Cerebral vasomotor reactivity in neurodegenerative diseases

Elevating understanding: Linking high-altitude hypoxia to brain aging through EEG functional connectivity and spectral analyses

High-altitude hypoxia triggers brain function changes reminiscent of those in healthy aging and Alzheimer's disease, compromising cognition and executive functions. Our study sought to validate high-altitude hypoxia as a model for assessing brain activity disruptions akin to aging. We collected EEG data from 16 healthy volunteers during acute high-altitude hypoxia (at 4,000 masl) and at sea level, focusing on relative changes in power and aperiodic slope of the EEG spectrum due to hypoxia. Additionally, we examined functional connectivity using wPLI, and functional segregation and integration using graph theory tools. High altitude led to slower brain oscillations, that is, increased δ and reduced α power, and flattened the 1/f aperiodic slope, indicating higher electrophysiological noise, akin to healthy aging. Notably, functional integration strengthened in the θ band, exhibiting unique topographical patterns at the subnetwork level, including increased frontocentral and reduced occipitoparietal integration. Moreover, we discovered significant correlations between subjects' age, 1/f slope, θ band integration, and observed robust effects of hypoxia after adjusting for age. Our findings shed light on how reduced oxygen levels at high altitudes influence brain activity patterns resembling those in neurodegenerative disorders and aging, making high-altitude hypoxia a promising model for comprehending the brain in health and disease.

Altered Cerebral Vasoreactivity on Transcranial Color-Coded Sonography Related to Akinetic-Rigid Phenotype of Parkinson's Disease: Interim Analysis of a Cross-Sectional Study

BACKGROUND

A correlation between worse functional outcomes in Parkinson's disease (PD) patients with cerebrovascular disease (CVD) or the Akinetic-rigid phenotype has been argued in recent studies. We aimed to evaluate the association of cerebral hemodynamics impairments, assessed by Transcranial Color-coded Doppler sonography (TCCS), on PD patients with different phenotypes of the disease and with risk factors for CVD.

METHODOLOGY

Idiopathic PD patients (n = 51) were divided into motor subtypes: Akinetic-rigid (AR) (n = 27) and Tremor-dominant (TD) (n = 24) and into two groups regarding vascular risk factors: when ≥2 were present (PDvasc) (n = 18) and <2 (PDnvasc) (n = 33). In a parallel analysis, the Fazekas scale on brain magnetic resonance imaging (MRI) was applied to a sample to assess the degree of leukoaraiosis. TCCS examinations were prospectively performed obtaining middle cerebral artery Mean Flow Velocities (Vm), Resistance Index (RI), and Pulsatility Index (PI). The Breath-Holding Index (BHI) was calculated to assess cerebrovascular reactivity (cVR). Standardized functional scales were administered (UPDRS III and Hoehn&Yahr).

RESULTS

The phenotype groups were similar in age, disease duration and demographic parameters, but there were significantly higher H&Y scores than TD group. cVR was impaired in 66.7% of AR vs. 37.5% of TD. AR group exhibited lower BHI (0.53 ± 0.31 vs. 0.91 ± 0.62; p = 0.000), lower Vm after apnea (44.3 ± 9.0 cm/s vs. 53.4 ± 11.4 cm/s; p = 0.003), higher PI (0.91 ± 0.26 vs. 0.76 ± 0.12; p = 0.000) and RI (0.58 ± 0.11 vs. 0.52 ± 0.06; p = 0.021). PDvasc group showed higher PI (0.98 vs. 0.76; p = 0.001) and higher frequency of altered cVR (72.2% vs. 42.2%; p = 0.004). There was a significant predominance of higher values on Fazekas scale in the PDvasc group. We found no difference between the Fazekas scale when comparing motor subtypes groups but there was a trend toward higher scores in the AR phenotype.

CONCLUSIONS

TCCS, a cost-effective method, displayed impaired cVR in Parkinsonian patients with risk factors for CVD with higher degree of MRI leukoaraiosis. PD patients with the AR disease phenotype also presented impaired cVR on TCCS and greater functional impairment, although with just a trend to higher scores on MRI Fazekas.

Can Alterations in Cerebrovascular CO2 Reactivity Be Identified Using Transfer Function Analysis without the Requirement for Carbon Dioxide Inhalation?

