Measurement Of Blood Flow Research Articles

Laser Speckle Contrast Imaging-based diagnosis of severe mesenteric traction syndrome: Hemodynamics and prostacyclin - A prospective cohort study.

Today, the diagnosis and grading of mesenteric traction syndrome relies on a subjective assessment of facial flushing. However, this method has several limitations. In this study, Laser Speckle Contrast Imaging and a predefined cut-off value are assessed and validated for the objective identification of severe mesenteric traction syndrome. Severe mesenteric traction syndrome (MTS) is associated with increased postoperative morbidity. The diagnosis is based on an assessment of the developed facial flushing. Today this is performed subjectively, as no objective method exists. One possible objective method is Laser Speckle Contrast Imaging (LSCI), which has been used to show significantly higher facial skin blood flow in patients developing severe MTS. Using these data, a cut-off value has been identified. This study aimed to validate our predefined LSCI cut-off value for identifying severe MTS. A prospective cohort study was performed on patients planned for open esophagectomy or pancreatic surgery from March 2021 to April 2022. All patients underwent continuous measurement of forehead skin blood flow using LSCI during the first hour of surgery. Using the predefined cut-off value, the severity of MTS was graded. In addition, blood samples for prostacyclin (PGI2) analysis and hemodynamics were collected at predefined time points to validate the cut-off value. Sixty patients were included in the study. Using our predefined LSCI cut-off value, 21 (35%) patients were identified as developing severe MTS. These patients were found to have higher concentrations of 6-Keto-PGFaα (p=0.002), lower SVR (p<0.001), lower MAP (p=0.004), and higher CO (p<0.001) 15min into surgery, as compared with patients not developing severe MTS. This study validated our LSCI cut-off value for the objective identification of severe MTS patients as this group developed increased concentrations of PGI2 and more pronounced hemodynamic alterations compared with patients not developing severe MTS.

Clinical Value of Positron Emission Tomography Myocardial Perfusion Imaging and Blood Flow Quantification

Myocardial blood flow (MBF) and flow reserve (MFR) measurements by PET/computed tomography provide incremental diagnostic and prognostic information over traditional quantification of ischemia and scar by myocardial perfusion imaging. A normal stress MBF and MFR (>2.0) have a very high negative predictive value for excluding high-risk obstructive coronary artery disease (CAD). These flow measurements are also used for surveillance of coronary allograft vasculopathy after heart transplantation. A global normal MFR (>2.0) identifies patients at lower clinical risk, whereas a severely reduced MFR (<1.5) identifies patients at high risk for adverse events, even among patients without regional perfusion abnormalities.

The Impact of Intraoperative Graft Blood Flow Measurement on Early Graft Function

The aim of this study is to evaluate the impact of intraoperative allograft vascular flow on early kidney graft function. A total of 159 patients underwent kidney transplantation from January 2017 to March 2022 at Linkou Chang Gung Memorial Hospital. Graft arterial and venous blood flow was measured separately with a transient time flowmeter (Transonic HT353; Transonic Systems, Inc, Ithaca, NY, United States) after ureteroneocystostomy. The early outcomes, including the postoperative creatinine level, were analyzed accordingly. There were 83 males and 76 females, with a mean age of 44.5 years. The mean graft arterial flow measured was 480.6 mL/min, and the mean venous flow was 506.2 mL/min. Delayed graft function (DGF) incidence was 36.5%, 32.5%, and 40.8% in total, living, and deceased donor groups, respectively. Living donor and deceased donor kidney transplantation were analyzed separately. In the DGF subgroup, there were lower graft venous flows, higher body mass index (BMI), and more male patients in the living kidney transplant group. Similarly, the deceased donor kidney transplantation group with delayed graft function tended to have higher body height, higher body weight, higher BMI, and more diabetes mellitus. The multivariate analysis showed that lower graft venous blood flow (odds ratio [OR]=0.995, P=.008) and higher BMI (OR=1.144, P=.042) were significantly correlated with delayed graft function in living donor kidney transplantations. In the deceased donor group, a multivariate analysis of risk factors showed that BMI had a significant correlation with delayed graft function (OR=1.41, P=.039). Graft venous blood flow was significantly associated with delayed graft function in living donor kidney transplantation, and high BMI was correlated with DGF in all patients receiving kidney transplantation.

