Predicting Compression Pressure of Knitted Fabric Using a Modified Laplace’s Law

The aim of this study is to develop a mathematical model for the prediction of compression pressure based on fabric parameters, such as engineering stress, engineering strain and engineering modulus of elasticity. Four knitted compression fabrics with different fibrous compositions and knit structures were used. Rectangular-cut strips were employed for the force–elongation characterization of the fabrics. The experimental pressure values between the fabric and rigid cylinder were assessed using a Picopress pressure measuring device. The mechanical and physical parameters of the fabric that influence the interface pressure, such as strain, elasticity modulus/stress and thickness, were determined and integrated into Laplace’s law. A good correlation was observed between the experimental and calculated pressure values for all combinations of fabrics, mounted with variable tension on the cylinder. Over the considered range of pressures, the difference between the two datasets was generally less than 0.5 mmHg. The effect of washing after five, ten and fifteen washing cycles on the fabric–cylinder interface pressure was found to be significant.

Inability of Laplace's law to estimate sub-bandage pressures after applying a compressive bandage: a clinical study

Objective: The aim of the current study was to compare pressures exerted on the lower limb by a high compression bandage as recorded by sub-bandage sensors and those estimated by Laplace's law. The correlation between pressures obtained in each anatomical zone and the corresponding limb perimeters were explored. Method: For the measurement of sub-bandage pressures, four anatomical zones in the lower right limb were determined. Pressures were recorded by nine pneumatic sensors and a PicoPress transducer. A two-layer compression bandage system (UrgoK2, Urgo Group, France) was used for the dressing. Pressures were registered in supine position. Sensor pressures were compared with those estimated by a modified Laplace's equation. Results: A total of 47 female volunteers were recruited (mean age: 21.9±2.3 years) to the study. In the four anatomical segments studied, pressures obtained by the sensors were lower than would be expected by applying Laplace's law (p<0.05). The biggest difference between the two methods was found at the supramalleolar level (42.1% lower by sensors compared with Laplace's equation). The correlation coefficient between pressure recorded by the sensors and that calculated at the perimeters was very weak, ranging from 0.5233 to 0.9634. Conclusion: Laplace's law, used to predict the sub-bandage pressure after applying a compressive bandage in the lower limb, was not useful, providing significantly higher pressures than those obtained by pneumatic sensors. Laplace's law underestimates the variable musculoskeletal components at the different segments of lower limb that act as compression damping forces.

A novel pressure-regulated deployment strategy for improving the safety and efficacy of balloon-expandable transcatheter aortic valves

Background Annular rupture is a catastrophic complication of Transcatheter Aortic Valve Implantation, more commonly seen with balloon expandable valves. Size selection and deployment of these valves often presents a serious challenge as prosthesis oversizing increases the risk of rupture, while undersizing results in greater paravalvular regurgitation (PVR). Current deployment protocols are volume-regulated and susceptible to undesired prosthesis over or under-expansion. Laplace's Law demonstrates that the stress exerted on the aortic wall is determined by both the valve area and internal pressure during deployment. Yet the issue of balloon pressure during deployment has been thus far ignored. Purpose In this feasibility study, we aimed to develop a novel pressure-regulated deployment method that allows optimising apposition between valve and annulus, while preventing significant tissue injury and rupture. Methods We analysed a cohort of 278 consecutive patients with severe aortic stenosis and intermediate-severe surgical risk who underwent TAVI using Sapien 3 valves. This included 88 patients (32%) considered at high risk of annular rupture based on accepted factors such as moderate-severe subannular calcification. A pressure gauge was connected to the apparatus and in each case the valve was deployed until reaching a pre-determined pressure limit. In earlier cases lower pressures of 4–4.5atm were used to establish safety, while in later cases pressure limit was increased to maximum of 7atm. In some patients post-dilatation was performed to improve angiographic regurgitation. Using a biomechanical application of Laplace's Law, the estimated annular wall stress was calculated for each case and assessed against recorded complications such as annular rupture, PPM insertion, new LBBB and PVR on post-procedure TTE. Based on these analyses we then determined the optimal pressure limit for each available valve size. Results Distribution of deployment pressures and associated estimated wall stress are shown in attached Figure. 1 case of annular rupture (0.4%) occurred in high risk patient at 3.81MPa. Wall stress levels &gt;3.0MPa were associated with reduced rates of post dilatation (13% vs 37%, p&lt;0.001) and ≥mild PVR (10.7% vs 20%, p=0.093). In patients (148) with estimated wall stress between 3–3.8MPa rates of new PPM and LBBB were 7.4% and 8.1%, respectively. Greater wall stress was not associated with increased new PPM/LBBB risk. Therefore, we suggest the optimal deployment pressure limit to minimise risk of rupture, rates of post-dilatation and clinically significant PVR is: 6atm for 23mm valves, 5.5atm for 26mm valves and 5atm for 29mm valves. Conclusion Pressure-regulated deployment strategy is a reproducible, safe and effective method for balloon expandable TAVI, alleviating concerns of valve oversizing in high risk patients. Further trials are needed to validate this novel method and compare it with current volume-regulated techniques. Abstract Figures Funding Acknowledgement Type of funding source: None

