Basal cerebral blood flow (CBF) and CBF regulation after hypercapnia and hypotensive hemorrhage were investigated using H2 clearance in the frontal cortex of awake 2-, 14-, or 23-mo-old Wistar or Fischer 344 rats. Basal CBF decreased in old Wistar but not in mature Wistar (old 64.4 +/- 2.8, mature 87.6 +/- 2.6, young 79.6 +/- 2.2 ml.min-1 x 100 g-1) or in old Fischer 344 (old 71.9 +/- 2.9, young 73.3 +/- 1.6 ml.min-1 x 100 g-1) rats. Cerebrovascular reactivity to hypercapnia decreased in mature and old Wistar (old 2.1 +/- 0.3, mature 3.1 +/- 0.7, young 7.0 +/- 2.1 ml.min-1 x 100 g-1 x mmHg-1) but not in old Fischer 344 rats (old 4.6 +/- 1.4, young 4.9 +/- 0.9 ml.min-1 x 100 g-1 x mmHg-1). The lower limit of CBF autoregulation increased by 20 mmHg during maturation and/or aging in the two strains. Because blood gases and pH evolved similarly in both strains, we postulate that differences in cerebrovascular structure and/or function explain the differences in CBF regulation in the older representatives of the two strains.
The radial artery compliance may be paradoxically increased in untreated arterial hypertension. However, the effect of blood pressure normalization on the radial artery compliance is not well known. We performed a cross-sectional study in order to investigate the effects of blood pressure control on the radial artery diameter and compliance (echotracking and digital photoplethysmography) by comparing these variables in a group of untreated hypertensive patients and in another group of adequately treated hypertensive patients as well as in a group of healthy normotensive subjects. All groups were sex- and age-matched. Radial artery internal diameter was increased in both untreated hypertensive patients and effectively treated hypertensive patients comparatively to controls. Cross-sectional compliance and volumic distensibility were not different between groups. As compared to controls (2.85 +/- 0.39 x 10(-3) mm2 x mm Hg(-1) and 0.42 +/- 0.05 x 10(-3) mm Hg(-1)), isobaric (100 mm Hg) compliance and distensibility were significantly increased in untreated hypertensive patients (4.46 +/- 0.44 and 0.65 +/- 0.07, P < .01) but not significantly different in treated hypertensive patients (3.19 +/- 0.33 and 0.45 +/- 0.04, P = NS). The results of this cross-sectional study suggest that compliance abnormalities of the radial artery, but not internal diameter changes may be reversed by effective therapeutic control of blood pressure in arterial hypertension.
Age-related changes in systemic arterial blood pressure, basal cerebral blood flow (CBF), and CBF regulatory capacity were investigated in awake 6-, 12-, 24-, and 30-mo-old male Wistar (WAG/Rij) rats, one-half of which received the angiotensin I-converting enzyme inhibitor (ACEI) perindopril from 6 mo onward. There was no age-dependent change in mean arterial blood pressure, basal CBF, or cerebrovascular reactivity to hypercapnia, but the lower limit of CBF autoregulation rose from 70 mmHg at 6 and 12 mo to 90 mmHg in 24- and 30-mo-old animals. ACEI lowered mean arterial blood pressure but had no effect on basal CBF or on cerebrovascular reactivity to hypercapnia. ACEI shifted the lower limit of CBF autoregulation to a 20-mmHg-lower level in 12- and 24-mo animals but not in rats treated for 2 yr, i.e., from the ages of 6 to 30 mo. In conclusion, the main age-related change in CBF regulation was an increase in the lower limit of CBF autoregulation to a higher blood pressure level. Treatment with ACEI partially restored the lower limit of CBF autoregulation.
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