title: Increases in cerebrovascular impedance in older adults.
abstract: This study explored a novel method for measuring cerebrovascular impedance to quantify the relationship between pulsatile changes in cerebral blood flow (CBF) and arterial pressure. Arterial pressure in the internal or common carotid artery (applanation tonometry), CBF velocity in the middle cerebral artery (transcranial Doppler), and end-tidal CO(2) (capnography) were measured in six young (28 ± 4 yr) and nine elderly subjects (70 ± 6 yr). Transfer function method was used to estimate cerebrovascular impedance. Under supine resting conditions, CBF velocity was reduced in the elderly despite the fact that they had higher arterial pressure than young subjects. As expected, cerebrovascular resistance index was increased in the elderly. In both young and elderly subjects, impedance modulus was reduced gradually in the frequency range of 0.78-8 Hz. Phase was negative in the range of 0.78-4.3 Hz and fluctuated at high frequencies. Compared with the young, impedance modulus increased by 38% in the elderly in the range of 0.78-2 Hz and by 39% in the range of 2-4 Hz (P < 0.05). Moreover, increases in impedance were correlated with reductions in CBF velocity. Collectively, these findings demonstrate the feasibility of assessing cerebrovascular impedance using the noninvasive method developed in this study. The estimated impedance modulus and phase are similar to those observed in the systemic circulation and other vascular beds. Moreover, increases in impedance in the elderly suggest that arterial stiffening, besides changes in cerebrovascular resistance, contributes to reduction in CBF with age.
authors: Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231, USA.
authors: Yong-Sheng
authors: YS
authors: Zhu
authors: Benjamin Y
authors: BY
authors: Tseng
authors: Shigeki
authors: S
authors: Shibata
authors: Benjamin D
authors: BD
authors: Levine
authors: Rong
authors: R
authors: Zhang
references: Med Clin North Am. 2009 May;93(3):583-604, Table of Contents
references: 19427493
references: Nat Rev Neurol. 2010 May;6(5):256-65
references: 20368741
references: J Appl Physiol (1985). 1997 Dec;83(6):2139-45
references: 9390992
references: Hypertension. 2005 Nov;46(5):e15; author reply e15-6
references: 16230513
references: Circ Res. 1967 Apr;20(4):365-80
references: 6025401
references: Clin Physiol Funct Imaging. 2007 May;27(3):191-6
references: 17445071
references: Stroke. 2009 Jul;40(7):2552-6
references: 19478233
references: Nat Rev Neurosci. 2004 May;5(5):347-60
references: 15100718
references: Clin Sci. 1970 Feb;38(2):10P
references: 4906423
references: Med Biol Eng Comput. 2009 Feb;47(2):153-63
references: 18853214
references: Am J Physiol Heart Circ Physiol. 2001 Apr;280(4):H1472-9
references: 11247756
references: Clin Sci (Lond). 2009 Mar;116(6):513-20
references: 18939945
references: Hypertension. 2007 Jun;49(6):1248-55
references: 17404183
references: Radiology. 1998 Dec;209(3):667-74
references: 9844657
references: J Chronic Dis. 1956 May;3(5):478-86
references: 13306754
references: J Am Coll Cardiol. 1992 Oct;20(4):952-63
references: 1527307
references: Pharmacol Ther. 1996;72(3):193-214
references: 9364575
references: Cerebrovasc Brain Metab Rev. 1990 Summer;2(2):161-92
references: 2201348
references: Hypertension. 2005 Jul;46(1):244-8
references: 15911747
references: J Neurosurg. 1982 Dec;57(6):769-74
references: 7143059
references: Ultrasound Med Biol. 1994;20(2):101-5
references: 7912867
references: Ultrasound Med Biol. 1996;22(4):373-82
references: 8795163
references: Eur Heart J. 2006 Nov;27(21):2588-605
references: 17000623
references: Circ Res. 1990 Jan;66(1):8-17
references: 2403863
references: Stroke. 2006 Jan;37(1):33-7
references: 16339468
references: Med Biol Eng Comput. 2009 Feb;47(2):131-41
references: 18543011
references: Brain. 1990 Feb;113 ( Pt 1):27-47
references: 2302536