Cerebral Vasoreactivity
Cerebral blood flow is regulated by two critical mechanisms, cerebral autoregulation and neurovascular coupling (NVC). Cerebral autoregulation maintains a constant blood flow within the physiological range of systemic pressures, which is primarily conduct
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Cerebral Vasoreactivity
Abstract Cerebral blood flow is regulated by two critical mechanisms, cerebral autoregulation and neurovascular coupling (NVC). Cerebral autoregulation maintains a constant blood flow within the physiological range of systemic pressures, which is primarily conducted through myogenic response. The cerebral microcirculation is supplied by parenchymal arterioles, which form a functional unit with the adjacent nerve terminals, and astrocytes that encase the arterioles, known as neurovascular unit. Such a morphological arrangement ensures rapid spatial and temporal increases in cerebral blood flow in response to neuronal activation, known as NVC. A broad range of metabolic factors, vascular active agents, and neuronal activities are involved in the processes of autoregulation and NVC through affecting vascular reactivity. Among them, the most prominent ones that include O2, CO2, adenosine, nitric oxide, prostaglandins, epoxyeicosatrienoic acids, and neuronal regulation will be discussed in this chapter. Keywords Cerebral circulation • Autoregulation • Neurovascular coupling • Hypoxia • CO2 • Adenosine • Nitric oxide • Prostaglandin • Epoxyeicosatrienoic acids • Neuronal regulation
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Introduction
The human brain is made up of roughly 100 billion neurons, organized into extensive networks (Herculano-Houzel 2009). It weighs ~2% of the total body mass but consumes ~20% of the O2 taken up by the whole body at rest. Brain functions are heavily dependent on an uninterrupted O2 supply. If cerebral O2 delivery is halted, consciousness could be lost in a few seconds (Lassen 1959; Cipolla 2016). Under most conditions including sleep, the resting waking state, and during intellectual activities, the total cerebral metabolism is relatively unchanged, and cerebral blood flow (CBF) remains fairly constant. In distinct local areas of the brain, however, an increased neuronal activity and consequently increased metabolic demand and increased blood flow may well occur (Lassen 1959; Heistad and Kontos 2011; Joyner and Casey 2015). To adapt such unique characteristics, the cerebral circulation has developed two key mechanisms to fulfill its function: the © Springer Nature Singapore Pte Ltd. 2017 Y. Gao, Biology of Vascular Smooth Muscle: Vasoconstriction and Dilatation, DOI 10.1007/978-981-10-4810-4_16
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Cerebral Vasoreactivity
autoregulatory mechanism and neurovascular coupling (NVC) mechanism. The vascular autoregulation ensures a globally relatively stable perfusion pressure in the face of systemic blood pressure fluctuations (Tzeng and Ainslie 2014; Willie et al. 2014; Cipolla 2016), while NVC ensures sufficient blood flow to the needed brain area with distinct spatial and temporal signatures (Mu~noz et al. 2015; Filosa et al. 2016; Lecrux and Hamel 2016). In this chapter, the general anatomy of cerebral vasculature, the characteristics of cerebral autoregulation and NVC, and the various factors involved in the regulation of cerebral vasoreactivities will be discussed.
16.2
The Anatomy of
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