Reduced Cerebrovascular Oxygenation in Individuals with Post-Acute COVID-19 Syndrome (PACS) ("long COVID").

There is evidence that hypoxia occurs in the brain of some individuals who contracted the COVID-19 disease. Furthermore, it has been widely reported that about 13% of individuals who contracted the COVID-19 disease report persistent symptoms after the acute infection stage (>2 months post-acute infection). This is termed post-acute COVID-19 syndrome (PACS) or ("long COVID"). In this study, we aimed to determine if hypoxia measured non-invasively with frequency domain near-infrared spectroscopy (fdNIRS) occurs in asymptomatic and symptomatic individuals with post-acute COVID-19 disease. We show that 26% of our symptomatic group, measured on average 9.6 months post-acute COVID-19 disease, were hypoxic and 12% of the asymptomatic group, measured on average 2.5 months post-acute infection, were hypoxic. Our study indicates that fdNIRS measure of hypoxia in the brain may be a useful tool to identify individuals that are likely to respond to treatments targeted at reducing inflammation and improving oxygenation.

Temporal Pattern of Cortical Hypoxia in Multiple Sclerosis and Its Significance on Neuropsychological and Clinical Measures of Disability.

OBJECTIVE: Multiple sclerosis (MS) is a degenerative disease of the central nervous system (CNS) characterized by inflammation, demyelination, and axonal damage. It has been hypothesized that hypoxia plays a role in the pathogenesis of MS. This study was undertaken to investigate the reproducibility of non-invasively measured cortical microvascular hemoglobin oxygenation (St O2 ) using frequency domain near-infrared spectroscopy (fdNIRS), investigate its temporal pattern of hypoxia in people with MS (pwMS), and its relationship with neurocognitive function and mood. METHODS: We investigated the reproducibility of fdNIRS measurements. We measured cortical hypoxia in pwMS, and the relationships between St O2 , neurocognitive function, fatigue, and measures of physical disability. Furthermore, we cataloged the temporal pattern of St O2 measured at 1-week intervals for 4 weeks, and at 8 weeks and ~1 year. RESULTS: We show that fdNIRS parameters were highly reproducible in 7 healthy control participants measured over 6 days (p > 0.05). There was low variability between and within subjects. In line with our previous findings, we show that 33% of pwMS (n = 88) have cortical microvascular hypoxia. Over 8 weeks and at ~1 year, St O2 values for normoxic and hypoxic groups did not change significantly. There was no significant association between cognitive function and St O2 . This conclusion should be revisited as only a small proportion of the relapsing-remitting MS group (21%) was cognitively impaired. INTERPRETATION: The fdNIRS parameters have high reproducibility and repeatability, and we have demonstrated that hypoxia in MS is a chronic condition, lasting at least a year. The results show a weak relationship between cognitive functioning and oxygenation, indicating future study is required. ANN NEUROL 2023;94:1067-1079.

Brain hypoxia, neurocognitive impairment, and quality of life in people post-COVID-19.

OBJECTIVE: Systemic hypoxia occurs in COVID-19 infection; however, it is unknown if cerebral hypoxia occurs in convalescent individuals. We have evidence from other conditions associated with central nervous system inflammation that hypoxia may occur in the brain. If so, hypoxia could reduce the quality of life and brain function. This study was undertaken to assess if brain hypoxia occurs in individuals after recovery from acute COVID-19 infection and if this hypoxia is associated with neurocognitive impairment and reduced quality of life. METHODS: Using frequency-domain near-infrared spectroscopy (fdNIRS), we measured cerebral tissue oxygen saturation (StO2) (a measure of hypoxia) in participants who had contracted COVID-19 at least 8 weeks prior to the study visit and healthy controls. We also conducted neuropsychological assessments and health-related quality of life assessments, fatigue, and depression. RESULTS: Fifty-six percent of the post-COVID-19 participants self-reported having persistent symptoms (from a list of 18), with the most reported symptom being fatigue and brain fog. There was a gradation in the decrease of oxyhemoglobin between controls, and normoxic and hypoxic post-COVID-19 groups (31.7 ± 8.3 µM, 27.8 ± 7.0 µM and 21.1 ± 7.2 µM, respectively, p = 0.028, p = 0.005, and p = 0.081). We detected that 24% of convalescent individuals' post-COVID-19 infection had reduced StO2 in the brain and that this relates to reduced neurological function and quality of life. INTERPRETATION: We believe that the hypoxia reported here will have health consequences for these individuals, and this is reflected in the correlation of hypoxia with greater symptomology. With the fdNIRS technology, combined with neuropsychological assessment, we may be able to identify individuals at risk of hypoxia-related symptomology and target individuals that are likely to respond to treatments aimed at improving cerebral oxygenation.

