Venous SO2 Research Articles

Comparison of compartmental analytical Blood-Oxygen-Level-Dependent functional Magnetic Resonance Imaging models against Monte Carlo simulations performed over cortical micro-angiograms.

Blood oxygen level-dependent functional magnetic resonance imaging (BOLD fMRI) arises from a physiological and physical cascade of events taking place at the level of the cortical microvasculature which constitutes a medium with complex geometry. Several analytical models of the BOLD contrast have been developed, but these have not been compared directly against detailed bottom-up modeling methods. Using a 3D modeling method based on experimentally measured images of mice microvasculature and Monte Carlo simulations, we quantified the accuracy of two analytical models to predict the amplitude of the BOLD response from 1.5 to 7T, for different echo time (TE) and for both gradient echo and spin echo acquisition protocols. We also showed that accounting for the tridimensional structure of the microvasculature results in more accurate prediction of the BOLD amplitude, even if the values for SO2 were averaged across individual vascular compartments. A secondary finding is that modeling the venous compartment as two individual compartments results in more accurate prediction of the BOLD amplitude compared with standard homogenous venous modeling, arising from the bimodal distribution of venous SO2 across the microvasculature in our data.

Association Between Corneal Changes and Retinal Oximetry in Diabetes Mellitus.

Diabetes mellitus (DM) causes different corneal changes that are associated with the severity of diabetic retinopathy. To identify the pathophysiological reasons for this, corneal tomography and optical densitometry (COD) were combined with retinal oximetry. Patients with DM and healthy subjects were included in this pilot study. Spatially resolved corneal thickness and COD were assessed using the Pentacam HR (Oculus). The pachymetry difference (PACDiff) was calculated as an indicator of an increase in the peripheral corneal thickness. Oxygen saturation (SO2) of the retinal vessels was measured using the Retinal Vessel Analyzer (Imedos Systems UG). Subsequently, the associations between corneal and retinal parameters were analyzed. Data from 30 patients with DM were compared with those from 30 age-matched healthy subjects. In DM, arterial (P = 0.048) and venous (P < 0.001) SO2 levels were increased, and arteriovenous SO2 difference was decreased (P < 0.001). In patients, PACDiff was higher than that in healthy subjects (P < 0.05), indicating a stronger increase in peripheral corneal thickness. The COD was reduced in DM (P = 0.004). The PACDiff of concentric rings with a diameter of 4 mm (r = -0.404; P = 0.033) to 8 mm (r = -0.522; P = 0.004) was inversely correlated with the arteriovenous SO2 difference. Furthermore, PACDiff 4 mm was negatively associated with arterial SO2 (r = -0.389; P = 0.041), and the COD of the peripheral corneal areas correlated positive with arterial SO2 (COD total 10-12 mm: r = 0.408; P = 0.025). These associations might indicate a common pathogenesis of corneal and retinal changes in DM, which could be caused by reduced oxygen supply, mitochondrial dysfunction, oxidative stress, and cytokine effects.

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep.

We tested whether the brain and kidney respond differently to cardiopulmonary bypass (CPB) and to changes in perfusion conditions during CPB. Therefore, in ovine CPB, we assessed regional cerebral oxygen saturation (rSO2 ) by near-infrared spectroscopy and renal cortical and medullary tissue oxygen tension (PO2 ), and, in some protocols, brain tissue PO2 , by phosphorescence lifetime oximetry. During CPB, rSO2 correlated with mixed venous SO2 (r = 0.78) and brain tissue PO2 (r = 0.49) when arterial PO2 was varied. During the first 30 min of CPB, brain tissue PO2 , rSO2 and renal cortical tissue PO2 did not fall, but renal medullary tissue PO2 did. Nevertheless, compared with stable anaesthesia, during stable CPB, rSO2 (66.8 decreasing to 61.3%) and both renal cortical (90.8 decreasing to 43.5 mm Hg) and medullary (44.3 decreasing to 19.2 mm Hg) tissue PO2 were lower. Both rSO2 and renal PO2 increased when pump flow was increased from 60 to 100 mL kg-1 min-1 at a target arterial pressure of 70 mm Hg. They also both increased when pump flow and arterial pressure were increased simultaneously. Neither was significantly altered by partially pulsatile flow. The vasopressor, metaraminol, dose-dependently decreased rSO2 , but increased renal cortical and medullary PO2 . Increasing blood haemoglobin concentration increased rSO2 , but not renal PO2 . We conclude that both the brain and kidney are susceptible to hypoxia during CPB, which can be alleviated by increasing pump flow, even without increasing arterial pressure. However, increasing blood haemoglobin concentration increases brain, but not kidney oxygenation, whereas vasopressor support with metaraminol increases kidney, but not brain oxygenation.

