Changes In Blood Flow Velocity Research Articles

Cerebrovascular hemodynamics association with brain structure and function in Multiple Sclerosis

BackgroundVascular risk factors seem to contribute to disease progression in Multiple Sclerosis (MS), but the mechanistic connection between vascular risk and MS is unknown. Understanding cerebrovascular hemodynamics (CVH) in MS may help advance our understanding of the link between vascular risk and MS. ObjectivesExamine the relationship between CVH [dynamic cerebral autoregulation (dCA) and vasoreactivity (VR)] and brain structure (MRI) and function (cognition, and gait) in individuals with MS. MethodsTranscranial Doppler ultrasound (TCD) was utilized to assess two key markers of CVH: dCA and VR. dCA (reported as phase and gain) is calculated from the spontaneous blood pressure and flow velocity oscillations. VR is calculated as the slope of change in cerebral blood flow velocity in response to end-tidal CO2. Global gray matter (GM), white matter (WM), WM hyperintensity (WMH) volumes and WM lesion counts were measured from brain MRI. All participants underwent detailed cognitive and gait assessments. ResultsEighty participants were included (age 44 ± 11, 26 % male); 75 had relapsing-remitting MS (94 %), with disease duration of 8 (11) years [median (IQR)] since MS diagnosis and an Expanded Disability Status Scale (EDSS) of 2.0 (4.0). Higher phase (better dCA) was associated with greater GM volume, lower WHM burden and higher cognitive scores in the memory and global cognitive domains (all P values <0.05). There was no relationship between CVH and gait speed in our study participants. There was no relationship between VR and any measures of brain structure and function. ConclusionsMore efficient cerebral autoregulation is associated with better brain structure (larger GM and lower WMH volumes) and function (cognition, but not gait) in patients with MS.

Multi-Modal Assessment of Cerebral Hemodynamics in Resuscitated Out-of-Hospital Cardiac Arrest Patients: A Case-Series.

We assessed the feasibility of concurrent monitoring of cerebral hemodynamics in adult, comatose out-of-hospital cardiac arrest (OHCA) patients admitted to the National University Heart Centre Singapore from October 2021 to August 2023. Patients underwent continuous near-infrared spectroscopy (NIRS) monitoring in the first 72 h after return of spontaneous circulation (ROSC) and 30-min transcranial Doppler ultrasound (TCD) monitoring at least once. With constant mechanical ventilatory settings and continuous electrocardiographic, pulse oximeter and end-tidal carbon dioxide monitoring, blood pressure was manipulated via vasopressors and cerebral autoregulation assessed by measuring changes in regional cerebral oxygenation (NIRS) and cerebral blood flow velocities (TCD) in response to changes in mean arterial pressure. The primary outcome was neurological recovery at hospital discharge. Amongst the first 16 patients (median age 61, 94% males), we observed four unique patterns: preserved cerebral autoregulation, loss of cerebral autoregulation, cardio-cerebral asynchrony and cerebral circulatory arrest. Patients with preserved cerebral autoregulation had lower levels of neuro-injury biomarkers (neurofilaments light and heavy) and the majority (86%) were discharged with good neurological recovery. Multi-modal assessment of cerebral hemodynamics after OHCA is feasible and derived patterns correlated with neurological outcomes. The between- and within-patient heterogeneity in cerebral hemodynamics calls for more research on individualized treatment strategies.

Age and dose dependent changes to the bone and bone marrow microenvironment after cytotoxic conditioning with busulfan.

Preparative regimens before Hematopoietic Cell Transplantation (HCT) damage the bone marrow (BM) microenvironment, potentially leading to secondary morbidity and even mortality. The precise effects of cytotoxic preconditioning on bone and BM remodeling, regeneration, and subsequent hematopoietic recovery over time remain unclear. Moreover, the influence of recipient age and cytotoxic dose have not been fully described. In this study, we longitudinally investigated bone and BM remodeling after busulfan treatment with low intensity (LI) and high intensity (HI) regimens as a function of animal age. As expected, higher donor chimerism was observed in young mice in both LI and HI regimens compared to adult mice. Noticeably in adult mice, significant engraftment was only observed in the HI group. The integrity of the blood-bone marrow barrier in calvarial BM blood vessels was lost after busulfan treatment in the young mice and remained altered even 6weeks after HCT. In adult mice, the severity of vascular leakage appeared to be dose-dependent, being more pronounced in HI compared to LI recipients. Interestingly, no noticeable change in blood flow velocity was observed following busulfan treatment. Ex vivo imaging of the long bones revealed a reduction in the frequency and an increase in the diameter and density of the blood vessels shortly after treatment, a phenomenon that largely recovered in young mice but persisted in older mice after 6weeks. Furthermore, analysis of bone remodeling indicated a significant alteration in bone turnover at 6weeks compared to earlier timepoints in both young and adult mice. Overall, our results reveal new aspects of bone and BM remodeling, as well as hematopoietic recovery, which is dependent on the cytotoxic dose and recipient age.

