Middle Cerebral Artery Velocity Research Articles

Compression garments do not alter cerebrovascular responses to orthostatic stress after mild passive heating

Whole-body heating increases the likelihood of syncope, whereas utilizing lower-body compression garments may reduce syncope risk. We hypothesized that graded compression garments would reduce the typically observed large postural reductions in arterial blood pressure and middle cerebral artery velocity, in normothermia and especially once passively heat stressed. Fifteen men (age: 27 ± 4 years, aerobic fitness range: 30-75 mL/kg(/) min) completed a supine-to-stand orthostatic challenge for 3 min at normothermia and after passive heating (esophageal temperature, +0.5 °C from baseline) on two occasions (> 7 days): once wearing commercially available compression trousers and once wearing low-compression placebo trousers (randomized order). Blood flow velocity in the middle cerebral artery (transcranial Doppler), mean arterial blood pressure (mean BP: Finometer) and end-tidal carbon dioxide pressure were measured continuously. During normothermia, compression, garments did not alter the magnitude of the postural changes in mean BP or middle cerebral artery velocity. After passive heating, although the magnitudes of these changes were exaggerated, they were not significantly affected by compression garments. Compression garments did not attenuate the initial or sustained orthostatic hypotension associated with posture change, either during normothermia or following passive heat stress.

The interaction of carbon dioxide and hypoxia in the control of cerebral blood flow

Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide. Middle cerebral artery velocity, as an index of CBF; partial pressures of carbon dioxide and oxygen and concentration of oxygen in arterial blood; and mean arterial blood pressure were monitored. The product of middle cerebral artery velocity and arterial concentration of oxygen was used as an index of cerebral oxygen delivery. Two-way repeated measures analyses of variance (rmANOVA) found a significant interaction of carbon dioxide and hypoxia factors for both CBF and cerebral oxygen delivery. Regression models using sigmoidal dependence on carbon dioxide and a rectangular hyperbolic dependence on hypoxia were fitted to the data to illustrate this interaction. We concluded that carbon dioxide and hypoxia act synergistically in their control of CBF so that the delivery of oxygen to the brain is enhanced during hypoxic hypercapnia and, although reduced during normoxic hypocapnia, can be restored to normal levels with progressive hypoxia.

Constraint-Induced Movement Therapy Alters Cerebral Blood Flow in Subacute Post-Stroke Patients

We attempted to evaluate patterns of hemispheric activation, according to cerebral blood flow changes, in post-stroke patients during motor tasks with and without arm restriction. Bilateral continuous middle cerebral artery monitoring of 6 healthy subjects (control group) and 28 post-stroke patients by transcranial Doppler sonography was executed while performing three simple motor tasks using the paretic or nondominant (in controls) hand: ball grasping, pegs insertion, and "eating" with a spoon. The nonaffected or dominant (in controls) arm was free and thereafter restricted. Mean blood flow velocity and flow velocity changes during the tests were estimated. No significant mean blood flow velocity changes were found in the healthy subjects. Significant elevation of mean blood flow velocity in damaged middle cerebral artery was recorded in post-stroke patients after restricting the undamaged hand. This may explain the positive effect of constraint-induced movement therapy on upper limb function.

Effects of Indomethacin Test on Intracranial Pressure and Cerebral Hemodynamics in Patients With Refractory Intracranial Hypertension

