Middle Cerebral Artery Flow Velocity Correlates With Common Carotid Artery Volume Flow Rate After CO2 Inhalation

Cerebral vasoreactivity can be studied with transcranial Doppler (TCD) by monitoring CO2-induced middle cerebral artery (MCA) velocity changes. Expected MCA mean velocity (Vm) changes due to changes in end-expiratory CO2 (EE-CO2) are established, but reactivity of common carotid artery (CCA) volume flow rate (VFR) has not been extensively reported. The authors assess the relationship between MCA Vm, CCA VFR, and EE-CO2. Ten normal individuals without cerebrovascular disease and with CCA diameters of more than 3.0 mm were studied. CCA VFR was obtained by Color Velocity Imaging Quantification and Ipsilateral MCA Vm by standard TCD methods. Each side was studied before, during, and after inhalation of 5% CO2. EE-CO2, blood pressure, and pulse rate were monitored. Four women and 6 men with mean age of 36 years were included. Significant correlations between MCA Vm and EE-CO2, CCA VFR and EE-CO2, and MCA Vm and CCA VFR were found. MCA Vm and CCA VFR increased 5.2% and 4.3% per mm Hg increase in EE-CO2, respectively. MCA Vm increased 0.3 cm/s for each ml/min increase in CCA VFR. In normal individuals, there is a direct correlation between MCA Vm, CCA VFR, and EE-CO2. Measurement of CCA VFR changes during CO2 inhalation may be an alternative method to estimate cerebral vasoreactivity when the MCA velocity cannot be obtained because of inadequate acoustic temporal windows.     

Point/counterpoint: We should take the direction of blood pressure change into consideration for dynamic cerebral autoregulation quantification

Accumulating evidence suggests asymmetrical responses of cerebral blood flow during large transient changes in mean arterial pressure. Specifically, the augmentation in cerebral blood flow is attenuated when mean arterial pressure acutely increases, compared with declines in cerebral blood flow when mean arterial pressure acutely decreases. However, common analytical tools to quantify dynamic cerebral autoregulation assume autoregulatory responses to be symmetric, which does not seem to be the case. Herein, we provide the rationale supporting the notion we need to consider the directional sensitivity of large and transient mean arterial pressure changes when characterizing dynamic cerebral autoregulation.     

Clinical Investigative Studies: Relationship Between Absolute Mean Cerebral Transit Time and Absolute Mean Flow Velocity on Transcranial Doppler Ultrasound After Ischemic Stroke

BACKGROUND AND PURPOSE: Previous studies of transcranial Doppler (TCD) sonography in acute stroke have used the relative difference between the symptomatic and asymptomatic arteries to assess arterial occlusion. However, a simple measure of absolute mean flow velocity might provide a direct assessment of "perfusion reserve" in acute ischemic stroke. METHODS: In a prospective study, 62 patients with ischemic stroke had TCD and a mean cerebral transit time examination within 48 hours of stroke. Absolute intracranial arterial mean flow velocities were correlated with the corresponding absolute mean transit times. RESULTS: The authors found a significant correlation between middle cerebral artery (MCA) mean flow velocity and transit time in the symptomatic (Spearman rank correlation coefficient [rho] = -0.65, P < .01) but not in the asymptomatic (rho = -0.04, P = ns) MCA territory. Equations relating absolute mean flow velocity to absolute transit time were derived. CONCLUSION: The findings suggest that in the normal hemisphere (with intact autoregulation on the horizontal portion of the autoregulation curve), flow velocity and transit time are not closely related to each other, but in the symptomatic hemisphere (on the downward slope of the autoregulation curve), flow velocity is directly proportional to the transit time and, therefore, to its inverse, perfusion reserve. The use of absolute mean flow velocity values on TCD should be further explored as a simple way of assessing "perfusion" in acute ischemic stroke.     

