Differential blood flow responses to CO₂ in human internal and external carotid and vertebral arteries

Abstract

Key points• Arterial CO 2 serves as a mediator of cerebral blood flow, and its relative influence on the regulation of cerebral blood flow is defined as cerebral CO 2 reactivity.• Because of methodological limitations, almost all previous studies have evaluated the response of blood flow velocity in the middle cerebral artery to changes in CO 2 as a measure of CO 2 reactivity across the whole brain.• We found that the vertebral artery has lower CO 2 reactivity than the internal carotid artery.Moreover, CO 2 reactivity in the external carotid artery was markedly lower than in the cerebral circulation.• These results demonstrate regional differences in CO 2 regulation of blood flow between the internal carotid, external carotid, and vertebro-basilar circulation.Abstract Arterial CO 2 serves as a mediator of cerebral blood flow (CBF), and its relative influence on the regulation of CBF is defined as cerebral CO 2 reactivity. Our previous studies have demonstrated that there are differences in CBF responses to physiological stimuli (i.e. dynamic exercise and orthostatic stress) between arteries in humans. These findings suggest that dynamic CBF regulation and cerebral CO 2 reactivity may be different in the anterior and posterior cerebral circulation. The aim of this study was to identify cerebral CO 2 reactivity by measuring blood flow and examine potential differences in CO 2 reactivity between the internal carotid artery (ICA), external carotid artery (ECA) and vertebral artery (VA). In 10 healthy young subjects, we evaluated the ICA, ECA, and VA blood flow responses by duplex ultrasonography (Vivid-e, GE Healthcare), and mean blood flow velocity in middle cerebral artery (MCA) and basilar artery (BA) by transcranial Doppler (Vivid-7, GE healthcare) during two levels of hypercapnia (3% and 6% CO 2 ), normocapnia and hypocapnia to estimate CO 2 reactivity. To characterize cerebrovascular reactivity to CO 2 , we used both exponential and linear regression analysis between CBF and estimated partial pressure of arterial CO 2 , calculated by end-tidal partial pressure of CO 2 . CO 2 reactivity in VA was significantly lower than in ICA (coefficient of exponential regression 0.021 ± 0.008 vs. 0.030 ± 0.008; slope of linear regression 2.11 ± 0.84 vs. 3.18 ± 1.09% mmHg −1 : VA vs. ICA, P < 0.01). Lower CO 2 reactivity in the posterior cerebral circulation was persistent in distal intracranial arteries (exponent 0.023 ± 0.006 vs. 0.037 ± 0.009; linear 2.29 ± 0.56 vs. 3.31 ± 0.87% mmHg −1 : BA vs. MCA). In contrast, CO 2 reactivity in ECA was markedly lower than in the intra-cerebral circulation (exponent 0.006 ± 0.007; linear 0.63 ± 0.64% mmHg −1 , P < 0.01). These findings indicate that vertebro-basilar circulation has lower CO 2 reactivity than internal carotid circulation, and that CO 2 reactivity of the external carotid circulation is

Morphometric evaluation of the delayed cerebral arteries response to acetazolamide test in patients with chronic carotid artery stenosis using computed tomography angiography

“…Therefore, our study supports earlier physiological reports suggesting regional differences in CO 2 reactivity [16,17]. Nevertheless, both Sato et al [16] and Skow et al [17] used Doppler ultrasound and measured CBF velocity as a surrogate of CBF in healthy subjects.…”

“…Therefore, our study supports earlier physiological reports suggesting regional differences in CO 2 reactivity [16,17]. Nevertheless, both Sato et al [16] and Skow et al [17] used Doppler ultrasound and measured CBF velocity as a surrogate of CBF in healthy subjects. Doppler ultrasound as a method to estimate CBF is even more questionable in patients with chronic artery stenosis due to turbulent blood flow in the area of stenosis [7,11,14].…”

“…Physiological studies suggest regional differences in CO 2 regulation of blood flow between the internal carotid artery (ICA) and vertebrobasilar circulation. Lower CO 2 reactivity in the vertebrobasilar system may be beneficial for preserving blood flow to the medulla oblongata to maintain vital systemic functions, while higher CO 2 reactivity in the ICA system may imply a larger tolerance for varied blood flow in the cerebral cortex [16,17].…”

Blood Flow Distribution during Heat Stress: Cerebral and Systemic Blood Flow

“…Previously, we demonstrated that CO 2 reactivity at ICA was much higher than that at ECA. 31 Similar to this, during heat stress, ICA blood flow would be more influenced by hyperventilation-induced hypocapnia, whereas ECA blood flow might not be influenced largely by hypocapnia. Thus, the regional difference in CO 2 reactivity might affect distribution of these blood flows during heat stress.…”

Immunologic and cerebrovascular reactivity relationships in patients with initial manifestations of chronic cerebral ischemia

“…Показники цереброваскулярної реактивностi (ЦВР) були отриманi в ходi транскранiального дуплексного сканування судин головного мозку з використанням функцiональних навантажувальних тестiв (ФНТ). Для оцiнки функцiональної спромож-ностi метаболiчного механiзму ауторегуляцiї мозкового кровообiгу застосовувалися проба iз затримкою дихання та проба iз гiпер-вентиляцiєю у каротидному басейнi (у середнiй мозковiй артерiї (СМА)) т а у вертебро-базилярному басейнi (у хребтовiй артерiї у сегментi V 4 (ХА (V 4 ))) [16]. Для оцiнки функцiональної спроможностi мiо-генного механiзму використовувалися орто-статична (вазоконстрикторна реакцiя) i Церебро-васкулярна патологiя займає одну з провiдних позицiй у структурi iнва-лiдизацiї населення як у нашiй країнi, так i у всьому свiтi [11].…”