A mathematical model for blood flow through an arterial bifurcation

By introducing the finite element technique, a study of blood flow through an arterial bifurcation is presented in this paper. The blood is represented by a modified model of thixotropic power-law fluids, for which the parametric values for blood, both in normal and pathological states, have already been established. The results for the velocity profiles, pressure and wall shear stress distributions are elucidated and discussed for normal old and diseased states. The separation and reattachment points are also located for different values of the Reynolds number and the flow behaviour index (n) of the model representing the blood. The analysis identifies low shear stress zones behind the stenosis along the outer wall and high shear stresses downstream of the apex. The increasing percentage of the stenosis and the increasing values of the Reynolds number facilitate the high shear stress zones, whereas the thixotropy of the blood depicts an inbuilt mechanism of reducing high shear stresses as well as flow reversal regions.     

Pulsatile tinnitus associated with a high jugular bulb and slow venous blood flow

A case of permanent pulsatile tinnitus of the left ear in a patient with hypertriglyceridemia is reported. The combined radiological study with computed tomography, magnetic resonance imaging, and digital angiography excluded a glomus tumor and revealed an enlarged, high-position jugular bulb with slow blood flow. Causes of pulsatile tinnitus are discussed. We conclude that imaging techniques play a major role in the diagnosis of head and neck vascular abnormalities.     

Pulsatile ocular blood flow variations with axial length and refractive error

Benign symmetric lipomatosis (BSL), also known as Madelung's disease, is a rare condition and characterized by diffuse but painless growth of unencapsulated lipomas. A close correlation to alcohol and nicotine abuse, metabolic disturbances and malignant tumours have been observed. Surgical treatment is frequently followed by recurrence, nevertheless, it can yield satisfactory functional and cosmetic results. A case of BSL with uncommonly distributed tumors is reported.     

Asymptomatic carotid artery bifurcation disease in patients with claudication

Deep vein thrombosis may occur in the axillary or subclavian veins in the upper extremities, sometimes in young patients without the typical risk factors for thrombus development. This unusual clinical situation usually follows strenuous activity and is often referred to as "effort" thrombosis. Since some cases have occurred with mild exertion and there is a lack of obvious predisposing vessel trauma, a more correct term might be "primary" thrombosis. Early recognition of this condition is necessary to prevent potentially fatal acute effects and minimize chronic sequelae.     

Pulsatile stretch in coronary arteries elicits release of endothelium-derived hyperpolarizing factor: a modulator of arterial compliance

We evaluated the effect of ketamine on the excitability of rabbits vagus nerve by measuring evoked compound action potentials. Histological examination was also done by means of electron microscopy on the nerves incubated in ketamine-Ringer's bicarbonate (RB) solution. We found that 0.05% ketamine causes complete suppression of the compound action potentials. The suppressed compound action potentials by incubating in 0.1% ketamine RB solution recovered completely after washing with ketamine-free RB solution. The electron microscopic examinations revealed no histological changes of the nerves incubated in 0.1% ketamine RB solution. We conclude that ketamine suppresses the nerve excitability causing no histological changes at the concentration below 0.1%.     

Colour flow duplex imaging of occlusive arterial disease of the lower limb

BACKGROUND: The development of duplex ultrasonography and colour flow imaging has greatly extended the scope of non-invasive assessment of lower limb arterial disease. This review questions whether recent advances might allow colour duplex imaging to displace arteriography as the primary imaging modality for native vessel occlusive disease. METHODS: A literature review was carried out based predominantly on a Medline database search of English language publications from 1985 to 1996. RESULTS: Increasing evidence indicates that colour duplex ultrasonography can accurately image the lower limb native arterial tree, and that colour duplex imaging can replace diagnostic arteriography in a large proportion of patients. CONCLUSION: Arteriography should no longer be considered the gold standard of imaging of peripheral arterial occlusive disease. Future studies should concentrate on the efficacy of colour duplex sonography in guiding clinical decision making.     