Changes in cerebral hemodynamics during simple partial motor seizures

Changes in cerebral perfusion were studied during nine short-lasting simple partial motor seizures (SPS) in an 11-year-old girl. Blood flow velocity changes in both middle cerebral arteries (MCAs) were assessed by transcranial Doppler sonography during simultaneous EEG monitoring. Within 7.4 +/- 1.4 s after electroencephalographic seizure onset, flow velocity in the MCA ipsilateral to the electrical discharges started to increase and then gradually rose up to 70% above baseline values. Spread of the epileptic activity to the other hemisphere in the late stage of seizure was associated with a slight increase in blood flow velocity (<30%) in the contralateral MCA. After the end of the seizure, flow velocities returned to baseline within 47 +/- 7 s. Our findings indicate that focal epileptic seizures evoke asymmetric perfusion increases which are closely related to the onset and cessation of the electroencephalographic seizure activity.     

Optimal Values of Flow Velocity on Transcranial Doppler in Grading Middle Cerebral Artery Stenosis in Comparison With Magnetic Resonance Angiography

BACKGROUND AND PURPOSE: To investigate the optimal values of flow velocity on transcranial Doppler (TCD) in grading the severity of middle cerebral artery (MCA) stenosis in comparison with magnetic resonance angiography (MRA). METHODS: Both TCD and MRA examinations were performed on 148 asymptomatic patients. The peak flow velocities of each MCA were recorded. Severity of MCA stenosis on MRA was classified as normal-mild (< 50% lumen diameter reduction), moderate (50%-75%), and severe-void (> 75% and void of flow signal). RESULTS: Among 296 MCAs evaluated, normal-mild stenosis was found in 75 (25%), moderate stenosis in 112 (38%), and severe stenosis in 109 (37%). The mean of systolic velocity (Vs) of MCA differed significantly among these three groups: mean Vs = 121.83 +/- 22.52 cm/s in the normal-mild group; 155.96 +/- 21.62 cm/s for the moderate group; and 199.39 +/- 43.86 cm/s for the severe group (P < .001). The optimal cutoff velocity for detection of MCA (> 50%) stenosis was found at Vs > 140 cm/s on TCD (area under the ROC curve is 0.87, P < 0.001). The best cutoff points for grading severity of on TCD were 140 cm/s and 180 cm/s. CONCLUSION: TCD enables grading of the severity of MCA stenosis according to the flow velocity. This method provides a noninvasive and reliable method for grading MCA stenosis and allows longitudinal monitoring of the relationship between clinical outcome and hemodynamic change.     

Assessment of intracranial hemodynamics in sleep apnea syndrome.

BACKGROUND AND PURPOSE: Sleep apnea syndrome may lead to changes in cerebral hemodynamics due to altered alveolar ventilation. We investigated the dynamics of CO2- and blood pressure-regulated alterations of cerebral blood flow velocities during apneic episodes and evaluated CO2 reactivity during different sleep stages. METHODS: A computer-assisted pulsed Doppler system (2 MHz) was used for continuous overnight recordings of middle cerebral artery flow patterns together with simultaneous polysomnography, continuous blood pressure recordings, and measurements of end-expiratory CO2 in six patients with sleep apnea syndrome. RESULTS: Increases in mean flow velocity of 19-219% and in blood pressure of 12.5-83.1% could be observed during the apneic episodes, with maximum increases during rapid eye movement (REM) sleep. CO2 reactivity was in the normal range (4.4 +/- 1.2%) in the waking state and was markedly increased during sleep stages 1 and 2 (p less than 0.005 compared with awake). The greatest increase was found during REM sleep, with a rise of up to three times the waking value (p less than 0.0001 compared with sleep stage 2). CONCLUSIONS: The changes of mean flow velocity could be interpreted as reactive adaptation processes because of CO2 and blood pressure increases corresponding to apnea. The increased CO2 reactivity during sleep may indicate a "hypersensitivity" of intracranial vascular CO2 or pH receptors and a disturbance of central catecholaminergic and cholinergic systems. The pronounced velocity changes during apneic episodes and the concomitant alterations of vessel wall tension might lead to microangiopathies and macroangiopathies due to chronic strain on the brain vessels.     

