Tortuous Capillaries Research Articles

Nailfold Video-Capillaroscopy in Sarcoidosis: New Perspectives and Challenges.

Nailfold video-capillaroscopy (NVC) is a non-invasive cost-effective technique involving the microscopic examination of small blood vessels of the distal nailfold with a magnification device. It provides valuable information regarding the microcirculation including anomalies such as tortuous or dilated capillaries, hemorrhages, and avascular areas, which can characterize connective tissue diseases. The utility of NVC in the diagnosis and monitoring of systemic sclerosis (SSc) has been investigated in numerous studies allowing the distinction of the specific microvascular pattern of scleroderma from different conditions other than scleroderma (non-scleroderma pattern). Sarcoidosis (SA) is a systemic inflammatory disease that can affect various organs, including the lungs, skin, and lymph nodes. The purpose of our review was to evaluate the current state of the art in the use of NVC in the diagnosis of SA, to understand the indications for its use and any consequent advantages in the management of the disease in different settings in terms of benefits for patients. We searched for the key terms "sarcoidosis" and "video-capillaroscopy" in a computerized search of Pub-Med, extending the search back in time without setting limits. We provided a critical overview of the literature, based on a precise evaluation. After our analysis, we examined the six yielded works looking for answers to our questions. Few studies have evaluated that microcirculation is often compromised in SA, with alterations in blood flow and consequent tissue damage. Basing on highlighted findings, NVC appears to be a useful tool in the initial evaluation of sarcoidosis patients. Furthermore, capillaroscopy is useful in the evaluation of the coexistence of sarcoidosis and scleroderma spectrum disorder or overlap syndromes. In conclusions, no specific pattern has been described for sarcoidosis, and further re-search is needed to fully understand the implications of nailfold capillaroscopy find-ings in this disease and to establish standardized guidelines for its use in clinical practice.

Electrical conductivity model for reactive porous media under partially saturated conditions with hysteresis effects

The electrical conductivity of a porous medium is strongly controlled by the structure of the medium at the microscale as the pore configuration governs the distribution of the conductive fluid. The pore structure thus plays a key role since different geometries translate in variations of the fluid distribution, causing different behaviors measurable at the macroscale. In this study, we present a new physically-based analytical model derived under the assumption that the pore structure can be represented by a bundle of tortuous capillary tubes with periodic variations of their radius and a fractal distribution of pore sizes. By upscaling the microscale properties of the porous medium, we obtain expressions to estimate the total and relative electrical conductivity. The proposed pore geometry allows us to include the hysteresis phenomenon in the electrical conductivity estimates. The variations on these estimates caused by pore structure changes due to reactive processes are accounted by assuming a uniform dissolution of the pores. Under this hypothesis, we describe the evolution of the electrical conductivity during reactive processes. The expressions of the proposed model have been tested with published data from different soil textures, showing a satisfactory agreement with the experimental data. Hysteretic behavior and mineral dissolution are also successfully addressed. By including hysteresis and mineral dissolution/precipitation in the estimates of the electrical conductivity, this new analytical model presents an improvement as it relates those macroscopic physical phenomena to its origins at the microscale. This opens up exciting possibilities for studies involving electrical conductivity measurements to monitor water movement, and hysteretic and reactive processes in porous media.

