Mean Cerebral Blood Flow Velocity Research Articles

Transcranial Doppler ultrasound measurements of cerebral hemodynamic parameters in healthy volunteers at 2850 meters altitude

BackgroundTranscranial Doppler ultrasound (TDU) is useful in cerebrovascular patients. TDU findings are operator-dependent; they can also be influenced by anatomical and physiological variables as well as by the altitude at which the study is done. ObjectiveTo report the cerebral hemodynamic parameters measured by TDU in subjects who live in Quito, Ecuador (altitude 2850m). Material and methodsWe recruited 47 volunteers with no history or clinical evidence of stroke, hypertension, metabolic disorders, or hematologic disorders; 2 patients were excluded because they did not have a viable cranial window for TDU study. Thus, we recorded mean cerebral blood flow velocity, peak systolic flow velocity, end-diastolic flow velocity, and pulsatility indices in 45 patients (28 (62.2%) women; mean age, 35.9 years). We recorded patients’ age, sex, and hematocrit. We analysed cerebrovascular hemodynamic parameters by sex and age group. ResultsNo significant differences between hemispheres were observed in mean flow velocities, except in the anterior cerebral arteries with right predominance. Flow velocities were higher in women and in the youngest age group. No significant differences in the pulsatility indices were found between sexes or between age groups. The flow velocities in this series are lower than those reported for other series. ConclusionsThe hemodynamic parameters in this series are lower than in other series and are influenced by the altitude, age, and sex.

Effects of Resistance Exercise and Nutritional Supplementation on Dynamic Cerebral Autoregulation in Head-Down Bed Rest.

Head-down bed rest (HDBR) is commonly considered as ground-based analog to spaceflight and simulates the headward fluid shift and cardiovascular deconditioning associated with spaceflight. We investigated in healthy volunteers whether HDBR, with or without countermeasures, affect cerebral autoregulation (CA). Twelve men (at selection: 34 ± 7 years; 176 ± 7 cm; 70 ± 7 kg) underwent three interventions of a 21-day HDBR: a control condition without countermeasure (CON), a condition with resistance vibration exercise (RVE) comprising of squats, single leg heel, and bilateral heel raises and a condition using also RVE associated with nutritional supplementation (NeX). Cerebral blood flow velocity was assessed using transcranial Doppler ultrasonography. CA was evaluated by transfer function analysis and by the autoregulatory index (Mxa) in order to determine the relationship between mean cerebral blood flow velocity and mean arterial blood pressure. In RVE condition, coherence was increased after HDBR. In CON condition, Mxa index was significantly reduced after HDBR. In contrast, in RVE and NeX conditions, Mxa were increased after HBDR. Our results indicate that HDBR without countermeasures may improve dynamic CA, but this adaptation may be dampened with RVE. Furthermore, nutritional supplementation did not enhance or worsen the negative effects of RVE. These findings should be carefully considered and could not be applied in spaceflight. Indeed, the subjects spent their time in supine position during bed rest, unlike the astronauts who perform normal daily activities.

CEREBRAL HEMODYNAMIC CHANGES DURING MODERATE INTENSITY EXERCISE IN OLDER ADULTS WITH HIGH AND NORMAL RESTING PULSATILITY INDEX

A large body of recent evidence shows a substantial overlap exists among abnormality in the pulsatility index (PI) and cognitive decline. PI can be quantified using transcranial Doppler (TCD) measurement of cerebral blood flow velocities (CBFV) in the middle cerebral artery (MCA). PI of the MCA is postulated to reflect the vascular resistance in the arteries distal from the location of acoustic insonation. Higher PI indicates increased arterial rigidity and decreased arterial compliance and it is associated with a clinical diagnosis of Alzheimer disease. Physical exercise is suggested to have a beneficial effect on cognition in older adults. The study aimed to compare cerebral hemodynamic changes during exercise in older adults with normal and high resting PI. We enrolled eighty-one cognitively normal elderly subjects aged from 65 to 86 years old with a Clinical Dementia Rating (CDR) score of 0. TCD envelope, end-tidal carbon dioxide (PETCO2) and beat-to-beat mean arterial blood pressure (MAP) were recorded during moderate intensity exercise. The pulsatility index (PI) for each cardiac cycle during rest was calculated and averaged. The participants were divided into two groups based on the resting PI value: Fifty participants with normal resting PI, and thirty-one with high resting PI. The threshold for normal resting PI was age-adjusted using a formula adapted from the Rotterdam study 0.97 + (0.01*(Participant age - 65)). Percentage change from rest to exercise in TCD parameters, PETCO2, and MAP between the two groups were compared. Both groups showed a significant increase in mean CBFV, PETCO2, and MAP (P=0.01). Participants with normal resting PI showed a significant increase in PI during exercise. No change in PI during exercise was observed in those with high resting PI. This was mainly driven by a significant increase in diastolic velocity (Vd).

