Middle Cerebral Artery Mean Blood Flow Velocity Research Articles

Combined Transcranial Doppler and Melatonin Levels to Predict Delayed Cerebral Ischemia After Subarachnoid Hemorrhage.

To investigate the early prediction value of transcranial Doppler ultrasound (TCD) combined with serum melatonin level for delayed cerebral ischemia (DCI) caused by subarachnoid hemorrhage (SAH). This paper is a prospective study. A total of 120 patients with SAH treated were included. The patients were divided into the DCI group (40 cases) and non-DCI group (80 cases) according to whether DCI occurred 14 days after SAH (DCI usually occurs 4 to 14d after bleeding). Baseline data, serum melatonin level, and TCD test results within 24hours after admission were compared between the 2 groups. Multivariate logistic analysis was used to analyze the factors affecting the occurrence of DCI after SAH. The value of serum melatonin level, middle cerebral artery mean blood flow velocity (MBFV) and their combination in predicting DCI in SAH patients was evaluated. Univariate analysis showed that there were statistically significant differences in the proportion of Fisher grade, Hunt-Hess grade, serum melatonin level, middle cerebral artery systolic blood flow velocity (Vs), MBFV and pulse index (PI) between the 2 groups (P<0.05). Serum melatonin levels, middle cerebral artery Vs, MBFV, and PI in the DCI group were higher than those in non-DCI group. Logistic regression (LR) analysis showed that serum melatonin level (OR=1.796, 95% CI: 1.575-4.123) and middle cerebral artery MBFV (OR=3.279, 95% CI: 2.112-4.720] were the influencing factors for DCI in SAH patients (P<0.05). Middle cerebral artery MBFV and serum melatonin levels were higher in patients with SAH complicated with DCI, and the combination of the 2 could provide a reference for early clinical prediction of DCI in patients with aneurysmal subarachnoid hemorrhage (aSAH).

The value of transcranial Doppler monitoring of cerebral blood flow changes during carotid endarterectomy performed under regional anesthesia - A case series.

Patients with unilateral hemodynamically significant carotid stenosis scheduled for elective CEAs were included. Ultrasound-guided intermediate plexus block was used for regional anesthesia. TCD monitoring of the middle cerebral artery mean blood flow velocity (MCAV) was performed throughout the procedure. MCAVs were offline analyzed during different phases of CEA: (1) resting state, before regional block, (2) after block, before incision, (3) before cross-clamp, (4) after cross-clamp, (5) 5 min after cross-clamp, (6) 10 min after cross-clamp, (7) after declamping, and (8) during the postoperative period (4-6 h). Shunt insertion based on the deterioration of neurological symptoms after cross-clamping was necessary for 11/66 patients (16.6%). In these symptomatic patients, the ipsilateral percent decrease of the MCAV was more than 70% in 8 out of 11 cases (72.7%). In asymptomatic patients, without shunt insertion, the average decrease of MCAV was less than 50%. Neurological symptoms referring to cerebral ischemia may be superior to TCD monitoring of cerebral blood flow for detecting the necessity of a shunt. Regional anesthesia enables reliable, symptom-based monitoring of CEAs.

Middle cerebral artery blood flow stability in response to high-definition transcranial electrical stimulation: A randomized sham-controlled clinical trial

Since neuronal activity is coupled with neurovascular activity, we aimed to analyze the cerebral blood flow hemodynamics during and following high-definition transcranial direct current stimulation (HD-tDCS). We assessed the mean middle cerebral artery blood flow velocity (MCA-BFv) bilaterally using transcranial doppler ultrasound, during and after HD-tDCS, in eleven right-handed healthy adult participants (6 women, 5 men; mean age 31 ± 5.6 years old), with no evidence of brain or cardiovascular dysfunction. The HD-tDCS electrode montage was centered over the right temporo-parietal junction. The stimulation protocol comprised 3 blocks of 2 min at each current intensity (1, 2, and 3 mA) and an inter-stimulus interval of 5 min between blocks. Participants received three electrical stimulation conditions (anode center, cathode center, and sham) on three different days, with an interval of at least 24 h. Stimulation was well tolerated across HD-tDCS conditions tested, and the volunteers reported no significant discomfort related to stimulation. There was no significant difference in the right or the left MCA-BFv during or after the stimulation protocol across all stimulation conditions. We conclude that at a range of intensities, vascular reaction assessed using middle cerebral artery blood flow is not significantly altered during or after HD-tDCS both locally and remotely, which provides further evidence for the safety of HD-tDCS.

