Structural changes in resistance and capacitance vessels in borderline hypertension.

Vascular resistance at rest may be normal in humans with borderline or mild hypertension. However, this finding is a facade which can obscure the presence of vascular structural alterations that may have an important influence on resistance and capacitance functions of the circulation. This paper reviews several studies regarding vascular structural changes in borderline hypertension (BHT). First, forearm vasodilator capacity is limited in BHT and in normotensive young men with a family history of hypertension; this suggests the presence of structural changes in forearm resistance vessels. Second, forearm venous distensibility is decreased in BHT. Most of this decrease is caused by nonadrenergic mechanisms--which suggests that there may be structural changes in veins in BHT. Third, the studies of Takeshita and colleagues suggest that sodium intake may influence vascular structural changes. In hypertensive patients who responded to salt loading with increased blood pressure and vascular resistance, salt loading limited vasodilator responses to 10 minutes of ischemia. This effect of salt loading on vasodilator responses occurred in some patients (salt-responders), but not in others (salt-nonresponders). Functional studies support the concept that structural changes in resistance and capacitance vessels occur during the early stages of human hypertension. These changes may not be entirely adaptive responses to elevated arterial pressure, since they occur in capacitance as well as resistance vessels. In addition, the structural changes appear to be responsive to factors such as sodium intake. These observations suggest that vascular structural changes in human hypertension may be related in part to neurohumoral influences or to primary vascular abnormalities.