Changes In Oxygen Metabolism Research Articles

Effect of Comprehensive Cerebral Protection Program on Cerebral Oxygen Metabolism and Vascular Endothelial Function in Elderly Patients with Acute Cerebral Infarction

We aimed to explore the effect of comprehensive cerebral protection on cerebral oxygen metabolism and vascular endothelial function in elderly patients with acute cerebral infarction. A total of 168 elderly patients with acute cerebral infarction treated in The First Affiliated Hospital of Nanchang University, China from January 2016 to January 2018 were selected. The patients were divided into a control group and an observation group using random number method, n=84. Patients in the observation group were given comprehensive cerebral protection treatment, and patients in the control group were treated with conventional standardized treatments. The changes of cerebral oxygen metabolism, hemorheology and vascular endothelial function before and after treatment were compared between the two groups. After treatment, oxygen content in arteries and internal jugular veins (Da-vO2), ofoxygen uptake fraction (OEF), Oxygen saturation (SpO2), nitric oxide (NO) were increased in both groups in comparison to before treatment, jugular venous oxygen saturation (SjvO2), brain oxygen uptake rate (ERO2), endothelin (ET), intracranial pressure (ICP), whole blood viscosity, plasma viscosity, reduced viscosity of whole blood, and hematocrit were decreased. However, the changes in the observation group were larger than those in the control group, the difference was statistically significant (P<0.05). The treatment of cerebral infarction in elderly patients with acute cerebral infarction can effectively improve the cerebral oxygen metabolism and vascular endothelial function and improve the blood rheology, which has important clinical value.

A pilot study of exercise-induced changes in mitochondrial oxygen metabolism measured by a cellular oxygen metabolism monitor (PICOMET)

Impaired tissue oxygenation is the key pathomechanism in the development of organ dysfunction in shock; mitochondrial impairment can aggravate the condition. However, measuring tissue oxygenation directly and non-invasively still poses a clinical challenge. A novel device (COMET) allows the assessment of mitochondrial oxygen metabolism using the Protoporphyrin IX Triplet State Lifetime Technique (PpIX-TSLT). Critically ill patients, especially in sepsis, often exhibit oedema which may interfere with the COMET measurement. Furthermore, patients' physical activity level differs significantly before and during hospitalisation. Thus, the aim of this study was to identify the effects of physical activity and body composition on mitochondrial oxygen tension (mitoPO2) and consumption (mitoVO2) in healthy controls (N = 40). Furthermore, the study tested the repeatability of the COMET variables and identified covariates. Multiple COMET measurements were performed before (T1, T2), during and after (T3, T4) ergometry. Body composition was assessed by bioimpedance analysis. Physiological variables (blood pressure, heart rate, oxygen saturation) were recorded. In the analytical sample (n = 26), physical activity significantly decreased mitoVO2; other COMET variables remained unchanged between T2 and T3. During ergometry, mitoPO2 increased significantly. The distribution of body water significantly influenced mitoVO2. In our setting, the method demonstrated moderate repeatability. Variables of fitness (heart rate recovery, phase angle and physical activity level), signal quality and duration of exposure to 5-aminolevulinic acid (obligatory for PpIX-TSLT) were identified as significant covariates of mitoVO2. Mitochondrial oxygen delivery (mitoDO2) was established as a new variable of COMET analysis. Results of this pilot study should be validated in future studies.

