Skin microvascular reactivity in patients with hypothyroidism

Hypothyroidism is associated with impaired vascular function; however, little is known about its impact on microcirculation. We aimed to determine skin microvascular reactivity in hypothyroidism focusing on endothelial function and the sympathetic response. We measured skin laser Doppler (LD) flux (LDF) on the volar forearm and the finger pulp using LD flowmetry in hypothyroid patients (N = 13) and healthy controls (N = 15). Skin microvascular reactivity was assessed by a three-minute occlusion of the brachial artery, inducing postocclusive reactive hyperaemia (PRH), and by a four-minute local cooling of the hand. An electrocardiogram (ECG), digital artery blood pressure and skin temperature at the measuring sites were recorded. Baseline LDF, the digital artery blood pressure and the heart rate were comparable between patients and controls. On the other hand, patients exhibited significantly longer PRH duration, significantly higher blood pressure during cooling (unpaired t-test, p <0.05) and lower, albeit not significant, LDF in the ipsilateral finger pulp during cooling compared to controls. Unexpectedly, the results of the present study point to an increased vasodilator capacity of skin microcirculation and an apparent increase in sympathetic reactivity after local cooling in hypothyroid patients. Hypothyroidism induces subtle changes of some haemodynamic parameters in skin microcirculation implying altered endothelial function and altered sympathetic reactivity.