Yorio Kimura

Effects of Meal Ingestion and Active Standing on Blood Pressure in Patients ≥60 Years of Age

Postprandial hypotension and orthostatic hypotension occur often in elderly patients. In the present study, we examined hemodynamic and humoral responses to meal ingestion and active standing in 20 patients > or = 60 years of age who were free of apparent autonomic and cardiac dysfunction. For a time-control study, water was given instead of a meal to 19 of the 20 patients. After the meal ingestion, there was a fall in systolic blood pressure (BP) in 6 patients of > 20 mm Hg, whereas the fall in systolic BP during the control study was not > 20 mm Hg in any patient. The low-frequency power of the systolic BP wave, an index of peripheral sympathetic activity, was significantly increased only in the patients without postprandial hypotension. The postprandial changes in systolic BP were correlated with the changes in the low-frequency power of the systolic BP wave (r = 0.61; p < 0.01), but they were not correlated with the changes in plasma norepinephrine, insulin, cardiac output, or parameters obtained by the spectral analysis of the RR interval. The systolic BPs in the upright position were comparable after the meal and the water ingestion. Thus, the effects of meal ingestion and upright position on BP are not additive. Dysfunction of peripheral sympathetic control of vascular tone may contribute to the postprandial hypotension in elderly patients.

MILD MENTAL STRESS INCREASES INSULIN SENSITIVITY IN HEALTHY YOUNG MEN

We examined if mental stress alters insulin sensitivity and renal sodium handling in 11 normotensive young men. Following a 60-minute period of equilibration, we performed euglycemic hyperinsulinemic glucose clamp for 150 minutes. The clamp period was divided into three phases; control phase for 90 minutes (I), mental arithmetic phase for 30 minutes (II), and recovery phase for 30 minutes (III). Blood pressure, heart rate and glucose disposal rate (M value) significantly elevated during phase II of the stress study. In a time control study, in which mental arithmetic was not loaded during phase II, blood pressure was kept constant and the changes in M value from phase I to phase II were significantly smaller than those in the stress study. In both studies, fractional excretion of sodium did not significantly change throughout the study period. Thus, insulin sensitivity concerning glucose metabolism increased in response to mild mental stress. However, the effect of insulin on sodium handling was not altered by the stress.

Baroreceptor reflex in elderly essential hypertensives: effect of chronic inhibition of angiotensin converting enzyme.

Baroreflex function and plasma angiotensin II (Ang II) were examined in five elderly and five young or middle-aged essential hypertensive patients before and after enalapril treatment. Baroreflex sensitivity (BS) during blood pressure (BP) elevation by phenylephrine (PE) but not during BP reduction by sodium nitroprusside (SNP) was significantly attenuated in the elderly compared with the younger group, while plasma Ang II concentration was not different between the two groups. Enalapril treatment reduced BP without significant changes in heart rate and plasma norepinephrine in both groups, suggesting a leftward shift of barofunction curve. It also increased the BS in some cases in each group. However, plasma Ang II was not significantly reduced during enalapril treatment. The changes in BS did not correlate with changes in plasma Ang II. These results suggest that BS may be attenuated with increasing age independent of plasma Ang II and that ACE inhibitor influences the set point of the barofunction curve and BS by different mechanisms.

Effect of Chronic Inhibition of Angiotensin Converting Enzyme on Baroreceptor Reflex in Essential Hypertension

We examined baroreflex function and plasma angiotensin II (Ang II) before and after the treatment with an angiotensin converting enzyme inhibitor (ACEI) in eight inpatients with essential hypertension (EHT). Baroreflex sensitivity (BS), expressed as a slope of linear relationship between %-changes in mean blood pressure (BP) and those in plasma concentration of norepinephrine (pNE), was greater during BP reduction by sodium nitroprusside (SNP) than during BP elevation by phenylephrine (PE). Enalapril treatment for 7 days reduced BP without a significant change in heart rate and pNE. It also increased the BS in two cases during SNP infusion and in four cases during PE infusion. Ang II was not significantly reduced after enalapril, while plasma ACE activity was suppressed by about 80% and plasma renin activity (PRA) was elevated. The changes in BS did not correlate with the changes in Ang II. The shift of barofunction curve with an enhancement of BS by enalapril therapy might not be attributed solely to the interaction between circulating Ang II and central baroreflex mechanisms.

Renin responses in patients with orthostatic hypotension: case reports.

In orthostatic hypotensive patients renin is reported to increase in response to head-up tilt unless the lesion involves postganglionic sympathetic efferent nerves. The authors examined responses of plasma renin activity (PRA) to acute blood pressure reduction in 4 patients with orthostatic hypotension. When the coexistence of normal plasma norepinephrine (PNE) and normal or high-nor mal pressor response to alpha stimulant is considered to be a sign of preserved function of postganglionic fibers, 2 of the patients had sympathetic lesions mainly confined to central and/or preganglionic fibers. They were diagnosed as having multiple system atrophy (MSA). The other 2 were diagnosed as having idiopathic orthostatic hypotension with possible postganglionic lesions. Al though 1 MSA patient showed an increase in PRA from 2.0 to 4.7 ng/mL/hr in response to the tilt, the other MSA patient showed no PRA response to the tilt. The head-up tilt did not provoke an apparent PRA response in patients with idiopathic orthostatic hypotension. The authors infused sodium nitroprusside (SNP) in the 3 patients whose PRA did not respond to the head-up tilt. The infusion decreased blood pressure by 40 mmHg or more, but PRA responses were inappropriately small or suppressed. In all cases, PNE did not respond at all to the head-up tilt and to the infusion of SNP. These findings suggest that possible preservation of postganglionic fibers does not necessarily indicate an intact responsiveness of PRA. The PRA profiling may not be an accurate pre dictor for the site of the fiber degeneration in orthostatic hypotension.