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This study employs the transmitter part of an ultrasonic proximity sensor to generate a powerful ultrasonic field for medical humidification. This field is created using an arrangement of small ultrasonic transmitter transducers configured in an acoustic levitator-style setup. As droplets pass through this ultrasonic field, they undergo disintegration, leading to an accelerated evaporation process. The research findings highlight a significant change in droplet size distribution due to ultrasonics, resulting in a notable increase in the rate of evaporation. As a result, this study presents a conceptual framework for reimagining humidification devices for lung therapeutic purposes through the utilization of simple sensor technology. [ABSTRACT FROM AUTHOR]

Focused ultrasound (FUS) is emerging as one of the most promising, non-invasive treatment techniques. The advancement of transducer technology has paved the way for dermatological applications. A comprehensive review is presented for healthcare practitioners and researchers, summarizing the effect of various operational parameters on the injury zone produced by ultrasound beams for various dermatological applications, which include skin tightening, fat reduction, hyperpigmentation and cancer treatment. In this article, we aim to highlight the efficient operational parameters of FUS to enhance pain relief during surgery and its affordability for skin treatment. Finally, a prospective future technique for efficient FUS is discussed. [ABSTRACT FROM AUTHOR]

Lung supportive devices (LSDs) have been extensively utilized in treating patients diagnosed with various respiratory disorders. However, these devices can cause moisture depletion in the upper airway by interfering with the natural lubrication and air conditioning process. To remedy this, current technologies implement heated humidification processes, which are bulky, costly, and nonfriendly. However, it has been demonstrated that in a breath cycle, the amount of water vapor in the exhaled air is of a similar quantity to the amount needed to humidify the inhaled air. This research proposes to trap the moisture from exhaled air and reuse it during inhalation by developing a state-of-the-art hydrophilic/hydrophobic polymer tuned to deliver this purpose. Using the atom transfer radical polymerization (ATRP) method, a substrate was successfully created by incorporating poly (N-isopropyl acrylamide) (PNIPAM) onto cotton. The fabricated material exhibited a water vapor release rate of 24.2 ± 1.054%/min at 32 °C, indicating its ability to humidify the inhaled air effectively. These findings highlight the potential of the developed material as a promising solution for applications requiring rapid moisture recovery. [ABSTRACT FROM AUTHOR]

This paper presents a Patient-Specific Aneurysm Model (PSAM) analyzed using Computational Fluid Dynamics (CFD). The PSAM combines the energy strain function and stress–strain relationship of the dilated vessel wall to predict the rupture of aneurysms. This predictive model is developed by analyzing ultrasound images acquired with a 6–9 MHz Doppler transducer, which provides real-time data on the arterial deformations. The patient-specific cyclic loading on the PSAM is extrapolated from the strain energy function developed using historical stress–strain relationships. Multivariant factors are proposed to locate points of arterial weakening that precede rupture. Biaxial tensile tests are used to calculate the material properties of the artery wall, enabling the observation of the time-dependent material response in wall rupture formation. In this way, correlations between the wall deformation and tissue failure mode can predict the aneurysm's propensity to rupture. This method can be embedded within the ultrasound measures used to diagnose potential AAA ruptures. [ABSTRACT FROM AUTHOR]

Piezoelectric transducers have numerous applications in a wide range of sensing and actuation applications. Such a variety has resulted in continuous research into the design and development of these transducers, including but not limited to their geometry, material and configuration. Among these, cylindrical-shaped piezoelectric PZT transducers with superior features are suitable for various sensor or actuator applications. However, despite their strong potential, they have not been thoroughly investigated and fully established. The aim of this paper is to shed light on various cylindrical piezoelectric PZT transducers, their applications and design configurations. Based on the latest literature, different design configurations such as stepped-thickness cylindrical transducers and their potential application areas will be elaborated on to propose future research trends for introducing new configurations that meet the requirements for biomedical applications, the food industry, as well as other industrial fields. [ABSTRACT FROM AUTHOR]