Nail fold capillaroscopy in leprosy: Unveiling the microvascular changes

BackgroundLeprosy, a chronic infectious disease, is associated with various nail changes. Its etiopathogenesis is multifaceted, with microvascular damage being crucial. Nail fold capillaroscopy (NFC) emerges as a novel tool for detecting early vascular deficits in leprosy. The study aimed to assess and provide a complete clinical characterization of NFC changes in leprosy patients. MethodsIt is an observational cross-sectional study, done over a period of 1.5 year (January 2021 to august 2022) in a tertiary care hospital, encompassing 60 patients diagnosed with leprosy (18–60 years). After obtaining informed consent; detailed history, complete cutaneous and neurological examinations were conducted. All fingernails and toenails were examined for clinical changes. Subsequently, onychoscopy was performed using USB type of video-dermatoscope (Model AM7115MZT Dino-lite), a non-invasive tool. This was followed by NFC which was done for all fingernails and images were recorded by single operator, which were then assessed for quantitative and qualitive changes and statistical analysis was conducted using SPSS v20, with mean capillary density compared using Student's t-test, morphological change frequencies assessed by proportions, and group comparisons made using Chi-square or Fischer exact tests, with a significance threshold of p < 0.05. ResultsAmong the 60 patients, 39 were in the lepromatous group, which included both borderline lepromatous (BL) and lepromatous leprosy (LL) patients, and 17 were in the tuberculoid group, which included borderline tuberculoid (BT) leprosy patients; 23.3 % had Type 1 reactions, and 18.3 % had Type 2 reactions. Nail fold capillaroscopy (NFC) showed microvasculature changes in 93.3 % of patients. The average capillary density was 6.8 ± 1.5 capillaries per mm, with the lepromatous group having a lower density (6.5 ± 1.09) compared to the tuberculoid group (7.0 ± 0.86). The most common NFC changes in the tuberculoid group were tortuous capillaries (70 %), capillary dropouts, and dilated capillaries (both 64.7 %). In the lepromatous group, capillary dropouts (82 %) were most frequent, followed by tortuous (69 %), receding (69 %), and dilated capillaries (66 %). A dilated and prominent subpapillary plexus was more common in the lepromatous group (35 %, p = 0.04). Patients with trophic changes in the lepromatous group had more capillary dropouts and bizarre capillaries. Capillary dropouts, dilated capillaries, and visible subpapillary venous plexus were more prevalent in patients with Type 2 reactions. ConclusionNFC changes are prevalent in both tuberculoid and lepromatous leprosy, which may be an indicator of peripheral vascular compromise and trophic changes, especially in lepromatous leprosy. NFC can be an auxiliary tool for detecting microvascular abnormalities in leprosy patients.

Evaluation of nail fold capillaroscopy changes in patients with diabetic retinopathy and healthy controls, and its correlation with disease duration, HbA1c levels and severity of diabetic retinopathy: An observational study.

Background Diabetic retinopathy (DR) is an important microvascular complication of long-term type 2 diabetes mellitus (T2DM) leading to blindness if not properly diagnosed and managed. It can develop as early as 7 years before the diagnosis of diabetes. Nail fold capillaroscopy (NFC) is a non-invasive technique for observing capillary microvasculature and there are few studies which have explored the use of NFC in diabetes mellitus patients. Objective To study the nail fold capillaroscopic alterations in patients with T2DM having diabetic retinopathy and compare them to healthy controls. The secondary objective was to correlate the NFC findings with the duration of diabetes, haemoglobin A1c (HbA1c) levels and the severity of DR. Materials and methods This cross-sectional observational study enrolled 200 patients - 100 cases with T2DM having diabetic retinopathy (as per the American Diabetes Association criteria and Diabetic Retinopathy Disease Severity Scale) and 100 healthy age and sex-matched controls. All patients were subjected to NFC and ophthalmological assessment. Results NFC revealed that patients with DR showed significantly higher frequencies of tortuous, dilated, bushy, meandering, angulated capillaries, avascular areas and micro-haemorrhages as compared to healthy controls (p < 0.05). In proliferative DR (PDR), the frequency of tortuous, bushy capillaries, and avascular areas was statistically high and the capillary density was reduced as compared to non-proliferative DR. The DR patients with longer disease duration (>20) years had a significantly higher frequency of tortuous capillaries, avascular areas, meandering, angulated and dilated capillaries. The frequency of tortuosity, avascular areas, and bushy areas was significantly higher in patients with poor glycaemic control (HbA1c >11). Limitations A larger sample size study with different demographic populations could have provided a broader picture of NFC changes in T2DM patients with DR. Discussion NFC may act as a surrogate marker of retinal involvement in patients with DM and should be performed at regular intervals. Conclusion NFC is a quick, simple, safe, and non-invasive method to assess the capillaroscopic alterations in diabetic patients which inturn can help in assessing the severity of DR.

