Measurement Of Oxygen Partial Pressure Research Articles

Hand-held electron spin resonance scanner for subcutaneous oximetry using OxyChip.

Electron spin resonance (ESR) is used to measure oxygen partial pressure (pO2) in biological media with many clinical applications. Traditional clinical ESR involves large magnets that encompass the subject of measurement. However, certain applications might benefit from a scanner operating within local static magnetic fields. Our group recently developed such a compact scanner for transcutaneous (surface) pO2 measurements of skin tissue. Here we extend this capability to subsurface (subcutaneous) pO2 measurements and verify it using an artificial tissue emulating (ATE) phantom. We introduce a new scanner, tailored for subcutaneous measurements up to 2 mm beneath the skin's surface. This scanner captures pulsed ESR signals from embedded approximate 1-mm oxygen-sensing solid paramagnetic implant, OxyChip. The scanner features a static magnetic field source, producing a uniform region outside its surface, and a compact microwave resonator, for exciting and receiving ESR signals. ESR readings derived from an OxyChip, positioned approximately 1.5 mm from the scanner's surface, embedded in ATE phantom, exhibited a linear relation of 1/T2 versus pO2 for pO2 levels at 0, 7.6, 30, and 160 mmHg, with relative reading accuracy of about 10%. The compact ESR scanner can report pO2 data in ATE phantom from an external position relative to the scanner. Implementing this scanner in preclinical and clinical applications for subcutaneous pO2 measurements is a feasible next phase for this development. This innovative design also has the potential to operate in conjunction with artificial skin graft for wound healing, combining therapeutic and pO2 diagnostic features.

Determination of Krogh Coefficient for Oxygen Consumption Measurement from Thin Slices of Rodent Cortical Tissue Using a Fick's Law Model of Diffusion.

To investigate the impact of experimental interventions on living biological tissue, ex vivo rodent brain slices are often used as a more controllable alternative to a live animal model. However, for meaningful results, the biological sample must be known to be healthy and viable. One of the gold-standard approaches to identifying tissue viability status is to measure the rate of tissue oxygen consumption under specific controlled conditions. Here, we work with thin (400 μm) slices of mouse cortical brain tissue which are sustained by a steady flow of oxygenated artificial cerebralspinal fluid (aCSF) at room temperature. To quantify tissue oxygen consumption (Q), we measure oxygen partial pressure (pO2) as a function of probe depth. The curvature of the obtained parabolic (or parabola-like) pO2 profiles can be used to extract Q, providing one knows the Krogh coefficient Kt, for the tissue. The oxygen trends are well described by a Fick's law diffusion-consumption model developed by Ivanova and Simeonov, and expressed in terms of ratio (Q/K), being the rate of oxygen consumption in tissue divided by the Krogh coefficient (oxygen diffusivity × oxygen solubility) for tissue. If the fluid immediately adjacent to the tissue can be assumed to be stationary (i.e., nonflowing), one may invoke conservation of oxygen flux K·(∂P/∂x) across the interface to deduce (Kt/Kf), the ratio of Krogh coefficients for tissue and fluid. Using published interpolation formulas for the effect of salt content and temperature on oxygen diffusivity and solubility for pure water, we estimate Kf, the Krogh coefficient for aCSF, and hence deduce the Kt coefficient for tissue. We distinguish experimental uncertainty from natural biological variability by using pairs of repeated profiles at the same tissue location. We report a dimensionless Krogh ratio (Kt/Kf)=0.562±0.088 (mean ± SD), corresponding to a Krogh coefficient Kt=(1.29±0.21)×10-14 mol/(m·s·Pa) for mouse cortical tissue at room temperature, but acknowledge the experimental limitation of being unable to verify that the fluid boundary layer is truly stationary. We compare our results with those reported in the literature, and comment on the challenges and ambiguities caused by the extensive use of 'biologically convenient' non-SI units for tissue Krogh coefficient.