The present study aimed to examine the validity of a novel method to assess cerebrovascular carbon dioxide (CO₂) reactivity (CVR) that does not require a CO₂ inhalation challenge, e.g., for use in patients with respiratory disease or the elderly, etc. In twenty-one healthy participants, CVR responses to orthostatic stress (50° head-up tilt, HUT) were assessed using two methods: (1) the traditional CO₂ inhalation method, and (2) transfer function analysis (TFA) between middle cerebral artery blood velocity (MCA V) and predicted arterial partial pressure of CO₂ (PaCO₂) during spontaneous respiration. During HUT, MCA V steady-state (i.e., magnitude) and MCA V onset (i.e., time constant) responses to CO₂ inhalation were decreased (p < 0.001) and increased (p = 0.001), respectively, indicative of attenuated CVR. In contrast, TFA gain in the very low-frequency range (VLF, 0.005-0.024 Hz) was unchanged, while the TFA phase in the VLF approached zero during HUT (-0.38 ± 0.59 vs. 0.31 ± 0.78 radians, supine vs. HUT; p = 0.003), indicative of a shorter time (i.e., improved) response of CVR. These findings indicate that CVR metrics determined by TFA without a CO₂ inhalation do not track HUT-evoked reductions in CVR identified using CO₂ inhalation, suggesting that enhanced cerebral blood flow response to a change in CO₂ using CO₂ inhalation is necessary to assess CVR adequately.

The impact of cerebral vasomotor reactivity on cerebrovascular diseases and cognitive impairment

The regulation of cerebral blood flow (CBF) is a complex and tightly controlled function ensuring delivery of oxygen and nutrients and removal of metabolic wastes from brain tissue. Cerebral vasoreactivity (CVR) refers to the ability of the nervous system to regulate CBF according to metabolic demands or changes in the microenvironment. This can be assessed through a variety of nuclear medicine and imaging techniques and protocols. Several studies have investigated the association of CVR with physiological and pathological conditions, with particular reference to the relationship with cognitive impairment and cerebrovascular disorders (CVD). A better understanding of the interaction between CVR and cognitive dysfunction in chronic and particularly acute CVD could help improving treatment and rehabilitation strategies in these patients. In this paper, we reviewed current knowledge on CVR alterations in the context of acute and chronic CVD and cognitive dysfunction. Alterations in CVR and hemodynamics have been described in patients with both neurodegenerative and vascular cognitive impairment, and the severity of these alterations seems to correlate with CVR derailment. Furthermore, an increased risk of cognitive impairment progression has been associated with alterations in CVR parameters and hemodynamics. Few studies have investigated these associations in acute cerebrovascular disorders and the results are inconsistent; thus, further research on this topic is encouraged.

Regulation of blood vessels by ATP in the ventral medullary surface in a rat model of Parkinson's disease

Parkinson's disease (PD) patients often experience impairment of autonomic and respiratory functions. These include conditions such as orthostatic hypotension and sleep apnea, which are highly correlated with dysfunctional central chemoreception. Blood flow is a fundamental determinant of tissue CO₂/H⁺, yet the extent to which blood flow regulation within chemoreceptor regions contributes to respiratory behavior during neurological disease remains unknown. Here, we tested the hypothesis that 6-hydroxydopamine injection to inducing a known model of PD results in dysfunctional vascular homeostasis, biochemical dysregulation, and glial morphology of the ventral medullary surface (VMS). We show that hypercapnia (FiCO₂ = 10%) induced elevated VMS pial vessel constriction in PD animals through a P2-receptor dependent mechanism. Similarly, we found a greater CO₂-induced vascular constriction after ARL67156 (an ectonucleotidase inhibitor) in control and PD-induced animals. In addition, we also report that weighted gene correlational network analysis of the proteomic data showed a protein expression module differentially represented between both groups. This module showed that gene ontology enrichment for components of the ATP machinery were reduced in our PD-model compared to control animals. Altogether, our data indicate that dysfunction in purinergic signaling, potentially through altered ATP bioavailability in the VMS region, may compromise the RTN neuroglial vascular unit in a PD animal model.

Cerebrovascular reactivity is blunted in young adults with major depressive disorder: The influence of current depressive symptomology

BACKGROUND

In middle-aged adults with depression, cerebral vasodilatory reactivity is blunted; however, this has not been examined in treatment-naïve young adults with major depressive disorder (MDD). We tested the hypothesis that cerebrovascular reactivity would be blunted in young adults (18-30 yrs) with MDD compared to healthy non-depressed adults (HA) and would be attenuated to a greater extent in adults with symptomatic MDD (sMDD) compared to adults with MDD in remission (euthymic MDD; eMDD).

METHODS

Sixteen adults with MDD [21±3yrs; n = 8 sMDD (6 women); n = 8 eMDD (5 women)] and 14 HA (22±3yrs; 9 women) participated. End-tidal carbon dioxide concentration (P_ETCO₂; capnograph), beat-to-beat mean arterial pressure (MAP; finger photoplethysmography), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), and internal carotid artery (ICA) diameter and blood velocity (Doppler ultrasound) were continuously measured during baseline and rebreathing-induced hypercapnia. Cerebrovascular reactivity was calculated as the relative increase in vascular conductance during hypercapnia.