In Vivo Real-Time Study of Drug Effects on Carotid Blood Flow in the Ovine Fetus.

The ability of an organism to maintain a constant blood flow to the brain in response to sudden surges in systemic blood pressure (BP) is known as cerebral autoregulation (CAR), which occurs in the carotid artery. In contrast to full-term neonates, preterm neonates are unable to reduce the cerebral blood flow (CBF) in response to increased systemic BP. In preterm neonates, this exposes the fragile cerebral vessels to high perfusion pressures, leading to their rupture and brain damage. Ex vivo studies using wire myography have demonstrated that carotid arteries from near-term fetuses constrict in response to the activation of adrenergic alpha1 receptors. This response is blunted in the preterm fetus. Thus, to examine the role of alpha1-AR in vivo, presented here is an innovative approach to determine the effects of drugs on a carotid arterial segment in vivo in an ovine fetus during the developmental progression of gestation. The presented data demonstrate the simultaneous measurement of fetal blood flow and blood pressure. The perivascular delivery system can be used to conduct a long-term study over several days. Additional applications for this method could include viral delivery systems to alter the expression of genes in a segment of the carotid artery. These methods could be applied to other blood vessels in the growing organism in utero as well as in adult organisms.

Time–frequency analysis of laser speckle contrast for transcranial assessment of cerebral blood flow

Improving noninvasive approaches to monitoring blood microcirculation is an urgent topic in modern biomedical engineering. One of the actively developing methods is laser speckle contrast imaging (LSCI), which allows not only the visualization of microvessels but also the quantitative measurements of microcirculatory blood flow. This work shows the application of LSCI for mapping the cerebral vessels of a laboratory animal, and also presents the time–frequency processing of the registered signal. Thus, we expand the capabilities of the existing LSCI approach and demonstrate spatial mapping of blood flow rhythms. The proposed technology makes it possible not only to measure the relative cerebral blood flow but also to expand diagnostic capabilities for a detailed analysis of the physiological mechanisms of changes in blood flow.

P160 Pilot study to determine whether skin blood flow, oxygenation and skin colour are related in patients with systemic sclerosis

Abstract Background/Aims Improved treatments are needed for Raynaud’s phenomenon. Clinical trials can be difficult since it is challenging to measure Raynaud’s ‘attacks’ outside the laboratory. Ambulatory monitoring would allow testing of new treatments in the patients’ home environment where they usually experience attacks, thus allowing a much more realistic assessment of efficacy. Smartphone technology advancements mean that ambulatory monitoring of, and capture of biomarkers from, patients is now possible and could facilitate clinical trials. The aim of this study was to establish whether smartphone monitoring of skin temperature, an indirect measure of blood flow, and changes in skin colour as compared to laboratory measures of oxygenation could inform outcome measures in future clinical trials. Methods Following acclimatisation in a temperature-controlled room, participants underwent finger occlusion in order to simulate a decrease in perfusion and oxygenation. Simultaneous images were taken of the whole hand at baseline, during occlusion, at release and at 1 and 5 minute(s) post-release. Images of skin temperature (henceforth referred to as blood flow) and skin colour were taken with smartphone thermography (FLIRone) and camera respectively. Oxygenation was measured with multispectral imaging. Blood flow, colour and oxygenation data were extracted from images using automated bespoke software that identified the boundary of the hand and selected regions of interest. Colour data was split into red, green and blue channels. Data were plotted over time at each time point. Results Thirty patients with systemic sclerosis (SSc, median 62 interquartile range [57-69] years of age, 26[87%] female, duration of Raynaud’s phenomenon 20[10-32] years, duration of SSc 17[6-25] years, 6[20%] smokers) and 25 healthy controls (53[40-56] years of age, 23[92%] female, 0[0%] smokers) were recruited into the study. The measures of blood flow, colour (red channel) and oxygenation followed similar trajectories over time for both patients and controls (decreasing during occlusion and increasing post occlusion). Oxygenation data was significantly different between patients and controls for baseline to occlusion (-0.24[-0.30 - -0.14] vs. -0.34[-0.46 - -0.26] arb units, p = 0.004) and occlusion to release (0.42[0.12-0.53] vs. 0.74[0.64-0.82] arb units, p &amp;lt; 0.0001). Grouping all data together (at occlusion to release), correlations were identified between colour (red channel) and blood flow r=-0.36 p = 0.003; colour (red channel) and oxygenation r = 0.31 p = 0.003 and between oxygenation and blood flow r=-0.38 p = 0.003. Conclusion Blood flow, skin colour and oxygenation in both patients with SSc and healthy controls follow similar distributions with time under occlusion and release. Blood flow, skin colour and oxygenation are related suggesting that measuring skin colour (redness) may be an alternative way to assess perfusion and oxygenation. Further larger studies are now required to validate this. Smartphone measures of outcomes offer promise for the future of ambulatory monitoring for clinical trials of Raynaud’s phenomenon. Disclosure G. Dinsdale: None. C. Heal: None. J. Manning: None. S. Wilkinson: None. J. Wilkinson: None. M. Dickinson: None. A. Herrick: None. A. Murray: None.

