Luminal Diameter Ratio Research Articles

Ultrasonographic measurement of the prostatic dimension-to-aortic luminal diameter in healthy intact male dogs and dogs with benign prostatic hyperplasia.

To establish ultrasonographic measurements of the prostatic dimension-to-aortic luminal diameter ratios including the prostatic volume-to-aortic luminal diameter ratio in healthy, intact male dogs and compare these ratios between healthy dogs and dogs affected by benign prostatic hyperplasia. Healthy dogs (n = 75) and dogs affected by benign prostatic hyperplasia (n=104) were included in the study. Prostate length, width, average height and aortic luminal diameter were measured from ultrasonographic images. In addition, prostatic volume was calculated, and prostatic volume-to-aortic luminal diameter were also compared. In healthy dogs, aortic luminal diameter was significantly associated with bodyweight and the prostatic width while body condition scores, prostate length and prostatic average height were not associated. Prostatic dimension-to-aortic luminal diameter ratios and prostatic volume-to-aortic luminal diameter ratio was not significantly different among dogs with different body condition scores either in healthy dogs or dogs affected by benign prostatic hyperplasia, except prostatic volume-to-aortic luminal diameter ratio in benign prostatic hyperplasia. Prostatic dimension-to-aortic luminal diameter ratios were significantly higher in benign prostatic hyperplasia while prostatic volume-to-aortic luminal diameter ratio significantly higher in healthy dogs. Prostatic dimension-to-aortic luminal diameter ratios demonstrated medium to high sensitivity and specificity when distinguishing between healthy dogs and dogs affected by benign prostatic hyperplasia. Prostatomegaly, should be considered when the prostatic dimension-to-aortic luminal diameter ratios increase. The calculated cut-off values were 3.68, 4.46 and 3.06 for prostate length-to-aortic luminal diameter, prostatic width- to-aortic luminal diameter and prostatic average height-to-aortic luminal diameter, respectively. The prostatic dimension-to-aortic luminal diameter ratios could be useful to evaluate the size of the prostate in dogs, as it is unaffected by the body condition scores.

Diagnosis of Hirschsprung disease by hydrocolonic sonography in children.

To compare hydrocolonic sonography with histopathology for diagnosing children with symptoms highly suggestive of Hirschsprung disease (HD). In this prospective study, patients presenting refractory constipation highly suggestive of HD underwent hydrocolonic sonography with retrograde infusion of saline into the colon. The dilated segments, narrowed segments, luminal diameter ratio, transition zone (TZ), thickening, and blood perfusion of the upstream bowel were evaluated. The sensitivity and specificity of combined and single parameters were determined in comparison with biopsy. One hundred and three children were included in this study; 49 were confirmed to have HD. The luminal diameter ratio showed superiority over other parameters. An area under the curve (AUC) of 0.969 (95% confidence interval [CI]: 0.936-1.000) and a cutoff value of 1.51 were established by receiver operating characteristic (ROC) curve analysis of the luminal diameter ratio (sensitivity: 89.8%; specificity: 96.3%). By combining the luminal diameter ratio as the major criterion with two minor criteria, hydrocolonic sonography showed the same sensitivity (91.8%) and better specificity (96.3% vs 87%) than contrast enema, but this difference was not statistically significant (p = 0.063). Consistency analysis showed a kappa value of 0.825 (p < 0.001), indicating excellent agreement between hydrocolonic sonography and contrast enema. Hydrocolonic sonography is a valuable diagnostic tool with both high sensitivity and specificity for HD diagnosis, allowing morphological and vascular assessments of the colon, and correlates well with contrast enema. In the appropriate setting, hydrocolonic sonography may be an alternative screening method for HD in a large group of children with constipation. Key Points • Hydrocolonic sonography is a simple, well-tolerated diagnostic tool with both high sensitivity and specificity for HD diagnosis. • Hydrocolonic sonography allows morphological and vascular assessments of the colon, and correlates well with contrast enema. • Hydrocolonic sonography is a possible alternative modality for paediatric patients highly suggestive of HD.

Cutting balloon angioplasty on branch pulmonary artery stenosis in pediatric patients.

