Remodeling of the cardiovascular hemodynamic environment by lower limb heat exposure: A computational fluid dynamic study.

BACKGROUND: Lower limb heat exposure (LLHE) is a promising strategy for the daily management of cardiovascular health because of its non-pharmaceutical advantages. To support the application of this strategy in cardiovascular protection, we examined its impact on the global hemodynamic environment. METHODS: Skin blood flow (SBF) of eight locations on the lower limbs was measured before and after LLHE (40 °C and 44 °C) in ten healthy subjects by using a laser Doppler flowmeter. A closed-loop model of circulation uses changes in SBF to quantify the influence of LLHE on the blood flow of the arterial trunk (from ascending aorta to the femoral artery) and visceral branches (coronary, celiac, renal, and mesenteric arteries). RESULTS: The SBF in all locations tested on the lower limbs increased significantly (p<0.001) with LLHE and a 3.39-fold and 7.40-fold increase in mean SBF were observed under 40 °C and 44 °C conditions, respectively. In the model, the peak (3.9-25.1%), end-diastolic (13.7-107.3%), and mean blood flow (8.5-86.5%) in the arterial trunk increased with the increase in temperature, but the retrograde flow in the thoracic aorta and abdominal aorta Ⅰ increased at least twice in the diastolic period. Furthermore, LLHE also increased the blood flow of the visceral branches (2.5-20.7%). CONCLUSION: These findings suggest that LLHE is expected to be a daily strategy for enhancing the functions of both the arterial trunk and visceral arteries, but the increased blood flow reversal in the thoracic and abdominal aortas warrants further investigation.

[Animal experimental study on the effects of different levels of amputation on cardiovascular system].

Vascular injury resulting from lower limb amputation leads to the redistribution of blood flow and changes in vascular terminal resistance, which can affect the cardiovascular system. However, there was no clear understanding of how different amputation levels affect the cardiovascular system in animal experiments. Therefore, this study established two animal models of above-knee amputation (AKA) and below-knee amputation (BKA) to explore the effects of different amputation levels on the cardiovascular system through blood and histopathological examinations. The results showed that amputation caused pathological changes in the cardiovascular system of animals, including endothelial injury, inflammation, and angiosclerosis. The degree of cardiovascular injury was higher in the AKA group than in the BKA group. This study sheds light on the internal mechanisms of amputation's impact on the cardiovascular system. Based on the amputation level of patients, the findings recommend more comprehensive and targeted monitoring after surgery and necessary interventions to prevent cardiovascular diseases.

Shear Adhesion of Ice on Large-Sized Grooved Aluminum Surfaces.

Ice adhesion is important when designing aircraft anti-icing/de-icing systems. Major and minor grooves are common in the skin of aircraft. However, the effects of millimeter-scale grooves on ice adhesive strength have not been given due attention. Specimens with varying depths, widths, and numbers of grooves were fabricated by machining to investigate the ice adhesive characteristics of large-sized grooved aluminum surfaces. After the ice cube was frozen on the surface using a silicon mold, the adhesive force was measured using a self-assembled shear adhesive force setup. A correlation between groove size and apparent adhesive strength in the perpendicular loading direction was established based on the experimental results. Every 1% increase in the groove width ratio was associated with an 18.7 kPa increase in apparent adhesive strength. The increasing speed of the adhesion rapidly decayed as the groove depth increased. The increase in adhesion reached 99% of the maximum increase when the groove depth reached 0.8 times the width. The number of grooves had little effect on the adhesion when the total width of the grooves was kept constant. Stress distribution analysis was conducted using the finite element method, and the results were in accordance with the cracking phenomena in the experiments. The adhesive strength in the parallel loading direction was 30% lower than that in the perpendicular loading direction for all six chosen surfaces. This study is the first to propose a quantitative relationship between the surface textures of millimeter-sized grooves and ice adhesive strength. The loading orientation also had a substantial influence on adhesion. The results will serve as a valuable reference for future studies on ice adhesion on textured surfaces and for improving the performance of anti-icing/de-icing systems.

