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

Lipsitz, Lewis A.; Mukai, Sonoyo; Hamner, Jason W.; Gagnon, Margaret; Babikian, Viken L.

doi:10.1161/01.str.31.8.1897

Cited by 245 publications

(239 citation statements)

References 23 publications

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“…As expected due to intact cerebral autoregulation with age (66), there were no changes in the response of mean MCA velocity to sitting and standing with age; however, with more erect posture, systolic MCA velocity decreased more in the younger groups. Many researchers have observed lower MCA velocity in participants over 70 yr old (35,48,57), and Sorond et al (57) observed a greater decrease in MCA velocity in participants over 70 yr old during standing. Contrary to the results of Sorond et al (57), we observed an attenuated loss of mean and diastolic MCA velocity during the transitions to sitting and standing with age.…”

Section: Discussionmentioning

confidence: 99%

Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men

Edgell

Robertson

Hughson

2012

Journal of Applied Physiology

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Edgell H, Robertson AD, Hughson RL. Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men. J Appl Physiol 112: 1482-1493, 2012. First published February 23, 2012 doi:10.1152/japplphysiol.01204.2011.-Increased incidence of orthostatic hypotension and presyncopal symptoms in young women could be related to hormonal factors that might be isolated by comparing cardiovascular and cerebrovascular responses to postural change in young and older men and women. Seven young women, 11 young men, 10 older women (Ͼ1 yr postmenopausal, no hormone therapy), and 9 older men participated in a supine-to-sit-to-stand test while measuring systemic hemodynamics, end-tidal PCO2, and blood flow velocity of the middle cerebral artery (MCA). Women had a greater reduction in stroke volume index compared with age-matched men (change from supine to standing: young women: Ϫ22.9 Ϯ 1.6 ml/m 2 ; young men: Ϫ14.4 Ϯ 2.4 ml/m 2 ; older women: Ϫ17.4 Ϯ 3.3 ml/m 2 ; older men: Ϫ13.8 Ϯ 2.2 ml/m 2 ). This was accompanied by offsetting changes in heart rate, particularly in young women, resulting in no age or sex differences in cardiac output index. Mean arterial pressure (MAP) was higher in older subjects and increased with movement to upright postures. Younger men and women had higher forearm vascular resistance that increased progressively in the upright posture compared with older men and women. There was no difference between sexes or ages in total peripheral resistance index. Women had higher MCA velocity, but both sexes had reduced MCA velocity while upright, which was a function of reduced blood pressure at the MCA and a significant reduction in end-tidal PCO2. The reductions in stroke volume index suggested impaired venous return in women, but augmented responses of heart rate and forearm vascular resistance protected MAP in younger women. Overall, these results showed significant sex and age-related differences, but compensatory mechanisms preserved MAP and MCA velocity in young women. cerebrovascular; sex; age; orthostatic ORTHOSTATIC HYPOTENSION (a condition that sometimes leads to fainting) is an important and sometimes dangerous condition that particularly affects young women during daily life, as reflected by admission to emergency rooms (51). It has been speculated that female sex hormones might modulate reflex neural or vascular properties, resulting in the greater incidence of orthostatic hypotension in young women (5,14,15,52,69). An additional indication of impaired orthostatic responses in women includes the observation that women have a greater propensity towards postural orthostatic tachycardia syndrome (18, 60).Contrary to observations for young women, clinical evidence supports the concept that orthostatic hypotension occurs less frequently in women ages 40 -60 yr (many of whom could be postmenopausal) (51). Investigations of men and women from 23-77 yr of age indicated that the heart rate response to tilt was reduced with aging, but vascular responses a...

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Section: Discussionmentioning

confidence: 99%

Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men

Edgell

Robertson

Hughson

2012

Journal of Applied Physiology

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“…We also assessed cerebral autoregulation using a traditional Fourier-transform-based transfer function analysis [8,35]. The time series BP and BFV were first linearly detrended and divided into 5000-point (100-sec) segments with 50% overlap.…”

Section: E Transfer Function Analysismentioning

confidence: 99%

“…The Fourier transform of BP (S P (f)) and BFV (S V (f)) were calculated for each segment with a spectral resolution 0.01Hz, and were used to calculated the transfer function (5) where is the conjugate of S V (f); |S P (f)| 2 is the power spectrum density of BP; G(f) = |H (f)| is the transfer function amplitude (gain); and ø(f) is the transfer function phase at a specific frequency f. The amplitude and the phase of the transfer function reflect the linear amplitude and time relationship between the two signals. The reliability of these linear relationships can be evaluated by coherence that ranges from 0 to 1: (6) It has been proposed that a coherence value <0.5 indicates a nonlinear BP-BFV relationship and engagement of autoregulation [8,35]. The estimates of BP-BFV relationship based on transfer function become unreliable for coherence values approaching zero.…”

