Capillary Tortuosity Research Articles

Intraretinal Microvascular Abnormalities in Eyes with Advanced Stages of Nonproliferative Diabetic Retinopathy: Comparison Between UWF-FFA, CFP, and OCTA-The RICHARD Study.

This study aimed to evaluate intraretinal microvascular abnormalities (IRMA) in eyes with advanced nonproliferative diabetic retinopathy (NPDR) using multimodal approach in co-located areas focusing on central retina (up to 50°) and to look at possible correlations between IRMA and other structural changes, like ischemia and presence of microaneurysms. The RICHARD study (NCT05112445) included 60 eyes from 60 patients with type2 diabetes with moderate-severe NPDR, diabetic retinopathy severity levels 43, 47, and 53 (DRSS). IRMA were defined as capillary tortuosity covering a minimum circular area of 300µm (calculated to correspond to the Early Treatment Diabetic Retinopathy Study standard photo 8A) and were identified using multimodal imaging with distinct fields of view (FoV): color fundus photography (CFP) using a Topcon TRC-50DX camera (Topcon Medical Systems, Japan), Optos California ultra wide field fundus fluorescein angiography (UWF-FFA) (Optos plc, UK), and swept-source optical coherence tomography angiography (SS-OCTA) (PLEX® Elite 9000, ZEISS, USA). Different areas of the retina were examined: central macula (up to 20°) and posterior pole (between 20° and 50°). Multimodal imaging was used to identify IRMA in co-located areas (FoV < 50°) including UWF-FFA, CFP, and SS-OCTA. In eyes with DRSS levels 47 and 53, IRMA were identified in both areas of the retina, while in eyes with DRSS level 43, IRMA were detected only outside of the central macula (FoV > 20°). Our results show that when evaluating the presence of IRMA (FoV < 50°), UWF-FFA detected 203 IRMA, SS-OCTA detected 133 IRMA, and CFP detected 104 IRMA. Our results also show that the presence of IRMA was positively associated with presence of microaneurysms. Identification of IRMA in eyes with advanced NPDR is better achieved by UWF-FFA than CFP and SS-OCTA. A statistically significant correlation was found between the presence of IRMA and the increase in number of microaneurysms. ClinicalTrials.gov, identifier NCT05112445.

Fiber-type composition and 3D capillary analysis of the human splenius capitis muscle.

Despite the significance of neck muscles in musculoskeletal disorders, their microscopic anatomy remains poorly characterized. This study examined the splenius capitis muscle, focusing on its fiber-type composition, fiber size, and capillary network characteristics. For comparison and validation, the vastus lateralis muscle was also analyzed. Muscle samples from 13 young male subjects (mean age ± SD: 35.7 ± 8.6 years) were collected within 24-h post-mortem during autopsy. Myosin heavy chain (MyHC) isoform expression was characterized immunohistochemically in 10 μm sections, while the capillary network architecture was assessed in 100 μm sections. Immunofluorescence staining, confocal microscopy, and 3D image analysis were employed to quantify capillary tortuosity, anisotropy, branch density (Br dens), and the length of capillaries per muscle volume (LV), per muscle fiber length (LL), per fiber surface area (LS), and per fiber volume (LVf). Compared to the vastus lateralis muscle, the splenius capitis muscle had a higher percentage of type 1 fibers (51.2% vs 39.7%), fewer type 2a fibers (16.2% vs 31.4%), and smaller fiber diameters (35.5-40.9 μm vs 47-56.1 μm). It also displayed lower Br dens (P = 0.0069), higher anisotropy (P = 0.0004), and lower LL (P < 0.0001) but higher LVf (P = 0.0486). In the splenius capitis muscle, body mass index (BMI) negatively correlated with LV (P = 0.0155), LS (P = 0.0091), LVf (P = 0.0137), and anisotropy (P = 0.0425), and positively correlated with tortuosity (P = 0.0473), indicating a reduction in the capillary network. In the vastus lateralis muscle, only LV (P = 0.0161) decreased with high BMI. This study characterized the fiber-type composition, fiber size, and 3D capillary network of the splenius capitis muscle, establishing a baseline for investigations into pathological muscle alterations.