Early effects of inactivated (CoronaVac) SARS-CoV-2 vaccine on retrobulbar vascular blood flow and retinal vascular density

AimsWe aimed to investigate the early effects of inactivated SARS-CoV-2 vaccine on retrobulbar vascular blood flow and retinal vascular density in healthy subjects. MethodsThirty-four eyes of 34 healthy volunteers who received the CoronaVac (Sinovac Life Sciences, China) were included in this prospective study. Resistive index (RI), pulsatility index (PI) and peak systolic velocity (PSV) of the ophthalmic artery (OA), central retinal artery (CRA), and the temporal and nasal posterior ciliary arteries (PCA) were evaluated with color Doppler ultrasonography (CDUS) before vaccination, at the 2nd and 4th weeks after vaccination. Superficial capillary plexus (SCP) and deep capillary plexus (DCP) vessel density (VD), foveal avascular zone (FAZ), and choriocapillaris blood flow (CCF) measurements were made using optical coherence tomography angiography (OCTA). ResultsWhen compared to the pre-vaccination values, there was no significant change in OA-PSV, temporal-nasal PCA-PSV, CRA-EDV, temporal-nasal PCA-EDV at 2nd and 4th weeks after vaccination. However statistically significant reductions were found in the OA-RI, OA-PI, CRA-RI, CRA-PI, temporal-nasal PCA-RI, temporal-nasal PCA-PI values, CRA-PSV at post-vaccination 2nd week (p<0.05 for all). While there was sustained reduction in OA-RI, OA-PI, CRA-PSV, and nasal PCA-RI values at 4th week after vaccination, the change in CRA-RI, CRA-PI, temporal PCA-RI, temporal-nasal PCA-PI values were not significant compared to pre-vaccination values. There was no statistically significant difference in the SCP-VD, DCP-VD, FAZ and CCF measurements. ConclusionsOur findings demonstrating that CoronaVac vaccine did not affect retinal vascular density in the early period, but it caused alterations in the retrobulbar blood flow.

Toward accurate cerebral blood flow estimation in mice after accounting for anesthesia.

Purpose: To improve the accuracy of cerebral blood flow (CBF) measurement in mice by accounting for the anesthesia effects. Methods: The dependence of CBF on anesthesia dose and time was investigated by simultaneously measuring respiration rate (RR) and heart rate (HR) under four different anesthetic regimens. Quantitative CBF was measured by a phase-contrast (PC) MRI technique. RR was evaluated with a mouse monitoring system (MouseOX) while HR was determined using an ultrashort-TE MRI sequence. CBF, RR, and HR were recorded dynamically with a temporal resolution of 1min in a total of 19 mice. Linear regression models were used to investigate the relationships among CBF, anesthesia dose, RR, and HR. Results: CBF, RR, and HR all showed a significant dependence on anesthesia dose (p < 0.0001). However, the dose in itself was insufficient to account for the variations in physiological parameters, in that they showed a time-dependent change even for a constant dose. RR and HR together can explain 52.6% of the variations in CBF measurements, which is greater than the amount of variance explained by anesthesia dose (32.4%). Based on the multi-parametric regression results, a model was proposed to correct the anesthesia effects in mouse CBF measurements, specifically . We also reported awake-state CBF in mice to be 142.0 ± 8.8mL/100g/min, which is consistent with the model-predicted value. Conclusion: The accuracy of CBF measurement in mice can be improved by using a correction model that accounts for respiration rate, heart rate, and anesthesia dose.