A hemodynamic model of artery bypass graft considering microcirculation function.

The incidence of arterial stenosis is increasing year by year. In order to better diagnose and treat arterial stenosis, numerical simulation technology has become a popular method. A novel model is constructed to investigate the influence of microcirculation on the hemodynamics of artery bypass graft. In this paper, a severely narrow artery bypass graft model is considered. The geometric shape includes a narrow artery tube and a bypass graft of the same diameter with a 45° suture angle. The fluid-structure interaction model is considered by finite element numerical calculation, and the flow is simulated with microcirculation as the outlet boundary condition. The changes of blood flow velocity, pressure and wall shear stress are analyzed. The results show that blood almost entirely flows into the graft tube and there is no recirculation area at the anastomosis. The artery bypass graft model considering microcirculation function could simulate the physiological characteristics of blood flow more reasonably, and it provide helps for clinicians to diagnose and treat arterial stenosis.

Blunted Brachial Blood Flow Velocity Recovery to Acute Mental Stress in Young Women with PTSD Compared to Controls

Introduction: Post-traumatic stress disorder (PTSD) is a debilitating mental illness associated with increased cardiovascular disease (CVD) risk, a major cause of death among women in the United States. Women are twice as likely as men to develop PTSD after trauma exposure, and cardiovascular reactivity to stress is a known risk factor for CVD. Therefore, our aim was to investigate if young women diagnosed with PTSD will present with impaired hemodynamic responses to acute stress compared to controls. We hypothesized that women with PTSD will have high blood pressure (BP), heart rate (HR) and blood flow velocity (BFV) response to a mental stress protocol, and a blunted recovery. Methods: We recruited for this study ten young women with PTSD and nine trauma-exposed women without PTSD (controls) between the ages of 18 to 40 years. We collected data in a single laboratory visit after informed consent and PTSD symptoms severity questionnaire. After demographics and resting hemodynamics, we continuously measured HR using a three-lead EKG, beat-to-beat BP using finger plethysmography and continuous brachial BFV using Doppler ultrasound. A Doppler audio translator was used to transfer the doppler signal in our data analysis software for simultaneous recording of all hemodynamics variables. All variables were recorded during 5 min of supine rest, 5 min of mental stress (via mental arithmetic) and 5 min of recovery. The response and recovery to stress was analyzed using an analysis of covariance with timepoint as within factor and PTSD diagnosis as between-factor. Results: Women with a clinical diagnosis of PTSD had a mean age of 27±10 years and body mass index (BMI) of 30.1±2.9 kg/m2. Controls (trauma-exposed women without PTSD) had a mean age of 26±7 years and body mass index (BMI) of 24± 2.1 kg/m2. Resting seated BP and HR were not different between the groups. The slopes of the overall changes in BFV from baseline to mental stress to recovery were different between young women with PTSD and controls (timepoint*group, P= 0.057) when controlling for PTSD symptoms severity. Specifically, although mental stress elicited similar increases in BFV in women with PTSD (Δ0.80±1.8 cm/sec) and in controls [Δ0.45±1.2 cm/sec, P= 0.44 (timepoint*group)], BFV recovery from stress was impaired in PTSD (Δ0.64±1.3 cm/sec), but not in controls [Δ-2.20±0.84 cm/sec, P= 0.047 (timepoint*group)]. BP and HR reactivity to mental stress and recovery were not different between the groups (P&gt;0.05). Conclusion: The current pilot study revealed that PTSD is associated with blunted recovery from acute mental stress, suggesting early impairment of vascular function in these women at a young age. Young pre-menopausal women are overlooked in prevention strategies and health policies targeting populations at-risk for CVD; with the rising prevalence of trauma exposure in young women, evidence is pointing to a parallel increase in CVD risk. K01HL161027 and UMN CTSI UL1TR002494 No Disclosure. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Heme oxidation of NO-receptor soluble guanylyl cyclase is an important contributor to cerebrovascular and cognitive dysfunctions