Effects of Somatosensory Afferent on Cerebral Hemodynamics during Orthostatic Stimulation

PURPOSE: The effect of somatosensory afferent on the cerebral circulatory control is not clear. This study aimed to reveal whether the somatosensory input from lower extremities can affect cerebral hemodynamic regulation during orthostatic stimulation. METHODS: Eleven young adults (4 women) underwent two consecutive 6-min lower body negative pressure (LBNP) stimulations (-30 mmHg and -50 mmHg) under following two conditions: hanging up the body by a harness (leg-free) and bracing feet on the wood board in the LBNP chamber with slight knee flexion (leg-resisted) against suction. These conditions were conducted in random order. Heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), end-tidal CO2 (EtCO2), and cerebral blood flow velocity (CBFv) from the middle cerebral artery were continuously recorded. Dynamic cerebral autoregulation (dCA) was evaluated by transfer function analysis. RESULTS: HR was significantly higher, and CO and EtCO2 were significantly lower during -50 mmHg of LBNP stimulation than each baseline value irrespective of leg conditions, whereas MAP and mean CBFv remained at similar levels throughout the LBNP stimulation under both leg conditions. Power spectral density of mean CBFv in the low-frequency range (0.07-0.2 Hz) significantly increased at -30 and -50 mmHg of LBNP stimulations in the leg-resisted condition (from 1.41 ±0.62 to 5.42±3.27 and 5.19±3.46) but not in the leg-free condition. Likewise, transfer function gain in the low-frequency range were significantly augmented at -30 and -50 mmHg of LBNP stimulations in the leg-resisted condition (from 1.22±0.34 to 1.58±0.39 and 1.56±0.43) but not in the leg-free condition. CONCLUSIONS: These results suggest that somatosensory afferent from lower extremities may modify cerebral hemodynamic regulation during orthostatic stimulation.

Causality analysis reveals the link between cerebrovascular control and acute kidney dysfunction after coronary artery bypass grafting

Background: Patients undergoing coronary artery bypass graft (CABG) surgery might experience postoperative complications and some of them, such as acute kidney dysfunction (AKD), are the likely consequence of hypoperfusion. We hypothesized that an impaired cerebrovascular control is a hallmark of a vascular damage that might favor AKD after CABG. Objective: Our aim is to characterize cerebrovascular control in CABG patients through the assessment of the relationship between mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV) and to check whether markers describing MCBFV-MAP dynamical interactions could identify subjects at risk to develop postoperative AKD. Approach: MAP and MCBFV beat-to-beat series were extracted from invasive arterial pressure and transcranial Doppler recordings acquired simultaneously in 23 patients just before CABG after the induction of propofol general anesthesia. Subjects were divided into AKD group (n = 9, age: 68 ± 9, 8 males) and noAKD group (n = 14, age: 65 ± 8, 12 males) according to whether they developed postoperative AKD or not after CABG. We computed MAP and MCBFV time-domain and spectral markers as well as MCBFV-MAP cross-spectral indexes in very-low-frequency (VLF, 0.02–0.07 Hz), low-frequency (LF, 0.07–0.15 Hz) and high-frequency (HF, 0.15–0.30 Hz) bands. We also calculated model-based transfer entropy (TE) to quantify the degree of MCBFV dependence on MAP and vice versa. The null hypothesis of MCBFV-MAP uncoupling was tested via a surrogate approach associating MAP and MCBFV in different patients. Main results: Time, spectral and cross-spectral markers had a limited power in separating AKD from noAKD individuals. Conversely, TE from MAP to MCBFV was significantly above the level set by surrogates only in AKD groups and significantly larger than that computed in noAKD. Significance: The reduced cerebrovascular autoregulation in AKD patients suggest a vascular impairment likely making them more at risk of hypoperfusion during CABG and AKD after CABG.

