Cerebral blood flow changes in a patient recovered from hypocarbia

The changes of cerebral blood flow velocity (CBFV) and pulsatility index (PI) in anterior cerebral artery were examined by cranial color Doppler ultrasonography while a patient recovered from hypocarbia. As arterial PCO2 was elevated, PI was decreased and color imaging of CBF from basilar artery to anterior cerebral artery were improved in sagittal view. Hypocarbia is considered to induce the constriction of the cerebral vessels and the decrease of CBF in premature infants.     

Usefulness of Doppler method for evaluating intracranial hemodynamics in infantile hydrocephalus

The changes of pulsatility index (PI) were followed for anterior cerebral artery (ACA) and basilar artery (BA) in 8 hydrocephalic infants. PI increased with the progression of hydrocephalus in both ACA and BA, from an average of 0.69 to 0.80 and from 0.73 to 0.81, respectively. The index made a sharp dip in 6 hours 0.65 for ACA and 0.70 for BA after placing a V-P shunt. It eventually stabilized within mean +/- SE. (ACA:0.69 +/- 0.0042, BA:0.71 +/- 0.0036). The index enabled us to observe objectively cerebral vascular resistance of the illness in numerical values. It may become a useful tool for setting criteria for placing a shunt (about 0.80) as well as for judging the shunt effectiveness. Throughout the entire observation, changes in PI of both ACA and BA were well correlated. Anterior fontanel pressure was also correlated with PI in the period, except PI of BA before the shunt operation. However, the pre-shunt correlation of PI to lateral ventricle enlargement was lost after the shunt operation. And the ventricle size reduced only slightly when PI rapidly decreased in 6 hours after the V-P shunt. These facts indicated that the changes in PI was affected directly by the intracranial pressure rather than the enlarged ventricle. The findings of this study indicated the necessity of evaluating of the intracranial hemodynamics with other diagnostic approaches in managing infantile hydrocephalus.     

Cerebral blood flow velocity in term infants treated with phototherapy.

The relationship between phototherapy and changes in the cerebral circulation was studied in 50 jaundiced newborn infants. The aim of the study was to determine whether important alterations in cerebral hemodynamic occur under blue light therapy. Blood flow velocity, i.e., the pulsatility index (PI) and the area under the velocity curve (AUVC), was measured in the anterior cerebral arteries (ACA) using a Duplex scan technique. No prominent changes compromise flow in the ACA. PI and AUVC values were similar during and after phototherapy (p greater than 0.5) suggesting effective cerebral autoregulation in term infants undergoing light treatment for hyperbilirubinemia.     

Transcranial Doppler and real-time cranial sonography in neonatal hydrocephalus

Nine hydrocephalic infants who were less than 1 year old and 7 age-matched control subjects were examined by real-time and transcranial Doppler sonography to evaluate cerebral blood flow and to correlate it to ventricular size. These 16 infants were placed in one of three groups: infants in group 1 (n = 7) had a normal ventricular size, infants in group 2 (n = 3) had a progressively increasing ventricular size, and infants in group 3 (n = 6) had ventriculomegaly with either stable or decreasing ventricular size or a functioning ventriculoperitoneal shunt. All scans performed on group-2 infants showed markedly increased ventricular size and increased pulsatility index, while those on group-1 infants showed a normal ventricular size and pulsatility index. However, the scans of group-3 infants revealed increased ventricular size and pulsatility index for all groups. Regression analysis of the data showed rather weak correlations between ventricular size and pulsatility index for all groups. The regression data suggest that ventricular size is not the main determinant of cerebral blood flow in the neonate with hydrocephalus and that intracranial pressure may be a more critical factor. These data suggest that pulsatility index, as measured by transcranial Doppler, can be clinically more important than just the anatomical data alone in the evaluation of hydrocephaly. This points to a possible use of transcranial Doppler sonography in the evaluation of hydrocephalic patients for placement of ventriculoperitoneal shunts.     

