Cerebral blood flow velocity underestimates cerebral blood flow during modest hypercapnia and hypocapnia

Coverdale, Nicole S.; Gati, Joseph S.; Opalevych, Oksana; Perrotta, Amanda; Shoemaker, J. Kevin

doi:10.1152/japplphysiol.00285.2014

Cited by 298 publications

(290 citation statements)

References 27 publications

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“…However, the degree to which transcranial Doppler may underestimate CBF because of dilation of the large cerebral vessels (ie, middle cerebral artery) with hypercapnia remains controversial. 48 Similarly, recent meta-analyses demonstrate that arterial spin labeling magnetic resonance imaging may overestimate gCBF compared with […”

Section: Discussionmentioning

confidence: 99%

Higher Aortic Stiffness Is Associated With Lower Global Cerebrovascular Reserve Among Older Humans

DuBose¹,

Ponto²,

Moser³

et al. 2018

Hypertension

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Abstract-Greater aortic stiffness and pulse pressure are associated with cerebrovascular remodeling, reduced white matter microstructure, and cognitive performance with aging in humans. However, it is unclear whether aortic stiffness and pulse pressure are associated with reduced basal global cerebral blood flow (CBF) and cerebrovascular reserve among older adults. Global CBF was quantified in 205 adults (range, 19-87 years; mean±SE: 30.6±1.3 years) using quantitative [ 15 O] water brain positron emission tomography imaging. In a subset of older adults (n=24; 70.0±2.0 years), aortic stiffness (carotid femoral pulse wave velocity) and cerebrovascular reserve (change in global CBF after intravenous infusion of acetazolamide) were assessed. In the entire cohort, global CBF was lower in older compared with young adults (36.5±1.1 versus 50.5±0.7 mL/min per 100 mL; P<0.001). Global CBF was higher in young women compared with young men (51.0±0.30 versus 47.4±0.03 mL/min per 100 mL; P<0.001) but did not differ between older women and men (P=0.63). In older adults, greater carotid femoral pulse wave velocity was associated with lower cerebrovascular reserve (r=−0.68; P=0.001 adjusted for age, sex, and mean arterial pressure) but not global CBF (r=0.13; P=0.60). Brachial pulse pressure was not associated with lower cerebrovascular reserve (r=−0.37; P=0.159) when adjusted for age and sex. These data indicate that the age-related increases in aortic stiffness may contribute, in part, to the brain's impaired ability to augment blood flow in response to a stimulus with aging in humans. (Hypertension. 2018;72:476-482.

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Section: Discussionmentioning

confidence: 99%

Higher Aortic Stiffness Is Associated With Lower Global Cerebrovascular Reserve Among Older Humans

DuBose¹,

Ponto²,

Moser³

et al. 2018

Hypertension

View full text Add to dashboard Cite

show abstract

“…In fact, the YA group is characterized by considerable variability in this response, an outcome that we have observed previously in two separate groups of similarly aged individuals. 13,14 Determining the mechanism(s) involved in the impaired CVC outcome in the OA group was beyond the scope of this study but may include arterial stiffening or impaired endothelial function as it pertains to hypercapnic or shear stress stimuli. Extracellular pH of the cerebrovasculature is the main mediator of the hypercapnia-induced increase in CBF 26 via an effect on potassium channels 27 and it is unclear how aging may affect these channels.…”

Section: Discussionmentioning

confidence: 99%

Impact of age on cerebrovascular dilation versus reactivity to hypercapnia

Coverdale

Badrov

Shoemaker

2016

J Cereb Blood Flow Metab

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This study quantified the effect of age on cerebrovascular reactivity and cerebrovascular conductance while accounting for differences in grey matter volume in younger (YA: n ¼ 12; 24 AE 4 years, six females) and older adults (OA: n ¼ 10; 66 AE 7 years; five females). Cerebral blood flow velocity (CBFV; transcranial Doppler) in the middle cerebral artery (MCA), MCA cross-sectional area (CSA), intracranial volumes (magnetic resonance imaging), and mean arterial pressure (MAP; Finometer), were measured under normocapnic and hypercapnic (6% carbon dioxide) conditions. Cerebral blood flow (CBF) was quantified from CBFV and MCA CSA and normalized to grey matter volume. Grey matter volume was 719 AE 98 mL in YA and 622 AE 50 mL in OA (P ¼ 0.009). Cerebrovascular reactivity (%ÁCBF/ÁP ET CO 2 ) was not different between YA and OA. In contrast, cerebrovascular conductance (CBF/MAP) in response to hypercapnia was reduced in OA (P ¼ 0.02). Of note, MAP increased more with hypercapnia in OA compared with YA. Therefore, the central hemodynamic response to hypercapnia compensated for a diminished dilatory response downstream from the MCA so that the CBF response to hypercapnia per unit of brain mass was not affected by age. This impairment was not detected by traditional measures of cerebrovascular reactivity.

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“…It is now clear that the diameter of the MCA (and hence possibly the PCA) is influenced by marked changes in arterial PCO 2 (>8 mmHg above or below resting) and arterial PO 2 (<50 mmHg) 84,96 (reviewed in literature 9,97 ). It is less clear that changes in blood pressure will affect the diameter of these intra-cranial arteries.…”

Section: Transcranial Dopplermentioning

confidence: 99%

Neurovascular coupling in humans: Physiology, methodological advances and clinical implications

Phillips

Chan

Zheng

et al. 2015

J Cereb Blood Flow Metab

361

364

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Neurovascular coupling reflects the close temporal and regional linkage between neural activity and cerebral blood flow. Although providing mechanistic insight, our understanding of neurovascular coupling is largely limited to nonphysiological ex vivo preparations and non-human models using sedatives/anesthetics with confounding cerebrovascular implications. Herein, with particular focus on humans, we review the present mechanistic understanding of neurovascular coupling and highlight current approaches to assess these responses and the application in health and disease. Moreover, we present new guidelines for standardizing the assessment of neurovascular coupling in humans. To improve the reliability of measurement and related interpretation, the utility of new automated software for neurovascular coupling is demonstrated, which provides the capacity for coalescing repetitive trials and time intervals into single contours and extracting numerous metrics (e.g., conductance and pulsatility, critical closing pressure, etc.) according to patterns of interest (e.g., peak/minimum response, time of response, etc.). This versatile software also permits the normalization of neurovascular coupling metrics to dynamic changes in arterial blood gases, potentially influencing the hyperemic response. It is hoped that these guidelines, combined with the newly developed and openly available software, will help to propel the understanding of neurovascular coupling in humans and also lead to improved clinical management of this critical physiological function.

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Cerebral blood flow velocity underestimates cerebral blood flow during modest hypercapnia and hypocapnia

Cited by 298 publications

References 27 publications

Higher Aortic Stiffness Is Associated With Lower Global Cerebrovascular Reserve Among Older Humans

Higher Aortic Stiffness Is Associated With Lower Global Cerebrovascular Reserve Among Older Humans

Impact of age on cerebrovascular dilation versus reactivity to hypercapnia

Neurovascular coupling in humans: Physiology, methodological advances and clinical implications

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