Vascular-centric mapping of in vivo blood oxygen saturation in preclinical models.

Assessing intravascular blood oxygen saturation (SO2) is crucial for characterizing in vivo microenvironmental changes in preclinical models of injury and disease. However, most conventional optical imaging techniques for mapping in vivo SO2 assume or compute a single value of the optical path-length in tissue. This is especially detrimental when mapping in vivo SO2 in experimental disease or wound healing models that are characterized by vascular and tissue remodeling. Therefore, to circumvent this limitation we developed an in vivo SO2 mapping technique that utilizes hemoglobin-based intrinsic optical signal (IOS) imaging combined with a vascular-centric estimation of optical path-lengths. In vivo arterial and venous SO2 distributions derived with this approach closely matched those reported in the literature, while those derived using the single path-length (i.e. conventional) approach did not. Moreover, in vivo cerebrovascular SO2 strongly correlated (R2>0.7) with changes in systemic SO2 measured with a pulse oximeter during hypoxia and hyperoxia paradigms. Finally, in a calvarial bone healing model, in vivo SO2 assessed over four weeks was spatiotemporally correlated with angiogenesis and osteogenesis (R2>0.6). During the early stages of bone healing (i.e. day 10), angiogenic vessels surrounding the calvarial defect exhibited mean SO2 that was elevated by10% (p<0.05) relative to that observed at a later stage (i.e., day 26), indicative of their role in osteogenesis. These correlations were not evident with the conventional SO2 mapping approach. The feasibility of our wide field-of-view in vivo SO2 mapping approach illustrates its potential for characterizing the microvascular environment in applications ranging from tissue engineering to cancer.

Screening of idiopathic epiretinal membrane using fundus images combined with blood oxygen saturation and vascular morphological features.

PurposeTo achieve an accurate diagnosis of idiopathic epiretinal membrane (iERM) through analyzing retinal blood vessel oxygen saturation (SO2) and vascular morphological features in fundus images.MethodsDual-modal fundus camera was used to obtain color fundus image, 570-nm, and 610-nm images. As iERM affects the macular area, a macular-centered semicircle area as region of interest (MROI) was selected and analyzed SO2 and vascular morphologies in it. Eventually, random forest (RF) and support vector machine (SVM) were as classifiers to diagnose iERM patients.ResultsThe arterial and venous SO2 levels of the iERM group were significantly higher than that of the control group. There were significant differences in the vessel density and fractal dimension on the artery for vascular morphology, while the tortuosity had a significant difference in the vein. By feeding the SO2 and the vascular morphological features into classifiers, an accuracy of over 82% was obtained, which is significantly better than the two separate inputs for classification.ConclusionSignificant differences in SO2 and vascular morphologies between control and iERM groups confirmed that the occurrence of iERM may affect blood supply and vascular structures. Benefiting from the dual-modal fundus camera and machine learning models, accurate judgments can be made on fundus images. Extensive experiments proved the importance of blood vessel SO2 and vascular morphologies for diagnosis, which is of great significance for clinical screening.

A Baseline Study of Oxygen Saturation in Parafoveal Vessels Using Visible Light Optical Coherence Tomography.

The retinal macula is at the center of our visual field, and thus pathological damage in the macula significantly impacts an individual's quality of life. The parafoveal vessels form the inner retina provide oxygen perfusion, and the measurement of parafoveal oxygen saturation (sO2) can evaluate macular metabolism and provide pathophysiological insight. In this paper, for the first time, we present a baseline study of microvascular oxygen saturation (sO2) in perifoveal macular region using visible light optical coherence tomography (VIS-OCT) on normal eyes. The arterial and venous sO2 from all eyes was 92.1 ± 7.1 (vol %) and 48.4 ± 5.0 (vol %) (mean ± SD), respectively. Arteriovenous sO2 difference was 43.8 ± 9.5 (vol %). Marginal correlation was found between venous sO2 and intraocular pressure (IOP) among eyes. No significant correlation was found between sO2 and vessel topological features, including length, diameter, and distance to fovea. This baseline study could serve as a benchmark for the future sO2 investigation of retinal macular pathologies.