110 μm thin endo-microscope for deep-brain in vivo observations of neuronal connectivity, activity and blood flow dynamics

Light-based in-vivo brain imaging relies on light transport over large distances of highly scattering tissues. Scattering gradually reduces imaging contrast and resolution, making it difficult to reach structures at greater depths even with the use of multiphoton techniques. To reach deeper, minimally invasive endo-microscopy techniques have been established. These most commonly exploit graded-index rod lenses and enable a variety of modalities in head-fixed and freely moving animals. A recently proposed alternative is the use of holographic control of light transport through multimode optical fibres promising much less traumatic application and superior imaging performance. We present a 110 μm thin laser-scanning endo-microscope based on this prospect, enabling in-vivo volumetric imaging throughout the whole depth of the mouse brain. The instrument is equipped with multi-wavelength detection and three-dimensional random access options, and it performs at lateral resolution below 1 μm. We showcase various modes of its application through the observations of fluorescently labelled neurones, their processes and blood vessels. Finally, we demonstrate how to exploit the instrument to monitor calcium signalling of neurones and to measure blood flow velocity in individual vessels at high speeds.

Quantification of myocardial blood flow using dynamic myocardial CT perfusion compared with 82Rb PET

PurposeAbsolute measures of myocardial blood flow (MBF) obtained with dynamic myocardial CT perfusion (DM-CTP) are underestimated when compared with reference standards. This is to some extent explained by incomplete extraction of iodinated contrast agent (iCA) to the myocardial tissue. We aimed to establish an extraction function for iCA, use the function to calculate MBFCT and to compare this with MBF measured with 82Rb positron emission tomography (PET). Materials and methodsHealthy individuals without coronary artery disease (CAD) were examined with 82Rb PET and DM-CTP. The factors a and β of the generalized Renkin-Crone model were estimated using a non-linear least squares model. The factors providing the best fit for the data were subsequently used to calculate MBFCT. ResultsOf consecutive 91 individuals examined, 79 were eligible for analysis. The factors a and β providing the best fit of the nonlinear least-squares model to the data were a ​= ​0.614 and β ​= ​0.218 (R-squared ​= ​0.81). Conversion of the CT inflow parameter (K1) values using the derived extraction function resulted in a significant correlation between MBF measured during stress using CT and PET (P ​= ​0.039). ConclusionIn healthy individuals, flow estimates obtained with dynamic myocardial CT perfusion during stress were, after conversion to MBF using the extraction of iodinated CT contrast agent, correlated with absolute MBF quantified with 82Rb PET.

High-speed measurement of retinal arterial blood flow in the living human eye with adaptive optics ophthalmoscopy.

We present a technique to measure the rapid blood velocity in large retinal vessels with high spatiotemporal resolution. Red blood cell motion traces in the vessels were non-invasively imaged using an adaptive optics near-confocal scanning ophthalmoscope at a frame rate of 200 fps. We developed software to measure blood velocity automatically. We demonstrated the ability to measure the spatiotemporal profiles of the pulsatile blood flow with a maximum velocity of 95-156 mm/s in retinal arterioles with a diameter >100 µm. High-speed and high-resolution imaging increased the dynamic range, enhanced sensitivity, and improved the accuracy when studying retinal hemodynamics.

