Search

Objectives: The InVITE study, starting in August 2021, was designed to examine the immunogenicity of different vaccine regimens in several countries including the Democratic Republic of Congo, Guinea, Liberia, and Mali. Prevaccination baseline samples were used to obtain estimates of previous SARS-CoV-2 infection in the study population. Methods: Adult participants were enrolled upon receipt of their initial COVID-19 vaccine from August 2021 to June 2022. Demographic and comorbidity data were collected at the time of baseline sample collection. SARS-CoV-2 serum anti-Spike and anti-Nucleocapsid antibody levels were measured. Results: Samples tested included 1016, 375, 663, and 776, from DRC, Guinea, Liberia, and Mali, respectively. Only 0.8% of participants reported a prior positive SARS-CoV-2 test, while 83% and 68% had anti-Spike and anti-Nucleocapsid antibodies, respectively. Conclusions: Overall SARS-CoV-2 seroprevalence was 86% over the accrual period, suggesting a high prevalence of SARS-CoV-2 infection. Low rates of prior positive test results may be explained by asymptomatic infections, limited access to SARS-CoV-2 test kits and health care, and inadequate surveillance. These seroprevalence rates are from a convenience sample and may not be representative of the population in general, underscoring the need for timely, well-conducted surveillance as part of global pandemic preparedness.

In this study, we investigated whether the first impression of a crowd of faces—crowd perception—is influenced by social background and cognitive processing. Specifically, we explored whether males and females, two groups that are distinct biologically and socially, differ in their ability to extract ensemble characteristics from crowds of faces that were comprised of different identities. Participants were presented with crowds of similar faces and were instructed to scroll through a morphed continuum of faces until they found a face that was representative of the average identity of each crowd. Consistent with previous research, females were more precise in single face perception. Furthermore, the results showed that females were generally more accurate in estimating the average identity of a crowd. However, the correlation between single face discrimination and crowd averaging differed between males and females. Specifically, male subjects’ ensemble integration superiority slightly compensated for their poor single face perception; their performance on the crowd perception task was not as poor as would be expected from their single face discrimination ability. Overall, the results suggest that group perception is not an isolated or uniform cognitive mechanism, but rather one that interacts with biological and social processes.

Previous studies suggest that normal vision extracts statistical information from sets of objects across the visual field (e.g., mean size). In this study, we explore whether patients with left unilateral neglect extract statistical summaries in a typical manner. We tested 4 patients with left unilateral neglect using a visual search task that varied the mean size of a group of circles within the display. The task was to report whether a target circle was present or not. On each trial, we first presented a single circle in the center of the screen (the target) which varied in size from trial to trial. The circles in the subsequent search display varied in size but were grouped together either on the left or right side of the display. The circles were accompanied by a group of irrelevant triangles that did not vary in size and appeared on the opposite side of the display. On 50% of trials the mean size of the circles was the size of the target and on 50% the mean size was different from the target. We analyzed accuracy when the circles were on the left compared to the right side of the display. When the targets were absent, patients produced more false alarms on the contralesional side when the mean size of the group was the target size than when it was not, a typical pattern of response demonstrating that the distractors on the ipsilesional side could be rejected in the summary statistic of the group of circles. Conversely, the ipsilesional side did not produce this difference, and if anything showed the reverse pattern. Further analyses demonstrated that the size of the distractor triangles on the contralesional side were pooled with ipsilesional circles under these conditions (i.e., distractor size could not be rejected and thus distorted the group summary statistic). These findings are discussed as they relate to statistical summary processing in patients with spatial attention deficits and to their performance on visual search tasks.