Quantitative analysis of oxygen partial pressure measurements based on photoacoustic pump-probe imaging

Pump-probe-based photoacoustic imaging is an innovative technique for high-specificity molecular imaging in deep tissues. Compared with conventional photoacoustic imaging, this method effectively eliminates the interference from blood signal and other background signal, enabling the detection of subtle target molecules. Additionally, the manipulating of the time delay between the pump laser and probe laser can facilitate non-invasive mapping of oxygen partial pressure distribution within tissues. To quantify the photoacoustic pump-probe imaging, we use methylene blue as the molecular probe to monitor changes in oxygen partial pressure within a hemoglobin solution. Utilizing a Gaussian noise model, we investigate the relationship between the stability of the triplet-state difference signal and the average number, and also evaluate the error associated with measuring oxygen partial pressure. The results demonstrate that the detection accuracy of the system is better than 33 mmHg (1 mmHg = 133 Pa) in the oxygen partial pressure range of about 300 to 550 mmHg after 200 times of averaging. This research will play a significant role in guiding the further advancement and application of pump-probe-based photoacoustic imaging technology.

Monitoring of cerebral perfusion via oxygen partial pressure (ptiO2) measurement and near-field infrared spectroscopy (NIRS) in aneurysmatic subarachnoid haemorrhage

Monitoring of cerebral perfusion via oxygen partial pressure (ptiO2) measurement and near-field infrared spectroscopy (NIRS) in aneurysmatic subarachnoid haemorrhage

Europium and erbium co-doped yttria-stabilized zirconia as a potential dual-sensor for simultaneous oxygen partial pressure and temperature measurements

In this study, the phosphorescence properties of Eu3+ and Er3+ co-doped yttria stabilized zirconia (YSZ: Eu3+, Er3+) as a function of oxygen partial pressure and temperature are investigated to explore the possibility of using this phosphor for pressure and temperature measurements at elevated temperature (up to 600 °C). The YSZ: Eu3+, Er3+ phosphors have a fixed Eu3+ concentration (1 mol%) and a varied Er3+ concentration (0.5–5 mol%). The phosphorescence intensity and lifetime of Eu3+ bands are sensitive to both oxygen partial pressure and temperature when temperature exceeds 400 °C. This oxygen/pressure sensitivity is related to the oxygen vacancy-induced non-radiative decay through charge transfer state (CTS), and is inversely correlated with Er3+ concentration. In contrast, the phosphorescence intensity and lifetime of Er3+ bands are temperature-sensitive but oxygen-insensitive, which is related to the dominant oxygen-independent 4S3/2 → 2H11/2 transition. Accordingly, two measurement strategies are proposed including an intensity ratio method and a lifetime method. The intensity ratio of the oxygen-sensitive Eu3+ bands and the oxygen-insensitive Er3+ reference bands is capable of 2D pressure measurement using a dual-camera system. But temperature-induced errors exist due to the temperature-sensitivity of intensity ratio. Simultaneous pressure and temperature measurements (point by point) can be achieved utilizing two PMTs that record the lifetimes of Eu3+ and Er3+, respectively. This method can resolve the issue of temperature sensitivity of Eu3+ and accurately correct the temperature-induced errors. The YSZ: Eu, Er phosphors show great potential for applications in high-temperature environment where the existing organic PSPs and TSPs cannot survive.

Phosphorescent Microneedle Array for the Measurement of Oxygen Partial Pressure in Tissue.

The knowledge of the exact oxygen partial pressure in tissue is crucial for patient care and in the treatment of ischemic medical conditions. However, current methods to assess oxygen partial pressure in tissue suffer from a variety of disadvantages, including complex equipment and procedures that necessitate trained personnel. Additionally, the barrier function of the stratum corneum reduces oxygen exchange and can consequently hamper surface measurements of rapidly changing oxygen partial pressure in tissue. To overcome these challenges, a novel, easy-to-use technique to monitor the oxygen partial pressure in tissue using microneedle arrays (MNAs) has been developed. The MNAs can be made from poly(ethyl methacrylate) and poly(propyl methacrylate) and overcome the skin's barrier function to measure oxygen in the capillary bed and interstitial fluid of the skin. The MNAs' tips are embedded with an oxygen-sensitive phosphorescent metalloporphyrin, where the oxygen partial pressure inversely correlates to changes in both emission intensity and phosphorescence lifetime of the in-house developed red emitting Pt-core porphyrin. It was demonstrated that the oxygen-sensing MNAs are sufficiently robust to puncture human skin via rupture of the stratum corneum, and that the MNAs can detect changes in oxygen partial pressure in skin within the physiologically relevant range (0-160 mmHg). Additionally, the MNAs can be combined with a wearable wireless optical readout system, making these oxygen-sensing MNAs a novel wearable and portable method for user-friendly monitoring of oxygen partial pressure in skin.