Intracranial hypertension is the final pathway of many neurocritical entities, such as spontaneous intracerebral hemorrhage (sICH) and severe traumatic brain injury (sTBI). This study aimed to (1) determine alterations in intracranial pressure (ICP) and cerebral hemodynamics after an indomethacin (INDO) infusion test and the related association with survival in patients with refractory intracranial hypertension (RICH) secondary to sICH or sTBI and (2) assess the safety profile after INDO. INDO was administered in a loading dose (0.8 mg/kg/15 min), followed by a 2-hour continuous infusion (0.5 mg/kg/h) in RICH patients with ICP greater than 20 mm Hg who did not respond to first-line therapies. Changes in ICP, cerebral perfusion pressure (CPP), and cerebrovascular variables (assessed by transcranial Doppler and jugular bulb saturation) were observed. Clinical outcome was assessed at 1 and 6 months according to the Glasgow Outcome Scale and correlated with INDO infusion test response. Analysis of INDO safety profile was conducted. Thirteen sICH and 10 sTBI patients were studied. The median GCS score at admission was 6. Within 30 minutes of INDO infusion, ICP decreased (42.0 ± 13.5 vs 27.70 ± 12.7 mm Hg; Δ%: -48.4%; P < .001), and both CPP (57.7 ± 4.8 vs 71.9 ± 7.0 mm Hg; Δ%: +26.0%; P < .001) and middle cerebral artery velocity (35.2 ± 5.6 vs 42.0 ± 5.1 cm·s(-1); Δ%: +26.1%; P < .001) increased. The CPP response to a 2-hour INDO infusion test was correlated (R2 = 0.72, P < .001) with survival. No adverse events were observed after INDO. Our findings support the effectiveness and feasibility of an INDO test in decreasing ICP and improving cerebral hemodynamics in surviving RICH patients. Future studies to evaluate different doses, lengths of infusion, and longer term effects are needed.

Influence of Posture on the Regulation of Cerebral Perfusion

Posture has a major influence on cerebral blood flow (CBF). Unlike head-up tilt (HUT), less is known about how CBF is regulated during head-down tilt (HDT). We hypothesized that CBF would be elevated during HDT and decreased during HUT. In 21 healthy young adults, while controlling for end-tidal Pco2, we combined concurrent measurements of middle cerebral artery velocity and posterior cerebral artery velocity (MCAv and PCAv, respectively), blood pressure (BP), and heart rate (HR). Measures were made at rest and, in a randomized order, during -90 degrees HDT and +900 HUT. Dynamic cerebral autoregulation was quantified using transfer function analysis. In a subgroup, volumetric blood flow recordings were obtained in the common carotid artery (CCA; N=11), internal and external carotid arteries (ICA; N=8 and ECA; N=6), and vertebral artery (VA; N=4). End-tidal Pco2, CCA, ICA, VA, MCAv(mean) and PCAv(mean) remained unchanged during -90 degrees HDT and +90 degrees HUT compared to supine. During -90 degrees HDT, mean BP (+22 mmHg) and cerebral vascular resistance (CVR) in both the MCA and PCA were elevated relative to supine, whereas HR remained unchanged. During +900 HUT, when compared to supine, HR increased (+18 bpm), and mean arterial pressure (MAP) total power and low frequency (LF) power in the MCA and PCA increased. In both the very low frequency (VLF) and LF ranges, coherence during +90 degrees HUT increased (P < 0.05 vs. supine) in both the MCA and PCA. In contrast, coherence was reduced during -90 degrees HDT. Despite marked changes in perfusion pressure with HUT or HDT, our findings indicate that cerebral perfusion is well maintained during acute severe changes in posture.

A successful treatment of arterial ischemic stroke with stent insertion in a child with congenital heart disease

Diagnosis of arterial ischemic stroke in pediatric patients is often delayed due to the uncertainty and variability of clinical symptoms. Early diagnosis of arterial ischemic stroke can bring a favorable prognosis with prompt thrombolytic therapy or stent insertion, via transfemoral cerebral arteriogram. Acute thrombolytic therapy is rarely attempted in children because of the delayed diagnosis. We report a case of a 4-year-old girl with complex heart disease who was presented with arterial ischemic stroke at the right distal internal carotid artery and successfully treated by stent insertion in which repeated thrombolysis or ballooning had failed. Left hemiparesis was nearly recovered 6 days after the stent insertion. The mean flow velocity of the right middle cerebral artery has slightly improved compared to that of the initial study. She has been followed-up for 6 months in the outpatient clinic without neurologic sequelae. This case suggests that intracranial stent insertion may be a safe and an effective modality in young children, when the thrombolytic therapy or ballooning is inapplicable. Additionally, transcranial Doppler ultrasonography is useful to monitor the cerebral blood flow after stent insertion in children.

