Effects of sensory modality on cerebral blood flow velocity during vigilance

Transcranial Doppler sonography was used to measure cerebral blood flow velocity (hemovelocity, CBFV) from the left and right middle cerebral arteries during the performance of 40-min auditory and visual vigilance tasks. Reductions in stimulus duration were the critical signals for detection in both tasks, which were equated for stimulus salience and discrimination difficulty. Signal detection responses (correct detections and false alarms) and CBFV declined significantly over time in a linear manner for both modalities. In addition, the overall level of CBFV and the temporal decline in this measure were greater in the right than the left cerebral hemisphere. The results are consistent with the view that a right hemispheric system is involved in the functional control of vigilance and that this system operates in a similar manner in the auditory and visual channels.     

视空间认知与脑血流速度的相关性研究

目的:探讨视觉空间认知活动对脑血流速度(CBFV)的影响及性别和任务完成质量对相对的CBFV变化的影响。方法:在完成视觉空间认知活动时及其先前的休息期,对45个正常的志愿者(右利手)用经颅超声多普勒(TCD)监测其双侧大脑中动脉血流速度的变化。结果:完成认知任务时与休息时期相比,所有认知任务的完成均诱导出双侧大脑中动脉血流速度的显著变化(P<0.001),这种变化显示出显著的右侧大脑半球偏侧化(P<0.01)。性别对认知活动所诱导的脑血流速度未产生显著的影响(P >0.05),任务表现质量(得分)对CBFV的变化不产生显著的影响。结论:视觉空间认知活动可诱导CBFV的右侧偏侧化。     

How measurement artifacts affect cerebral autoregulation outcomes: A technical note on transfer function analysis

Cerebral autoregulation (CA) is the mechanism that aims to maintain adequate cerebral perfusion during changes in blood pressure (BP). Transfer function analysis (TFA), the most reported method in literature to quantify CA, shows large between-study variability in outcomes. The aim of this study is to investigate the role of measurement artifacts in this variation. Specifically, the role of distortion in the BP and/or CBFV measurement on TFA outcomes was investigated. The influence of three types of artifacts on TFA outcomes was studied: loss of signal, motion artifacts, and baseline drifts. TFA metrics of signals without the simulated artifacts were compared with those of signals with artifacts. TFA outcomes scattered highly when more than 10% of BP signal or over 8% of the CBFV signal was lost, or when measurements contained one or more artifacts resulting from head movement. Furthermore, baseline drift affected interpretation of TFA outcomes when the power in the BP signal was 5 times the power in the LF band. In conclusion, loss of signal in BP and loss in CBFV, affects interpretation of TFA outcomes. Therefore, it is vital to validate signal quality to the defined standards before interpreting TFA outcomes.     

Regional cerebral blood flow increases during preparation for and processing of sensory stimuli

 Preparing for and processing of sensory stimuli are energy-requiring processes. We attempted to assess the relative contributions of these processes to increases in regional cerebral perfusion. Nineteen healthy right-handed subjects were examined while they were engaged in detecting tactile stimuli to the index finger 5 s after a cueing tone. Cerebral blood flow velocity (CBFV) modulations in the middle cerebral arteries (MCAs) were continuously measured by bilateral simultaneous transcranial Doppler ultrasonography. Tactile stimuli well above threshold per se did not produce a significant, relative CBFV increase in the contralateral MCA. However, when subjects were expecting a threshold tactile stimulus, there was a significant regional increase in CBFV in the hemisphere contralateral to the attended index finger for approximately 15 s, starting within the first seconds after the cueing. This increase was present even before the tactile stimulus was applied and also in sessions when the stimulus was omitted. We conclude that preparation of the cortex causes a stronger regional cerebral blood flow increase than the processing of the tactile stimulus itself. Received: 1 August 1996 / Accepted: 7 March 1997     

Deficient adjustment of cerebral blood flow to cognitive activity due to chronically low blood pressure

The present study aimed to investigate aberrances in the adjustment of cerebral blood flow to cognitive activity due to chronically low blood pressure. By means of transcranial Doppler sonography blood flow velocities in both middle cerebral arteries (MCA) were recorded during the execution of a serial subtraction task in 40 subjects with constitutional hypotension and 40 normotensive control persons. Additionally, blood pressure was continuously monitored. As a main result significant correlations between the task-induced changes in blood pressure and those in MCA blood flow velocities were found in hypotensives, but not in control subjects. The dependence of the regulation of cerebral blood flow on blood pressure points towards deficits in cerebral autoregulation in hypotension. Over the total sample the extent of the task-induced MCA flow velocity increase was positively related to cognitive performance. This underlines the importance of the adjustment of cerebral blood flow to current demands for optimal cognitive functioning.     

