Cerebral Metabolic Rate Of Oxygen Research Articles

Oxygenation differs among white matter hyperintensities, intersected fiber tracts and unaffected white matter.

White matter hyperintensities of presumed vascular origin are frequently observed on magnetic resonance imaging in normal aging. They are typically found in cerebral small vessel disease and suspected culprits in the etiology of complex age- and small vessel disease-related conditions, such as late-onset depression. White matter hyperintensities may interfere with surrounding white matter metabolic demands by disrupting fiber tract integrity. Meanwhile, risk factors for small vessel disease are thought to reduce tissue oxygenation, not only by reducing regional blood supply, but also by impairing capillary function. To address white matter oxygen supply–demand balance, we estimated voxel-wise capillary density as an index of resting white matter metabolism, and combined estimates of blood supply and capillary function to calculate white matter oxygen availability. We conducted a cross-sectional study with structural, perfusion- and diffusion-weighted magnetic resonance imaging in 21 patients with late-onset depression and 21 controls. We outlined white matter hyperintensities and used tractography to identify the tracts they intersect. Perfusion data comprised cerebral blood flow, blood volume, mean transit time and relative transit time heterogeneity—the latter a marker of capillary dysfunction. Based on these, white matter oxygenation was calculated as the steady state cerebral metabolic rate of oxygen under the assumption of normal tissue oxygen tension and vice versa. The number, volume and perfusion characteristics of white matter hyperintensities did not differ significantly between groups. Hemodynamic data showed white matter hyperintensities to have lower blood flow and blood volume, but higher relative transit time heterogeneity, than normal-appearing white matter, resulting in either reduced capillary metabolic rate of oxygen or oxygen tension. Intersected tracts showed significantly lower blood flow, blood volume and capillary metabolic rate of oxygen than normal-appearing white matter. Across groups, lower lesion oxygen tension was associated with higher lesion number and volume. Compared with normal-appearing white matter, tissue oxygenation is significantly reduced in white matter hyperintensities as well as the fiber tracts they intersect, independent of parallel late-onset depression. In white matter hyperintensities, reduced microvascular blood volume and concomitant capillary dysfunction indicate a severe oxygen supply–demand imbalance with hypoxic tissue injury. In intersected fiber tracts, parallel reductions in oxygenation and microvascular blood volume are consistent with adaptations to reduced metabolic demands. We speculate, that aging and vascular risk factors impair white matter hyperintensity perfusion and capillary function to create hypoxic tissue injury, which in turn affect the function and metabolic demands of the white matter tracts they disrupt.

Misery perfusion and amyloid deposition in atherosclerotic major cerebral artery disease.

Although experimental studies have shown that global cerebral hypoperfusion leads to amyloid deposition in the hemisphere with carotid artery occlusion in rodents, the results of such occurrence are controversial in humans. Hence, we aim to determine whether global cerebral hypoperfusion leading to decreased blood flow relative to metabolic demand [increased oxygen extraction fraction (OEF), misery perfusion] is associated with increases in amyloid deposition in the hemisphere with atherosclerotic major cerebral artery disease in patients. We evaluated the distribution of β-amyloid plaques using positron emission tomography and a [18F]-pyridylbenzofuran derivative (18F-FPYBF-2) in 13 patients with unilateral atherosclerotic disease of the internal carotid artery (ICA) or middle cerebral artery (MCA) disease and no cortical infarction. The distribution volume ratio (DVR) of 18F- FPYBF-2 was calculated using dynamic data and Logan graphical analysis with reference tissue and was correlated with the cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), and OEF, obtained from 15O-gas PET. The mean cortical value was calculated as the mean value within the frontal, posterior cingulate, precuneus, parietal, and lateral temporal cortical regions. Significant reductions in CBF and CMRO2 and increases in OEF were found in the hemisphere ipsilateral to the arterial lesion compared with the contralateral hemisphere. There was no significant difference for 18F-FPYBF-2 DVR between hemispheres. The ipsilateral to contralateral ratio of the 18F- FPYBF-2 DVR was increased in 3 patients, while the ipsilateral to contralateral OEF ratio was increased in 4 patients. The incidence of an increased hemispheric DVR ratio was significantly higher in patients with an increased hemispheric OEF ratio (3/4) than in patients without (0/9) (p < 0.02). Although the 18F- FPYBF-2 DVR in the ipsilateral hemisphere was positively correlated with OEF after adjustment for the 18F- FPYBF-2 DVR in the contralateral hemisphere using multiple regression analysis (p < 0.05), the contribution rate of OEF was small (R2 = 5.5%). Only one of the 4 patients with an increased hemispheric OEF ratio showed amyloid positivity based on the DVR value. In atherosclerotic major cerebral artery disease, misery perfusion accompanied only small increases of amyloid deposition at best. Misery perfusion was not associated with amyloid positivity.

Human brain blood flow and metabolism during isocapnic hyperoxia: the role of reactive oxygen species.