Common features in patients with intracerebral hemorrhage following superficial temporal artery-middle cerebral artery bypass in steno-occlusive cerebrovascular disease.

Five patients treated for intracranial cerebral hemorrhage after superficial temporal artery-middle cerebral artery bypass in Xuwu Hospital, Capital Medical University, Beijing, China, from 2005-2011 were included in this study. Prior to superficial temporal artery-middle cerebral artery bypass, all patients showed diminished cerebrovascular reactivity and an ipsilateral ischemic lesion. Intracranial cerebral hemorrhage developed within 1–4 days following superficial temporal artery-middle cerebral artery bypass. Transcranial Doppler showed increased middle cerebral artery velocity of 50–100% in the operated hemisphere. These findings suggested that focal hyperperfusion, an ipsilateral ischemic lesion and diminished cerebrovascular reactivity are the important characteristics of intracerebral hemorrhage following superficial temporal artery-middle cerebral artery bypass in patients with steno-occlusive cerebrovascular disease.

Impaired hypoxic cerebral vasodilation in younger adults with metabolic syndrome

Metabolic syndrome (MetSyn) increases the risk of cerebrovascular disease and stroke; however, its impact on human cerebral circulation remains unclear. Reduced cerebral dilation is also associated with an increased risk of stroke and may occur in MetSyn adults. We hypothesised that MetSyn adults would exhibit reduced cerebral vasodilation to hypoxia and hypercapnia. Middle cerebral artery velocity (MCAv) was insonated with Doppler ultrasound in younger (approximately 35 years) MetSyn and healthy adults. We measured mean arterial blood pressure (MABP), arterial oxygen saturation (S(p)O(2)) and end tidal carbon dioxide (Pet (CO2)). Cerebrovascular conductance index (CVCi) was calculated as MCAv*100/MABP. Cerebral vasodilation (ΔCVCi) to hypoxia (S(p)O(2) = 90% and 80%) and hypercapnia (+10 mm Hg Pet (CO2)) was assessed. Baseline MCAv was similar, while adults with MetSyn had lower baseline CVCi. MetSyn adults demonstrated markedly reduced ΔCVCi compared to healthy adults in response to hypoxia (90% S(p)O(2): 1±2 vs 6±2; 80% S(p)O(2): 5±2 vs 15±3 cm/s/mmHg, p<0.05). Both groups demonstrated similar ΔCVCi to hypercapnia (18±2 vs 20±2 cm/s/mmHg). These data are the first to demonstrate that younger MetSyn adults have impaired hypoxia-mediated cerebral vasodilation prior to clinically overt cerebrovascular disease. These findings provide novel insight into cerebrovascular disease onset in MetSyn adults.

Beyond a one‐track mind: understanding blood flow to the brain in humans

Beyond a one‐track mind: understanding blood flow to the brain in humans

A classification of patterns of fetal middle cerebral artery velocity waveforms as seen on Doppler ultrasound

To identify, classify, and study the clinical significance of different patterns of fetal middle cerebral artery peak systolic velocity waveforms that can be seen on Doppler ultrasound. The patterns of fetal middle cerebral artery (MCA) velocity waveforms encountered in our study (n = 1128) conducted on a rural obstetric population were analyzed. Broadly, three different waveform-patterns (type I to type III) were identified from 1100 cases on which satisfactory studies were conducted. Types IA and IB were found in normal fetuses of the first (n = 254, 23.1 %) and second (n = 386, 35.1 %) trimesters, respectively. Type IC (n = 418, 38 %) included normal fetuses in the second (n = 25) and third (n = 317) trimesters, and 76 of 118 IUGR fetuses. Type II consisted of IUGR category; 17 (1.5 %) cases in type IIA, 10 (0.9 %) in IIB, and 11 (1.0 %) in IIC. Type III (n = 4, 0.4 %) was found in the critical cases with severe anemia secondary to feto-maternal hemorrhage. Although different patterns of uterine and umbilical artery velocity waveforms have been described in the obstetric literature, there is no mention of patterns of fetal MCA velocity waveforms. This is the first study to demonstrate, classify, and state the clinical significance of different patterns of fetal middle cerebral artery peak systolic velocity waveforms.