Non-invasive Detection of Persistent Cortical Hypoxia in Multiple Sclerosis Using Frequency Domain Near-Infrared Spectroscopy (fdNIRS).

There may be a relationship between hypoxia and inflammation, which is important in the outcomes of a wide array of human diseases. Multiple sclerosis (MS) is one such disease. There is evidence that hypoxia may influence inflammation in MS. We showed previously that about 40% of participants with MS had hypoxia in the cortical grey matter using frequency-domain near-infrared spectroscopy (fdNIRS). In this study, we aimed to determine if hypoxia in MS persists chronically (for a year or more) by measuring at baseline and ≥12 months later. We found that hypoxia persists for at least a year in 80% of participants with MS. As more individuals remained hypoxic than returned to normoxia, the development of hypoxia may relate to disease progression.

NIRS Studies Show Reduced Interhemispheric Functional Connectivity in Individuals with Multiple Sclerosis That Exhibit Cortical Hypoxia.

Many with multiple sclerosis (MS) have low cortical microvascular oxygen levels (hypoxia), which have been previously proposed to exacerbate inflammation in MS. We do not know if hypoxia impacts or relates to brain function. We hypothesise that within the MS population, those who have hypoxia may show reduced brain functional connectivity (FC). We recruited 20 MS participants and grouped them into normoxic and hypoxic groups (n = 10 in each group) using frequency-domain near-infrared spectroscopy (fdNIRS). Functional coherence of the haemodynamic signal, quantified with functional near-infrared spectroscopy (fNIRS) was used as a marker of brain function and was carried out during resting-state, finger-tapping, and while completing two neurocognitive tasks. Reduced FC was detected in the hypoxic MS group. fNIRS measures of haemodynamic coherence in MS could be a biomarker of functional impairment and/or disease progression.

Carotid-femoral pulse wave velocity acquisition methods and their associations with cardiovascular risk factors and subclinical biomarkers of vascular health.

BACKGROUND: Different methods to measure carotid-femoral pulse wave velocity (CFPWV) may affect the measurements obtained and influence the association between CFPWV, cardiovascular risk factors and biomarkers of subclinical vascular health. The estimation of distance between the carotid and femoral artery measurement sites (the arterial path length) is particularly problematic. METHOD: We determined if CFPWV and equation-based estimates of CFPWV were influenced by arterial path length and if this affected the association of CFPWV with cardiovascular risk factors and subclinical vascular biomarkers. The CFPWV derived from the measurement of surface distance (CFPWV-D), arterial path length formula (CFPWV-F), and estimated CFPWV (ePWV) were obtained from 489 older adults (67.2 ±â€Š8.8 years). Macrovascular [carotid artery: lumen diameter (LD), inter-adventitial diameter (IAD), intima-media thickness (IMT) and total plaque area (TPA)] and microvascular [reactive hyperaemia index and urinary albumin-creatinine ratio (UACR)] biomarkers were also measured. RESULTS: CFPWV-D was significantly greater than CFPWV-F [9.6 (8.0-11.2) vs. 8.9 (7.6-10.5) m/s, P < 0.001], because of estimated path length being longer in CFPWV-D than CFPWV-F (495.4 ±â€Š44.8 vs. 465.3 ±â€Š20.6 mm, P < 0.001). ePWV was significantly greater than both CFPWV-F and CFPWV-D [11.0 (10.0-12.2) m/s, P < 0.001]. The three CFPWV methods were similarly associated with LD, IAD, IMT, TPA and UACR but not with cardiovascular risk factors. CONCLUSION: Different methods to measure CFPWV affect the derived measurement values and the association with cardiovascular risk factors but not the association with subclinical biomarkers of vascular health. These hitherto unreported observations are important considerations in experimental design, data interpretation and of particular importance, comparison between studies where CFPWV is measured.

