PubMed · 8858414
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H S Badeer. 1996. Attention exercise physiologists.. https://doi.org/10.1055/s-2007-972867
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During thrombolytic therapy and after recanalization is achieved, reduction in the volume of mural thrombi is desirable. Mural thrombi are known to contribute to rethrombosis and reocclusion. The lysis rate of mural thrombi has been demonstrated to increase with fluid flow in different experimental models, but the mechanisms responsible are unknown. An experimental and a theoretical study were developed to determine the contribution of outer convective transport to the lysis of mural fibrin clots. Normal human plasma containing recombinant tissue-type plasminogen activator (tPA; 0.5 microg/mL) was (re)perfused over mural fibrin clots with fluorescently labeled fibrin at low arterial, arterial, or higher wall shear stresses (4, 18, or 41 dyn/cm(2), respectively) and lysis was monitored in real time. Flow accelerated lysis, but significantly only at the highest shear stress: The average lysis front velocity was 3 x 10(-5) cm/s at 41 dyn/cm(2) vs. almost half of that at the lower shear stresses. Confocal microscopy showed fibrin fibers dissolving only in a narrow region close to the surface when permeation velocity was predicted to be low. A heterogeneous transport-reaction finite element model was used to describe mural fibrinolysis. After scaling the effects of outer and inner convection, inner diffusion, and chemical reactions, a simplified inner diffusion/reaction model was used. Correlation to fibrin lysis data in purified systems dictated higher rates of plasmin(ogen) and tPA adsorption onto fibrin and a decreased catalytic rate of plasmin-mediated fibrin degradation, compared with published parameters. At each shear stress, the model predicted a temporal pattern of lysis of mural fibrin (similar to that observed experimentally), and protease accumulation in a narrow fibrin region and significant lysis inhibition by plasma alpha(2)-antiplasmin (according to the literature). Increasing outer convection accelerated mural fibrinolysis, but the model did not predict the big increase in lysis rate at the highest shear stress. At higher than arterial flows, additional mechanisms not accounted for in the current model, such as fibrin collapse at the fibrin front, may regulate the lysis of mural clots and determine the outcome of thrombolytic therapy.
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PURPOSE: To investigate the interactions of a new lithotomy positioning device (LPD) with two intermittent pneumatic compression (IPC) devices by measuring femoral venous flow velocity. METHODS: Subjects were divided into three groups: 1) supine position as a control, 2) lithotomy position using a conventional LPD, and 3) lithotomy position using a new LPD, Levitator(TM). These three groups were further divided in two according to the type of IPC device used: AV-impulse(TM) (rapid IPC) and SeQuel(TM) (standard IPC). Peak femoral venous flow velocity was measured by using an ultrasonic echo diagnostic device. Data were analyzed by one-way ANOVA with Fisher's test or by the unpaired two-tailed t test. RESULTS: Moving to the conventional lithotomy position from the supine position, venous flow velocity was decreased by 38% in both IPC device groups. Even when the new LPD was used to support the lithotomy position, the flow velocity was decreased by 24%, but the velocity was significantly higher than in the conventional lithotomy position. Both rapid and standard IPC devices increased flow velocity to 77% and 107% (first compression) and to 71% and 84% (fifth compression) of the control values during compression, respectively. In the lithotomy position group using the new LPD, similar increases in flow were seen with the use of IPC devices. CONCLUSION: Both rapid and standard IPC devices are useful for maintaining venous flow of the lower extremities in the lithotomy position.