To identify medium-term results following cutting balloon angioplasty (CBA) for branch pulmonary artery stenosis (PAS) and predictors of successful intervention. CBA has emerged as a successful alternative therapy for PAS resistant to conventional balloon angioplasty techniques but there is little information on medium and long-term outcomes. This is a descriptive, single center, retrospective chart review of pediatric patients who underwent CBA for PAS at Arkansas Children's Hospital between May 2005 and December 2020. We reviewed demographics, procedural specifics, and 30-day complications. Forty-four patients underwent pulmonary artery CBA on 114 pulmonary artery segments through 126 catheterization cases, totaling 148 CBA events. Thirty-three individual pulmonary arteries underwent repeat intervention. Average minimal luminal diameter increase from pre-CBA to end of follow-up was 57% (CI, 38%-75%). Absence of Tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries (TOF/PA/MAPCAs) and the absence of Alagille Syndrome, Williams Syndrome, or Arterial Tortuosity Syndrome (ATS) were associated with increased odds of sustained success by 70% (CI, 0.11-0.79) and 91% (CI, 0.02-0.56), respectively. Increasing the cutting balloon diameter-to-minimal luminal diameter ratio by 0.5 increased odds of successful intervention by 2.37-fold (CI, 1.7-3.3). Seven patients had 30-day complications including one death. In the longest follow-up to date of children and adolescents who underwent CBA for branch PAS, we found that there was moderate medium-term success. Additionally, absence of TOF/PA/MAPCAs, absence of Alagille Syndrome, Williams Syndrome, or ATS, and high cutting balloon diameter-to-minimal luminal diameter ratio are predictors of sustained results.

Low-GDP, pH-neutral solutions preserve peritoneal endothelial glycocalyx during long-term peritoneal dialysis.

During peritoneal dialysis (PD), solute transport and ultrafiltration are mainly achieved by the peritoneal blood vasculature. Glycocalyx lies on the surface of endothelial cells and plays a role in vascular permeability. Low-glucose degradation product (GDP), pH-neutral PD solutions reportedly offer higher biocompatibility and lead to less peritoneal injury. However, the effects on the vasculature have not been clarified. Peritoneal tissues from 11 patients treated with conventional acidic solutions (acidic group) and 11 patients treated with low-GDP, pH-neutral solutions (neutral group) were examined. Control tissues were acquired from 5 healthy donors of kidney transplants (control group). CD31 and ratio of luminal diameter to vessel diameter (L/V ratio) were evaluated to identify endothelial cells and vasculopathy, respectively. Immunostaining for heparan sulfate (HS) domains and Ulex europaeus agglutinin-1 (UEA-1) binding was performed to assess sulfated glycosaminoglycans and the fucose-containing sugar chain of glycocalyx. Compared with the acidic group, the neutral group showed higher CD31 positivity. L/V ratio was significantly higher in the neutral group, suggesting less progression of vasculopathy. Both HS expression and UEA-1 binding were higher in the neutral group, whereas HS expression was markedly more preserved than UEA-1 binding in the acidic group. In vessels with low L/V ratio, which were found only in the acidic group, HS expression and UEA-1 binding were diminished, suggesting a loss of glycocalyx. Peritoneal endothelial glycocalyx was more preserved in patients treated with low-GDP, pH-neutral solution. The use of low-GDP, pH-neutral solutions could help to protect peritoneal vascular structures and functions.

Luminal diameter ratio of Vieussens' arterial ring is valuable in determining appropriate clinical management for patients with pathologic Vieussens' arterial ring

BackgroundAlthough the adverse events of pathologic Vieussens' arterial ring (VAR) have been reported, it is difficult to determine optimal clinical management. Thus, we hypothesized that the luminal diameter ratio of VAR obtained from coronary computed tomography angiography (CCTA) could be used as a clinical tool to inform appropriate patient management. MethodA total of 29 patients with pathologic VAR were retrospectively recruited for this study. The VAR luminal diameter ratio was defined as a quotient of VAR fistula divided by the orifice of RCA or LAD, based on which, patients were divided into small fistula group and large fistula group. The AUC, sensitivity, specificity, positive and negative predictive values were obtained from ROC curve. The cutoff value of the VAR luminal diameter ratio was calculated and assessed during the follow-up. ResultsThe VAR luminal diameter ratio of fistula/RCA orifice was 0.505 ± 0.098 in small fistula group and 1.020 ± 0.150 in large fistula group. The VAR luminal diameter ratio of fistula/LAD orifice was 0.507 ± 0.123 in small fistula group and 1.039 ± 0.151 in large group. The value was correlated with the choice of the treatment (r = 0.643 p < 0.01, r = 0.627 p < 0.01). The AUC, sensitivity, specificity, positive and negative predictive values were 0.803, 54.5%, 100%, 100% and 78.3% of the fistula/RCA orifice ratio and 0.833, 63.64%, 94.44%, 87.5% and 81.0% of the fistula/LAD orifice ratio, respectively. The cutoff values of both fistula/RCA orifice and fistula/LAD orifice ratios were 0.676. ConclusionsThe VAR luminal diameter ratio may be a valuable index to determine appropriate treatment for patients with pathologic VAR.

