Sympathetic and parasympathetic baroreflex dysfunction in familial dysautonomia.

OBJECTIVE: To assess the possible abnormalities in the baroreflex modulation of both the heart and the arterial vasculature, in order to better evaluate the role of baroreflex abnormalities in the generation of the cardiovascular symptoms and complications affecting the familial dysautonomia (FD) patient.

METHODS: Twenty-one FD patients and 22 controls underwent 3 minutes of passive head-up tilt (HUT) and baroreceptor stimulation by means of sinusoidal neck suction (NS; 0 to -30 mm Hg; 0.1 Hz [LF] and 0.2 Hz [HF]). Respiration was maintained constant during NS at 15 breaths/minute. The authors monitored RR-intervals (RRI), blood pressure (BP) (Colin), and respiration. NS induced changes of RRI and BP were determined by spectral analysis.

RESULTS: HUT showed orthostatic hypotension without compensatory tachycardia in FD patients but not in controls. LF-NS increased LF power of RRI and BP and HF-NS increased HF power of RRI in controls, but not in FD patients.

CONCLUSIONS: Familial dysautonomia patients have a widespread baroreflex abnormality, involving both the efferent sympathetic arm on the resistance vessels, and the sympathetic and parasympathetic efferent arms on the heart. Therefore, the abnormalities in the control of blood pressure-i.e., supine hypertension, orthostatic hypotension, blood pressure lability-and heart rate-i.e., bradyarrhythmias-are likely due to baroreflex abnormalities.