Serum sRAGE and sE-selectin levels are useful biomarkers of lung injury and prediction of mortality in calves with perinatal asphyxia

The objective of the present study was to evaluate the biomarkers specific to lung endothelial and epithelial damage in the determination of lung injury and its severity in calves with perinatal asphyxia and to evaluate their prognostic importance among survivors and non-survivor calves. Ten healthy calves and 20 calves with perinatal asphyxia were enrolled in the study. Clinical examination and laboratory analysis were performed at admission. Serum concentrations of soluble advanced glycation end-product receptor (sRAGE), soluble E-selectin (sE-selectin), clara cell secretory protein (CC16), and soluble intercellular adhesion molecule-1 (sICAM-1) were measured to assess lung injury. Venous pH, sO2, HCO3, and BE of calves with perinatal asphyxia were significantly lower than the healthy calves. sRAGE, sE-selectin, pCO2, and lactate were significantly high in calves with asphyxia. ROC analysis showed that sRAGE, sE-selectin, pCO2, lactate, and respiratory rate were higher while HCO3 and BE were lower in the nonsurvivor calves than survivors. In conclusion, serum sRAGE and sE-selectin concentrations highlight the utility of these biomarkers in determining lung injury in calves with asphyxia. Also, pH, pCO2, lactate, HCO3, BE, and respiratory rate along with serum sRAGE and sE-selectin were useful indicators in the prediction of mortality.

MO821OXYGEN EXTRACTION RATIO AND MORTALITY RISK IN HAEMODIALYSIS PATIENT: A MULTICENTRE STUDY

Abstract Background and Aims Patients on haemodialysis (HD) suffer a very high rate of cardiovascular mortality with some evidence suggesting a possible association with decreasing blood oxygen saturation (SO2) during sessions. The ratio between arterial SO2 (SaO2) and central venous SO2 (ScvO2) or Oxygen Extraction Ratio (OER), which represents an estimate of the amount of oxygen claimed by peripheral tissues and of the haemodialysis related hypoxic stress, might represent a new prognostic factor. Method We evaluate the relationship between OER values and mortality risks in HD patients in a prospective multicentre observational study. We enrolled chronic HD patients with permanent central venous catheter (CVC) and no fistula, in whom ScvO2 measurement is at hand and SaO2 is available with a peripheral oxymeter. OER ([(SaO2−ScvO2)/SaO2]×100) was measured before and after HD at enrolment (HD OER sessions) in each patients, and a one-year follow-up was planned to record the number of deaths. Results In 101 patients (age 71.5 ± 14 years on dialysis for 47 ± 38 months), during 9 ± 6 months of follow up, we recorded 35 deaths. Patients were then divided into two groups, above or below the median value of pre-HD OER, which was 30%. In these groups, the average incidence of deaths was 12% (24 deaths) and 5,5% (11 deaths) respectively (p&amp;lt;0.05), with significantly different survival curves (Kaplan-Meier log rank test = 0.04, fig). No difference in mortality was evident if we divided patients according to the median intradialytic change in OER value. Conclusion Patients with pre-HD OER &amp;gt; 30% have a higher mortality risk, most probably secondary to reduced capability to respond to HD related oxygen requirements. OER is novel biomarker to identify patients at greatest clinical risk.

POS-612 OXYGEN EXTRACTION RATIO (OER) IDENTIFIES PATIENTS AT RISK FOR INTRADIALYTIC HYPOTENSION (IDH)

Intradialytic hypotension (IDH) is a hemodynamic phenomenon recently associated with decreased blood oxygen saturation (SO2) occurring during haemodialysis (HD) sessions. The ratio between arterial SO2 (SaO2) and central venous SO2 (ScvO2) or Oxygen Extraction Ratio (OER), which represents a roughly estimate of the amount of oxygen claimed by peripheral tissues, could thus be used to measure HD related parenchyma hypoxic stress. Aim of this pilot study was to evaluate the relationship between OER values during dialysis sessions and episodes of IDH.