Introduction: Decreased cerebral blood flow (CBF) is one of the major hemodynamic alterations leading to neurodegeneration and age-related cognitive decline. Nitric Oxide (NO)-dependent vasomotor reactivity is central in regulating cerebrovascular hemodynamics and adequate brain blood perfusion. NO receptor Soluble Guanylyl Cyclase (sGC) is the primary mediator of NO-dependent vasodilation. Oxidative stress, often persisting in diseased vasculature, renders sGC insensitive to NO and impairs the NO signaling. The objective of our study was to investigate the role of sGC oxidation in regulation CBF and brain function. Hypothesis: Oxidative stress disrupts NO/cGMP signaling in brain by decreasing sGC activity via oxidation of sGC heme. Approach: To assess causal effect of sGC oxidation on NO signaling function we administered ODQ, a sGC-specific heme oxidizing agent, to simulate long-term effect of sGC oxidation in cerebral vasculature. Two groups of young wild-type male and female mice (4 months old C57BL/6) were treated intraperitoneally (IP) twice a week for one month with ODQ (20 mg/kg) or a solvent as control. Changes in cerebrovascular reactivity and memory function were assessed and compared in treated and control groups. Using a non-invasive pulsed Doppler ultrasound-based system we assessed the changes in blood flow velocity (PVF, % of baseline) in the mouse middle cerebral artery (MCA) of male and female groups. MCA vasodilation was induced by bolus IP injection of NO-donor sodium nitroprusside (SNP) or BAY 58-2667, an allosteric NO-independent sGC activator. Memory function was assessed by the Novel Object Recognition Task (NORT, RI, recognition index) in all experimental groups. Western blotting and densitometry assessed the expression of major sGC subunits (α1, α2 and β1) in cleared brain lysates from ODQ-treated and control groups. Results: We observed a significantly blunted vasodilative response to SNP (1 mg/kg) in ODQ-treated mice vs controls of both genders (PVF, max response at 2 min post-injection, males 73.9 ± 10.4% (n=7/7) vs 58.5 ± 8.6 %, p=0.01; females (n=6/6) 77.4 ± 10.6 % vs 61.9 ± 5.4 %, p=0.01). Changes in response to NO-donor were more pronounced in males than females. The difference in BAY 58-2667 response between ODQ-treated and control groups was not statistically significant. ODQ significantly reduced the long-term memory in males but not female, according to NORT (RI, males (n=7/7) 0.58 ± 0.13 vs 0.69 ± 0.05; p=0.01; females (n=6/6) ODQ 0.59 ± 0.17 vs 0.73 ± 0.1, p=0.13). No statistically significant difference in expression of sGC subunits between control and ODQ-treated (n= 4/4) of male and female groups was determined. Conclusions: ODQ treatment significantly impairs vasodilation response to NO-donor but not to NO-independent sGC activator in mice MCA. ODQ treatment negatively affects long-term memory function in male, but not female mice. ODQ treatment does not significantly affect the expression of sGC subunits. Together our data suggest that the oxidation of sGC heme moiety impairs the regulation of cerebral blood flow of both genders and impairs long-term memory function gender-specifically in young mice. This research was supported by National Institute of Health grants RAG071999A (Iraida Sharina), HL139838, and American Heart Association 23TPA1070711 (Emil Martin). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

SEX DIFFERENCES IN CEREBRAL BLOOD FLOW VELOCITY RESPONSES TO EXERCISE IN THE HEAT

INTRODUCTION &amp; AIMS Global warming poses a risk for the development of heat-related physiological impairment, which can be aggravated when exercising in hot conditions. The aim of the present study was to investigate acute effects of exercising in hot conditions on cerebral blood flow velocity and systolic function in healthy individuals and to explore possible sex differences. METHODS The experimental condition consisted of walking on a treadmill, at 5km/h and 2% incline, inside a heat chamber at 40°C (50%RH), for 90 minutes. Middle cerebral artery blood flow velocity (MCAv) and left ventricular global longitudinal strain (GLS; a sensitive index of systolic function), were assessed at baseline and every 30 minutes by means of transcranial Doppler and speckle-tracking echocardiography, respectively. Data is expressed in delta (Δ) and standard error. RESULTS Twenty-six individuals (13♂,13♀ 27.1±1.0yrs, P=0.02) completed the experimental protocol. Both males and females exhibited non-significant increases in MCAv from baseline at 30 minutes (♂Δ=2.55±2.15 P&amp;gt;0.05; ♀Δ=0.54±2.53cm.s-1, P&amp;gt;0.05; interaction P=0.63), followed by significant decreases relative to 30min, at 60min (♂Δ=-4.0±1.23 P=0.04; ♀Δ=-5.41±1.56cm.s-1, P=0.03; interaction P=0.63) and 90 minutes (♂Δ=-6.08±1.37 P&amp;lt;0.01; ♀Δ=-7.39±1.40cm.s-1, P&amp;lt;0.01; interaction P=0.63). In males, there was a significant decrease in GLS from baseline at 30min (Δ=2.44±0.69%, P&amp;lt;0.05), 60 (Δ=2.79±0.73%, P=0.03), and 90 (Δ=3.49±0.89%, P=0.03) minutes; no significant changes were observed in females. CONCLUSION Males and females presented similar patterns of change in cerebral blood flow velocity, including significant decreases with prolonged heat exertion. These changes occur in both sexes, despite changes in systolic strain only being apparent in males. These data suggest that sex differences may exist in the regulation of cerebrovascular responses to exercise in the heat in humans.