Section: E Transfer Function Analysismentioning

confidence: 99%

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Peng

Huang

et al. 2008

Physica A: Statistical Mechanics and its Applications

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Cerebral autoregulation (CA) is an important mechanism that involves dilation and constriction in arterioles to maintain relatively s cerebral blood flow in response to changes of systemic blood pressure. Traditional assessments of CA focus on the changes of cerebral blood flow velocity in response to large blood pressure fluctuations induced by interventions. This approach is not feasible for patients with impaired autoregulation or cardiovascular regulation. Here we propose a newly developed technique-the multimodal pressure-flow (MMPF) analysis, which assesses CA by quantifying nonlinear phase interactions between spontaneous oscillations in blood pressure and flow velocity during resting conditions. We show that CA in healthy subjects can be characterized by specific phase shifts between spontaneous blood pressure and flow velocity oscillations, and the phase shifts are significantly reduced in diabetic subjects. Smaller phase shifts between oscillations in the two variables indicate more passive dependence of blood flow velocity on blood pressure, thus suggesting impaired cerebral autoregulation. Moreover, the reduction of the phase shifts in diabetes is observed not only in previously-recognized effective region of CA (<0.1Hz), but also over the higher frequency range from ~0.1 to 0.4Hz. These findings indicate that Type 2 diabetes alters cerebral blood flow regulation over a wide frequency range and that this alteration can be reliably assessed from spontaneous oscillations in blood pressure and blood flow velocity during resting conditions. We also show that the MMPF method has better performance than traditional approaches based on Fourier transform, and is more sui for the quantification of nonlinear phase interactions between nonstationary biological signals such as blood pressure and blood flow.

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“…These findings suggest the presence of cerebral vasoconstriction associated with the augmented sympathetic nerve activity during orthostatic stress. 10,12 In addition, in contrast to the traditional concept of cerebral autoregulation, which suggests that steady-state CBF remains relatively constant despite large changes in arterial pressure, 1,14 we 15 and others 16,17 have found that beat-to-beat CBF velocity measured in the MCA in humans fluctuates spontaneously in response to dynamic changes in arterial pressure. If MCA diameter remains relatively constant, as has been shown by numerous studies, 18,19 these changes in CBF velocity reflect changes in CBF.…”

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confidence: 94%

“…Thus, estimation of transfer function between these 2 variables may identify frequencydependent properties of dynamic cerebral autoregulation. [15][16][17] This study was conducted to test directly the hypothesis that beat-to-beat CBF velocity, in response to dynamic changes in arterial pressure, is under tonic autonomic neural control in humans. For this purpose, we blocked both sym-pathetic and parasympathetic nerve activity with an intravenous infusion of trimethaphan (ganglion blockade).…”

mentioning

confidence: 99%

Autonomic Neural Control of Dynamic Cerebral Autoregulation in Humans

et al. 2002

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Background-The purpose of the present study was to determine the role of autonomic neural control of dynamic cerebral autoregulation in humans. Methods and Results-We measured arterial pressure and cerebral blood flow (CBF) velocity in 12 healthy subjects (aged 29Ϯ6 years) before and after ganglion blockade with trimethaphan. CBF velocity was measured in the middle cerebral artery using transcranial Doppler. The magnitude of spontaneous changes in mean blood pressure and CBF velocity were quantified by spectral analysis. The transfer function gain, phase, and coherence between these variables were estimated to quantify dynamic cerebral autoregulation. After ganglion blockade, systolic and pulse pressure decreased significantly by 13% and 26%, respectively. CBF velocity decreased by 6% (PϽ0.05). In the very low frequency range (0.02 to 0.07 Hz), mean blood pressure variability decreased significantly (by 82%), while CBF velocity variability persisted. Thus, transfer function gain increased by 81%. In addition, the phase lead of CBF velocity to arterial pressure diminished. These changes in transfer function gain and phase persisted despite restoration of arterial pressure by infusion of phenylephrine and normalization of mean blood pressure variability by oscillatory lower body negative pressure. Conclusions-These data suggest that dynamic cerebral autoregulation is altered by ganglion blockade. We speculate that autonomic neural control of the cerebral circulation is tonically active and likely plays a significant role in the regulation of beat-to

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

Cited by 245 publications

References 23 publications

Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men

Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Autonomic Neural Control of Dynamic Cerebral Autoregulation in Humans

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