A critique on “Modeling the spontaneous imbibition of non-Newtonian fluids into the fractal porous media of tight reservoirs”

In February 2022, this journal published the paper “Modeling the spontaneous imbibition of non-Newtonian fluids into the fractal porous media of tight reservoirs” (Zhu et al., 2022), which develops and validates an analytical model for the capillary absorption of (non-)Newtonian liquids in sandstone, founded on a fractal-based bundle-of-tubes model. This critique – a post-publication review – expresses concerns on that model development and validation. It is shown that agreement between calculated and measured absorbed moisture masses and moisture front heights is only attained with two strongly distinct sets of material and fluid properties, a dichotomy that is however not disclosed in the paper. It is moreover revealed that the input material and fluid properties and the output absorbed moisture masses and moisture front heights often defy physical plausibility. Detailed scrutiny of the mathematical model complementarily exposes concrete defects in the calculation of the ‘sample’ cross-section. It is displayed that this cross-section calculation is exclusively governed by the material properties, implying that the measured cross-section can (almost) never be equated. It is furthermore established that the cross-section calculation assumes the equality of the areal and volumetric porosity, which is incorrect for a bundle-of-tubes with tortuous capillaries. Additionally it is demonstrated that the cross-section calculation merges two conflicting relations between the porosity and the fractal properties. All these concerns bring about doubts concerning the reliability of (Zhu et al., 2022)'s model development and validation, and the authors are hence invited to placate these concerns in their reply.

Numerical Simulation of Mass Transfer in Hollow Fiber Membrane Module for Membrane-Based Artificial Organs.

The mass transfer behavior in a hollow fiber membrane module of membrane-based artificial organs (such as artificial liver or artificial kidney) were studied by numerical simulation. A new computational fluid dynamics (CFD) method coupled with K-K equation and the tortuous capillary pore diffusion model (TCPDM) was proposed for the simulations. The urea clearance rate predicted by the use of the numerical model agrees well with the experimental data, which verifies the validity of our numerical model. The distributions of concentration, pressure, and velocity in the hollow fiber membrane module were obtained to analyze the mass transfer behaviors of bilirubin and bovine serum albumin (BSA), and the effects of tube-side flow rate, shell-side flow rate, and fiber tube length on the bilirubin or BSA clearance rate were studied. The results show that the solute transport mainly occurred in the near inlet regions in the hollow fiber membrane module. Increasing the tube-side flow rate and the fiber tube length can effectively enhance the solute clearance rate, while the shell-side flow rate has less influence on the BSA clearance. The clearance of macromolecule BSA is dominated by convective solute transport, while the clearance of small molecule bilirubin is significantly affected by both convective and diffusive solute transport.

Capillaroscopic differences between primary Raynaud phenomenon and healthy controls indicate potential microangiopathic involvement in benign vasospasms.

For primary Raynaud phenomenon (PRP), an otherwise unexplained vasospastic disposition is assumed. To test the hypothesis of an additional involvement of distinct ultrastructural microvascular alterations, we compared the nailfold capillary pattern of patients with PRP and healthy controls. A total of 120 patients with PRP (with a median duration of vasospastic symptoms of 60 [IQR: 3-120] months) were compared against 125 controls. In both groups, nailfold capillaroscopy was performed to record the presence of dilatations, capillary edema, tortuous capillaries, ramifications, hemorrhages, and reduced capillary density and to determine a semiquantitative rating score. Further, the capacity of finger skin rewarming was investigated by performing infrared thermography in combination with cold provocation. Unspecific morphologic alterations were found in both, PRP, such as controls, whereby the risk for PRP was four times as high in the presence of capillary dilations (CI: 2.3-7.6) and five times as high if capillary density was reduced (CI: 1.9-13.5). Capillary density correlated with thermoregulatory capacity in both hands in the PRP group, but not in controls. In addition, a negative correlation between the microangiopathy score and the percentage degree of rewarming in both hands was found for patients with PRP only. We found specific differences within the microvascular architecture between patients with PRP and controls. As a conclusion, PRP may not be an entirely benign vasospastic phenomenon, but might be associated with subtle microcirculatory vasculopathy. In addition, we suggest that the implementation of a scoring system might serve as guidance in the diagnostic process at least of patients with long-standing PRP.