Effect of active and passive techniques used in thromboembolic prophylaxis on venous flow velocity in the post-procedure period.

Studies have shown that using mechanical thromboembolic prophylaxis methods speeds up venous flow and decreases stasis. These studies examine the post-intervention period of 1-10min. The length of the effect of procedures to raise venous flow velocity cannot be determined by clinical trials. To apply mathematical techniques to estimate how long mechanical thromboembolism prophylaxis procedures will increase venous flow rate. In the survey, we examined 25 persons (poststroke patients), with an average age of 57.2 ± 6.3 years. Regarding the proportion of genders, 13 (52%) participants were male and 12 (48%) female. The peak venous blood flow velocity was measured with a HADECO BIDOP ES-100V II type Doppler ultrasound device, using an 8MHz head, in the femoral vein, at the level of the hip joint. We estimated the change of the venous blood flow velocity from the available sampled data using the method of least squares. For the calculations, we used Microsoft Excel, version Mac Excel 2019. The decrease in peak venous flow velocity can be approximated by a logarithm function. Mathematical calculations show that after active thromboembolic prophylaxis interventions, resting venous flow velocity is restored at 26.8min on the intact limb and 85.1min on the hemiparetic side. Resting flow velocity is restored in 131.9min after passive mobilization of the hemiparetic side and in 137.7min after the consensual effect. An elementary mathematical function can be used to estimate the time to recovery of peak venous flow velocity to resting state from measurements taken 15min after the intervention. Active and passive mechanical thromboembolic prophylaxis after the intervention has a longer-term effect on venous flow velocity.

Numerical investigation of quantitative pulmonary pressure ratio in different degrees of stenosis.

Pulmonary artery stenosis endangers people's health. Quantitative pulmonary pressure ratio (QPPR) is very important for clinicians to quickly diagnose diseases and develop treatment plans. Our purpose of this paper is to investigate the effects of different degrees (50% and 80%) of pulmonary artery stenosis on QPPR. An idealized model is established based on the normal size of human pulmonary artery. The hemodynamic governing equations are solved using fluid-structure interaction. The results show that the QPPR decreases with the increase of stenosis degree, and it is closely related to the pressure drop at both ends of stenosis. Blood flow velocity and wall shear stress are sensitive to the stenosis degree. When the degree of stenosis is 80%, the amplitude of changes of blood flow velocity and wall shear stress at both ends of stenosis is lower. The results suggest that the degree of pulmonary artery stenosis has a significant impact on QPPR and hemodynamic changes. This study lays a theoretical foundation for further study of QPPR.

Slow‐breathing induced hypocapnia mitigates deficit of vasoreactivity measured in patients with cognitive impairment