This issue of Acta

This issue of Acta

This issue of Acta Sept 2018

The cover illustration shows a macular haemorrhage, as described by Schargus from Dusseldorf in the electronic part of this issue. Vaes et al in the Netherlands and Belgium point to microvascular changes in retina of patients with chronic obstructive pulmonary disease. Ramdas in Maastricht reviews the literature on dietary influences in glaucoma. Iron and selenium may increase risk, and leafy vegetables decrease risk of glaucoma. However, the data are limited. Bengtsson et al and Lindén et al in Sweden describe the ongoing GLAUCOMA INTENSIVE TREATMENT STUDY and show that intensive treatment lowers IOP more than monotherapy. The study will determine the effect of intensive glaucoma therapy on visual field progression and predict vision loss at life's end. Willekens et al in Belgium and Portugal found that some glaucoma patients have posterior vitreous detachment at an older age than healthy controls. Farhoudi et al in Sweden demonstrate that patients benefit from new spectacle following cataract surgery. Stolk-Vos et al in the Netherlands emphasize the advantage of recording patient-reported visual function and recommend the Catquest-9SF questionnaire. Grimfors et al in Sweden use the Swedish National Cataract Register to demonstrate a correlation between patient-reported improvement and visual function on the one hand and surgical complications, comorbidities, age, gender and visual acuity on the other. Næser et al in Denmark and Italy show that corneal astigmatism is stable until age 50 and changes by 0.25 dioptres every 10 years thereafter. Frimmel et al in the Netherlands and Switzerland report significant eye trauma from fireworks on new Year′s Eve. Sahraravand et al in Helsinki found falls at home to cause most eye injuries in elderly Finns. Bro and Lindblom in Sweden point out that visual requirement for driving are variable in Nordic countries. Mourits et al in the Netherlands looked at cosmetic outcomes following enucleation or radiation for retinoblastoma. Orbital implant complications were manageable, whereas external beam radiation gave less favourable cosmetic outcomes. Scheerlink et al in the Netherlands found better foveal sensitivity on microperimetry with gas compared with silicone oil tamponade for retinal detachment. Leinonen et al in Helsinki used intravitreal steroid implants to treat uveitis-related macular oedema. Pérez-Trullén et al in Spain propose that Goya had age-related cataract and this influenced his late paintings. The following articles are published electronically and are accessible on www.actaophthalmologica.com, as are all articles in Acta for the last century. Leal et al in Portugal and UK conclude that intravitreal injection of anti-TNF antibodies is a possible but not proven treatment for noninfectious uveitis. Zhu et al in China provide a comprehensive review on exercise and glaucoma, including the possible effect on IOP, blood flow and neuroprotection. Kang et al in United States and Australia found that total flavonoid intake does not influence glaucoma risk. Mataki et al in Japan correlated beta peripapillary atrophy with age, lower IOP and disc-fovea distance. Rabensteiner et al in Austria found Meibomian gland dysfunction to play a major role in dry eye, often in combination with reduces aqueous tear secretion. Klingensteiner et al in Munchen recommend PET scanning for orbital adnexal lymphomas. Liu et al in China influence angiotensin pathways in retina with microRNA. This affects proliferation and apoptosis in retinal endothelial cells in diabetic rats. Rose et al in Canada and Australia measure changes in retinal perfusion and oxygen metabolism in radiation retinopathy. Hanhart et al in Israel suggest that bevacizumab intravitreal injections may increase mortality in patients who have recently suffered TIA or stroke. Blixt et al in Denmark and Sweden found that endothelin-1 induced vasoconstriction in retina can be suppressed and this may offer treatment possibilities in retinal ischaemia. Subhi and Sörensen in Denmark view pigment epithelial detachment in 3D and measure volume. They suggest that such analysis may be superior to current practice. Shargus in Dusseldorf supplied the cover illustration of a picturesque retinal haemorrhage. Ferreira et al in Portugal used infrared pupillometry to demonstrate transient pupil changes following laser iridotomy. Diederen et al in the Netherlands recommend Baerveldt implants in uveitis glaucoma in young patients. Vohra et al in Denmark found vision loss in a patient with cerebral amyloid angiopathy. Grzybowski and Nowak in Poland found similar rate of myopia in Polish children as in other Caucasian cohorts. Schrader et al in Germany present a plastic compressed collagen device, which they transplanted onto the corneal surface of a patient with corneal ulcer. Krohn et al in Norway describe a slowly progressive RPE dysgenesis with severe visual loss. I hope this issue of Acta provides pleasant and informative reading in the cool and dark evenings ahead.

Perioperative Cerebral Oxygenation Metabolism in Neonates with Hypoplastic Left Heart Syndrome or Transposition of the Great Arteries.