Permeability prediction of porous aerostatic bearings through 3D morphology and fractal calculation method

AbstractPorous ceramics for aerostatic bearing restrictors were fabricated using carboxymethyl cellulose and polystyrene microspheres as pore formers. The three‐dimensional morphology of the porous ceramics was nondestructively obtained using laser scanning confocal microscopy, and the processing information was eliminated by fitting the pore area fractal dimensions at different heights. A mathematical model was developed based on the assumption of elliptical tortuous capillaries to relate microstructural pore parameters to permeability by combining fractal theory, Darcy's law, and the gas conservation equation. The calculated permeability closely matched the experimental results, with an error of less than 3.5%. This method has promising potential as an alternative to pressure drop experiments. Moreover, the capacity of the fractal calculation model to establish a correlation between microstructural parameters and permeability paves a new way to design future porous aerostatic bearings.

Permeability of Argillaceous Sandstone Modeled with Tortuous Capillary Tubes Using Fractal Geometry

Permeability of Argillaceous Sandstone Modeled with Tortuous Capillary Tubes Using Fractal Geometry

Post-COVID syndrome and capillary bed abnormalities detected by videocapillaroscopy

Post-COVID syndrome (PCS) is a pressing problem in clinical practice. Dyspnea, along with neurologic and cardiovascular symptoms, is the most common symptom indicating low exercise capacity (EC) that reduces quality of life. The aim of this study was to investigate shortness of breath and the capillary bed abnormalities detected video capillaroscopy (VCS) in patients with PCS.Methods. The study included patients with PCS (n = 60) suffering from shortness of breath. Dyspnea was assessed using the 6-minute walk test (6-MWT). The capillary bed abnormality was diagnosed using VCS.Results. Patients with ACL walked an average of 79.5% of the predicted distance in the 6-MWT. They also had a decrease in pulse oximetry readings. The patients were divided into 2 groups: 1st – patients with desaturation, 2nd – patients without desaturation. Significant differences were observed between patients with and without desaturation, especially in the 6-MWT distance, pulse oximetry, and dyspnea before and after the 6-MWT. Patients with desaturation had a higher desaturation-to-distance ratio, a higher O2-GAP index, and higher cardiac effort levels, as well as a significant decrease in the proportion of perfused capillaries (PPC), mean capillary density, and a marked increase in the proportion of tortuous and branched capillaries. There was a direct correlation between PPC and diffusing lung capacity for carbon monoxide (DLCO), and carbon monoxide transfer coefficient (DLCO/Va), distance traveled during the 6-MWT and percentage (%) of predicted distance, inverse correlation between PPC and cardiac effort. There was a direct correlation between the percentage (%) of capillary recovery and 6-MWT distance and the percentage (%) of predicted distance, as well as an inverse correlation with the ratio of desaturation indicators and walking distance. Similarly, there was a direct correlation between mean capillary density and DLCO/Va, while the proportion (%) of tortuous capillaries was inversely correlated with DLCO, and the proportion (%) of branched capillaries was inversely correlated with DLCO/Va.Conclusion. The multifactorial nature of the mechanisms of dyspnea in patients with PCS was demonstrated, with the important role of vasculopathy. Continuous monitoring of pulse oximetry, heart rate and VCS are effective methods to screen and assess the condition of patients with PCS and dyspnea.

Pseudo-chilblain lesions in children during the COVID-19 pandemic

Introduction and objective: During the COVID-19 pandemic, a range of uncommon cutaneous symptoms were observed, which were linked to the SARS-CoV-2 infection. These dermatological symptoms in the form of reddish or purple-coloured lesions on the fingers and toes, accompanied by blisters and ulcerations, were termed as “COVID fingers/toes” – a pseudo-chilblain cutaneous manifestation of COVID-19. The aetiopathogenesis of pseudo-chilblain lesions has not been conclusively determined. At first, SARS-CoV-2 infection was regarded as an evident cause of chilblains. Various studies conducted over a two-year period have not managed to plausibly confirm its direct implications. Materials and methods: The study was of a retrospective nature. The analysis involved clinical symptoms, results of selected laboratory tests, as well as capillaroscopy of the microcirculation in 15 children diagnosed with skin lesions of chilblain-like morphology. Results: All patients from the study population presented with lesions in distal body parts which were of erythematous or oedematous morphology, and resembled chilblains. None of the hospitalised patients suffered from fever or presented with other systemic symptoms. The reverse transcription polymerase chain reaction test for SARS-CoV-2 was negative in all the patients. SARS-CoV-2 antibodies were found in 5 out of 9 patients tested for their presence. Microcirculation abnormalities were diagnosed in 80% of the patients. In none of the children did capillaroscopy image correspond with microangiopathy characteristic of inflammatory connective tissue diseases. Frequent abnormalities found in more than two fingers/toes were: pericapillary oedema (57%), dilated capillaries (42.8%), venous stasis (35.7%), presence of branched and tortuous capillaries (28.5%). Conclusions: Pseudo-chilblain lesions observed during the SARS-CoV-2 pandemic are probably secondary to multifactorial epiphenomenon.