Cerebral small vessel disease, systemic vascular characteristics and potential therapeutic targets.

INTRODUCTION: Cerebral small vessel disease (SVD) is prevalent in the elderly population and is associated with increased risk of dementia, stroke and disability. Currently there are no clear targets or strategies for the treatment of cerebral SVD. We set out to identify modifiable vascular treatment targets. PATIENTS AND METHODS: 112 participants with and without a history of CVD underwent macrovascular, microvascular and endothelial function tests and an MRI head scan. RESULTS: Increased carotid intima media thickness and carotid-femoral pulse wave velocity were associated with cerebral WMH (ß=1·1 p=0·001 and ß=1·66, p<0·0001 respectively). Adjusted cerebral resistance index (p=0·03) and brachial flow mediated dilation time to peak (p=0·001) were associated with the severity of cerebral WMH independent of age and sex. Post occlusive reactive hyperaemia time as a measure of microvascular reactivity was associated with WMH after adjustment for age and sex (p=0·03). Ankle Brachial Pressure Index and urinary albumin excretion rate predicted the severity of cerebral WMH (p=0·02 and 0·01 respectively). Age and hypertension were the most important risk factors for WMH severity (p< 0·0001). DISCUSSION: In addition to hypertension, microalbuminuria, arterial stiffness, vascular reactivity and cerebrovascular resistance could be potential treatment targets to halt the development or progression of cerebral SVD.

Intestinal sodium/glucose cotransporter 3 expression is epithelial and downregulated in obesity.

AIM: We aimed to determine whether the sodium/glucose cotransporter family member SGLT3, a proposed glucose sensor, is expressed in the intestine and/or kidney, and if its expression is altered in mouse models of obesity and in humans before and after weight-loss surgery. MAIN METHODS: We used in-situ hybridization and quantitative PCR to determine whether the Sglt3 isoforms 3a and 3b were expressed in the intestine and kidney of C57, leptin-deficient ob/ob, and diabetic BTBR ob/ob mice. Western blotting and immunohistochemistry were also used to assess SGLT3 protein levels in jejunal biopsies from obese patients before and after weight-loss Roux-en-Y gastric bypass surgery (RYGB), and in lean healthy controls. KEY FINDINGS: Sglt3a/3b mRNA was detected in the small intestine (duodenum, jejunum and ileum), but not in the large intestine or kidneys of mice. Both isoforms were detected in epithelial cells (confirmed using intestinal organoids). Expression of Sglt3a/3b mRNA in duodenum and jejunum was significantly lower in ob/ob and BTBR ob/ob mice than in normal-weight littermates. Jejunal SGLT3 protein levels in aged obese patients before RYGB were lower than in lean individuals, but substantially upregulated 6 months post-RYGB. SIGNIFICANCE: Our study shows that Sglt3a/3b is expressed primarily in epithelial cells of the small intestine in mice. Furthermore, we observed an association between intestinal mRNA Sglt3a/3b expression and obesity in mice, and between jejunal SGLT3 protein levels and obesity in humans. Further studies are required to determine the possible role of SGLT3 in obesity.

Weight change and sulfonylurea therapy are related to 3 year change in microvascular function in people with type 2 diabetes.

