Variations In Blood Flow Research Articles

Retinal and choroidal blood flow variations after an endurance exercise: A real-life pilot study at the Paris Marathon

ObjectivesTo collect information about the retinal blood flow variations and other choroidal and retinal parameters during a prolonged effort such as marathon running. DesignNon-randomized prospective cohort study. MethodsPatients were recruited through an information campaign at the Rothschild Foundation Hospital (Paris, France). A first visit (V1) was planned in the month before the marathon. All participants underwent blood pressure measurement, fundus photography, spectral domain-optical coherence tomography (SD-OCT) and OCT-angiography (OCT-A). A second visit (V2) was scheduled within one hour of crossing the finish line. The same tests were repeated, using the same equipment. ResultsOf the 31 runners who were included, 29 finished the marathon and attended V2. At baseline, various ophthalmological abnormalities were found in 45.2% of the 58 eyes, among which almost a third concerned the optic nerve and a quarter the pachychoroid spectrum. A significant decrease in retinal vascular plexus density was found between V1 and V2 (p<0.01). While median macular and retinal nerve fiber layer (RNFL) thicknesses significantly increased after the marathon (p<0.01), median choroidal thickness significantly decreased (p<0.01). Both systolic and diastolic blood pressures significantly decreased (p<0.01 and p=0.021 respectively). ConclusionsProlonged physical effort impacts the structure and vascularization of the retina and the choroid. Hypoxia and dehydration due to such an effort may induce a low ocular blood flow rate resulting in a choroidal thinning, contrasting with a transient subclinical ischemic edema of the inner retina and optic nerve head. Clinical Trial Registration NumberNCT03864380.

Association of changes of retinal vessels diameter with ocular blood flow in eyes with diabetic retinopathy

We investigated morphological changes of retinal arteries to determine their association with the blood flow and systemic variables in type 2 diabetes patients. The patients included 47 non-diabetic retinopathy eyes, 36 mild or moderate nonproliferative diabetic retinopathy (M-NPDR) eyes, 22 severe NPDR (S-NPDR) eyes, 32 PDR eyes, and 24 normal eyes as controls. The mean wall to lumen ratio (WLR) measured by adaptive optics camera was significantly higher in the PDR groups than in all of the other groups (all P < 0.001). However, the external diameter of the retinal vessels was not significantly different among the groups. The mean blur rate (MBR)-vessel determined by laser speckle flowgraphy was significantly lower in the PDR group than in the other groups (P < 0.001). The WLR was correlated with MBR-vessel (r = − 0.337, P < 0.001), duration of disease (r = 0.191, P = 0.042), stage of DM (r = 0.643, P < 0.001), systolic blood pressure (r = 0.166, P < 0.037), and presence of systemic hypertension (r = 0.443, P < 0.001). Multiple regression analysis demonstrated that MBR-vessel (β = − 0.389, P < 0.001), presence of systemic hypertension (β = 0.334, P = 0.001), and LDL (β = 0.199, P = 0.045) were independent factors significantly associated with the WLR. The increased retinal vessel wall thickness led to a narrowing of lumen diameter and a decrease in the blood flow in the PDR group.

Osteopathy modulates brain\u2013heart interaction in chronic pain patients: an ASL study

In this study we used a combination of measures including regional cerebral blood flow (rCBF) and heart rate variability (HRV) to investigate brain–heart correlates of longitudinal baseline changes of chronic low back pain (cLBP) after osteopathic manipulative treatment (OMT). Thirty-two right-handed patients were randomised and divided into 4 weekly session of OMT (N = 16) or Sham (N = 16). Participants aged 42.3 ± 7.3 (M/F: 20/12) with cLBP (duration: 14.6 ± 8.0 m). At the end of the study, patients receiving OMT showed decreased baseline rCBF within several regions belonging to the pain matrix (left posterior insula, left anterior cingulate cortex, left thalamus), sensory regions (left superior parietal lobe), middle frontal lobe and left cuneus. Conversely, rCBF was increased in right anterior insula, bilateral striatum, left posterior cingulate cortex, right prefrontal cortex, left cerebellum and right ventroposterior lateral thalamus in the OMT group as compared with Sham. OMT showed a statistically significant negative correlation between baseline High Frequency HRV changes and rCBF changes at T2 in the left posterior insula and bilateral lentiform nucleus. The same brain regions showed a positive correlation between rCBF changes and Low Frequency HRV baseline changes at T2. These findings suggest that OMT can play a significant role in regulating brain–heart interaction mechanisms.