Nail Folds Capillaries Abnormalities Association with Type 2 Diabetes Progression and Correlation with Diabetic Retinopathy

Abstract Background Retinopathy is regarded one of the most important complications of diabetes that occurs after long duration of the disease with untight glycemic control, and it is regarded as one of the preventable causes of blindness so proper evaluation of diabetic patients and their complications can prevent blindness. Aim of the Work to assess the capillaroscopic changes in type 2 diabetes mellitus patients and correlate the findings to the microvascular complication of the retina (diabetic retinopathy). Patients and Methods Our study was conducted on 62 patients of type 2 diabetes mellitus (16 male, 46 female) their ages above 18 years lies between (36-66) years. All patients were subjected to full history taking and thorough clinical examination. Results Nailfold capillaroscopy imaging revealed that 31 patients with positive capillaroscopic findings had branched and tortuous capillaries, 34 patients had hemorrhage,5 patients with dilated apical capillary, 46 patients had elongated capillaries,16 with normal capillary length and 48 patients with dilated capillary width capillary. Fundus examination revealed 26 patients with DR and 36 patients nonDR. Our study reported that DR patients had higher duration of diabetes more than non-DR patients. Also, DR patients showed higher levels of HbA1c more than the non-DR patients. Patients with diabetic retinopathy show high percentages of tortuous, branched capillaries. 46.2% of the DR patients had precapillary edema verses 19.4% of the non-DR patients. The mean capillary width in the DR group of patients was 27.68 ± 5.7 verses 23.02 ± 3.29 in the non-DR patients which indicate that patients with DR had more wide capillaries than the non-DR patients. Higher fasting glucose levels were detected in the DR patients than the non-DR patients. Branched, tortuous capillaries, hemorrhage and dilated apical capillaries are documented in the patients with higher median diabetic years 15-20 years in the DR group of patients. Tortuosity, precapillary edema and dilated apical capillaries are positive in patients with higher median diabetic years. (24) patients documented to have DR with HbA1c ≥7% and only 2 DR patients with HbA1c &amp;lt;7. (29) patients had tortuous capillaries with HbA1c ≥7 verses 2 patients had tortuous capillaries with HbA1c &amp;lt;7. Also, (19) patients had precapillary edema in HbA1c ≥7 group while (0) patient had precapillary edema in the HbA1c &amp;lt;7 group. Capillary width and branched capillaries are found to be a predictor of diabetic retinopathy in multivariant analysis. Conclusion nailfold capillaroscopy is regarded a helpful noninvasive newly emerging tool to assess the capillaroscopic changes in diabetic patients as an indicator to diabetic complication development such as diabetic retinopathy.

Peripheral nailfold capillary microscopic abnormalities in rheumatoid arthritis are associated with arterial stiffness: Results from a cross-sectional study