Short-term effect of cigarette smoking on CO(2)-induced vasomotor reactivity in man: a study with near-infrared spectroscopy and tanscranial Doppler sonography

Cigarette smoking is a major risk factor for stroke, and quitting reduces the stroke risk within a few years. The aim of our study was to clarify whether CO(2)-induced vasomotor reactivity (VMR) is impaired in smokers after smoking a cigarette as a possible factor of an increased stroke risk. We compared VMR of 23 healthy smokers assessed at baseline, immediately, and 30 min after smoking a cigarette (1.2 mg nicotine) with values from nonsmoking, age-matched controls (n=24), obtained at identical time intervals. Cerebral blood flow velocities (CBFV) of both middle cerebral arteries (transcranial Doppler sonography), changes in concentration of cerebral oxygenated, deoxygenated, and total hemoglobin (HbO(2), Hb, and HbT, near-infrared spectroscopy), mean arterial blood pressure (MAP), and skin blood flow were recorded during normo- and hypercapnia. VMR was calculated as percentage change in CBFV and as micromolar change in concentration of HbO(2), Hb, and HbT per 1% increase in endtidal CO(2). CBFV in smokers was increased at baseline (left, p<0.05; right, p=0.05), immediately (p<0.01), and 30 min after smoking (p<0.05) as compared with nonsmokers. MAP rose immediately after smoking (p<0.01) and declined after 30 min. VMR in smokers at baseline did not differ from controls, decreased immediately after smoking (p<0.05), and normalized after 30 min (p>0.05). Increased baseline CBFV in smokers after smoking might be due to arteriolar dilation, increased MAP, and possibly constriction of basal cerebral arteries. Impaired VMR for about 30 min after smoking reflects endothelial dysfunction. This might contribute to the enhanced stroke risk in smokers.     

Comparison Between Magnetic Resonance Phase Contrast Imaging and Transcranial Doppler Ultrasound With Regard to Blood Flow Velocity in Intracranial Arteries: Work in Progress

OBJECTIVE: The authors evaluate blood flow velocities in the medial cerebral artery (MCA) and the basilar artery using magnetic resonance (MR) phase contrast technique in comparison with transcranial Doppler ultrasound (TCD). Eleven healthy male volunteers were studied. TCD of the MCA (n = 22) and basilar artery (n = 11) was performed. MR phase velocity mapping was done in each vessel at the same location where the TCD signal had been acquired. A 2-dimensional FLASH sequence with retrospective cardiac gating and an average temporal resolution of 45 ms was used. Resistance indices (RIs) and pulsatility indices (PIs) were calculated for both modalities. The TCD insonation angle was measured retrospectively with MR, and TCD velocities were corrected based on these measurements. The comparison of flow velocities obtained with TCD and MR led to a low correlation coefficient with regard to the basilar artery and the MCA: maximum systolic velocity, r = 0.02 and r = 0.50, respectively; enddiastolic velocity, r = 0.47 and r = 0.65, respectively; mean velocity, r = 0.52 and r = 0.66, respectively. The average PIs in the basilar artery and the MCA were 0.80 and 0.81 with MR and 0.65 and 0.85 with TCD, respectively. The average RIs in the basilar artery and the MCA were 0.52 and 0.54 with MR and 0.52 and 0.55 with TCD, respectively. The TCD insonation angle differed significantly from the ideal value in the basilar artery (mean value = 32.6 degrees) and the MCA (mean value = 26.5 degrees). The authors find a low correlation between velocities measured with MRI and TCD but similar results with regard to the PIs and RIs. Several sources of error, such as a nonideal TCD insonation angle, were identified.     

Three-dimensional transcranial Doppler in acute ischemic stroke in the territory of the middle cerebral artery: clinical and CT correlation.