RESULTS

In adults with MDD, cerebrovascular reactivity in the MCA (∆39±9 HA vs. ∆31±13% MDD, p = 0.04), but not the ICA (∆36±24 HA vs. ∆34±18% MDD, p = 0.84), was blunted compared to HA. In the MCA, cerebrovascular reactivity was reduced in adults with sMDD compared to adults with eMDD (∆36±11 eMDD vs. ∆25±13% sMDD, p = 0.02).

LIMITATIONS

The cross-sectional nature approach limits conclusions regarding the temporal nature of this link.

CONCLUSION

These data indicate that MCA cerebrovascular reactivity is blunted in young adults with MDD and further modulated by current depressive symptomology, suggesting that the management of depressive symptomology may secondarily improve cerebrovascular health.

Targeting Endothelin in Alzheimer's Disease: A Promising Therapeutic Approach

Endothelin is a chemical mediator that helps in maintaining balance within the blood-brain barrier by regulating the levels of toxicants and molecules which pass through the brain, suggesting that a rise in its production determines Alzheimer's disease. The inequity in the amyloid β occurs due to a problem in its clearance from the brain initiating the production of reactive oxygen species and superoxide that activates a cascade wherein the release of inflammatory mediators and various enzymes like endothelin-converting enzymes take place. Furthermore, the cascade increases the levels of endothelin in the brain from endothelial cells. Endothelin levels are upregulated, which can be regulated by modulating the action of endothelin-converting enzymes and endothelin receptors. Hence, endothelin paves a pathway in the treatment of Alzheimer's disease. In this article, we have covered various mechanisms and preclinical studies that support and direct endothelin involvement in the progression of Alzheimer's disease by using various search tools such as PubMed, Science Direct, and Medline. Conclusive outcome data were extracted that all together defy contrivance pathways, potential drugs, endothelin receptors, and endothelin enzymes in our article giving profound importance to target endothelin for prevention and treatment of Alzheimer's disease.

Age-related impairment of cerebral blood flow response to KATP channel opener in Alzheimer's disease mice with presenilin-1 mutation

Local cerebral blood flow (CBF) responses to neuronal activity are essential for cognition and impaired CBF responses occur in Alzheimer's disease (AD). In this study, regional CBF (rCBF) responses to the K_ATP channel opener diazoxide were investigated in 3xTgAD, WT and mutant Presenilin 1(PS1_M146V) mice from three age groups using Laser-Doppler flowmetry. The rCBF response was reduced early in young 3xTgAD mice and almost absent in old 3xTgAD mice, up to 30%-40% reduction with altered CBF velocity and mean arterial pressure versus WT mice. The impaired rCBF response in 3xTgAD mice was associated with progression of AD pathology, characterized by deposition of intracellular and vascular amyloid-β (Aβ) oligomers, senile plaques and tau pathology. The nitric oxide synthase (NOS) inhibitor N^ω-nitro-L-arginine abolished rCBF response to diazoxide suggesting NO was involved in the mediation of vasorelaxation. Levels of phosphor-eNOS (Ser1177) diminished in 3xTgAD brains with age, while the rCBF response to the NO donor sodium nitroprusside remained. In PS1_M146V mice, the rCBF response to dizoxide reduced and high molecular weight Abeta oligomers were increased indicating PS1_M146V contributed to the dysregulation of rCBF response in AD mice. Our study revealed an Aβ oligomer-associated compromise of cerebrovascular function in rCBF response to diazoxide in AD mice with PS1_M146V mutation.

The Contribution of Small Vessel Disease to Neurodegeneration: Focus on Alzheimer's Disease, Parkinson's Disease and Multiple Sclerosis

Brain small vessel disease (SVD) refers to a variety of structural and functional changes affecting small arteries and micro vessels, and manifesting as white matter changes, microbleeds and lacunar infarcts. Growing evidence indicates that SVD might play a significant role in the neurobiology of central nervous system (CNS) neurodegenerative disorders, namely Alzheimer's disease (AD) and Parkinson's disease (PD), and neuroinflammatory diseases, such as multiple sclerosis (MS). These disorders share different pathophysiological pathways and molecular mechanisms (i.e., protein misfolding, derangement of cellular clearance systems, mitochondrial impairment and immune system activation) having neurodegeneration as biological outcome. In these diseases, the actual contribution of SVD to the clinical picture, and its impact on response to pharmacological treatments, is not known yet. Due to the high frequency of SVD in adult-aged patients, it is important to address this issue. In this review, we report preclinical and clinical data on the impact of SVD in AD, PD and MS, with the main aim of clarifying the predictability of SVD on clinical manifestations and treatment response.