The cold pressor test (CPT) involves cold water immersion of either the upper or lower limb(s) and elicits increases in sympathetic nervous activity (SNA), heart rate (HR), and mean arterial pressure (MAP) via stimulation of pain and cutaneous thermoreceptors. Greater pain perception during the CPT is associated with greater increases in SNA and more robust physiological responses. Due to potential differential sensitivity to both painful and thermal stimuli between upper and lower limbs, as well as potential effects of total exposure area, it is unclear whether the choice of limb(s) in CPT protocol design differentially affects systemic and cerebral hemodynamic responses. Our objective was to assess systemic and cerebral hemodynamic and ventilatory responses to different CPT protocols of the hand (CPT H ), foot (CPT F ), or bilateral feet (CPT BF ). We hypothesized CPT BF would elicit greatest physiological responses due to increased exposure area to the cold stimulus. Twenty-eight (14 M, 14 F) healthy young adults [23.4 (SD: 2.4) yr] participated in three 3-min CPT protocols during a single visit. Blood pressure, HR, middle cerebral artery blood velocity (MCAv) and cerebrovascular conductance index, and end-tidal carbon dioxide ([Formula: see text]) were averaged over the final 30 s of each minute of the CPT for each protocol, and perceived pain was recorded at the end of each minute of the CPT. We found significant effects of the time-CPT protocol interaction on systolic blood pressure ( P = 0.02), diastolic blood pressure ( P < 0.01), MAP ( P < 0.01), and HR ( P < 0.001). There were no differences between CPT protocols on either MCAv ( P = 0.4) or cerebrovascular conductance index ( P = 0.1). HR responses peaked in the first minute of the CPT, and changes from baseline were greater in CPT BF [Δ14(16) beats/min] compared with CPT H [Δ5(13) beats/min; P = 0.01] and CPT F [Δ4.04(13.3) beats/min; P = 0.02]. MAP responses peaked in minute 2 of the CPT, and changes from baseline were greater in CPT H [Δ12(8) mmHg) and CPT BF (Δ13(9) mmHg] compared with CPT F [Δ8(7) mmHg; P < 0.01]. Perceived pain was significantly greater in the CPT BF [CPT1 7(2.3), CPT2 6.5(2.3), CPT3 6(3)] condition compared with CPT H [CPT1 6(1.3), CPT2 6(2.3), CPT3 6(2.3)] and CPT F [CPT1 6(3.0), CPT2 6(2.0), CPT3 5.5(3.0)] protocols at all three stages of the CPT ( P ≤ 0.01). Our findings suggest choice of limb(s) in CPT protocols may lead to differences in systemic hemodynamic responses, with pain perception potentially influencing these responses. Based on our results, we suggest that choice of limb should be considered in future design of CPT studies, with hand CPT providing the best balance between participant tolerability and robust physiological responses. NEW & NOTEWORTHY Choice of limb(s) in cold pressor test (CPT) studies appears to influence systemic hemodynamics. Hand and bilateral feet induce more robust responses than single-foot CPT, potentially due to increased exposure area and pain perception. Despite no significant cerebrovascular effects, a sustained hyperventilatory response was noted in bilateral feet CPT. Hand CPTs may provide a balance between robust physiological responses and tolerability. These findings underscore the need for careful limb selection in future CPT studies.

Arterial stiffening and changes in brain structure both occur with normal aging and can be exacerbated via acquired health conditions. While cross-sectional associations exist, the longitudinal relationship between arterial stiffness and brain structure remains unclear. In this study, we investigated 1) associations between baseline arterial stiffness index (ASI) and brain structure (global and regional grey matter volumes (GMV), white matter hyperintensities (WMH)) 10-years post-baseline (10.4±0.8 years) and 2) associations between the 10-year change in ASI from baseline and brain structure 10-years post-baseline in 650 healthy middle- to older-aged adults (53.4±7.5 years) from the UK Biobank. We observed significant associations between baseline ASI and GMV (p<0.001) and WMH (p=0.0036) 10-years post-baseline. No significant associations between 10-year change in ASI and brain structure (global GMV p=0.24; WMH volume p=0.87) were observed. There were significant associations of baseline ASI in 2 of 60 regional brain volumes analyzed (right posterior superior temporal gyrus p=0.001; left superior lateral occipital cortex p<0.001). Strong associations with baseline ASI, but not changes in ASI over 10-years, suggest arterial stiffness at the entry point of older adulthood is more impactful on brain structure 10-years later compared to age-related stiffening. Based on these associations, we suggest clinical monitoring and potential intervention for reducing arterial stiffness should occur in midlife to reduce vascular contributions to structural changes in the brain, supporting a healthy trajectory of brain aging. Our findings also support use of ASI as a surrogate for gold standard measures in showing overall relationships between arterial stiffness and brain structure.

Resistance training (RT) is associated with improved metabolism, bone density, muscular strength, and lower risk of osteoporosis, sarcopenia, and cardiovascular disease. Although RT imparts many physiological benefits, cerebrovascular adaptations to chronic RT are not well defined. Participation in RT is associated with greater resting peripheral arterial diameters, improved endothelial function, and general cardiovascular health, whereas simultaneously linked to reductions in central arterial compliance. Rapid blood pressure fluctuations during resistance exercise, combined with reduced arterial compliance, could lead to cerebral microvasculature damage and subsequent cerebral hypoperfusion. Reductions in cerebral blood flow (CBF) accompany normal aging, where chronic reductions in CBF are associated with changes in brain structure and function, and increased risk of neurodegeneration. It remains unclear whether reductions in arterial compliance with RT relate to subclinical cerebrovascular pathology, or if such adaptations require interpretation in the context of RT specifically. The purpose of this narrative review is to synthesize literature pertaining to cerebrovascular adaptations to RT at different stages of the life span. This review also aims to identify gaps in the current understanding of the long-term impacts of RT on cerebral hemodynamics and provide a mechanistic rationale for these adaptations as they relate to aging, cerebral vasculature, and overall brain health.