Interactions between systemic hemodynamics and cerebral blood flow during attentional processing

The study explored interactions between systemic hemodynamics and cerebral blood flow during attentional processing. Using transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries (MCA) of both hemispheres were recorded while 50 subjects performed a cued reaction time task. Finger arterial pressure and heart rate were also continuously monitored. Doppler sonography revealed a right dominant blood flow response. The extent of the increase measured in second two of the interstimulus interval showed a clear positive association with reaction speed. Task‐related changes in blood pressure and heart rate proved predictive of changes in MCA flow velocities in limited time windows of the response. Besides an association between cerebral blood flow and attentional performance, the results suggest a marked impact of systemic hemodynamics on the blood flow response. All observed interactions are highly dynamic in time.     

大脑中动脉供血区脑缺血后同侧丘脑继发性损害的MR实验研究

本文应用磁共振(magnetic resonance,MR)成像在体观察大脑中动脉(middle cerebral artery,MCA)供血区脑缺血后同侧丘脑的信号变化。结果显示:(1)通过MRA(magnetic resonance angiography)可以观测到单侧MCA的闭塞与血流再通,而供应丘脑的大脑后动脉信号无变化;(2)脑缺血后1d MR T2WI(T2weighted imaging)显示单侧MCA供血区原发病灶呈高信号,3d、7d时此原发病灶信号增高程度有所降低,至14d信号强度再次明显增高;(3)脑缺血后1d和3d时双侧丘脑T2信号无差别,7d和14d时脑缺血同侧丘脑T2信号减低,T2值降低;(4)MCA供血区脑缺血后原发病灶和同侧丘脑T2值的变化不同步。上述结果证实MR能够在活体显示MCA供血区脑缺血后同侧丘脑的继发性损害。     

Functional transcranial Doppler sonography as a tool in psychophysiological research

Functional transcranial Doppler sonography (fTCD) allows the noninvasive and uncomplicated registration of intracranial blood flow parameters under defined conditions of stimulation. Although local distribution patterns of regional blood perfusion can be measured with high spatial resolution through neuroimaging methods (e.g., PET or SPECT), these methods are limited by their low temporal resolution. The high temporal resolution provided by fTCD, however, allows the recording of the dynamic component of cerebral blood perfusion by continuously measuring the cerebral blood flow velocity in the basal cerebral arteries. Hence, this method is especially appropriate for the investigation of fast neuronal activation processes, which are generally accompanied by changes in local blood perfusion. In this review, we present methodical issues regarding fTCD, as well its application in the field of psychology, especially psychophysiology. The relevant studies available to date investigate processes of attention and perception, higher cognitive functions, and emotional and psychomotor processes. Considering the current state of methodology and research, fTCD can be seen to be an important complement to the other psychophysiological methods for studying brain function.     

Diameter and length changes in cerebral collaterals after middle cerebral artery occlusion in the young rat

Rapid occlusion of the middle cerebral artery (MCA) in the 36-day-old normal Wistar rat results in change of the dorsal collaterals joining branches of the anterior and middle cerebral arteries. As compared to similarly positioned vessels on the opposite hemisphere and arterioles in unoperated rats of 56 days, of age, there were significantly (P < 0.001) more large (60–120 μm)diameter collaterals on the occluded side 20 days after MCA occlusion. There were fewer small (0-59μm) diameter collaterals on the occluded side as compared to unoperated rats. The data suggest small diameter arterioles existing at occlusion became large diameter collaterals. The mean number of collaterals per hemisphere was not significantly different (P > 0.05) between occluded and unoperated rats. There was no evidence that new vessels were added during the 20-day ligation period. The mean collateral tortuosity value was significantly (P < 0.01) greater for large diameter vessels on the right occluded side as compared to vessels on the left hemisphere or vessels in unoperated age-matched control rats. The greater tortuosity values of vessels on the occluded side were evidence that collateral vessel length was increased by 24–29% after MCA occlusion. Speculation was made about possible mechanisms responsible for these vascular changes.     

Perception of posture and cerebral blood flow.