Impaired cerebral microcirculation in isolated REM sleep behaviour disorder

During the prodromal period of Parkinson's disease and other α-synucleinopathy-related parkinsonisms, neurodegeneration is thought to progressively affect deep brain nuclei, such as the locus coeruleus, caudal raphe nucleus, substantia nigra, and the forebrain nucleus basalis of Meynert. Besides their involvement in the regulation of mood, sleep, behaviour, and memory functions, these nuclei also innervate parenchymal arterioles and capillaries throughout the cortex, possibly to ensure that oxygen supplies are adjusted according to the needs of neural activity. The aim of this study was to examine whether patients with isolated REM sleep behaviour disorder, a parasomnia considered to be a prodromal phenotype of α-synucleinopathies, reveal microvascular flow disturbances consistent with disrupted central blood flow control. We applied dynamic susceptibility contrast MRI to characterize the microscopic distribution of cerebral blood flow in the cortex of 20 polysomnographic-confirmed patients with isolated REM sleep behaviour disorder (17 males, age range: 54-77 years) and 25 healthy matched controls (25 males, age range: 58-76 years). Patients and controls were cognitively tested by Montreal Cognitive Assessment and Mini Mental State Examination. Results revealed profound hypoperfusion and microvascular flow disturbances throughout the cortex in patients compared to controls. In patients, the microvascular flow disturbances were seen in cortical areas associated with language comprehension, visual processing and recognition and were associated with impaired cognitive performance. We conclude that cortical blood flow abnormalities, possibly related to impaired neurogenic control, are present in patients with isolated REM sleep behaviour disorder and associated with cognitive dysfunction. We hypothesize that pharmacological restoration of perivascular neurotransmitter levels could help maintain cognitive function in patients with this prodromal phenotype of parkinsonism.

Cerebrovascular reactivity and its correlation with age in patients with multiple sclerosis

We assessed cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) within gray matter (GM), normal appearing white matter (NAWM) and white matter (WM) lesions in a group of multiple sclerosis (MS) patients. Furthermore, correlations between CBF, CVR and age were investigated. 31 MS patients and 25 healthy controls (HC) were examined on a 1.5 T MRI scanner, using pseudo-continuous arterial spin labeling MRI. MS vs HC CBF and CVR differences were assessed in GM regions of interest (i.e. resting state networks and vascular territories), and within WM. Correlations between CBF/CVR and age were then computed for MS and HC groups. Whereas no significant CBF and CVR differences were observed between MS and HC in any of the considered brain areas, significantly lower CBF was found in WM lesions with respect to NAWM (p < 0.001) in MS patients. Furthermore, CVR was significantly correlated with age in HC, but not in MS patients. The relatively low-grade of inflammation of our MS cohort may be associated with the observed lack of significant CVR differences between MS patients and HC. The loss of correlation between CVR and age in the MS group suggests that CVR may be influenced by MS-related factors.

Assessment of Cerebral Vasomotor Reactivity in Patients With Primary Open-angle Glaucoma and Ocular Hypertension Using the Breath-Holding Index

PRCIS

Patients with ocular hypertension (OHT) do not show impaired cerebral vasodilation responses to hypercapnia but patients with primary open-angle glaucoma (POAG) do. Impaired vasoreactivity in patients with POAG may have neuronal or vascular origins and increase stroke risk.

PURPOSE

To investigate changes in cerebral blood flow and cerebral vasomotor reactivity using the breath-holding index in patients with POAG and OHT, to examine whether these parameters contribute to the risk of ischemic stroke.

METHODS

Thirty patients with POAG, 30 patients with OHT, and 30 age- and sex-matched healthy control subjects were included in this university hospital-based, cross-sectional, and observational study. Eyes with a greater degree of visual field loss and/or more severe optic disc damage were selected for the study in patients with POAG, whereas in patients with OHT and controls, the study eye was chosen randomly. The mean blood flow velocity and breath-holding index were measured in the middle cerebral artery ipsilaterally in patient and control groups, by using transcranial Doppler ultrasonography.

RESULTS

The mean blood flow velocity and breath-holding indexes were significantly lower in patients with POAG than in the control group (all P<0.05). In the OHT group, the mean blood flow velocity and breath-holding indexes were not different from those in the control group.

CONCLUSIONS

Patients with POAG have impaired vasodilation response to hypercapnia. Presumably, the neuronal changes and deterioration of the endothelium-mediated vasodilatation in patients with glaucoma may disrupt the regulation of arteries and potentially present functional insufficiency on vasoreactivity. Moreover, impaired cerebral vascular regulation may contribute to the increased risk of stroke in patients with POAG.