Oxygen Monitoring in Model Solutions and In Vivo in Mice During Proton Irradiation at Conventional and FLASH Dose Rates.

FLASH is a high-dose-rate form of radiation therapy that has the reported ability, compared with conventional dose rates, to spare normal tissues while being equipotent in tumor control, thereby increasing the therapeutic ratio. The mechanism underlying this normal tissue sparing effect is currently unknown, however one possibility is radiochemical oxygen depletion (ROD) during dose delivery in tissue at FLASH dose rates. In order to investigate this possibility, we used the phosphorescence quenching method to measure oxygen partial pressure before, during and after proton radiation delivery in model solutions and in normal muscle and sarcoma tumors in mice, at both conventional (Conv) (∼0.5 Gy/s) and FLASH (∼100 Gy/s) dose rates. Radiation dosimetry was determined by Advanced Markus Chamber and EBT-XL film. For solutions contained in sealed glass vials, phosphorescent probe Oxyphor PtG4 (1 µM) was dissolved in a buffer (10 mM HEPES) containing glycerol (1 M), glucose (5 mM) and glutathione (5 mM), designed to mimic the reducing and free radical-scavenging nature of the intracellular environment. In vivo oxygen measurements were performed 24 h after injection of PtG4 into the interstitial space of either normal thigh muscle or subcutaneous sarcoma tumors in mice. The "g-value" for ROD is reported in mmHg/Gy, which represents a slight modification of the more standard chemical definition (µM/Gy). In solutions, proton irradiation at conventional dose rates resulted in a g-value for ROD of up to 0.55 mmHg/Gy, consistent with earlier studies using X or gamma rays. At FLASH dose rates, the g-value for ROD was ∼25% lower, 0.37 mmHg/Gy. pO2 levels were stable after each dose delivery. For normal muscle in vivo, oxygen depletion during irradiation was counterbalanced by resupply from the vasculature. This process was fast enough to maintain tissue pO2 virtually unchanged at Conv dose rates. However, during FLASH irradiation there was a stepwise decrease in pO2 (g-value ∼0.28 mmHg/Gy), followed by a rebound to the initial level after ∼8 s. The g-values were smaller and recovery times longer in tumor tissue when compared to muscle and may be related to the lower initial endogenous pO2 levels in the former. Considering that the FLASH effect is seen in vivo even at doses as low as 10 Gy, it is difficult to reconcile the amount of protection seen by oxygen depletion alone. However, the phosphorescence probe in our experiments was confined to the extracellular space, and it remains possible that intracellular oxygen depletion was greater than observed herein. In cell-mimicking solutions the oxygen depletion g-vales were indeed significantly higher than observed in vivo.

Partial Pressure of Oxygen in Stunted and Normal Growth Children and Risk Factors for Stunting by Altitude

Background Risk factors for stunting are not only during a child’s growth period, but also during maternal period. Pregnant mothers at high altitude could influence stunted growth to the child due to low oxygen partial pressure. Aim Observing and comparing risk factors for stunting by altitude and other contributing factors. Methods This was a cross-sectional study conducted to patients <5 years old in Ulu Pungkut highland (700 meters above sea level) and Desa Singkuang lowland (4 – 6 meters above sea level) from March 2019. Anthropometric and oxygen partial pressure measurements were done to 38 children in the highland and 38 children in the lowland with stunted and normal growth. Results PaCO2, total CO2 and HCO3 values were significantly different among the research subjects residing in the lowland and highland (p<0.0001). There were no significant differences in oxygen partial pressure between children with stunted and normal growth. Conclusion Subjects in highland and lowland had significant differences in PaCO2, total CO2 and HCO3 between different altitudes in this study. However, oxygen partial pressure was not significantly different between stunted and normal growth children.