Venous Flow Variation Predicts Preoperative Pulmonary Venous Obstruction in Children with Total Anomalous Pulmonary Venous Connection

Identifying preoperative pulmonary venous obstruction in total anomalous pulmonary venous connection is important to guide treatment planning and risk prognostication. No standardized echocardiographic definition of obstruction exists in the literature. Definitions based on absolute velocities are affected by technical limitations and variations in pulmonary venous return. The authors developed a metric to quantify pulmonary venous blood flow variation: pulmonary venous variability index (PVVI). The aim of this study was to demonstrate its accuracy in defining obstruction. All patients with total anomalous pulmonary venous connection at a single institution were identified. Echocardiograms were reviewed, and maximum (Vmax), mean (Vmean), and minimum (Vmin) velocities along the pulmonary venous pathway were measured. PVVI was defined as (Vmax-Vmin)/Vmean. These metrics were compared with pressures measured on cardiac catheterization. Echocardiographic measures were then compared between patients with and without clinical preoperative obstruction (defined as a need for preoperative intubation, catheter-based intervention, or surgery within 1day of diagnosis), as well as pulmonary edema by chest radiography and markers of lactic acidosis. One hundred thirty-seven patients were included, with 22 having catheterization pressure recordings. Vmax and Vmean were not different between patients with catheter gradients ≥ 4 and<4mm Hg, while PVVI was significantly lower and Vmin higher in those with gradients ≥ 4mm Hg. The composite outcome of preoperative obstruction occurred in 51 patients (37%). Absolute velocities were not different between patients with and without clinical obstruction, while PVVI was significantly lower in patients with obstruction. All metrics except Vmax were associated with pulmonary edema; none were associated with blood gas metrics. The authors developed a novel quantitative metric of pulmonary venous flow, which was superior to traditional echocardiographic metrics. Decreased PVVI was highly associated with elevated gradients measured by catheterization and clinical preoperative obstruction. These results should aid risk assessment and diagnosis preoperatively in patients with total anomalous pulmonary venous connection.

Simultaneous measurements of tissue blood flow and oxygenation using a wearable fiber-free optical sensor.

.Significance: There is an essential need to develop wearable multimodality technologies that can continuously measure both blood flow and oxygenation in deep tissues to investigate and manage various vascular/cellular diseases.Aim: To develop a wearable dual-wavelength diffuse speckle contrast flow oximetry (DSCFO) for simultaneous measurements of blood flow and oxygenation variations in deep tissues.Approach: A wearable fiber-free DSCFO probe was fabricated using 3D printing to confine two small near-infrared laser diodes and a tiny CMOS camera in positions for DSCFO measurements. The spatial diffuse speckle contrast and light intensity measurements at the two different wavelengths enable quantification of tissue blood flow and oxygenation, respectively. The DSCFO was first calibrated using tissue phantoms and then tested in adult forearms during artery cuff occlusion.Results: Phantom tests determined the largest effective source–detector distance (15 mm) and optimal camera exposure time (10 ms) and verified the accuracy of DSCFO in measuring absorption coefficient variations. The DSCFO detected substantial changes in forearm blood flow and oxygenation resulting from the artery occlusion, which meet physiological expectations and are consistent with previous study results.Conclusions: The wearable DSCFO may be used for continuous and simultaneous monitoring of blood flow and oxygenation variations in freely behaving subjects.

A Compact Multi-Distance DCS and Time Domain NIRS Hybrid System for Hemodynamic and Metabolic Measurements.