Effect of lower extremity amputation on cardiovascular hemodynamic environment: An in vitro study.

Lower extremity amputation (LEA) was associated with a greater risk of cardiovascular disease, but its hemodynamic mechanisms have not been fully studied. Therefore, to clarify the interrelationship between them, and figure out the potential pathogenesis, the exploration of the hemodynamic environment change of patients after LEA was premeditatedly executed. A near-physiological mock circulatory system (MCS) was employed in the present work to replicate the cardiovascular circulation after LEA in a short time and the unsteady-state numerical simulation was utilized as an auxiliary method to observe the changes of the hemodynamic environment inside the blood vessel. Higher severity of LEA leads to higher peripheral vascular impedance, higher blood pressure, and more obvious redistribution of blood perfusion volume. In addition, higher severity of LEA leads to lower wall shear stress (WSS), higher oscillatory shear index (OSI), and higher relative residence time (RRT) appeared in the infrarenal abdominal aorta and the iliac artery, while these changes are closely related to the higher probability of cardiovascular diseases. Results showed that different degrees of LEA (varying heights, unilateral/bilateral) have diverse effects on the patient's hemodynamic environment. This study explained the potential pathogenesis of cardiovascular diseases after LEA from a hemodynamic perspective and provided a certain reference value for the improvement of the cardiovascular hemodynamic environment and the prevention of cardiovascular diseases in lower extremity amputees.

[Establishment of an animal model to study the effects of amputation on the cardiovascular system].

Lower limb amputation is a significant change in body structure. Loss of muscle, blood vessels, and blood leads to a redistribution of blood flow and changes in resistance at the end of blood vessels. In view of the significant increase in the prevalence of cardiovascular disease after lower limb amputation, the mechanism of which is still unclear, this study aims to establish an animal research model that can verify and explore the effects of amputation on cardiovascular system, and provide the experimental basis for subsequent animal experiments when exploring the effect of different amputation levels on the cardiovascular system. SPF New Zealand rabbits were divided into normal group ( n = 6) and amputation group ( n = 6). The amputation group was treated with above-knee amputation. The changes of low-density liptein cholesterol (LDL-C) and total cholesterol (TC) in serum of all the rabbits were monitored regularly after the surgery. The arterial pathological examination was conducted after the experimental rabbits were executed. The results showed that compared with the normal group, serum LDL-C content and TC content in the amputation group were significantly increased ( P<0.05); The blood vessels of the amputated rabbits had pathological changes such as degeneration and necrosis of smooth muscle cells in the middle membrane layer and rupture of elastic fibers. At the abdominal aorta and aortic arch, the elastic fiber area expression percentage (EFEP) of the experimental group was significantly lower than that of the normal group. The results suggest that the cardiovascular system of rabbits has the tendency of decreased arterial elasticity and lipid deposition in blood after amputation, indicating that the animal research model on the effect of amputation on the cardiovascular system has been successfully established, and can provide an experimental platform for further study on the mechanism of the effect of amputation on the cardiovascular system.

Reallocation of cutaneous and global blood circulation during sauna bathing through a closed-loop model.

OBJECTIVE: Sauna bathing (SB) is an important strategy in cardiovascular protection, but there is no mathematical explanation for the reallocation of blood circulation during heat-induced superficial vasodilation. We sought to reveal such reallocation via a simulated hemodynamic model. METHODS: A closed-loop cardiovascular model with a series of electrical parameters was constructed. The body surface was divided into seven blocks and each block was modeled by a lumped resistance. These resistances were adjusted to increase skin blood flow (SBF), with the aim of reflecting heat-induced vasodilation during SB. Finally, the blood pressure was compared before and after SB, and the blood flow inside the aorta and visceral arteries were also analyzed. RESULTS: With increasing SBF in this model, the systolic, diastolic, and mean blood pressure in the arterial trunk decreased by 13-29, 18-36, and 19-37 mmHg, respectively. Despite the increase in the peak and mean blood flow in the arterial trunk, the diastolic blood flow reversal in the thoracic and abdominal aortas increased significantly. Nevertheless, the blood supply to the heart, liver, stomach, spleen, kidney, and intestine decreased by at least 25%. Moreover, the pulmonary blood flow increased significantly. CONCLUSION: Simulated heat-induced cutaneous vasodilation in this model lowers blood pressure, induces visceral ischemia, and promotes pulmonary circulation, suggesting that the present closed-loop model may be able to describe the effect of sauna bathing on blood circulation. However, the increase of retrograde flow in the aortas found in this model deserves further examination.