Stress sensitivity analysis of vuggy porous media based on two-scale fractal theory

Interparticle pore space and vugs are two different scales of pore space in vuggy porous media. Vuggy porous media widely exists in carbonate reservoirs, and the permeability of this porous media plays an important role in many engineering fields. It has been shown that the change of effective stress has important effects on the permeability of vuggy porous media. In this work, a fractal permeability model for vuggy porous media is developed based on the fractal theory and elastic mechanics. Besides, a Monte Carlo simulation is also implemented to obtain feasible values of permeability. The proposed model can predict the elastic deformation of the fractal vuggy porous media under loading stress, which plays a crucial role in the variations of permeability. The predicted permeability data based on the present fractal model are compared with experimental data, which verifies the validity of the present fractal permeability model for vuggy porous media. The parameter sensitivity analysis indicates that the permeability of stress-sensitivity vuggy porous media is related to the capillary fractal dimension, capillary fractal tortuosity dimension, Young’s modulus, and Poisson’s ratio.

Description of the characteristics of the nailfold capillary structure in healthy children: a multi-centric study.

Nailfold videocapillaroscopy (NVC) is the primary diagnostic tool for the assessment of microcirculation in the pediatric population. To define and standardize age-specific normal NVC patterns in healthy children and adolescents. A cross-sectional observational multicentric study was conducted in 564 participants aged 5-17 years. Dino-Lite CapillaryScope 200 Pro Model MEDL4N Pro was performed at 200× magnification. Quantitative and qualitative NVC parameters were analysed separately for each age group and divided into four groups based on age categories. Of the 564 healthy participants, 54.9% were female. A total of 1184 images and 3384 capillaries were analysed. Positive correlations were observed between age and capillary density (P< 0.001, R = 0.450, CI95% 0.398-0.503). There was also a positive correlation between age and arterial/venous, loop diameter and capillary length, whereas there was a weak negative correlation between intercapillary distance. However, no correlation was found between age and capillary width. In addition, capillary density was significantly lower in the 5-7 age group compared with the other patient groups. Arterial limb diameter was lower in the 5-7 age group, while venous limb diameter was significantly wider in the 15-17 age group compared with the other patient groups. Dilated capillaries (8.7%), capillary tortuosity (14.4%), crossed capillaries (43.1%), micro-haemorrhages (2.7%) and avascular area (4.8%) were present in all age groups. Excellent intra- and interobserver ICC values were obtained for all parameters. These findings hold potential significance for future studies, aiding in the analysis and differentiation of children suspected of rheumatological diseases with potential microangiopathy.

Characterizing permeability-porosity relationships of porous rocks using a stress sensitivity model in consideration of elastic-structural deformation and tortuosity sensitivity

Clarifying the relationship between stress sensitivities of permeability and porosity is of great significance in guiding underground resource mining. More and more studies focus on how to construct stress sensitivity models to describe the relationship and obtain a comprehensive stress sensitivity of porous rock. However, the limitations of elastic deformation calculation and incompleteness of considered tortuosity sensitivity lead to the fact that the existing stress sensitivity models are still unsatisfactory in terms of accuracy and generalization. Therefore, a more accurate and generic stress sensitivity model considering elastic-structural deformation of capillary cross-section and tortuosity sensitivity is proposed in this paper. The elastic deformation is derived from the fractal scaling model and Hooke's law. Considering the effects of elastic-structural deformation on tortuosity sensitivity, an empirical formula is proposed, and the conditions for its applicability are clarified. The predictive performance of the proposed model for the permeability-porosity relationships is validated in several sets of publicly available experimental data. These experimental data are from different rocks under different pressure cycles. The mean and standard deviation of relative errors of predicted stress sensitivity with respect to experimental data are 2.63% and 1.91%. Compared with other models, the proposed model has higher accuracy and better predictive generalization performance. It is also found that the porosity sensitivity exponent α, which can describe permeability-porosity relationships, is 2 when only elastic deformation is considered. α decreases from 2 when structural deformation is also considered. In addition, α may be greater than 3 due to the increase in tortuosity sensitivity when tortuosity sensitivity is considered even if the rock is not fractured.