It is unknown whether excessive reactive oxygen species (ROS) production drives the isocapnic hyperoxia (IH)-induced decline in human cerebral blood flow (CBF) via reduced nitric oxide (NO) bioavailability and leads to disruption of the blood-brain barrier (BBB) or neural-parenchymal damage. Cerebral metabolic rate for oxygen (CMR ) and transcerebral exchanges of NO end-products, oxidants, antioxidants and neural-parenchymal damage markers were simultaneously quantified under IH with intravenous saline and ascorbic acid infusion. CBF and were reduced during IH, responses that were followed by increased oxidative stress and reduced NO bioavailability when saline was infused. No indication of neural-parenchymal damage or disruption of the BBB was observed during IH. Antioxidant defences were increased during ascorbic acid infusion, while CBF, , oxidant and NO bioavailability markers remained unchanged. ROS play a role in the regulation of CBF and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage. To test the hypothesis that isocapnic hyperoxia (IH) affects cerebral blood flow (CBF) and metabolism through exaggerated reactive oxygen species (ROS) production, reduced nitric oxide (NO) bioavailability, disturbances in the blood-brain barrier (BBB) and neural-parenchymal homeostasis, 10 men (24± 1years) were exposed to a 10min IH trial (100% O2 ) while receiving intravenous saline and ascorbic acid (AA, 3 g) infusion. Internal carotid artery blood flow (ICABF), vertebral artery blood flow (VABF) and total CBF (tCBF, Doppler ultrasound) were determined. Arterial and right internal jugular venous blood was sampled to quantify the cerebral metabolic rate of oxygen (CMR ), transcerebral exchanges (TCE) of NO end-products (plasma nitrite), antioxidants (AA and AA plus dehydroascorbic acid (AA+DA)) and oxidant biomarkers (thiobarbituric acid-reactive substances (TBARS) and 8-isoprostane), and an index of BBB disruption and neuronal-parenchymal damage (neuron-specific enolase; NSE). IH reduced ICABF, tCBF and , while VABF remained unchanged. Arterial 8-isoprostane and nitrite TCE increased, indicating that CBF decline was related to ROS production and reduced NO bioavailability. AA, AA+DA and NSE TCE did not change during IH. AA infusion did not change the resting haemodynamic and metabolic parameters but raised antioxidant defences, as indicated by increased AA/AA+DA concentrations. Negative AA+DA TCE, unchanged nitrite, reductions in arterial and venous 8-isoprostane, and TBARS TCE indicated that AA infusion effectively inhibited ROS production and preserved NO bioavailability. Similarly, AA infusion prevented IH-induced decline in regional and total CBF and re-established . These findings indicate that ROS play a role in CBF regulation and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage.

Roles of cerebral metabolic rate for oxygen in evaluating the prognosis of cerebral function after cardiopulmonary resuscitation

Objective To investigate the roles of cerebral metabolic rate for oxygen (CMRO2) monitoring in the evaluation of cerebral function after cardiopulmonary resuscitation (CPR) through transcranial doppler (TCD) and SjvO2. Methods In this prospective/retrospective analysis, we included 46 cases admitted to the general intensive care unit (GICU) of the Second Affiliated Hospital of Soochow University from January 2012 to December 2014. Upon admission, TCD and SjvO2 were performed, and the patients’ characteristics were recorded. Based on the CPC score upon GICU discharge, the patients were divided into two groups with satisfactory cerebral function and poor cerebral function, respectively. Then the clinical symptoms, cerebral blood flow (CBF), a-vDO2, SjvO2 and CMRO2 were analyzed, followed by investigating their correlation with the prognosis of cerebral function. The measurement data that were normally distributed were presented by mean ± standard deviation. Student’s t test was utilized for the inter-group comparison. Correlation analysis was performed. ROC was plotted, followed by evaluating roles of each index in the specificity and sensitivity of nervous prognosis. Results No statistical differences were noted in the gender, age, initial monitoring indicators, ICU duration and initial GCS between the two groups (P>0.05). The CA-ROSC time and APACHE II score in the satisfactory cerebral function group were significantly shorter than those of the poor cerebral function group (P<0.05). The SjvO2 in the satisfactory cerebral function group was significantly lower than that of the poor function group (67.33±10.30 vs. 76.89±13.08, t=-3.579, P<0.05). The Vs and Vd as revealed by TCD in the satisfactory function group were higher than those of the poor function group, together with the CBF. Significant decrease was noted in the PI and RI in the satisfactory function group compared with that of the poor function group (P<0.05). Besides, the CMRO2 and a-vDO2 in the satisfactory function group showed significant increase compared with those of the poor function group (P<0.05). ROC indicated that CMRO2, CBF, a-vDO2 and SjvO2 could be utilized for the evaluation of cerebral function, among which CMRO2 showed the highest accuracy for the cerebral function prognosis. Conclusions CMRO2, CBF, a-vDO2 and SjvO2 were associated with cerebral function prognosis. CMRO2 was the most appropriate parameter to evaluate the oxygen metabolism in brain tissues, which could evaluate the prognosis of cerebral function. Key words: Cardiac arrest; Resuscitation; Jugular venous oxygen saturation; Transcranial Doppler; Cerebral metabolic rate for oxygen