Vascular injury eventually resulting in the establishment of cardiovascular disease is a serious complication in rheumatoid arthritis (RA). Nailfold videocapillaroscopy (NVC) is a non-invasive imaging modality that enables the quantitative and qualitative assessment of the peripheral microvasculature. Nevertheless, capillaroscopic patterns remain inadequately defined in RA, especially regarding their clinical significance as potential markers of systemic vascular impairment. Consecutive RA patients underwent NVC using a standardized protocol, to assess the following parameters: capillary density, avascular areas, capillary dimensions, microhemorrhages, subpapillary venous plexus, and presence of ramified, bushy, crossed and tortuous capillaries. Carotid-femoral pulse wave velocity (PWV) and pulse pressure were measured as well-acknowledged markers of large artery stiffening. The vast majority of our cohort (n = 44) presented a combination of non-specific and abnormal capillaroscopic parameters. Capillary ramification was associated with both PWV and pulse pressure, even after adjustment for cardiovascular risk factors and systemic inflammation. Our study highlights the high prevalence of a wide range of capillaroscopic deviations from the normal patterns in RA. Furthermore, it provides for the first time evidence of an association between structural disorders of the microcirculation and markers of macrovascular dysfunction, suggesting that NVC might have a role as an index of generalised vascular impairment in RA.

Nailfold Video-Capillaroscopic Changes in Adult Bangladeshi Patients With Systemic Lupus Erythematosus: Correlation With Disease Activity

Background: Peripheral microangiopathy is an important feature in systemic lupus erythematosus (SLE). Nailfold capillary (NFC) changes observed by nailfold videocapillaroscopy (NVC) may play a role in early detection of microangiopathy and assessment of disease activity in SLE. The aim of the study was to evaluate nailfold capillary changes, their diagnostic accuracy and NFC-pattern of changes in a group of Bangladeshi SLE patients in comparison to healthy subjects and to determine the correlation with disease activity in SLE. Methods: This cross-sectional study with a comparison group was conducted in CMCH, Chattogram; a Tertiary Care Hospital in Bangladesh. Results: Twenty-seven (n=27) Bangladeshi SLE patients who were diagnosed by ACR-1997 revised criteria for diagnosis of SLE and Twenty-seven (n=27) age-sex matched health subjects were included. All participants were subjected to full history taking, clinical examination, laboratory investigations as well as NVC examination. SLE disease activity was assessed by SLEDIA scoring tool and nailfold capillary changes were assessed with NFC-pattern of changes by applying NVC. Results: Mean (±SD) age of the SLE patient group was 31.2 (±7.8) years and female to male ratio was around 6:1. 23 out of 27(85.2%) patients had multiple phenotypes and 18 (66.6%) had either high or very high disease activity. Sub-papillary venous plexus (SPVP) was prominently visible more frequently in SLE patients and capillary density was reduced in SLE patients compared with healthy controls. Capillary changes in NVC were observed in 26 out of 27 (96.3%) patients. Major and scleroderma pattern were detected in 51.9% and 11.1% of the SLE patients; respectively. Nailfold capillary abnormalities were significantly more frequent in SLE patient than in healthy controls. More frequently found different abnormal morphological changes were seen with crossed capillary (66.7%), tortuous capillary (63%) and meandering capillary (37%). There was a significant positive correlation between disease activity of SLE and NFC-pattern of changes (r=0.443, p=0.021). Conclusion: Different abnormal nailfold capillary changes are quite common among patients with SLE, and nailfold capillary changes positively correlate with disease activity in SLE. Bangladesh J Medicine 2023; Vol. 34, No. 2(1) Supplement: 208

Developing Biomarkers for the Skin: Biomarkers for the Diagnosis and Prediction of Treatment Outcomes of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory decline and cognitive impairment. Research on biomarkers can aid in early diagnosis, monitoring disease progression, evaluating treatment efficacy, and advancing fundamental research. We conducted a cross-sectional longitudinal study to see if there is an association between AD patients and age-matched healthy controls for their physiologic skin characteristics, such as pH, hydration, transepidermal water loss (TEWL), elasticity, microcirculation, and ApoE genotyping. The study used the Mini-Mental State Examination (MMSE) and Clinical Dementia Rating-Sum of the Boxes (CDR-SB) scales as references to quantify the presence of disease, if any. Our findings demonstrate that AD patients have a dominantly neutral pH, greater skin hydration, and less elasticity compared to the control subjects. At baseline, the tortuous capillary percentage negatively correlated with MMSE scores in AD patients. However, AD patients who carry the ApoE E4 allele and exhibit a high percentage of tortuous capillaries and capillary tortuous numbers have shown better treatment outcomes at six months. Therefore, we believe that physiologic skin testing is a rapid and effective way to screen, monitor progression, and ultimately guide the most appropriate treatment for AD patients.