AbstractBackgroundA multi‐center study in Los Angeles (USC), Kansas City (KUMC) and Dallas (UT‐SWMC) has been quantifying the dynamics of CO2 vasoreactivity in MCI/AD patients and cognitively normal controls under spontaneous resting conditions. The goal is to develop effective vasoreactivity physio‐markers for early diagnosis of MCI and pre‐clinical AD, based on previous findings of significantly reduced vasoreactivity in MCI patients [Marmarelis et al., J. Alzh. Dis. 56:89‐105, 2017]. Here, we report on the effects of slow‐paced breathing upon these physio‐markers.MethodSpontaneous changes in arterial blood pressure (ABP), end‐tidal CO2 (etCO2), and cerebral blood flow velocity (CBFV) in middle cerebral arteries were recorded under resting conditions over two 6‐8 min sessions, separated by session of slow‐paced breathing (6 breaths/minute), in 47 MCI and 25 AD patients and 58 age‐matched cognitively normal controls. Using our novel methodology, we obtained predictive models of the dynamic effects of ABP and etCO2 upon CBFV using the universal convolutional form of linear dynamic models, which are defined by the respective “kernels” estimated from time‐series data. The etCO2‐to‐CBFV kernel is used to compute indices (physio‐markers) that quantify the vasoreactivity in each participant.ResultThe vasoreactivity index for each participant is computed from the integrated etCO2‐to‐CBFV kernel as the time‐average over the first 30 sec. The average kernels for patients and controls are shown in Figures 1‐2 for the two sessions respectively. Note the smaller kernel values for patients – while the difference is reduced after slow‐paced breathing. The obtained vasoreactivity indices are significantly smaller for 72 patients (MCI and AD taken together) vs 58 controls for the first session [p = 0.018; mean (SD): 0.057 (0.539) vs 0.424 (1.076)] but NOT for the session after slow‐paced breathing [p = 0.237; mean (SD): 0.193 (0.731) vs 0.361 (0.863)]. Average etCO2 was lower after paced‐breathing [p = 10−6; mean (SD): 36.23 (6.18) vs 33.44 (6.36)].ConclusionQuantitative analysis of cerebral CO2 vasoreactivity under resting spontaneous conditions in 72 MCI/AD patients vs 58 age‐matched controls, before and after slow‐paced breathing, revealed that the significant vasoreactivity deficit in MCI/AD patients is mitigated (at least temporarily) after slow‐paced breathing. This effect may be due to observed hypocapnia induced by slow‐paced breathing.

Abstract 12782: Serial Cerebral Hemodynamic Monitoring in Patients With HeartMate 3 Left Ventricular Assist Devices

Introduction: Left ventricular assist device (LVAD) implantation improves cardiopulmonary hemodynamics and vital organ perfusion, but cerebral blood flow is not routinely measured despite the clinical significance of neurologic complications. We aimed to quantify the short and long-term impact of LVAD on cerebral hemodynamics by serially monitoring patients before and after LVAD implantation. Hypothesis: We hypothesize that LVAD implantation improves dynamic measures of cerebral blood flow: cerebral autoregulation (CA) and cerebrovascular reactivity (CVR). Methods: 20 patients with advanced heart failure with planned LVAD implantation participated in serial cerebral hemodynamic monitoring: (1) &lt;72-hours pre-implant, (2) &lt;72-hours post-implant, (3) 14-days post-implant, and (4) 90-days post-implant. Cerebral blood flow velocity was measured at each visit by transcranial Doppler. CA, quantified by Mx index , characterized the relationship between blood pressure and cerebral blood flow. CVR quantified the cerebral hemodynamic reserve, based on the response to a hypercapnic stimulus (5% inhaled CO 2 ). Results: As compared to the pre-implant assessment, no change was noted in absolute cerebral blood flow velocity ( Figure 1a ). However, CA improved immediately post-implant (0.47 vs 0.26; p=0.0007), at 14-days (0.47 vs 0.33; p=0.007), and at 90-days (0.47 vs 0.31; p=0.03), Figure 1b . Pre-implant CVR was not significantly altered at 14-days (1.14 vs 1.70, p=0.25) but improved at 90-days (1.14 vs 2.11, p=0.03), Figure 1c . Conclusions: Despite no change in cerebral blood flow velocity, LVAD implantation improves dynamic measures of cerebral blood flow, CA and CVR. Future studies should include longer follow-up and correlate post-LVAD cerebral hemodynamics with clinically meaningful neurologic endpoints such as stroke and cognitive decline.

Prospects Using of Colour Doppler Imaging to Study Ocular Hemodynamics in Pregnant Women with Diabetic Retinopathy. Review

Color Doppler imaging became widespread for study hemodynamics in patients with vascular eyes pathologies. A number of studies have shown changes in ocular blood flow velocity and Doppler indices in patients with diabetes mellitus in both the absence and presence of diabetic retinopathy. With the progression of diabetic retinopathy, an increase in parameters’ changes was revealed, variations in ocular blood flow were studied after conservative treatment, retinal laser photocoagulation, against the background of anti-VEGF therapy. Due to its non-invasiveness, color Doppler imaging is used to assess orbital blood flow in pregnant patients at any gestational age. The works of this direction concern the assessment the changes in orbital blood flow during the physiological course of pregnancy and preeclampsia. However, there is still no information on the state of ocular blood flow in pregnant women with diabetes mellitus, which can serve as a basis for further research.