The Influence of Topically Administered Heparin on Peripheral Microcirculation of the Skin: A Double-Blind, Randomized, Controlled Preliminary Study on 50 Healthy Subjects.

Venous thrombosis is the most common cause of flap failure in the first days after surgery. Although heparin is one of the most important antithrombotic substances and is implemented in the therapy of various diseases, there are only a few studies addressing its topical administration in the field of flap surgery. Especially, very little is known about the effects of topical heparin and its impact on microcirculation. In this study we evaluated to what extent topically administered heparin influences skin microcirculation (capillary venous oxygen saturation SO2, blood filling of microvessels, blood flow, and velocity) in healthy subjects. Skin perfusion parameters on the forearm were measured with the O2C device in a double-blinded, controlled, and randomized study with 50 healthy subjects after administration of heparin ointment in three different concentrations and a control ointment (dexpanthenol). Topically administrated heparin slightly increased SO2 (max. 187 ± 285 SD or standard deviation % vs. 145 ± 129 SD %), flow (max. 264 ± 427 SD % vs. 151.74 ± 111 SD %), and velocity (max. 153 ± 149 SD % vs. 122 ± 56 SD %) after an incubation time of 60 minutes in comparison to control. No statistically significant difference could be detected regarding heparin concentration. As a first important step in possible future implementing of heparin as a topical administration in flap surgery, our data-although not statistically significant-indicate that heparin can improve microcirculation (SO2, flow) in healthy subjects. Nevertheless, further research in subjects with impaired microcirculation is necessary.

Oxygen extraction ratio to identify patients at increased risk of intradialytic hypotension

Intradialytic hypotension (IDH) is a hemodynamic phenomenon recently associated with decreased blood oxygen saturation (SO2). The ratio between peripheral oxygen saturation (SpO2) and central venous SO2 (ScvO2) or Oxygen Extraction Ratio (OER), which represents a roughly estimate of the amount of oxygen claimed by peripheral tissues, might be used to estimate haemodialysis (HD) related hypoxic stress. Aim of this pilot study was to evaluate the relationship between OER increments during dialysis sessions (ΔOER) and episodes of IDH. We enrolled chronic HD patients with permanent central venous catheter (CVC) and no fistula, in whom ScvO2 measurement is at hand. OER ([(SpO2 − ScvO2)/SpO2] × 100) was measured in three consecutive HD sessions (HD OER sessions) before HD, after 15′, 30′ and 60′ min and at the end of HD. Then, a one-year follow-up was planned to record the number of IDH episodes. In the 28 enrolled patients (age 74 ± 2.6 years), during 12 ± 1.2 months of follow up, incidence of IDH was 3.6%. We divided patients into two groups, above or below the median value of ΔOER at the end of HD, which was 36%. In these groups, the average incidence of IDH was 7% and 2% respectively (p < 0.01), while OER values before HD were not different. Notably, in the high ΔOER group the OER increment was evident since after 15′ and was significantly higher than in the low ∆OER group (∆OER-15′ = 19 ± 3.0% vs. 9.0 ± 3.0%; p < 0.05). By comparison, blood volume changes overlapped in the two groups (average change − 9 ± 0.8%). Values of ∆OER > 19% after only 15′ of HD treatment or > 36% at the end of the session characterize patients with higher rates of hypotension. Intradialytic ∆OER, a parameter of tissue hypoxic stress, identifies more fragile patients at greater risk of IDH.

Assessment of retinal vascular oxygenation and morphology at stages of diabetic retinopathy in African Americans