Results of Nailfold Videocapillaroscopy in Patients with Pseudoexfoliative Glaucoma.

The studied group consisted of 39 Caucasian patients with XFG and 32 patients in a control group. The patients were classified into two subgroups: the hypertensive pseudoexfoliative glaucoma (hXFG) subgroup and the normotensive pseudoexfoliative glaucoma (nXFG) subgroup. The nailfold videocapillaroscopy (NVC) was performed on all participants. The results of each NVC were classified as having a normal or abnormal pattern. There was no statistical difference between the results of an abnormal NVC pattern in the study group vs. the control group (p = 0.8773). Microhemorrhages were shown in 30.0% of patients with nXFG vs. the control group (6.25%) (p = 0.0520). Microhemorrhages tended to be more frequent in the XFG group (p = 0.1221). A prevalent number of tortuous capillaries was observed in hXFG patients with advanced glaucomatous neuropathy. Dilatation in the capillaries and microbleedings were observed in the group of patients with lower IOP values. Tortuosity in the capillaries was significantly more frequent in PEXG patients (XFG vs. control: p = 0.0386). No relationships between the results of NVC and age, c/d, BCVA, time of treatment, and visual field defect were found. Specific features of NVC examination differentiate nXFG from hXFG patients. Some capillaroscopic features may correlate with the patient's clinical status of XFG.

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.

A two-scale fractal permeability model for vuggy porous media

A vug is a small cavity in a porous medium that is relatively larger than interparticle pore spaces. Vuggy porous media are common in carbonate petroleum reservoirs and karst aquifers. Although small, the vugs can significantly affect the porosity and permeability of a rock. The real rock cores and outcrops indicate that the cumulative size distributions of interparticle pores and vugs both follow the fractal scaling law. In this paper, a two-scale fractal permeability model for natural vuggy porous media is developed based on the fractal characteristics of interparticle pores and vugs. In the proposed model, the interparticle pores of rock matrix are described as a bundle of tortuous capillary tubes. The vugs are embedded in rock matrix and are regarded as equipotential bodies, which change the tortuosity of matrix capillary tubes. Then, different matching relations between matrix capillary tubes and vugs are conducted to predict the permeability of a vuggy porous medium. The results show that the predicted permeability varies within a certain range. The maximum permeability is the case of larger vugs matching with the larger capillary tubes, and the minimum permeability is the converse case. The most probable permeability is calculated based on a set of random matching relations by using the Monte Carlo method. The validity of the proposed model is verified by comparing with experimental results and reference data in the literature. The parameter sensitivity analysis indicates that the fractal dimension of capillary tubes and their tortuosity, and the maximum diameter of capillary tubes and vugs have significant effects on the predicted permeability.

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.

Non-Darcian Displacement of Oil by a Micellar Solution in Fractal Porous Media

A Buckley–Leverett analysis with capillary pressure to model the oil displacement in fractal porous media is herein presented. The effective permeability for a non-Newtonian micellar fluid is calculated by a constitutive equation used to describe the rheological properties of a displacement fluid. The main assumption of this model involves a bundle of tortuous capillaries with a size distribution and tortuosity that follow fractal laws. The BMP model predicts two asymptotic (Newtonian) regions at low and high shear and a power-law region between the two Newtonian regions corresponding to a stress plateau. Both the stress at the wall and the fluidity are calculated using an imposed pressure gradient in order to determine the mobility of the solution. We analyze different mobility ratios to describe the behavior of the so-called self-destructive surfactants. Initially, the viscosity of the displacing fluid (micellar solution) is high; however, interactions with the porous media lead to a breakage process and degradation of the surfactant, producing low viscosity. This process is simulated by varying the applied pressure gradient. The resulting equation is of the reaction–diffusion type with various time scales; a shock profile develops in the convective time scale, as in the traditional Buckley-Leverett analysis, while at longer times diffusion effects begin to affect the profile. Predictions include shock profiles and compressive waves. These results may find application when selecting surfactants for enhanced oil recovery processes in oilfields.