Parámetros hemodinámicos cerebrales, determinados mediante Doppler transcraneal, en un grupo de voluntarios sanos a 2.850 metros de altura

BackgroundTranscranial Doppler ultrasound (TDU) is useful in cerebrovascular patients. TDU findings are operator-dependent; they can also be influenced by anatomical and physiological variables as well as by the altitude at which the study is done. ObjectiveTo report the cerebral hemodynamic parameters measured by TDU in subjects who live in Quito, Ecuador (altitude 2850 meters). Material and methodsWe recruited 47 volunteers with no history or clinical evidence of stroke, hypertension, metabolic disorders, or hematologic disorders; 2 patients were excluded because they did not have a viable cranial window for TDU study. Thus, we recorded mean cerebral blood flow velocity, peak systolic flow velocity, end-diastolic flow velocity, and pulsatility indices in 45 patients (28 (62.2%) women; mean age, 35.9 years). We recorded patients’ age, sex, and hematocrit. We analyzed cerebrovascular hemodynamic parameters by sex and age group. ResultsNo significant differences between hemispheres were observed in mean flow velocities, except in the anterior cerebral arteries with right predominance. Flow velocities were higher in women and in the youngest age group. No significant differences in the pulsatility indices were found between sexes or between age groups. The flow velocities in this series are lower than those reported for other series. ConclusionsThe hemodynamic parameters in this series are lower than in other series and are influenced by the altitude, age, and sex.

Cross-Frequency Coupling Between Cerebral Blood Flow Velocity and EEG in Ischemic Stroke Patients With Large Vessel Occlusion.

Background: Neurovascular coupling enables a rapid adaptation of cerebral blood flow (CBF) to support neuronal activities. Whether this mechanism is compromised during the acute phase after ischemic stroke remains unknown. In this study, we applied a phase-amplitude cross-frequency coupling (PAC) algorithm to investigate multimodal neuro signals including CBF velocity (CBFV), and electroencephalography (EEG).Methods: Acute ischemic stroke patients admitted to the Neurointensive Care Unit, Tiantan Hospital, Capital Medical University (Beijing, China) with continuous monitoring of 8-lead EEG (F3-C3, T3-P3, P3-O1, F4-C4, T4-P4, P4-O2), non-invasive arterial blood pressure (ABP), and bilateral CBFV of the middle cerebral arteries or posterior cerebral arteries were retrospectively analyzed. PAC was calculated between the phase of CBFV in frequency bands (0–0.05 and 0.05–0.15 Hz) and the EEG amplitude in five bands (δ, θ, α, β, γ). The global PAC was calculated as the sum of all PACs across the six EEG channels and five EEG bands for each patient. The hemispherical asymmetry of cross-frequency coupling (CFC) was calculated as the difference between left and right PAC.Results: Sixteen patients (3 males) met our inclusion criteria. Their age was 60.9 ± 7.9 years old. The mean ABP, mean left CBFV, and mean right CBFV were 90.2 ± 31.2 mmHg, 57.3 ± 20.6 cm/s, and 68.4 ± 20.9 cm/s, respectively. The PAC between CBFV and EEG was significantly higher in β and γ bands than in the other three bands. Occipital region (P3-O1 and P4-O2 channels) showed stronger PAC than the other regions. The deceased group tended to have smaller global PAC than the survival group (the area under the receiver operating characteristic curve [AUROC] was 0.81, p = 0.57). The unfavorable outcome group showed smaller global PAC than the favorable group (AUROC = 0.65, p = 0.23). The PAC asymmetry between the two brain hemispheres correlates with the degree of stenosis in stroke patients (p = 0.01).Conclusion: We showed that CBFV interacts with EEG in β and γ bands through a phase-amplitude CFC relationship, with the strongest PAC found in the occipital region and that the degree of hemispherical asymmetry of CFC correlates with the degree of stenosis.

Effects of Alternating Standing and Sitting Compared to Prolonged Sitting on Cerebrovascular Hemodynamics.

