Endovenous laser ablation (EVLA) is a commonly used and very effective minimally invasive therapy to manage leg varicosities. Yet, and despite a clinical history of 16 years, no international consensus on a best treatment protocol has been reached so far. Evidence presented in this paper supports the opinion that insufficient knowledge of the underlying physics amongst frequent users could explain this shortcoming. In this review, we will examine the possible modes of action of EVLA, hoping that better understanding of EVLA-related physics stimulates critical appraisal of claims made concerning the efficacy of EVLA devices, and may advance identifying a best possible treatment protocol. Finally, physical arguments are presented to debate on long-standing, but often unfounded, clinical opinions and habits. This includes issues such as (1) the importance of laser power versus the lack of clinical relevance of laser energy (Joule) as used in Joule per centimeter vein length, i.e., in linear endovenous energy density (LEED), and Joule per square centimeter vein wall area, (2) the predicted effectiveness of a higher power and faster pullback velocity, (3) the irrelevance of whether laser light is absorbed by hemoglobin or water, and (4) the effectiveness of reducing the vein diameter during EVLA therapy.
Minimally invasive treatment of varicose veins by endovenous laser ablation (EVLA) becomes more and more popular. However, despite significant research efforts performed during the last years, there is still a lack of agreement regarding EVLA mechanisms and therapeutic strategies. The aim of this article is to address some of these controversies by utilizing optical-thermal mathematical modeling. Our model combines Mordon's light absorption-based optical-thermal model with the thermal consequences of the thin carbonized blood layer on the laser fiber tip that is heated up to temperatures of around 1,000 °C due to the absorption of about 45% of the laser light. Computations were made in MATLAB. Laser wavelengths included were 810, 840, 940, 980, 1,064, 1,320, 1,470, and 1,950 nm. We addressed (a) the effect of direct light absorption by the vein wall on temperature behavior, comparing computations by using normal and zero wall absorption; (b) the prediction of the influence of wavelength on the temperature behavior; (c) the effect of the hot carbonized blood layer surrounding the fiber tip on temperature behavior, comparing wall temperatures from using a hot fiber tip and one kept at room temperature; (d) the effect of blood emptying the vein, simulated by reducing the inside vein diameter from 3 down to 0.8 mm; (e) the contribution of absorbed light energy to the increase in total energy at the inner vein wall in the time period where the highest inner wall temperature was reached; (f) the effect of laser power and pullback velocity on wall temperature of a 2-mm inner diameter vein, at a power/velocity ratio of 30 J/cm at 1,470 nm; (g) a comparison of model outcomes and clinical findings of EVLA procedures at 810 nm, 11 W, and 1.25 mm/s, and 1,470 nm, 6 W, and 1 mm/s, respectively. Interestingly, our model predicts that the dominating mechanism for heating up the vein wall is not direct absorption of the laser light by the vein wall but, rather, heat flow to the vein wall and its subsequent temperature increase from two independent heat sources. The first is the exceedingly hot carbonized layer covering the fiber tip; the second is the hot blood surrounding the fiber tip, heated up by direct absorption of the laser light. Both mechanisms are about equally effective for all laser wavelengths. Therefore, our model concurs the finding of Vuylsteke and Mordon (Ann Vasc Surg 26:424-433, 2012) of more circumferential vein wall injury in veins (nearly) devoid of blood, but it does not support their proposed explanation of direct light absorption by the vein wall. Furthermore, EVLA appears to be a more efficient therapy by the combination of higher laser power and faster pullback velocity than by the inverse combination. Our findings suggest that 1,470 nm achieves the highest EVLA efficacy compared to the shorter wavelengths at all vein diameters considered. However, 1,950 nm of EVLA is more efficacious than 1,470 nm albeit only at very small inner vein diameters (smaller than about 1 mm, i.e., veins quite devoid of bloo...
Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45% of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95 °C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104 °C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures.
Обосновывается целесообразность лечения больных аллергическим ринитом с сопутствующей бронхиальной астмой физическими факторами и целесообразность осуществления его в два этапа. Наблюдение выполнено у 66 больных. Заключение об эффективности проводимого лечения базировалось на данных динамики клинического состояния основного и сопутствующего заболеваний, выраженности активности воспаления в дыхательных путях (исследовались риноцитограммы, биохимические показатели назальных смывов, уровень оксида азота в выдыхаемом воздухе), их проходимость (манометрия, спирография). Сравнивались два варианта лечения: двух-и одноэтапное. Больные 1-й группы (30 человек) получали в течение 3-5 сут элиминационную терапию с последующим назначением аппликаций торфа, токов надтональной частоты, массажа, ингаляций, а также лечебную физкультуру. Больные 2-й группы (36 человек) элиминационной терапии не получали. Выявлено уменьшение выраженности клинических проявлений основного и сопутствующего заболевания, снижение активности воспаления, улучшение носовой и бронхиальной проходимости, мукоцилиарной функции у больных 1-й группы. В группе сравнения на фоне улучшения клинического состояния не происходило восстановления покровного эпителия, не восстанавливалась проходимость носа.Ключевые слова: бронхиальная астма, аллергический ринит, лечение физическими факторами.The efficiency of treatment of patients with allergic rhinitis and associated bronchial asthma by physical factors and advisability of two-stage treatment are justified. Sixty six patients were observed. The conclusion on the efficiency of treatment was based on the data about the dynamics clinical state of the primary and associated diseases, intensity of inflammation activity in respiratory tract (rhinocytograms, biochemical indices of nasal lavages, level of nitrogen oxide in expired air were studied), patency of airways (manometry, spirography). We compared two versions of treatment: two-and one-stage. Patients of the first group (30 patients) received elimination therapy for 3 to 5 days with the following peaty mud application, current of supersonic frequency, massage, inhalations, physical therapy. Patients of the second group (36 patients) did not receive elimination therapy. We have found a decrease in intensity of clinical implications of the primary and associated diseases, decrease in inflammation activity, better nasal and bronchial носовой patency, improvement of the mucociliary function in patients of the first group. In the second group, the recovery of the surface epithelium and nasal patency was not observed against the background of improvement of the clinical state.
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