Stenting-induced Vasa Vasorum compression and subsequent flow resistance: a finite element study.

Vascular stenting is a common intervention for the treatment for atherosclerotic plaques. However, stenting still has a significant rate of restenosis caused by intimal hyperplasia formation. In this study, we evaluate whether stent overexpansion leads to Vasa Vasorum (VV) compression, which may contribute to vascular wall hypoxia and restenosis. An idealized multilayered fibroatheroma model including Vasa Vasorum was expanded by three coronary stent designs up to a 1.3:1 stent/artery luminal diameter ratio (exp1.1, exp1.2, exp1.3) using a finite element analysis approach. Following Poiseuille's law for elliptical sections, the fold increase in flow resistance was calculated based on VV compression in the Intima (Int), Media (Med) and Adventitia (Adv). The VV beneath the plaque experiences the smallest degree of compression, while the opposite wall regions are highly affected by stent overexpansion. The highest compressions for Adv, Med and Int at exp1.1 are 60.7, 65.9, 72.3%, at exp1.2 are 62.1, 67.3, 73.5% and at expp1.3 are 63.2, 68.7, 74.8%. The consequent fold increase in resistance to flow for Adv, Med and Int at exp1.1 is 3.3, 4.4, 6.6, at exp1.2 is 3.5, 4.7, 7.2 and at exp1.3 is 3.8, 5.1, 7.9. Stent overexpansion induces significant VV compression, especially in the Intima and Media layers, in agreement with previously observed Media necrosis and loss in elasticity after stenting. The observed steep increase in flow resistance suggests the blood flow and associated oxygen delivery would drop up to five times in the Media and almost eight in the Intima, which may lead to intimal hyperplasia and restenosis.

Potential MR Enterography Features to Differentiate Primary Small Intestinal Lymphoma From Crohn Disease.

OBJECTIVE. The purpose of this study was to assess the MR enterographic features of primary small intestinal lymphoma (PSIL) and compare them with active Crohn disease (CD) presenting with severe (≥ 10 mm) mural thickening of the small bowel. MATERIALS AND METHODS. This retrospective study included 15 patients with pathologically proven PSIL and 15 patients with active inflammatory CD with severe mural thickening. Various morphologic, enhancement, and diffusion parameters were compared between the two groups at MR enterography. The ratios of the upstream to involved luminal diameter and mural thickness to luminal diameter in the involved segment were calculated. An attempt was made to define a predictive model (morphologic score) for discriminating PSIL from CD with severe mural thickening. RESULTS. Patients with PSIL were more likely than those with CD to have unifocal disease (66.7% vs 20.0%, p = 0.025), circumferential involvement (86.7% vs 26.7%, p < 0.001), luminal dilatation (60.0% vs 7.0%, p = 0.005), and an attenuated fold pattern (53.3% vs none, p < 0.001). They were less likely to have serosal surface involvement (40.0% vs 100%, p = 0.001) and mesenteric fat infiltration (33.3% vs 100%, p < 0.001). Median upstream to involved luminal diameter ratio (1.5 vs 9.6, p < 0.001) and mural thickness to involved luminal diameter ratio (1.1 vs 4.3, p = 0.044) were significantly lower in patients with PSIL than in those with CD with severe mural thickening. No significant difference was observed in enhancement and diffusion measures. Morphologic score was based on the presence of luminal dilatation, unifocal involvement, mesenteric fat infiltration, and luminal stricture, yielding accuracy of 98% for differentiation between PSIL and CD with severe mural thickening. CONCLUSION. Morphologic features seen at MR enterography rather than enhancement or diffusion parameters may be valuable for differentiation of PSIL from active CD with severe mural thickening with significantly lower ratios of upstream to involved luminal diameter and mural thickness to involved luminal diameter in PSIL.

Vasculopathy plays an important role during the development and relapse of encapsulating peritoneal sclerosis with conventional peritoneal dialysis solutions.