Previous research suggests that prolonged sitting may acutely reduce cerebral blood flow velocity (CBFv). The purpose of this study was to evaluate the effects of alternating standing and sitting vs prolonged sitting on CBFv. This randomized crossover study enrolled working adults (N=25) with pre-to-stage 1 hypertension not using antihypertensive medications, and a body mass index from 25 to < 40 kg/m2. Subjects participated in two simulated workday conditions: 1) sitting continuously (SIT), and 2) alternating standing and sitting every 30 min (SS). Beat-to-beat systolic, mean and diastolic CBFv were recorded bilaterally for 1 min via insonation of the middle cerebral artery using transcranial Doppler ultrasonography before (morning), between (midday) and following (afternoon) two 3-hr 40 min work periods. Mean±SD age was 42±12 years, blood pressure (BP) was 132±9/83±8 mmHg, and BMI was 32±5 kg/m2. Cerebrovascular hemodynamics did not differ across condition (P>0.05). There were, however, significant nonlinear effects of time (decrease from morning to midday; increase from midday to afternoon) on systolic CBFv (P=0.014), mean CBFv (P=0.001), diastolic CBFv (P=0.002), and pulsatility index (P=0.038). When overall time effects were evaluated during each time interval, mean and diastolic CBFv significantly decreased morning to midday and all CBFv increased from midday to afternoon. When separated by condition, significant time effects were observed for all CBFv during SIT (P<0.02) but not SS (P>0.05). In individuals with elevated BP and BMI, CBFv significantly decreased by midday and increased by afternoon, especially during a workday of prolonged sitting. Future studies should evaluate the combination of frequent walks and a sit-stand desk to break up prolonged sitting.

Dynamic Cerebral Autoregulation and Critical Closing Pressure in Experimental Human Endotoxemia and Sepsis Patients

Background: To investigate the influence of systemic inflammation on dynamic cerebral autoregulation and vascular tone during experimental human endotoxemia and sepsis. Methods: Healthy volunteers received 3 h continuous infusion of LPS (c-LPS, 4 ng/kg, n = 11, Clinicaltrials.gov NCT02922673) or a bolus of LPS (b-LPS, 2 ng/kg, n = 8, Clinicaltrials.gov NCT02675868) and 10 sepsis patients were studied. Mean arterial pressure (MAP) and cerebral blood flow velocity (CBFV) were monitored simultaneously. Cerebral autoregulation was analysed by transfer function analysis (TFA). Critical closing pressure (CrCP) was estimated as a measure of cerebral vascular tone. Results: c-LPS resulted in a more pronounced and prolonged plasma cytokine response compared with b-LPS. MAP decreased from 89 ± 3 to 75 ± 2 mmHg (p < 0.05) and from 91 ± 2 to 77 ± 3 mmHg (p < 0.001) in the c-LPS and b-LPS groups, respectively. MAP in sepsis patients was 65 ± 4 mmHg. TFA in both LPS groups showed no significant changes over time in coherence, gain and phase. Phase in sepsis patients was lower compared with both LPS groups (7 (2 to 33) [median (interquartile range)] in sepsis versus 57 (36 to 74) in the c-LPS (p = 0.02) and 53 (43 to 64) degrees in the b-LPS group (p = 0.01)). CrCP decreased from 49 ± 2 to 41 ± 2 mmHg (p = 0.16) in the c-LPS and from 50 ± 2 to 42 ± 2 mmHg in the b-LPS group (p < 0.01), and was 36 ± 2 mmHg in sepsis patients. Conclusions: Dynamic cerebral autoregulation is impaired in sepsis patients, but remains intact during experimental human endotoxemia. CrCP decreased during endotoxemia and was low in sepsis, reflecting decreased vascular tone. This indicates activation of a cerebrovascular adaptive process, also during experimental endotoxemia with intact cerebral autoregulation. Trial Registration: Clinicaltrials.gov NCT02922673 and Clinicaltrials.gov NCT02675868

Inter-subject analysis of transfer function coherence in studies of dynamic cerebral autoregulation

Objective: The gain and phase of the arterial blood pressure (BP)-cerebral blood flow velocity (CBFV) relationship, assessed by transfer function analysis (TFA), are widely used dynamic cerebral autoregulation (CA) metrics, but their reliability depend on the statistical significance of the magnitude squared coherence (MSC) function. We tested a new approach, based on inter-subject data, to estimate the confidence limits of MSC. Approach: Five minute beat-to-beat time series of mean arterial BP (MAP, Finometer) and CBFV (transcranial Doppler) were used for intra-subject (MAP and CBFV from same subject) and inter-subject (BP and CBFV swapped between subjects) estimates of MSC. The 95% confidence limit of MSC was obtained by non-parametric methods for the cases of single frequency harmonics in the range (0.02–0.50 Hz), and also from the mean value of all possible frequency intervals in this range. Main results: Intra-subject estimates of MSC were obtained from 100 healthy subjects (48 female, age range: 21–82 years old) allowing calculation of 9900 inter-subject estimates, with 95% confidence limits in excellent agreement with classical values derived from surrogate random data. Confidence limits of MSC, derived from mean values, decreased asymptotically to around 0.16 with the increasing number of harmonics averaged. Significance: Replacing estimates of MSC at a single frequency harmonic by the mean calculated over the range (0.02–0.30 Hz) could lead to more robust studies of dynamic CA with greater acceptance of recordings, an important consideration in clinical studies where measurements tend to be more susceptible to noise and artefacts.