AIMS/HYPOTHESIS: Although cardiovascular disease is the biggest cause of death in people with diabetes, microvascular complications have a significant impact on quality of life and financial burden of the disease. Little is known about the progression of microvascular dysfunction in the early stages of type 2 diabetes before the occurrence of clinically apparent complications. We aimed to explore the determinants of endothelial-dependent and -independent microvascular function progression over a 3 year period, in people with and without both diabetes and few clinical microvascular complications. METHODS: Demographics were collected in 154 participants with type 2 diabetes and in a further 99 participants without type 2 diabetes. Skin microvascular endothelium-dependent response to iontophoresis of acetylcholine and endothelium-independent responses to sodium nitroprusside were measured using laser Doppler fluximetry. All assessments were repeated 3 years later. RESULTS: People with type 2 diabetes had impaired endothelial-dependent microvascular response compared with those without (AUC 93.9 [95% CI 88.1, 99.4] vs 111.9 [102.3, 121.4] arbitrary units [AU] × min, p < 0.001, for those with vs without diabetes, respectively). Similarly, endothelial-independent responses were attenuated in those with diabetes (63.2 [59.2, 67.2] vs 75.1 [67.8, 82.4] AU × min, respectively, p = 0.002). Mean microvascular function declined over 3 years in both groups to a similar degree (pinteraction 0.74 for response to acetylcholine and 0.69 for response to sodium nitroprusside). In those with diabetes, use of sulfonylurea was associated with greater decline (p = 0.022 after adjustment for co-prescriptions, change in HbA1c and weight), whereas improving glycaemic control was associated with less decline of endothelial-dependent microvascular function (p = 0.03). Otherwise, the determinants of microvascular decline were similar in those with and without diabetes. The principal determinant of change in microvascular function in the whole population was weight change over 3 years, such that those that lost ≥5% weight had very little decline in either endothelial-dependent or -independent function compared with those that were weight stable, whereas those who gained weight had a greater decline in function (change in endothelial-dependent function was 1.2 [95% CI -13.2, 15.7] AU × min in those who lost weight; -15.8 [-10.5, -21.0] AU × min in those with stable weight; and -37.8 [-19.4, -56.2] AU × min in those with weight gain; ptrend < 0.001). This association of weight change with change in endothelial function was driven by people with diabetes; in people without diabetes, the relationship was nonsignificant. CONCLUSIONS/INTERPRETATION: Over 3 years, physiological change in weight was the greatest predictor of change in microvascular function.

SGLT2 inhibition with empagliflozin improves coronary microvascular function and cardiac contractility in prediabetic ob/ob-/- mice.

BACKGROUND: Sodium-glucose cotransporter 2 inhibitors (SGLT2i) is the first class of anti-diabetes treatment that reduces mortality and risk for hospitalization due to heart failure. In clinical studies it has been shown that SGLT2i's promote a general shift to fasting state metabolism characterized by reduced body weight and blood glucose, increase in glucagon/insulin ratio and modest increase in blood ketone levels. Therefore, we investigated the connection between metabolic changes and cardiovascular function in the ob/ob-/- mice; a rodent model of early diabetes with specific focus on coronary microvascular function. Due to leptin deficiency these mice develop metabolic syndrome/diabetes and hepatic steatosis. They also develop cardiac contractile and microvascular dysfunction and are thus a promising model for translational studies of cardiometabolic diseases. We investigated whether this mouse model responded in a human-like manner to empagliflozin treatment in terms of metabolic parameters and tested the hypothesis that it could exert direct effects on coronary microvascular function and contractile performance. METHODS: Lean, ob/ob-/- untreated and ob/ob-/- treated with SGLT2i were followed for 10 weeks. Coronary flow velocity reserve (CFVR) and fractional area change (FAC) were monitored with non-invasive Doppler ultrasound imaging. Food intake, urinary glucose excursion and glucose control via HbA1c measurements were followed throughout the study. Liver steatosis was assessed by histology and metabolic parameters determined at the end of the study. RESULTS: Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob-/- animals resulted in a switch to a more catabolic state as observed in clinical studies: blood cholesterol and HbA1c were decreased whereas glucagon/insulin ratio and ketone levels were increased. SGLT2i treatment reduced liver triglyceride, steatosis and alanine aminotransferase, an indicator for liver dysfunction. L-Arginine/ADMA ratio, a marker for endothelial function was increased. SGLT2i treatment improved both cardiac contractile function and coronary microvascular function as indicated by improvement of FAC and CFVR, respectively. CONCLUSIONS: Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob-/- mice mimics major clinical findings regarding metabolism and cardiovascular improvements and is thus a useful translational model. We demonstrate that SGLT2 inhibition improves coronary microvascular function and contractile performance, two measures with strong predictive values in humans for CV outcome, alongside with the known metabolic changes in a preclinical model for prediabetes and heart failure.

Radial artery intima-media thickness regresses after secondary prevention interventions in patients' post-acute coronary syndrome and is associated with cardiac and kidney biomarkers.