Encapsulating peritoneal sclerosis (EPS) is an uncommon but life-threatening complication of peritoneal dialysis (PD) therapy. The causative factors of EPS remain unclear. Pathological studies of the peritoneum affected by EPS and relationships with clinical factors including PD solutions remain lacking. The objective of this study was to examine peritoneal samples from EPS patients and to identify the associations of peritoneal pathology with different clinical factors. Peritoneal specimens were obtained at the time of surgical enterolysis in Tsuchiya General Hospital from 1993 to 2016. A total of 223 PD patients were enrolled and analyzed. Tissues were fixed with formalin and processed with hematoxylin and eosin and Masson's trichrome staining, as well as immunohistochemical staining for CD31 and CD68. Evaluations could be made in 174 patients who received surgical enterolysis. Conventional or pH-neutral low-glucose degradation product PD solutions were utilized during PD treatment. The conventional PD solution group showed less angiogenesis (P = 0.013) but more severe vasculopathy, in the form of a lower ratio of luminal diameter to vessel diameter (L/V ratio) (P < 0.001) in association with longer PD treatment. Multivariate Cox proportional hazard models revealed that L/V ratio (per 0.1 increase, hazard ratio = 0.88, 95% confidence interval 0.77-0.99, P = 0.047) was significantly associated with a lower incidence of EPS relapse. In contrast, most of the cases in the pH-neutral solution group showed milder vasculopathy. The pathology of EPS differed between conventional and pH-neutral solution groups. Vasculopathy was related to the development and relapse of EPS in the conventional solution group.

Impact of gonadal status on ultrasonographic renal parenchymal dimensions in healthy cats.

The aim of this study was to evaluate the effect of gonadal status on ultrasonographic renal parenchymal dimensions in healthy cats. Forty healthy cats (10 intact males, 10 intact females, 10 castrated males and 10 spayed females) presented to the Division of Obstetrics, Gynecology and Reproduction, and the Diagnostic Imaging Unit at The Small Animal Teaching Hospital, Faculty of Veterinary Science, Chulalongkorn University. They were ultrasonographically examined to assess renal length, aortic luminal diameter, cortical thickness and medullary thickness. Regardless of gonadal status, the renal length, aortic luminal diameter, cortical thickness and medulla thickness of males were greater than those of females (P <0.05). In general, neutered cats had thicker medullae (0.36 ± 0.08 cm) and higher mean renal length:aortic luminal diameter ratio (12.15 ± 1.48) than intact cats (0.32 ± 0.08 cm and 11.22 ± 1.37 cm, respectively) (P <0.05), but no differences were observed in renal length, cortical thickness or aortic luminal diameter. Interestingly, when comparing between sexes with relatively equal body weight, only sex had an impact on renal length. Gonadal status has an effect on medullary thickness and mean renal length:aortic luminal diameter ratio.

Effects of long-term treatment with low-GDP, pH-neutral solutions on peritoneal membranes in peritoneal dialysis patients.

The morphological changes induced by bio-incompatible peritoneal dialysis (PD) solutions are well known. However, the morphological damage induced by long-term low-glucose degradation product (GDP), pH-neutral solutions has not been reported in detail. The aim of this study was to investigate the long-term effects of pH-neutral PD solutions on morphological and functional changes in the peritoneal membrane. We assessed peritoneal membrane biopsy samples from PD patients treated with acidic (Conventional group) or pH-neutral solutions (pH-neutral group) using pathology and immunopathology techniques. Analyses of 54 Conventional and 73 pH-neutral group samples showed that the peritoneal membrane was thicker (P < 0.001), the ratio of luminal diameter to vessel diameter (L/V ratio) was significantly smaller (P < 0.001), and advanced glycation end-product (AGE) accumulation was higher in the Conventional than in the pH-neutral group (P < 0.001). Comparison of samples from patients in the Conventional (n = 33) and pH-neutral groups (n = 33) who were treated for 4-10years also showed significant differences in peritoneal thickness, L/V ratio and AGE score. Furthermore, the L/V ratio in the Conventional group significantly decreased over time (P < 0.01); however, no such change was seen in the pH-neutral group. Peritoneal membrane thickness was not associated with PD duration in both groups. Dialysate-to-plasma ratio of creatinine and L/V ratio negatively correlated with PD treatment duration in the Conventional group, but not in the pH-neutral group. These findings suggest that pH-neutral solutions prevent the morphological and functional peritoneal changes induced by long-term PD treatment.