Application of dexmedetomidine in intracranial arterial stenting and its influence on the serum myocardial enzyme, cTnI and LVEF

Objective To analyze the application of dexmedetomidine in intracranial arterial stenting and its influence on the serum myocardial enzyme, cardiac troponin I(cTnI) and left ventricular ejection fraction(LVEF). Methods From March 2015 to March 2017, 94 cases with intracranial arterial stenting in the People's Hospital of Lishui were divided into control group and observation group by the random number table method, with 47 cases in each group.The control group was treated with conventional anesthesia, the observation group was treated with dexmedetomidine.The enzyme creatine phosphate kinase isoenzyme(CK-MB), creatine phosphate kinase(CK), cTnI, LVEF, inflammatory factor, neural function, brain oxygen metabolism and complications in the two groups were compared. Results After surgery, the CK-MB, CK, cTnI levels of the observation group were lower than those of the control group[(35.27±4.41)U/L, (488.30±61.03)U/L, (3.85±0.49)μg/L vs.(46.40±5.79)U/L, (611.21±76.40)U/L, (4.72±0.59)μg/L], the LVEF of the observation group was higher than that of the control group[(45.60±5.72)% vs.(43.12±5.39)%], the differences were statistically significant(t=10.484, 8.619, 7.777, 2.163, all P<0.05). The interleukin-6(IL-6) and interleukin-8(IL-8), tumor necrosis factor-α(TNF-α), S-100β, specificity enolization enzyme(NSE), cerebral metabolic rate of oxygen(ERO2), arterial blood oxygen saturation(PaO2), carotid venous blood oxygen saturation(SjvO2) of the observation group were better than those of the control group(t=5.794, 6.177, 15.065, 6.964, 5.606, 3.147, 2.116, 2.807, all P<0.05). The incidence rate of complication of the observation group was lower than that of the control group(χ2=17.091, P<0.05). Conclusion Application of dexmedetomidine in intracranial arterial stenting can protect myocardium, inhibit the serum levels of myocardial enzyme, cTnI rise, and is conducive to the recovery of LVEF. Key words: Intracranial arterial diseares; Stents; Myocardial enzymes; Cardiac troponin I; Cardiac output; Dexmedetomidine

Reduced Cerebral Metabolic Rate of Oxygen in Adults with Sickle Cell Disease

Introduction:Cerebral blood flow (CBF) is increased in sickle cell disease (SCD) to compensate for chronic hemolytic anemia. Since the brain is strongly dependent on adequate oxygen levels, severe anemia may result in ischemia and silent cerebral infarctions (SCIs), which are present in the majority of patients with SCD. Besides CBF, the cerebral metabolic rate of oxygen (CMRO2), representing the cerebral oxygen consumption, can be measured using specialized MRI techniques. CMRO2 is dependent on CBF, OEF oxygen extraction fraction (OEF) and the hematocrit in the cerebral circulation. In order to maintain stable CMRO2 the OEF changes to compensate for fluctuations in CBF. Previous studies found either elevated or reduced rather than stable CMRO2 in SCD. To further explore the regulation of cerebral oxygenation in SCD, we measured CMRO2, OEF and CBF using MRI at rest and upon administration of acetazolamide (ACZ), a non-metabolic vasodilator. In addition, we related the CMRO2 to the prevalence and location of SCIs and to laboratory parameters of hemolysis.Methods:Adult SCD patients (HbSS/HbSβ0) without a history of stroke, and healthy age-, sex, and race-matched controls were recruited for this IRB-approved MRI study with ACZ-induced vasodilation and venous blood sampling. MRI images were acquired at 3T (Philips Healthcare, Best, NL). Sequences included 3D FLAIR with 1mm isotropic resolution for lesion evaluation, longitudinal and transverse relaxation times of blood (T1b and T2b) in the cerebral sagittal sinus using a T2 prepared tissue relaxation with inversion recovery sequence (T2-TRIR), and pseudo-continuous arterial spin labeling (ASL) for whole brain CBF measurements. T1b was used to correct ASL-based CBF values. T2b was converted to venous saturation (Yv) using a recently published SCD-specific model, which was calibrated in sickle blood rather than bovine blood. CBF was measured at baseline and 10 min post acetazolamide (ACZ) (16mg/kg intravenous infusion over 3min). Images were co-registered and quantified using the ExploreASL toolbox.CMRO2 was calculated as follows: CMRO2 = CBF * OEF * Ca, where CBF is the whole brain CBF map from ASL, OEF is the arteriovenous oxygen saturation (Y) difference (Ya-Yv/Ya) derived from T2 measurements, and Ca is the oxygen carrying capacity of blood calculated from hematocrit sampled immediately prior to MRI. Blood markers of hemolysis (reticulocyte count and bilirubin) were correlated to MRI hemodynamic markers using bivariate Spearman's rho (ρ). Group comparisons were tested using Student's t-tests. P values <0.05 were considered statistically significant.Results:As expected, CBF was significantly higher in patients with SCD (69 ± 16 mL/100g/min) compared to healthy controls (42 ± 4 mL/100g/min, P <0.001), whereas oxygen carrying capacity (Ca) was significantly lower in patients with SCD vs healthy controls due to lower hematocrit (485 ± 83 vs 794 ± 66 μmol O2/100ml blood, P=0.001). At baseline, mean CMRO2 was lower in patients with SCD compared to healthy controls (88 ± 20 vs 117 ± 18 μmol/100 g/min, P = 0.002), contrary to our hypothesis, indicating a reduced oxygen metabolism in patients with SCD. After acetazolamide, CMRO2 remained the same due to an increase in CBF (P<0.001) and a compensatory reduction in OEF. The reduction in OEF in patients with SCD and healthy controls (20 ± 7 vs 19 ± 6, respectively P= 0.76) indicates that OEF adjusts appropriately according to the increased flow. By mapping CMRO2 and the locations of SCIs, we found that lesions were most prevalent in the regions with the lowest CMRO2 corresponding to the deep white matter and borderzone regions, supporting an ischemic etiology of lesions. High hemolytic rate was associated with higher CMRO2 most likely due to an increased CBF.Conclusion:We observed reduced CMRO2 in patients with SCD compared to healthy controls due to low OEF. A reduced CMRO2 could pose a risk for ischemia, despite high flow rate delivering oxygen, because of low OEF. This is supported by the fact that the silent cerebral infarcts are located in regions with the lowest CMRO2. We postulate that patients with SCD have a reduced capacity to increase the OEF in regions with inadequate CBF resulting in local ischemia and local infarction. The pathogenesis of the reduced OEF remains unclear but could be related to arteriovenous shunting whereby there is insufficient time for oxygen to dissociate. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Comparison of Resting-State Brain Activation Detected by BOLD, Blood Volume and Blood Flow.