BackgroundDiabetic retinopathy (DR) is a microvascular complication of diabetes and a leading cause of blindness in working-age adults. The likelihood of visual impairment associated with DR is two-fold higher in the African-American (AA) compared to non-Hispanic white. Although alterations in retinal vessel oxygenation and morphology have been reported in DR, there is limited knowledge about these vascular changes in AA subjects. The purpose of the current study was to investigate alterations in retinal vascular oxygen saturation (SO2), vessel diameter (D) and tortuosity at severity stages of DR in AA subjects.MethodsA nested case-control study of 56 AA subjects was conducted. Right eyes were grouped as non-diabetic (ND) (N = 26), no clinical DR (NDR) (N = 19), or moderate/severe non-proliferative DR (NPDR) (N = 11). Imaging was performed using a commercially available scanning laser ophthalmoscope. Images were analyzed to determine retinal arterial and venous SO2 (SO2A and SO2V), diameter (DA and DV), and vessel tortuosity index (VTI) (VTIA and VTIV).ResultsSO2V and DV were higher in NPDR compared to ND and NDR groups (P < 0.05). There were no significant differences in SO2A and DA among ND, NDR, and NPDR groups (P > 0.8). Maximum VTIA was higher in diabetics (NDR and NPDR) compared to non-diabetics (P < 0.03). There was no significant difference in maximum VTIV among the 3 groups (P = 0.5).ConclusionsThe findings advance our understanding of DR pathophysiology in the AA population and may propel identification of race-specific retinal vascular biomarkers for improved diagnosis and monitoring of DR.

P1061ACID-BASE MODELLING AND TREND IN CENTRAL VENOUS OXYGEN SATURATION IN HEMODIALYSIS

Abstract Background and Aims Central venous oxygen saturation (sO2cv) is commonly used as a proxy of cardiac output in non-uremic populations. Recently, the decrease in sO2cv commonly observed in many hemodialysis (HD) sessions was correlated with ultrafiltration volume (UFV) and was suspected to be linked with a treatment-induced decrease in cardiac output (Zhang et al, NDT 2018). High variability in sO2cv has also been associated with all-cause mortality in this group of patients (Zhang et al, Blood Purif 2019). We adapted a comprehensive mathematical model of whole body oxygen (O2) and carbon dioxide (CO2) biochemistry, storage and transport and applied it to simulate the changes in sO2cv during bicarbonate hemodialysis to test their connection with changes in CO. Method The original model of biochemistry and transport of base excess, CO2 and O2 was originally developed by Rees and Andreassen (Crit Rev Biomed Eng 2005), and describes in detail the chemical and respiratory mechanisms that regulate the biochemical status in different physiological compartments of the patients’ body (venous blood, arterial blood, tissue cells, interstitial fluid). The model was modified to include the effect of the HD treatment on these systems, allowing to calculate the variations in venous and arterial sO2. Treatment perturbations included the removal via ultrafiltration of interstitial fluid and plasma volume (and consequent hemoconcentration), and infusion of bicarbonate. Simulation experiments of 4h HD sessions were carried out with bicarbonate dialysate concentration = 35 mmol/L and dialysance = 198 mL/min, and various ultrafiltration volumes (UFV); CO was assumed to decrease by 2% for each 1% change in blood volume. The initial biochemical status of the patient was defined assuming 20 mEq/L bicarbonate concentration, 7.4 pH, and 97% oxygen saturation in the arterial compartment, resulting in initial sO2cv equal to 66.6%. Both artero-venous and veno-venous access were simulated. Results The model predicted a negative linear trend for sO2cv with variable slope depending on UFV, as shown in the table: The trend in sO2cv was directly proportional to the decrease in CO during HD and inversely proportional to UFV. In case of constant CO, the simulated sO2cv would actually increase during the session. Although the type of vascular access determined changes in other simulated quantities, partial pressures of CO2 and O2 and oxygen saturation in both arterial and venous blood were practically unchanged. Conclusion Our model confirmed the correlation between the trend in sO2cv and UFV already highlighted in previous works. Moreover, it showed that the decrease in cardiac output is a major determinant of the decrease in sO2cv during the HD session. The developed mathematical model may provide physiological insights in the development of new technologies to monitor changes in cardiac performance during HD.