The perception of posture in man is made possible by the information of the vestibular organs, the visual system, the proprioception and the blood volume distribution. The present study examined the cerebral blood flow velocity (CBFV) and the fluid volume of the thoracic cavity under different pressure conditions and their effects on the perception of posture. Changes in blood flow velocity were measured by transcranial Doppler sonography (TCD), and changes in the blood volume distribution of the upper torso were registered by impedance plethysmography. The results indicated that the cerebral blood flow volume and the thoracic blood volume changed in the same manner. Lower Body Positive Pressure (+30 mmHg) led to an increase in central volume and CBFV. During the Lower Body Negative Pressure Treatment (-30 mmHg), the central blood volume and the cerebral blood flow velocity decreased while venous pooling occurred. Additionally, the changes in both parameters were associated with an altered posture perception. The correlations between the SHP and the two physiological parameters cerebral blood flow velocity and fluid shift in the upper thorax indicate that the fluid shift in the thoracic cavity was more closely related to the SHP than to the changes in cerebral blood volume.     

Rapid measurement of somatosensory evoked potential response to cerebral artery occlusion

The aim of the paper is to determine the speed of the neurological response to cerebral artery occlusion by monitoring transient changes in somatosensory evoked potentials (SEPs). SEPs, continuously monitored during temporary clipping of the middle cerebral artery (MCA) in anaesthetised cats, are analysed. The SEP signals are modelled by a quasi-periodic Fourier series, the coefficients of which are estimated with the aid of two adaptive least squares estimation algorithms. The energy levels at various harmonics throughout the protocol are obtained directly from the filter weights. Noise covariance is estimated from pre-stimulus recording, and the adaptation rate of the algorithm is adjusted sweep-by-sweep to accomodate transient changes in the pre-stimulus noise level. After the occlusion, a significant decrease (p<0·05) in SEP amplitude is observed. The change in latency is not statistically significant (p≅0·5). The spectral trends show a sudden decline in energy at all harmonics immediately following occlusion, although when the amplifier bandwidth is changed to 5–1500 Hz (from an initial setting of 30–1500 Hz), the fundamental frequency component of the SEP signal shows the greatest responsiveness to injury. The average time constant of the decline in amplitude resulting from MCA occlusion is only 10·6±4·0 s. It is concluded that rapid detection of cerebral artery occlusion and ischaemia may be feasible by continuously monitoring SEP signals and analysing transient changes in time and frequency domains.     

Estimating normal and pathological dynamic responses in cerebral blood flow velocity to step changes in end-tidal pCO2

The regulation of cerebral blood flow (CBF) following changes in arterial blood pressure (ABP) and end-tidal pCO₂ (EtCO₂) are of clinical interest in assessing cerebrovascular reserve capacity. Linear finite-impulse-response modelling is applied to ABP, EtCO₂ and CBF velocity (CBFV, from transcranial Doppler measurements), which allows the CBFV response to ideal step changes in EtCO₂ to be estimated from clinical data showing more sluggish, and additional random variations. The confounding effects of ABP changes provoked by hypercapnia on the CBFV are also corrected for. Data from 56 patients suffering from stenosis of the carotid arteries (with normal or diminished cerebrovascular reactivity to EtCO₂ changes—CVR_{CO 2} were analysed. The results show the expected significant differences (p<0.05) between EtCO₂ steps up and down, the significant contribution from ABP variation, and also differences in the dynamic responses of patients with reduced CVR_{CO 2} (p<0.01 after 10 s). For the latter the CBFV response appears exhausted after about 15s, whereas for normals CBFV continues to increase. While dispersion of individual step responses remains large, the method gives encouraging results for the non-invasive study of compromised haemodynamics in different patient groups.     

U0126对蛛网膜下腔出血小鼠细胞外信号调节激酶途径的调节作用

目的:研究细胞外信号调节激酶(ERK)、天冬氨酸特异性半胱氨酸蛋白酶-8(caspase-8)在蛛网膜下腔出血(SAH)后早期脑损伤中的作用,并探讨ERK特异性抑制剂U0126通过此途径发挥作用的保护机制。方法:采用稳定的非开颅血管内穿线法制备小鼠SAH模型,并于术前30 min经尾静脉给予U0126(0.1 mg/kg),分别在术后12、24、48 h 3个时相点取右侧大脑动脉标本,HE染色观察大脑动脉的形态改变,并检测大脑中动脉(MCA)的直径变化;应用免疫印迹法检测各组p-ERK1/2、caspase-8蛋白表达,TUNEL法检测MCA内皮细胞凋亡。结果:模型组小鼠MCA出现严重血管痉挛,直径减小,p-ERK1/2、caspase-8蛋白均有不同程度增强,凋亡细胞增多。与模型组比较,治疗组小鼠各时相点上述3项指标的表达均呈不同程度下调,MCA管径增加,脑血管痉挛缓解。SAH 12～48 h时p-ERK1/2与caspase-8的表达呈正相关。结论:SAH后ERK表达增强可通过激活caspase-8信号途径诱导大脑动脉内皮细胞凋亡;U0126可减少大脑动脉内皮细胞凋亡,其机制之一可能是通过阻抑ERK通路活化实现的。     