Renin-Angiotensin System and Alzheimer's Disease Pathophysiology: From the Potential Interactions to Therapeutic Perspectives

New roles of the Renin-Angiotensin System (RAS), apart from fluid homeostasis and Blood Pressure (BP) regulation, are being progressively unveiled, since the discoveries of RAS alternative axes and local RAS in different tissues, including the brain. Brain RAS is reported to interact with pathophysiological mechanisms of many neurological and psychiatric diseases, including Alzheimer's Disease (AD). Even though AD is the most common cause of dementia worldwide, its pathophysiology is far from elucidated. Currently, no treatment can halt the disease course. Successive failures of amyloid-targeting drugs have challenged the amyloid hypothesis and increased the interest in the inflammatory and vascular aspects of AD. RAS compounds, both centrally and peripherally, potentially interact with neuroinflammation and cerebrovascular regulation. This narrative review discusses the AD pathophysiology and its possible interaction with RAS, looking forward to potential therapeutic approaches. RAS molecules affect BP, cerebral blood flow, neuroinflammation, and oxidative stress. Angiotensin (Ang) II, via angiotensin type 1 receptors may promote brain tissue damage, while Ang-(1-7) seems to elicit neuroprotection. Several studies dosed RAS molecules in AD patients' biological material, with heterogeneous results. The link between AD and clinical conditions related to classical RAS axis overactivation (hypertension, heart failure, and chronic kidney disease) supports the hypothesized role of this system in AD. Additionally, RAStargeting drugs as Angiotensin Converting Enzyme inhibitors (ACEis) and Angiotensin Receptor Blockers (ARBs) seem to exert beneficial effects on AD. Results of randomized controlled trials testing ACEi or ARBs in AD are awaited to elucidate whether AD-RAS interaction has implications on AD therapeutics.

Optical coherence tomography angiography of central serous chorioretinopathy patients' response to breath-holding manoeuvre

PURPOSE

To demonstrate through the use of optical coherence tomography angiography (OCTA) that normal vasoreactivity cannot be monitored in central serous chorioretinopathy (CSR) patients in the presence of vasoactive stimuli owing to hypoxia caused by the breath-holding manoeuvre (BHM).

METHODS

This cross-sectional study included a total of 210 eyes, including 70 CSR patients (70 symptomatic eyes, 70 asymptomatic eyes) and 70 control group. Images of the macula (3 × 3 mm) and the optic disc (4.5 × 4.5 mm) were obtained at the baseline and after BHM using OCTA. The change in vascular parameters in the OCTA after BHM was evaluated in CSR patients and the control group.

RESULTS

In the symptomatic eyes of CSR patients, the mean whole image vessel density (VD) in the superficial capillary plexus decreased from 48.0 ± 3.5% under baseline conditions to 46.0 ± 4.5% after BHM (p < 0.01), and the mean whole VD in the deep capillary plexus decreased from 47.9 ± 8.0% under baseline conditions to 46.9 ± 6.7% after BHM (p < 0.01). The OCTA after BHM revealed a decrease in the mean whole image VD of the optic disc in both symptomatic (50.4 ± 2.1% to 49.6 ± 2.0%, p < 0.05) and asymptomatic (50.9 ± 1.8% to 50.4 ± 1.9%, p < 0.05) eyes of CSR patients. No difference for any mean VD of the control group was seen between the baseline and after BHM. Outer retinal flow areas increased significantly after BHM compared with the baseline in both eyes of CSR patients.

CONCLUSION

These results suggest that CSR pathogenesis is related to an imbalance in local vascular regulation and the sympathetic activity of the autonomic nervous system. This technique constitutes a new way of studying retinal vascular changes and may be applied to CSR patients.

Quantitative assessment of near-infrared spectroscopy time course under hypercapnia using an a priori model-based fitting

BACKGROUND

Partial arterial pressure of carbon dioxide (CO₂) modulates cerebral blood flow through a vasoreactivity mechanism. Near infrared spectroscopy (NIRS) can be used to record these changes in cerebral hemodynamics. However, no laterality comparison of the NIRS signal has been performed despite being a prerequisite for the use of such a method in a vasoreactivity monitoring context. We propose to investigate the NIRS signal laterality in response to a CO₂-inhalation-based hypercapnia paradigm in healthy volunteers.

METHODS

Eleven healthy volunteers (6 women, 5 men, mean age: 31 ± 11) underwent a 3-block-design inhalation paradigm: normoxia (5min, "baseline") - hypercapnia (2min, "stimulation") - normoxia (5min, "post-stimulation"). NIRS signal was measured using a two-channel oximeter (INVOS 5100C, Medtronic, USA) with sensors placed symmetrically on both left and right sides on each subject's forehead. Additional heart rate (HR) monitoring was performed simultaneously. Based on the NIRS mean signal pattern, an a priori model of parametric identification was applied for each channel to quantify parameters of interest (amplitude, time delay, excitation and post-stimulation time) for each inhalation block.