Regional brain blood flow in man during acute changes in arterial blood gases

Despite the importance of blood flow on brainstem control of respiratory and autonomic function, little is known about regional cerebral blood flow (CBF) during changes in arterial blood gases.We quantified: (1) anterior and posterior CBF and reactivity through a wide range of steady-state changes in the partial pressures of CO2 (PaCO2) and O2 (PaO2) in arterial blood, and (2) determined if the internal carotid artery (ICA) and vertebral artery (VA) change diameter through the same range.We used near-concurrent vascular ultrasound measures of flow through the ICA and VA, and blood velocity in their downstream arteries (the middle (MCA) and posterior (PCA) cerebral arteries). Part A (n =16) examined iso-oxic changes in PaCO2, consisting of three hypocapnic stages (PaCO2 =∼15, ∼20 and ∼30 mmHg) and four hypercapnic stages (PaCO2 =∼50, ∼55, ∼60 and ∼65 mmHg). In Part B (n =10), during isocapnia, PaO2 was decreased to ∼60, ∼44, and ∼35 mmHg and increased to ∼320 mmHg and ∼430 mmHg. Stages lasted ∼15 min. Intra-arterial pressure was measured continuously; arterial blood gases were sampled at the end of each stage. There were three principal findings. (1) Regional reactivity: the VA reactivity to hypocapnia was larger than the ICA, MCA and PCA; hypercapnic reactivity was similar.With profound hypoxia (35 mmHg) the relative increase in VA flow was 50% greater than the other vessels. (2) Neck vessel diameters: changes in diameter (∼25%) of the ICA was positively related to changes in PaCO2 (R2, 0.63±0.26; P<0.05); VA diameter was unaltered in response to changed PaCO2 but yielded a diameter increase of +9% with severe hypoxia. (3) Intra- vs. extra-cerebral measures: MCA and PCA blood velocities yielded smaller reactivities and estimates of flow than VA and ICA flow. The findings respectively indicate: (1) disparate blood flow regulation to the brainstem and cortex; (2) cerebrovascular resistance is not solely modulated at the level of the arteriolar pial vessels; and (3) transcranial Doppler ultrasound may underestimate measurements of CBF during extreme hypoxia and/or hypercapnia.

Differential blood flow responses to CO2 in human internal and external carotid and vertebral arteries

Arterial CO2 serves as a mediator of cerebral blood flow(CBF), and its relative influence on the regulation of CBF is defined as cerebral CO2 reactivity. Our previous studies have demonstrated that there are differences in CBF responses to physiological stimuli (i.e. dynamic exercise and orthostatic stress) between arteries in humans. These findings suggest that dynamic CBF regulation and cerebral CO2 reactivity may be different in the anterior and posterior cerebral circulation. The aim of this study was to identify cerebral CO2 reactivity by measuring blood flow and examine potential differences in CO2 reactivity between the internal carotid artery (ICA), external carotid artery (ECA) and vertebral artery (VA). In 10 healthy young subjects, we evaluated the ICA, ECA, and VA blood flow responses by duplex ultrasonography (Vivid-e, GE Healthcare), and mean blood flow velocity in middle cerebral artery (MCA) and basilar artery (BA) by transcranial Doppler (Vivid-7, GE healthcare) during two levels of hypercapnia (3% and 6% CO2), normocapnia and hypocapnia to estimate CO2 reactivity. To characterize cerebrovascular reactivity to CO2,we used both exponential and linear regression analysis between CBF and estimated partial pressure of arterial CO2, calculated by end-tidal partial pressure of CO2. CO2 reactivity in VA was significantly lower than in ICA (coefficient of exponential regression 0.021 ± 0.008 vs. 0.030 ± 0.008; slope of linear regression 2.11 ± 0.84 vs. 3.18 ± 1.09% mmHg−1: VA vs. ICA, P <0.01). Lower CO2 reactivity in the posterior cerebral circulation was persistent in distal intracranial arteries (exponent 0.023 ± 0.006 vs. 0.037 ± 0.009; linear 2.29 ± 0.56 vs. 3.31 ± 0.87% mmHg−1: BA vs. MCA). In contrast, CO2 reactivity in ECA was markedly lower than in the intra-cerebral circulation (exponent 0.006 ± 0.007; linear 0.63 ± 0.64% mmHg−1, P <0.01). These findings indicate that vertebro-basilar circulation has lower CO2 reactivity than internal carotid circulation, and that CO2 reactivity of the external carotid circulation is markedly diminished compared to that of the cerebral circulation, which may explain different CBF responses to physiological stress.