Reliability of the transcranial Doppler ultrasound-derived mean flow index for assessing dynamic cerebral autoregulation in healthy volunteers

The transcranial Doppler ultrasound-derived mean flow index (Mxa) is widely used for assessing dynamic cerebral autoregulation (dCA) in different clinical populations. This study aimed at estimating the relative and absolute reliability of Mxa in healthy participants in the supine position and during head-up tilt (HUT). Fourteen healthy participants were examined on two separate occasions during which, mean middle cerebral artery blood flow velocity (MCAv), non-invasive blood pressure, and heart rate were continuously recorded in the supine position and during HUT. Mxa was calculated as the correlation coefficient between mean arterial blood pressure and MCAv using either 3-, 5-, or 10-second averages collected over a 300 second period. Intraclass correlation coefficient (ICC1.1) was calculated to assess relative reliability, while the standard error of measurement (SEM), and limits of agreement (LOA) were used to assess absolute reliability. Mxa-based 3-second averages yielded a similar relative and absolute reliability in both positions. When Mxa was calculated from 5-second averages, the most reliable values were obtained during HUT. The poorest reliability was achieved using 10-second averages, regardless of posture. The Mxa shows fair reliability with acceptable LOA in healthy volunteers when based on 3-second averages, both in the supine position and during HUT.

Preoperative transcranial Doppler and cerebral oximetry as predictors of delirium following valvular heart surgery: a case-control study.

Delirium is a frequent and serious complication after cardiac surgery with cerebral hypoperfusion as one from the key pathophysiological mechanisms. Middle cerebral artery (MCA) mean blood flow velocity (MFV) measured by transcranial Doppler has been used as a marker of cerebral perfusion, and cerebral oximetry (rSO2) value as a marker of its adequacy. This prospective observational trial examined the predictive value of MCA MFV and rSO2, measured immediately before induction of anesthesia, for delirium after valvular heart surgery in elderly patients. In 113 patients, delirium was evaluated for 7days postoperatively, using the confusion assessment method for the intensive care unit. The primary endpoint was the occurrence of postoperative delirium. Overall, 16 patients (14%) exhibited delirium. MCA MVF values could not predict the development of delirium. Preoperative statin use, geriatric depression scale score, and low preoperative rSO2 (< 60%) showed association with delirium occurrence in univariable analysis. After multivariable analysis, only the low preoperative rSO2 (< 60%) (OR 6.748, 95% CI 1.647-27.652, P = 0.008) remained as an independent predictor of delirium. Preoperative MCA MFV was not significantly associated with delirium after valvular heart surgery in elderly patients, while a low baseline rSO2 value was associated with a sevenfold increased risk of delirium.

Effects of Mild Orthostatic Stimulation on Cerebral Pulsatile Hemodynamics.

The augmented cerebral hemodynamic pulsatility could lead to the elevated risk of cerebrovascular disease. To determine the impact of an acute orthostatic challenge on a pulsatile component of cerebral hemodynamics, mild lower body negative pressure (LBNP, -30 mmHg) was applied to 29 men. Middle cerebral artery blood flow velocity (MCAv) was measured by transcranial Doppler technique. Stroke volume (SV) was estimated by the Modelflow method with adjustment by the Doppler ultrasound-measured SV at rest. SV, peak and pulsatile MCAv, and pulsatility index were significantly lower during the LBNP stimulation than those at the baseline (e.g., supine resting) (P < 0.05 for all), whereas mean arterial pressure and mean MCAv remained unchanged. The change in SV with the LBNP stimulation significantly correlated with corresponding changes in peak and pulsatile MCAv (r = 0.617, P < 0.001; r = 0.413, P = 0.026, respectively). These results suggest that pulsatile components of cerebrovascular hemodynamics are dampened during the transient period of orthostatic challenge (as simulated using LBNP) when compared to supine rest, and which is partly due to the modified SV.

