Effect of aging on salt sensitivity of blood pressure in patients with essential hypertension

Background. Aging is considered to modulate the salt sensitivity of blood pressure (BP), but its mechanisms have not been precisely elucidated. We investigated aging-related changes in salt sensitivity and their mechanisms in patients with essential hypertension. Methods. A high-sodium (Na, 250 mEq/day, for 6 days) diet was given to 32 essential hypertensive patients of different ages (younger, aged <30 years, n = 8; middle-aged, 30- 50 years, n = 10; older, ≥50 years, n = 14) after they had had a low-Na diet (25 mEq Na/day) for 3 days. Cardiac output was measured by dye-dilution, and forearm blood flow (FBF) and venous volume (VV40) by strain-gauge plethysmography. Results. The Na-induced rise in mean BP increased with age (3.2 ± 2.0%: 6.9 ± 2.1%; and 11.7 ± 1.4% respectively, in the younger, middle-aged, and older groups, and this was accompanied by a salt-induced rise in cardiac index and FBF. VV40 decreased with the high-Na diet in older hypertensives (-15.7 ± 6.1%) and the change was significantly less (P < 0.05) than in the younger group (9.3 ± 9.0%). Conclusion. The enhanced salt sensitivity of BP that occurs with aging in patients with essential hypertension is due to increased cardiac output, probably through a venous constriction-related elevation of venous return.