Sympathetic and reflex alterations in systo-diastolic and systolic hypertension of the elderly.

Abstract

Previous studies have shown that young and middle-aged essential hypertensives are characterized by a sympathetic activation coupled with an impaired baroreflex-heart rate control. The present study aimed to determine whether these neuroadrenergic and reflex alterations also characterize systo-diastolic and systolic hypertension of the elderly. In 20 untreated elderly essential hypertensive subjects [10 with a systo-diastolic and 10 with an isolated systolic hypertension, aged 67.2 +/- 1.5 years and 66.9 +/- 1.7 years (mean +/- SEM)], we measured beat-to-beat arterial blood pressure (finger photoplethysmographic device), heart rate (electrocardiogram) and efferent postganglionic muscle sympathetic nerve activity (microneurography) at rest and during baroreceptor stimulation and deactivation induced by stepwise intravenous infusions of phenylephrine and nitroprusside, respectively. Data were compared with those obtained in 11 age-matched normotensive control subjects. Compared to the elderly normotensive group, muscle sympathetic nerve activity was increased to a similar degree in the group of systo-diastolic and systolic hypertension (50.8 +/- 4.2 versus 75.2 +/- 5.2 and 70.4 +/- 5.1 bursts per 100 heart beats, respectively, P< 0.01 for both). In the control group, the stepwise increase in arterial pressure induced by phenylephrine caused progressive bradycardia and sympathoinhibition, while the stepwise decrease in arterial pressure had opposite effects. While baroreceptor-heart rate control was markedly impaired (average reduction 41.6%), in both systo-diastolic and systolic hypertensive patients, baroreceptor modulation of sympathetic nerve traffic was similar to that seen in normotensive individuals. These data demonstrate that sympathetic activation is not only a feature of young and middle-aged, but also of elderly hypertensives, regardless of whether both systolic and diastolic or only systolic blood pressure is increased. They also show that hypertension of the elderly is not accompanied by an impaired baroreceptor modulation of sympathetic nerve traffic.