Cerebral hemodynamics and oxygenation after serial CSF drainage in infants with PHVD

The aim of our study was to assess consecutive changes in cerebral oxygenation and hemodynamics after serial cerebrospinal fluid (CSF) drainage from a subcutaneous ventricular catheter reservoir (SVCR) in infants with PHVD. Infants with PHVD were studied during CSF drainage from a SVCR on the day of SVCR placement, half a week and one week after SVCR placement. Changes in cHbD and CBV were assessed using near infrared spectrophotometry. Time averaged peak flow velocity (TAPFV), end diastolic flow velocity (EDFV), peak systolic flow velocity (PSFV) and pulsatility index (PI) were measured before (baseline) and after CSF drainage using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models. Seven patients (GA 26.7–40.4 weeks, BW 800–4575 g) were studied. CSF drainage resulted in a statistically significant increase in CBV during each measurement. The change in CBV was maximal on the day of SVCR placement. A significant increase in cHbD and EDFV, and decrease in PI was observed after CSF drainage only on the day of SVCR placement. Baseline values of all Doppler variables improved consecutively after serial CSF removal in the first week after SVCR placement. Frequent CSF drainage results in consecutive improvement of cerebral perfusion and oxygenation in infants with PHVD.     

Evaluation of cerebral blood flow changes by transfontanelle Doppler ultrasound in infantile hydrocephalus

Doppler ultrasound investigation of cerebral blood flow velocity was performed in hydrocephalic infants through the anterior fontanelle. Systolic (S) and end-diastolic (D) frequency values recorded on the anterior cerebral artery were used to define the pulsatility index (PI) calculated from the equation PI=S-D/S. Comparison between systolic, end-diastolic and pulsatility index values of 50 normal infants and 10 hydrocephalic infants showed a statistically significant difference (P<0.05) for systolic and pulsatility index values. However, no significant difference was found for end-diastolic values. The authors believe that the phenomenon could be explained as an increase of the cerebrovascular compliance which counteracts the increase of the perivascular pressure in an attempt to maintain a normal cerebral blood flow. Therefore, the transfontanelle Doppler ultrasound technique may provide a useful and early tool in diagnosing cerebral blood-flow changesin hydrocephalic infants.     

Transcranial Doppler findings during balloon test occlusion of the internal carotid artery.

The authors performed transcranial Doppler ultrasonography (TCD) during internal carotid artery (ICA) balloon test occlusion (BTO) and observed changes in mean flow velocity (Vm) in the middle cerebral artery (MCA), and pulsatility index (PI) while monitoring the stump pressure (Sp) of the internal carotid artery (ICA), and neurologic findings. A group of 17 patients requiring possible temporary or permanent occlusion of the ICA in the course of planned procedures first underwent BTO. A patient who either developed neurologic changes or maintained less than 60% of preocclusion Sp or Vm in the ipsilateral MCA during BTO was considered to have a positive test. Eleven patients had negative results, while in six patients, tests were positive. Mean flow velocity showed a decrease after occlusion in all cases but not to a remarkable extent in some patients. Stump pressure decreased in all negative cases after balloon inflation and than tended to increase progressively during 15 minutes of BTO. Pulsatility index tended to decrease gradually during BTO in all negative patients. However, in positive cases, PI and Sp fell steeply. Only one positive case had a neurologic symptom of severe headache. The decreased PI in the MCA reflected autoregulatory dilation of cerebral vessels to compensate for decreased absolute cerebral blood volume following ICA occlusion. Changes in PI are a good indicator for evaluating blood flow during BTO.     

Cerebral blood flow velocity and failure of autoregulation in neonates: their relation to outcome of birth asphyxia.

Using the continuous wave Doppler technique, we examined the pulsatility index (PI) of the anterior cerebral artery in 14 asphyxiated infants. We also measured the blood pressure (BP) and fontanel pressure (FP) and calculated the cerebral perfusion pressure (CPP). According to the neurological prognosis, we divided the 14 infants into two groups and studied correlation of each factor. In the good-prognosis group (n = 11), PIs are within normal limits. There is a negative correlation between BP, CPP and PI, suggesting that the autoregulation of cerebral blood flow has been lost. On the other hand, there is no significant correlation between BP, CPP and PI in the poor-prognosis group (n = 3). These infants are thought to have lost the autoregulation, but their cerebral blood flow is not pressure-passive. Not only BP but also brain edema, vasodilation, and possibly other factors may contribute to determine the cerebral blood flow. Concerning FP, no remarkable correlations are found between two groups. It is therefore very important to monitor the PI, BP, FP in asphyxiated infants even if the degree of asphyxia is mild.     