Optimizing oxygen delivery to the brain is one of the main goals in children with congenital heart defects after surgery. It has been shown that cerebral oxygen saturation (cSO2) is depressed within the first day after neonatal cardiopulmonary bypass surgery. However, peri-operative cerebral oxygen metabolism has not yet been assessed in previous studies. The aim of this study was to describe the peri-operative changes in cerebral oxygen metabolism in neonates with congenital heart defects following cardiopulmonary bypass surgery. Prospective observational cohort study. PICU of a tertiary referral center. Fourteen neonates with hypoplastic left heart syndrome (HLHS) undergoing Norwood procedure and 14 neonates with transposition of great arteries (TGA) undergoing arterial switch operation (ASO) were enrolled. Pediatric heart surgery. We measured non-invasively regional cSO2 and microperfusion (rcFlow) using tissue spectrometry and laser Doppler flowmetry before and after surgery. Cerebral fractional tissue oxygen extraction (cFTOE), the arterio-cerebral difference in oxygen content (acDO2) and approximated cerebral metabolic rate of oxygen (aCMRO2) were calculated. According to the postsurgical hemodynamics, arterial saturation (aSO2) normalized immediately after surgery in the TGA group, whereas HLHS patients still were cyanotic. cSO2 significantly increased in TGA group over 48h after ASO (p = 0.004) and was significantly higher compared to HLHS group after Norwood procedure. cFTOE as a risk marker for brain injury was elevated before surgery (TGA group 0.37 ± 0.10, HLHS group 0.42 ± 0.12) and showed a slight decrease after ASO (p = 0.35) but significantly decreased in patients after Norwood procedure (p = 0.02). Preo-peratively, acDO2 was significantly higher in patients with HLHS compared to patients with TGA (7.7 ± 2.5 vs. 5.2 ± 1.6ml/dl, p = 0.005), but normalized in the posto-perative course. Before surgery, the aCMRO2 was slightly higher in the HLHS group (5.1 ± 1.5 vs. 3.9 ± 2.5 AU, p = 0.14), but significantly decreased after Norwood procedure (- 1.6 AU, p = 0.009). There was no difference in rcFlow between both groups and between the points in time prior and after surgery. Neonates undergoing cardiac surgery suffer from peri-operative changes in hemodynamics and cerebral hypoxemic stress. The cerebral oxygen metabolism seems to be more affected in cyanotic children with functionally univentricular hearts compared to post-operative acyanotic patients. Additional stress factors must be avoided to achieve the best possible neurological outcome.

Nitro-Oxidative Stress Correlates with Se Tolerance of Astragalus Species.

At high concentrations, selenium (Se) exerts phytotoxic effects in non-tolerant plant species partly due to the induction of nitro-oxidative stress; however, these processes are not fully understood. In order to obtain a more accurate view of the involvement of nitro-oxidative processes in plant Se sensitivity, this study aims to characterize and compare Se-triggered changes in reactive oxygen (ROS) and nitrogen species (RNS) metabolism and the consequent protein tyrosine nitration as a marker of nitrosative stress in the non-accumulator Astragalus membranaceus and the Se hyperaccumulator Astragalus bisulcatus. The observed parameters (Se accumulation, microelement homeostasis, tissue-level changes in the roots, germination, biomass production, root growth and cell viability) supported that A. membranaceus is Se sensitive while the hyperaccumulator A. bisulcatus tolerates high Se doses. We first revealed that in A. membranaceus, Se sensitivity coincides with the Se-induced disturbance of superoxide metabolism, leading to its accumulation. Furthermore, Se increased the production or disturbed the metabolism of RNS (nitric oxide, peroxynitrite and S-nitrosoglutathione), consequently resulting in intensified protein tyrosine nitration in sensitive A. membranaceus. In the (hyper)tolerant and hyperaccumulator A. bisulcatus, Se-induced ROS/RNS accumulation and tyrosine nitration proved to be negligible, suggesting that this species is able to prevent Se-induced nitro-oxidative stress.

Показники гемодинаміки та обміну кисню при різних типах поповнення крововтрати у постраждалих з політравмою

Показники гемодинаміки та обміну кисню при різних типах поповнення крововтрати у постраждалих з політравмою

Changes in MRI-Based Quantitative Brain Oxygen Metabolism in Preterm Newborns with Anemia, A Pilot Study

Changes in MRI-Based Quantitative Brain Oxygen Metabolism in Preterm Newborns with Anemia, A Pilot Study

Retinal Oximetry Discovers Novel Biomarkers in Retinal and Brain Diseases.

