Abstract 2179: Assessment of Posture-Related Dynamic Changes in Cerebral Blood Flow Using Near-Infrared Time-Resolved Spectroscopy: A New Tool To Evaluate Effects of Antihypertensives on Cerebral Circulation
Elderly hypertensive patients treated with blood pressure (BP) lowering agents often complain of orthostatic faintness without a significant fall of BP in standing posture. However the effect of antihypertensives on cerebral blood flow (CBF) is not clear. The aim of this study was to evaluate the effect of various hypertensives on posture-related dynamic changes in CBF using near-infrared time-resolved spectroscopy (TRS). This method allows for measurement of absolute concentrations of oxy-, deoxy- and total hemoglobin (Hb), dynamically, in tissues at various postures. In a randomized 3-phase crossover study, 8 healthy volunteers received a single oral dose of 5 mg nifedipine, 10 mg inderal, or placebo. Optical fibers for TRS were attached to the forehead skin. After assessing basal CBF at supine position, posture-related changes in CBF were then measured at standing position. CBF was 75 +/− 11 units at supine position and reduced by 5 +/− 4 units when standing. The change in CBF was closely related to the changes in oxy-Hb but not deoxy-Hb concentrations, suggesting the critical role of arterial blood flow in posture-related changes in CBF. Inderal did not affect CBF at supine position, but further reduced CBF by 4 +/− 3 units when standing. Nifedipine, on the other hand, attenuated the fall of CBF when standing, while it did not affect CBF at supine position. Inderal and nifedipine lowered BP equally but did not cause further reduction in BP when standing. We conclude that TRS is a very sensitive and reliable method for non-invasive assessment of posture-related dynamic changes in CBF. Inderal seems more likely to cause orthostatic faintness than nifedipine. This technique should represent a novel, valuable tool for assessment of characteristics of various antihypertensives on cerebral circulation.