A step towards pigmentation independent retinal vessel oximetry

AbstractPurposeRetinal vessel oximetry is a promising tool to gain information on the microcirculation of the retina. Due to the ratio of reflectance’s of the vessel plane and the neighbouring tissue, computation of oxygen saturation values (SO2) varies between individuals. The aim of this study was to develop a data transformation approach to overcome pigmentation‐ dependency, allowing for inter‐subject comparison of SO2 values.MethodsArterial and venous SO2 results of 67 healthy subjects (mixed ethnicities) were related to the pigmentation value (RP) provided by the Vesselmap software (RVA Imedos, Jena). After normalization of the axis values, a regression line was rotated around the intercept with the y‐axis applying a rotation matrix (clockwise rotation).ResultsRegression lines before rotation were aSO2=0.808*RP+84.61 (R2 = 0.74) and vSO2 = 0.358*RP+39.17 (R2 = 0.56) for arteries and veins, respectively. Transformed arterial and venous regression lines were aSO2 = 0.066*RP+84.57 (R2 = 0.05) and vSO2 = 0.028*RP+39.09 (R2 = 0.01), respectively.ConclusionClockwise rotation of the regression lines for arteries and veins was able to reduce R2 from 0.74 to 0.05 for arteries and from 0.56 to 0.01 for veins, confirming that the data transformation resulted in retinal pigmentation independent SO2 results. The proposed approach might improve comparability of inter‐subject results and allow for determination of normative data.

The flicker response of venous oxygen saturation is significantly reduced in the early and late stages of age-related macular degeneration.

Retinal oxygen saturation (SO2) during flicker light stimulation was measured non-invasively in humans with age-related macular degeneration (AMD). Furthermore, the differences between early and late stages of AMD were evaluated. In 60 eyes of 45 AMD patients (74 ± 8.3 years) and 23 eyes of 23 healthy controls (73.4 ± 7.4 years), the SO2 of arterioles and venules was measured with the oximetry module of the Retinal Vessel Analyzer. Arterial SO2, venous SO2 and arteriovenous SO2 difference at baseline and with the flicker were assessed and compared with controls. From the difference between the arteriovenous SO2 under flicker stimulation and at baseline, the parameter delta av. Diff was calculated. Subgroup analyses of non-exudative (dry) AMD, exudative (wet) AMD and their end stages, geographic atrophy (GA) and disciform scar (DS) were performed. In comparison with healthy subjects (mean - 4.90, CI [- 6.32, - 3.43]), the parameter delta av. Diff was significantly reduced in all AMD patients (mean - 2.20, CI - 3.15, -1.23, p = 0.003), dry AMD (mean - 1.97, CI - 3.31, -0.63, p = 0.013) and wet AMD (mean - 2.35, CI - 3.50, - 1.19, p = 0.025). The comparison between wet and dry AMD revealed no significant results (p = 1). The comparison between AMD subgroups and healthy controls (median (IQR) - 4.29 (- 8.32; - 2.42) %) showed significant differences in non-neovascular (early dry AMD) (median (IQR) - 2.43 (- 4.59; - 0.74) %, p = 0.038), GA (median (IQR) 0.10 (- 4.02; 3.15) %, p = 0.019) and DS (median (IQR) - 1.67 (- 3.52; - 0.12) %, p = 0.03). A nearly significant reduction was observed in exudative (early wet) AMD (median (IQR) - 2.71 (- 5.84; - 0.2) %, p = 0.055). Minimal, not statistically significant differences of delta av. Diff were found between AMD subgroups. None of the baseline parameters was significantly different between patients and healthy controls, even after flicker light stimulation. Non-invasive retinal oximetry with flicker light stimulation seems to be a suitable method to study the pathogenetic mechanisms of AMD. The mathematically derived parameter delta av. Diff appears to be more sensitive than arteriovenous SO2 difference. Results suggest that the regulation of retinal oxygen supply, oxygen consumption or both is impaired in AMD.

Fundus-simulating phantom for calibration of retinal vessel oximetry devices

Retinal vessel oxygen supply is important for retinal tissue metabolism. Commonly used retinal vessel oximetry devices are based on dual-wavelength spectral measurement of oxyhemoglobin and deoxyhemoglobin. However, there is no traceable standard for reliable calibration of these devices. In this study, we developed a fundus-simulating phantom that closely mimicked the optical properties of human fundus tissues. Microchannels of precisely controlled topological structures were produced by soft lithography to simulate the retinal vasculature. Optical properties of the phantom were adjusted by adding scattering and absorption agents to simulate different concentrations of fundus pigments. The developed phantom was used to calibrate the linear correlation between oxygen saturation (SO2) level and optical density ratio in a dual-wavelength oximetry device. The obtained calibration factors were used to calculate the retinal vessel SO2 in both eyes of five volunteers aged between 24 and 27 years old. The test results showed that the mean arterial and venous SO2 levels after phantom calibration were coincident with those after empirical value calibration, indicating the potential clinical utility of the produced phantom as a calibration standard.

