[Autonomic dysfunction in chronic hypotension associated with uremia]

Chronic hypotension is a not uncommon complication among hemodialyzed patients which is responsible of an important morbidity. The autonomic nervous system (ANS) dysfunction seems to play a key role in the pathogenesis of chronic hypotension.

In order to study whether ANS dysfunction is responsible for chronic hypotension in hemodialyzed patients, the authors evaluated the integrity of the whole baroreflex arc by the Valsalva's manoeuver, of parasympathetic efferent pathway by the deep-breathing test and of sympathetic efferent pathway by the hand-grip test in 16 hemodialyzed patients with chronic hypotension, 17 normotensive hemodialyzed patients and 17 normal control subjects. Plasma catecholamine levels were also measured in these patients.

In normotensive patients, Valsalva's manoeuver response (p < 0.005) and deep-breathing test response (p < 0.05) were lowered, while hand-grip test response was preserved. In chronic hypotensive patients, in addition to an impaired deep-breathing test (p < 0.05), a further reduced Valsalva's manoeuver response and a lower pressor response to hand-grip test were observed (p < 0.001). Catecholamine levels were higher in both groups of patients (p < 0.01) with respect to control subjects, specially in chronic hypotensive patients.

In hemodialyzed patients (both normotensive and hypotensive) the whole baroreflex function and parasympathetic response are impaired. The lower pressor response to hand-grip test observed in hypotensive patients, in spite of the higher catecholamine levels, suggest that in these patients the cardiovascular dysfunction cannot be ascribed to a reduced sympathetic "outflow" but to a resistance of the target organs (heart and vessels) to the sympathetic stimulation.