Department of Biomedical Engineering, Toyo University, Kawagoe-Shi, Saitama, Japan.
Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan.
Exp Physiol. 2019 Sep;104(9):1363-1370. doi: 10.1113/EP087744. Epub 2019 Jul 19.
What is the central question of this study? There is an interaction between the regulatory systems of respiration and cerebral blood flow, because the mediator (CO ) is the same for both physiological systems. We examined whether the traditional method for determining cerebrovascular reactivity to CO is modified by changes in respiration. What is the main finding and its importance? Cerebrovascular reactivity was modified by voluntary changes in respiration during hypercapnia. This finding suggests that an alteration in the respiratory system may result in under- or overestimation of cerebrovascular reactivity determined by traditional methods in healthy adults.
The cerebral vasculature is sensitive to changes in the arterial partial pressure of CO . This physiological mechanism has been well established as a cerebrovascular reactivity to CO (CVR). However, arterial CO may not be an independent variable in the traditional method for assessment of CVR, because the cerebral blood flow response is also affected by the activation of respiratory drive or higher centres in the brain. We hypothesized that CVR is modified by changes in respiration. To test our hypothesis, in the present study, 10 young, healthy subjects performed hyper- or hypoventilation to change end-tidal CO ( ) with different concentrations of CO in the inhaled gas (0, 2.0 and 3.5%). We measured middle cerebral artery mean blood flow velocity by transcranial Doppler ultrasonography to identify the cerebral blood flow response to change in during each set of conditions. In each set of conditions, was significantly altered by changes in ventilation, and middle cerebral artery mean blood flow velocity changed accordingly. However, the relationship between changes in middle cerebral artery mean blood flow velocity and as a response curve of CVR was reset upwards and downwards by hypo- and hyperventilation, respectively, compared with CVR during normal ventilation. The findings of the present study suggest the possibility that an alteration in respiration might lead to under- or overestimation of CVR determined by the traditional methods.
本研究的核心问题是什么？呼吸和脑血流的调节系统之间存在相互作用，因为这两个生理系统的中介物（CO）是相同的。我们研究了在 CO 引起的脑血管反应性的测定中，呼吸的变化是否会改变传统方法。主要发现及其重要性是什么？在高碳酸血症期间，通过自愿改变呼吸，脑血管反应性发生了改变。这一发现表明，在健康成年人中，呼吸系统的改变可能导致传统方法测定的脑血管反应性被低估或高估。
脑血管对动脉 CO 分压的变化很敏感。这一生理机制已被很好地确立为 CO 引起的脑血管反应性（CVR）。然而，在传统的 CVR 评估方法中，动脉 CO 可能不是一个独立的变量，因为脑血流反应也受到呼吸驱动或大脑更高中枢的激活的影响。我们假设 CVR 会受到呼吸变化的影响。为了验证我们的假设，在本研究中，10 名年轻健康的受试者通过过度通气或低通气来改变呼气末 CO（ ），同时吸入气体中的 CO 浓度（0、2.0 和 3.5%）也发生变化。我们通过经颅多普勒超声测量大脑中动脉平均血流速度，以确定在每种条件下 变化引起的脑血流反应。在每组条件下，通过通气变化显著改变了 ，相应地，大脑中动脉平均血流速度也发生了变化。然而，与正常通气期间的 CVR 相比，中动脉平均血流速度变化与作为 CVR 响应曲线的 变化之间的关系分别通过过度通气和低通气向上和向下重置。本研究的结果表明，呼吸的改变可能导致传统方法测定的 CVR 被低估或高估。