In this work, we present a new multi-distance diffuse correlation spectroscopy (DCS) device integrated with a compact state-of-the-art time domain near infrared spectroscopy (TD-NIRS) device. The hybrid DCS and TD-NIRS system allows to retrieve information on blood flow, tissue oxygenation, and oxygen metabolic rate. The DCS device performances were estimated in terms of stability, repeatability, ability in retrieving variations of diffusion coefficient, influence of the tissue optical properties, effect of varying count rates and depth sensitivity. Crosstalk between DCS and TD-NIRS optical signals was also evaluated. Finally, in vivo experiments (venous and arterial cuff occlusions on the arm) were conducted to test the ability of the hybrid system in measuring blood flow variations.

Deep Brain Stimulation in Alzheimer's Disease: Targeting the Nucleus Basalis of Meynert.

Alzheimer's disease (AD) is becoming a prevalent disease in the elderly population. Past decades have witnessed the development of drug therapies with varying targets. However, all drugs with a single molecular target fail to reverse or ameliorate AD progression, which ultimately results in cortical and subcortical network dysregulation. Deep brain stimulation (DBS) has been proven effective for the treatment of Parkinson's disease, essential tremor, and other neurological diseases. As such, DBS has also been gradually acknowledged as a potential therapy for AD. The current review focuses on DBS of the nucleus basalis of Meynert (NBM). As a critical component of the cerebral cholinergic system and the Papez circuit in the basal ganglia, the NBM plays an indispensable role in the subcortical regulation of memory, attention, and arousal state, which makes the NBM a promising target for modulation of neural network dysfunction and AD treatment. We summarized the intricate projection relations and functionality of the NBM, current approaches for stereotactic localization and evaluation of the NBM, and the therapeutic effects of NBM-DBS both in patients and animal models. Furthermore, the current shortcomings of NBM-DBS, such as variations in cortical blood flow, increased temperature in the target area, and stimulation-related neural damage, were presented.

Speckle contrast diffuse correlation tomography of cerebral blood flow in perinatal disease model of neonatal piglets.

We adapted and tested an innovative noncontact speckle contrast diffuse correlation tomography (scDCT) system for 3D imaging of cerebral blood flow (CBF) variations in perinatal disease models utilizing neonatal piglets, which closely resemble human neonates. CBF variations were concurrently measured by the scDCT and an established diffuse correlation spectroscopy (DCS) during global ischemia, intraventricular hemorrhage, and asphyxia; significant correlations were observed. Moreover, CBF variations associated reasonably with vital pathophysiological changes. In contrast to DCS measurements of mixed signals from local scalp, skull and brain, scDCT generates 3D images of CBF distributions at prescribed depths within the head, thus enabling specific determination of regional cerebral ischemia. With further optimization and validation in animals and human neonates, scDCT has the potential to be a noninvasive imaging tool for both basic neuroscience research in laboratories and clinical applications in neonatal intensive care units.

A Case Report about Persistent Left Superior Vena Cava: Is it Always Asymptomatic?

A persistent left superior vena cava (PLSVC) is a rare malformation which affects approximately 0.3% - 0.5% of the population and it is presented along with a right-sided superior vena cava in 82.2% of the cases reported [1]. Clinicians diagnose it incidentally by difficulties with pacemaker implantation, central venous catheterization or screening for another etiologies when it is not accompanied by other anomalies it is typically asymptomatic. W. Schummer et al. described the embryogenesis and the anatomic variations of persistent LSVC according to the positioning of a central venous catheter on the chest radiograph: type I, normal; type II, only PLSVC; type IIIa, right and left superior vena cava with connection; type IIIb, right and left superior vena cava without connection [2]. In 92% of individuals with PLSVC, the PLSVC drains into a dilated coronary sinus (CS) and rest 8% drain directly into the left atrium. PLSVC is caused by a failure in the closure of the left anterior cardinal vein during embryogenic development [3]. The coronary sinus (CS) is a vein that transmits venous blood to the right atrium though atrioventricular groove. The CS wall contains atrial myocardium. Thus, its size extensively depends on variability of blood flow and pressure. We present a variant PLSVC with unknown prevalence and a mild platypnea-orthodeoxia syndrome after recovery of COVID-19 related acute respiratory distress syndrome (ARDS).

