The primary objective of this study was to examine in man, how induced changes in global cerebral blood flow (gCBF) affected a regional cerebral blood flow (rCBF) increase resulting from a neural activation task (opening of eyes). A secondary objective was to quantify how such induced changes in gCBF were distributed between representative regions of either predominantly grey matter or white matter. 2. Positron emission tomography with intravenous infusion of H2(15)O, was used to measure gCBF in six normal males. Concomitant measures of rCBF were obtained in three different regions of interest (ROI): a representative area of predominantly grey matter, a representative area of predominantly white matter and an area of visual cortex. 3. Cerebral blood flow was altered by establishing steady-state changes in PCO2 at a near constant ventilation of approximately 30 l min-1. The mean PET,CO2 (+/- S.D.) levels (mmHg) that resulted were: low, 21.8 +/- 1.8; normal, 39.8 +/- 1.0, and high, 54.8 +/- 1.2. The normal and high levels were obtained by adding appropriate amounts of CO2 to the inspirate. The corresponding mean gCBF levels across all six subjects with eyes closed were: low, 24.2 +/- 4.6; normal, 37.2 +/- 3.9 and high, 66.8 +/- 7.6 ml min-1 dl-1. 4. Blood flow in grey matter (insular cortex) and white matter (centrum semiovale) at normal levels of PCO2 averaged 56.8 +/- 10.1 and 20.3 +/- 3.4 ml min dl-1 respectively. As PCO2 rose, the increase in rCBF to grey matter was approximately three times greater than that to white matter. 5. An activation state of eyes open in a brightly lit room was compared to a baseline state of eyes closed in a darkened room at the three levels of PCO2 (and hence at three levels of gCBF). Over the whole gCBF range a significant (P = 0.028) effect of increasing rCBF in the visual cortex ROI was found in response to opening the eyes; the effect of this activation on rCBF was not significantly dependent (P = 0.34) on the PCO2 (and hence gCBF) level. The effect of the activation on the rCBF was apparently 'additive' to the rise of rCBF associated with PCO2-related gCBF increase. 6. The results confirm the need to normalize for changes in gCBF during studies of rCBF in response to an activation protocol. They also provide support for the use of an 'additive' model to achieve such normalization provided that other cortical areas behave in a similar manner to that of the visual cortex.
摘要
本研究的主要目的是在人体中研究，全身脑血流量（gCBF）的诱导变化如何影响由神经激活任务（睁眼）引起的局部脑血流量（rCBF）增加。次要目的是量化这种gCBF的诱导变化如何在主要为灰质或白质的代表性区域之间分布。2. 对六名正常男性静脉注射H2(15)O后，使用正电子发射断层扫描来测量gCBF。在三个不同的感兴趣区域（ROI）获得rCBF的同步测量值：一个主要为灰质的代表性区域、一个主要为白质的代表性区域和一个视觉皮质区域。3. 通过在约30 l min-1的近乎恒定通气下建立PCO2的稳态变化来改变脑血流量。得到的平均PET、CO2（±标准差）水平（mmHg）为：低，21.8±1.8；正常，39.8±1.0，高，54.8±1.2。通过向吸入气体中添加适量的CO2获得正常和高水平。所有六名受试者闭眼时相应的平均gCBF水平为：低，24.2±4.6；正常，37.2±3.9，高，66.8±7.6 ml min-1 dl-1。4. 在正常PCO2水平下，灰质（岛叶皮质）和白质（半卵圆中心）的血流量平均分别为56.8±10.1和20.3±3.4 ml min dl-1。随着PCO2升高，rCBF向灰质的增加约为向白质增加的三倍。5. 在三种PCO2水平（因此在三种gCBF水平）下，将明亮房间中睁眼的激活状态与黑暗房间中闭眼的基线状态进行比较。在整个gCBF范围内，发现视觉皮质ROI中rCBF增加的显著（P = 0.028）效应是由于睁眼；这种激活对rCBF的影响不显著依赖（P = 0.34）于PCO2（因此gCBF）水平。激活对rCBF的影响显然与PCO2相关的gCBF增加引起的rCBF升高“相加”。6. 结果证实了在研究rCBF对激活方案的反应时需要对gCBF的变化进行标准化。它们还为使用“相加”模型来实现这种标准化提供了支持，前提是其他皮质区域的行为与视觉皮质相似。