Study of oxygen-ion conductivity and luminescence in the ZrO2 – Nd2O3 system: Impact of local heterogeneity

Stabilized fluorites and pyrochlores with different types of substitution in the (Nd2O3 − ZrO2 system (NdZrO)) have been studied by Raman spectroscopy, X-ray diffraction, and impedance spectroscopy methods. Ionic and proton conductivity maps for 9 compositions in the NdZrO system are presented. Oxygen partial pressure measurements show a typical ionic conductor behavior, with a significantly increase of conductivity for (Nd2−xZrx)Zr2O7+x/2 (x = 1.27) fluorite and (Nd2−xZrx)Zr2O7+x/2 (x = 0.4, 0.2) pyrochlores. For the same compositions the strong luminescence was observed. Strong luminescence and high oxygen-ion conductivity of these solid solutions can be associated with the presence of phases with the different degree of structural disorder (tetragonal phase, fluorite) in local nanodomains in fluorite or pyrochlore matrix in the ZrO2 − Nd2Zr2O7 region. Really, Raman spectra of (Nd2−xZrx)Zr2O7+x/2 (x = 0.5 − 0.2) solid solutions demonstrated the fluorite + pyrochlore structural type in the short-range order. Fluorite nanodomains in pyrochlore matrix (ZrO2 – Nd2Zr2O7 region) resulting from an order–disorder transition can only be detected at a radiation wavelength comparable to the fluorite nanodomain size. Thus, using Raman spectroscopy the broad isomorphism range in the ZrO2 – Nd2Zr2O7 system has been shown to be nonuniform.

Application of Intelligent Monitoring of Percutaneous Partial Oxygen Pressure in Evaluating the Evolution of Scar Hyperplasia.

The study aimed to investigate the dynamic changes of percutaneous partial oxygen pressure during the development and evolution of a hypertrophic scar. Twenty cases of hypertrophic scar patients at different stages were selected. A percutaneous oxygen monitor was used to measure oxygen partial pressure in the scar and normal skin tissue at 14, 30, 60, and 90 days after surgery. The changes of oxygen partial pressure, tissue structure, HIF-1α, and VEGF expression in the scar tissue were observed, and the correlation was analyzed. In the scar maturation process, with the prolongation of time, the partial oxygen pressure in the tissue increased gradually. The expression intensity of HIF-1α and VEGF decreased gradually, HIF-1α was positively correlated with VEGF (r = 0.98, P < 0.01), there was a negative correlation between oxygen partial pressure and HIF-1 α expression (r = −0.92, P < 0.01), and it was negatively correlated with VEGF (r = −0.88, P < 0.01). TcPO2 measurement can be used to assess scar maturity; HIF-1 α and VEGF may play an essential role in regulating partial oxygen pressure in the scar tissue.

Effect of electrode temperature on measurements of transcutaneous carbon dioxide partial pressure and oxygen partial pressure in very low birth weight infants.

To evaluate the accuracy and safety of measurements of transcutaneous carbon dioxide partial pressure (TcPCO2) and transcutaneous oxygen partial pressure (TcPO2) at electrode temperatures lower than the value used in clinical practice in very low birth weight infants. A total of 45 very low birth weight infants were enrolled. TcPCO2 and TcPO2 measurements were performed in these infants. Two transcutaneous monitors were placed simultaneously for each subject. One electrode was set and maintained at 42℃ used in clinical practice for neonates (control group), and the other was successively set at 38℃, 39℃, 40°C, and 41℃ (experimental group). The paired t-test was used to compare the measurement results between the groups. A Pearson correlation analysis was used to analyze the correlation between the measurement results of the experimental group and control group, and between the measurement results of experimental group and arterial blood gas parameters. There was no significant difference in TcPCO2 between each experimental subgroup (38-41℃) and the control group. TcPCO2 in each experimental subgroup (38-41℃) was strongly positively correlated with TcPCO2 in the control group (r>0.9, P<0.05) and arterial carbon dioxide partial pressure (r>0.8, P<0.05). There were significant differences in TcPO2 between each experimental subgroup (38-41℃) and the control group (P<0.05), but TcPO2 in each experimental subgroup (38-41℃) was positively correlated with TcPO2 in the control group (r=0.493-0.574, P<0.05) and arterial oxygen partial pressure (r=0.324-0.399, P<0.05). No skin injury occurred during transcutaneous measurements at all electrode temperatures. Lower electrode temperatures (38-41℃) can accurately measure blood carbon dioxide partial pressure in very low birth weight infants, and thus can be used to replace the electrode temperature of 42°C. Transcutaneous measurements at the lower electrode temperatures may be helpful for understanding the changing trend of blood oxygen partial pressure.