Chapter 28 - Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Vibrocarotidography: A Novel Measurement Technique to Quantify Pulsations at Common Carotid Arteries

In this article, aortic-ejected blood flow and aortic pressure are investigated as an independent tool for diagnosing cardiovascular risk. This study presents vibrocarotidography (ViCG), a novel noninvasive and nonintrusive way to measure aortic blood-flow variations in each heartbeat through carotid arteries. Most of the existing state-of-the-art works suggested to use contact-based pressure sensors and noncontact sensing devices, including wave radar and laser Doppler vibrometer (LDV) for carotid pulse acquisition. However, these sensors have operational design limitations and poor immunity against environmental noises. To address these issues, the proposed method uses a miniaturized and cost-efficient microelectromechanical system (MEMS)-based accelerometer sensor to record the vibrational pulsations on common carotid artery. This article presents our developed electronic circuitry for ViCG signal acquisition and signal processing perspective for estimating indispensable cardiac events. The study focuses to show the ViCG signal as an alternative measure of central blood-flow variations. Significance of the ViCG signal is exhibited by assessing the rate of pulsations and comparing with the heart rhythms measured from the reference electrocardiogram (ECG) and photoplethysmogram (PPG) signals. A quantitative Bland–Altman analysis shows a mean difference (MD) of −0.01 ms and a correlation coefficient of 0.93 ( $R$ -squared) between the cardiac intervals measured from the ViCG and ECG signals, whereas they are found to be 0.03 ms and 0.92 for the ViCG–PPG signal pair. They reveal a highly strong correlation and agreement for heart cycle estimation. The performance analysis suggests that the ViCG signal acquired through a simple MEMS-based accelerometer can be utilized as a surrogate of central blood flow measurement and may be employed for continuous health monitoring in personalized-, home-, and hospital-healthcare systems.

Presentation of a Segmentation Method for a Diabetic Retinopathy Patient's Fundus Region Detection Using a Convolutional Neural Network.

Diabetic retinopathy is characteristic of a local distribution that involves early-stage risk factors and can forecast the evolution of the illness or morphological lesions related to the abnormality of retinal blood flows. Regional variations in retinal blood flow and modulation of retinal capillary width in the macular area and the retinal environment are also linked to the course of diabetic retinopathy. Despite the fact that diabetic retinopathy is frequent nowadays, it is hard to avoid. An ophthalmologist generally determines the seriousness of the retinopathy of the eye by directly examining color photos and evaluating them by visually inspecting the fundus. It is an expensive process because of the vast number of diabetic patients around the globe. We used the IDRiD data set that contains both typical diabetic retinopathic lesions and normal retinal structures. We provided a CNN architecture for the detection of the target region of 80 patients' fundus imagery. Results demonstrate that the approach described here can nearly detect 83.84% of target locations. This result can potentially be utilized to monitor and regulate patients.

Short-term cerebral blood flow variability in major depressive disorder

BackgroundPrevious research has documented reduced heart rate and blood pressure variability in major depressive disorder (MDD), suggesting a limited capacity for cardiovascular regulation and diminished homeostatic resources in the disorder. This study aimed to complement this knowledge by investigating short-term cerebral blood flow (CBF) variability in MDD. MethodsUsing transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries of both hemispheres were recorded in 35 MDD patients and 35 healthy controls, at rest and during serial subtraction task-induced mental stress. CBF variability was represented by the root mean square of successive differences (RMSSD) in the beat-to-beat mean, systolic and diastolic flow velocity. ResultsPatients, as compared to controls, exhibited smaller mean and diastolic blood flow variability in MCA both at rest and during mental stress. Mean, systolic and diastolic blood flow variability were greater during the task than at rest. CBF variability did not differ between patient subgroups composed according to medication use. LimitationsPotential effects of blood pressure and respiration on CBF variability could not be investigated. ConclusionsThe study revealed evidence of reduced short-term CBF variability in MDD. The task-induced CBF variability increase may be ascribed to neural activity associated with arithmetic processing. Lower blood pressure variability and deficient autonomic cardiovascular control may contribute to the reduction of short-term CBF variability seen in MDD. Short-term CBF variability reflects preserved interplay of regulatory mechanisms ensuring optimal blood and energy supply to the brain. Therefore, the results suggest impaired cerebroprotective mechanisms, associated with suboptimal cerebral performance.