Association Between Champagne Bottle Neck Sign of Internal Carotid Artery and Ipsilateral Hemorrhagic Stroke in Patients with Moyamoya Disease

To assess association between champagne bottle neck sign (CBNS) in carotid artery and intracranial hemorrhage in patients with moyamoya disease (MMD). This retrospective study included 76 consecutive patients with MMD without definite risk factors associated with intracranial hemorrhage who underwent preoperative angiography from January 2016 to December 2017. CBNS was defined as luminal diameter ratio of internal carotid artery/common carotid artery ≤0.5 on angiography. The right and left cerebral hemisphere in each patient was separately identified as hemorrhagic and nonhemorrhagic. Association between CBNS and intracranial hemorrhage was analyzed. Of 76 patients with MMD, intracranial hemorrhage was found in 44 of 152 (28.9%) hemispheres, and 6.8% (3/44) had multiple events. Comparing carotid arteries without intracranial hemorrhage in ipsilateral hemispheres, patients with intracranial hemorrhage in the ipsilateral hemisphere had significantly smaller luminal diameter ratio of internal carotid artery/common carotid artery (0.49 ± 0.11 vs. 0.55 ± 0.12, P < 0.01) and higher prevalence of CBNS (63.7% vs. 41.7%, P= 0.01). Comparing hemispheres with intracranial hemorrhage, patients with ipsilateral carotid artery CBNS had significantly higher prevalence of hemorrhage in posterior territories than patients without CBNS (57.1% vs. 23.1%, P= 0.05). Logistic regression revealed that CBNS was significantly associated with ipsilateral intracranial hemorrhage before (odds ratio= 2.45; 95% confidence interval, 1.19-5.05; P= 0.02) and after (odds ratio= 3.43; 95% confidence interval, 1.50-7.87; P < 0.01) adjusting for female sex, lenticulostriate anastomosis, and choroidal anastomosis. CBNS is significantly associated with intracranial hemorrhage in the ipsilateral hemisphere in patients with MMD, particularly intracranial hemorrhage in posterior territories.

12주간 복합운동이 비만 성인여성의 경동맥 순응도 및 수축기 혈류속도와 내경 비에 미치는 영향

12주간 복합운동이 비만 성인여성의 경동맥 순응도 및 수축기 혈류속도와 내경 비에 미치는 영향

Non-Invasive Assessment of Coronary Arterial Tone Using Trans-Thoracic Doppler Echocardiography

As coronary flow velocity (CFV) is inversely related to the luminal size that exists for the myocardial bed, the elevated arterial tone can be assessed as the higher flow velocity in the epicardial artery. We examined the usefulness of transthoracic Doppler echocardiography (TTDE) for the assessment of coronary arterial tone. A total of 32 patients underwent TTDE and angiography. The luminal diameter (LD) in the left anterior descending artery (LAD) was measured by using quantitative coronary angiography before and after nitroglycerin (NTG) administration. The ratio of post NTG LD to the control (LD(NTG/Pre)) was assessed as a standard parameter of coronary arterial tone. We also measured CFV and CFV reserve (CFVR) at the LAD by TTDE. We evaluated the change of CFV (CFV(NTG/Pre)) and CFVR (CFVR(NTG/Pre)) following NTG administration. The LD increased from 1.98+/-0.46 to 2.51+/-0.34 mm (p<0.001), while the CFV decreased from 23.9+/-10.0 to 16.3+/-5.6 cm/s (p<0.03), and the CFVR increased from 2.39+/-0.65 to 3.56+/-1.12 (p<0.001). There were significant correlations between CFV(NTG/Pre) and LD(NTG/Pre) (p<0.0001, R2 = 0.532), and between the CFVR(NTG/Pre) and LD(NTG/Pre) (p<0.0001, R2 = 0.715). TTDE can assess the coronary arterial tone by measuring the responses of CFV and CFVR to NTG administration.

Prediction of restenosis after coronary angioplasty by use of a new index: TIMI frame count/minimal luminal diameter ratio.