Efeitos do sulfato de magnésio e da milrinona sobre o vasoespasmo cerebral após hemorragia subaracnoidea por aneurisma: estudo randômico

BackgroundAneurysmal subarachnoid hemorrhage is an important cause of premature death and disability worldwide. Magnesium sulphate is shown to have a neuroprotective effect and it reverses cerebral vasospasm. Milrinone is also used in the treatment of cerebral vasospasm. The aim of the present study was to compare the effect of prophylactic magnesium sulphate and milrinone on the incidence of cerebral vasospasm after subarachnoid hemorrhage. MethodsThe study included 90 patients with aneurysmal subarachnoid hemorrhage classified randomly (by simple randomization) into two groups: magnesium sulphate was given as an infusion of 500mg.day−1 without loading dose for 21 days. Group B: milrinone was given as an infusion of 0.5μg.kg−1.min−1 without loading dose for 21 days. The cerebral vasospasm was diagnosed by mean cerebral blood flow velocity in the involved cerebral artery (mean flow velocity≥120cm.s−1), neurological deterioration by Glasgow coma scale, or angiography (the decrease in diameter of the involved cerebral artery >25%). ResultsThe mean cerebral blood flow velocity decreased significantly in the magnesium group compared to milrinone group through Day 7, Day 14 and Day 21 (p<0.001). The incidence of cerebral vasospasm decreased significantly with magnesium compared to milrinone (p=0.007). The Glasgow coma scale significantly improved in the magnesium group compared to milrinone group through Day 7, Day 14 and Day 21 (p=0.036, p=0.012, p=0.016, respectively). The incidence of hypotension was higher with milrinone than magnesium (p=0.012). ConclusionsThe incidence of cerebral vasospasm after aneurysmal subarachnoid hemorrhage was significantly lower and Glasgow coma scale significantly better with magnesium when compared to milrinone. Milrinone was associated with a higher incidence of hypotension and requirement for dopamine and norepinephrine when compared to magnesium.

Effect of magnesium sulphate and milrinone on cerebral vasospasm after aneurysmal subarachnoid hemorrhage: a randomized study

BackgroundAneurysmal subarachnoid hemorrhage is an important cause of premature death and disability worldwide. Magnesium sulphate is shown to have a neuroprotective effect and it reverses cerebral vasospasm. Milrinone is also used in the treatment of cerebral vasospasm. The aim of the present study was to compare the effect of prophylactic magnesium sulphate and milrinone on the incidence of cerebral vasospasm after subarachnoid hemorrhage. MethodsThe study included 90 patients with aneurysmal subarachnoid hemorrhage classified randomly (by simple randomization) into two groups: magnesium sulphate was given as an infusion of 500mg.day−1 without loading dose for 21 days. Group B: milrinone was given as an infusion of 0.5μg.kg−1.min−1 without loading dose for 21 days. The cerebral vasospasm was diagnosed by mean cerebral blood flow velocity in the involved cerebral artery (mean flow velocity≥120cm.s−1), neurological deterioration by Glasgow coma scale, or angiography (the decrease in diameter of the involved cerebral artery >25%). ResultsThe mean cerebral blood flow velocity decreased significantly in the magnesium group compared to milrinone group through Day 7, Day 14 and Day 21 (p<0.001). The incidence of cerebral vasospasm decreased significantly with magnesium compared to milrinone (p=0.007). The Glasgow coma scale significantly improved in the magnesium group compared to milrinone group through Day 7, Day 14 and Day 21 (p=0.036, p=0.012, p=0.016, respectively). The incidence of hypotension was higher with milrinone than magnesium (p=0.012). ConclusionsThe incidence of cerebral vasospasm after aneurysmal subarachnoid hemorrhage was significantly lower and Glasgow coma scale significantly better with magnesium when compared to milrinone. Milrinone was associated with a higher incidence of hypotension and requirement for dopamine and norepinephrine when compared to magnesium.