This Month in Anesthesiology

This Month in Anesthesiology

Extreme hypoxia and highlactate concentrations in early chicken embryos show that cutaneous oxygen uptake is limited by diffusion and metabolism is partially anaerobic.

Respiratory gas exchange in avian embryos progresses through three stages inside the egg. During the first 3-5days of incubation, the chicken embryo has no specialised respiratory organs and is not reliant on blood circulation. At this stage, it obtains oxygen mainly by diffusion through the eggshell, albumen, amniotic fluid and embryonic tissues. In the second stage, gas exchange relies on diffusion through the shell in the gas phase and convection by blood circulation through the chorioallantoic membrane and body. Day 19 starts the third stage, the transition from chorioallantoic to pulmonary gas exchange, which is complete when the chick hatches on day 20. Metabolism is thought to be aerobic throughout incubation, although the early embryo is covered by fluids (albumen and amniotic fluid) which would greatly resist oxygen diffusion. This study uses fibre-optic sensors to measure oxygen partial pressure (PO2) near, and inside of, the embryo during days 3-5, and relates the data to total body lactate levels. The study shows that fluids surrounding the embryo greatly impede oxygen diffusion, with PO2 becoming severely hypoxic near the embryo, occasionally almost anoxic inside it. Meanwhile, lactate rises to high levels, and the stored lactate can be later oxidised by the embryo when the chorioallantois takes over and metabolism becomes entirely aerobic.

Electrical properties of CaWO4–SiO2 composites

Composite materials (1 − f) CaWO4 – fSiO2 with volume fraction of SiO2f ≤ 1.0 were prepared by the solid state method. The obtained composites have been examined by SEM-EDS, the electrochemical impedance technique, conductivity measurements versus oxygen partial pressure and EMF measurements in order to evaluate ion transport numbers. It was shown that heterogeneous doping of the poor oxygen ion conductor CaWO4 with nano-SiO2 even at low concentration (f < 0.03) leads to an increase in ionic conductivity of the composites by more than an order of magnitude. The enhancement of conductivity in this system was explained by an additional contribution of the interface regions formed between the host and nanoparticles of dispersoid. A general mixing rule was applied for the calculation of electric conductivity of the (1 − f)CaWO4 – fSiO2 composite as a function of SiO2 concentration. Theoretical dependences were analyzed and compared with the experimental results.

Estimation of mercury and zinc concentration in the vapour phase by measuring oxygen partial pressure

Indirect on-line estimation of metal vapours of Hg and Zn using YSZ based electrochemical oxygen sensor is attempted. Change in oxygen partial pressure, in presence and absence of these metals vapours, enables the estimation by using oxygen sensor. Using this method, the Zn metal vapours has been detected down to 13.3 ± 0.7 vppm and for Hg vapour, the lowest detection limit is 68.1 ± 0.7 vppm. The measured vapour pressure is in agreement with the predicted values.

The Influence of Combined Physical Therapy Procedures on Oxygen Partial Pressure in Tissues Surrounding Ulcer in Patients With Venous Leg Ulcers.