Nonwetting flow of a liquid through a packed bed with gas cross-flow

In this study, the effect of a cross-flow gas field on the percolating flow of a non-wetting liquid through a packed bed was investigated. Experiments were conducted to measure the liquid shift, due to the cross-flow of air, for the flow of aqueous barium chloride solutions and mercury percolating through beds of polyethylene and expanded polystyrene particles. An X-ray technique was used to visualize the liquid flow pattern through the packed bed. The liquid percolates through a packed bed as a series of rivulets and droplets which are continuously breaking up and coalescing. A mathematical model to predict the direction of the liquid rivulet/droplet flow under the influence of a gas flow field was developed. The model treats the liquid as a discrete phase and includes the effects of gravity, gas drag, and inertial and viscous bed resistance. The effective droplet/rivulet size is an important model parameter, and the model postulates that the droplet/rivulet size is a function of both the effective capillary size of the bed and the liquid flow rate. A simplified population balance analysis for droplet coalescence is used to predict the effect of liquid flow rate on droplet/rivulet size. The model predictions are consistent with the experiments.     

Unsteady flow in a rigid 3-D model of the carotid artery bifurcation

Colominic acid (CA), an alpha-(2-->8) N-acetylneuraminic acid (sialic acid) polymer (average molecular weight of 10 kDa) was activated by periodate oxidation of carbon 7 at the non-reducing end of the saccharide. The oxidized CA was then coupled to catalase by reductive amination in the presence of sodium cyanoborohydride. The extent of sialylation of catalase, estimated by ammonium sulfate precipitation as 3.8+/-0.4 (mean+/-S.D.) moles of CA per mole of catalase, did not improve significantly when depolymerized CA was used in the coupling reaction. At the end of the coupling reaction, sialylated catalase exhibited a two-fold (70%) retention of initial activity compared to enzyme controls (29-35%) subjected to the same conditions. Formation of sialylated catalase was confirmed by ammonium sulfate or trichloroacetic acid precipitation, molecular sieve chromatography and SDS-PAGE electrophoresis. Enzyme kinetics studies revealed an increase in the apparent Km of the enzyme from 70.0 (native) to 122.9 mmol l-1 H2O2 (sialylated catalase) indicating a reduction of enzyme affinity for the substrate (hydrogen peroxide) on sialylation. Compared to native enzyme, sialylated catalase was much more stable in the presence of specific proteinases, completely resisting degradation by chymotrypsin and losing only some of its activity in the presence of trypsin. The increased stability conferred to catalase by sialylation agrees with similar observations on enzymes modified by other hydrophilic molecules (e.g., monomethoxypoly(ethyleneglycol)) and suggests that steric stabilization with the biodegradable polysialic acid may prove an alternative means to render therapeutic proteins more effective in vivo.     

Ocular arterial flow hemodynamics in patients with diabetes mellitus

The purpose of this study was to investigate ocular blood flow hemodynamics in patients with diabetes mellitus. We used color Doppler sonography, in 22 normal subjects and 52 patients with (n = 25) or without (n = 27) diabetic retinopathy, to determine blood flow velocities and the resistive index of the central retinal artery. The resistive index of the central retinal artery in patients with diabetic retinopathy (0.85 +/- 0.09) was significantly greater (P < 0.01) than that in normal subjects (0.72 +/- 0.08) and in patients without diabetic retinopathy (0.81 +/- 0.09). The resistive index of the central retinal artery in the patients without diabetic retinopathy was also significantly greater than that of normal subjects (P < 0.01). The resistive index of ocular arterial flow was increased in the patients with diabetes mellitus and further increased in the presence of retinopathy. Increased resistance in the peripheral ocular vascular bed contributes to diabetic retinopathy, and this change is present before the appearance of overt diabetic retinopathy.     