The effects of mydriatic eye drops on cerebral blood flow and oxygenation in retinopathy of prematurity examinations.

Mydriatic eye drops used during retinopathy examination have been associated with cardiovascular, respiratory, and gastrointestinal side effects. The aim of our study was to investigate the effects of the drops used for pupil dilatation on cerebral blood flow and cerebral oxygenation. The study included 62 infants who underwent retinopathy screening exams. Vital signs, heart rate (HR), arterial oxygen saturation (SpO2), and mean arterial pressure (MAP) were recorded. Cerebral oxygenation and middle cerebral artery blood flow velocity were evaluated using near-infrared spectroscopy (NIRS) and Doppler ultrasonography, respectively, and the cerebral metabolic rate of oxygen (CMRO2) was also calculated. The mean gestational age of the infants included was 31.29 ± 1.42weeks, and the mean birth weight was 1620 ± 265g. Heart rate was found to be significantly decreased after mydriatic eye drop instillation; however, there were no significant differences regarding blood pressure and oxygen saturation levels (HR: p < 0.001; MAP: p = 0.851; SpO2: p = 0.986, respectively). After instillation while cerebral regional oxygen saturation (rScO2) measurements were significantly decreased at the 60th minute (p = 0.01), no significant difference was found in Vmax and Vmean of MCA before and after mydriatic eye drop instillation (p = 0.755, p = 0.515, respectively). Regarding CMRO2 measurements, we also did not find any statistical difference (p = 0.442). Conclusion:Our study has shown that although eye drops may affect heart rate and regional cerebral oxygen saturation, they do not alter cerebral blood flow velocities and metabolic rate of oxygen consumption. Current recommendations for mydriatic eye drop use in retinopathy exam appear to be safe. What is Known: • Mydriatic eye drop installation is recommended for pupil dilatation during ROP screening exams. • It's known that mydriatics used in ROP examination have affects on the vital signs, cerebral oxygenation and blood flow. What is New: • This is the first study evaluating the changes in cerebral oxygenation and blood flow velocity after mydriatic drop instillation using NIRS and Doppler US concomitantly. • While the eye drops may affect heart rate and regional cerebral oxygen saturation, they do not alter cerebral blood flow velocities and metabolic rate of oxygen consumption.

Characterization of cerebral macro- and microvascular hemodynamics during transient hypotension.

The aim of the current study was to establish the interplay between blood flow patterns within a large cerebral artery and a downstream microvascular segment under conditions of transiently reduced mean arterial pressure (MAP). We report data from nine young, healthy participants (5 women; 26 ± 4 yr) acquired during a 15-s bout of sudden-onset lower body negative pressure (LBNP; -80 mmHg). Simultaneous changes in microvascular cerebral blood flow (CBF) and middle cerebral artery blood velocity (MCAvmean) were captured using diffuse correlation spectroscopy (DCS) and transcranial Doppler ultrasound (TCD), respectively. Brachial blood pressure (finger photoplethysmography) and TCD waveforms were extracted at baseline and during the nadir blood pressure (BP) response to LBNP and analyzed using a modified Windkessel model to calculate indices of cerebrovascular resistance (Ri) and compliance (Ci). Compared with baseline, rapid-onset LBNP decreased MAP by 22 ± 16% and Ri by 14 ± 10% (both P ≤ 0.03). Ci increased (322 ± 298%; P < 0.01) but MCAvmean (-8 ± 16%; P = 0.09) and CBF (-2 ± 3%; P = 0.29) were preserved. The results provide evidence that changes in both vascular resistance and compliance preserve CBF, as indexed by no significant changes in MCAvmean or DCS microvascular flow, during transient hypotension.NEW & NOTEWORTHY To characterize the relationship between cerebrovascular patterns within the large middle cerebral artery (MCA) and a downstream microvascular segment, we used a novel combination of transcranial Doppler ultrasound of the MCA and optical monitoring of a downstream microvascular segment, respectively, under conditions of transiently reduced mean arterial pressure (i.e., lower body negative pressure, -80 mmHg). A rapid increase in vessel compliance accompanied the maintenance of MCA blood velocity and downstream microvascular flow.

Neurovascular coupling in severe aortic valve stenosis.