The driving force of water absorption in cementitious materials: An analysis of surface-free energies and pore structure

Upon the initial contact of hydrophilic cementitious materials with water, capillary absorption becomes the dominant phenomenon leading to durability deterioration of structures. The water absorption characteristics of such materials are governed by the interplay between pore structure and surface-free energies, with the latter being a factor often overlooked. In this study, advanced inverse gas chromatography (IGC) measurement techniques were employed to investigate the one-dimensional capillary water absorption of ordinary Portland cement (OPC) and alkali-activated slag (AAS). Results revealed water sorptivity values for OPC, AAS(NaOH), and AAS(Waterglass) as 0.0112, 0.0137, and 0.0187 mm/s0.5, respectively. This phenomenon can be attributed to the higher total surface-free energies observed at the liquid-solid interface in AAS materials, measuring 100.10 and 119.56 mJ/m2, compared with 74.25 mJ/m2 for OPC, consequently increasing capillary pressures. Moreover, it is observed that OPC exhibited a more complex pore tortuosity in comparison to AAS. This study underscores the dual role played by both capillary pressures and pore tortuosity in determining the water absorption characteristics of cementitious materials.

Proximal nailfold videocapillaroscopy findings of patients with idiopathic macular telangiectasia type 2.

Idiopathic macular telangiectasia type 2 (IMT) is a neurodegenerative disease characterized by bilateral, idiopathic, and perifoveal retinal telangiectatic vessel formations. We aimed to compare proximal nailfold videocapillaroscopy (NV) findings between patients with IMT and healthy individuals and evaluate the optical coherence tomography angiography (OCTA) parameters of the patients with IMT according to their NV findings. The study included 43 patients with IMT and 92 healthy controls of similar age and gender without any additional diseases. The OCTA and NV findings of the patients and controls were examined. The mean age was 59.76 ± 5.73 years in the IMT group and 58.23 ± 4.96 years in the control group. Of the 43 patients with IMT, 19 were found to have increased capillary tortuosity, six had microhemorrhage, and 18 had bizarre capillaries (P < 0.001). In the IMT group, the total vascular density value of the superficial capillary plexus was higher among the patients with capillary microhemorrhage (P = 0.001), and the subfoveal choroidal thickness was lower among those with increased capillary tortuosity and bizarre capillaries (P = 0.04 and P = 0.07, respectively). This is the first study in which the NV findings of patients with IMT were compared with those of a control group. We found higher rates of increased capillary tortuosity, microhemorrhage, and bizarre capillaries in the IMT group compared to the controls. We consider that this situation is caused by microvascular damage. We also think that IMT is a systemic disease that affects both proximal nailfold capillaries and eye vessels.

Refined express method for evaluation of porous structure ceramic materials

The express method for evaluating the porous structure of ceramic materials has been refined by replacing a smooth change in gas pressure with a stepwise one with pressure holding at each stage. After determining the average radius, the maximum pressure drop is determined until only one chain of gas bubbles remains. The average coordination number for the solid phase and the coefficient of capillary tortuosity were calculated. The experimental and calculated mean radii are in good agreement with the data, while the tortuosity coefficients differ.

Fractal model of spontaneous imbibition in low-permeability reservoirs coupled with heterogeneity of pore seepage channels and threshold pressure

Spontaneous imbibition (SI) is an important mechanism for enhancing oil recovery in low-permeability reservoirs. Due to the strong heterogeneity, and the non-Darcy flow, the construction of SI model for low-permeability reservoirs is extremely challenging. Commonly, traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure (TP) on imbibition. Therefore, in this work, based on capillary model and fractal theory, a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established. On this basis, the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil. The proposed new SI model was verified by imbibition experimental data. The study shows that for weakly heterogeneous cores with permeability of 0–1 mD, the traditional SI model can characterize the imbibition process relatively accurately, and the new imbibition model can increase the coefficient of determination by 1.05 times. However, traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10–50 mD. The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem, and the determination coefficient is increased from 0.344 to 0.922, which is increased by 2.68 times. For low-permeability reservoirs, the production of the oil in transitional pores (0.01–0.1 μm) and mesopores (0.1–1 μm) significantly affects the imbibition recovery, as the research shows that when the heterogeneity of pore seepage channels is ignored, the oil recovery in transitional pores and mesopores decreases by 7.54% and 4.26%, respectively. Sensitivity analysis shows that increasing interfacial tension, decreasing contact angle, oil–water viscosity ratio and threshold pressure will increase imbibition recovery. In addition, there are critical values for the influence of these factors on the imbibition recovery, which provides theoretical support for surfactant optimization.