Biomarkers for several eye and brain diseases are reviewed, where retinal oximetry may help confirm diagnosis or measure severity of disease. These include diabetic retinopathy, central retinal vein occlusion (CRVO), retinitis pigmentosa, glaucoma, and Alzheimer's disease. Retinal oximetry is based on spectrophotometric fundus imaging and measures oxygen saturation in retinal arterioles and venules in a noninvasive, quick, safe manner. Retinal oximetry detects changes in oxygen metabolism, including those that result from ischemia or atrophy. In diabetic retinopathy, venous oxygen saturation increases and arteriovenous difference decreases. Both correlate with diabetic retinopathy severity as conventionally classified on fundus photographs. In CRVO, vein occlusion causes hypoxia, which is measured directly by retinal oximetry to confirm the diagnosis and measure severity. In both diseases, the change in oxygen levels is a consequence of disturbed blood flow with resulting tissue hypoxia and vascular endothelial growth factor (VEGF) production. In atrophic diseases, such as retinitis pigmentosa and glaucoma, retinal oxygen consumption is reduced and this is detected by retinal oximetry. Retinal oximetry correlates with visual field damage and retinal atrophy. It is an objective metabolic measure of the degree of retinal atrophy. Finally, the retina is part of the central nervous system tissue and reflects central nervous system diseases. In Alzheimer's disease, a change in retinal oxygen metabolism has been discovered. Retinal oximetry is a novel, noninvasive technology that opens the field of metabolic imaging of the retina. Biomarkers in metabolic, ischemic, and atrophic diseases of the retina and central nervous system have been discovered.

Experimental animal study of cerebral oxygen metabolism changes during the process of brain death

To reproduce a stable animal model of brain death in pigs, observe the change regularity of cerebral oxygen metabolism during the process of brain death, and to evaluate the significance and value of cerebral oxygen metabolism parameters for the diagnosis of brain death. Twelve landrace pigs were used to create the brain death models using modified method of increasing epidural intracranial pressure (ICP). The mean arterial pressure (MAP) and ICP were monitored continuously during the process. The pigs were divided into four groups according to cerebral perfusion pressure (CPP) decreasing degree during brain death, namely CPP normal group and CPP decreasing 0%-30%, 30%-70%, and 70%-100% groups. Blood gas analysis of the external carotid artery and internal jugular vein were monitored discontinuously. The changes in cerebral oxygen metabolism parameters, including external carotid artery-internal jugular vein bulb oxygen content difference (AJDO2), internal jugular bulb-external carotid artery carbon dioxide partial pressure difference (DPCO2) and DPCO2/AJDO2 ratio, were observed. Brain death model were successfully reproduced in 12 experimental pigs. With MAP and ICP monitoring, the models at different stages of CPP could be repeatedly induced. The levels of AJDO2 and DPCO2 were increased gradually and then decreased, while the ratio of DPCO2/AJDO2 was constantly increased with the decrease of CPP. The level of AJDO2 in CPP decreasing 0%-30% group was significantly higher than that in CPP normal group [(5.86±1.21)% vs. (3.92±0.64)%], the levels of DPCO2 in CPP decreasing 0%-30% and CPP decreasing 30%-70% groups were significantly higher than those in CPP normal group [mmHg (1 mmHg = 0.133 kPa): 10.33±1.83, 11.48±2.32 vs. 6.11±1.43], and the ratios of DPCO2/AJDO2 in CPP decreasing 30%-70% and CPP decreasing 70%-100% groups were significantly higher than those in CPP normal group and CPP decreasing 0%-30% group (2.81±0.53, 4.12±1.07 vs. 1.57±0.64, 1.62±0.81). All the differences above were statistically significant (all P < 0.05). With the decrease of CPP, cerebral oxygen metabolism showed a regular change during brain death. DPCO2 combined with DPCO2/AJDO2 is a reliable blood gas analysis index indicating intracranial hypoperfusion, which has certain reference value for the determination of brain death.