Exercise intensity and middle cerebral artery dynamics in humans

Despite its necessity for understanding healthy brain aging, the influence of exercise intensity on cerebrovascular kinetics is currently unknown. We, therefore characterized middle cerebral artery blood flow velocity (MCAv) kinetics associated with two exercise intensities: low and moderate. We hypothesized that increasing exercise intensity would increase the MCAv amplitude response (Amp) and that age and estimated fitness (V̇O2max) would be related to Amp. Baseline (BL) values were collected for 90-seconds followed by a 6-minute exercise bout. Heart rate, end-tidal CO2, mean arterial pressure and MCAv were recorded throughout. MCAv kinetics were described by Amp, time delay (TD) and time constant (τ). Sixty-four adults completed the study. Amp was greater during moderate compared to low exercise intensity (p < 0.001) while no difference was observed in either TD (p = 0.65) or τ (p = 0.47). Amp was negatively associated with age (p < 0.01) and positively correlated with estimated V̇O2max (p < 0.01). Although Amp declines with age, maintaining higher V̇O2max may benefit the cerebrovascular response to exercise.

Cerebral Blood Flow Pulse Is Influenced By Ascending Aortic Flow During Acute Hypotension

PURPOSE: Recently, it has been suggested that cardiac function is one of important physiological factors to determine cerebral blood flow (CBF). However, dynamic relationship between cardiac outflow and CBF is still unknown. The purpose of the present study was to assess the dynamic relationship between arterial blood pressure (BP) or ascending aortic blood flow and CBF. METHODS: Six male healhy subjects participated (age, height, and weight; 33±6 yrs, 173±3 cm, and 72±8 kg) in the present study. Continuous beat-by-beat arterial BP was recorded from a finger using the Penaz method. Ascending aortic blood flow velocity (Ao-BFV) and middle cerebral artery blood flow velocity (MCA-BFV) were continuously measured using supra-sternum and transcranial Doppler ultrasound. After 10 min of resting condition, bilateral thigh cuffs were rapidly inflated to 200 mmHg and maintained for 2 min. Then both cuffs were rapidly deflated, and data were subsequently collected for 1 min. The same measurements were performed in the supine and 45-degree semi- Fowler’s positions. Pearson’s correlation coefficients were calculated to identify the relationship between relative change of BP or Ao-BFV and those of MCA-BFV among individuals. RESULTS: Correlation coefficient of mean BP and mean MCA-BFV was much larger than that of mean Ao-BFV and mean MCA-BFV in both the supine and semi-Fowler’s positions (R=0.615 vs. 0.009 and 0.353 vs. -0.753). In contrast, the correlation coefficient of pulse BP and pulse MCA-BFV was much smaller than that of pulse Ao-BFV and pulse MCA-BFV in the supine position (R=-0.068 vs 0.659), while it was comparable in the semi-Fowler’s position (R=0.555 vs 0.435). CONCLUSIONS: Dynamic change in mean CBF are likely to be only influenced by mean BP. However, dynamic change in pulse CBF seems to be more influenced by that of pulse ascending aortic blood flow rather than pulse BP especially in the supine position.

Influence of sex, menstrual cycle, and oral contraceptives on cerebrovascular resistance and cardiorespiratory function during Valsalva or standing.

Women experience orthostatic intolerance more than men, and they experience faintness more in the early follicular [i.e., low-hormone (LH)] than luteal [i.e., high-hormone (HH)] phase of the menstrual cycle. Men (n = 13, 25.8 ± 1.8 yr old) and women in the LH (days 2-5; placebo) and HH (days 18-24; high dose) phases of the menstrual cycle with (OC; n = 14, 22.0 ± 0.8 yr old) or without (NOC; n = 12, 21.8 ± 0.5 yr old) oral contraceptive (OC) use underwent the Valsalva maneuver and a supine-sit-stand protocol. Blood pressure, normalized stroke volume [stroke volume index (SVi)], cardiac output index, heart rate, end-tidal CO2, and middle cerebral artery (MCA) blood flow velocity were measured. When subjected to the Valsalva maneuver, all women had a greater increase in diastolic and mean MCA blood flow velocity than men (P ≤ 0.065), with no significant effect of menstrual cycle phase or OC use. When subjected to the supine-sit-stand protocol, men had lower MCA blood flow velocity (P < 0.038) than all women, and SVi was higher in men than in the NOC group in all postures (P < 0.011) and in the OC group in the LH phase of the menstrual cycle during standing (P = 0.010). Only men experienced higher resistance index (P < 0.001) and pulsatility index (P < 0.001) with standing. The OC group had lower end-tidal CO2 (P = 0.002) than the NOC group (P = 0.030) and men (P ≤ 0.067). SVi (P = 0.004) and cardiac output index (P = 0.008) were higher in the OC than NOC group. A tendency toward a lower mean MCA blood flow velocity (P = 0.058) and higher SVi (P = 0.059) and pulsatility index (P = 0.058) was noted in the HH than LH phase. Mean arterial pressure was higher in the OC than NOC group in the LH phase (P = 0.049) and lower in the HH than LH phase (P = 0.014). Our results indicate that cycling estrogens/progestins can influence ventilatory, cardiovascular, and/or cerebrovascular physiology.NEW & NOTEWORTHY We have found sex differences in the cerebrovascular response to the Valsalva maneuver and standing. Men have greater cerebral vasoconstriction (or women have greater cerebral vasodilation) during late phase II of the Valsalva maneuver, and the cerebrovascular resistance index increases in men, but not in women, during standing. Furthermore, our findings indicate that both the menstrual cycle phase and oral contraceptive use can influence cardiovascular function both at rest and during active standing.