FUNDAMENTALS OF PHYSICS IN SURGERY- REVIEW

Physics is everywhere in our daily life. It helps in understanding concepts of surgery easily. Application of physics in surgical field is very helpful especially for a surgeon. In this article we have summarized some common laws of physics, many of them we see in our operation theatre like Poiseuille’s Law, Pascal’s Law, Laplace’s Law, Bernoulli Equation or Theorem, Ohm’s Law, Floating Ball Valve Mechanism, Newton’s Law of Cooling, Laws of Vector and Air-Water Seal System. The application and understanding of these laws would make a surgeon think more like a scientist. Doppler Effect is used in ultrasonography to evaluate the direction and velocity of blood flow. Reynolds number (NR) is used to predict whether the flow of blood will be laminar or turbulent. The laws of Thermodynamics, Mechanics, and Vectors as they apply to soft and bony tissues. These include the Laplace’s Law as applied to colonic perforation and esophageal varices etc. In Electrocautery, alternating current is passed through a resistant metallic wire electrode and generates heat. The heated electrode is used to achieve hemostasis and dissection. The Pascal’s Law finds use in hernia repair Keywords: Physics, Surgery, Fundamentals.

Comparison and Evaluation of Sizing Systems Used in Commercial Women’s Compression Sportswear

Currently, there is no published research evaluating sizing methodologies for commercial sports compression garments (SCGs), so this study addresses the research gap by analysing sizing systems used for women-specific SCGs. Firstly, fit trials with whole-body SCGs were conducted with 33 active females. Secondly, the upper and lower body size charts of 12 SCG brands were analysed. Thirdly, the fitness of the size charts for the sample was assessed. Findings of the fit trials indicated that the fit of the SCGs varied from the intended fit in most participants at certain body locations, which is problematic for consistent pressure delivery. New sizing approaches are needed for SCGs, as fit requirements differ from conventional clothing, and current approaches appear to be inappropriate. The inclusion of a limb circumference measurement as a key dimension could be beneficial due to the interrelation of fabric tension and limb girth in pressure delivery (Laplace’s Law).

Analysis of Stress and Strain to Determine the Pressure Changes in Tight-Fitting Garment

Based on the mechanical properties of stretch fabrics and Laplace’s law, the mathematical models have been developed enabling one to determine the values of the relationship between the fabric strain and the circumferential stress depending on pressure and diameter of the body. The results obtained refer to the values of the parameters assessed for the initial phase of their exploitation, which allow us to preliminarily predict the values of these parameters.

Clothing Pressure Modeling Using the Modified Laplace’s Law

Today, various kinds of pressure garments are designed for specific applications in medical and sports fields. Knitted garments are the most used in these applications due to their high extensibility. The objective of the investigation reported in this article was to develop a theoretical relationship based on Laplace’s law, which describes the compression behavior of knitted compression samples in quasi-static deformation from an initially relaxed state to an extended state. Even though several researchers have used Laplace’s law, there is some discord between theoretical and experimental results. So, it is essential to pinpoint the most important parameters that influence the mechanical properties of the compression knitted garment in order to better describe the interface pressure it applies to the human body. Fabric parameters that influenced the interface pressure, such as elasticity modulus, strain, and thickness, were determined and integrated into Laplace’s law.