Retinal oximetry in branch retinal vein occlusion.

To measure retinal oxygen saturation (SO2 ) in eyes with branch retinal vein occlusion (BRVO). Retinal oximetry was performed using the Oxymap T1 retinal oximeter in 50 eyes (50 patients) with resolved BRVO. SO2 was calculated in each major retinal artery and vein in four quadrants. The superior or inferior hemisphere with BRVO was categorized as the affected hemisphere and the other as the unaffected hemisphere. Oxymap T1 allowed us to measure SO2 in major retinal vessels. Both arterial and venous SO2 in the affected hemisphere were significantly higher than those in the unaffected hemisphere. However, there was no significant difference in arteriovenous (A-V) difference in SO2 between the affected and unaffected hemispheres. Of the 50 included eyes, 32 had non-ischemic BRVO and 18 had ischemic BRVO. In the affected hemisphere, arterial SO2 was significantly higher in ischemic BRVO (106.9±8.8%) than in non-ischemic BRVO (101.3±9.2%, p=0.044). There were no significant differences in venous SO2 between non-ischemic and ischemic BRVO. Consequently, the A-V difference in SO2 was significantly higher in ischemic BRVO (51.9±13.9%) than in non-ischemic BRVO (43.4±11.5%, p=0.028). In multiple regression analysis, the type of perfusion (non-ischemic or ischemic) had associations with arterial SO2 (β=0.365, p=0.013) and with A-V differences in SO2 in the affected hemisphere (β=0.406, p=0.006). In ischemic BRVO, arterial SO2 and the A-V difference in SO2 in the affected hemisphere were significantly higher than in non-ischemic BRVO.

Comprehensive Characterization of Cerebrovascular Dysfunction in Blast Traumatic Brain Injury Using Photoacoustic Microscopy.

Blast traumatic brain injury (bTBI) is a leading contributor to combat-related injuries and death. Although substantial emphasis has been placed on blast-induced neuronal and axonal injuries, co-existing dysfunctions in the cerebral vasculature, particularly the microvasculature, remain poorly understood. Here, we studied blast-induced cerebrovascular dysfunctions in a rat model of bTBI (blast overpressure: 187.8 ± 18.3 kPa). Using photoacoustic microscopy (PAM), we quantified changes in cerebral hemodynamics and metabolism-including blood perfusion, oxygenation, flow, oxygen extraction fraction, and the metabolic rate of oxygen-4 h post-injury. Moreover, we assessed the effect of blast exposure on cerebrovascular reactivity (CVR) to vasodilatory stimulation. With vessel segmentation, we extracted these changes at the single-vessel level, revealing their dependence on vessel type (i.e., artery vs. vein) and diameter. We found that bTBI at this pressure level did not induce pronounced baseline changes in cerebrovascular diameter, blood perfusion, oxygenation, flow, oxygen extraction, and metabolism, except for a slight sO2 increase in small veins (<45 μm) and blood flow increase in large veins (≥45 μm). In contrast, this blast exposure almost abolished CVR, including arterial dilation, flow upregulation, and venous sO2 increase. This study is the most comprehensive assessment of cerebrovascular structure and physiology in response to blast exposure to date. The observed impairment in CVR can potentially cause cognitive decline due to the mismatch between cognitive metabolic demands and vessel's ability to dynamically respond to meet the demands. Also, the impaired CVR can lead to increased vulnerability of the brain to metabolic insults, including hypoxia and ischemia.

Determination of Reference Intervals for Umbilical Cord Arterial and Venous Blood Gas Analysis of Healthy Thoroughbred Foals