Anthropomorphic cardiac phantom for dynamic SPECT

BackgroundAs myocardial blood flow measurement (MBF) in SPECT systems became recently available, significant effort has been devoted to its validation. For that purpose, we have developed a cardiac phantom that is able to mimic physiological radiotracer variation in the left ventricle cavity and in the myocardium, while performing beating-like motion. The new phantom is integrated inside a standard anthropomorphic torso allowing a realistic tissue attenuation and gamma-ray scattering Methods and ResultsA mechanical cardiac phantom was integrated in a commercially available anthropomorphic torso. Using a GE Discovery 530c SPECT, measurements were performed. It was found that gamma-ray attenuation effects are significant and limit the MBF measurements to global/three-vessel resolution. Dynamic SPECT experiments were performed to validate MBF accuracy and showed mean relative error of 14%. Finally, the effect of varying radiotracer dose on the accuracy of dynamic SPECT was studied ConclusionsA dynamic cardiac phantom has been developed and successfully integrated in a standard SPECT torso. A good agreement was found between SPECT-reported MBF values and the expected results. Despite increased noise-to-signal ratio when radiotracer doses were reduced, MBF uncertainty did not increase significantly down to very low doses, thanks to the temporal integration of the activity during the measurement

The effect of immediate postoperative increase in blood flow velocity in predicting maturation of arteriovenous fistula for dialysis

Background Doppler ultrasonography is the main imaging modality for hemodialysis arteriovenous fistula (AVF) as it is safe, accurate, and noninvasive. Published literature related to the utility of early postoperative ultrasound in predicting AVF maturation is scarce. With the KDOQI guidelines recommending an AVF first catheter last approach, the quest to increase AVF maturation is of utmost importance. This study aims at measuring blood flow immediately postoperatively and assessing its predictive role in AVF maturation. Methods We correlated the ultrasound parameters with maturation in newly created AVFs measured preoperatively, immediately postoperatively, 6 weeks, and 3, 6, and12 months postoperatively. Both demographics and vascular parameters were compared between the group of patients whose AVFs successfully maturated and those whose AVFs did not. Primary endpoint was AVF maturation; secondary endpoints included patency, functional success, and predictive value of increased vein blood flow on fistula patency. Results A total of 50 procedures were performed; the mean age was 52.12 years (±6.58). The overall technical success rate was 86% (43) and 39 (90.7%) of them were functionally mature according to KDOQI guidelines for maturation. Primary patency was 93.02%, 92.7%, and 88.89%; and the primary-assisted patency was 97.7%, 95.12%, and 91.67% at 3, 6, and 12 months, respectively. Receiver-operated curve (ROC) showed a cutoff value of 322.8 ml/min increase in blood flow above which the AVF is more likely to become mature. Binary logistic regression showed that arterial depth greater than 3.92 mm, arterial flow velocity greater than 88 ml/min, preoperative average vein diameter of greater than 2.5 mm, arterial flow velocity of greater than 73 ml/min immediately postoperatively, and average vein diameter of greater than 3.94 mm immediately postoperatively were significant predictors of successful maturation at 6 weeks postoperatively (P values 0.001, &lt;0.0001, &lt;0.0001, &lt;0.0001, and &lt;0.0001, respectively). Conclusion Immediately postoperative flow measurement is a reliable parameter that can be used to predict successful fistula maturation, especially if flow velocities exceed 326.15 ml/min.