We studied 34 patients with acute ischemic stroke in the territory of the middle cerebral artery (MCA) by three-dimensional transcranial Doppler (TCD-3D). The parameters analyzed were: mean blood flow velocity, systolic and diastolic velocities; indices of pulsatility, hemisphere asymmetry and pulsatility transmission. Of the 34 patients 11 presented marked slowing of flow velocity in the MCA on the infarct side with an asymmetry index (AI) of over 40%, 8 patients with slightly reduced flow velocity in the MCA and an AI of 25-40%, 2 patients in whom there was indirect evidence of collateral circulations in the anterior cerebral artery distribution together with slowing of MCA flow; 5 patients had stenosis of the MCA, 9 patients showed no alterations of the Doppler parameters. The correlation between neurological symptom pattern and AI was significant (r = 0.76). Noninvasive, easy to perform, performable at once and reliable, TCD-3D is a great improvement on traditional transcranial Doppler and is especially useful in assessing the hemodynamics of the cerebral circulation in ischemic stroke.     

Three-dimensional transcranial Doppler in acute ischemic stroke in the territory of the middle cerebral artery: Clinical and CT correlation

We studied 34 patients with acute ischeiic stroke in the territory of the middle cerebral artery (MCA) by three-dimensional transcranial Doppler (TCD-3D). The parameters analyzed were: mean blood flow velocity, systolic and diastolic velocities; indices of pulsatility, hemisphere asymmetry and pulsatility transmission. Of the 34 patients 11 presented marked slowing of flow velocity in the MCA on the infarct side with an asymmetry index (AI) of over 40%, 8 patients with slightly reduced flow velocity in the MCA and an AI of 25–40%, 2 patients in whom there was indirect evidence of collateral circulations in the anterior cerebral artery distribution together with slowing of MCA flow; 5 patients had stenosis of the MCA, 9 patients showed no alterations of the Doppler parameters. The correlation between neurological symptom pattern and AI was significant (r=0.76). Noninvasive, easy to perform, performable at once and reliable, TCD-3D is a great improvement on traditional transcranial Doppler and is especially useful in assessing the hemodynamics of the cerebral circulation in ischemic stroke.     

Blood Flow Velocities in the Basal Cerebral Vein After Head Trauma: A Prospective Study in 82 Patients

BACKGROUND AND PURPOSE: The authors' aim was to evaluate the time course of the basal vein's (BVR) mean flow velocity (VBVR) in patients after traumatic brain injury and its relation to intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the clinical outcome. METHODS: In 82 head-injured patients (13 women and 69 men, median age = 31 years, Glasgow Coma Score = 15 to 3), daily measurement of the basal cerebral vein's and the middle cerebral artery's (MCA) flow velocities and pulsatilities was performed during each patient's entire stay in the intensive care unit. No angle correction was performed. A computerized sonography system (SD 800, Philips, Irvine, CA) with a 2.0-MHz to 2.5-MHz transducer was used for all measurements. The Glasgow Outcome Score (GOS) was evaluated after 6 months. RESULTS: During the study period, VBVR values on the side of trauma were higher in the patients with favorable outcomes (GOS = 4 and 5) compared to patients with unfavorable outcomes (GOS = 2 and 3). This was statistically significant on days 4, 6, 7, and 11 and was not observed in the mean flow velocity of the MCA (VMCA). VBVR values among the good-outcome group tended to exceed the normal mean flow velocity (9.1 cm/s), whereas the unfavorable-outcome group was below this level. A correlation between venous flow velocity or pulsatility and ICP or CPP was not observed. CONCLUSIONS: Repetitive Doppler examination of the basal cerebral veins may add new aspects to the monitoring of head-injured patients.     

