[Investigation of orthostatic hypotension by the provoked hypercapnia test (author's transl)].

Orthostatic hypotension results from an alteration in the baroreflex at any level with subsequent disturbance in blood pressure homeostasis in response to variations. The second part of this reflex arc, from the bulbar vasopressor centre to the peripheral effector sites, can be explored directly by studying the hemodynamic response to an increase in arterial CO2 levels. Normally the response is an increase in blood pressure, but under abnormal conditions there is a reduction. Orthostatic hypotension with a normal hemodynamic response to increased CO2 levels indicates that the first part of the reflex arc is involved, an abnormal response is due to the second part being affected. The CO2 test was conducted in 8 subjects with orthostatic hypotension (bulbar lesions, medullary lesions, idiopathic orthostatic hypotension, polyradiculoneuritis, primary amylosis). Comparing the typical anatomoclinical characteristics of each of the lesions explored with the results of the hemodynamic response to CO2 test suggests that the interpretation proposed is a valid one.