The textile industries in the Kingdom of Saudi Arabia are considered one of the important industries in which the produced parts are linked to the consumer who may choose them later to buy them. The culture of preserving fabric sustainability in the living room is not intended to retain the history of fabric. Therefore, it was necessary to think of more sustainable ways of implementing and manufacturing textiles by involving consumers in the manufacturing processes. The production of textile pieces in a way that meets his needs and fulfills his own desires and inclinations is the reason for creating that link between them, which makes him aware of the importance of each piece and thus the necessity of preserving it and striving for its sustainability by creating that sense of responsibility towards it. Among them, the aim of the research was to search for the most important different methods of implementing textile manufacturing in internal spaces and highlighting them through a comparison of five different methods. The research followed the analytical and comparative methodology, whereby each method was studied separately and analysed, then a comparison was made between the five different methods. After that, a set of important points were drawn up in the form of research recommendations in the process of sustaining industrial implementation. [ABSTRACT FROM AUTHOR]

Atherosclerosis causes blockages to the main arteries such as the aorta preventing blood flow from delivering oxygen to the organs. Non-invasive diagnosis of these blockages is difficult, particularly in primary healthcare. In this paper, the effect of arterial blockage development and growth is investigated at the descending aorta on some possible non-invasive assessment parameters including the blood pressure waveform, wall shear stress (WSS), time-average WSS (TAWSS) and the oscillation shear index (OSI). Blockage severity growth is introduced in a simulation model as 25%, 35%, 50% and 65% stenosis at the descending aorta based on specific healthy control aorta data clinically obtained. A 3D aorta model with invasive pulsatile waveforms (blood flow and pressure) is used in the CFD simulation. Blockage severity is assessed by using blood pressure measurements at the left subclavian artery. An arterial blockage growth more than 35% of the lumen diameter significantly affects the pressure. A strong correlation is also observed between the ascending aorta pressure values, pressure at the left subclavian artery and the relative residence time (RRT). An increase of RRT downstream from the stenosis indicates a 35% stenosis at the descending aorta which results in high systolic and diastolic pressure readings. The findings of this study could be further extended by transferring the waveform reading from the left subclavian artery to the brachial artery. [ABSTRACT FROM AUTHOR]

With the rapid development of wearable devices in recent years, stretchable strain sensors based on electrically conductive composites have attracted a great deal of attention owing to their good stretchability and piezoresistivity. However, due to the intrinsic restriction of these types of composites, the conventional stretchable strain sensors cannot do well in all aspect of sensing performance. A stretchable strain sensor based on carbon nanotubes/poly(dimethylsiloxane) composite with the serpentine shape was devised and fabricated. The sensor was readily manufactured through a molding technique. Not only can this sensor distinguish tension strain from transverse or longitudinal direction, but also exhibits good linearity of response to tensile strain. In terms of sensitivity, hysteresis and response time, the stretchable strain sensor showed significant performance. The sensing performance of this proposed stretchable sensor has been demonstrated to be good in this work and it also shows a good prospect for utilization in multifunctional wearable devices. [ABSTRACT FROM AUTHOR]

Lung supportive devices are widely used for respiratory ventilation and therapy to help providing breathing support for patients with various lung diseases including Obstructive Sleep Apnea. These devices deliver continuous air to the patient through a nasal or a facial mask. However, the use of these devices normally results in dryness in the upper airways. Various methods have been developed to improve the continuous positive pressure features using pressure oscillations, which can reduce the patient requirements such as reduction in the titration pressure and humidification requirements. Thus, the objective of this research is to investigate the differences between continuous positive pressure and positive pressure oscillation on the upper airway humidification. Human nasal (RPMI 2650) and bronchial (Calu-3) epithelial cells grown in air-liquid interface on permeable supports are used as a respiratory model. Trans-epithelial electrical resistance is measured before and after each experiment to evaluate the cell layer integrity and permeability. [ABSTRACT FROM AUTHOR]