RESULTS

HR increased significantly during the stimulation block. The quality of the model was satisfactory: mean absolute errors between modeled and experimental signals were lower than the resolution of the device. No significant lateralization was found between left and right values of most of the parameters.

CONCLUSION

Due to the lack of lateralization, this parametric identification of NIRS responses to hypercapnia could bring light to a potential asymmetry and be used as a biomarker in patients with cerebrovascular diseases.

Cerebrovascular carbon dioxide reactivity and flow-mediated dilation in young healthy South Asian and Caucasian European men

South Asians living in the United Kingdom have a 1.5-fold greater risk of ischemic stroke than the general population. Impaired cerebrovascular carbon dioxide (CO₂) reactivity is an independent predictor of ischemic stroke and cardiovascular mortality. We sought to test the hypothesis that cerebrovascular CO₂ reactivity is reduced in South Asians. Middle cerebral artery blood velocity (MCA V_m) was measured at rest and during stepwise changes in end-tidal partial pressure of CO₂ (PETCO2) in South Asian (n = 16) and Caucasian European (n = 18) men who were young (~20 yr), healthy, and living in the United Kingdom. Incremental hypercapnia was delivered via the open-circuit steady-state method, with stages of 4 and 7% CO₂ (≈21% oxygen, nitrogen balanced). Cerebrovascular CO₂ reactivity was calculated as the change in MCA V_m relative to the change in PETCO2. MCA V_m was not different in South Asians [59 (9) cm/s, mean (standard deviation)] and Caucasian Europeans [61 (12) cm/s; P > 0.05]. Similarly, cerebrovascular CO₂ reactivity was not different between the groups [South Asian 2.53 (0.76) vs. Caucasian European 2.61 (0.81) cm·s^-1·mmHg^-1; P > 0.05]. Brachial artery flow-mediated dilation was lower in South Asians [5.48 (2.94)%] compared with Caucasian Europeans [7.41 (2.28)%; P < 0.05]; however, when corrected for shear rate no between-group differences in flow-mediated dilation were observed (P > 0.05). Flow-mediated dilation was not correlated with cerebrovascular CO₂ reactivity measures. In summary, cerebrovascular CO₂ reactivity and flow-mediated dilation corrected for shear rate are preserved in young healthy South Asian men living in the United Kingdom.NEW & NOTEWORTHY Previous reports have identified an increased risk of ischemic stroke and peripheral endothelial dysfunction in South Asians compared with Caucasian Europeans. The main finding of this study is that cerebrovascular carbon dioxide reactivity (an independent predictor of ischemic stroke) is not different in healthy young South Asian and Caucasian European men.

When classical music relaxes the brain: An experimental study using Ultrasound Brain Tissue Pulsatility Imaging

INTRODUCTION

Recent evidence suggests that biomechanical parameters of the brain, such as Brain Tissue Pulsatility (BTP), could be involved in emotional reactivity. However, no study has investigated the impact of an emotional task on BTP. We used the ultrasound method of Tissue Pulsatility Imaging (TPI) to assess changes in BTP to exciting and relaxing classical music, in a musical perception task, as a validated paradigm to assess emotional reactivity.

METHODS

25 healthy volunteers were exposed via earphones to four 5-minute musical excerpts (two exciting and two relaxing musical excerpts) presented in a randomized order and intersected by 5 silence periods. Measures of BTP, Heart Rate (HR) and Skin Conductance (SC) were collected during the entire task.

RESULTS

The BTP significantly decreased with relaxing music compared to silence, and especially with the excerpt 'Entrance of the Shades' by Minkus. The HR and SC, but not Heart Rate Variability, were also decreased with relaxing music. We found no significant effect of exciting music.

DISCUSSION

We report, for the first time, that classical relaxing music decreases the amplitude of the brain pulsatile movements related to cerebral blood flow and mechanical properties of the brain parenchyma, which provides further evidence of the involvement of BTP in emotional reactivity. In addition, we validate the use of TPI as a non-invasive, portable and low cost tool for studies in psychophysiology, with the potential to be implemented as a biomarker in musicotherapy trials notably.