Storm event-scale nutrient attenuation in constructed wetlands experiencing a Mediterranean climate: A comparison of a surface flow and hybrid surface-subsurface flow system

Among different Water Sensitive Urban Design options, constructed wetlands (CWs) are used to protect and restore downstream water quality by attenuating nutrients generated by stormwater runoff. This research compared the nutrient attenuation ability during a diverse population of storm events of two CWs: (a) a hybrid CW with multiple alternating surface flow (SF) and laterite-based subsurface flow (SSF) compartments, and (b) a single stage SF CW. Within-storm variability, nutrient concentrations were assessed at 2 to 3-h intervals at both the main inlet and outlet of each CW. Dissolved oxygen concentrations of the surface waters were also monitored at 10-min intervals using high frequency in situ sensors. Nutrient loads into the CWs were observed to be higher when a high rainfall event occurred, particularly after longer antecedent dry conditions. Longer hydraulic retention times promoted higher attenuation at both sites. However, the relative extent of nutrient attenuation differed between the CW types; the mean total nitrogen (TN) attenuation in the hybrid and SF CW was 45 and 48%, respectively. The hybrid CW attenuated 67% total phosphorus (TP) loads on average, while the SF CW acted as a net TP source. Periodic storm events transitioned the lentic CW into a lotic CW and caused riparian zone saturation; it was therefore hypothesized that such saturation of organic matter rich-riparian zones led to release of TP in the system. The hybrid CW attenuated the released TP in the downstream laterite-based SSF compartments. Diel oxygen metabolism calculated before and after the storm events was found to be strongly correlated with water temperature, solar exposure and antecedent dry condition during the pre-storm conditions. Furthermore, the SF CW showed a significant relationship between overall nutrient load attenuation and the change in oxygen metabolism during the storm perturbation, suggesting oxygen variation could be a useful proxy indicator of CW function.

Physiological Impact of Platelet Apheresis in Pigs: Oxygen Metabolism and Coagulation.

Platelet apheresis is a routine clinical practice, but the physiological impact on the donors has been incompletely characterized. This study measured the effects of platelet apheresis on hemodynamics, oxygen metabolism, and coagulation in pigs to assess its impact before employing the animals in experimental studies. Forty pigs (39.8 ± 0.6 kg) were anesthetized and catheterized with an apheresis catheter in the femoral vein. During the platelet apheresis process, blood was withdrawn from the pig to separate platelets, and the remaining red blood cells and plasma returned back to the pigs, using the Haemonetics MCS+9000 system. A total of 12 cycles of blood withdrawn and return were performed during the entire apheresis procedure to reduce platelet counts to a target of 50% of baseline. During the process, hemodynamics was recorded in each cycle. Blood samples were collected before and after apheresis to assess changes in oxygen metabolism and coagulation by prothrombin time, activated partial thromboplastin time (STA-R Evolution Stago), and using Rotem thrombelastometry, and platelet aggregation using a Chrono-Log 700 aggregometer. During each cycle of the apheresis, mean arterial pressure (MAP) was decreased and heart rate was increased by blood withdrawal, but both recovered after blood return. On the completion of the apheresis, platelet count decreased from baseline 345 ± 15 109/L to 141 ± 14 109/L and fibrinogen levels were reduced from 124 ± 5 to 99 ± 4 mg/dL (both p < 0.05). Although oxygen delivery remained unchanged, oxygen consumption was decreased from 4.0 ± 0.2 to 3.2 ± 0.0 mL O2/kg/min (p < 0.05). Rotem alpha (clotting speed) decreased from 79 ± 0 to 69 ± 1° and maximum clot firmness (MCF or clot strength) decreased from 71 ± 1 to 57 ± 1 mm (both p < 0.05). No changes were observed in prothrombin time or activated partial thromboplastin time. Platelet aggregation induced by arachidonic acid or collagen was decreased to 28 ± 6% or 71 ± 3% of baseline values (p < 0.05), respectively. Platelet apheresis caused significant fluctuations in hemodynamics, reduced oxygen consumption, in addition to the compromised platelet aggregation and clotting function expected. The observations warrant consideration in humans undergoing apheresis over extended periods.