Venous thrombosis causing arterial embolization to the same limb through a patent foramen ovale

We describe a patient who presented with acute ischemia affecting the left lower limb. Because a transthoracic echocardiogram was abnormal, a transesophageal study was arranged. This demonstrated an atrial septal aneurysm and right-to-left shunting of contrast, raising the possibility of paradoxical embolism. The diagnosis was confirmed by contrast venography, which showed extensive thrombosis in the deep veins of the left thigh, and a ventilation-perfusion scan which was consistent with multiple pulmonary emboli. Among the lessons from this case was the finding that in patients with arterial embolism the likely origin of the embolus should be considered and, in the absence of common risk factors (atrial fibrillation, rheumatic heart disease, left ventricular dilatation, widespread atheroma), occult venous thrombosis and a right-to-left shunt should be sought. In this select group of patients, transesophageal echocardiography is significantly more sensitive than transthoracic study and should be the investigation of choice. Second, in the patient described in this report the clinical signs of deep venous thrombosis (DVT) were masked by the more prominent features of acute arterial ischemia. Without the incidental echocardiographic abnormality, it is likely that the important diagnoses of DVT, pulmonary embolism, and paradoxical embolism would not have been made.     

Fluid flow through a solid-liquid dendritic interface

Fluid flow through a dendritic solid-liquid interfacial zone, during solidification, has been observed in a series of Sn-Pb alloys. It was found that liquid penetrates only a short distance into the zone, relative to the total thickness of the zone. The amount of solid present at the point of maximum penetration varies from 12 to 22 pct, and depends on the alloy concentration. Flow due to volume shrinkage, thermal convection, or solute convection well inside the zone, was not detected. Fluid flow through a wire mesh model of a thin section of the solid-liquid dendritic zone was examined. The results are not in agreement with that predicted for flow through a porous barrier, which had been found applicable to interdendritic fluid flow. Formerly Graduate Student, University of British Columbia, Vancouver, British Columbia, Canada     

Occlusive arterial disease of the hand due to repetitive blunt trauma: a review with illustrative cases

OBJECTIVE: to increase clinical awareness of the role of repetitive blunt trauma, often occupational, in the development of occlusive arterial disease of the hand. STUDY DESIGN: illustrative cases are presented to emphasize the varied etiology and clinical features of occlusive arterial disease of the hand resulting from repetitive blunt trauma and an historical review of the literature is presented. RESULTS: Occlusive arterial disease of the hand due to repetitive blunt trauma is a common but often preventable disorder. The superficial location of many of the arteries of the hands and digits plus their close proximity to the bones of the hand makes them uniquely susceptible to injury from repetitive blunt trauma. An ever increasing number of occupations and leisure activities have been causally related to occlusive arterial disease of the hand. The diagnosis of occupational occlusive arterial disease due to blunt trauma is suggested by eliciting a history of repetitive blunt trauma to the hand in a patient with symptoms and/or signs of digital ischemia. The dominant hand is most commonly involved, but the non-dominant hand or both hands are affected in certain occupations. Possible predisposing or aggravating factors include tobacco use and working in a cold environment. The diagnosis of occlusive arterial disease confined to the hand or digits is confirmed by non-invasive studies in the vascular laboratory and demonstrated by arteriography. Conservative measures and protection of the hand from further trauma is sufficient for most patients, with surgical therapy being reserved for patients refractory to medical therapy or those with more severe ischemia. CONCLUSION: occlusive arterial disease of the hand may be more common than formerly thought and is often preventable by the proper use of hand tools or instruments and hand protection. This is another type of occlusive arterial disease in which tobacco may be a predisposing or aggravating factor.     