In this work, thickness variations are introduced around the circumference of a piezoelectric cylindrical shell. The aim is to investigate the vibration characteristics of the shells and the effect of these step-thickness variations on the mode shape of vibration. These thickness variations require stress distribution analysis as well to avoid failure of the cylindrical shell. To this aim, two configurations of stepped-thickness shells with two and three circumferential thickness variations are investigated using FEA software, ANSYS. The results show that these steps assist in localizing vibration in the thin sections and excite mode shapes having the same circumferential wave number as the number of thickness variations. This can be a suitable approach to control and forcibly excite certain vibration mode shapes, which might be required for some applications. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a new approach to amplify the acoustic field generated by a uniform thickness piezoelectric cylindrical shell by introducing a stepped thickness variation at predetermined axial locations. The acoustic field and corresponding mode shapes of a uniform thickness piezoelectric tube are analyzed first and then, axial thickness variations are machined within the specified designed regions of the tube. The machining leads to the formation of thin-walled regions in the tube which localize the vibration amplitude within the machined spaces with higher amplitude. This results in a conspicuous increase of approximately 85% on average in the strength of the resultant acoustic field, though both specimens the uniform and stepped-thickness tubes have the same power consumption. The results of the simulations and experiments are in good agreement. Highlights • Acoustic radiation of stepped-thickness piezoelectric cylindrical tubes is studied. • Steps help localize vibration with large amplitudes within the thin regions. • Suitable interference of the radiated waves with larger amplitude increases SPL. • SPL increases by 85% for the same power input for stepped over uniform thickness. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of developing arterial blockage at the abdominal aorta on the blood pressure waves at an externally accessible location suitable for invasive measurements such as the brachial and the femoral arteries. Arterial blockages are created surgically within the abdominal aorta of healthy Wistar rats to create narrowing resemblance conditions. Blood pressure is measured using a catheter inserted into the right femoral artery. Measurements are taken at the baseline healthy condition as well as at four different severities (20, 50, 80 and 100 %) of arterial blockage. In vivo and in vitro measurements of the lumen diameter and wall thickness are taken using magnetic resonance imaging and microscopic techniques, respectively. These data are used to validate a 3D computational fluid dynamics model which is developed to generalize the outcomes of this work and to determine the arterial stress and strain under the blockage conditions. This work indicates that an arterial blockage in excess of 20 % of the lumen diameter significantly influences the pressure wave and reduces the systolic blood pressure at the right femoral artery. High wall shear stresses and low circumferential strains are also generated at the blockage site. [ABSTRACT FROM AUTHOR]

Obesity is a major risk factor for obstructive sleep apnea patients. In obese patients the severity of this risk can be reduced by bariatric surgery. This pilot study investigates the perioperative effects of bariatric surgery on obstructive sleep apnea and on the physical and biomechanical characteristics of the upper airway. Polysomnography and computer tomography data for 10 morbid obese patients promoted for bariatric surgery were conducted before surgery and at 6 and 12 months postoperatively for assessment of the oropharyngeal anatomy, and subsequent three-dimensional modelling of the airway. Mean values for the apnea/hypopnea index and body mass index significantly reduced after surgery. To combine the effect of changes in the upper airway volume and body mass index, a new volume body mass index is introduced. This index increases with a successful bariatric surgery. Although bariatric surgery leads to an effective weight reduction for all age groups, for obstructive sleep apnea patients it may be effective for middle age, less effective for 50–60 years, and further less effective for patients over the age of 60 years. [ABSTRACT FROM AUTHOR]

In an effort to better understand the droplet evaporation characteristics in nebulizer based humidification and aerosol based drug delivery, this paper investigates the variation in the droplet size distribution and the amount of water evaporated from the droplets. The experimental part was conducted on droplets generated by an ultrasound atomizer and delivered to a stream of air flowing along a conduit as is typically found in medical respiratory therapy devices. For the theoretical part a poly-disperse droplet evaporation model was developed and validated by the experimental results. A feature of this investigation is the consideration of the changes to different droplet size ranges (lower, middle and upper) within the droplet size distribution to better understand the evaporation process and also provide a more detailed comparison with the analytical model. As expected the experimental results show that increasing the air temperature and conduit length increase the amount of water evaporated and cause a shift in the droplet size distribution. However, changes to the droplet size distribution are also attributed to the fact that large droplets are possibly being removed from the air stream due to settling in the apparatus. The poly-disperse evaporation model accurately predicted water evaporation and changes to the median droplet sizes in the distribution. [ABSTRACT FROM AUTHOR]