Application of oxygen-sensing technology to measure seed quality of Ginkgo biloba

Germination tests are currently the most widely used method to evaluate seed quality of Ginkgo biloba L., but they are time-consuming and labor intensive. Oxygen-sensing technology, based on the principle of fluorescence quenching to detect oxygen and assess seed quality was used to rapidly evaluate seed quality of two varieties (Shandong Tancheng 202 and Zhejiang Dafoshou) of G. biloba from five mother plants. Fifteen samples of three vigor levels were produced by accelerated aging treatments. This process was applied in duplicate. A portable oxygen-sensing detector was employed to measure oxygen content during seed germination in a closed system at 25 °C each day until day 14. Four oxygen metabolism indices were calculated: oxygen consumption index, oxygen consumption rate, critical oxygen concentration, and theoretical germination time (TGT). Additionally, we tested laboratory germination and field emergence. The results of a one-way analysis of variance and correlation analysis showed that TGT was the candidate index to evaluate seed quality of G. biloba. Therefore, the TGT value was used to validate the reliability of oxygen-sensing evaluation for Zhejiang Dafoshou seeds kept under four storage conditions. The trend in the change in oxygen metabolism agreed completely agreement with that of seed germination under all storage conditions. The oxygen-sensing test reliably and rapidly assessed seed quality of G. biloba. The germination rate of Zhejiang Dafoshou was accurately predicted by TGT.

Hemodynamic and metabolic effects of a new pediatric dobutamine formulation in hypoxic newborn pigs.

The aim of our study was to measure drug-related changes in hemodynamics and oxygen metabolism in response to different doses of an age-appropriate dobutamine formulation in hypoxic pigs. A secondary aim was to validate superior vena cava flow (SVCF) as a marker of cardiac index (CI) for subsequent clinical trials of this formulation in humans. Newborn pigs (n = 18) were exposed to 2-h hypoxia (10-15% oxygen) followed by reoxygenation (21-30% oxygen 4 h). After 1-h reoxygenation, pigs were randomized to: control group (no treatment), dobutamine infusion at a rate of 10-15 or 15-20 µg/kg/min. Dobutamine groups received two dobutamine doses during 30 min with a 60 min washout period between doses. Cardiovascular profile and oxygen metabolism were monitored. In four animals, an ultrasonic perivascular flow probe was placed around superior vena cava to measure SVCF. Hypoxia significantly decreased CI, systemic vascular resistance and mean arterial blood pressure (MABP). Dobutamine doses significantly increased heart-rate, CI, and oxygen-delivery without changes in stroke-volume and MABP. Only 10-15 µg/kg/min increased oxygen consumption and peripheral tissue oxygenation measured by Near-infrared spectroscopy. A positive correlation was observed between SVCF and CI. The new pediatric dobutamine formulation improved hemodynamic status, with dose-specific differences in metabolic response. SVCF may be a useful surrogate for CI in subsequent clinical trials.

Normative values of retinal vessel oximetry in healthy children against adults

PurposeRetinal oximetry (RO) has been established as a non‐invasive method to analyze oxygen saturation in retinal vessels. The aim of our study was to compare metabolic (oxygen saturation) and anatomical (retinal vessel diameter) RO parameters of healthy children against adults.MethodsA total of 157 eyes of 79 healthy subjects were examined: 20 eyes of children (7–18 year) were compared to adults of different age groups [20–29 year (n = 16); 30–39 year (n = 46); 40–49 year (n = 38); 50–59 year (n = 25), 60–87 year (n = 12)]. RO was performed with the oxygen saturation measurement tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). The oxygen saturation in all four major peripapillary retinal arterioles (A‐SO2) and venules (V‐SO2) were measured and their difference (A‐V SO2) was calculated. In addition, we evaluated the corresponding diameter in retinal arterioles (D‐A) and venules (D‐V). For statistical evaluation non‐parametric tests (Friedman test for multiple comparisons, paired Wilcoxon rank sum test for pairwise comparisons) were performed.ResultsChildren showed statistically significant lower arterial oxygen saturation values (A‐SO2) compared to all adult subgroups (Friedman test, p = 0.0005). Although not statistically significant, the values of V‐SO2 (p = 0.06) and A‐V SO2 (p = 0.30) showed a trend to be lower in children. The D‐A (p = 0.49) and D‐V (p = 0.82) values were not significantly different between groups.ConclusionsThese data indicate that the retinal oxygen metabolism changes throughout lifetime. Therefore, normative data for different age groups are mandatory.