It has been shown recently that postangioplasty coronary flow reserve and the degree of residual stenosis have a modest predictive value for short- and long-term clinical outcomes after coronary angioplasty. Corrected TIMI frame count (CTFC) is a simple quantitative index of coronary blood flow. Its relationship with Doppler coronary flow velocity and clinical outcome after coronary angioplasty has not been fully clarified. The aim of this study was to identify clinical, angiographic, and functional predictors of clinical and angiographic restenosis after conventional coronary angioplasty. We studied 70 consecutive patients in whom intracoronary Doppler flow-velocity measurements were performed before and after angioplasty. Patients were evaluated for restenosis by clinical follow-up, exercise stress test/(201)Tl scintigraphy, and follow-up angiography, which was performed at 10. 5+/-10.3 months in 63 patients. According to the results of univariate analysis, a new index, postangioplasty CTFC/minimal luminal diameter (MLD) ratio, was created. Multivariate analysis revealed that CTFC/MLD ratio was the only independent predictor of angiographic (OR 2.02; 95% CI 1.37 to 2.97; P<0.0004) and clinical (OR 1.60; 95% CI 1.15 to 2.21; P<0.005) restenosis. The receiver operating characteristic curve area of this index was 79% for angiographic and 73% for clinical restenosis. The optimal CTFC/MLD ratio cutoff values were 7.88 for angiographic and 7.94 for clinical restenosis, respectively. Our data indicate that postangioplasty CTFC/MLD ratio, which incorporates both the angiographic and functional features of coronary lesions, is a reliable, objective, and inexpensive index for prediction of angiographic and clinical restenosis after conventional coronary angioplasty.

The microvascular venous pool and its ultrastructural associations in mouse molar periodontal ligament — Periodontal Microvasculature &amp; Nerves

Abstract This transmission electron microscopic investigation revealed that the periodontal ligament of mouse mandibular molars contained a microvascular bed typified by a predominance of vessels corresponding in luminal diameter with postcapillary-venules. Vessels in the cervical region showed large areas of the endothelium and basement membrane directly exposed to the investing collagen fibre bundles. Cervical venous capillaries had a ratio of luminal diameter to wall thickness averaging 20:1, whereas postcapillary-sized venules approximated 30:1. In the apical third of the ligament the venous vessels became significantly larger and morphologically conformed to ‘apericytic' postcapillary venules, since they appeared to be devoid of pericytes, and comprised endothelial-like tubes with only the basement membrane and occasional veil cells intervening between the endothelium and the enveloping collagen fibre bundles. The ratio of luminal diameter to wall thickness exceeded 60:1 in these apical vessels. This venous capillary pool of the ligament consisted of vessels which differed ultrastructurally from the postcapillary venules described as being typical of other microcirculatory systems. Nerve endings, indicated by aggregations of mitochondria, were present adjacent to encapsulated myelinated and unmyelinated nerves located alongside cervical venous capillaries and postcapillary-sized vessels. Encapsulated nerves and nerve groups in the apical region corresponded with descriptions of putative periodontal mechanoreceptors in man, but differed in being related to postcapillary-sized vessels and not collecting veins as reported in human ligament. Unmyelinated axons were frequently located within 0.25 microns of the endothelium of venous capillaries and venules. The oxytalan meshwork fibres were associated with all categories of vessels observed including capillaries having luminal diameters less than six microns. These findings demonstrate that the mouse periodontal ligament has unique, and previously unreported, vascular and neural anatomical features related to its operant role and dynamic behaviour in supporting masticatory loads. Some functional implications of the present findings are discussed.

Ultrastructure of mammalian venous capillaries, venules, and small collecting veins

A combination of light microscopical and electron microscopical techniques were used in this investigation of the venous drainage system of the subdermal microvessels of rabbit skin. The vessels were sectioned longitudinally to facilitate analysis of different segments of the venules. By using as criteria the luminal diameter, the perivascular elements, and the relationship of the vessel to the local vascular pattern, the venous part of the microcirculatory bed is divided into the following segments. (a) Venous capillary: capillaries with a diameter of up to about 8 μ which can be identified as being continuous with the larger postcapillary venules. The endothelium is usually thin, and occasionally displays fenestrations. Occasional pericytes occur. The ratio of luminal diameter to vascular wall thickness is about 20:1. (b) Postcapillary venule: microvessels with a diameter of about 8–30 μ, continuous with venous capillaries. With increasing luminal diameter, these vessels show a gradual increase in the number of pericytes and veil cells (fibroblasts). The ratio of luminal diameter to vascular wall thickness averages 10:1. (c) Collecting venule: 30–50 μ. Vessels with one complete layer of pericytes and a complete layer of veil cells. Occasional primitive smooth muscle cells occur. The ratio of luminal diameter to vascular wall thickness is 30:1. (d) Muscular venule: 50–100 μ. Nearly all periendothelial cells are smooth muscle cells that overlap and sometimes form two layers. Myoendothelial junctions occur, but are rare. The ratio of luminal diameter to vascular wall thickness is 50:1. (e) Small collecting veins: 100–300 μ. Vessels with a prominent media consisting of continuous layers of smooth muscle cells. The ratio of luminal diameter to vascular wall thickness averages about 100:1.