Venous ulcers in lower legs remain a profound treatment problem in contemporary medicine. Proper healing requires, among other things, sufficient blood supply and provision of suitable amount of oxygen to the treated tissues. The aim of the study was to assess the influence of combined physical therapy applied in patients with chronic venous leg ulcers on the oxygen partial pressure values. Fifty-four patients (25 females and 29 males), in the age range of 38 to 89 years with chronic venous leg ulcers, underwent a cycle of 15 procedures with the use of Laserobaria-S device. During a procedure, the patient's lower limb was simultaneously exposed to oxygen having the pressure of 1.5 ATA, low-frequency magnetic field, and low-energy light radiation. Before procedures, directly after the first procedure, as well as on completion of the entire therapeutic cycle, the patients underwent oxygen partial pressure measurements in the tissues surrounding the ulceration area, by means of transcutaneous oximetry, with the use of Medicap Précise 8008s device. The combined physical therapy shows a statistically significant increase of oxygen partial pressure values in tissues surrounding the ulceration, from the average of 68.63 ± 17.04 mm Hg before commencing the therapeutic cycle, to the average of 74.20 ± 18.92 mm Hg after the first procedure (P < .001) and to the average value of 83.79 ± 20.74 mm Hg (P < .001) after completion of therapeutic cycle. Combined physical therapy procedures cause a statistically significant increase of oxygen partial pressure values in tissues surrounding the ulceration, assessed using the objective method of transcutaneous oximetry, both in women and men.

Noninvasive Monitoring of Deep Tissue Oxygenation in Buried Flaps by Time-Resolved Near-Infrared Spectroscopy in Pigs.

Flap monitoring in reconstructive surgery is particularly important because flap failure is a dramatic event for the patient and for the medical team. Noninvasive deep tissue oxygenation monitoring is a challenge. The aim of this experimental study was to assess the performance of time-resolved near-infrared spectroscopy compared with continuous-wave near-infrared spectroscopy and with invasive oxygen partial pressure measurement in pigs. Thirty fasciocutaneous flaps based on the superficial epigastric inferior pedicle were harvested and buried under the transcutaneous dorsal muscle (approximately 1 cm thick). An optical probe was placed on the skin above each buried flap. For each pig, two buried flaps were performed, one submitted to arterial occlusion and one to venous occlusion. Oxyhemoglobin and deoxyhemoglobin concentrations were observed for over 40 minutes before clamping, almost 20 minutes during clamping and during a period of release of approximately 20 minutes. Variations in time-resolved near-infrared spectroscopy were compared to the oxygen partial pressure and continuous-wave near-infrared spectroscopy variations. All vascular events were detected by the time-resolved near-infrared spectroscopy. During arterial clamping, oxyhemoglobin decreased rapidly, whereas deoxyhemoglobin increased moderately. The divergence of oxyhemoglobin and deoxyhemoglobin curves indicated arterial occlusion. During venous clamping, deoxyhemoglobin increased, whereas oxyhemoglobin increased briefly then remained stable or decreased moderately. The initial increases in the oxyhemoglobin and deoxyhemoglobin curves indicated venous occlusion. Oxygen partial pressure failed to detect vascular events in three cases. Continuous-wave near-infrared spectroscopy could not clearly identify vascular occlusions. Thus, the authors demonstrated the relevance of time-resolved near-infrared spectroscopy to buried flap monitoring. Time-resolved near-infrared spectroscopy could differentiate between arterial occlusion and venous occlusion.

Single cell-based fluorescence lifetime imaging of intracellular oxygenation and metabolism

Oxidation-reduction chemistry is fundamental to the metabolism of all living organisms, and hence quantifying the principal redox players is important for a comprehensive understanding of cell metabolism in normal and pathological states. In mammalian cells, this is accomplished by measuring oxygen partial pressure (pO2) in parallel with free and enzyme-bound reduced nicotinamide adenine dinucleotide (phosphate) [H] (NAD(P)H) and flavin adenine dinucleotide (FAD, a proxy for NAD+). Previous optical methods for these measurements had accompanying problems of cytotoxicity, slow speed, population averaging, and inability to measure all redox parameters simultaneously. Herein we present a Förster resonance energy transfer (FRET)-based oxygen sensor, Myoglobin-mCherry, compatible with fluorescence lifetime imaging (FLIM)-based measurement of nicotinamide coenzyme state. This offers a contemporaneous reading of metabolic activity through real-time, non-invasive, cell-by-cell intracellular pO2 and coenzyme status monitoring in living cells. Additionally, this method reveals intracellular spatial heterogeneity and cell-to-cell variation in oxygenation and coenzyme states.

