Cerebral haemodynamic response to somatosensory stimulation in near-term fetal sheep
Cerebral haemodynamic response to somatosensory stimulation in near-term fetal sheep
复制标题
近足胎羊对体感刺激的脑血流动力学反应
DOI：
10.1113/jp273163
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Wong F.Y.
中科院分区：
文献类型：
--
作者：
1.Nakamura S;Walker D.W.;Wong F.Y.
神经刺激的脑血流动力学反应在动物和临床研究中得到了广泛的研究，无论是在成人还是在儿童群体中，但对胎儿大脑中的脑血流动力学功能反应知之甚少。本研究描述了用近红外光谱测量胎羊对体感刺激的脑血流动力学反应。随着体感刺激持续时间的增加，胎羊的脑血流动力学反应从阳性(氧合血红蛋白)增加的反应模式转变为负或双相反应模式，可能是由于脑血管收缩和长时间刺激所致。与成人研究相比，我们发现，在高碳酸血症期间，胎儿脑血流量和氧合Hb的变化正向增加，以响应体感刺激。我们认为这与高二氧化碳时胎儿脑内血管阻力降低和脑血管的募集有关。摘要由于声刺激后功能磁共振成像记录到的血氧水平依赖(BOLD)信号阳性，因此由神经元活动局部增加引起的胎儿脑功能充血被认为是发生的。为了研究体感输入对局部脑血流灌注的影响，我们在麻醉的、部分外化的胎羊上使用了近红外光谱分析，其中正中神经受到脉冲序列(2毫秒，3.3赫兹)刺激，持续时间分别为1.8，4.8和7.8赫兹，对S来说，对20个刺激序列的大脑近红外光谱反应的信号平均显示，较短的刺激时间(1.8 S)与阳性的功能反应一致地增加了对侧皮质中的氧合血红蛋白，而较长的刺激时间(4.8，7.8 S)产生了更多的可变的氧合血红蛋白反应，包括阳性、阴性和双相变化模式。激光多普勒血流仪监测的平均动脉压和脑血流灌注量总是很小，但无论NIRS在对侧皮质检测到的反应类型如何，刺激正中神经后平均动脉压和脑血流灌注都有相应的增加。与正常碳酸血症时记录的反应相比，高碳酸血症显著增加了基线总血红蛋白和脱氧血红蛋白，8只胎羊中有7只对S 7.8小时刺激训练的反应产生了对侧总血红蛋白和氧合血红蛋白的正向增加。这些结果表明，活动驱动的脑血流和氧气输送的变化存在于胎儿大脑中，甚至在高碳酸血症诱导的脑血管扩张期间也持续存在。
Key pointsCerebral haemodynamic response to neural stimulation has been extensively investigated in animal and clinical studies, in both adult and paediatric populations, but little is known about cerebral haemodynamic functional response in the fetal brain.The present study describes the cerebral haemodynamic response measured by near‐infrared spectroscopy to somatosensory stimulation in fetal sheep.The cerebral haemodynamic response in the fetal sheep brain changes from a positive (increase in oxyhaemoglobin (oxyHb)) response pattern to a negative or biphasic response pattern when the duration of somatosensory stimulation is increased, probably due to cerebral vasoconstriction with prolonged stimulations.In contrast to adult studies, we have found that changes in fetal cerebral blood flow and oxyHb are positively increased in response to somatosensory stimulation during hypercapnia. We propose this is related to reduced vascular resistance and recruitment of cerebral vasculature in the fetal brain during hypercapnia.AbstractFunctional hyperaemia induced by a localised increase in neuronal activity has been suggested to occur in the fetal brain owing to a positive blood oxygen level‐dependent (BOLD) signal recorded by functional magnetic resonance imaging following acoustic stimulation. To study the effect of somatosensory input on local cerebral perfusion we used near‐infrared spectroscopy (NIRS) in anaesthetised, partially exteriorised fetal sheep where the median nerve was stimulated with trains of pulses (2 ms, 3.3 Hz) for durations of 1.8, 4.8 and 7.8 s. Signal averaging of cerebral NIRS responses to 20 stimulus trains repeated every 60 s revealed that a short duration of stimulation (1.8 s) increased oxyhaemoglobin in the contralateral cortex consistent with a positive functional response, whereas longer durations of stimulation (4.8, 7.8 s) produced more variable oxyhaemoglobin responses including positive, negative and biphasic patterns of change. Mean arterial blood pressure and cerebral perfusion as monitored by laser Doppler flowmetry always showed small, but coincident increases following median nerve stimulation regardless of the type of response detected by the NIRS in the contralateral cortex. Hypercapnia significantly increased the baseline total haemoglobin and deoxyhaemoglobin, and in 7 of 8 fetal sheep positively increased the changes in contralateral total haemoglobin and oxyhaemoglobin in response to the 7.8 s stimulus train, compared to the response recorded during normocapnia. These results show that activity‐driven changes in cerebral perfusion and oxygen delivery are present in the fetal brain, and persist even during periods of hypercapnia‐induced cerebral vasodilatation.