[Experimental study on the relationship between foam pressure difference and foam stability].

Foam stability affects the efficacy and incidence of side effects of foam sclerotherapy. Exploring the relationship between foam pressure difference and foam stability can provide ideas and basis for obtaining more stable foam. In the experiment, sodium cod liver oleate foam was selected, and poloxamer 188 (concentration of 0%, 4%, 8%, 12%) was added to realize the change of foam pressure. By using the self-written program to process the foam pictures, the foam pressure difference and the relationship between the foam stability indicators (water separation rate curve, half-life) and the foam pressure difference were obtained. The results showed that at first the foam pressure increased with the increase of the concentration, and then it decreased with the increase of the concentration and reached a peak at the concentration of 4%. The foam pressure difference decreases continuously with the increase of decay time. When the additive concentration is low, the foam average pressure difference increases. And if the additive concentration is too high, the foam average pressure difference decreases. The smaller the foam pressure difference is, the better the foam stability is. This paper lays a foundation for the research on the stability of foam hardener.

An Optical Method for Immediate Evaluation of Microfoam Stability in Foam Sclerotherapy.

OBJECTIVES: The objective of our study was to develop an optical method that instantly evaluates the stability of sclerosing foam, which would enable early predictions of the clinical performance of the foam and reduce the occurrence of clinical side effects. METHODS: Based on the principle of light scattering, we developed a method to optically test foam stability and verified it experimentally using sodium morrhuate (2 mL; 0.05 g/mL) and carbon dioxide. A self-made foam preparation instrument was used to achieve a preparation speed of 275 mm/s. The liquid-gas ratios were considered as 1:3, 1:4, and 1:5. Curves of illuminance with respect to the drainage rate and decay time were obtained. By fitting the curve, the relationship between foam half-life time (FHT) and foam decay was obtained. Thus, foam stability was evaluated using the initial illuminance value; the foam transfer time was approximately 3 s. RESULTS: The experimental FHT varies between 205 and 232 s. Illuminance is exponentially related to drainage rate and linearly related with time. FHT can be expressed by the initial illuminance and illuminance curve fitting coefficients. The half-life of the foam decreases as the initial illuminance value increases, for the same sclerosing drug. The suitability of foam stability is determined by the position of the initial value in the chart. CONCLUSION: Optical methods are feasible for evaluating foam stability over a short period of time. Clinically predicting the stability of freshly prepared foam can reduce number of incidences of further complications. This will promote the development of foam sclerotherapy and provide a basic understanding of the internal mechanical properties of foam.

A Review of Sclerosing Foam Stability in the Treatment of Varicose Veins.

BACKGROUND: Varicose veins are common clinical entities. Foam sclerotherapy is a minimally invasive and simple procedure; however, the side effects, efficacy, and stability of sclerosing foam are not ideal. OBJECTIVE: To summarize the current studies on sclerosing foam stability and promote foam sclerotherapy development. MATERIALS AND METHODS: We reviewed the literature before June 2018 and included only representatives studies on sclerosing foam stability. We summarized the foam half-life time (FHT) of polidocanol (POL) under 17 preparation conditions and the FHT of sodium tetradecyl sulfate under 21 preparation conditions. The preparation conditions included various combinations of temperature, liquid-gas ratio, preparation method, etc. RESULTS: The FHT of POL varied between 40 and 4,000 seconds under different conditions. The FHT of sodium tetradecyl sulfate varied from 25.7 to 390 seconds. The higher the drug concentration, the lower the temperature required to increase foam stability. The addition of surfactant greatly increased foam stability. For different gas compositions, the FHT sequence was as follows: CO2 < CO2 + O2 < O2 < air. CONCLUSION: Foam stability can be improved by changing the preparation conditions; therefore, the role of surfactants and predictive methods for FHT are worth investigating further.