Correlation between optical coherence tomography angiography-based data and postoperative visual acuity in patients that underwent surgery for macula-on RRD and macula-off RRD

Background: Despite advances in surgical techniques for rhegmatogenous retinal detachment (RRD) repair, patients are still at high risk for low functional outcomes. Given the above, it is important to find reasons for disappointment at the outcomes of vitreoretinal surgery for RRD. Impaired retinal microcirculation is a possible cause of insufficiently good functional outcomes in surgery for RRD. Purpose: To compare postoperative optical coherence tomography angiography (OCTA)-based changes in retinal microcirculation in the eyes of patients that underwent surgery for macula-on RRD versus the eyes of patients that underwent surgery for macula-off RRD and (2) to establish a relationship between OCTA data and best-corrected visual acuity (BCVA). Material and Methods: This prospective study included 116 patients. Of these, 65 underwent surgery for macular-on RRD (group 1) and 51, surgery for macular-off RRD (group 2). OCTA-based retinal vasculature parameters (foveal avascular zone (FAZ) area, parafoveal superficial capillary plexus (SCP) density and deep capillary plexus (DCP) density, vessel diameter, and vessel tortuosity index (VTI)) and their correlation with BCVA were assessed. Follow-up duration was 12 months. Results: In group 1, there was a negative correlation between the FAZ area and the macular thickness (r = - 0.299, p = 0.025) at month 12. The final BCVA was associated with the parafoveal DCP density (r = - 0.340, p = 0.010) and FAZ area (r= 0.390, p = 0.003). At 12 months, in group 2, the BCVA negatively correlated with the FAZ area (r = - 0.408, p = 0.012) and parafoveal SCP density (r = - 0.451, p = 0.005). In addition, there was a negative correlation between the parafoveal DCP density and the postoperative BCVA (r = - 0.418). There was no correlation between the FAZ area and the macular thickness (r = - 0.282, p = 0.080). Conclusion: The poorer vessel tortuosity index and parafoveal vessel density and diameter, the lower was postoperative visual acuity.

Central and peripheral changes in the retina and choroid in patients with diabetes mellitus without clinical diabetic retinopathy assessed by ultra-wide-field optical coherence tomography angiography.

To explore the central and peripheral retinal and choroidal changes in diabetic patients without clinical diabetic retinopathy (DM-NoDR) using ultra-wide-field swept-source optical coherence tomography angiography (UWF-SS-OCTA). 67 DM-NoDR eyes and 32 age-matched healthy eyes were recruited. Retinal and choroidal parameters, including qualitative retinal microangiopathy, vessel flow (VFD) and linear density (VLD), thickness, and volume, were measured in the central and peripheral areas of the 24 × 20 mm2 UWF-SS-OCTA images. DM-NoDR eyes had significantly more nonperfusion area and capillary tortuosity than controls in the central and peripheral areas (p < 0.05). The presence of central capillary tortuosity was associated with higher levels of serum creatinine (OR 1.049, 95%CI 1.001-1.098; p = 0.044) and blood urea nitrogen (OR 1.775, 95%CI 1.051-2.998; p = 0.032) in DM-NoDR eyes. For DM-NoDR eyes versus controls, VFD in the 300-μm annulus around the foveal avascular zone, superficial capillary plexus (SCP), and full retina, and SCP-VLD significantly decreased, while VFD in the deep capillary plexus (DCP), retinal thickness, and retinal volume increased (p < 0.05). Analysis in the central and peripheral areas recapitulated all these findings, except for decreased peripheral thickness and volume and no difference in peripheral DCP-VFD. In DM-NoDR eyes, choriocapillaris-VFD, choroidal thickness, and choroidal volume increased in the central area, while VFD in the large and medium choroidal vessel layer decreased in the whole image (p < 0.05). Retinal and choroidal changes already existed in the central and/or peripheral areas of DM-NoDR eyes. UWF-SS-OCTA, enabling the visualization of the peripheral fundus area, is a promising image technique for the early detection of fundus changes in DM-NoDR patients.