Emotion-related cerebral asymmetry: hemodynamics measured by functional ultrasound

This study assessed the use of transcranial Doppler ultrasound in detecting selective changes in cerebral blood flow velocity during emotional processes. The role of the respective hemispheres in emotional processing is controversial. Cerebral control of emotional processing has previously been investigated by analysis of patients with unilateral brain damage, experiments with selective stimulation of only one hemisphere, and more recently by imaging techniques measuring local cerebral blood flow. We investigated mean flow velocity continuously and simultaneously in both the right and left middle cerebral arteries (MCAs) in 16 healthy right-handed young subjects at rest and during the performance of three tasks: task 1: 15 slides with nonemotional content; task 2: 15 slides with negative emotional content; task 3: 15 slides with nonemotional content with different content from that in task 1. The three tasks produced significantly different effects on the right and left hemispheres. During the two nonemotional tasks the increase in mean flow velocity over basal values was similar in the two MCAs (task 1: left MCA = 3.27 ± 1.9%; right MCA = 3.63 ± 2.1%; task 3: left MCA = 2.42 ± 0.7%; right MCA = 2.56 ± 1.3%); the negative emotional task was accompanied by a significantly higher increase in the right (11.31 ± 1.6%) than in the left MCA (4.72 ± 3.7%; analysis of variance two-way interaction: side of recording x task, F = 43.6, P < 0.001). These results show the possibility of obtaining specific functional information from bilateral transcranial Doppler ultrasound and suggest the involvement of the right hemisphere in emotional processing. Received: 4 March 1999 Received in revised form: 29 June 1999 Accepted: 5 August 1999     

Blood Flow Increase by Cervical Spinal Cord Stimulation in Middle Cerebral and Common Carotid Arteries

The effect of spinal cord stimulation (SCS) on cerebral blood flow (CBF) has, in the past, been evaluated by semiquantitative techniques, but has not been used to treat CBF diseases. The aim of this study was to assess the effect of cervical SCS on regional blood flow by both semiquantitative and quantitative methods. Thirty‐five patients with cervical SCS‐implanted devices were enrolled. The following parameters were measured before and after cervical SCS: systolic and diastolic velocity (cm/s) in the middle cerebral artery (MCA) by transcranial Doppler (TCD) and volume blood flow quantification (ml/min) in the common carotid artery (CCA) by color Doppler. During cervical SCS there was a significant and bilateral increase in systolic (21%) and diastolic (26%) velocity in the MCA and in CCA blood flow (50%). We conclude that cervical SCS increases blood flow in the middle cerebral artery and common carotid artery. The consistent increase supports the potential usefulness of cervical SCS as an adjuvant treatment for cerebral blood flow diseases.     

Acute effects of cigarette smoking on cerebral oxygenation and hemodynamics: a combined study with near-infrared spectroscopy and transcranial Doppler sonography

Cigarette smoking has been shown to increase cerebral blood flow velocity (CBFV) and reduce vasomotor reactivity temporarily. The aim of our study was to clarify whether this results from dilation of resistance vessels alone with subsequent increase in regional cerebral blood flow (rCBF), or an additional constriction of basal cerebral arteries. In 24 healthy smokers (mean age+/-S.D., 32.7+/-10.5 years), cerebral oxygenation and hemodynamics were monitored by transcranial Doppler sonography and near-infrared spectroscopy before, during, and after smoking a cigarette (nicotine 0.9 mg). We simultaneously recorded CBFV of both middle cerebral arteries, mean arterial blood pressure, skin blood flow, end-tidal CO(2), changes in concentration of cerebral oxyhemoglobin, deoxyhemoglobin, and total hemoglobin (micromol/l), and a cerebral tissue oxygenation index. Smoking increased CBFV (p<0.01), oxyhemoglobin (p<0.01), and total hemoglobin (p<0.01). After smoking, the increase in CBFV and total hemoglobin persisted (p<0.01), while oxyhemoglobin returned to baseline. Deoxyhemoglobin and cerebral tissue oxygenation index did not change during the whole procedure. During, but not after smoking, CBFV increase was correlated to ipsilateral changes in oxyhemoglobin and total hemoglobin (p<0.05).The increase in oxyhemoglobin only during smoking and the lack of changes in deoxyhemoglobin and cerebral tissue oxygenation index indicate that smoking did not substantially increase rCBF. The smoking-induced elevation in CBFV might therefore be due to an additional constriction of the middle cerebral artery. The combined effects of smoking on basal cerebral arteries and arterioles might contribute to the increased stroke risk in smokers.     

