ABSTRACT
A hybrid method for investigating pulsatile fluid flow in a long, thin, artery-like tube subjected to external excitations is presented. The non-linear partial differential equations governing the motion of the system, which incorporate the influence of circumferential strains, are solved by a combination of a finite element method, a finite difference method and a method of characteristics with interpolation. An initially axially stretched elastic tube conveying pulsating fluid, simply supported at both ends, is modelled to assess the effect of external harmonic excitation on the dynamic responses of the tube and the fluid flow. The results agree well with new experimental data. Comparison of the predicted results with those of a decoupled model demonstrates that it is necessary to consider the mechanism of fluid-structure interaction fully in the study of initially stretched cylindrical tubes conveying pulsatile fluid flow. An analysis of these coupling effects is presented for Womersley numbers alpha = 2.81 and 3.97 and a mean flow Reynolds number Re = 875.
Subject(s)
Aorta/physiology , Hemodynamics , Prostheses and Implants , Vibration , Biomedical Engineering , Blood Flow Velocity , Humans , Materials Testing , Models, Cardiovascular , Models, Statistical , Nonlinear Dynamics , Pulse , United KingdomABSTRACT
Hemodynamic forces such as fluid shear stress have been shown to modulate the activity of an expanding family of genes involved in vessel wall homeostasis and the pathogenesis of vascular disease. We have investigated the effect of shear stress on tissue factor (TF) gene expression in human endothelial cells (ECs) and in a rat arterial model of occlusion. As measured by reverse transcriptase polymerase chain reaction, exposure of ECs to 1.5 N/m2 shear stress resulted in a time-dependent induction of endogenous TF transcripts of over 5-fold. Transient transfection of TF promoter mutants into cultured ECs suggests the involvement of the transcription factor Egr-1 in mediating the response of the TF promoter to shear stress. To address the importance of flow induction of Egr-1 in vivo, we have established a flow-restricted rat arterial model and determined the level of expressed Egr-1 and TF at the site of restricted flow using immunohistochemistry. We report an increase in the level of Egr-1 and TF protein in ECs expressed at the site of restricted flow. Elevated expression of Egr-1 and TF is restricted to a highly localized area, as evidenced by the fact that no significant increase in level can be detected at arterial sites distal to the site of occlusion. These findings suggest a direct role for Egr-1 in flow-mediated induction of TF and further substantiate the importance of shear stress as a modulator of vascular endothelial gene function in vivo.
Subject(s)
DNA-Binding Proteins/physiology , Immediate-Early Proteins , Promoter Regions, Genetic/physiology , Thromboplastin/genetics , Transcription Factors/physiology , Animals , Binding Sites/physiology , Cells, Cultured , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Early Growth Response Protein 1 , Endothelium, Vascular/cytology , Endothelium, Vascular/physiology , Humans , Male , Mutation/physiology , Promoter Regions, Genetic/genetics , Rats , Rats, Wistar , Response Elements/genetics , Stress, Mechanical , Transcription Factors/genetics , Transcription Factors/metabolism , TransfectionABSTRACT
A mathematical model is developed to investigate blood flow in arterial stenoses up to Reynolds numbers of 1000. The approach is based on Thwaites' method, normally used to treat laminar boundary layer development over a body in a freestream. The model is applicable to any axisymmetric stenosis geometry in all laminar physiological flow regimes, has a minimum of externally input parameters and is implemented as a short program on a personal computer. Maximum bounds on the expected errors are derived by comparison with known results from Poiseuille flow in a pipe. Agreement with shear stresses reported by other researchers using computational fluid dynamics is within 13% rms. The method has been specifically designed to be a useful predictive tool for biomedical investigators.
Subject(s)
Arteriosclerosis/physiopathology , Blood Flow Velocity , Computer Simulation , Models, Cardiovascular , Stress, Mechanical , HumansSubject(s)
Erythromycin/therapeutic use , Infant, Premature/microbiology , Ureaplasma Infections/drug therapy , Ureaplasma urealyticum/isolation & purification , Data Interpretation, Statistical , Humans , Infant, Low Birth Weight/microbiology , Infant, Newborn , Selection Bias , Trachea/microbiologyABSTRACT
Recent studies show an association between the presence of Ureaplasma urealyticum in tracheal aspirates and bronchopulmonary dysplasia. We hypothesized that among infants with birth weights < or = 1,250 g and respiratory disease, those with U. urealyticum in their tracheal aspirates would have radiographic evidence of more-severe pulmonary disease more often than would those without this organism. A total of 292 low-birth-weight infants who had endotracheal aspirate cultured within 7 days of birth were enrolled. The radiographic outcome variables were pneumonia, early severe bronchopulmonary dysplasia (precocious), and chronic lung disease. Microorganisms were isolated from 128 infants (44%); U. urealyticum was isolated from 44 (15%). Pneumonia was significantly more common in infants with than without U. urealyticum (30% vs. 16%, P = .03). U. urealyticum also was associated with precocious bronchopulmonary dysplasia independent of prematurity, race, and sex (odds ratio, 2.2; P < .05). Tracheal isolation of U. urealyticum within 7 days of birth is associated with pneumonia and precocious bronchopulmonary dysplasia.
Subject(s)
Bronchopulmonary Dysplasia/diagnostic imaging , Trachea/microbiology , Ureaplasma urealyticum/isolation & purification , Bronchopulmonary Dysplasia/etiology , Bronchopulmonary Dysplasia/microbiology , Female , Humans , Infant, Low Birth Weight , Infant, Newborn , Infant, Premature , Male , Pneumonia/complications , Radiography , Ureaplasma Infections/complications , Ureaplasma urealyticum/pathogenicitySubject(s)
Adolescent Medicine/methods , Child Development , Puberty , Adolescent , Adolescent, Hospitalized/psychology , Adult , Child , Chronic Disease , Confidentiality , Death , Energy Metabolism , Female , Gender Identity , Humans , Male , Peer Group , Physical Examination , Pituitary Hormone-Releasing Hormones/metabolism , Sleep, REM/physiologyABSTRACT
Urine specimens from 23 children and 9 adults who were undergoing treatment for malignancy as well as urines from 40 normal individuals were concentrated and examined for evidence of papovavirus infection. Papovavirus particles were detected in 6 of 64 urines examined by electron microscopy. Three of the particle-positive urines induced BK virus-specific immunofluorescence after inoculation of WI38 cells, and three isolations of BK virus were made by inoculation of urines from virus-excreting patients into Vero cells. BK virus-specific hemagglutination-inhibiting and immunofluorescence neutralizing antibodies were found in a majority of urines from adult patients, in about a fifth of pediatric patients, and less often in normal urines. Urines of virus-excreting patients generally had antibodies. In indirect fluorescent antibody tests, BK virus-specific antibodies of the immunoglobulin G class were found in five urine specimens from patients; immunoglobulin A antibodies were not detected in any urine. These data suggest that activation of BK virus is related to immunosuppression and not to transplantation itself and that the occurrence of virus-specific antibodies in urine may be indicative of virus multiplication in the urinary tract.