Rapid pressure-to-flow dynamics of cerebral autoregulation induced by instantaneous changes of arterial CO2

Continuous assessment of CA is desirable in a number of clinical conditions, where cerebral hemodynamics may change within relatively short periods. In this work, we propose a novel method that can improve temporal resolution when assessing the pressure-to-flow dynamics in the presence of rapid changes in arterial CO₂. A time-varying multivariate model is proposed to adaptively suppress the instantaneous effect of CO₂ on CBFV by the recursive least square (RLS) method. Autoregulation is then quantified from the phase difference (PD) between arterial blood pressure (ABP) and CBFV by calculating the instantaneous PD between the signals using the Hilbert transform (HT). A Gaussian filter is used prior to HT in order to optimize the temporal and frequency resolution and show the rapid dynamics of cerebral autoregulation. In 13 healthy adult volunteers, rapid changes of arterial CO₂ were induced by rebreathing expired air, while simultaneously and continuously recording ABP, CBFV and end-tidal CO₂ (ETCO₂). Both simulation and physiological studies show that the proposed method can reduce the transient distortion of the instantaneous phase dynamics caused by the effect of CO₂ and is faster than our previous method in tracking time-varying autoregulation. The normalized mean square error (NMSE) of the predicted CBFV can be reduced significantly by 38.7% and 37.7% (p < 0.001) without and with the Gaussian filter applied, respectively, when compared with the previous univariate model. These findings suggest that the proposed method is suitable to track rapid dynamics of cerebral autoregulation despite the influence of confounding covariates.     

基于Hermite滤波器的稳态视觉诱发电位背景标记Stroop效应包络分析

Stroop效应能够反映大脑对冲突干扰的注意。为了深入分析Stroop效应中大脑的认知活动过程,设计了稳态视觉诱发电位（SSVEP）背景标记的Stroop实验范式,记录同时含有事件相关电位（ERP）信号和SSVEP信号的脑电信号,并提出基于Hermite滤波器的脑电信号包络分析方法。采集了10例受试的脑电数据,分离得到ERP信号和SSVEP信号。在刺激后400～600 ms时间窗内,不一致条件的ERP信号比一致条件的ERP信号更负。条件之间的差异具有统计显著性,差异主要分布在前额区域,可视为Stroop效应在脑电上的体现。通过包络分析发现,SSVEP信号的包络在刺激后存在明显的下降过程。ERP信号Alpha频带总包络刺激之后的变化与其刺激之前的水平有关,若刺激之前Alpha频带总包络的水平较高,刺激之后包络先小幅上升后下降到比刺激前更低的水平;若刺激之前水平较低,刺激之后的包络上升后下降到与刺激前相当的水平。通过SSVEP背景标记Stroop实验范式和包络分析,可进一步研究Stroop效应的认知活动过程,也可为其他认知实验提供参照。     

Examining the relationship between degree of handedness and degree of cerebral lateralization for processing facial emotion

This paper examines the relationship between degree of handedness and degree of cerebral lateralization on a task of processing positive facial emotion in right-handed individuals. Three hundred and thirteen right-handed participants (157 women) were given two behavioral tests of lateralization: a handedness questionnaire and a chimeric faces test. Two further handedness measures were taken: familial left-handedness and writing posture. Regression analysis showed that both degree of handedness and sex were predictive of degree of lateralization. Individuals who were strongly right-handed were also more strongly lateralized to the right hemisphere for the task. Men were more strongly lateralized than women. Data were reanalyzed for men and women separately. The relationship between handedness and lateralization remained for men only. Neither familial left-handedness nor writing posture were associated with cerebral lateralization for men or women. The results suggest a positive relationship between degree of handedness and degree of cerebral lateralization, and further that there is a sex difference in this relationship.     

Influence of lateralized neuropsychological activities with and without sensorimotor components on EEG spectral power (alpha-rhythm).

Spectral analysis of the EEG (alpha-rhythm) was studied in 8 young right-handed men who underwent 6 experimental tasks which were compared with rest, and included two pure motor activities using only the right and then the left hand, two pure neuropsychological tasks, and two "mixed" tasks with both neurophysiological and motor activities. The electrophysiological parameters studied were the log of spectral power and an asymmetry index (RP-LP)/(RP + LP). In order to demonstrate lateralization of the EEG, one must associate lateralized motor and neuropsychological tasks (which are supposed to preferentially involve one of the cerebral hemispheres). These results may reconcile apparently divergent views published in the literature with respect to lateralized EEG modifications associated with cognitive activities.     