BACKGROUND: Radial artery intima-media thickness (rIMT) measured by ultra-high-resolution ultrasound is associated with increased cardiovascular risk and predicts outcomes. We performed non-invasive high-resolution ultrasound of the radial artery to investigate vascular changes in subjects presenting with acute coronary syndrome (ACS) and who had undergone percutaneous coronary intervention (PCI). PURPOSE: In the present work, we aimed to follow rIMT change over time post-acute coronary syndrome as a tool to monitor potential response to intensified medical therapy. METHODS: We examined 256 subjects who underwent PCI due to ACS and healthy controls (n= 39) and we measured a number of biomarkers, which are known to be associated with cardiovascular disease. Images of radial artery were acquired bilaterally in the longitudinal view using a 50 MHz transducer (Vevo 2100 VisualSonics, Inc, Toronto, Ontario, Canada). Carotid IMT (cIMT) and rIMT were measured at <1 month after index PCI followed by a repeated measurement of rIMT at 4 months from the ACS in a sub-set (n=117). RESULTS: rIMT measured within 1 month post ACS was significantly higher than rIMT after 4 months from ACS, (p < 0.0001), mean ± SD (rIMT right 0.35 ± 0.08; rIMT left 0.37 ± 0.08) vs. (rIMT right 0.29 ± 0.08; rIMT left 0.31 ± 0.09) respectively. There was no statistically significant change in cIMT. In healthy controls there were no changes in rIMT or cIMT overtime. High levels of CX3CL1 and myeloperoxidase measured within one month post ACS are associated with increase of rIMT, r=0.38 (p< 0.0001) and r=0.41 (p< 0.0001) respectively. CONCLUSIONS: rIMT seem to decrease systemically after ACS and is accompanied with corresponding biomarker change. The cause and clinical implications of the observed decrement in rIMT after ACS need further studies.

Hyperglycemia Induced by Glucokinase Deficiency Accelerates Atherosclerosis Development and Impairs Lesion Regression in Combined Heterozygous Glucokinase and the Apolipoprotein E-Knockout Mice.

Aim. Models combining diabetes and atherosclerosis are important in evaluating the cardiovascular (CV) effects and safety of antidiabetes drugs in the development of treatments targeting CV complications. Our aim was to evaluate if crossing the heterozygous glucokinase knockout mouse (GK+/-) and hyperlipidemic mouse deficient in apolipoprotein E (ApoE-/-) will generate a disease model exhibiting a diabetic and macrovascular phenotype. Methods. The effects of defective glucokinase on the glucose metabolism and on the progression and regression of atherosclerosis on high-fat diets were studied in both genders of GK+/-ApoE-/- and ApoE-/- mice. Coronary vascular function of the female GK+/-ApoE-/- and ApoE-/- mice was also investigated. Results. GK+/-ApoE-/- mice show a stable hyperglycemia which was increased on Western diet. In oral glucose tolerance test, GK+/-ApoE-/- mice showed significant glucose intolerance and impaired glucose-stimulated insulin secretion. Plasma lipids were comparable with ApoE-/- mice; nevertheless the GK+/-ApoE-/- mice showed slightly increased atherosclerosis development. Conclusions. The GK+/-ApoE-/- mice showed a stable and reproducible hyperglycemia, accelerated atherosclerotic lesion progression, and no lesion regression after lipid lowering. This novel model provides a promising tool for drug discovery, enabling the evaluation of compound effects against both diabetic and cardiovascular endpoints simultaneously in one animal model.

Reactivity to low-flow as a potential determinant for brachial artery flow-mediated vasodilatation.

Previous studies have reported a vasoconstrictor response in the radial artery during a cuff-induced low-flow condition, but a similar low-flow condition in the brachial artery results in nonuniform reactivity. This variable reactivity to low-flow influences the subsequent flow-mediated dilatation (FMD) response following cuff-release. However, it is uncertain whether reactivity to low-flow is important in data interpretation in clinical populations and older adults. This study aimed to determine the influence of reactivity to low-flow on the magnitude of brachial artery FMD response in middle-aged and older individuals with diverse cardiovascular risk profiles. Data were analyzed from 165 individuals, divided into increased cardiovascular risk (CVR: n = 115, 85M, 67.0 ± 8.8 years) and healthy control (CTRL: n = 50, 30M, 63.2 ± 7.2 years) groups. Brachial artery diameter and blood velocity data obtained from Doppler ultrasound were used to calculate FMD, reactivity to low-flow and estimated shear rate (SR) using semiautomated edge-detection software. There was a significant association between reactivity to low-flow and FMD in overall (r = 0.261), CTRL (r = 0.410) and CVR (r = 0.189, all P < 0.05) groups. Multivariate regression analysis found that reactivity to low-flow, peak SR, and baseline diameter independently contributed to FMD along with sex, the presence of diabetes, and smoking (total R(2) = 0.450). There was a significant association between reactivity to low-flow and the subsequent FMD response in the overall dataset, and reactivity to low-flow independently contributed to FMD These findings suggest that reactivity to low-flow plays a key role in the subsequent brachial artery FMD response and is important in the interpretation of FMD data.