Resting-state brain activity has been widely investigated using blood oxygenation level dependent (BOLD) contrast techniques. However, BOLD signal changes reflect a combination of the effects of cerebral blood flow (CBF), cerebral blood volume (CBV), as well as the cerebral metabolic rate of oxygen (CMRO2). In this study, resting-state brain activation was detected and compared using the following techniques: (a) BOLD, using a gradient-echo echo planar imaging (GE-EPI) sequence; (b) CBV-weighted signal, acquired using gradient and spin echo (GRASE) based vascular space occupancy (VASO); and (c) CBF, using pseudo-continuous arterial spin labeling (pCASL). Reliable brain networks were detected using VASO and ASL, including sensorimotor, auditory, primary visual, higher visual, default mode, salience and left/right executive control networks. Differences between the resting-state activation detected with ASL, VASO and BOLD could potentially be due to the different temporal signal-to-noise ratio (tSNR) and the short post-labeling delay (PLD) in ASL, along with differences in the spin-echo readout of VASO. It is also possible that the dynamics of spontaneous fluctuations in BOLD, CBV and CBF could differ due to biological reasons, according to their location within the brain.

Cerebral oxygen metabolism during and after therapeutic hypothermia in neonatal hypoxic–ischemic encephalopathy: a feasibility study using magnetic resonance imaging

Therapeutic hypothermia is the standard-of-care treatment for infants diagnosed with moderate-to-severe hypoxic-ischemic encephalopathy (HIE). MRI for assessing brain injury is usually performed after hypothermia because of logistical challenges in bringing acutely sick infants receiving hypothermia from the neonatal intensive care unit (NICU) to the MRI suite. Perhaps examining and comparing early cerebral oxygen metabolism disturbances to those after rewarming will lead to a better understanding of the mechanisms of brain injury in HIE and the effects of therapeutic hypothermia. The objectives were to assess the feasibility of performing a novel T2-relaxation under spin tagging (TRUST) MRI technique to measure venous oxygen saturation very early in the time course of treatment, 18-24h after the initiation of therapeutic hypothermia, to provide a framework to measure neonatal cerebral oxygen metabolism noninvasively, and to compare parameters between early and post-hypothermia MRIs. Early (18-24h after initiating hypothermia) MRIs were performed during hypothermia treatment in nine infants with HIE (six with moderate and three with severe HIE). Six infants subsequently had an MRI after hypothermia. Mean values of cerebral blood flow, oxygen extraction fraction, and cerebral metabolic rate of oxygen from MRIs during hypothermia were compared between infants with moderate and severe HIE; and in those with moderate HIE, we compared cerebral oxygen metabolism parameters between MRIs performed during and after hypothermia. During the initial hypothermia MRI at 23.5±5.2h after birth, infants with severe HIE had lower oxygen extraction fraction (P=0.04) and cerebral metabolic rate of oxygen (P=0.03) and a trend toward lower cerebral blood flow (P=0.33) compared to infants with moderate HIE. In infants with moderate HIE, cerebral blood flow decreased and oxygen extraction fraction increased between MRIs during and after hypothermia (although not significantly); cerebral metabolic rate of oxygen (P=0.93) was not different. Early MRIs were technically feasible while maintaining hypothermic goal temperatures in infants with HIE. Cerebral oxygen metabolism early during hypothermia is more disturbed in severe HIE. In infants with moderate HIE, cerebral blood flow decreased and oxygen extraction fraction increased between early and post-hypothermia scans. A comparison of cerebral oxygen metabolism parameters between early and post-hypothermia MRIs might improve our understanding of the evolution of HIE and the benefits of hypothermia. This approach could guide the use of adjunctive neuroprotective strategies in affected infants.