Blood flow velocities in middle cerebral artery branches after subarachnoid hemorrhage.

In a prospective study, 55 patients were examined by transcranial duplex sonography (TCCS) after subarachnoid hemorrhage (SAH) to determine whether additional transcranial duplex examination on the middle cerebral artery M2 segments would aid in the examination of the MCA stem segment. The mean blood flow velocities and pulsatility index were correlated to the occurrence of delayed ischemic neurologic deficits (DIND). Out of 47 patients included, 21 did not experience any delayed deficit (group I), 15 did (group II), and in 11 the extent to which vasospasm contributed to a neurologic deficit was unclear (group III). The highest blood flow velocity and the greatest increase of mean blood flow velocity on 1 day were significantly higher in groups II and III both in M1 and in M2. In 10 patients in group II, where the onset day of DIND was known exactly, Doppler data indicating ischemia before or at the time of DIND were observed in nine. In eight patients, Doppler of the MCA stem alone would have provided enough information to recognize the risk of symptomatic vasospasm; in one patient, only the M2 Doppler gave an indication of ischemic complication. Transcranial duplex sonography may provide additional information to TCD by accurate delineation of M1/M2 vasospasm and therefore may help plan cerebral angiography and neurointerventional treatment.     

Little association between intracranial arterial stenosis and lacunar stroke

Atheromatous middle cerebral artery (MCA) stenosis could cause lacunar stroke by occluding lenticulostriate artery origins, but atheroma is common, and previous studies lacked suitable controls. We aimed to determine if intracranial atheroma was more common in lacunar than in cortical ischaemic stroke. We recruited patients with lacunar stroke and controls with mild cortical stroke, confirmed the stroke subtype with magnetic resonance imaging and used transcranial Doppler ultrasound imaging to record flow velocity and focal stenoses in the basal intracranial arteries 1 month after stroke. We compared ipsi- and contralateral MCA mean flow velocities between stroke subtypes and tested for associations using linear mixed models. Amongst 67 lacunar and 67 mild cortical strokes, mean age 64 and 67 years, respectively, we found no difference in MCA mean flow velocity between cortical and lacunar patients. Increasing age and white matter lesion scores were independently associated with lower MCA flow velocities (0.2 cms(-1) fall in velocity per year increase in age, p = 0.045; 3.75 cms(-1) fall in flow velocity per point increase in white matter lesion score, p = 0.004). We found no intracranial arterial stenoses. MCA atheromatous stenosis is unlikely to be a common cause of lacunar stroke in white populations. Falling velocities with increasing white matter lesion scores may reflect progressive brain tissue loss leaving less tissue to supply.     

