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Air Law Issues
Published in Ruwantissa I.R. Abeyratne, Frontiers of Aerospace Law, 2017
In 1856, scientist Rudolf Virchow conducted detailed autopsies on 76 patients, eleven of whom had died from massive thrombi in the pulmonary arteries. He identified through scientific methodolgy that ten of the 11 patients’ thrombi in the pulmonary arteries had started in the legs and concluded that arterial thrombosis had emanated from the leg veins. This led to the development of the famous ‘Virchow’s Triad’ of causation of thromboembolism: trauma to the vein wall; decreased velocity of venous blood flow; and increased blood coagulability.347 The syndrome was first identified and described in 1940, as a result of a finding that, during the war, cramped seating in air raid shelters for prolonged periods during the London ‘blitz’ had frequently resulted in pulmonary embolisms in many instances.348 However, embolisms related to air travel were first described in 1946 after a 54-year-old man had developed thrombophlebitis after sitting for 14 hours during a flight from Boston to Venezuela.349 There have been several subsequent cases of thrombophlebitis reported as a consequence of air travel.350 It is reported that at least 20 of the cases reported in the research have been definitely linked to air travel.351
Haemodialysis catheters – a review of design and function
Published in Expert Review of Medical Devices, 2022
Side holes are designed to provide alternate channels for blood entering and leaving the terminal end of the HD catheter. Side holes are brandished by most devices on the market today, both tunneled and non-tunneled. Proposed benefits include mitigating recirculation, lowering negative pressure at the arterial lumen aperture and hence reduced vein collapse, and allowance of inter-dialytic leaching of anticoagulant lock solution to discourage fibrinisation. The purported disadvantage is promotion of clot formation. Side holes may be accompanied by turbulent flow, and their edges may be roughened resulting in shear stress. As dictated by Virchow’s triad, these conditions potentially increase thrombogenicity and fibrin sheath formation. Non-laminar flow creates eddies and regions of blood stagnation, also raising the risk of infection.
Histopathologic and physiologic effect of overlapping vs single coronary stents: impact of stent evolution
Published in Expert Review of Medical Devices, 2018
Atsushi Sakamoto, Sho Torii, Hiroyuki Jinnouchi, Renu Virmani, Aloke V. Finn
Virchow’s triad describes the three main factors related to thrombus formation which include endothelial injury, disturbance of blood flow, and hypercoagulability. Vascular endothelial injury is unavoidable during a catheter intervention because of the use of balloon expansion which results in stent strut penetration into the vessel wall. Moreover, the site of stent overlapping is potentially at higher risk of vascular wall injury not only from two stent deployment but also from over stretching during post-dilatation in order to avoid incomplete stent strut apposition. Also, the local blood flow disturbance is greater due to excessive stent strut density and greater thickness due to overlap of struts and increase in flow disturbance both contributing to thrombogenicity. To better understand these alterations, computed flow dynamics (CFD) and fluid-structure interaction (FSI) assessment of flow disturbances following stenting are needed. Flow separation from the underlying artery wall especially at curvatures and branches results in the inability of the blood flow to follow the natural geometry resulting in recirculating flow patterns. This idea that hemodynamic forces influence atherogenesis was introduced nearly 60 years ago [31]. Similarly, stenting results in flow disturbances proximal and distal to stent struts where recirculating zones occur, leading to activation of platelets and other coagulation factors [32] (Figure 2). Kolandaivelu et al. showed not only that thick (162 μm) struts increase thrombogenicity 1.5-fold as compared to thin (81 μm) struts but that overlapping configuration had an additive effect especially in BMS with recirculating zones observed throughout the length of the overlapping zone [33]. In a porcine model, the authors showed a 1.6-fold greater thrombus coverage 3 days after implantation in coronary arteries in thick versus thin struts (p = 0.004). In ex vivo model they also showed the effects of malapposition, that is, mild (0–60 μm), moderate (150–210 μm), and severe (350–400 μm) malapposition, all of which resulted in greater thrombogenicity and showed variable responses. Jimenez and Davies have well shown that stent configuration (i.e. rectangular vs. circular arc) has dramatic effects on recirculation zones and endothelial regrowth, with greater effects on the downstream versus upstream areas, determined by the ratio of the width to the height of the strut [32] (Figure 2(a)). The authors showed that pro-coagulant conditions are greatly increased around stent struts when there is (i) accelerated flow over the stent edges resulting in greater shear stress that leads to activation of platelets, (ii) platelets are retained in the recirculating zones along with pro-coagulant factors that can reach a critical level and precipitate clot formation, (iii) de-endothelialization during stenting and balloon angioplasty removes anticoagulants that are naturally present in the endothelium exposing highly thrombogenic surfaces composed of matrix, and (iv) low shear stress also inhibits re-endothelialization [32] (Figure 2(b)).