Minimal PaO2 threshold after traumatic brain injury and clinical utility of a novel brain oxygenation ratio.

Avoiding decreases in brain tissue oxygenation (PbtO2) after traumatic brain injury (TBI) is important. How best to adjust PbtO2 remains unclear. The authors investigated the association between partial pressure of oxygen (PaO2) and PbtO2 to determine the minimal PaO2 required to maintain PbtO2 above the hypoxic threshold (> 20 mm Hg), accounting for other determinants of PbtO2 and repeated measurements in the same patient. They also explored the clinical utility of a novel concept, the brain oxygenation ratio (BOx ratio = PbtO2/PaO2) to detect overtreatment with the fraction of inspired oxygen (FiO2). A retrospective cohort study at an academic level 1 trauma center included 38 TBI patients who required the insertion of a monitor to measure PbtO2. Various determinants of PbtO2 were collected simultaneously whenever a routine arterial blood gas was drawn. A PbtO2/PaO2 ratio was calculated for each blood gas and plotted over time for each patient. All patients were managed according to a standardized clinical protocol. A mixed effects model was used to account for repeated measurements in the same patient. A total of 1006 data points were collected. The lowest mean PaO2 observed to maintain PbtO2 above the ischemic threshold was 94 mm Hg. Only PaO2 and cerebral perfusion pressure were predictive of PbtO2 in multivariate analysis. The PbtO2/PaO2 ratio was below 0.15 in 41.7% of all measures and normal PbtO2 values present despite an abnormal ratio in 27.1% of measurements. The authors' results suggest that the minimal PaO2 target to ensure adequate cerebral oxygenation during the first few days after TBI should be higher than that suggested in the Brain Trauma Foundation guidelines. The use of a PbtO2/PaO2 ratio (BOx ratio) may be clinically useful and identifies abnormal O2 delivery mechanisms (cerebral blood flow, diffusion, and cerebral metabolic rate of oxygen) despite normal PbtO2.

Non-invasive optical neuromonitoring of the temperature-dependence of cerebral oxygen metabolism during deep hypothermic cardiopulmonary bypass in neonatal swine

Management of deep hypothermic (DH) cardiopulmonary bypass (CPB), a critical neuroprotective strategy, currently relies on non-invasive temperature to guide cerebral metabolic suppression during complex cardiac surgery in neonates. Considerable inter-subject variability in temperature response and residual metabolism may contribute to the persisting risk for postoperative neurological injury. To characterize and mitigate this variability, we assess the sufficiency of conventional nasopharyngeal temperature (NPT) guidance, and in the process, validate combined non-invasive frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS) for direct measurement of cerebral metabolic rate of oxygen (CMRO2). During CPB, n = 8 neonatal swine underwent cooling from normothermia to 18℃, sustained DH perfusion for 40 min, and then rewarming to simulate cardiac surgery. Continuous non-invasive and invasive measurements of intracranial temperature (ICT) and CMRO2 were acquired. Significant hysteresis (p < 0.001) between cooling and rewarming periods in the NPT versus ICT and NPT versus CMRO2 relationships were found. Resolution of this hysteresis in the ICT versus CMRO2 relationship identified a crucial insufficiency of conventional NPT guidance. Non-invasive CMRO2 temperature coefficients with respect to NPT (Q10 = 2.0) and ICT (Q10 = 2.5) are consistent with previous reports and provide further validation of FD-DOS/DCS CMRO2 monitoring during DH CPB to optimize management.

Cerebral blood volume changes during the BOLD post-stimulus undershoot measured with a combined normoxia/hyperoxia method

Cerebral blood flow (CBF) and blood oxygenation level dependent (BOLD) signal measurements make it possible to estimate steady-state changes in the cerebral metabolic rate of oxygen (CMRO2) with a calibrated BOLD method. However, extending this approach to measure the dynamics of CMRO2 requires an additional assumption: that deoxygenated cerebral blood volume (CBVdHb) follows CBF in a predictable way. A test-case for this assumption is the BOLD post-stimulus undershoot, for which one proposed explanation is a strong uncoupling of flow and blood volume with an elevated level of CBVdHb during the post-stimulus period compared to baseline due to slow blood volume recovery (Balloon Model). A challenge in testing this model is that CBVdHb differs from total blood volume, which can be measured with other techniques. In this study, the basic hypothesis of elevated CBVdHb during the undershoot was tested, based on the idea that the BOLD signal change when a subject switches from breathing a normoxic gas to breathing a hyperoxic gas is proportional to the absolute CBVdHb. In 19 subjects (8F), dual-echo BOLD responses were measured in primary visual cortex during a flickering radial checkerboard stimulus in normoxia, and the identical experiment was repeated in hyperoxia (50% O2/balance N2). The BOLD signal differences between normoxia and hyperoxia for the pre-stimulus baseline, stimulus, and post-stimulus periods were compared using an equivalent BOLD signal calculated from measured R2* changes to eliminate signal drifts. Relative to the pre-stimulus baseline, the average BOLD signal change from normoxia to hyperoxia was negative during the undershoot period (p = 0.0251), consistent with a reduction of CBVdHb and contrary to the prediction of the Balloon Model. Based on these results, the BOLD post-stimulus undershoot does not represent a case of strong uncoupling of CBVdHb and CBF, supporting the extension of current calibrated BOLD methods to estimate the dynamics of CMRO2.

