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

Background Previous studies have shown that young and middle-aged essential hypertensives are characterized by a sympathetic activation coupled with a n impaired baroreflex-heart rate control. The present study aimed to determ ine whether these neuroadrenergic and reflex alterations also characterize systo-diastolic and systolic hypertension of the elderly. Subjects and methods In 20 untreated elderly essential hypertensive subject s [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 measure d beat-to-beat arterial blood pressure (finger photoplethysmographic device ), heart rate (electrocardiogram) and efferent postganglionic muscle sympat hetic nerve activity (microneurography) at rest and during baroreceptor sti mulation and deactivation induced by stepwise intravenous infusions of phen ylephrine and nitroprusside, respectively. Data were compared with those ob tained in 11 age-matched normotensive control subjects. Results Compared to the elderly normotensive group, muscle sympathetic nerv e activity was increased to a similar degree in the group of systo-diastoli c 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 con trol group, the stepwise increase in arterial pressure induced by phenyleph rine caused progressive bradycardia and sympathoinhibition, while the stepw ise 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 modulatio n of sympathetic nerve traffic was similar to that seen in normotensive ind ividuals. Conclusions These data demonstrate that sympathetic activation is not only a feature of young and middle-aged, but also of elderly hypertensives, rega rdless of whether both systolic and diastolic or only systolic blood pressu re is increased. They also show that hypertension of the elderly is not acc ompanied by an impaired baroreceptor modulation of sympathetic nerve traffi c. I Hypertens 2000, 18:587-593 (C) Lippincott Williams & Wilkins.