Correlation between the arterial pulse wave of the cerebral microcirculation and CBF during breath holding and hyperventilation in human

ObjectiveTo evaluate if relative changes in the amplitude of the arterial pulse wave of the cerebral microcirculation (APWCM) measured by near-infrared spectroscopy (NIRS) may provide information about relative changes of cerebral blood flow (CBF) in cerebral cortex. MethodsIn 10 healthy human volunteers, through simultaneous recording of the APWCM amplitude by means of NIRS and the mean blood flow velocity (MBFV) of middle cerebral artery by means of transcranial Doppler (TCD) at rest and during breath holding and hyperventilation, we evaluate a possible correlation between relative changes of the mean APWCM amplitude and relative changes of MBFV. ResultsWe found a significant linear correlation: breath holding: R2 0.84, p<0.001, hyperventilation: R2 0.81, p<0.001. ConclusionThe relative changes of the mean APWCM amplitude seem able to provide information about relative changes of CBF of cerebral cortex in healthy adult humans during breath holding and hyperventilation. SignificanceAPWCM detected by NIRS, a safe, repeatable, inexpensive technology and at the bedside may improve the study of cerebral cortex microcirculation in neurological diseases.

Role of TCD in sickle cell disease: A review

Summary Stroke is an important complication of sickle cell disease. Approximately twenty-four percent of patients have a stroke by the age of 45. Blood transfusions decrease stroke risk in patients deemed at high risk by transcranial Doppler (TCD) by evidence of elevated intracranial internal carotid or middle cerebral artery velocity. This review describes the practical procedure of patient evaluation and illustrates, through Brazilian guidelines, the importance of uniform methodology in a setting with high prevalence of this disease.

Overnight oximetry in African children with human immunodeficiency virus

<h3>Aims</h3> Obstructive sleep apnoea (OSA) has been described in 2 small studies of adults with human immunodeficiency virus (HIV) and appears to be associated with higher body mass index1 and adenotonsillar hypertrophy.2 However, there are few data in children and the possibility of an association with cerebrovascular disease has not been addressed. The aim of this prospective study, funded by the Heinz fellowship, was to examine the prevalence of OSA in African children with HIV and any association with middle cerebral artery velocity (MCAV) measured using transcranial Doppler (TCD) ultrasound. <h3>Methods</h3> We undertook TCD and overnight pulse oximetry using the Masimo motion-resistant portable oximeter in 12 unselected African children (8 male; median age 4; range 2.5-10 years) with HIV. We analysed the data using Download 2001, which includes delta12, a measure of OSA if &gt;0.4,3 as well as mean and minimum haemoglobin oxygen saturation (SpO₂), the percentage of the total sleep study spent with SpO₂&lt;95% and the number of desaturations per hour. <h3>Results</h3> Median (range) for mean and minimum overnight SpO₂ were 98.5 (94.6-99.6)% and 81 (33-94)% respectively, while the percentage of the total study with SpO₂&lt;95% was 99.3 (76.9-99.9). The median number of dips in SpO₂ &gt;4% per hour was 1.34 (0.29-4.54) and the median delta12 index was 0.36 (0.29-0.83). Five children (42%) had delta12&gt;0.4, consistent with a diagnosis of OSA. Delta12 and the number of desaturations per hour were correlated with CD4% (r=0.83, p=0.012 and r=0.71, p=0.049 respectively). Minimum SpO₂ was correlated with haemoglobin (r=0.93, p=0.001) and respiratory rate (r=−0.71, p=0.01). None of the oximetry indices were correlated with body mass index. Right MCA correlated with mean overnight SpO₂ (r=−0.74, p=0.01). <h3>Discussion</h3> Our data suggest that OSA is common in African children with HIV, especially those with a high CD4%, while hypoxia may be associated with cerebrovascular disease.