Longitudinal determination of cerebral blood flow velocity in neonates with the Doppler technique

Using the Doppler technique, we followed the postnatal changes of the cerebral blood flow velocity longitudinally. Pulsatility index (PI) was measured in 91 neonates. In 26 normal term infants who were supine, PIs were initially raised (PI = 0.91 +/- 0.10), gradually falling over the first 12 hours after birth and remaining stable thereafter (PI = 0.78 +/- 0.05). PIs tended to be lower in neonates born by caesarean section but remained grossly within the normal range. Low birthweight infants showed high PIs during the first 12 hours after birth. Infants with a prone position showed a narrow standard deviation in PI soon after birth. There was a negative correlation between PI and the conceptional age and the coefficient of the correlation was 0.97156. The stage of active sleep, especially the REM period, was found to be an important factor which decreased the PI. We concluded that neonatal cerebral circulation significantly changes during the perinatal period and is affected by various physiological factors, especially sleep stages, the position of the infant and the conceptional age.     

Free Communications (Section D)

In TCD studies, the pulsatility index (PI), which is based on flow waveform analysis, are widely used for assessment of cerebral vascular resistance (CVR). However, PI is not very accurate, because it has many sources of variability and error. We propose a ratio between mean arterial pressure (MAP) and mean velocity (Vm) for an index of CVR. If we assume that the lumen of basal cerebral vessels is constant than MAPNm should be directly proportional to CVR. The aim of our study was to evaluate validity of MAPNm. For this purpose different vasodilatatory stimuli, which affected cerebral resistance and conductive vessels, were used. Hyperventilation (HV) and rebreathing (RE) change blood pCO2, which has predominantly an influence on resistance vessels. Clonidine, alfa-adrenegic blocker, produce vasodilation on perifery. L-arginine (L-arg), precursor of nitro oxide, supposed to be able to induce vasodilatation of cerebral vessels. Nitroglicerinc (NTG) acts primarily on conductive vessels. Ten heathy subjects, both gender, aged from 21 to 57 years (mean 33.4+?11.9 years) participated in our study. HV and RE were performed using capnograph (Oxicap, Ohmeda) We registered end-tidel (ET) CO2. Clonidin was administrated intramusculary at dose? L-arg was infused at rate 5mg/kg/min for 30 minutes. NTG was applied sublingualy at dose 0.6 mg. The response of cerebral circulation was continously monitored by Multi-dop X (OWL, Germany), usmg bitemporal probes for recording of Vm in middle cerebral artenes. Simultaneously the MAP and heart rate (HR) were sampled by pletysmographic device (Finapress. Ohmeda, USA).During RE MAP increased (p=.035), HR did not change, PI (p=.0006) and MAP/Vm (p=.0002) decreased. Dunng HV MAP decreased (p=014), HR increased (p=.048), PI (p=.0001) and MAPNm (p<0001) increased. We found good correlation between changes of PI and MAPNm (r=73, p<01) as well as between changes of MAP/Vm and ET CO2 (r=78, p<01) and moderate correlation between changes of PI and ET CO2 (r=53, p=016) After Clonidine administration MAP decreased (p<0001). HR did not change significantly,PI (p=.04) as well as MAP/Vm (p=.017) decreased. There was no correlation between PI and MAV/Vm. After L=arg infusion MAP and HR did not change, while PI (p<.001) and MAP/Vm (p<.001) decreased. No correlation between PI and MAP/Vm was found. After NTG MAP decreased (p=0.019), HR did not change as well as PI, while MAP/Vm (p=0084) mcrcased There was no correlation between PI and MAP/Vm     