Middle cerebral artery blood flow velocity during a 4km cycling time trial.

This study sought to describe middle cerebral artery blood flow velocity (MCAv) during a 4km cycling time trial, and relate it to different pacing strategies adopted by participants. After familiarisation and a standardised exercise protocol, 15 male trained cyclists rode a 4km time trial on a cycling ergometer. MCAv was assessed via transcranial Doppler ultrasound in the right hemisphere at resting baseline, and throughout the time trial. Mean arterial pressure, end-tidal partial pressure of carbon dioxide (PetCO2) and heart rate were assessed alongside MCAv. Plasma lactate was assessed post time trial. Data were compared depending upon whether participants completed the time trial with a positive (first half faster than the last) or negative pacing profile although there was no difference in the time to completion with either pacing strategy (positive 344±23s, negative 334±14s; p=0.394). Lower mean MCAv (positive pacing -7.6±14.2%, negative pacing +21.2±15.0% compared to resting baseline measures; p=0.004) and lower PetCO2 (significant interaction p<0.001) towards the end of the time trial were observed with positive compared to negative pacing. Heart rate and lactate did not differ between pacing strategies. Changes in MCAv appear to depend on the pacing strategy adopted, with a positive pacing strategy likely to contribute to a hyperventilatory drop in PetCO2 and subsequent reduction in MCAv. Although lower cerebral blood flow cannot be directly linked to an inability to raise or maintain power output during the closing stages of the time trial, this potential contributor to fatigue is worth further investigation.

OP.3C.05] CHARACTERISTICS OF CEREBRAL HEMODYNAMICS AND CAROTID STIFFNESS IN PATIENTS WITH ISCHEMIC LEUKOARAIOSIS AND NEW ULTRASOUND INDICES OF ISCHEMIC LEUKOARAIOSIS

Objective: Leukoaraiosis (ILA) is believed to be ischaemic in origin due its association with cerebrovascular risk factors and similar location as lacunar infarctions. Its pathophysiology is not well understood and its diagnosis is still based on magnetic resonance imaging (MRI) as well as exclusion of other causes of white matter hyperintensities (WMH). So far there are no known confirming or screening diagnostic tests of ILA. Ultrasound studies have recently shown increased large artery stiffness, increased cerebrovascular resistance and lower cerebral blood flow in ILA patients. Increased arterial stiffness and decreased blood flow could have a synergistic effect and their ratio could be a useful diagnostic index of ILA. Design and method: We used Trans Cerebral Doppler sonography (TCD) and carotid duplex ultrasound to compeare cerebral blood flow and carotid stiffness in 53 ILA patients to 40 risk factor matched controls. The ILA diagnosis was based on head MRI and exclusion of other causes of WMH. Middle cerebral artery (MCA) systolic, diastolic and mean blood flow velocities (v-MCAs, v-MCAd, v-MCAm) and resistance indices (RI, PI) were determined. Carotid stiffness was accessed by pulse wave velocityβ (PWVβ, m/s), pressure–strain elasticity modulus (Ep, kPa) and β index. In addition we introduced new ILA indices (ILAi) that are rations of carotid stiffness parameters and MCA mean blood flow velocity. The diagnostic significance of ILAi for the prediction of ILA was analysed. Results: We found significantly lower diastolic, systolic and mean MCA blood flow velocities and increased carotid stiffness in the ILA group (p < 0,05). Higher pulsatility and resistivity indices of MCA were found in the ILA group, but they did not reached statistical significance. All the ILAi were significantly higher in the ILA group, the most significant was PWVβ/v-ACMm (p = 0.003). All ILAi were allso significantly associated with ILA and were sensitive and specific for predicting ILA (p < 0.05). Conclusions: MCA blood flow velocities are lower and carotid stiffness increased in ILA patients compared to risk factors matched controls. The combination of lower velocities and increased carotid stiffness represented as ILA indices could have a potential diagnostic value for ILA.