Confounding of Cerebral Blood Flow Velocity by Blood Pressure During Breath Holding or Hyperventilation in Transient Ischemic Attack or Stroke

Background and Purpose- Breath holding (BH) and hyperventilation are used to assess abnormal cerebrovascular reactivity, often in relation to severity of small vessel disease and risk of stroke with carotid stenosis, but responses may be confounded by blood pressure (BP) changes. We compared effects of BP and end-tidal carbon dioxide (etCO₂) on middle cerebral artery mean flow velocity (MFV) in consecutive transient ischemic attack and minor stroke patients. Methods- In the population-based, prospective OXVASC (Oxford Vascular Study) phenotyped cohort, change in MFV on transcranial Doppler ultrasound (ΔMFV, DWL-DopplerBox), beat-to-beat BP (Finometer), and etCO₂ was measured during 30 seconds of BH or hyperventilation. Two blinded reviewers independently assessed recording quality. Dependence of ΔMFV on ΔBP and ΔetCO₂ was determined by general linear models, stratified by quartiles. Results- Four hundred eighty-eight of 602 (81%) patients with adequate bone windows had high-quality recordings, more often in younger participants (64.6 versus 68.7 years; P<0.01), whereas 426 had hyperventilation tests (70.7%). During BH, ΔMFV was correlated with a rise in mean blood pressure (MBP; r²=0.15, P<0.001) but not ΔCO₂ (r²=0.002, P=0.32), except in patients with ΔMBP <10% (r²=0.13, P<0.001). In contrast during hyperventilation, the fall in MFV was similarly correlated with reduction in CO₂ and reduction in MBP (ΔCO₂: r²=0.13, P<0.001; ΔMBP: r²=0.12, P<0.001), with a slightly greater effect of ΔCO₂ when ΔMBP was <10% (r²=0.15). Stratifying by quartile, MFV increased linearly during BH across quartiles of ΔMBP, with no increase with ΔetCO₂. In contrast, during hyperventilation, MFV decreased linearly with ΔetCO₂, independent of ΔMBP. Conclusions- In older patients with recent transient ischemic attack or minor stroke, cerebral blood flow responses to BH were confounded by BP changes but reflected etCO₂ change during hyperventilation. Correct interpretation of cerebrovascular reactivity responses to etCO₂, including in small vessel disease and carotid stenosis, requires concurrent BP measurement.

Cerebral blood flow and cerebrovascular reactivity correlate with severity of motor symptoms in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is mainly characterized by movement dysfunction. Neurovascular unit (NVU) disruption has been proposed to be involved in the disease, but its role in PD neurodegenerative mechanisms is still unclear. The aim of this study was to investigate cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) within the regions belonging to the motor network, in patients with mild to moderate stages of PD.

METHODS

Twenty-eight PD patients (66.6 ± 8.6 years, 22 males, median [interquartile range, IQR] Hoehn & Yahr = 1.5 [1-1.9]) and 32 age- and sex-matched healthy controls (HCs) were scanned with arterial spin labeling (ASL) magnetic resonance imaging (MRI) for CBF assessment. ASL MRI was also acquired in hypercapnic conditions to induce vasodilation and subsequently allow for CVR measurement in a subgroup of 13 PD patients and 13 HCs. Median CBF and CVR were extracted from cortical and subcortical regions belonging to the motor network and compared between PD patients and HCs. In addition, the correlation between these parameters and the severity of PD motor symptoms [quantified with Unified Parkinson's Disease Rating Scale part III (UPDRS III)] was assessed. The false discovery rate (FDR) method was used to correct for multiple comparisons.

RESULTS

No significant differences in terms of CBF and CVR were found between PD patients and HCs. Positive significant correlations were observed between CBF and UPDRS III within the precentral gyrus, postcentral gyrus, supplementary motor area, striatum, pallidum, thalamus, red nucleus, and substantia nigra (pFDR < 0.05). Conversely, significant negative correlation between CVR and UPDRS III was found in the corpus striatum (pFDR < 0.05).

CONCLUSION

CBF and CVR assessment provides information about NVU integrity in an indirect and noninvasive way. Our findings support the hypothesis of NVU involvement at the mild to moderate stages of PD, suggesting that CBF and CVR within the motor network might be used as either diagnostic or prognostic markers for PD.

Cerebrovascular Reactivity Impairment in Preclinical Alzheimer's Disease

BACKGROUND AND PURPOSE

A substantial overlap exists between declines in cerebral vasoreactivity (CVR) and symptomatic Alzheimer's disease (AD). CVR can be quantified using transcranial Doppler (TCD) measurement of cerebral blood flow velocities (CBFV) in the middle cerebral artery (MCA) with CO₂ as a vasodilatory stimulus. The breath-hold acceleration index (BHAI) is a new, more reliable measure of CVR developed recently in our laboratory. Our primary goal is to explore the possibility of using TCD for asymptomatic AD screening.