Placental Corticotrophin-Releasing Hormone is a Modulator of Fetal Liver Blood Perfusion.

Variation in fetal liver blood flow influences fetal growth and postnatal body composition. Placental corticotrophin-releasing hormone has been implicated as a key mediator of placental-fetal perfusion. To determine whether circulating levels of placental corticotrophin-releasing hormone across gestation are associated with variations in fetal liver blood flow. Prospective cohort study. Fetal ultrasonography was performed at 30 weeks' gestation to characterize fetal liver blood flow (quantified by subtracting ductus venosus flow from umbilical vein flow). Placental corticotrophin-releasing hormone was measured in maternal circulation at approximately 12, 20, and 30 weeks' gestation. Multiple regression analysis was used to determine the proportion of variation in fetal liver blood flow explained by placental corticotrophin-releasing hormone. Covariates included maternal age, parity, pre-pregnancy body mass index, gestational weight gain, and fetal sex. A total of 79 uncomplicated singleton pregnancies were analyzed. Fetal liver blood flow was 68.4 ± 36.0 mL/min (mean ± SD). Placental corticotrophin-releasing hormone concentrations at 12, 20, and 30 weeks were 12.5 ± 8.1, 35.7 ± 24.5, and 247.9 ± 167.8 pg/mL, respectively. Placental corticotrophin-releasing hormone at 30 weeks, but not at 12 and 20 weeks, was significantly and positively associated with fetal liver blood flow at 30 weeks (r = 0.319; P = 0.004) and explained 10.4% of the variance in fetal liver blood flow. Placental corticotrophin-releasing hormone in late gestation is a possible modulator of fetal liver blood flow and may constitute a biochemical marker in clinical investigations of fetal growth and body composition.

Detecting Pulse Wave From Unstable Facial Videos Recorded From Consumer-Level Cameras: A Disturbance-Adaptive Orthogonal Matching Pursuit.

Modern consumer-level cameras can detect subtle changes in human facial skin color due to varying blood flow; they are beginning to be used as noncontact devices to detect pulse waves. Little, however, do we know about their capacity to perform pulse wave detection when the recorded faces are unstable. Here, we propose a novel method that can extract pulse waves from videos with drastic facial unsteadiness such as head twists and alternating expressions. The method first uses chrominance characteristics in multiple facial sub-regions to construct a raw pulse matrix. Subsequently, it employs a disturbance-adaptive orthogonal matching pursuit (DAOMP) algorithm to recover the underlying pulse matrix corrupted by facial unsteadiness. To evaluate the efficacy of the method, we perform analyses on two datasets including 268 samples from 67 testing subjects. The results demonstrate that the proposed method outperforms state-of-the-art algorithms, especially in the terrain where drastic facial unsteadiness is present. The proposed framework shows promise to achieve videos-based noncontact pulse wave detection from both steady and unsteady faces recorded by consumer-level cameras. By employing the proposed method, disturbance robustness in noncontact pulse wave detection can be significantly improved.

Longitudinal stability of retinal blood flow regulation in response to flicker stimulation and systemic hyperoxia in mice assessed with laser speckle flowgraphy

This study aimed to evaluate longitudinal changes in retinal blood flow in response to flicker stimulation and systemic hyperoxia in mice using a laser speckle flowgraphy (LSFG-Micro). The retinal blood flow in vascular area surrounding the optic nerve head was measured in 8-week-old male mice every 2 weeks until age 20-week. The coefficient of variation of retinal blood flow under resting condition was analyzed every 2 weeks to validate the consistency of the measurement. On day 1 of the experiment, retinal blood flow was assessed every 20 s for 6 min during and after 3 min flicker light (12 Hz) stimulation; on day 2, retinal blood flow was measured every minute for 20 min during and after 10 min systemic hyperoxia; and on day 3, electroretinography (ERG) was performed. Body weight, systemic blood pressure, and ocular perfusion pressure increased significantly with age, but the resting retinal blood flow and ERG parameters remained unchanged. Retinal blood flow significantly increased with flicker stimulation and decreased with systemic hyperoxia, independent of age. The LSFG-Micro provides consistent and reproducible retinal blood flow measurement in adult mice. Longitudinal assessments of retinal blood flow in response to flicker stimulation and systemic hyperoxia may be useful indexes for noninvasive monitoring of vascular function in retinas.