Characteristics of Cerebral Hemodynamics in Patients with Ischemic Leukoaraiosis and New Ultrasound Indices of Ischemic Leukoaraiosis

The diagnosis of ischemic leukoaraiosis (ILA) is based on head magnetic resonance imaging (MRI) and exclusion of other causes of white matter hyperintensities (WMHs). Recent studies have shown increased arterial stiffness and diminished carotid flow in ILA patients. So far, there are very little data on intracerebral hemodynamic parameters in ILA. Due to the specific structure of the intracranial arteries, our aim was to investigate intracerebral hemodynamic parameters in ILA patients and, possibly, to find a reliable ultrasound index of combined intra- and extracranial cerebral arteries. We compared different hemodynamic parameters in the middle cerebral artery (MCA) and local carotid stiffness parameters in 53 ILA patients to 40 gender and risk factor-matched controls with normal head MRI. The ILA diagnosis was based on head MRI and exclusion of other causes of WMH. In addition, we introduced new ischemic leukoariosis indices (ILAi) that are ratios of carotid stiffness parameters and MCA mean blood flow velocity. The diagnostic significance of ILAi for the prediction of ILA was analyzed. We found significantly lower diastolic, systolic, and mean MCA blood flow velocities and increased carotid stiffness in the ILA group (P ≤ .05). All ILAi significantly differed between the groups (P < .05), were significantly associated with ILA (P < .01), and were sensitive and specific for predicting ILA (P < .05). MCA blood flow velocities in ILA patients are lower compared to risk factor-matched controls. A combination of lower velocities and increased carotid stiffness represented as ILAi could have a potential diagnostic value for ILA.

Short-arm human centrifugation with 0.4g at eye and 0.75g at heart level provides similar cerebrovascular and cardiovascular responses to standing.

Orthostatic intolerance continues to be a problem with astronauts upon return to Earth as a result of cerebral and cardiovascular adaptations to weightlessness. We tested the hypothesis that artificial gravity from a short-arm human centrifuge (SAHC) could provide cerebral and cardiovascular stimuli similar to upright posture and thereby serve as a suitable countermeasure. We compared cardiovascular and cerebrovascular responses before, during, and after exposure to hyper-G with that of standing in healthy young participants. The head was positioned such that the middle cerebral artery (MCA) was 0.46 m from the center of rotation. Two levels of hyper-G that provided 1g and 2g at foot level were investigated. Continuous blood pressure, heart rate, calf blood volume, MCA mean blood flow velocity (MFV) and end-tidal CO2 were measured. Blood pressure at the level of the MCA (BP-MCA) and MFV was reduced during stand and at 2g. The relationship between MFV and BP-MCA at 2g was different from supine and similar to standing, while 1g centrifugation was not different from supine. The cardiovascular system was also not different from supine at 1g but was similarly challenged in 2g compared to stand. Our data suggest that short-arm centrifugation 2g at the feet, with the head offset 0.5 m from the center, provides similar cardiovascular and cerebral responses to standing. This supports the hypothesis that passive 2g SAHC exposure at the feet could be used as a countermeasure for in-flight cardiovascular and cerebrovascular deconditioning.

Genes count: attenuated cerebral vasodilator capacity in young African Americans

A video slideshow of the Viewpoint by Michael J. White is available here.