Abstract Although umbilical cord blood gas analysis is considered the best way to assess in utero oxygenation in human neonates, there is limited evaluation of this method in equine neonatology. Our objectives were to assess the practicality of obtaining umbilical cord blood gas samples in the field and to determine umbilical cord arterial and venous blood gas reference intervals (RI) for healthy, newborn foals. Thoroughbred foals >320 days gestation from healthy mares with uneventful pregnancies at one stud farm were evaluated. All parturitions were observed, with paired umbilical arterial and venous whole-blood samples obtained immediately following parturition for blood gas and lactate concentrations measured in duplicate. Apgar scores were assigned immediately and 10 min after birth, with all foals subsequently examined on days 1–28 to monitor for development of perinatal asphyxia syndrome. Foals were excluded from analysis based on abnormalities of stage 2 labour, Apgar scores and gross and histological placental assessment. Data was analysed using a Student's t-test, Pearson's correlation and the Robust method with P ≤ 0.05 significant. Umbilical cord samples were simple to obtain with minimal disruption to the foaling environment. Of the n = 34 foals assessed, n = 7 were excluded based on premature placental separation deliveries. The mean time for stage 2 labour and blood gas analysis after parturition was 17.3 ± 5.1 min and 5.0 ± 2.3 min, respectively. RI were identified for umbilical arterial and venous pH (7.19–7.42 vs. 7.34–7.44), PO2 (15.5–48.39 mmHg vs. 16.6–52.7 mmHg), PCO2 (49.5–82.29 mmHg vs. 45.4–63.1 mmHg), SO2 (9.19–76.89% vs. 39.9–84.88%), bicarbonate (27.3–38.7 mmol/l vs. 27.7–37.8 mmol/l), base excess (0.36–12.9 mmol/l vs. 1.97–13.1 mmol/l), TCO2 (28.99–40.3 mmHg vs. 29.0–39.5 mmHg) and lactate (1.4–7.3 mmol/l vs. 1.3–4.9 mmol/l). Umbilical arterial samples had lower pH (P

Determination of reference intervals for umbilical cord arterial and venous blood gas analysis of healthy Thoroughbred foals

Although umbilical cord blood gas analysis is considered the best way to assess in utero oxygenation in human neonates, there is limited evaluation of this method in equine neonatology. Our objectives were to assess the practicality of obtaining umbilical cord blood gas samples in the field and to determine umbilical cord arterial and venous blood gas reference intervals (RI) for healthy, newborn foals. Thoroughbred foals >320 days gestation from healthy mares with uneventful pregnancies at one stud farm were evaluated. All parturitions were observed, with paired umbilical arterial and venous whole-blood samples obtained immediately following parturition for blood gas and lactate concentrations measured in duplicate. Apgar scores were assigned immediately and 10 min after birth, with all foals subsequently examined on days 1–28 to monitor for development of perinatal asphyxia syndrome. Foals were excluded from analysis based on abnormalities of stage 2 labour, Apgar scores and gross and histological placental assessment. Data was analysed using a Student's t-test, Pearson's correlation and the Robust method with P ≤ 0.05 significant. Umbilical cord samples were simple to obtain with minimal disruption to the foaling environment. Of the n = 34 foals assessed, n = 7 were excluded based on premature placental separation deliveries. The mean time for stage 2 labour and blood gas analysis after parturition was 17.3 ± 5.1 min and 5.0 ± 2.3 min, respectively. RI were identified for umbilical arterial and venous pH (7.19–7.42 vs. 7.34–7.44), PO2 (15.5–48.39 mmHg vs. 16.6–52.7 mmHg), PCO2 (49.5–82.29 mmHg vs. 45.4–63.1 mmHg), SO2 (9.19–76.89% vs. 39.9–84.88%), bicarbonate (27.3–38.7 mmol/l vs. 27.7–37.8 mmol/l), base excess (0.36–12.9 mmol/l vs. 1.97–13.1 mmol/l), TCO2 (28.99–40.3 mmHg vs. 29.0–39.5 mmHg) and lactate (1.4–7.3 mmol/l vs. 1.3–4.9 mmol/l). Umbilical arterial samples had lower pH (P < 0.0001), PO2 (P = 0.002) and SO2 (P < 0.0001) and higher PCO2 (P < 0.0001) and lactate (P < 0.0001) than venous samples. The initial Apgar score was positively correlated to umbilical arterial SO2 (r = 0.4, P = 0.05) and negatively with umbilical arterial TCO2 (r = −0.6, P = 0.004). Overall, umbilical cord sampling was simple and minimally disruptive, with RI obtained for blood gas measurements. RI for umbilical blood gas measurements from a larger population of healthy and unhealthy foals is required to evaluate the accuracy of this method for assessing in utero oxygenation.