METHODS

A pilot study population was divided into three groups: 9 healthy control subjects, 8 subjects identified as preclinical AD, and 10 patients diagnosed with prodromal or mild AD. Control subjects had a Clinical Dementia Rating (CDR) score of 0 without elevated amyloid-β (Aβ) on amyloid positron emission tomography (PET) imaging, preclinical AD subjects had CDR = 0 with elevated Aβ, and prodromal to mild AD subjects had CDR scores ≥.5 and elevated Aβ. CVR was calculated using two indices: the conventional breath-holding index (BHI) and the new BHAI. TCD parameters between the three groups were compared.

RESULTS

BHAI was able to distinguish between 9 normal control subjects and 8 preclinical-AD subjects with high statistical significance (P < .001). BHI and pulsatility index were able only to distinguish AD from healthy and preclinical subjects (P < .001).

CONCLUSIONS

In this exploratory pilot study, CVR was significantly decreased in preclinical, prodromal, and mild AD subjects as compared to the healthy group. Lower CVR in the preclinical AD group was detected using the new BHAI index but not the conventional BHI index.

Assessment of cerebrovascular reserve impairment using the breath-holding index in patients with leukoaraiosis

Many studies have demonstrated that leukoaraiosis is associated with impaired cerebrovascular reserve function. However, the definitive hemodynamic changes that occur in leukoaraiosis are not clear, and there are many controversies. This study aimed to investigate hemodynamic changes in symptomatic leukoaraiosis using transcranial Doppler ultrasonography and the breath-holding test in a Chinese Han population, from northern China. A total of 203 patients who were diagnosed with ischemic stroke or clinical chronic progressive ischemic symptoms were enrolled in this study, including 97 males and 106 females, with an age range of 43–93 years. The severity of leukoaraiosis was evaluated according to the Fazekas grading scale, and patients were divided into four groups accordingly. Grade 0 was no leukoaraiosis, and grades I, II, and III were mild, moderate, and severe leukoaraiosis, respectively, with 44, 79, 44, and 36 cases in each group. Transcranial Doppler ultrasonography and the breath-holding test were performed. The mean blood flow velocity of the bilateral middle cerebral artery was measured and the breath-holding index was calculated. The breath holding index was correlated with leukoaraiosis severity and cognitive impairment. Patients with a low breath holding index presented poor performance in the Montreal Cognitive Assessment (MoCA) and executive function tests. That is, the lower the breath holding index, the lower the scores for the MoCA and the higher for the trail-making test Parts A and B. These results indicate that the breath-holding index is a useful parameter for the evaluation of cerebrovascular reserve impairment in patients with leukoaraiosis. In addition, the breath-holding index can reflect cognitive dysfunction, providing a new insight into the pathophysiology of leukoaraiosis. This study was approved by the Ethics Committee of the Fifth People’s Hospital of Shenyang, China (approval No. 20160301) and registered in the Chinese Clinical Trial Registry (registration number: ChiCTR1800014421).

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.

Effects of sevoflurane versus propofol on cerebrovascular reactivity to carbon dioxide during laparoscopic surgery

Purpose

Cerebrovascular reactivity to carbon dioxide (CVR-CO₂) reflects cerebrovascular reserve capacity, which is important in many brain disorders, including cerebrovascular and Alzheimer’s diseases. Meanwhile, there is a relationship between CVR-CO₂ and cognitive function. Therefore, the study is aimed at investigating the effects of sevoflurane versus propofol on CVR-CO₂ during laparoscopic surgery, as well as the role of CVR-CO₂ on cognitive function during perioperative period.

Patients and methods

Eighty-eight patients, aged 18–65 years undergoing elective laparoscopic cholecystectomy, were randomly assigned to group S and group P. The patients in group S were induced with propofol and maintained with sevoflurane. The patients in group P were induced and maintained with propofol (target-controlled infusion). Remifentanil was given to both groups. CVR-CO₂ at baseline (before induction), before pneumoperitoneum and during pneumoperitoneum, as well as Mini-Mental State Examination scores at baseline and 24 hours after surgery were recorded.

Results

In group S, CVR-CO₂ before and during pneumoperitoneum increased significantly compared with baseline (P<0.05). In group P, CVR-CO₂ before pneumoperitoneum increased significantly (P<0.05), but CVR-CO₂ during pneumoperitoneum was not different compared with baseline. In either group, there was no significant correlation between mean blood pressure and CVR-CO₂ during surgery, and there was no significant difference between Mini-Mental State Examination scores at baseline and 24 hours after surgery.

Conclusion

Sevoflurane could maintain CVR-CO₂ at a higher level during pneumoperitoneum in surgery. Therefore, in patients with impaired cerebrovascular reserve capacity, inhaled anesthetic could be a priority strategy for anesthesia maintenance to improve the compensatory vasodilation ability of cerebral small vessels.