Correlation of Cerebral Blood Flow Velocities and Event-related Potentials in Patients with MS

Objective: Studies on the relationship between cerebral blood flow velocities and event related potential (ERP) changes in non-dementia multiple sclerosis (MS) are completely lacking. The aim of the present study was to evaluate the association between cerebral blood flow velocities and ERP parameters in MS patients. Methods: 30 patients (8 male, 22 female,) with a mean age of 37 ± 8 years (range: 21-56) with a diagnosis of relapsing remitting MS according to Mc Donald’s criteria were included. Their mean EDSS score was 1.8 ± 1.7 (range: 0-5.5) and mean duration of disease was 70 ± 64 (range: 3-228) months. The patients were subdivided according to their mean disease duration. The group with the shorter disease duration comprised 15 MS patients who had been diagnosed with MS for less than 5 years(MS-short), and the group with the longer duration comprised 15 patients with disease durations exceeding 5 years(MS-long) Results: In the MS patients, the N200 potentials recorded from the frontal, central, and parietal regions were prolonged relative to the controls and the differences were significant The P300 latencies recorded from the frontal, central and parietal regions were significantly longer in patients with disease durations exceeding 5 years. The mean middle cerebral artery (MCA) blood flow velocities did not differ from those of normal controls. Conclusion: Although there was a negative correlation between MCA velocity and frontal and parietal N100 latencies, there was no clear correlation between MCA blood flow velocity and ERP parameters. An important finding of this study is a positive correlation between MCA blood flow velocity and Mini Mental State Examination scores. This is the first study to evaluate the relationship between ERP and cerebral blood flow velocity using transcranial Doppler ultrasound. No definite relationship was shown.

Intentional Hypertension During Dissection of Carotid Arteries in Endarterectomy Prevents Postoperative Development of New Cerebral Ischemic Lesions Caused by Intraoperative Microemboli

Low blood flow velocity in the middle cerebral artery (MCA) correlates with the development of postoperative cerebral ischemic lesions related to generation of microemboli during dissection of carotid arteries in carotid endarterectomy (CEA). The purpose of this prospectively controlled trial was to determine whether increased mean blood flow velocity in the MCA by intentional hypertension during carotid dissection in CEA prevented postoperative development of new cerebral ischemic lesions caused by intraoperative microemboli. Patients with ipsilateral internal carotid artery stenosis (>70%) underwent CEA under transcranial Doppler monitoring of mean blood flow velocity and microembolic signals in the ipsilateral MCA. Attempts were made to keep systolic blood pressure during carotid dissection between -10% and +10% of the preoperative value (controls, n = 65) or above a +10% increase (intentional hypertension group, n = 65). Incidence of new ischemic lesions on postoperative diffusion-weighted magnetic resonance imaging was significantly lower in the intentional hypertension group both for all patients (controls, 15.4%; intentional hypertension group, 3.1%; P = .03) and in a subgroup of 37 patients showing microembolic signals during carotid dissection (controls, 52.6%; intentional hypertension group, 11.1%; P = .013). Logistic regression analysis demonstrated the absence of intentional hyperperfusion (95% confidence interval: 1.77-100.00; P = .012) and high number of microembolic signals (95% confidence interval: 1.00-1.62; P = .05) during carotid dissection were significant independent predictors of the postoperative development of new ischemic lesions on diffusion-weighted magnetic resonance imaging. Increased MCA mean blood flow velocity by intentional hypertension during dissection of the carotid artery in CEA prevents the postoperative development of new cerebral ischemic lesions caused by intraoperative microemboli.

Transcranial Doppler Ultrasound in the Acute Phase of Aneurysmal Subarachnoid Hemorrhage