MP27-13 PERIPHERAL NEUROMODULATION OF VAGINAL BLOOD FLOW: A POTENTIAL TREATMENT FOR FEMALE SEXUAL DYSFUNCTION

You have accessJournal of UrologyCME1 Apr 2023MP27-13 PERIPHERAL NEUROMODULATION OF VAGINAL BLOOD FLOW: A POTENTIAL TREATMENT FOR FEMALE SEXUAL DYSFUNCTION Priyanka Gupta, Elizabeth Bottorff, Patricia Maymi-Castrodad, Mackenzie Moore, Giulia Lane, Gianna Rodriguez, and Tim Bruns Priyanka GuptaPriyanka Gupta More articles by this author , Elizabeth BottorffElizabeth Bottorff More articles by this author , Patricia Maymi-CastrodadPatricia Maymi-Castrodad More articles by this author , Mackenzie MooreMackenzie Moore More articles by this author , Giulia LaneGiulia Lane More articles by this author , Gianna RodriguezGianna Rodriguez More articles by this author , and Tim BrunsTim Bruns More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003255.13AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Female sexual dysfunction (FSD) is a potentially life altering condition that impacts an estimated 40% of women. Unfortunately, the few treatment options available have limited success due to their high incidence of adverse events and inability to improve subjective arousal. One potential treatment option, peripheral neuromodulation, has been successful in improving female sexual function index scores. However, the underlying mechanisms of how neuromodulation improves FSD are still largely unknown. We hypothesize that improvements in FSD symptoms are due to improvements in genital hemodynamics. METHODS: We developed a clinical study to investigate changes in vaginal blood flow (VBF) in response to dorsal genital nerve (DGN) and tibial nerve stimulation in three cohorts of women: healthy controls, women with FSD, and women with spinal cord injury (SCI). Incorporating women with SCI allows us to investigate which neural pathways contribute to genital sexual arousal. Each participant attends two study visits: one for each nerve target, randomly ordered. At each visit, a vaginal photoplethysmography (VPP) sensor is used to measure blood flow during a 5-minute baseline, 20 minutes of nerve stimulation, and a 5-minute washout period. The VPP signals are filtered in the neurogenic energy frequency spectrum (0.76 – 0.20 Hz) for analysis. RESULTS: Seven out of eight participants reported genital sensations due to nerve stimulation, three of whom have SCI. One participant with a complete SCI had increases in their VPP neurogenic energy during dorsal genital nerve stimulation (Figure 1). An animal study is being planned to investigate the VBF response observed in complete SCI. CONCLUSIONS: This work provides further support for neuromodulation as a treatment for neurogenic and non-neurogenic FSD. Source of Funding: Craig H. Neilsen Foundation and International Society for the Study of Women’s Sexual Health © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e367 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Priyanka Gupta More articles by this author Elizabeth Bottorff More articles by this author Patricia Maymi-Castrodad More articles by this author Mackenzie Moore More articles by this author Giulia Lane More articles by this author Gianna Rodriguez More articles by this author Tim Bruns More articles by this author Expand All Advertisement PDF downloadLoading ...

Blood flow characteristics of the bilateral internal thoracic artery: implications of optimal graft configuration for coronary artery bypass grafting to maximize blood supply.

There is controversy regarding which internal thoracic artery (ITA) should be anastomosed to the left anterior descending artery (LAD). Here, we propose an optimal graft design based on measurement of blood flow in the ITA. Sixty-one patients (53 men, median age 68 [62-75] years) undergoing first elective coronary artery bypass grafting were enrolled. Fifty-seven left ITAs (LITAs) and 28 right ITAs (RITAs) were harvested in either a semi-skeletonized manner using a harmonic scalpel covered with papaverine-soaked gauze (group-A, n = 45) or a fully skeletonized manner using electrocautery with intraluminal papaverine injection (group-B, n = 41). Free flow of 33 ITAs was measured after pharmacological dilatation and in situ ITA-LAD flow was measured in 59 patients by transit-time flowmetry. RITA and LITA free flow were 147.0 [87.8-213.0] mL/min and 108.0 [90.0-144.0] mL/min, respectively (P = 0.199). The group-B had significantly higher ITA free flow (135.0 [102.0-171.0] mL/min) than group-A (63.0 [36.0-96.0] mL/min, P = 0.009). In 13 patients with bilateral ITA harvesting, free flow of the RITA (138.0 [79.5-204.0] mL/min) was also significantly higher than the LITA (102.0 [81.0-138.0] mL/min, P = 0.046). There was no significant difference between RITA and LITA flow anastomosed to the LAD. The group-B had significantly higher ITA-LAD flow (56.5 [32.3-73.6] mL/min) than group-A (40.9 [20.1-53.7] mL/min, P = 0.023). RITA provides significantly higher free flow than LITA but similar blood flow to the LAD. Full skeletonization with intraluminal papaverine injection maximizes both free flow and ITA-LAD flow.

Influence of oversimplifying the head anatomy on cerebral blood flow measurements with diffuse correlation spectroscopy.

