantly different between the groups. The frequency domain HRV parameter reflecting parasympathetic tone (high-frequency normalized units, HFnu) was significantly reduced in aging third groups group. The parameters which reflect sympathetic activation (Heart rate, low-frequency normalized units; LFnu and the LF/HF ratio) were significantly increased in the aging group. HFnu was significantly and negatively correlated with age, whereas LFnu and LF/HF ratio were significantly and positively correlated with the above mentioned parameters. No significant relationships were noted between the HRV parameters and the levels of TSH or thyroid hormones. Cardiac autonomic dysfunction in aging human is not linked with underlying thyroid disturbance.
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