Influence of fibrillar collagen structure on the mechanisms of platelet thrombus formation under flow.
(25/1782)
We have used real-time video microscopy to study the mechanisms of platelet adhesion to type I collagen fibrils of distinct structure exposed to flowing blood. Electron microscopy analysis by surface replication demonstrated morphological differences between acid-insoluble fibrils, displaying a regularly repeating striated pattern (banded collagen), and acid-soluble fibrils generated by pepsin treatment of insoluble collagen, smaller in size with a helical configuration (nonbanded collagen). These structural differences proved to be related to the role of platelet integrin alpha(2)beta(1) in stabilizing adhesion to collagen under a variety of flow conditions. Blocking alpha(2)beta(1) function with a monoclonal antibody had no effect on platelet adhesion to insoluble type I collagen coated at high density on a glass surface, whereas there was an absolute dependence of alpha(2)beta(1) function for the initial permanent arrest of platelets and subsequent thrombus formation on pepsin-solubilized type I collagen under the same conditions. In contrast, reconstituted, banded fibrils prepared from pepsin-solubilized type I collagen supported platelet adhesion and thrombus development even when platelet alpha(2)beta(1) function was blocked, a process that was greatly accelerated by pre-exposure of this substrate to autologous plasma under flow. These results implicate a collagen receptor(s) on platelets other than alpha(2)beta(1) that can selectively engage domains in banded, but not nonbanded type I collagen when alpha(2)beta(1) function is blocked. In addition, collagen structure may regulate the extent and affinity of the binding under flow of plasma components such as von Willebrand factor and/or other alpha(IIb)beta(3) ligands. (+info)
Ultrasound evaluation of uterine wound healing following laparoscopic myomectomy: preliminary results.
(26/1782)
The purpose of our work was to study the evolution of the uterine scar following laparoscopic myomectomy, as imaged by ultrasonography and Doppler velocimetry of the uterine arteries. We prospectively studied 30 patients. In the first phase, 15 patients were submitted to two-dimensional (2D) endovaginal ultrasound on day -1, 1, 7, 30 and 60 (surgery = day 0). In the second phase an additional 15 patients were studied by both 2D ultrasound and by Doppler velocimetry. The resistance index (RI) was calculated from the flow velocity waveform of the uterine arteries, at the origin of their ascending branch. Only one ultrasonic pattern was found, which was a dense echogenic area having an ill-defined, heterogeneous texture. In one case a small anechoic area (1 cm) was detected in the scar, possibly due to a haematoma. The evolution of uterine healing showed a progressive reduction in the size of the scar. On day 1 its mean diameter was 37.04% less than the myoma diameter and on day 30 71.7% less. The difference was significant at P < 0.001. A further significant (P < 0.001) reduction was found at day 60 in the 15 patients studied in phase I. On both day 1 and day 30 following surgery, there was no correlation between the sizes of the myoma and the scar. There was a statistically significant increase (P < 0.01) in the RI value of the ipsilateral uterine artery from 0.64 on day -1 to 0.79 on day 1. On day 30, 12/15 (80%) cases had RI values ranging between 0.80 and 0.98, while in three cases there was absence of end diastolic flow. The RI values of the contralateral uterine artery were high (0.90) before surgery and did not change afterwards. There was no correlation between the size of the myoma and the increase in the uterine artery RI value following surgery. Considering the velocimetric findings, 30 days are a reference point for assessing the healing process. Ultrasound imaging and Doppler velocimetry can be used for studying the evolution of the uterine scar following myomectomy. (+info)
Structural origins of fibrin clot rheology.
(27/1782)
The origins of clot rheological behavior associated with network morphology and factor XIIIa-induced cross-linking were studied in fibrin clots. Network morphology was manipulated by varying the concentrations of fibrinogen, thrombin, and calcium ion, and cross-linking was controlled by a synthetic, active-center inhibitor of FXIIIa. Quantitative measurements of network features (fiber lengths, fiber diameters, and fiber and branching densities) were made by analyzing computerized three-dimensional models constructed from stereo pairs of scanning electron micrographs. Large fiber diameters and lengths were established only when branching was minimal, and increases in fiber length were generally associated with increases in fiber diameter. Junctions at which three fibers joined were the dominant branchpoint type. Viscoelastic properties of the clots were measured with a rheometer and were correlated with structural features of the networks. At constant fibrinogen but varying thrombin and calcium concentrations, maximal rigidities were established in samples (both cross-linked and noncross-linked) which displayed a balance between large fiber sizes and great branching. Clot rigidity was also enhanced by increasing fiber and branchpoint densities at greater fibrinogen concentrations. Network morphology is only minimally altered by the FXIIIa-catalyzed cross-linking reaction, which seems to augment clot rigidity most likely by the stiffening of existing fibers. (+info)
Influence of a natural and a synthetic inhibitor of factor XIIIa on fibrin clot rheology.
(28/1782)
We investigated the origins of greater clot rigidity associated with FXIIIa-dependent cross-linking. Fibrin clots were examined in which cross-linking was controlled through the use of two inhibitors: a highly specific active-center-directed synthetic inhibitor of FXIIIa, 1,3-dimethyl-4,5-diphenyl-2[2(oxopropyl)thio]imidazolium trifluoromethylsulfonate, and a patient-derived immunoglobulin directed mainly against the thrombin-activated catalytic A subunits of thrombin-activated FXIII. Cross-linked fibrin chains were identified and quantified by one- and two-dimensional gel electrophoresis and immunostaining with antibodies specific for the alpha- and gamma-chains of fibrin. Gamma-dimers, gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrids were detected. The synthetic inhibitor was highly effective in preventing the production of all cross-linked species. In contrast, the autoimmune antibody of the patient caused primarily an inhibition of alpha-chain cross-linking. Clot rigidities (storage moduli, G') were measured with a cone and plate rheometer and correlated with the distributions of the various cross-linked species found in the clots. Our findings indicate that the FXIIIa-induced dimeric cross-linking of gamma-chains by itself is not sufficient to stiffen the fibrin networks. Instead, the augmentation of clot rigidity was more strongly correlated with the formation of gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrid cross-links. A mechanism is proposed to explain how these cross-linked species may enhance clot rigidity. (+info)
Assessment of Doppler velocimetry of the fetal umbilical artery by multigate spectral Doppler scanning and traditional pulsed Doppler ultrasonography plus color flow mapping.