Aortic stenosis (AS) is characterized by obstruction of blood outflow from the left ventricle, which can impair target organ perfusion such as the brain. We hypothesized that hemodynamic changes in AS may lead to dysfunction of cerebral blood flow regulatory mechanisms. The aim of our study was to evaluate neurovascular coupling in patients with AS by Transcranial Doppler ultrasonography. Neurovascular coupling was assessed using visually evoked cerebral blood flow velocity responses (VEFR) calculated as relative blood flow velocity changes in the posterior cerebral artery upon visual stimulation. We analyzed peak systolic, mean and end diastolic VEFR in 54 patients with severe AS and 43 controls in 10 consecutive cycles of visual stimulation. Repeated-measures ANOVA test was used to compare cerebral hemodynamic data by group. Patients with AS had significantly higher peak systolic (12.9%±5.6% and 10.5%±4.5%; p=.009) and mean VEFR (14.4%±5.8% and 12.2%±4.9%; p=.021) compared to controls, whereas only a tendency for higher end diastolic VEFR was observed (16.7%±6.9% and 14.4%±6.2%; p=.061). We have shown for the first time that patients with severe AS exhibit higher VEFR than controls indicating dysregulation of neurovascular coupling, which can be one of the factors contributing to development of cognitive decline.

Association Between Long-Term Exposure to Fine Particulate Matter Constituents and Progression of Cerebral Blood Flow Velocity in Beijing: Modifying Effect of Greenness.

Few studies have explored the effects of fine particulate matter (PM2.5) and its constituents on the progression of cerebral blood flow velocity (BFV) and the potential modifying role of greenness. In this study, we investigated the association of PM2.5 and its constituents, including sulfate (SO4 2-), nitrate (NO3 -), ammonium (NH4 +), organic matter (OM), and black carbon (BC), with the progression of BFV in the middle cerebral artery. Participants from the Beijing Health Management Cohort who underwent at least two transcranial Doppler sonography examinations during 2015-2020 were recruited. BFV change and BFV change rate were used to define the progression of cerebral BFV. Linear mixed effects models were employed to analyze the data, and the weighted quantile sum regression assessed the contribution of PM2.5 constituents. Additionally, greenness was examined as a modifier. Among the examined constituents, OM exhibited the strongest association with BFV progression. An interquartile range increase in PM2.5 and OM exposure concentrations was associated with a decrease of -16.519cm/s (95% CI: -17.837, -15.201) and -15.403cm/s (95% CI: -16.681, -14.126) in BFV change, and -10.369cm/s/year (95% CI: -11.387, -9.352) and -9.615cm/s/year (95% CI: -10.599, -8.632) in BFV change rate, respectively. Furthermore, stronger associations between PM2.5 and BFV progression were observed in individuals working in areas with lower greenness, those aged under 45years, and females. In conclusion, reducing PM2.5 levels in the air, particularly the OM constituent, and enhancing greenness could potentially contribute to the protection of cerebrovascular health.

Changes in Rat Cerebral Blood Flow Velocities at Different Stages of Aging

Changes in Rat Cerebral Blood Flow Velocities at Different Stages of Aging

Non-invasive Assessment by B-Mode Ultrasound of Arterial Pulse Wave Intensity and Its Reduction During Ventricular Dysfunction.

Arterial pulse waves contain clinically useful information about cardiac performance, arterial stiffness and vessel tone. Here we describe a novel method for non-invasively assessing wave properties, based on measuring changes in blood flow velocity and arterial wall diameter during the cardiac cycle. Velocity and diameter were determined by tracking speckles in successive B-mode images acquired with an ultrafast scanner and plane-wave transmission. Blood speckle was separated from tissue by singular value decomposition and processed to correct biases in ultrasound imaging velocimetry. Results obtained in the rabbit aorta were compared with a conventional analysis based on blood velocity and pressure, employing measurements obtained with a clinical intra-arterial catheter system. This system had a poorer frequency response and greater lags but the pattern of net forward-traveling and backward-traveling waves was consistent between the two methods. Errors in wave speed were also similar in magnitude, and comparable reductions in wave intensity and delays in wave arrival were detected during ventricular dysfunction. The non-invasive method was applied to the carotid artery of a healthy human participant and gave a wave speed and patterns of wave intensity consistent with earlier measurements. The new system may have clinical utility in screening for heart failure.