Eucapnic voluntary hyperpnoea (EVH) challenge provides objective criteria for exercise-induced asthma (EIA) or exercise-induced bronchoconstriction (EIB), and it was recommended to justify the use of inhaled β2-agonists by athletes for the Olympics. This paper presents the development of a compact and easy-to-use EVH apparatus for assessing EIB in human subjects. The compact apparatus has been validated on human subjects and the results have been compared to the conventional EVH system. Twenty-two swimmers, including eleven healthy subjects and eleven subjects who had been physician-diagnosed with asthma, were recruited from sport and recreation centers throughout Auckland, New Zealand. Each subject performed two EVH challenge tests using the proposed breathing apparatus and the conventional Phillips EVH apparatus on separate days, respectively. Forced expiratory volume in one second (FEV1) was measured before and after the challenges. A reduction in FEV1 of 10% or more was considered positive. Of the eleven subjects who were previously diagnosed with asthma, EIB was present in all subjects (100%) in the compact EVH group, while it was presented in ten subjects (90.91%) in the conventional EVH challenge group. Of the eleven healthy subjects, EIB was present in one subject (4.55%) in the compact EVH group, while it was not present in the conventional EVH group. Experimental results showed that the compact EVH system has potential to become an alternative tool for EIB detection. [ABSTRACT FROM AUTHOR]

This paper reviews the evolution of focused ultrasonic transducers of various kinds for fluid atomization and vaporization. Ultrasonic transducers used for atomization purposes in biomedical, pharmaceutical, or industrial applications, such as surface acoustic wave (SAW) transducers, array of micromachined nozzles, and Fourier horn micromachined nozzles with or without a central channel, are all presented and compared. For simplicity of manufacturing and low cost, we focus on plates and curved and corrugated structures for biomedical humidification. [ABSTRACT FROM AUTHOR]

Airway smooth muscle (ASM) hyperconstriction is the cause of many respiratory diseases including asthma. In vitro testing has demonstrated that the active forces of ASM are reduced by length oscillation (LO) mimicking tidal breathing. In a previous study, we demonstrated that this force reduction can be further enhanced when superimposing oscillations (with certain frequencies and amplitudes) on this LO. In contrast, it has been reported that pressurizing the lung may help in relieving asthmatic airway constrictions. Ultimately, this pressurizing stretches the ASM and may disturb the acto-myosin cross-bridges in a manner similar to LO; however, it is of a static rather than dynamic nature. This research investigates the effect of combining both prestretch- and LO-applications on contracted porcine ASM. Isolated porcine ASM relaxation was tested with a 0.56%, 2%, or 4% stretch of its reference length (Lref) in addition to LO. These oscillations are composed of a main wave mimicking the normal breathing (frequency of 0.33 Hz and amplitude of 4% Lref) and superimposed oscillations (frequencies of 20, 30, 40, 60 and 80 Hz and amplitude of 1% Lref). The oscillations were maintained for 10 min. The results demonstrate that a prestretch of 0.56% and 2% Lref does enhance the contracted ASM relaxation at certain superimposed length oscillations frequencies while of 4% Lref does not. [ABSTRACT FROM AUTHOR]

Continuous positive airway pressure (CPAP) devices are popularly used for obstructive sleep apnoea (OSA) treatment. However, the noise level emission from these devices has been identified as a potential factor for patient’s discomfort and rejection. There is a need to obtain information on the noise characteristics and source locations in order to tackle the most serious noise source within these devices. A typical CPAP device was used for the investigation and its sound characteristics and sound power levels were determined. The noise generated from a centrifugal fan was also independently investigated to address its contribution to the overall noise of the device. Frequency analysis suggested that the noise generated from both the CPAP device and the fan is broadband in nature with discrete peaks containing rotational and non-rotational components. The broadband components were then studied in detail using numerical simulation approach. Computational aeroacoustics (CAA) method with hybrid approach was used to a three-dimensional (3-D) CPAP fluid model to predict the aerodynamic and aeroacoustics behaviours of the device. This showed a complicated flow structure involving flow separation, rotation, and vortices in several locations which resulted in high level of flow turbulence inside the device. The turbulent components were used to estimate the broadband noise level at source using the broadband noise source (BNS) models. It shows the most critical location is at the fan region and at the fan inlet. [ABSTRACT FROM AUTHOR]