Equivalent permeability model of dual-porosity and bi-dispersed porous media based on the intermingled fractal units

Dual-porosity and bi-dispersed porous media (DBPM) widely exist in geotechnical engineering, material engineering, soil science, and groundwater exploitation. Therefore, it is significant to quantify the relationship between permeability and matrix–fracture structure parameters for mastering fluid's seepage and transport characteristics. Hence, this paper derives an analytical solution of equivalent permeability for DBPM based on the intermingled fractal units (IFU). The developed model considers the capillary pressure of fractures and capillaries and the tortuosity of fractures and capillaries. Specifically, the number of porous matrix fractal units in IFU is quantified, and then, the dimensionless permeability is calculated, defined as the ratio of the permeability of np matrix fractal units to a single fracture fractal unit. The results reveal that equivalent permeability is mainly contributed by fracture permeability. Next, the second dimensionless permeability is defined to compare further and quantify the permeable ability of fracture and porous matrix. The results highlight that the permeability difference between a single fracture fractal unit and a single porous matrix fractal unit is approximately 7–11 orders of magnitude. Overall, through this paper, the preferential flow mechanism of DBPM can be better described and understood by introducing the above two dimensionless permeabilities and analyzing the influence of structural parameters on them.

PECULIARITIES OF ENDOTHELIAL DYSFUNCTION AND CAPILLARY BLOOD FLOW IN PATIENTS WITH COVID-19 CORONAVIRUS DISEASE AND CONCOMITANT TYPE 2 DIABETES MELLITUS

The aim of the study was to investigate the indicators of endothelial dysfunction and capillary blood flow in patients with coronavirus disease (COVID-19) and concomitant type 2 diabetes mellitus.Materials and methods. We examined 60 patients with moderate and severe coronavirus disease (COVID-19): Group I (main) – 30 patients with coronavirus disease (COVID-19) with concomitant type 2 diabetes mellitus, mean age (66.70±1.47) years; Group II (comparison group) – 30 patients with coronavirus disease (COVID-19) without diabetes mellitus, mean age (60.13±2.21) years; control group (practically healthy) - 20 people. Nail capillaroscopy, determination of endothelin-1, D-dimer levels, and coagulation parameters were performed on the 2-3rd day after admission to the hospital.Results. In patients of both groups, a significant increase in the level of D-dimer, endothelin-1 was observed. The average values of D-dimer in patients of group I significantly exceeded the average values in patients of group II: 1543.20±254.01 ng FEU/ml and 522.74±39.45 ng FEU/ml respectively (p&lt;0.001). During capillaroscopy in patients of group I, a high frequency of capillary branching (25.8%), bushy capillaries (25.8%) and tortuosity of capillaries (63.3%) was found, microthrombosis and microbleeding were observed more often. In patients of group II, the most common abnormalities were pericapillary edema (83.3%), capillary dilatation (36.7%), dilated and tortuous capillaries (13.3%), and hemosiderin deposits (36.7%). Conclusions. In patients with coronavirus disease (COVID-19) with concomitant type 2 diabetes mellitus, the levels of D-dimer and endothelin-1 indicated a more pronounced endothelial dysfunction. Changes in nail capillaroscopy indicating microvascular damage associated with COVID-19 were more pronounced in patients with concomitant type 2 diabetes.

Numerical simulation of gas breakdown characteristics in porous dielectric and theoretical analysis based on the capillary network model

Gas discharge in heterogeneous porous dielectric (PD) is becoming a reliable and popular low-temperature plasma technique in surface modification and plasma catalysis. However, the exact breakdown characteristics in the PD are not well studied due to experimental and diagnostic limitations. In this paper, a fluid model is then used to simulate the gas breakdown characteristics in real PD. It is found that the breakdown will selectively occur in PDs. The spatial distribution of PD determines regions of local breakdown. Variations in pressure result in the rearrangement of breakdown probability in each region of PD so that breakdown regions will change. In order to explain the selective breakdown phenomenon, based on the assumption that a PD can be simplified into a network consisting of multiple tortuous capillaries, we developed a theoretical model of the breakdown in a capillary network. Three geometrical factors, i.e. capillary tortuosity, capillary radius, and line porosity, are taken into the model to account for the effect of electric field distortion and electron loss on the dielectric walls in the presence of PD. The calculated results explain the selective breakdown phenomenon occurring in the numerical simulation. This paper simulates the breakdown in a real PD and provides a quantitative theoretical model to analyze the geometrical effect of PD on the breakdown. This paper will also provide insights into the design of optimal parameters for porous dielectric discharge in surface modification and plasma catalysis.

