Cardiopulmonary baroreflex control of brachial artery diameter in sustained essential hypertension

An exaggerated reflex response of forearm resistance vessels following stimulation of cardiac mechanoreceptors has been observed in human hypertension. In the present study we analyze the possibility that such an increased response also involves the large brachial artery. For that purpose, the influence of leg elevation in subjects in a supine position on brachial artery diameter and blood flow velocity was studied in 12 healthy, normal males and 17 males of the same age with sustained essential hypertension. Brachial artery diameter and blood flow velocity were measured using a two-dimensional pulsed Doppler velocimeter, with subjects in a supine horizontal position, after passive elevation of the legs and again in a supine horizontal position. Blood pressure and heart rate remained unchanged throughout the study. Elevation of the legs induced an immediate increase in brachial artery diameter (P less than 0.001) and blood flow velocity (P less than 0.001) in both normal subjects and hypertensive patients. The maximal increase in these two parameters was similar in the two groups. In normal subjects, the increases were short-lived, with values returning to baseline levels even when leg elevation was maintained. In hypertensive patients, the increases persisted throughout the period of leg elevation, and brachial artery diameter remained significantly increased in comparison with normal subjects (P less than 0.01). This study provides evidence that loading cardiac mechanoreceptors causes a large dilation of the conduit arteries which is long-lasting in essential hypertensives and short-lived in normal subjects.