经颅多普勒超声结合呼气末二氧化碳分压评价颅内血管狭窄患者脑血管储备功能的初步研究

目的 探讨采用经颅多普勒超声(TCD)结合呼气末二氧化碳分压(ETCO2)的方法 评价颅内血管狭窄患者脑血管储备(CVR)功能,包括脑血管扩张储备、收缩储备和整体储备功能.方法 对病例组(42例)和健康对照组(30名)进行CVR功能的检查,病例组均经TCD和(或)DSA检查发现一侧或双侧大脑中动脉(MCA)狭窄,并合并其他颅内、外大动脉狭窄患者.受试者均采用DWL公司生产的Multi-Dop*4经颅多普勒超声检测仪,运用DWL公司开发的QL软件,通过外接CO2监测设备监测ETCO2.采用吸入自身CO2气体诱导高碳酸血症,过度换气诱导低碳酸血症的方法 来测定CVR功能.结果 (1)一侧MCA狭窄组的患侧[(3.65%±2.62%)/mm Hg(1 mm Hg=0.133 kPa)]、多血管狭窄组病变较重侧[(1.99%±2.78%)/mm Hg]、对照组的扩张储备值[左侧(3.54%±1.66%)/mm Hg;右侧(3.81%±1.63%)/mm Hg]之间的差异具有统计学意义(F=3.755,P＜0.05),多血管狭窄组病变较重侧的扩张储备值明显低于对照组(t=-2.546,P＜0.05);(2)一侧MCA狭窄组的患侧[(3.22%±1.27%)/mm Hg]、多血管狭窄组病变较重侧[(2.30%±1.14%)/mm Hg]、对照组[左侧(3.19%±0.81%)/mm Hg;右侧(3.23%±0.70%)/mm Hg]的整体储备值之间的差异具有统计学意义(F=5.894,P＜0.01),多血管狭窄组病变较重侧整体储备值明显低于对照组(t=-3.357,P＜0.01);多血管狭窄组病变较重侧整体储备值低于一侧中动脉狭窄组的患侧(t=2.471,P＜0.05);(3)血管病变程度与病变较重侧的脑血管扩张储备值、整体储备值之间呈负相关,相关系数分别为r=-0.322,P＜0.05;r=-0.364,P＜0.05.结论 TCD结合ETCO2作为一种简单、方便、经济的手段可有效地用于CVR功能的评价与研究.颅内血管病变患者由于血管狭窄、闭塞、血流受阻使CVR功能降低,狭窄程度越重,脑血管的储备能力越差.

Abstract：

Objective The method transcranial Doppler (TCD)and end-tidal carbon dioxide partial pressure (ETCO2 ) was used to investigate the cerebrovascular reserve capacity in patients with intracranial artery stenosis.Including the cerebral vasodilator reserve,contracted reserve and the overall reserve.Methods The 72 cases were enrolled in this study,include of 42 patients with one or two sides middle cerebral artery (MCA) stenosis,or other intracranial artery stenosis and 30 normal persons. All the patients were routinely examined with TCD,and the TCD QL software was used to evaluate the cerebrovascular reserve. Hypercapnia was induced by inhaling the CO2 who breathed himself,and hypocapnia was induced by voluntary hyperventilation. The changes of velocities were recorded in both side of MCA,and the ETCO2 was recorded by the external measuring device. Results ( 1 ) The cerebral vasodilator reserve of one side of MCA stenosis group ( ( 3.65% ± 2. 62% )/mm Hg),the heavier side of multi-vessel stenosis group ( ( 1.99% ± 2. 78% )/mm Hg ),and normal control group ( left ( 3.54% ± 1.66% )/ mm Hg; right (3. 81% ± 1.63% )/mm Hg) had significant difference( F = 3. 755 ,P ＜ 0. 05 ). The heavier side of multivessel stenosis group' s cerebral vasodilator reserve were significantly lower than normal control group ( t =- 2. 546,P ＜ 0. 05 ). (2) The overall reserve of one side of MCA stenosis group ( ( 3.22% ± 1. 27% )/mm Hg),the heavier side of multi-vessel stenosis group( (2. 30% ± 1.14% )/mm Hg),and normal control group(left (3. 19% ±0. 81% )/mm Hg;right (3. 23% ±0. 70% )/mm Hg)had significant difference(F=5. 894,P ＜0. 01 ). The heavier side of multi-vessel stenosis group' s overall reserve were significantly lower than normal control group( t = - 3. 357,P ＜ 0. 01 ) and they were also significantly lower than one side of MCA stenosis group (t = 2.471,P ＜ 0. 05 ). (3) The extent of vascular disease correlated inveresely to the cerebral vasodilator reserve( r = - 0. 322,P ＜ 0. 05 ) and the overall reserve( r = - 0. 364,P ＜ 0. 05 ) in the heavier side of patients who have vascular disease.Conclusions ( 1 ) TCD with ETCO2 is a simple,economic and effective method for assessing CVR. (2)The capacity of cerebrovascular reserve was reduced in patients with intracranial artery stenosis.     

