Borderline hypertension: Relationship between age, hemodynamics and circulating catecholamines

Abstract

The relationship between age, systemic and renal hemodynamics, circulating catecholamines (norepinephrine, epinephrine and dopamine) and intravascular volumes were studied in 38 normotensive subjects and in 77 patients with borderline essential hypertension. Borderline hypertensive patients had a higher cardiac index (p<0.02) and renal blood flow (p<0.05) than normotensive subjects if they were younger than 30 years of age, whereas in older patients no difference was observed. In contrast, total peripheral resistance was normal in young borderline hypertensive patients, but significantly increased (p<0.02) in patients older than age 40 years. Cardiac output (r=0.28, p<0.01) and renal blood flow (r=-0.47, p<0.001) correlated inversely with age in the entire population and in both subgroups. Cardiac output also correlated closely with renal blood flow in all subjects (r=0.45, P<0.001). Circulating norepinephrine levels increased with age (r=0.25, p<0.05), whereas epinephrine concentration tended to decrease. Plasma and total blood volume correlated directly with cardiac output (r=0.39, p<0.001) and inversely with peripheral resistance (r=-0.34, p<0.001). These date indicate that the hyperdynamic circulation (high cardiac output and renal blood flow) of borderline hypertension is found predominantly in patients younger than age 30 years. Older patients are characterized by an elevated total peripheral resistance and normal cardiac output. The age-dependent increase in circulating norepinephrine and decrease in epinephrine levels may participate in the shift of the hemodynamic profile from high-cardiac-output hypertension in the young to a high-arteriolar-resistance hypertension in the older patient.