The comparison of postoperative multiple organ failure with arterial disease to that with gastrointestinal cancer]

The clinical features of 22 postoperative multiple organ failure (MOF) patients, comprised of 8 with arterial disease (A-MOF) and 14 with gastrointestinal cancer (G-MOF), were investigated. Differences in the operative time, blood loss, and mortality were not significant. The initial organ impaired was the lungs in 78.6% of G-MOF patients and the heart or kidneys in all A-MOF patients. Infection developed in over 80% of both groups. In many A-MOF patients, the pneumonia or septicemia developed secondary to organ failure, while intraabdominal infection triggered respiratory failure in many G-MOF patients. Our organisms in infected specimens and their antibiotic sensitivities was valuable for the early administration of effective antibiotics. Upper gastrointestinal tract bleeding was important in the prognosis of both groups and occurred more frequently in A-MOF than in G-MOF patients. Consumption coagulopathy in A-MOF patients and DIC induced by infection in G-MOF patients mainly caused such bleeding. Preoperative administration of heparin was effective in improving coagulopathy. Furthermore, measurement of intramural pH with tonometer in the stomach and gastric irrigation with oxygenated perfluorochemicals were effective in the prediction and prevention of gastrointestinal bleeding.     

Carotid arterial blood flow in the ovine fetus as a continuous measure of cerebral blood flow

Principles derived from a group of 46 ML of the mantle zone are presented: Mantle pattern of a ML and its cytological structure are mostly sufficient for positive basic diagnosis. Diffuse mantle zone ML need detection of BCL-1 and CD5 hyperexpression which are characteristic for small-cell and centrocytoid forms when compared with BCL-2 positive centrofollicular lymphomas. B monocytoid lymphomas from the parafollicular subgroup as well as plasmacytoid ML from the marginal subgroup retain faint BCL-1 positivity but lose CD5 positivity. That may results in attempt of problematic narrowing of mantle zone definition because of existence of the mixed cellularity forms of mantle zone ML. Nodular mantle zone ML are clinically recognized late and are unsensitive to treatment which is opposite to the original idea of their relative benignity. M-coding of mantle zone ML is very defective because the codes do not separate nodular (perifollicular) and diffuse variants.     

Asymptomatic coelio-mesenteric arterial thrombosis in a patient with Vaquez''s disease (author''s transl)

A female infant with total monosomy 21 identified by Q banding is described. The main clinical features were hypertonia, prominent occiput, hypertelorism, antimongoloid slant of the eyes, broad nose, "antimongoloid", character of dermatoglyphics. Both parents are phenotypically as well as karyotypically normal.     

A model for blood flow through a stenotic tube

This article deals with the introduction of the modified Casson's fluid model as the true representation for the blood for the steady laminar flow through a small diameter artery with axi-symmetric identical double stenoses in series. The governing equations are solved by using the finite element method. The results for the velocity profiles, the pressure and the wall shear stress distributions in addition to the location and length of the flow reversal zones have been brought out and discussed in reference to the severity of the disease. It has been observed that the non-Newtonian nature of the blood helps in reducing the magnitude of the peak wall shear stress at the throat and the length of the reversed flow regions in the post stenotic dilatation.     

Outcomes of balloon coronary angioplasty of bifurcation stenoses in patients with ischemic heart disease

Specialists of the Research Institute of Urology have practiced combination of transurethral resection (TUR) with electrovaporization in endoscopic treatment of bladder cancer (BC) since 1995. A total of 46 patients with transient cell BC (29 males and 17 females aged 49-87) stage Ta-T1 (32 patients) and T2-T3b (14 patients) underwent TUR or electrovaporization (if morphologically verified) of the exophytic part of the tumor. In addition, electrovaporization of the base of the tumor was made. Main indications for such treatment were standard indications for TUR in contraindications for more radical treatment. 6-24-month follow-up was possible in 23(71.9%) patients with superficial BC (group 1) and in 9(64.2%) patients with invasive BC (group 2). Endoscopically, the recurrence was detected in 3(13%) and 5(55.5%) patients of group 1 and 2, respectively. They were reoperated on with electrovaporization. It is inferred that TUR-vaporization of the bladder is an effective endoscopic treatment of superficial BC. Electrovaporization is a good palliative treatment in patients with invasive BC when radical surgery is impossible. It inhibits the progression of the disease, prevents hemorrhages due to the tumor destruction, reduces intraoperative blood loss, improves endoscopic visualization. It may also increase the operation ablasticity.