Dynamic Regulation of Middle Cerebral Artery Blood Flow Velocity in Aging and Hypertension

• Published in: Stroke (1970) Vol. 31; no. 8; pp. 1897 - 1903
• Main Authors: Lipsitz, Lewis A., Mukai, Seiji, Hamner, Jason, Gagnon, Margaret, Babikian, Viken
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 01.08.2000; American Heart Association, Inc
• Subjects: Adult; Aged; Aging - physiology; Arterial hypertension. Arterial hypotension; Biological and medical sciences; Blood and lymphatic vessels; Blood Flow Velocity - physiology; Blood Gas Analysis; Blood Pressure - physiology; Cardiology. Vascular system; Cerebrovascular Circulation - physiology; Clinical manifestations. Epidemiology. Investigative techniques. Etiology; Female; Homeostasis - physiology; Humans; Hypertension - blood; Hypertension - diagnostic imaging; Hypertension - physiopathology; Hypotension, Orthostatic - blood; Hypotension, Orthostatic - diagnostic imaging; Hypotension, Orthostatic - physiopathology; Male; Medical sciences; Middle Cerebral Artery - diagnostic imaging; Middle Cerebral Artery - physiopathology; Pilot Projects; Posture - physiology; Prognosis; Ultrasonography, Doppler, Transcranial; Sonography; Human; Doppler ultrasound study; Regional blood flow; Nervous system diseases; Senescence; Middle cerebral artery; Cardiovascular disease; Exploration; Transcranial route; Postural hypotension; Spectrum analysis; Diseases of the autonomic nervous system; Adult; Self regulation; Arterial pressure; Hemodynamics; Induced hypercapnia; Elderly; Age; Brain (vertebrata)
• ISSN: 0039-2499; 1524-4628
• DOI: 10.1161/01.STR.31.8.1897

Background and Purpose —-Although aging and hypertension may predispose hypertensive elderly subjects to cerebral hypoperfusion during orthostatic stress, their effects on the acute cerebral autoregulatory response to hypotension are not known. Methods —-Continuous middle cerebral artery blood flow velocity (BFV) (transcranial Doppler ultrasound) and mean arterial pressure (MAP, Finapres) were measured in response to (1) acute hypotension during standing, (2) steady-state sitting and standing, and (3) hypercarbia during CO 2 rebreathing in 10 healthy young subjects (age 24±1 years), 10 healthy elderly subjects (age 72±3 years), and 10 previously treated hypertensive elderly (age 72±2 years) subjects. CO 2 reactivity was computed as the slope of cerebrovascular conductance (CVC=BFV/MAP) versus end-expiratory CO 2 . Coherence, transfer magnitudes, and phases between low-frequency MAP and BFV signals were computed from their autospectra during 5 minutes of sitting and standing. Results —-MAP fell to a similar extent in all groups by an average of 21 to 26 mm Hg (22% to 26%) within 30 seconds of standing. Mean BFV also fell in all subjects but significantly less in the older subjects (−4.7±0.7 cm/s in hypertensives and −5.3±1.2 cm/s in normotensives, P =NS) compared with younger subjects (−10.1±1.1 cm/s, P <0.05). CO 2 reactivity was greater in the young subjects (0.19±0.01) compared with normotensive (0.14±0.01, P <0.05) and hypertensive elderly subjects (0.11±0.02, P <0.05) ( P =NS between elderly groups). Fewer hypertensive subjects had coherence between MAP and BFV signals; for subjects with coherence, there were no significant group differences in phase or transfer magnitudes in either sitting or standing positions. Conclusions —-Despite reduced CO 2 reactivity, elderly normotensive and previously treated hypertensive subjects retain cerebral autoregulatory capacity in response to acute orthostatic hypotension.