Hypertonic Lactate to Improve Cerebral Perfusion and Glucose Availability After Acute Brain Injury*

Lactate promotes cerebral blood flow and is an efficient substrate for the brain, particularly at times of glucose shortage. Hypertonic lactate is neuroprotective after experimental brain injury; however, human data are limited. Prospective study (clinicaltrials.gov NCT01573507). Academic ICU. Twenty-three brain-injured subjects (13 traumatic brain injury/10 subarachnoid hemorrhage; median age, 59 yr [41-65 yr]; median Glasgow Coma Scale, 6 [3-7]). Three-hour IV infusion of hypertonic lactate (sodium lactate, 1,000 mmol/L; concentration, 30 µmol/kg/min) administered 39 hours (26-49 hr) from injury. We examined the effect of hypertonic lactate on cerebral perfusion (using transcranial Doppler) and brain energy metabolism (using cerebral microdialysis). The majority of subjects (13/23 = 57%) had reduced brain glucose availability (baseline pretreatment cerebral microdialysis glucose, < 1 mmol/L) despite normal baseline intracranial pressure (10 [7-15] mm Hg). Hypertonic lactate was associated with increased cerebral microdialysis lactate (+55% [31-80%]) that was paralleled by an increase in middle cerebral artery mean cerebral blood flow velocities (+36% [21-66%]) and a decrease in pulsatility index (-21% [13-26%]; all p < 0.001). Cerebral microdialysis glucose increased above normal range during hypertonic lactate (+42% [30-78%]; p < 0.05); reduced brain glucose availability correlated with a greater improvement of cerebral microdialysis glucose (Spearman r = -0.53; p = 0.009). No significant changes in cerebral perfusion pressure, mean arterial pressure, systemic carbon dioxide, and blood glucose were observed during hypertonic lactate (all p > 0.1). This is the first clinical demonstration that hypertonic lactate resuscitation improves both cerebral perfusion and brain glucose availability after brain injury. These cerebral vascular and metabolic effects appeared related to brain lactate supplementation rather than to systemic effects.

Pooling data from different populations: should there be regional differences in cerebral haemodynamics?

BackgroundThough genetic and environmental determinants of systemic haemodynamic have been reported, surprisingly little is known about their influences on cerebral haemodynamics. We assessed the potential geographical effect on cerebral haemodynamics by comparing the individual differences in cerebral blood flow velocity (CBFv), vasomotor tone (critical closing pressure- CrCP), vascular bed resistance (resistance-area product- RAP) and cerebral autoregulation (CA) mechanism on healthy subjects and acute ischaemic stroke (AIS) patients from two countries.MethodsParticipants were pooled from databases in Leicester, United Kingdom (LEI) and São Paulo, Brazil (SP) research centres. Stroke patients admitted within 48 h of ischaemic stroke onset, as well as age- and sex-matched controls were enrolled. Beat-to-beat blood pressure (BP) and bilateral mean CBFv were recorded during 5 min baseline. CrCP and RAP were calculated. CA was quantified using transfer function analysis (TFA) of spontaneous oscillations in arterial BP and mean CBFv, and the derived autoregulatory index (ARI).ResultsA total of 100 participants (50 LEI and 50 SP) were recruited. No geographical differences were found. Both LEI and SP AIS participants showed lower values of CA compared to controls. Moreover, the affected hemisphere presented lower resting CBFv and higher RAP compared to the unaffected hemisphere in both populations.ConclusionsImpairments of cerebral haemodynamics, demonstrated by several key parameters, was observed following AIS compared to controls irrespective of geographical region. These initial results should encourage further research on cerebral haemodynamic research with larger cohorts combining different populations.

Impaired Cerebral Vasomotor Reactivity in Alzheimer's Disease.

Background Recent studies have shown that cerebral vascularity may be impaired in Alzheimer's disease. Cerebral vasomotor reactivity could be an important biomarker for this pathology. Aims The aim of this study was to investigate the alterations in cerebral vascular motor reactivity in Alzheimer's disease subjects and to associate these changes with their cognitive scores. Methods We recruited subjects with a diagnosis of Alzheimer's disease and healthy controls. Demographic, clinical, imaging, and cognitive test were obtained. Then all participants performed a cerebral vascular motor reactivity test with 7% CO2 and cerebral blood flow velocities (CBFV) were recorded with transcranial doppler ultrasound before and after the test. Results We recruited 45 subjects, 26 (21 female) Alzheimer's disease participants and 19 (15 female) healthy controls. There were no differences in baseline cerebral blood flow velocities between the groups. After the cerebral vasomotor reactivity test, absolute mean difference in mean CBFV (ΔCBFV-m) was 8.70±4.14 versus 4.81±6.96 (p<0.01), respectively. Calculated percentage of change (%CVMR) was lower in the AD group 7.45±18.25 versus 23.29±17.48, and there was a positive but weak correlation with mini-mental scores (ρ=0.337, p=0.023). Conclusions In this study, Alzheimer's disease subjects showed significant changes in all absolute cerebral blood flow velocities after the cerebral vasomotor reactivity test with CO2, but only diastolic phase responses were statistically significant. There was a positive but weak correlation between cerebral vasomotor reactivity and cognitive scores. Further studies are needed to investigate these effects in larger Latin-American samples.