Transcranial Doppler Ultrasonographic Evaluation of Middle Cerebral Artery Hemodynamics During Mild Hypothermia

BACKGROUND AND PURPOSE: Induced hypothermia holds promise as an effective neuroprotective strategy following cerebral ischemia. The effect of mild hypothermia on cerebral hemodynamics is not well known. The authors investigated the influence of brain temperature on middle cerebral artery (MCA) mean flow velocity (MCA FV) and pulsatility index (MCA PI) in nonintubated, healthy volunteers undergoing mild induced hypothermia. METHODS: Mild hypothermia (target tympanic membrane temperature [T tym] degrees C) was induced in subjects using the Arctic Sun Temperature Management System (Medivance, Inc, Louisville, CO). MCA FV and MCA PI were recorded bilaterally with a 2 MHz pulsed probe every 30 minutes via the transtemporal window. RESULTS: Eighteen subjects (8 males, 10 females) 32 +/- 8 years of age were studied. Multivariate analysis indicated that MCA FV increased with increasing change in temperature (baseline tympanic temperature-tympanic temperature [DeltaT tym]) (P< .001), heart rate (HR) (P< .001), end-tidal CO 2(P= .025), arterial oxygen saturation (O2%) (P= .001), and with decreasing mean arterial blood pressure (P= .004). Multivariate analysis also indicated that ln(MCA PI) (natural logarithm of MCA PI) decreased with decreasing T tym(P< .001) and increasing HR (P< .001). CONCLUSIONS: Mild induced hypothermia is associated with an increase in MCA FV and a decrease in MCA PI. The increase in MCA FV may be partially due to microcirculatory vasodilation.     

Blood flow velocity in the middle cerebral artery during transnasal endoscopic skull base surgery performed in controlled hypotension

Background and purposeTo assess blood flow velocity in the middle cerebral artery (MCA) during transnasal endoscopic procedures performed with decreased hemodynamic parameters.Materials and methodsIn 40 patients who underwent endoscopic skull base surgery in controlled hypotension (studied group) and in 13 patients operated without reduction of hemodynamic parameters (control group), blood flow velocity in MCA was assessed with transcranial color Doppler sonography.ResultsBlood flow velocity in MCA remained within the range of age-specific reference values in all patients before operation. It decreased significantly in both groups after induction of anesthesia and then dropped even further in studied group of patients when hemodynamic parameters were reduced; the systolic velocity fell below the normal reference values in 25% of patients, the mean velocity in 50% and the diastolic velocity in 57% of patients. The diastolic velocity was much more heavily influenced by diminished hemodynamic parameters than systolic velocity in the studied group as opposed to the control group where reduction of blood flow velocity pertained equally systolic and diastolic velocity.ConclusionDuring transnasal endoscopic procedures performed in moderate hypotension, in addition to significant drop of blood flow velocity to values well below the normal reference range, a divergent reduction of systolic and diastolic velocity was detected. Since divergent systolic and diastolic velocity may indicate an early phase of cerebral autoregulation compromise, and the decrease of mean blood flow velocity in MCA corresponds with a decrease of cerebral blood flow, further investigations in this field seem warranted.     

Cerebrovascular response to dynamic changes in pCO2

Fifty-six subjects with carotid artery disease were assessed by measuring the cerebral blood flow velocity (CBFV) change in response to inhalation of 5% CO2 in air whilst continuously monitoring the blood pressure (BP). Coherent averaging of the data characterised differences in CBFV, BP, resistance area product and critical closing pressure during changes in end-tidal CO2 (ETCO2). The results primarily demonstrate that the augmentation of ETCO2 increases the CBFV and BP, causing a pressure autoregulatory response, and allows the processes of pressure autoregulation and cerebral vascular reserve to be differentiated.