A comparison of different surfactants on foam stability in foam sclerotherapy in vitro.

OBJECTIVE: This article compares the effect of different surfactants on foam stability and determines the foam decay relationship, so that the suitability of surfactants in a clinical setting can be evaluated. METHODS: Five different surfactants were used to prepare sclerosing foam at room temperature using a liquid:gas ratio of 1:4 in vitro. Foam decay experiments were performed for each sample using a laboratory-made foaming apparatus, and the process was recorded using a video camera. The stability indices used included the drainage time, drainage rate, half-life, foam half-life volume, surfactant stability index, and foaming index. RESULTS: The sodium morrhuate foam was relatively more stable than the polidocanol foam, but exhibited weak foaming. After the addition of the surfactants, the foam half-life was less than 300 seconds. The effect of the surfactants on the stability of the sodium morrhuate foam was more pronounced. The surfactant stability indices could be arranged as follows: poloxamer 188 > Tween 80 > macrogol 4000 > propanediol > lecithin. However, the differences in the foaming indices were small. CONCLUSIONS: Of the five surfactants tested, poloxamer 188 has best performance to enhance sclerosing foam stability. The addition of the surfactants improved the stability of the sclerosing foams. It was observed that the relationships between the foam half-life and the surfactant stability index and the surfactant concentration follow the power law.

Effect of Multiple Factors on Foam Stability in Foam Sclerotherapy.

Foam sclerotherapy is a widely used treatment for varicose veins. However, complications caused by poor foam stability still remain. Most studies ignore multiple influencing factors and only study a single factor. Furthermore, a stable foam preparation using different preparation conditions has not been developed. This study aimed to explore the changing laws of foam stability under multifactorial conditions, and to determine the influence of various factors and optimal preparation conditions on the half-life of foam. A two-level orthogonal test was conducted using four factors (syringe size, surfactant, preparation temperature, and pump speed). Classifications were established as follows: syringe sizes, 2.5 mL and 5 mL; surfactant concentrations, 6% and 0%; preparation temperatures, 20 °C and 10 °C; and pump speeds, 250 mm/s and 125 mm/s, respectively. Eight experimental group (EG) multi-factor combinations were tested. Half-life and drainage time were recorded for analysis. The initial drainage time was within 200 s, but the difference between the groups was also about 200 s. The drainage rate curves of all EGs gradually increased over time. Conversely, the foam half-life extended by about 10 times for the four factors. In addition, the analyses revealed that the order of influence was surfactant >temperature >pump speed >syringe size. The most stable foam preparation was determined. Syringe size, surfactant, temperature, and pump speed had markedly observable influences on foam half-life. A combination of multiple factors can be used to prepare a more stable foam in clinical scenarios and to suitably superimpose favorable conditions to avoid unfavorable conditions.

Influence of Syringe Volume on Foam Stability in Sclerotherapy for Varicose Vein Treatment.

BACKGROUND: Despite the popularity of sclerotherapy for treating varicose veins, it still exhibits various problems, such as pulmonary embolism, deep-vein thrombosis, phlebitis, and visual disorders. OBJECTIVE: To investigate syringe volume influence on foam stability, obtain the foam decay rule, and provide a reference for clinics. MATERIALS AND METHODS: Five types of syringes are used to prepare foam at room temperature with various liquid-gas ratios. Foam decay process experiments were performed 5 times and recorded by video. The stability indices used include drainage time, half-life, bubble diameter, bubble surface density, and drainage rate. RESULTS: The 30 and 2-mL syringes, respectively, recorded the highest and lowest drainage speeds. Foam drainage time and half-life, differences varied between 15 and 70 seconds, and 20 and 100 seconds, respectively. Foam bubble diameters were distributed over 0.1 to 2.0 mm with roughly 200 to 700 bubbles per square centimeter. CONCLUSION: Increased syringe volume causes the bubble diameter to increase. Thus, foam dispersion increases and foam half-life decreases; hence, foam becomes unstable. It is, thus, better to use a small syringe several times to prepare foam in clinics using segmented injections.