Diffuse correlation spectroscopy (DCS) is an emerging optical modality for non-invasive assessment of an index of regional cerebral blood flow. By the nature of this noninvasive measurement, light must pass through extracerebral layers (i.e., skull, scalp, and cerebral spinal fluid) before detection at the tissue surface. To minimize the contribution of these extracerebral layers to the measured signal, an analytical model has been developed that treats the head as a series of three parallel and infinitely extending slabs (mimicking scalp, skull, and brain). The three-layer model has been shown to provide a significant improvement in cerebral blood flow estimation over the typically used model that treats the head as a bulk homogenous medium. However, the three-layer model is still a gross oversimplification of the head geometry that ignores head curvature, the presence of cerebrospinal fluid (CSF), and heterogeneity in layer thickness. Determine the influence of oversimplifying the head geometry on cerebral blood flow estimated with the three-layer model. Data were simulated with Monte Carlo in a four-layer slab medium and a three-layer sphere medium to isolate the influence of CSF and curvature, respectively. Additionally, simulations were performed on magnetic resonance imaging (MRI) head templates spanning a wide-range of ages. Simulated data were fit to both the homogenous and three-layer model for CBF. Finally, to mitigate the errors in potential CBF estimation due to the difficulty in defining layer thickness, we investigated an approach to identify an equivalent, "optimized" thickness via a pressure modulation. Both head curvature and failing to account for CSF lead to significant errors in the estimation of CBF. However, the effect of curvature and CSF on relative changes in CBF is minimal. Further, we found that CBF was underestimated in all MRI-templates, although the magnitude of these underestimations was highly influenced by small variations in the source and detector optode positioning. The optimized thickness obtained from pressure modulation did not improve estimation accuracy of CBF, although it did significantly improve the estimation accuracy of relative changes in CBF. In sum, these findings suggest that the three-layer model holds promise for improving estimation of relative changes in cerebral blood flow; however, estimations of absolute cerebral blood flow with the approach should be viewed with caution given that it is difficult to account for appreciable sources of error, such as curvature and CSF.

Vascular parameters and endothelin-1 measurements in glaucoma patients with low- and high-tension optic disc hemorrhages

This prospective study aimed to compare vascular parameters (endothelin-1 [ET-1] blood levels, laser Doppler imaging [LDI] of distal phalanxes, and nailfold capillaroscopy) between open-angle glaucoma patients with low- and high-tension optic disc hemorrhages (LTDH and HTDH, respectively). The 33 enrolled patients (mean age, 62.3 ± 13 years) were classified as LTDH or HTDH if they presented at the time of DH detection an intraocular pressure (IOP) < 16 mmHg or ≥ 16 mmHg, respectively. Demographic and ophthalmological data, ET-1 concentrations, LDI (before and 1, 10, and 20 min after cold stimulation), and nailfold capillaroscopy findings were evaluated. The ET-1 blood level was 65% higher in the LTDH (2.27 ± 1.46 pg/ml) than in the HTDH (1.37 ± 0.57 pg/ml; p = 0.03) group. Moreover, there was a statistically significant negative correlation between ET-1 blood concentration and IOP at the time of DH detection (r = −0.45, p = 0.02). Blood flow measurements 10 and 20 min after cold stimulation were lower in the LTDH group than in the HTDH group (p < 0.01). Patients developing DH with lower IOPs have higher ET-1 blood levels and more peripheral vascular dysfunction as estimated by LDI than those with higher IOPs. These findings suggest that distinct underlying mechanisms may be involved in patients developing DH within different IOP ranges.

In vivo deep-brain 2-photon fluorescent microscopy labeled with near-infrared dyes excited at the 1700 nm window

2-Photon fluorescence microscopy (2PFM) is an indispensable imaging technology for neuroscience. However, the imaging depth is usually limited to the cortical layer in mouse brain in vivo. Here, we demonstrate deep brain 2PFM in vivo excited at the 1700 nm window, using IR780 and aza-IR780 as fluorescent labels. Our detailed characterization of the multiphoton excitation and emission properties of IR780 and aza-IR780 show that: (1) IR780 or aza-IR780 generate 2-photon fluorescence excited at the 1700 nm window and are promising for 2PFM; (2) aza-IR780 exhibits a larger ησ2 with better anti-photobleaching property compared to IR780; The 2-photon action cross-sections of IR780 and aza-IR780 in plasma are an order-of-magnitude larger than those in PBS; (3) In vivo 2-photon emission spectra for both dyes show a notable red shift compared to those in vitro. Based on these characterization results, we demonstrate deep brain 2PFM labeled by them. A maximum imaging depth of 1585 μm (labeled by IR780) and 1800 μm (labeled by aza-IR780) into the mouse brain in vivo readily penetrates the subcortical region of hippocampus. Besides, a maximum of 1528 μm hemodynamic imaging depth is realized via 2PFM with aza-IR780 labeling, enabling us to measure blood flow speed in the hippocampus.

