Reversible autonomic dysfunction in hyperthyroid patients affects gastric myoelectrical activity and emptying

The autonomic nervous system (ANS) function in hyperthyroidism has been so far investigated mainly from the cardiovascular point of view. The aim of t his study is to show that the ANS dysfunction in hyperthyroidism is also ex pressed in gastric myoelectrical activity disturbances and gastric emptying disorders and to search for a correlation between the severity of clinical manifestation and free thyroid hormone levels and the degree of the ANS dy sfunction. The analyzed group included 50 recently diagnosed patients with hyperthyroidism who were examined twice: before and after 3 months of thyro static treatment. Results were compared with those of a sex-, age- and BMI- matched control group of 50 healthy volunteers. The study included: heart r ate variability analysis in time and frequency domain, at rest and during a deep-breathing test, surface electrogastrography in preprandial and postpr andial periods measured simultaneously with the ultrasound assessment of ga stric emptying time by Bolondi method. In patients with hyperthyroidism in comparison with the control group, the following significant differences we re observed: a sharp reduction of the high-frequency component and a decrea se of heart rate variability, a high incidence of dysrhythmia with dominant bradyarrhythmia, and a delay of gastric emptying. The degree of disorders related to the degree of clinical manifestation of hyperthyroidism's sympto ms and free triiodothyronine serum concentration both. All the disorders we re functional and disappeared in a stable euthyroidism. To conclude, the AN S dysfunction in hyperthyroidism results not only in withdrawal of vagal in hibitory effect on sinoatrial node, but in impaired mutual neuro-hormonal r egulation (decrease of vagal influence) of gastric myoelectrical activity f ollowed by delay of gastric emptying.