A Method of Evaluating the Lower Limit of Cerebral Autoregulation and Its Correlation with Blood Pressure by Transcranial Doppler in Rats

The aim of present study was to validate the assessment of lower limit of cerebral autoregulation (LLCA) as derived from mean artery blood pressure (MABP) and cerebral zero flow pressure (ZFP) by means of transcranial Doppler (TCD) and to determine the accurate relationship between LLCA and MABP in stroke-prone renovascular hypertensive rats (RHRSP). We studied two groups of rats: RHRSP and normal controls. Blood flow velocity of middle cerebral artery was monitored by TCD and arterial blood pressure was recorded in right femoral artery to compute the ZFP. The value of LLCA was determined as the difference between MABP and ZFP and validated by the value determined by blood withdrawal-induced cerebral autoregulation. In normal rats, the LLCA derived from the new method was 69.8 ± 8.7 mm Hg, from the change of blood velocity was 69.4 ± 9.8 mmHg and from blood volume flow after blood withdrawal was 68.8 ± 9.7 mmHg. In the RHRSP group, the corresponding values of LLCA were 109.1 ± 17.2 mm Hg, 110.0 ± 18.0 mm Hg and 109.0 ± 19.3 mm Hg, respectively. In each group, there was no statistically significant difference among the three values. LLCA in RHRSP began to increase 6 weeks after hypertension-induced operation, significantly higher than controls (p < 0.05), and stabilized at 110 mm Hg, 10 weeks after operation. The increase of LLCA was positively correlated with MABP, following an “S” curve, demonstrating that the change of LLCA was more obvious in the middle range of MABP in RHRSP (R2 = 0.8848, p < 0.05). In conclusion, TCD is a valid and noninvasive method for determination of LLCA compared with the classic method in rats. Our data demonstrated that the change of LLCA may be correlated with MABP, following an “S” curve relationship.

Exaggerated Vasopressor Response to Exercise and Cerebral Blood Flow Velocity

We studied 10 young adults, normotensive at rest, comprising a control group (n = 5) with normal blood pressure responsiveness to exercise and an experimental group exhibiting greater percentage of body fat and body mass index (BMI) than the controls, with exaggerated blood pressure (vasopressor) responsiveness to exercise (EEBPR) (n = 5). Lower absolute and varying oxygen consumption/body weight normalized units of middle cerebral arterial blood flow velocity (MCAV) were found during exercise in the experimental group (P < .01). These findings support the hypothesis that the combination of EEBPR and high BMI is associated with low MCAV that may put such individuals at risk for cerebral hypoperfusion and cognitive deficits.