(29/1782)
The Doppler signal of blood flow originates from the sonographic scattering from the circulating red blood cells. However, the physics of blood flow is complex as expressed by the Bernoulli equation, and the flow velocity at different positions in the laminar flow of the same vessel is variable. Using multigate spectral Doppler scanning, we recorded multiple Doppler flow signals over a segment of the umbilical artery and compared the results with traditional pulsed Doppler ultrasonography. The intraobserver variations of the pulsatility index, the resistive index, and the systolic-to-diastolic ratio were evaluated in 30 human fetuses between 29 and 42 weeks of gestation. The correlation coefficient was calculated to establish the relationship between the results of multigate spectral Doppler scanning and the traditional pulsed Doppler ultrasonographic method. The Doppler indices of these two measurements are all significantly correlated. However, since a significant difference exists between the Doppler flow measurements of multigate spectral Doppler scanning and the traditional pulsed Doppler ultrasonographic method, the range of measurement agreement for these two methods suggests that this difference should be taken into account in the interpretation of Doppler flow velocity measurements. (+info)
Fluoroscopically-guided manipulation of malfunctioning peritoneal dialysis catheters.
(30/1782)
OBJECTIVE: To review our experience with fluoroscopic evaluation and manipulation of malpositioned, malfunctioning, peritoneal dialysis (PD) catheters. MATERIALS AND METHODS: Thirty-one patients, over a 5-year period (1 May 1992 to 30 April 1997) with malfunctioning PD catheters, who had fluoroscopically-guided manipulation were reviewed. Catheters were manipulated using a malleable aluminum bar and, if necessary, guide wires or other stiffeners. Technical success was assessed on the basis of adequate, fluoroscopically verified, catheter placement at the time of the procedure and improved flows. A functional PD catheter at 30 days post manipulation was considered to be a clinically successful manipulation. RESULTS: There were 41 manipulations [33 initial (IM) and 8 remanipulations (RM)] for malpositioned or kinked catheters. In 31 (19 male, 12 female) patients ranging in age from 31 to 76 years (mean age 60 years), the initial technical success rate was 85% for IM (n = 28/33) and 63% (n = 5/8) for RM. The overall clinical success rate, or 30-day primary patency, was 55% for IM (n = 18/33) and 63% for RM. Catheter function (combined IM and RM) continued for a median 869 days (95% CI: 118, 1620). No early complications were noted. CONCLUSIONS: Fluoroscopic manipulation, including attempts at remanipulation, of PD catheters is a safe procedure. The technique is a simple, inexpensive, and effective way of prolonging PD catheter life, thereby reducing the number of surgical interventions. (+info)
CD11b/CD18-coated microspheres attach to E-selectin under flow.
(31/1782)
Neutrophils can attach to E-selectin under flow. Proposed ligands for E-selectin carry SLe(x)-type glycans. The leukocyte beta2 integrins are glycosylated with SLe(x). Thus, we speculated that beta2 integrins could support attachment to E-selectin. To test this hypothesis, we coated 10-microm-diameter microspheres with purified CD11b/CD18 (alphaMbeta2) and investigated the adhesion of the resulting alphaMbeta2 microspheres to E-selectin. Under in vitro flow conditions, the alphaMbeta2 microspheres attached to Chinese hamster ovary cells expressing E-selectin (CHO-E) and 4-h interleukin-1beta-activated human umbilical vein endothelial cells (HUVEC). At a shear stress of 1.8 dynes/cm2, the attachment events were eliminated by pretreatment of the cellular monolayers with a mAb to E-selectin. alphaMbeta2 microspheres did not attach to untransfected CHO cells or unactivated HUVEC at 1.8 dynes/cm2. Taken together, the results strongly suggest that the CD11b/CD18-E-selectin bond has sufficient biophysical properties to mediate attachment of neutrophil-sized particles to E-selectin under flow. (+info)
Age related compliance of the lamina cribrosa in human eyes.
(32/1782)
AIMS: To investigate changes in the mechanical compliance of ex vivo human lamina cribrosa with age. METHODS: A laser scanning confocal microscope was used to image the surface of the fluorescently labelled lamina cribrosa in cadaver eyes. A method was developed to determine changes in the volume and strain of the lamina cribrosa created by increases in pressure. The ability of the lamina cribrosa to reverse its deformation on removal of pressure was also measured. RESULTS: Volume and strain measurements both demonstrated that the lamina cribrosa increased in stiffness with age and the level of pressure applied. The ability of the lamina cribrosa to regain its original shape and size on removal of pressure appeared to decrease with age, demonstrating an age related decrease in resilience of the lamina cribrosa. CONCLUSIONS: The mechanical compliance of the human lamina cribrosa decreased with age. Misalignment of compliant cribriform plates in a young eye may exert a lesser stress on nerve axons, than that exerted by the rigid plates of an elderly lamina cribrosa. The resilience of the lamina cribrosa also decreased with age, suggesting an increased susceptibility to plastic flow and permanent deformation. Such changes may be of importance in the explanation of age related optic neuropathy in primary open angle glaucoma. (+info)