Cerebral blood flow velocity in preterm neonates

The postnatal changes of cerebral blood flow velocity in 35 preterm neonates with or without complications were measured with a bidirectional Doppler flow meter. In the cases without complications, the pulsatility index for the anterior cerebral artery (ACA-PI) was high shortly after birth, and gradually decreased after 6 hrs as that in normal term neonates. However ACA-PI showed large variations in the cases with respiratory distress. On the other hand, ACA-PI in the cases with subependymal hemorrhage (SEH) was low during the first 6 hrs after birth, and thereafter showed no significant changes. ACA-PI in the cases with intraventricular hemorrhage (IVH) was high during the first 6 hrs after birth and then decreased when IVH was found on ultrasound scanning. ACA-PI increased gradually with progression of post-hemorrhagic ventricular dilatation. The difference of high PI in IVH and low PI in SEH during the first few hrs after birth suggests that the pathogenesis of SEH may be different from the mechanism of intraventricular rupture from SEH. Low PI values in the infants with SEH may be related to intrapartum events, while the changing patterns of high to low PI in the infants with IVH suggest postnatal hemodynamic changes.     

Duplex color ultrasound study of infantile progressive ventriculomegaly

Sequential measurements of ventricular sizes and Doppler variables of anterior cerebral artery (ACA) by duplex color ultrasound were performed on 14 ventriculomegalic infants (mean age: 3.4 months): 9 were postmeningitic, 3 posthemorrhagic, and 2 congenital. According to changes of the frontal horn radius (FHR) after shunts, the FHR was decreased > 30% (n = 9) in group I and 10% (n = 5) in group II. Before shunting, Pourcelot index (PI) in group I was greater than in group II (P<0.01), but FHR in group II was higher than in group I (P<0.01). The intracranial pressure did not vary between groups. Serial preshunt examinations showed a significant correlation between the degree of cerebrovascular resistance and the degree of ventricular dilation only in group I. After surgery, significant changes of end-diastolic velocity, the area under the velocity curve, and PI were found only in group I. The reservoir pumping test performed on 2 cases of recurrent ventriculomegaly in group I and 3 cases in group II Showed a decreased PI only in group I, in which the outcome was better. PI is useful in differentiating between hydrocephalic and atrophic ventriculomegaly. These data suggest that a ventriculomegalic infant with an unelevated PI value hardly benefits from a ventricular shunt.     

Value of transcranial Doppler indices in predicting raised ICP in infantile hydrocephalus

Cerebral hemodynamic changes in infants with progressive hydrocephalus have been studied with the transcranial Doppler (TCD) technique. Several authors have referred to the correlation between the hemodynamic changes and increased intracranial pressure (ICP). Despite conflicting conclusions on the value of pulsatility index (PI) measurements for monitoring infantile hydrocephalus, these pulsatility indices are the most commonly used for this purpose. Although clinical signs of raised ICP are highly variable and unreliable in infants, assumptions have been made in most of the studies about the presence of elevated ICP on the basis of the patient's clinical state. Few studies have reported on actual ICP values, however, and a direct relationship between ICP and TCD changes has never been adequately demonstrated. In the present study, this relationship was investigated in long-term simultaneous TCD/ICP measurements, in an attempt to develop a noninvasive method of monitoring the effect of ICP on intracranial hemodynamics. Two groups of data sets were established. Group I consisted of pre- and postoperative (shunt implantation) TCD/ICP measurements. Group II were long-term simultaneous TCD/ICP recordings showing significant ICP variations. In most of the postoperative measurements there was a decrease in the average PI and RI values. The correlation between PI or RI and ICP in the long-term simultaneous recordings, however, was generally poor. The risk of obtaining false positive or false negative PI or RI values in short-term measurements was also demonstrated. It can be concluded from our results, besides the wide range of reference values for the Doppler indices and extracranial influences upon them, that the present Doppler indices are inadequate for monitoring the complex intracranial dynamic responses in patients with raised ICP.     