Validation of scatter limitation correction to eliminate scatter correction error in oxygen-15 gas-inhalation positron emission tomography images

High levels of radioactivity inside a facemask cause scatter correction (SC) errors that appear as photopenic artifacts on quantitative oxygen-15 (O) gas-inhalation positron emission tomography (PET) images. The present study aimed to validate the ability of scatter limitation correction (SLC) to eliminate SC errors in O gas-inhalation PET images acquired from patients and a phantom. We analyzed the SC errors in phantom images and calculated parametric images of the cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2). Phantoms comprised a cylinder and paper with radioactivity to simulate a facemask during (O)O2 gas inhalation. Parametric images were calculated from O gas-inhalation PET images of ten participants. All PET data were reconstructed using conventional SC as model-based SC and SLC. Images acquired from the phantoms and parametric images were assessed visually and quantitatively in the presence and absence of SC error. SC error was evident in images derived from the paper phantom and at the slice level of the cerebellum in CBF, OEF, and CMRO2 images. The radioactivity concentration in the cylindrical phantom with the paper phantom significantly improved with SLC. The SLC also increased the quantitative indices of CBF, OEF, and CMRO2 by 23.8, 42.2, and 44.4%, respectively. SLC visually eliminated the SC error and increased the quantitative parameters on O gas-inhalation images derived from a phantom and from patients.

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.

Relationship between intelligence quotient (IQ) and cerebral metabolic rate of oxygen in patients with neurobehavioural disability after traumatic brain injury

ABSTRACTObjective: Cerebral metabolism may play a significant role in neurobehavioural disability following traumatic brain injury (TBI). In this study, we examined the relationship between intelligence quotient (IQ) and the cerebral metabolic rate of oxygen (CMRO2) in the lateral prefrontal cortex, which was measured by 15O-labelled gas positron emission tomography (PET), in patients with TBI.Materials and methods: The subjects were 12 patients (eight males and four females) who suffered from neurobehavioural disability following TBI. Their mean age was 33.3 years. The cause of injury was traffic accidents in all patients and the mean period after injury was 44.8 months. These patients underwent 15O-labelled gas PET and tests using either the Wechsler Adult Intelligence Scale-Revised (WAIS-R) or the Wechsler Intelligence Scale for Children-Revised (WISC-R). Pearson’s correlation between CMRO2 and total IQ (TIQ) was calculated.Results: A statistically significant correlation was observed between TIQ and CMRO2 in the right Brodmann areas (BAs) 44 and 45. The lower the WAIS score, the higher the CMRO2 in both areas.Conclusion: Neurological function negatively correlated with the metabolism of oxygen. It was possible that changes in brain networks increased the neuronal activity in the undamaged areas and that the increased activity compensated for the function decline.

Baseline Cerebral Metabolic Rate Is a Critical Determinant of the Cerebral Vasodilating Potency of Volatile Anesthetic Agents.

A Comparison of the Direct Cerebral Vasodilating Potencies of Halothane and Isoflurane in the New Zealand White Rabbit. By Drummond JC, Todd MM, Scheller MS, and Shapiro HM. ANESTHESIOLOGY 1986; 65:462-7. Reprinted with permission.Halothane is commonly viewed as a more potent cerebral vasodilator than isoflurane. It was speculated that the lesser vasodilation caused by isoflurane might be the result of the greater reduction in cerebral metabolic rate (CMR) that it causes, and that the relative vasodilating potencies of halothane and isoflurane would be similar if the two agents were administered in a situation that precluded volatile-agent-induced depression of CMR. To test this hypothesis, cerebral blood flow (CBF) and the cerebral metabolic rate for oxygen (CMRO2) were measured in two groups of rabbits before and after the administration of 0.75 MAC halothane or isoflurane. One group received a background anesthetic of morphine and N2O, which resulted in an initial CMRO2 of 3.21 ± 0.17 (SEM) ml · 100 g · min; second group received a background anesthetic of high-dose pentobarbital, which resulted in an initial CMRO2 of 1.76 ± 0.16 ml · 100 g · min. In rabbits receiving a background of morphine sulfate/N2O, halothane resulted in a significantly greater CBF (65 ± 10 ml · 100 g · min) than did isoflurane (40 ± 5 ml · 100 g · min). Both agents caused a reduction in CMRO2, but CMRO2 was significantly less during isoflurane administration. By contrast, with a background of pentobarbital anesthesia, CBF increased by significant and similar amounts with both halothane and isoflurane. With halothane, CBF increased from 22 ± 2 ml · 100 g · min in the control stage to 39 ± 3, and with isoflurane from 24 ± to 38 ± 2 ml · 100 g · min. CMRO2 was not depressed further by either halothane or isoflurane. These results suggest that the relative effects of halothane and isoflurane on CBF are dependent on the CMR present prior to their administration. When the preexistent CMR is not markedly depressed, isoflurane decreases CMR and causes less cerebral vasodilation than does halothane. When initial CMR is depressed, halothane and isoflurane have similar vasodilating potencies.