Echogenicity of the Common Carotid Artery Intima-Media Complex in Stroke.

The grey-scale median of the common carotid artery intima-media complex (IM-GSM) characterizes arterial wall composition, and a low IM-GSM is associated with increased cardiovascular mortality in the elderly. We aimed to determine differences in the IM-GSM between a cohort with cerebrovascular disease and a healthy cohort. Eighty-two healthy individuals (control group: 63.2 ± 8.7 y) and 96 patients with either stroke or transient ischemic attacks (CRVD group: 68.6 ± 9.8 y) were studied. Common carotid artery intima-media thickness and IM-GSM obtained by ultrasound were analyzed using semi-automated edge-detection software. The IM-GSM was significantly lower in the CRVD group than in the control group (106 ± 24 vs. 124 ± 27 au, p < 0.001). The IM-GSM was similar for the infarct and non-infarct sides in CRVD. In the pooled cohort of all participants, the lower the quartile of IM-GSM, the greater were the carotid artery intima-media thickness and carotid artery remodeling. These results suggest the presence of an altered atherosclerotic phenotype in the intima-media complex of CRVD patients that can be detected by ultrasound.

Blood Oxygen Saturation After Ischemia is Altered With Abnormal Microvascular Reperfusion.

OBJECTIVE: We have previously described a distinct abnormality in the cutaneous microcirculation that is characterized by an abnormal reperfusion response following an ischemic stimulus. We investigated the physiological significance of this abnormality; by measuring microvascular perfusion and blood oxygen saturation in groups stratified by three distinct reperfusion responses. METHODS: Cutaneous microvascular reperfusion after four minutes of arterial occlusion above the ankle was measured on the foot using laser Doppler fluximetry and optical reflectance spectroscopy in almost 400 adults. Individuals were stratified into three groups according to the microvascular reperfusion response: normal and two abnormal patterns (DEP and NDEP). RESULTS: Our main findings were that abnormal microvascular reperfusion responses (DEP and NDEP) had a higher baseline oxygen saturation (p = 0.005), a lower plateau in oxygen saturation (p < 0.0001 and <0.0001, respectively), lower oxygen saturation area under the curve (p < 0.0001 and <0.0001), a longer time to reach oxygen saturation plateau (p = 0.002 and 0.001), and a longer time to initiate an increase in oxygen saturation (p = 0.007 and 0.001) compared to normal. Differences remained after adjustment for confounding variables. CONCLUSIONS: Individuals with abnormal microvascular reperfusion had a markedly altered pattern of oxygen increase during reperfusion. We propose that this may represent dysfunctional microvascular autoregulation that is clinically important in the etiopathology of target organ damage.

Microcirculation on a large scale: techniques, tactics and relevance of studying the microcirculation in larger population samples.

The role of microcirculatory dysfunction is increasingly being recognized in the etiopathogenesis of cardiovascular disease. Whilst the importance of detailed mechanistic studies to determine the exact nature of these disturbances is without question, it was large-scale population-based studies that first identified the associations between deranged microvascular perfusion, autoregulation or structure, and subsequent target organ damage. This is the subject of considerable studies to establish whether there is a causal effect in either direction, or simply represents shared risk factors, although it is most likely to be a complex combination of bidirectional interactions. The techniques for investigating microcirculatory function have evolved almost exponentially over the last 75 years: So too have the strategies for investigation. Current epidemiological studies are focusing on attempting to untangle the inter-relationship between risk factors and pathological mechanisms to attempt to determine whether these represent therapeutic targets or simple markers of unmeasured risk. We plan to review the techniques used for these population-based studies, the advances made, and the clinical implications derived.