Regional venous\u2013arterial CO2 to arterial\u2013venous O2 content difference ratio in experimental circulatory shock and hypoxia

BackgroundVenous–arterial carbon dioxide (CO2) to arterial–venous oxygen (O2) content difference ratio (Cv-aCO2/Ca-vO2) > 1 is supposed to be both sensitive and specific for anaerobic metabolism. What regional hemodynamic and metabolic parameters determine the ratio has not been clarified.ObjectivesTo address determinants of systemic and renal, spleen, gut and liver Cv-aCO2/Ca-vO2.MethodsPost hoc analysis of original data from published experimental studies aimed to address effects of different fluid resuscitation strategies on oxygen transport, lactate metabolism and organ dysfunction in fecal peritonitis and endotoxin infusion, and from animals in cardiac tamponade or hypoxic hypoxia. Systemic and regional hemodynamics, blood flow, lactate uptake, carbon dioxide and oxygen-derived variables were determined. Generalized estimating equations (GEE) were fit to assess contributors to systemic and regional Cv-aCO2/Ca-vO2.ResultsMedian (range) of pooled systemic Cv-aCO2/Ca-vO2 in 64 pigs was 1.02 (0.02 to 3.84). While parameters reflecting regional lactate exchange were variably associated with the respective regional Cv-aCO2/Ca-vO2 ratios, only regional ratios were independently correlated with systemic ratio: renal Cv-aCO2 /Ca-vO2 (β = 0.148, 95% CI 0.062 to 0.234; p = 0.001), spleen Cv-aCO2/Ca-vO2 (β = 0.065, 95% CI 0.002 to 0.127; p = 0.042), gut Cv-aCO2/Ca-vO2 (β = 0.117, 95% CI 0.025 to 0.209; p = 0.013), liver Cv-aCO2/Ca-vO2 (β = − 0.159, 95% CI − 0.297 to − 0.022; p = 0.023), hepatosplanchnic Cv-aCO2/Ca-vO2 (β = 0.495, 95% CI 0.205 to 0.786; p = 0.001).ConclusionIn a mixed set of animals in different shock forms or during hypoxic injury, hepatosplanchnic Cv-aCO2/Ca-vO2 ratio had the strongest independent association with systemic Cv-aCO2/Ca-vO2, while no independent association was demonstrated for lactate or hemodynamic variables.

Exploring neurodegenerative disorders using a novel integrated model of cerebral transport: Initial results.

The neurovascular unit (NVU) underlines the complex and symbiotic relationship between brain cells and the cerebral vasculature, and dictates the need to consider both neurodegenerative and cerebrovascular diseases under the same mechanistic umbrella. Importantly, unlike peripheral organs, the brain was thought not to contain a dedicated lymphatics system. The glymphatic system concept (a portmanteau of glia and lymphatic) has further emphasized the importance of cerebrospinal fluid transport and emphasized its role as a mechanism for waste removal from the central nervous system. In this work, we outline a novel multiporoelastic solver which is embedded within a high precision, subject specific workflow that allows for the co-existence of a multitude of interconnected compartments with varying properties (multiple-network poroelastic theory, or MPET), that allow for the physiologically accurate representation of perfused brain tissue. This novel numerical template is based on a six-compartment MPET system (6-MPET) and is implemented through an in-house finite element code. The latter utilises the specificity of a high throughput imaging pipeline (which has been extended to incorporate the regional variation of mechanical properties) and blood flow variability model developed as part of the VPH-DARE@IT research platform. To exemplify the capability of this large-scale consolidated pipeline, a cognitively healthy subject is used to acquire novel, biomechanistically inspired biomarkers relating to primary and derivative variables of the 6-MPET system. These biomarkers are shown to capture the sophisticated nature of the NVU and the glymphatic system, paving the way for a potential route in deconvoluting the complexity associated with the likely interdependence of neurodegenerative and cerebrovascular diseases. The present study is the first, to the best of our knowledge, that casts and implements the 6-MPET equations in a 3D anatomically accurate brain geometry.