Evaluation of the default-mode network by quantitative 15O-PET: comparative study between cerebral blood flow and oxygen consumption

ObjectiveResting-state functional MRI (rs-fMRI) has revealed the existence of a default-mode network (DMN) based on spontaneous oscillations of the blood oxygenation level-dependent (BOLD) signal. The BOLD signal reflects the deoxyhemoglobin concentration, which depends on the relationship between the regional cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen (CMRO2). However, these two factors cannot be separated in BOLD rs-fMRI. In this study, we attempted to estimate the functional correlations in the DMN by means of quantitative 15O-labeled gases and water PET, and to compare the contribution of the CBF and CMRO2 to the DMN.MethodsNine healthy volunteers (5 men and 4 women; mean age, 47.0 ± 1.2 years) were studied by means of 15O-O2, 15O-CO gases and 15O-water PET. Quantitative CBF and CMRO2 images were generated by an autoradiographic method and transformed into MNI standardized brain template. Regions of interest were placed on normalized PET images according to the previous rs-fMRI study. For the functional correlation analysis, the intersubject Pearson’s correlation coefficients (r) were calculated for all pairs in the brain regions and correlation matrices were obtained for CBF and CMRO2, respectively. We defined r > 0.7 as a significant positive correlation and compared the correlation matrices of CBF and CMRO2.ResultsSignificant positive correlations (r > 0.7) were observed in 24 pairs of brain regions for the CBF and 22 pairs of brain regions for the CMRO2. Among them, 12 overlapping networks were observed between CBF and CMRO2. Correlation analysis of CBF led to the detection of more brain networks as compared to that of CMRO2, indicating that the CBF can capture the state of the spontaneous activity with a higher sensitivity.ConclusionsWe estimated the functional correlations in the DMN by means of quantitative PET using 15O-labeled gases and water. The correlation matrix derived from the CBF revealed a larger number of brain networks as compared to that derived from the CMRO2, indicating that contribution to the functional correlation in the DMN is higher in the blood flow more than the oxygen consumption.

An investigation of cerebral oxygen utilization, blood flow and cognition in healthy aging.

BackgroundUnderstanding how vascular and metabolic factors impact on cognitive function is essential to develop efficient therapies to prevent and treat cognitive losses in older age. Cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF) and venous oxygenation (Yv) comprise key physiologic processes that maintain optimum functioning of neural activity. Changes to these parameters across the lifespan may precede neurodegeneration and contribute to age-related cognitive decline. This study examined differences in blood flow and metabolism between 31 healthy younger (<50 years) and 29 healthy older (>50 years) adults; and investigated whether these parameters contribute to cognitive performance.MethodParticipants underwent a cognitive assessment and MRI scan. Grey matter CMRO2 was calculated from measures of CBF (phase contrast MRI), arterial and venous oxygenation (TRUST MRI) to assess group differences in physiological function and the contribution of these parameters to cognition.ResultsPerformance on memory (p<0.001) and attention tasks (p<0.001) and total CBF were reduced (p<0.05), and Yv trended toward a decrease (p = .06) in the older group, while grey matter CBF and CMRO2 did not differ between the age groups. Attention was negatively associated with CBF when adjusted (p<0.05) in the older adults, but not in the younger group. There was no such relationship with memory. Neither cognitive measure was associated with oxygen metabolism or venous oxygenation in either age group.ConclusionFindings indicated an age-related imbalance between oxygen delivery, consumption and demand, evidenced by a decreased supply of oxygen with unchanged metabolism resulting in increased oxygen extraction. CBF predicted attention when the age-effect was controlled, suggesting a task- specific CBF- cognition relationship.

The effect of carotid artery stenting on capillary transit time heterogeneity in patients with carotid artery stenosis.