盐酸纳络酮对兔酒精中毒后脑外伤早期脑血流的影响

目的研究盐酸纳络酮(NAL)对兔急性酒精中毒后脑外伤早期脑血流动力学及脑血管形态变化的影响。方法家兔20只,随机分为NAL治疗组和生理盐水对照组,每组10只。乙醇灌胃法致使家兔急性酒精中毒,自由落体直接打击颅骨法制作实验性颅脑损伤模型。治疗组在伤后30min静注NAL2mg/kg,以后每隔60min重复注射一次。采用经颅多普勒(TCD)超声结合脑血管造影等方法,于伤前及伤后一定时间测定平均动脉压(MABP)、颅内压(ICP)、大脉中动脉舒张期流速(Vd)、脉搏指数(PI)、脑血管直径指数(CVI),进行统计学分析。结果两组动物伤后MABP明显下降,ICP及PI值显著升高,Vd明显减慢,CVI显著减小。NAL治疗后与治疗前及对照组各相对时间比较,MABP显著升高(P<0.05),Vd显著增快(P<0.01),PI值明显降低(P<0.01),CVI明显增大(P<0.05),TCD频谱接近正常。结论NAL(2mg/kg)可逆转酒精中毒所致的兔颅脑损伤后发生的显著的低血压及脑血管收缩、并可降低脑血管阻力,改善微循环,增加脑血流量,对兔急性酒精中毒后脑外伤有治疗作用。     

Transcranial Doppler during neurocardiogenic syncope

The purpose of the present study was to investigate changes in cerebral circulation during neurocardiogenic syncope (NCS). Twenty patients with a history of unexplained syncopes were studied over a 45 min period in a tilted position. Heart rate and arterial blood pressure were recorded non-invasively using Finapres. Cerebral blood flow velocity of both middle cerebral arteries was measured with transcranial Doppler (TCD). Ten patients (50%) developed a NCS during the tilt test, with a strong reduction in blood pressure (mean, 48/34 mmHg) and heart rate (mean, 54 beats/min). Simultaneously, diastolic blood flow velocities dropped to values close to zero. However, systolic blood flow velocities did not decrease. In consequence, the pulsatility index (PI) increased considerably from 0.93 to 2.01. The increase in PI suggests that there is a constriction of cerebral resistance vessels during NCS. Despite the drop in blood pressure and the putative increase in cerebrovascular resistance, systolic blood flow velocities remained unchanged in the TCD records. This fact can be explained by a lumen narrowing of the middle cerebral artery at the site of insonation. In conclusion, the typical changes in cerebral blood flow velocity during NCS are probably due to a strong constriction of both the proximal and the peripheral segments of cerebral arteries. It is clear that, in addition to vasodepression and cardiac inhibition, cerebral vasoconstriction is a further mechanism in the pathogenesis of a NCS.     

Transcranial and extracranial ultrasound assessment of cerebral hemodynamics in vascular and Alzheimer's dementia

BACKGROUND: Increasing life expectancy of the population leads to a higher incidence of dementia. Exact differentiation between the most common types, vascular dementia (VD) and Alzheimer's dementia (AD), is crucial to the development and application of new treatment strategies. Both conditions are thought to differ greatly by their extent of microvascular affection. Transcranial and extracranial ultrasound permits analysis of cerebral hemodynamics and should help to differentiate between VD and AD. We compare multimodal ultrasound data between VD, AD and controls, and give an overview of the literature on this topic. METHODS: Twenty VD and 20 AD patients were studied and compared with 12 age-matched controls. Transcranial color-coded ultrasound was performed to assess blood flow velocity (V(mean)) and pulsatility indices (PI) of the middle cerebral artery (MCA). Extracranial duplex and Doppler ultrasound techniques were used to assess the blood volume flow (BVF) in the anterior circulation (both internal carotid arteries [ICA]) and posterior circulation (both vertebral arteries [VA]), the global cerebral blood flow (CBF = BVF(ICA) + BVF(VA)), the global cerebral circulation time (CCT = time delay of echo-contrast bolus arrival between ICA and internal jugular vein) and global cerebral blood volume (CBV = CCT x CBF). RESULTS: MCA V(mean) in VD (36 +/- 8 cm/s) and AD (43 +/- 13 cm/s) were significantly lower than in controls (59 +/- 13 cm/s) but did not differ significantly between VD and AD groups. PI (1.1 +/- 0.2; 1 +/- 0.2; 0.9 +/- 0.2) only differed significantly between VD group and controls. CBF and CCT in VD (570 +/- 61 ml/min; 8.8 +/- 2.6 s) and AD (578 +/- 77 ml/min; 8.2 +/- 1.4 s) were similar but differed significantly from controls (733 +/- 54 ml/min; 6.4 +/- 0.8 s). BVF in the anterior and posterior circulation of VD group (412 +/- 62 and 158 +/- 38 ml/min) and AD group (428 +/- 62 and 150 +/- 41 ml/min) were significantly lower than in controls (537 +/- 48 and 199 +/- 26 ml/min) but did not differ significantly between the patient groups. DISCUSSION: Transcranial and extracranial ultrasound does not help to distinguish between VD and AD. However, our results add insight into the pathophysiology of dementia, arguing in favor of a common 'vascular' pathway in both conditions.     