Limited data exist regarding the effects of acute exercise and exercise training on cerebrovascular hemodynamic variables after stroke. This systematic review and meta-analysis 1 ) examined the effects of acute exercise and exercise training on cerebrovascular hemodynamic variables reported in the stroke exercise literature and 2 ) synthesized the peak middle cerebral artery blood velocity (MCAv) achieved during an acute bout of moderate-intensity exercise in individuals after stroke. Six databases (Medline, Embase, Web of Science, CINAHL, PsycINFO, AMED) were searched from inception to December 1st, 2021 for studies that examined the effect of acute exercise or exercise training on cerebrovascular hemodynamics in adults after stroke. Two reviewers conducted title and abstract screening, full-text evaluation, data extraction, and quality appraisal. Random-effects models were used in meta-analysis. Nine studies, including four acute exercise ( n = 61) and five exercise training studies ( n = 193), were included. Meta-analyses were not statistically feasible for several cerebrovascular hemodynamic variables. Descriptive analysis reveals that exercise training may increase cerebral blood flow and cerebrovascular reactivity to carbon dioxide among individuals after stroke. Meta-analysis of three acute exercise studies revealed no significant changes in MCAv during acute moderate-intensity exercise [ n = 48 participants, mean difference = 5.2 cm/s, 95% confidence interval (CI) [-0.6, 11.0], P = 0.08] compared with resting MCAv values. This review suggests that individuals after stroke may have attenuated cerebrovascular hemodynamics as measured by the MCAv during acute moderate-intensity exercise. Aerobic exercise training is beneficial for improving cardiovascular health and function after stroke; higher-quality research utilizing agreed-upon hemodynamic variables is needed to synthesize the effects of exercise training on poststroke cerebrovascular hemodynamics.

Ventricular arrhythmias are associated with neurological impairment and could represent a source of cerebral hypoperfusion. In the present study, data from healthy individuals (n = 11), patients with ischaemic heart disease (IHD; ejection fraction >40%; n = 9) and patients with heart failure with reduced ejection fraction (HFrEF; EF = 31 (5)%, n = 11), as well as data from swine surgeries, where spontaneous ventricular arrhythmias were observed during cerebrovascular examination (transcranial Doppler ultrasound in humans and laser Doppler in swine) were analysed retrospectively to investigate the effect of arrhythmia on cerebral microvascular haemodynamics. A subset of participants also completed the Montreal Cognitive Assessment (MoCA). Middle cerebral artery mean blood velocity (MCA Vmean ) decreased during premature ventricular contraction (PVC) in all groups, and data from swine indicate PVCs reduced cerebral microvascular perfusion. Overall MCA Vmean was decreased in the HFrEF vs. control group. Further, %∆MCA Vmean /%∆mean arterial pressure during the PVC was greater in the HFrEF vs. control group and was correlated with decreased MoCA scores. Subanalysis of HFrEF data revealed that during bigeminy MCA Vmean decreased owing to reductions during irregular beats only. During non-sustained ventricular tachycardia, MCA Vmean decreased but recovered above baseline upon return to sinus rhythm. Also, haemodynamic perturbations during and following the PVC were greater in the brachial artery vs. the MCA. Therefore, ventricular arrhythmias decreased indices of cerebral perfusion irrespective of IHD or HFrEF. The relative magnitude of arrhythmia-induced haemodynamic perturbations appears to be population specific and arrhythmia type and organ dependent. The cumulative burden of arrhythmia-induced deficits may exacerbate existing cerebral hypoperfusion in HFrEF and contribute to neurological abnormalities in this population. KEY POINTS: Irregular heartbeats are often considered benign in isolation, but individuals who experience them frequently have a higher prevalence of cerebrovascular and/or cognitive associated disorders. How irregular heartbeats affect blood pressure and cerebral haemodynamics in healthy and cardiovascular disease patients, those with and without reduced ejection fraction, remains unknown. Here it was found that in the absence of symptoms associated with irregular heartbeats, such as dizziness or hypotension, single, multiple non-sustained and sustained irregular heartbeats influence cerebral haemodynamics in a population-specific, arrhythmia-type and organ-dependent manner. Relative deficits in the index of cerebral blood flow normalized to relative deficits in blood pressure were greatest in patients with heart failure with reduced ejection and inversely related with cognitive performance. Chronic arrhythmias may exacerbate existing cerebral hypoperfusion in heart failure with reduced ejection fraction, thereby providing a mechanistic link between otherwise benign irregular heartbeats and cognitive dysfunction, independent of embolism., (© 2022 The Authors. The Journal of Physiology © 2022 The Physiological Society.)