Frequency-domain analysis of cerebral autoregulation from spontaneous fluctuations in arterial blood pressure

The dynamic relationship between spontaneous fluctuations of arterial blood pressure (ABP) and corresponding changes in crebral blood flow velocity (CBFV) is studied in a population of 83 neonates. Static and dynamic methods are used to identify two subgroups showing either normal (group A, n=23) or impaired (group B, n=21) cerebral autoregulation. An FFT algorithm is used to estimate the coherence and transfer function between CBFV and ABP. The significance of the linear dependence between these two variables in demonstrated by mean values of squared coherence >0.50 for both groups in the frequency range 0.02–0.50 Hz. However, group A has significanlty smaller coherences than group B in the frequency ranges 0.02–0.10 Hz and 0.33–0.49 Hz. The phase response of group A is also significantly more positive than that of group B, with slopes of 9.3±1.05 and 1.80±1.2 rad Hz⁻¹, respectively. The amplitude frequency response is also significantly smaller for group A in relation to group B for the frequency range 0.25–0.43 Hz. These results suggest that transfer function analysis may be able to identify different components of cerebral autoregulation and also provide a deeper understanding of recent findings by other investigators.     

Dynamic pressure–flow relationship of the cerebral circulation during acute increase in arterial pressure

The physiological mechanism(s) for the regulation of the dynamic pressure–flow relationship of the cerebral circulation are not well understood. We studied the effects of acute cerebral vasoconstriction on the transfer function between spontaneous changes in blood pressure (BP) and cerebral blood flow velocity (CBFV) in 13 healthy subjects (30 ± 7 years). CBFV was measured in the middle cerebral artery using transcranial Doppler. BP was increased stepwise with phenylephrine infusion at 0.5, 1.0 and 2.0 μg kg^–1 min^–1. Phenylephrine increased BP by 11, 23 and 37% from baseline, while CBFV increased (11%) only with the highest increase in BP. Cerebrovascular resistance index (BP/CBFV) increased progressively by 6, 17 and 23%, demonstrating effective steady-state autoregulation. Transfer function gain at the low frequencies (LF, 0.07–0.20 Hz) was reduced by 15, 14 and 14%, while the phase was reduced by 10, 17 and 31%. A similar trend of changes was observed at the high frequencies (HF, 0.20–0.35 Hz), but gain and phase remained unchanged at the very low frequencies (VLF, 0.02–0.07 Hz). Windkessel model simulation suggests that increases in steady-state cerebrovascular resistance and/or decreases in vascular compliance during cerebral vasoconstriction contribute to the changes in gain and phase. These findings suggest that changes in steady-state cerebrovascular resistance and/or vascular compliance modulate the dynamic pressure–flow relationship at the low and high frequencies, while dynamic autoregulation is likely to be dominant at the very low frequencies. Thus, oscillations in CBFV are modulated not only by dynamic autoregulation, but also by changes in steady-state cerebrovascular resistance and/or vascular compliance.     

Reproducibility and variability of dynamic cerebral autoregulation during passive cyclic leg raising

Dynamic cerebral autoregulation (dCA) estimates require mean arterial blood pressure (MABP) fluctuations of sufficient amplitude. Current methods to induce fluctuations are not easily implemented or require patient cooperation. In search of an alternative method, we evaluated if MABP fluctuations could be increased by passive cyclic leg raising (LR) and tested if reproducibility and variability of dCA parameters could be improved.Middle cerebral artery cerebral blood flow velocity (CBFV), MABP and end tidal CO₂ (PetCO₂) were obtained at rest and during LR at 0.1 Hz in 16 healthy subjects. The MABP–CBFV phase difference and gain were determined at 0.1 Hz and in the low frequency (LF) range (0.06–0.14 Hz). In addition the autoregulation index (ARI) was calculated.The LR maneuver increased the power of MABP fluctuations at 0.1 Hz and across the LF range. Despite a clear correlation between both phase and gain reproducibility and MABP variability in the rest condition, only the reproducibility of gain increased significantly with the maneuver. During the maneuver patients were breathing faster and more irregularly, accompanied by increased PetCO₂ fluctuations and increased coherence between PetCO₂ and CBFV. Multiple regression analysis showed that these concomitant changes were negatively correlated with the MABP–CBFV phase difference at 0.1 Hz Variability was not reduced by LR for any of the dCA parameters.The clinical utility of cyclic passive leg raising is limited because of the concomitant changes in PetCO₂. This limits reproducibility of the most important dCA parameters. Future research on reproducibility and variability of dCA parameters should incorporate PetCO₂ variability or find methods to keep PetCO₂ levels constant.