Background: Angiographic studies suggest that acute vasospasm within 48 h of aneurysmal subarachnoid hemorrhage (SAH) predicts symptomatic vasospasm. However, the value of transcranial Doppler within 48 h of SAH is unknown. Methods: We analyzed 199 patients who had at least 1 middle cerebral artery (MCA) transcranial Doppler examination within 48 h of SAH onset. Abnormal MCA mean blood flow velocity (mBFV) was defined as >90 cm/s. Delayed cerebral ischemia (DCI) was defined as clinical deterioration or radiological evidence of infarction due to vasospasm. Results: Seventy-six patients (38%) had an elevation of MCA mBFV >90 cm/s within 48 h of SAH onset. The predictors of elevated mBFV included younger age (OR = 0.97 per year of age, p = 0.002), admission angiographic vasospasm (OR = 5.4, p = 0.009) and elevated white blood cell count (OR = 1.1 per 1,000 white blood cells, p = 0.003). Patients with elevated mBFV were more likely to experience a 10 cm/s fall in velocity at the first follow-up than those with normal baseline velocities (24 vs. 10%, p < 0.01), suggestive of resolving spasm. DCI developed in 19% of the patients. An elevated admission mBFV >90 cm/s during the first 48 h (adjusted OR = 2.7, p = 0.007) and a poor clinical grade (Hunt-Hess score 4 or 5, OR = 3.2, p = 0.002) were associated with a significant increase in the risk of DCI. Conclusion: Early elevations of mBFV correlate with acute angiographic vasospasm and are associated with a significantly increased risk of DCI. Transcranial Doppler ultrasound may be an early useful tool to identify patients at higher risk to develop DCI after SAH.

Differential effects of acute hypoxia and high altitude on cerebral blood flow velocity and dynamic cerebral autoregulation: alterations with hyperoxia

We hypothesized that 1) acute severe hypoxia, but not hyperoxia, at sea level would impair dynamic cerebral autoregulation (CA); 2) impairment in CA at high altitude (HA) would be partly restored with hyperoxia; and 3) hyperoxia at HA and would have more influence on blood pressure (BP) and less influence on middle cerebral artery blood flow velocity (MCAv). In healthy volunteers, BP and MCAv were measured continuously during normoxia and in acute hypoxia (inspired O2 fraction = 0.12 and 0.10, respectively; n = 10) or hyperoxia (inspired O2 fraction, 1.0; n = 12). Dynamic CA was assessed using transfer-function gain, phase, and coherence between mean BP and MCAv. Arterial blood gases were also obtained. In matched volunteers, the same variables were measured during air breathing and hyperoxia at low altitude (LA; 1,400 m) and after 1-2 days after arrival at HA ( approximately 5,400 m, n = 10). In acute hypoxia and hyperoxia, BP was unchanged whereas it was decreased during hyperoxia at HA (-11 +/- 4%; P < 0.05 vs. LA). MCAv was unchanged during acute hypoxia and at HA; however, acute hyperoxia caused MCAv to fall to a greater extent than at HA (-12 +/- 3 vs. -5 +/- 4%, respectively; P < 0.05). Whereas CA was unchanged in hyperoxia, gain in the low-frequency range was reduced during acute hypoxia, indicating improvement in CA. In contrast, HA was associated with elevations in transfer-function gain in the very low- and low-frequency range, indicating CA impairment; hyperoxia lowered these elevations by approximately 50% (P < 0.05). Findings indicate that hyperoxia at HA can partially improve CA and lower BP, with little effect on MCAv.

Influence of respiratory instability during neurocardiogenic presyncope on cerebrovascular and cardiovascular dynamics

Objective:To analyse the influence of breathing activity on cerebrovascular dynamics during presyncope.Design:Retrospective study.Setting:University hospital.Patients:38 subjects developing neurocardiogenic syncope (syncope group), and 61 age-matched control subjects with negative tilt.Interventions:Middle cerebral artery...

Cerebral autoregulation is preserved in multiple system atrophy: A transcranial Doppler study

Patients with multiple system atrophy (MSA) present large changes in blood pressure (BP) due to autonomic disturbances. We analyzed how this change may influence dynamic cerebral autoregulation (DCA). Simultaneous recordings of arterial BP (Finapres) and middle cerebral artery (MCA) blood flow velocity (BFV) (transcranial Doppler) were performed in 10 patients with MSA (61 +/- 12 yr of age) and 12 healthy volunteers (61 +/- 11 yr of age): cerebral BFV response to oscillations in mean BP was studied in the supine position by cross-spectral analysis of mean BP and mean MCA BFV. The DCA was also studied during the decrease in BP the first seconds when standing up from a sitting position by the assessment of the cerebrovascular resistance index (CR; mean BP/mean MCA BFV ratio). The MCA BFV/BP cross-spectral analysis showed a phase for the mid-frequency band (0.07-0.2 Hz) significantly larger in MSA, suggesting more active autoregulation in response to larger changes in BP. Changes in CR reflecting the rate of autoregulation, when standing did not differ between the two groups. These data suggest that dynamic cerebral autoregulation is preserved in MSA.