IMPACT OF RELATIVE BLOOD FLOW VELOCITY HYPERPERFUSION DURING CARDIAC SURGERY WITH CARDIOPULMONARY BYPASS TO DELAYED NEUROCOGNITIVE RECOVERY

<h3>Objective</h3> Inflammation, neuronal, vascular damage/embolism, cerebral autoregulation and perfusion, oxygen delivery are known as etiological factors of delayed neurocognitive recovery (dNCR). Many researchers have identified that neuropsychological complications emerge from insufficient cerebral perfusion. Relative cerebral hyperperfusion also disrupts cerebral autoregulation and might play a significant role in dNCR development. The aim of this study was to determine the influence of increased a. cerebri media (ACM) blood flow velocity (BFV) during cardiac surgery with cardiopulmonary bypass (CPB) on delayed neurocognitive recovery. <h3>Design and Method</h3> This prospective - case control study included patients undergoing elective coronary artery bypass grafting (CABG) or/and valve surgery with CPB. For cognitive evaluation 110 patients completed ACE-III. To determine mild cognitive dysfunction, cut - off 88 was chosen. Mean BFV was monitored with transcranial Doppler ultrasonography (TCD) and performed before surgery and at the beginning, middle and ending of CPB. The average of three CPB measurements was used for calculation. Preoperative BFV was converted to 100% and used as a baseline. The percentage change of cerebral blood flow velocity during CPB was calculated from baseline. Patients with decreased blood flow velocity were included for further investigation. <h3>Results</h3> 101 patients were examined, 67 (69,1%) men and 29 (29,9%) women, age 67.9 (SD 9.2) Increased percentage of BFV was determined for 40 (39.60%) patients. Patients' demographic data are shown in Table 1. Percentage change of BFV was 105.60 % (min 100.21; max 148.02) in the non-dNCR group and 132.29 % (min 101.34; max 150.26) in the dNCR group, p=0.033 (Figure Nr. 1). During the study, we assessed the relationship between patients age and ACE-III test results together with ACM BFV. Spearman correlation analysis revealed that age had negative moderate correlation with ACE-III test results after surgery (Spearman r -0.597, p< 0.01) and negative moderate correlation with ACM BFV during CPB (Sprearman r -0 .529, p <0.01) (Figure 2 and 3). <h3>Conclusions</h3> Patients that develop dNCR were significantly older and had a lower baseline BFV. Results suggest that the main cause of hyperperfusion during CPB is age related lower BFV before surgery. Elderly patients are more sensitive to relative hyperperfusion during CPB, therefore dNCR was diagnosed more often in patients with higher percentage change of BFV.

Impairment of cerebral CO2 dynamic vasoreactivity in MCI &amp; AD patients: a multi‐center study of cerebral flow regulation

AbstractBackgroundAlzheimer’s Disease Centers in Los Angeles (USC), Dallas (UT‐SWMC) and Kansas City (KUMC) have joined together to study the regulation of cerebral perfusion through analysis of spontaneous time‐series data using a modeling methodology that previously yielded indications of reduced CO2 dynamic vasomotor reactivity (DVR) in amnestic MCI patients. We report initial results from this ongoing multi‐center study that confirm those preliminary findings and, furthermore, elucidate the effects of slow‐paced breathing.MethodFive‐minute spontaneous changes in arterial blood pressure (ABP), end‐tidal CO2 (etCO2) and cerebral blood flow velocity (CBFV) in middle cerebral arteries were obtained before and after 5‐min session of slow‐paced breathing (8 breaths/minute). Using data from 25 MCI patients, 7 AD patients and 45 age‐matched cognitively normal controls (NC), we obtained predictive models of the dynamic effects of ABP and etCO2 (proxy for blood CO2) upon CBFV via our kernel‐based modeling methodology. These predictive models were used to compute indices (physio‐markers) that quantify the DVR in each participant, as time‐average of the model‐predicted CBFV response to unit‐step change of etCO2 over the first 30 seconds.ResultThe obtained DVR indices were significantly different for the 32 patients (MCI and AD lumped together due to small number of AD) vs. 45 age‐matched controls (p= 0.0099). Notably, the delineation between patients and controls improved (p= 0.0011) after a 5‐min session of slow‐paced breathing. Figure 1 shows the average model‐predicted CBFV response to unit‐step change of etCO2 for 32 MCI/AD patients (red line) and 45 controls (blue line) before and after the 5‐min paced‐breathing session. Note the negative average steady‐state CBFV response of the patients (red) that indicates polarity reversal of the normal CO2 vasomotor reactivity (blue). Better delineation between patients and controls is achieved (p= 2x10‐5) when the DVR indices from the two sessions, before and after slow‐paced breathing, were averaged (see histograms in Figure 2).ConclusionSignificantly lower DVR indices under resting spontaneous conditions were observed in 32 MCI/AD patients relative to 45 age‐matched controls. This reduction is detected more reliably after 5‐min of slow‐paced breathing. Averaging of the DVR indices obtained before and after slow‐paced breathing improved further this delineation (p= 2x10‐5).