Studies on Foam Decay Trend and Influence of Temperature Jump on Foam Stability in Sclerotherapy.

OBJECTIVES: This study investigated the influence of temperature jump and liquid-gas ratio on foam stability to derive the foam-decay law. METHODS: The experimental group conditions were as follows: mutation temperatures (10°C, 16°C, 20°C, 23°C, 25°C, and 27°C to >37°C) and liquid-gas ratios (1:1, 1:2, 1:3, and 1:4). The control group conditions were as follows: temperatures (10°C, 16°C, 20°C, 23°C, 25°C and 27°C) and liquid-gas ratios (1:1, 1:2, 1:3, and 1:4). A homemade device manufactured using the Tessari DSS method was used to prepare the foam. The decay process was videotape recorded. In the drainage rate curve, the temperature rose, and the liquid-gas ratio varied from 1:1 to 1:4, causing faster decay. RESULTS: In the entire process, the foam volume decreased with increasing drainage rate. The relationships were almost linear. Comparison of the experimental and control groups shows that the temperature jump results in a drainage time range of 1 to 15 seconds. The half-life ranges from 10 to 30 seconds. The maximum rate is 18.85%. Changes in the preparation temperature yields a drainage time range of 3 to 30 seconds. The half-life varies from 20 to 60 seconds. CONCLUSION: Decreasing the temperature jump range and liquid-gas ratio gradually enhances the foam stability. The foam decay time and drainage rate exhibit an exponential function distribution.

[Development of Automatic Preparation Device of Sclerosing Foam Based on Tessari Method].

Based on the principle of manual preparation of sclerosing foam with Tessari method,using the analysis of user requirements and combining it with theory of mechanics,we designed an automatic equipment.The device could be used to replace the manual operation,and could overcome the shortcomings of manual sclerosing foam preparation,such as the difficulty in controlling of pushing speed and stroke and poor reproducibility.This automatic device has the functions of adjustable pushing speed,pushing frequency,pushing stroke and is suitable for a variety of different types of syringes.It can not only provide quantitative parameters for the study of foam properties,but also be used for the standardization of clinical sclerosing foam.The experimental study on"the effect of pushing speed on the stability of foam"was carried out with using the device,and the experimental results were quite satisfactory.

[Experimental Study on Influence of Driving Speed on Foam Stability in Sclerotherapy for the Treatment of Varicose Veins].

Foam sclerotherapy is one of the major therapies for varicose veins in lower limbs.It is important to know the influence factor of foam stability which is beneficial to curative effect.The present experiment explored influence of 9kinds of driving speed on foam stability when using the method of Tessari.Syringes of 5mL were chosen to do this experiment which was carried out at the liquid gas ratio of 1∶4and the environment temperature of 20 ℃.A home-made automatic sclerosing foam preparation equipment was used to prepare the foam.A camera recorded the entire process of foam decay.And foam stability indexes which includes drainage time,half-life,foam half-life volume and the drainage rate curve,were analyzed.The results showed that when driving speed ranged from 100mm/s to 275mm/s,foam drainage time and the half-life showed a trend of rising.When the driving velocity was greater than 275mm/s,the foam drainage time and half-life time reduced a little.The largest drainage time and the half-life differences were 340.0% and 118.8% compared to their minimum value.Meanwhile the pressure increased with the increase of driving speed,so that the solubility of carbon dioxide increased and the foam half-life volume decreased with the increase of the driving speed.It can be concluded that when using the method of Tessari to prepare sclerosing foam,driving speed has a significant effect on its stability.With driving speed increasing,foam decay mechanism changes from gas diffusion to liquid drainage as the main function,so the foam stability increased at first and then decreased later.The foam is relatively more stable at the speed of 275mm/s,which could be considered as the best driving speed.