Capillaroscopy, microangiopathy, and HIV. Descriptive study of capillaroscopy findings in HIV positive patients

In this study, we aim to evaluate microangiopathy in HIV positive patients by using capillaroscopy. To date, few studies have been published on the topic. Capillaroscopy may be a tool for early diagnosis of cardiovascular involvement in this patient population. Cross-sectional study with HIV positive patients >18 years. The enrolment period was set from January to June 2018. The following data were collected: demographic (sex, age), laboratory tests (duration of infection, CD4 cell count, CD4:CD8 ratio, coinfection with other viruses), antiretroviral treatment, dyslipidemia, and comorbidities (active smoking, alcoholism, high blood pressure, dyslipidaemia, diabetes, cardiopathy). The capillaroscopy and blood tests were performed simultaneously. The following alterations were evaluated in the capillaroscopy: congestion, tortuosity, haemorrhage, dilations, capillary loss, and presence of megacapillaries. One hundred and two patients were included; 73.5% were male, mean age was 40 years (SD: 10), and mean duration of infection 4.5 years (SD: 3.1). At diagnosis, mean CD4 cell count was 408/mm3 and CD4/CD8 ratio 0.4. A number of patients (14.7%) were coinfected with the hepatitis B virus; 31.3% were active smokers and 13.7% alcoholics. Capillaroscopy alterations were found in most study patients (93.1%): congestion (78.5%), tortuosity (77.5%), haemorrhage (13.8%), dilations (11.8%), capillary loss (5%), and megacapillaries (1%). Capillary tortuosity was associated with age and smoking; and haemorrhage with age, CD4, antiretroviral treatment, and hypertension. Prevalence of capillaroscopy alterations is high in HIV positive patients, particularly tortuosity and congestion. To the best of our knowledge, the later alteration has not been previously reported in this group of patients.

The Influence of Pore Structure of the Core-Scale Fracture-Controlled Matrix Unit on Imbibition: Model Construction and Definition of the Fractal Coefficient

Abstract Imbibition oil recovery plays an important role in the development of low-permeability fractured reservoirs. However, the effects of the complex pore structure of the matrix on imbibition have not been considered comprehensively at different scales in the scientific literature. This paper reports a study of the mechanisms of influence of different matrix pores on imbibition recovery ratio and defines the concept of a fractal coefficient using the method of combining numerical simulation at the core scale with mathematical methods at a pore scale. A matrix model with different pore fractal dimensions and tortuosity of the capillary was established using Python language programming. Y-type and S-type were used to characterize the fractures, and a two-dimensional fracture-controlled matrix unit core-scale numerical model with complex pore structures was established. Based on phase field theory, an oil-water two-phase imbibition numerical simulation was conducted. Comparisons of numerical simulation results and microscopic analysis indicated that imbibition recovery ratio was 39.28% and 50.94%, respectively. The imbibition law revealed by the numerical simulation results is consistent with the results of the microscopic imbibition experiment, and the imbibition effect of bifurcated fractures was better than that of simple curved fractures. As the pore fractal dimension and tortuosity of the capillary increased, the imbibition recovery ratio decreased. A comparison of results of the mathematical model demonstrated that there was a difference between the pore scale and core scale because the pore fractal dimension and capillary tortuosity changed dynamically with pore structure at the core scale. Thus, a parameter that characterizes the relative change of pore fractal dimension and tortuosity was defined and called the fractal coefficient. When the skeleton particles are 200, 400, and 500, the fractal coefficient were calculated to be 0.625 and 0.6, respectively, indicating that when the pore structure changes, the imbibition recovery ratio should be dominated by capillary tortuosity.

Multiscale modelling of brain tissue oxygen and glucose dynamics in tortuous capillary during ischaemia-reperfusion

Brain ischaemia causes reduction of cerebral blood flow, which interrupts the transport of oxygen and glucose to brain tissue. These transport inefficiencies have also been associated with the complex cerebral microvasculature. In this study, the importance of cerebral capillary complexity and tissue interstitial porosity in oxygen and glucose transport and metabolism during brain tissue ischaemia is investigated using an asymptotic expansion homogenization method. Applying this technique produces new macroscale governing equations with associated microscale cell problems. Solving the latter on the brain tissue microstructural geometry will obtain parametric tensors, namely the conductivities of the capillary, K and interstitial space, E; and the diffusivities of a substrate in the capillary, DM,c, and in interstitial space, DM,t. From the microscale simulations, increasing the capillary tortuosity resulted in a decrement of K and DM,c, but no significant changes in E and DM,t. Meanwhile, increasing the capillary radius resulted in the decrease of all parameters except K. Then, the parametric tensors obtained are used to solve the macroscale governing equations on a one-dimensional brain model under ischaemia-reperfusion conditions. From the macroscale simulations, changing the capillary tortuosity affects the uptake and metabolism of oxygen and glucose during brain ischaemia-reperfusion. In addition, in more tortuous capillaries, oxygen and glucose are utilized rapidly at tissues proximal to the capillary during the reperfusion process, leaving only a small amount of these substrates for distal tissues. This could be associated with severe stroke outcome. It is thus proposed that the capillary tortuosity of a patient could potentially be used as an additional indicator in determining the severity of ischaemic stroke.