Simultaneous photoplethysmography and blood flow measurements towards the estimation of blood pressure using speckle contrast optical spectroscopy.

Non-invasive continuous blood pressure monitoring remains elusive. There has been extensive research using the photoplethysmographic (PPG) waveform for blood pressure estimation, but improvements in accuracy are still needed before clinical use. Here we explored the use of an emerging technique, speckle contrast optical spectroscopy (SCOS), for blood pressure estimation. SCOS provides measurements of both blood volume changes (PPG) and blood flow index (BFi) changes during the cardiac cycle, and thus provides a richer set of parameters compared to traditional PPG. SCOS measurements were taken on the finger and wrists of 13 subjects. We investigated the correlations between features extracted from both the PPG and BFi waveforms with blood pressure. Features from the BFi waveforms were more significantly correlated with blood pressure than PPG features ( R = - 0.55, p = 1.1 × 10-4 for the top BFi feature versus R = - 0.53, p = 8.4 × 10-4 for the top PPG feature). Importantly, we also found that features combining BFi and PPG data were highly correlated with changes in blood pressure ( R = - 0.59, p = 1.7 × 10-4 ). These results suggest that the incorporation of BFi measurements should be further explored as a means to improve blood pressure estimation using non-invasive optical techniques.

Exercise Training to Improve Brain Health in Older People Living With HIV: Study Protocol for a Randomized Controlled Trial.

With the advent of antiretrovirals, people living with HIV are living near-normal lifespans. However, people living with HIV are at greater risk of experiencing cognitive impairment and reduced brain integrity despite well-controlled viremia. A robust literature supports exercise interventions as a method of improving cognition and structural brain integrity in older individuals without HIV. The effects of exercise on cardiometabolic, neurocognitive, and neural structures in middle-aged to older people living with HIV are less well known, with few prospective studies examining these measures. This prospective randomized clinical trial will examine the effects of a 6-month exercise training intervention compared to a 6-month stretching intervention (control) on cardiorespiratory fitness, physical function and strength, cognition, and neuroimaging measures of brain volumes and cerebral blood flow in people living with HIV. Sedentary middle-aged to older people living with HIV (ages≥40; n=150) with undetectable HIV viral load (<20 copies/mL) will be enrolled in the study. At the baseline and final visit, fasting plasma lipid, insulin, glucose, and brain neurotrophic factor concentrations; cardiorespiratory fitness; cognitive performance; brain volumes; and cerebral blood flow via a magnetic resonance imaging scan will be measured. Participants will be randomized in a 2:1 ratio to either the exercise or control stretching intervention. All participants will complete their assigned programs at a community fitness center 3 times a week for 6 months. A professional fitness trainer will provide personal training guidance at all sessions for individuals enrolled in both arms. Individuals randomized to the exercise intervention will perform endurance and strength training exercises, while those randomized to the control intervention will perform stretches to increase flexibility. A midpoint visit (at 3 months) will assess cognitive performance, and at the end point visit, subjects will undergo cardiorespiratory fitness and cognition testing, and a magnetic resonance imaging scan. Physical activity throughout the duration of the trial will be recorded using an actigraph. Recruitment and data collection are complete as of December 2020. Data processing, cleaning, and organization are complete as of December 2021. Data analysis began in January 2022, with the publication of study results for primary aims 1 and 2 expected by early 2023. This study will investigate the effects of a 6-month aerobic and resistance exercise training intervention to improve cardiometabolic risk factors, cognitive performance, cerebral structure, and blood flow in sedentary people living with HIV. Results will inform clinicians and patients of the potential benefits of a structured aerobic exercise training program on the cognitive, functional, and cardiometabolic health status of older people living with HIV. Assessment of compliance will inform the development and implementation of future exercise programs for people living with HIV. ClinicalTrials.gov NCT02663934; https://clinicaltrials.gov/ct2/show/NCT02663934. DERR1-10.2196/41421.