Circadian variation in renal blood flow and kidney function in healthy volunteers monitored with noninvasive magnetic resonance imaging.

Circadian regulation of kidney function is involved in maintaining whole body homeostasis, and dysfunctional circadian rhythm can potentially be involved in disease development. Magnetic resonance imaging (MRI) provides reliable and reproducible repetitive estimates of kidney function noninvasively without the risk of adverse events associated with contrast agents and ionizing radiation. The purpose of this study was to estimate circadian variations in kidney function in healthy human subjects with MRI and to relate the findings to urinary excretions of electrolytes and markers of kidney function. Phase-contrast imaging, arterial spin labeling, and blood oxygen level-dependent transverse relaxation rate (R2*) mapping were used to assess total renal blood flow and regional perfusion as well as intrarenal oxygenation in eight female and eight male healthy volunteers every fourth hour during a 24-h period. Parallel with MRI scans, standard urinary and plasma parameters were quantified. Significant circadian variations of total renal blood flow were found over 24 h, with increasing flow from noon to midnight and decreasing flow during the night. In contrast, no circadian variation in intrarenal oxygenation was detected. Urinary excretions of electrolytes, osmotically active particles, creatinine, and urea all displayed circadian variations, peaking during the afternoon and evening hours. In conclusion, total renal blood flow and kidney function, as estimated from excretion of electrolytes and waste products, display profound circadian variations, whereas intrarenal oxygenation displays significantly less circadian variation.

Effect of Local Vibrations on Plantar Skin Blood Flow Responses During Weight-bearing Standing in Healthy Volunteers

The objective of this study was to examine the effects of local vibrations on plantar skin blood flow (SBF) responses during weight-bearing standing. Wavelet analysis of plantar SBF was used to analyze microvascular regulation in response to standing with and without local vibrations. Fifteen (15) healthy participants (26.5 ± 5.7 years; 4 male and 11 female) received a local vibration intervention (35 Hz, 1 mm, 2 g vibration) and a sham vibration to the skin of the right first metatarsal head during 10-minute standing. Laser Doppler flowmetry was used to measure SBF before and after 10 minutes of standing. SBF after standing was expressed as a ratio of SBF before standing to minimize blood flow variations. The use of wavelet analysis allowed the authors to examine the frequency bands corresponding to the physiological controls in the vibration and sham areas of the foot, including metabolic (0.0095-0.02 Hz), neurogenic (0.02-0.05 Hz), myogenic (0.05-0.15 Hz), respiratory (0.15-0.4 Hz), and cardiac (0.4-2.0 Hz) regulations. Plantar SBF ratio changes in the vibration protocol (1.83 ± 0.27) were significantly higher compared with the sham protocol (0.97 ± 0.08) (P < .01). SBF before and after the 35 Hz vibrations were 41.96 ± 14.02 perfusion units (range 6.68-208.9 perfusion units) and 61.16 ± 14.74 perfusion units (range 7.76-155.37 perfusion units), respectively. SBF before and after the sham vibration were 37.32 ± 9.29 perfusion units (range 5.74-120.44 perfusion units) and 33.97 ± 8.11 perfusion units (range 6.95-108.44 perfusion units), respectively. Wavelet analysis of SBF oscillations showed a significant difference in all regulations: metabolic (P < .05), neurogenic (P < .05), myogenic (P < .05), respiratory (P < .05), and cardiac (P < .05) in response to 35 Hz local vibrations compared with the sham vibration. Local vibrations (35 Hz frequency, 1 mm amplitude) to the plantar tissues during 10 minutes of weight-bearing standing resulted in a significant increase in after-standing plantar SBF compared with sham vibration. The control mechanisms contributing to this increase in SBF were metabolic, neurogenic, myogenic, respiratory, and cardiac regulations. These findings confirm results of preclinical studies and support the need for additional research to examine the potential protective effects of local vibration to decrease the risk of plantar ulcers.