T2-Imaging to Assess Cerebral Oxygen Extraction Fraction in Carotid Occlusive Disease: Influence of Cerebral Autoregulation and Cerebral Blood Volume.

PurposeQuantitative T2'-mapping detects regional changes of the relation of oxygenated and deoxygenated hemoglobin (Hb) by using their different magnetic properties in gradient echo imaging and might therefore be a surrogate marker of increased oxygen extraction fraction (OEF) in cerebral hypoperfusion. Since elevations of cerebral blood volume (CBV) with consecutive accumulation of Hb might also increase the fraction of deoxygenated Hb and, through this, decrease the T2’-values in these patients we evaluated the relationship between T2’-values and CBV in patients with unilateral high-grade large-artery stenosis.Materials and MethodsData from 16 patients (13 male, 3 female; mean age 53 years) with unilateral symptomatic or asymptomatic high-grade internal carotid artery (ICA) or middle cerebral artery (MCA) stenosis/occlusion were analyzed. MRI included perfusion-weighted imaging and high-resolution T2’-mapping. Representative relative (r)CBV-values were analyzed in areas of decreased T2’ with different degrees of perfusion delay and compared to corresponding contralateral areas.ResultsNo significant elevations in cerebral rCBV were detected within areas with significantly decreased T2’-values. In contrast, rCBV was significantly decreased (p<0.05) in regions with severe perfusion delay and decreased T2’. Furthermore, no significant correlation between T2’- and rCBV-values was found.ConclusionsrCBV is not significantly increased in areas of decreased T2’ and in areas of restricted perfusion in patients with unilateral high-grade stenosis. Therefore, T2’ should only be influenced by changes of oxygen metabolism, regarding our patient collective especially by an increase of the OEF. T2’-mapping is suitable to detect altered oxygen consumption in chronic cerebrovascular disease.

Noninvasive assessment of hemodynamic and brain metabolism parameters following closed head injury in a mouse model by comparative diffuse optical reflectance approaches.

Optical techniques have gained substantial interest over the past four decades for biomedical imaging due to their unique advantages, which may suggest their use as alternatives to conventional methodologies. Several optical techniques have been successfully adapted to clinical practice and biomedical research to monitor tissue structure and function in both humans and animal models. This paper reviews the analysis of the optical properties of brain tissue in the wavelength range between 500 and 1000nm by three different diffuse optical reflectance methods: spatially modulated illumination, orthogonal diffuse light spectroscopy, and dual-wavelength laser speckle imaging, to monitor changes in brain tissue morphology, chromophore content, and metabolism following head injury. After induction of closed head injury upon anesthetized mice by weight-drop method, significant changes in hemoglobin oxygen saturation, blood flow, and metabolism were readily detectible by all three optical setups, up to 1h post-trauma. Furthermore, the experimental results clearly demonstrate the feasibility and reliability of the three methodologies, and the differences between the system performances and capabilities are also discussed. The long-term goal of this line of study is to combine these optical systems to study brain pathophysiology in high spatiotemporal resolution using additional models of brain trauma. Such combined use of complementary algorithms should fill the gaps in each system's capabilities, toward the development of a noninvasive, quantitative tool to expand our knowledge of the principles underlying brain function following trauma, and to monitor the efficacy of therapeutic interventions in the clinic.

Event-related changes of the prefrontal cortex oxygen delivery and metabolism during driving measured by hyperspectral fNIRS.