Carotid revascularisation improves haemodynamic compromise in cerebral circulation as an additional benefit to the primary goal of reducing future thromboembolic risk. We determined the effect of carotid artery stenting on cerebral perfusion and oxygenation using a perfusion-weighted MRI algorithm that is based on assessment of capillary transit-time heterogeneity together with other perfusion and metabolism-related metrics. A consecutive series of 33 patients were evaluated by dynamic susceptibility contrast perfusion-weighted MRI prior to and within 24 h of the endovascular procedure. The level of relative change induced by stenting, and relationship of these changes with respect to baseline stenosis degree were analysed. Stenting led to significant increase in cerebral blood flow (p < 0.001), and decrease in cerebral blood volume (p = 0.001) and mean transit time (p < 0.001); this was accompanied by reduction in oxygen extraction fraction (p < 0.001) and capillary transit-time heterogeneity (p < 0.001), but an overall increase in relative capillary transit-time heterogeneity (RTH: CTH divided by MTT; p = 0.008). No significant change was observed with respect to cerebral metabolic rate of oxygen. The median volume of tissue with MTT > 2s decreased from 24 ml to 12 ml (p = 0.009), with CTH > 2s from 29 ml to 19 ml (p = 0.041), and with RTH < 0.9 from 61 ml to 39 ml (p = 0.037) following stenting. These changes were correlated with the baseline degree of stenosis.Discussion: Stenting improved the moderate stage of haemodynamic compromise at baseline in our cohort. The decreased relative transit-time heterogeneity, which increases following stenting, is probably a reflection of decreased functional capillary density secondary to chronic hypoperfusion induced by the proximal stenosis.Conclusion: Carotid artery stenting, is not only important for prophylaxis of future vascular events, but also is critical for restoration of microvascular function in the cerebral tissue.

Cortical hypoperfusion and reduced cerebral metabolic rate of oxygen in the arcAβ mouse model of Alzheimer’s disease

The effect of cerebral amyloidosis on cerebral hemodynamics was investigated with photoacoustic tomography (PAT) and magnetic resonance imaging (MRI). First, the sensitivity and robustness of PAT for deriving metrics of vascular and tissue oxygenation in the murine brain was assessed in wild-type mice with a hyperoxia-normoxia challenge. Secondly, cerebral oxygenation was assessed in young and aged arcAβ mice and wild-type controls with PAT, while cerebral blood flow (CBF) was determined by perfusion MRI. The investigations revealed that PAT can sensitively and robustly detect physiological changes in vascular and tissue oxygenation. An advanced stage of cerebral amyloidosis in arcAβ mice is accompanied by a decreases in cortical CBF and the cerebral metabolic rate of oxygen (CMRO2), as oxygen extraction fraction (OEF) has been found unaffected. Thus, PAT constitutes a robust non-invasive tool for deriving metrics of tissue oxygenation, extraction and metabolism in the mouse brain under physiological and disease states.

Cerebral Oxygen Metabolism Before and After RBC Transfusion in Infants Following Major Surgical Procedures.

Although infants following major surgery frequently require RBC transfusions, there is still controversy concerning the best definition for requirement of transfusion in the individual patient. The aim of this study was to determine the impact of RBC transfusion on cerebral oxygen metabolism in noncardiac and cardiac postsurgical infants. Prospective observational cohort study. Pediatric critical care unit of a tertiary referral center. Fifty-eight infants (15 after pediatric surgery and 43 after cardiac surgery) with anemia requiring RBC transfusion were included. RBC transfusion. We measured noninvasively regional cerebral oxygen saturation and microperfusion (relative cerebral blood flow) using tissue spectrometry and laser Doppler flowmetry before and after RBC transfusion. Cerebral fractional tissue oxygen extraction and approximated cerebral metabolic rate of oxygen were calculated. Fifty-eight RBC transfusions in 58 patients were monitored (15 after general surgery, 24 after cardiac surgery resulting in acyanotic biventricular physiology and 19 in functionally univentricular hearts including hypoplastic left heart following neonatal palliation). The posttransfusion hemoglobin concentrations increased significantly (9.7 g/dL vs 12.8 g/dL; 9.7 g/dL vs 13.8 g/dL; 13.1 g/dL vs 15.6 g/dL; p < 0.001, respectively). Posttransfusion cerebral oxygen saturation was significantly higher than pretransfusion (61% [51-78] vs 72% [59-89]; p < 0.001; 58% [35-77] vs 71% [57-88]; p < 0.001; 51% [37-61] vs 58% [42-73]; p = 0.007). Cerebral fractional tissue oxygen extraction decreased posttransfusion significantly 0.37 (0.16-0.47) and 0.27 (0.07-039), p = 0.002; 0.40 (0.2-0.62) vs 0.26 (0.11-0.57), p = 0.001; 0.42 (0.23-0.52) vs 0.32 (0.1-0.42), p = 0.017. Cerebral blood flow and approximated cerebral metabolic rate of oxygen showed no significant change during the observation period. The increase in cerebral oxygen saturation and the decrease in cerebral fractional tissue oxygen extraction were most pronounced in patients after cardiac surgery with a pretransfusion cerebral fractional tissue oxygen extraction greater than or equal to 0.4. Following RBC transfusion, cerebral oxygen saturation increases and cerebral fractional tissue oxygen extraction decreases. The data suggest that cerebral oxygenation in postoperative infants with cerebral fractional tissue oxygen extraction greater than or equal to 0.4 may be at risk in instable hemodynamic or respiratory situations.