Morphologic Mapping of the Sublingual Microcirculation in Healthy Volunteers

Purpose: Monitoring the sublingual and oral microcirculation (SM-OM) using hand-held vital microscopes (HVMs) has provided valuable insight into the (patho)physiology of diseases. However, the microvascular anatomy in a healthy population has not been adequately described yet. Methods: Incident dark field-based HVM imaging was used to visualize the SM-OM. First, the SM was divided into four different fields; Field-a (between incisors-lingua), Field-b (between the canine-first premolar-lingua), Field-c (between the first-second premolar-lingua), Field-d (between the second molar-wisdom teeth-lingua). Second, we investigated the buccal area, lower and upper lip. Total/functional vessel density (TVD/FCD), focus depth (FD), small vessel mean diameters (SVMDs), and capillary tortuosity score (CTS) were compared between the areas. Results: Fifteen volunteers with a mean age of 29 ± 6 years were enrolled. No statistical difference was found between the sublingual fields in terms of TVD (p = 0.30), FCD (p = 0.38), and FD (p = 0.09). SVMD was similar in Field-a, Field-b, and Field-c (p = 0.20–0.30), and larger in Field-d (p < 0.01, p = 0.015). The CTS of the buccal area was higher than in the lips. Conclusion: The sublingual area has a homogenous distribution in TVD, FCD, FD, and SVMD. This study can be a description of the normal microvascular anatomy for future researches regarding microcirculatory assessment.

Experimental study on gas permeability of cement-based materials

Gas permeability is an important property associated with the durability of cement-based materials. In this study, an experimental method based on applying a quasi-stationary flow is adopted to evaluate the gas permeability of cement-based materials. The results indicate that the intrinsic permeability of dried cement-based materials is affected by the addition of limestone powder, fly ash, and aggregate. The Katz-Thompson equation could predict the intrinsic permeability by using the capillary porosity, average diameter, and pore tortuosity. The intrinsic permeability of partially saturated cement-based materials decreases when the water saturation increases. The Van Genuchten-Mualem model could describe the relative gas permeability of partially saturated cement-based materials, and the model parameters n value between 1 and 2 while m value ranging from 0.64 to 0.69 for cement and mortar. Moreover, the power function relationship between the intrinsic permeability and Klinkenberg constant of cement-based materials has also been corroborated. Finally, a prediction model of gas permeability of cement-based materials under arbitrary water saturation and pressure gradient is proposed.

A Fractal Model for Effective Thermal Conductivity in Complex Geothermal Media

Thermal conductivity is an important macroscopic thermo-physical parameter due to its significant effects on the temperature field distribution and heat flow magnitude in the material at heat conduction equilibrium. However, because of the extremely complex pore structure and disordered pore distribution, a well-accepted relationship between effective thermal conductivity (ETC) and geometric structural parameters is still lack. In this study, a novel fractal model with variation pore diameter is established systematically based on the assumption that the rough elements of wall surface, pore size distribution and capillary tortuosity follow the fractal scaling law. Thermal-electrical analogy is introduced to predict the ETC of unsaturated geothermal media. The proposed model explicitly relates the ETC to the microstructural parameters (relative roughness, porosity, fractal dimensions and radius fluctuation amplitude) and fluid properties. The proposed model is validated by comparing with existing experimental data. A parametric analysis is performed for presenting the effects of the structural parameters and fluid properties on the ETC. The results show that pore structure has significant effect on ETC of unsaturated porous media. ETC gradually decreases with the increment of porosity, relative roughness, and fractal dimensions. The present study improves the accuracy in predicting ETC and sheds light on the heat transfer mechanisms of geothermal media.