Investigation of Gas Transport Properties of PEMFC Catalyst Layers by Using a Microfluidic Device

Gas transport properties of catalyst layers (CLs) used in proton exchange membrane fuel cells (PEMFCs) are one of the important factors which affects cell performance. The gas transport properties are strongly affected by the porous structure of the CLs. In this study, a measurement system of gas diffusion flux through the CLs by using a microfluidic device was developed. Parallel channels were made on a Si chip by microfabrication techniques. Air and nitrogen were supplied to the two parallel channels in the device, respectively. Oxygen was transferred to a nitrogen flow channel through the CL under a rib between the two channels. Oxygen partial pressure in the nitrogen flow channel was measured at the outlet of the channel by using an optical oxygen sensor. The porous structure of the measured CLs was characterized. Effective gas diffusivity and tortuosity factor of the CLs can be calculated based on the measured gas transfer and porous structure properties. Several types of CLs were fabricated and characterized. The thickness and overall porosity of the CLs were evaluated from scanning electron microscopy and weight measurement. Pore size distribution and effective porosity were evaluated by using nitrogen physisorption measurement. Then effective diffusivity of CLs can be calculated by measuring oxygen partial pressure at the inlet and outlet of the flow channel. The CL, which has 1.0 of ionomer to carbon ratio, was evaluated. Oxygen partial pressure at the outlet of the nitrogen flow channel decreases with flow rate as shown in Figure 1. Effective gas diffusivities obtained from each flow rate showed almost constant value. Tortuosity factor was calculated from the effective diffusivity and measured structural properties and indicated around 3. This evaluation method was applied to the CLs containing a different type of carbon materials, which show different porous structure. Adding multi-walled carbon nanotube in the CL(1) instead of carbon black resulted in an increase of effective gas diffusivity, while geometrical porosity was decreased. Acknowledgments A part of this work was financially supported by JSPS KAKENHI Grant Number 16K18028. This study was supported by Osaka University Nanofabrication Platform [F-18-OS-0006] in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. References T. Suzuki, R. Hashizume and M. Hayase, J. Power Sources, 286, 109 (2015). Figure 1

Predictors of Wound Healing Following Revascularization for Chronic Limb-Threatening Ischemia.

After surgical or endovascular revascularization, some ischemic lesions will not heal, while some others will heal at a variable period of time from the intervention, indicating a multifactorial interaction between local and systematic "wound healing-promoting" factors. Our objective was to identify predictors of wound healing following revascularization for chronic limb-threatening ischemia (CLTI). A literature review was performed to identify published research concerning clinical, biochemical, and noninvasive methods as predictors of wound healing time and wound-free period after surgical and endovascular revascularization for CLTI. Our review indicated that potential predictors included local wound factors, wound depth, patient's comorbidities, medications, smoking and alcohol abuse, poor vessel runoff, and direct versus indirect revascularization. Among the clinical biomarkers, platelet-derived growth factor, transforming growth factor β, basic fibroblast growth factor, tumor necrosis factor α, interleukin (IL) 1, and IL-6 have been proposed as potential predictors. Furthermore, the potential of noninvasive microcirculation assessment to predict proper wound healing has been the topic of extensive investigation. Among the novel methods, transcutaneous measurement of oxygen partial pressure, skin perfusion pressure, oxygen-to-see method, indocyanine green fluorescence imaging, and multispectral optoacoustic tomography have shown promising results. The risk factor profile of an ischemic lesion in the lower extremities with a delayed/failed healing response, following a successful revascularization, is not fully clarified. Although many predictors have been assessed so far, further research needs to be done to identify the optimal clinical and biochemical indices and the noninvasive technique assessing the microcirculation that is associated with complete wound healing.