The influence of controlled breathing on cerebrovascular control

High frequency breathing (HF; &gt;0.2 Hz) may limit the influence of respiration at the low frequency (LF; 0.07–0.2 Hz) where cerebrovascular control is assessed. We tested the hypotheses that: 1) LF breathing will increase, and HF breathing will decrease LF coherence (COH) between mean arterial pressure (MAP) and mean middle cerebral artery velocity (MCAvmean ); and 2) reductions of COH expected when subjects breathe at 0.25 Hz are due, in part, to reduced CO2 associated with faster breathing. We recorded ECG, finger arterial pressure (Finometer), MCAvmean (transcranial Doppler), respiratory rate, and end‐tidal CO2 in 20 volunteers (28 ± 2 yrs). Four 7‐min breathing protocols were followed: 1) spontaneous breathing (SB); 2) paced breathing at 0.1 Hz; 3) paced breathing at 0.25 Hz; and 4) paced breathing at 0.25 Hz with CO2 control (5% CO2 bled in continuously; 0.25 Hz C). LF COH was assessed between MCAvmean and MAP. End‐tidal CO2 was lower during 0.25 Hz breathing than all other conditions (P&lt;0.05). COH was lower during 0.25 Hz breathing than both 0.1 Hz breathing and SB (P≤0.008). COH was indistinguishable during 0.25 Hz breathing with controlled and uncontrolled CO2 (P =0.299). Controlled breathing in the HF limits contributing influences of respiration on cerebrovascular control despite moderate reductions in end‐tidal CO2.

When to perform transcranial Doppler to predict cerebral hyperperfusion after carotid endarterectomy?

Cerebral hyperperfusion syndrome (CHS) after carotid endarterectomy (CEA) is a potential life-threatening disease. Identification of patients at risk for CHS commonly takes place with use of intra-operative transcranial Doppler (TCD), but is associated with both false positive and false negative results. We aimed to determine the diagnostic value for predicting CHS, by adding a TCD measurement in the early post-operative phase after CEA. We retrospectively included 72 patients who underwent CEA between January 2004 and August 2010 and in whom both intra- and post-operative TCD of the ipsilateral middle cerebral artery monitoring were performed. Twelve patients (17%) had an intra-operative mean blood flow velocity ( V mean ) increase >100% and 13 patients (18%) a post-operative V mean increase of >100%. In 5 patients (7%) CHS was diagnosed; 2 of those had an intra-operative V mean increase of >100% and all 5 a post-operative V mean increase >100%. This results in a positive predictive value of 17% for the intra-operative and 38% for the post-operative measurement. In conclusion, a post-operative increase of the mean velocity in the ipsilateral middle cerebral artery of >100% as measured by TCD is superior to an intra-operative velocity increase, for the identification of patients at risk for the development of CHS after CEA.

Cyclooxygenase inhibition abolishes age-related differences in cerebral vasodilator responses to hypercapnia

Blood flow and vasodilatory responses are altered by age in a number of vascular beds, including the cerebral circulation. To test the role of prostaglandins as regulators of cerebral vascular function, we examined cerebral vasodilator responses to CO(2) (cerebrovascular reactivity) in young (26 ± 5 yr; 6 males/6 females) and older (65 ± 6 yr, 5 males/5 females) healthy humans before and after cyclooxygenase inhibition (using indomethacin). Middle cerebral artery velocity (MCAv) responses to stepped hypercapnia were measured before and 90 min after indomethacin. Changes in MCAv during the recovery from hypercapnia (vasoconstrictor responses) were also evaluated before and after indomethacin. Cerebrovascular reactivity was calculated using linear regression between MCAv and end-tidal CO(2). Young adults demonstrated greater MCAv (55 ± 6 vs. 39 ± 5 cm/s: P < 0.05) and MCAv reactivity (1.67 ± 0.20 vs. 1.09 ± 0.19 cm·s(-1)·mmHg(-1); P < 0.05) to hypercapnia compared with older adults (P < 0.05). In both groups MCAv and MCAv reactivity decreased between control and indomethacin. Furthermore, the age-related differences in these cerebrovascular variables were abolished by indomethacin. During the recovery from hypercapnia, there were no age-related differences in MCAv reactivity; however, indomethacin significantly reduced the MCAv reactivity in both groups. Taken together, these results suggest that cerebral blood flow velocity and cerebrovascular reactivity are attenuated in aging humans, and may be due to a loss of prostaglandin-mediated vasodilation.