Time-Dependent Changes in Cerebral Blood Flow and Arterial Pressure During Mild +Gz Hypergravity.

Artificial hypergravity has been proposed to prevent or treat various forms of physiological deconditioning experienced during spaceflight. We have previously reported that cerebral blood flow decreased at 15-21 min of +1.5-Gz centrifugation without decreases in arterial pressure at heart level. We reanalyzed our previous data to clarify time-dependent changes in cerebral blood flow and arterial pressure during mild +Gz hypergravity. We reanalyzed data for 0-20 min during +1.5-Gz centrifugation on 13 male subjects for whom physiological data were steadily recorded. Mean cerebral blood flow velocity in the middle cerebral artery (MCBFVMCA), mean arterial pressure at heart level (MAPheart), and middle cerebral artery level (MAPMCA) during centrifugation were averaged every 5 min and compared with prehypergravity data (+1.0 Gz, 5 min). MAPheart did not change significantly, but MAPMCA decreased significantly throughout centrifugation compared to prehypergravity data (-16.7% to -24.7%). MCBFVMCA tended to be decreased at 0-5 min of +1.5-Gz centrifugation (-3.3%), but this was not statistically significant. MCBFVMCA was significantly decreased at 5-10 min (-5.5%). MCBFVMCA at 10-15 min and 15-20 min were also significantly decreased to almost the same level (-6.9% and -6.8%, respectively). No significant change in MAPheart was detected, whereas MAPMCA decreased significantly from the beginning of +1.5-Gz centrifugation. On the other hand, MCBFVMCA gradually decreased and became roughly flat in the latter half of 20-min centrifugation. Understanding the different time-dependent changes in cerebral blood flow and arterial pressure under mild +Gz hypergravity might be important for implementation of centrifuging as a countermeasure for spaceflight-induced deconditioning.Konishi T, Kurazumi T, Kato T, Takko C, Ogawa Y, Iwasaki K. Time-dependent changes in cerebral blood flow and arterial pressure during mild +Gz hypergravity. Aerosp Med Hum Perform. 2018; 89(9):787-791.

Short-term external counterpulsation augments cerebral blood flow and tissue oxygenation in chronic cerebrovascular occlusive disease.

Background and purposeExternal counterpulsation improves cerebral perfusion velocity in acute stroke and may stimulate collateral artery growth. However, whether (non‐acute) at‐risk patients with high‐grade carotid artery disease may benefit from counterpulsation needs to be validated.MethodsTwenty‐eight patients (71 ± 6.5 years, five women) with asymptomatic unilateral chronic severe internal carotid artery stenosis (>70%) or occlusion were randomized to receive 20 min active counterpulsation followed by sham treatment or vice versa. Cerebral blood flow velocity (CBFV) (measured bilaterally by transcranial middle cerebral artery Doppler), tissue oxygenation index (TOI) (measured over the bilateral prefrontal cortex by near‐infrared spectroscopy) and cerebral hemodynamic parameters, such as relative pulse slope index (RPSI), were monitored.ResultsIpsilateral mean CBFV (ΔV mean +3.5 ± 1.2 cm/s) and tissue oxygenation (ΔTOI +2.86 ± 0.8) increased significantly during active counterpulsation compared to baseline, whilst the sham had little effect (ΔV mean +1.13 ± 1.1 cm/s; ΔTOI +1.25 ± 0.65). On contralateral sides, neither counterpulsation nor sham control had any effect on either parameter. During counterpulsation, early dynamic changes in ΔRPSI of the ipsilateral CBFV signal predicted improved tissue oxygenation during counterpulsation (odds ratio 1.179, 95% confidence interval 1.01–1.51), whilst baseline cerebrovascular reactivity to hypercapnia failed to show an association.ConclusionsIn patients with high‐grade carotid disease, ipsilateral cerebral oxygenation and blood flow velocity are increased by counterpulsation. This is a necessary condition for the stimulation of regenerative collateral artery growth and thus a therapeutic concept for the prevention of cerebral ischaemia. This study provides a rationale for further clinical investigations on the long‐term effects of counterpulsation on cerebral hemodynamics and collateral growth.