Monitoring of somatosensory evoked responses during carotid endarterectomy

During carotid endarterectomy (CEA), we monitored somatosensory evoked responses (SERs) ipsilaterally over the scalp following stimulation of the contralateral median nerve at the wrist. Thirty-eight CEAs in 36 patients were studied. Of the 10 CEAs performed with patients under general anesthesia, three involved marked changes in SERs, reversed by shunt insertion. The remaining 28 CEAs were done with patients under local anesthesia. The SERs remained stable during an average clamp time of 30 minutes in all except one patient, in whom SER changes developed within a minute of clamping; the changes were reversed by shunt placement. Four of the 38 CEAs required a shunt based on SER changes, although measurement of stump pressure (less than 50 mm Hg) would have indicated the necessity of a shunt in eight additional operations. We concluded that SERs are useful in signaling cerebral ischemia and the need for a shunt during CEA.     

Intracranial pressure and cerebral arterial flow velocity indices in childhood hydrocephalus: current review

Because of its noninvasive and repeatable nature, Doppler ultrasound has been increasingly used to assess changes in cerebral haemodynamics in infants and children with hydrocephalus. There is general agreement that a direct correlation exists between the intracranial pressure (from experimental, fontanometric and direct measurement evidence) and the resistance index. In addition, this increasing index has been predominantly due to a reduction in the end-diastolic velocity. Stable ventriculomegaly is associated with normal pulsatility. The cerebral blood flow velocity parameters change significantly following CSF drainage by tapping or shunting. The measurement of intracranial pressure and cerebral blood flow velocity are currently the best ways of assessing the need for CSF diversion and monitoring subsequent shunt function.Presented at the Consensus Conference: Hydrocephalus '92, Assisi, Italy, 26–30 April 1992     

急性脑梗死各临床亚型患者的脑血管反应性的变化

目的 探讨急性脑梗死各临床亚型患者脑血管反应性(CVR)的变化.方法 将70例急性脑梗死患者分为3个亚组:动脉硬化性血栓形成性脑梗死(AI)组(22例)、腔隙性脑梗死(LI)组(33例)和心源性脑梗死(CI)组(15例).应用经颅多普勒超声(TCD)检测各组患者双侧大脑中动脉(MCA)的平均流速(Vm)、脉动指数(PI)、阻力指数(RI)指标,通过屏气试验测定屏气指数(BHI);并与20名正常对照组进行比较. 结果与正常对照组相比,AI组Vm、PI、RI均显著升高(P<0.05～0.01),BHI明显降低(P<0.01);LI组Vm、BHI均显著降低(均P<0.05);而CI组各参数与正常对照组相比差异无统计学意义. 结论急性脑梗死各亚组的CVR改变并不相同,AI、LI组CVR损害更为明显,CVR检测对急性脑梗死各亚型的血液动力学研究有重要意义.     

Cerebral blood flow in infants: comparison of carotid blood flow and cerebral blood velocity

Carotid blood was measured with a ultrasonic volume flow meter in 38 infants. The carotid blood flow was 1.50 +/- 0.55 ml/sec. At the same time peak systolic flow velocity, mean blood velocity, end diastolic velocity, pulsatility index (PI) and resistance index (RI) in the middle and anterior cerebral arteries were measured by duplex Doppler scanning. There was a correlation between the carotid blood flow and the mean blood velocity in middle and anterior cerebral arteries. However, PI and RI were not well correlated with carotid blood flow.