Recent technological advancements in optical spectroscopy allow for the construction of hyperspectral (broadband) portable tissue oximeters. In a series of our recent papers we have shown that hyperspectral NIRS (hNIRS) has similar or better capabilities in the absolute tissue oximetry as frequency-domain NIRS, and that hNIRS is also very efficient in measuring temporal changes in tissue hemoglobin concentration and oxygenation. In this paper, we extend the application of hNIRS to the measurement of event-related hemodynamic and metabolic functional cerebral responses during simulated driving. In order to check if hNIRS can detect event-related changes in the brain, we measured the concentration changes of oxygenated (HbO2) and deoxygenated (HHb) hemoglobin and of the oxidized state of cytochrome c oxidase, on the right and left prefrontal cortices (PFC) simultaneously during simulated driving on sixteen healthy right-handed participants (aged between 22-32). We used our in-house hNIRS system based on a portable spectrometer with cooled CCD detector and a driving simulator with a fully functional steering wheel and foot pedals. Each participant performed different driving tasks and participants were distracted during some driving conditions by asking general knowledge true/false questions. Our findings suggest that more complex driving tasks (non-distracted) deactivate PFC while distractions during driving significantly activate PFC, which is in agreement with previous fMRI results. Also, we found the changes in the redox state of the cytochrome C oxidase to be very consistent with those in the concentrations of HbO2 and HHb. Overall our findings suggest that in addition to the suitability of absolute tissue oximetry, hyperspectral NIRS may also offer advantages in functional brain imaging. In particular, it can be used to measure the metabolic functional brain activity during actual driving.

A novel Bayesian approach to accounting for uncertainty in fMRI-derived estimates of cerebral oxygen metabolism fluctuations

Calibrated blood oxygenation level dependent (BOLD) imaging is a multimodal functional MRI technique designed to estimate changes in cerebral oxygen metabolism from measured changes in cerebral blood flow and the BOLD signal. This technique addresses fundamental ambiguities associated with quantitative BOLD signal analysis; however, its dependence on biophysical modeling creates uncertainty in the resulting oxygen metabolism estimates. In this work, we developed a Bayesian approach to estimating the oxygen metabolism response to a neural stimulus and used it to examine the uncertainty that arises in calibrated BOLD estimation due to the presence of unmeasured model parameters. We applied our approach to estimate the CMRO2 response to a visual task using the traditional hypercapnia calibration experiment as well as to estimate the metabolic response to both a visual task and hypercapnia using the measurement of baseline apparent R2′ as a calibration technique. Further, in order to examine the effects of cerebral spinal fluid (CSF) signal contamination on the measurement of apparent R2′, we examined the effects of measuring this parameter with and without CSF-nulling. We found that the two calibration techniques provided consistent estimates of the metabolic response on average, with a median R2′-based estimate of the metabolic response to CO2 of 1.4%, and R2′- and hypercapnia-calibrated estimates of the visual response of 27% and 24%, respectively. However, these estimates were sensitive to different sources of estimation uncertainty. The R2′-calibrated estimate was highly sensitive to CSF contamination and to uncertainty in unmeasured model parameters describing flow-volume coupling, capillary bed characteristics, and the iso-susceptibility saturation of blood. The hypercapnia-calibrated estimate was relatively insensitive to these parameters but highly sensitive to the assumed metabolic response to CO2.

Hyperoxia and Functional MRI.

Oxygen plays a fundamental role in functional magnetic resonance imaging (FMRI). Blood oxygenation level-dependent (BOLD) imaging is the foundation stone of all FMRI and is still the essential workhorse of the vast majority of FMRI procedures. Hemoglobin may provide the magnetic properties that allow the technique to work, but it is oxygen that allows the contrast to effectively be switched on or off, and it is oxygen that we are interested in tracking in order to observe the oxygen metabolism changes. In general the changes in venous oxygen saturation are observed in order to infer changes in the correlated mechanisms, which can include changes in cerebral blood flow, metabolism, and the fraction of inspired oxygen. By independently manipulating the fraction of inspired oxygen it is possible to alter the amount of dissolved oxygen in the plasma, the venous saturation, or even the blood flow. The effects that these changes have on the observed MRI signal can be either a help or a hindrance depending on how well the changes induced are understood. The administration of supplemental inspired oxygen is in a unique position to provide a flexible, noninvasive, inexpensive, patient-friendly addition to the MRI toolkit to enable investigations to look beyond statistics and regions of interest, and actually produce calibrated, targeted measurements of blood flow, metabolism or pathology.