Design and Validation of an FPGA-Based Configurable Transcranial Doppler Neurofeedback System for Chronic Pain Patients.

Neurofeedback is a self-regulation technique that can be applied to learn to voluntarily control cerebral activity in specific brain regions. In this work, a Transcranial Doppler-based configurable neurofeedback system is proposed and described. The hardware configuration is based on the Red Pitaya board, which gives great flexibility and processing power to the system. The parameter to be trained can be selected between several temporal, spectral, or complexity features from the cerebral blood flow velocity signal in different vessels. As previous studies have found alterations in these parameters in chronic pain patients, the system could be applied to help them to voluntarily control these parameters. Two protocols based on different temporal lengths of the training periods have been proposed and tested with six healthy subjects that were randomly assigned to one of the protocols at the beginning of the procedure. For the purposes of the testing, the trained parameter was the mean cerebral blood flow velocity in the aggregated data from the two anterior cerebral arteries. Results show that, using the proposed neurofeedback system, the two groups of healthy volunteers can learn to self-regulate a parameter from their brain activity in a reduced number of training sessions.

Cerebral Haemodynamics following Acute Ischaemic Stroke: Effects of Stroke Severity and Stroke Subtype

Background: Acute ischaemic stroke (AIS) patients often show impaired cerebral autoregulation (CA). We tested the hypothesis that CA impairment and other alterations in cerebral haemodynamics are associated with stroke subtype and severity. Methods: AIS patients (n = 143) were amalgamated from similar studies. Data from baseline (< 48 h stroke onset) physiological recordings (beat-to-beat blood pressure [BP], cerebral blood flow velocity (CBFV) from bilateral insonation of the middle cerebral arteries) were calculated for mean values and autoregulation index (ARI). Differences were assessed between stroke subtype (Oxfordshire Community Stroke Project [OCSP] classification) and severity (National Institutes of Health Stroke Scale [NIHSS] score < 5 and 5–25). Correlation coefficients assessed associations between NIHSS and physiological measurements. Results: Thirty-two percent of AIS patients had impaired CA (ARI < 4) in affected hemisphere (AH) that was similar between stroke subtypes and severity. CBFV in AH was comparable between stroke subtype and severity. In unaffected hemisphere (UH), differences existed in mean CBFV between lacunar and total anterior circulation OCSP subtypes (42 vs. 56 cm•s^–1, p < 0.01), and mild and moderate-to-severe stroke severity (45 vs. 51 cm•s^–1, p = 0.04). NIHSS was associated with peripheral (diastolic and mean arterial BP) and cerebral haemodynamic parameters (CBFV and ARI) in the UH. Conclusions: AIS patients with different OCSP subtypes and severity have homogeneity in CA capability. Cerebral haemodynamic measurements in the UH were distinguishable between stroke subtype and severity, including the association between deteriorating ARI in UH with stroke severity. More studies are needed to determine their clinical significance and to understand the determinants of CA impairment in AIS patients.

No long-term impairment of cerebral autoregulation after preeclampsia.

Preeclampsia is a pregnancy-related hypertensive disorder with strongly impaired cerebral autoregulation in the acute stage. A history of preeclampsia is an independent cardiovascular and cerebrovascular risk factor. It is unclear whether impaired cerebral autoregulation persists after preeclampsia and thus contributes to the known increased cerebrovascular morbidity. Using transcranial Doppler, we compared cerebral hemodynamics and dynamic cerebral autoregulation of 25 women with a history of severe preeclampsia and 25 healthy mothers, on average 2-3 years postpartum. Mean arterial blood pressure (MAP) and cerebral blood flow velocities (CBFV) in the middle and posterior cerebral artery were recorded at rest, dynamic cerebral autoregulation was assessed via transfer function phase and gain between oscillations of CBFV and MAP during regular breathing at 0.1 Hz. MAP and body mass index were higher in former preeclamptic women compared with healthy mothers (p-value <0.001 and 0.006, respectively). CBFV in the middle cerebral artery was slightly increased in former preeclamptic women compared with healthy mothers (p-value 0.004), intima-media thickness (IMT) of the common carotid artery was higher by trend (p-value 0.065). Dynamic cerebral autoregulation was not impaired in women with a history of preeclampsia, phase even tended to be higher than in healthy mothers. Dynamic cerebral autoregulation is not persistently impaired in women after severe preeclampsia. Long-term cerebrovascular changes rather result from a higher incidence of cerebrovascular risk factors in women with a history of preeclampsia.