During respiration, upper airway (UA) collapse occurs when the forces generated from the negative UA pressures exceed the forces produced by the UA muscles; which leads to loose soft tissue at the back of the mouth. At predetermined titration pressure, the Continuous Positive Airway Pressure (CPAP) normally provides a continuous pressurized and humidified air to prevent airway collapse. However, high titration pressures are not always tolerated by patients and may lead to damaging effects including stroke symptoms for cardiovascular disease patients. This paper hypothesizes that superimposed pressure oscillation can modulate the loose tissue and allow unblocking the upper airway passages to help reduce the required titration pressure. Using MRI scans, this paper investigates the effects of using pressure oscillations superimposed on the CPAP to keep the airway open at lower pressure distributions inside the upper airway and consequently increase the patients’ comfort and reduce their rejection to the CPAP. [ABSTRACT FROM AUTHOR]

A novel robust finite time disturbance observer (RFTDO) based on an independent output-finite time composite control (FTCC) scheme is proposed for an air conditioning-system temperature and humidity regulation. The variable air volume (VAV) of the system is represented by two first-order mathematical models for the temperature and humidity dynamics. In the temperature loop dynamics, a RFTDO temperature (RFTDO-T) and an FTCC temperature (FTCC-T) are designed to estimate and reject the lumped disturbances of the temperature subsystem. In the humidity loop, a robust output of the FTCC humidity (FTCC-H) and RFTDO humidity (RFTDO-H) are also designed to estimate and reject the lumped disturbances of the humidity subsystem. Based on Lyapunov theory, the stability proof of the two closed-loop controllers and observers is presented. Comparative simulations are carried out to confirm that the proposed controller outperforms conventional methods and offers greater accuracy of temperature, humidity, and carbon dioxide concentration, having superior regulation performance in terms of a rapid finite time convergence, an outstanding disturbance rejection property, and better energy consumption. In addition to presenting the comparative simulation results from the control applications on the VAV system, the quantitative values are provided to further confirm the superiority of the proposed controller. In particular, the proposed method exhibits the shortest settling time of, respectively, 15 and 40 min to reach the expected temperature and humidity, whereas other comparative controllers require a longer time to settle down. [ABSTRACT FROM AUTHOR]

Asthma is associated with reductions in the airway lumen and breathing difficulties that are attributed to airway smooth muscles (ASM) hyperconstriction. Pharmaceutical bronchodilators such as salbutamol and isoproterenol are normally used to alleviate this constriction. Deep inspirations and tidal oscillations (TO) have also been reported to relax ASM in healthy airways with less response in asthmatics. Little information is available on the effect of other forms of oscillation on asthmatic airways. This study investigates the effect of length oscillations (LO), with amplitude 1 and 1.5% in the frequency range 5-20 Hz superimposed on breathing equivalent LO, on contracted ASM dissected from sensitized mice. These mice are believed to show some symptoms such as airway hyperreactivity similar to those associated with asthma in humans. In the frequency range used in this work, this study shows an increase in ASM relaxation of an average of 10% for 1.5% amplitude when compared with TO, ISO, or the combination of both. No similar finding is observed with 1% amplitude. This suggests that superimposed length oscillation acting over the interaction of myosin and actin during contraction may lead to temporal rearrangement and disturbance of the cross-bridge process in asthmatic airways. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on a model for the evaporation of mono-disperse water droplets into air that can be used to aid the design of nebuliser based humidification systems for respiratory treatments and also for predicting droplet size distributions for pulmonary drug delivery devices under either isothermal or adiabatic conditions. The governing equations are developed from the coupled mass and energy balances for the droplets and for the surrounding air. An adjustment to one of these equations allows for the modelling of either isothermal or adiabatic conditions. Additionally, the proposed model allows for the variation of fluid transport and thermodynamic properties during the solution of the governing equations. The model is compared to and validated against an overall mass and energy balance and the literature. Confirmation of the general evaporation characteristics of water droplets evaporating into air is gained from the model results and, its accuracy, usability and applicability are improved over existing models. The proposed model indicates that the droplet evaporation process in humidification devices is largely unaffected by the initial water temperature and also indicates advantages of adiabatic conditions when using cascade impactor technology for droplet sizing. [Copyright &y& Elsevier]

Abstract: This paper investigates the effect of the various terms in the one-dimensional acoustic wave equation on the pulse characteristics within the aorta. To mimic the physiological nature of the systemic arteries, the aorta is modelled as an elastic conical tube. The frequency spectrum is used to study the effect of different terms in this equation on the pressure ratio between the aortic root at the heart exit and the iliac bifurcation. For validation, the effective reflection distance calculated using this model is within 7% error of clinical observations, suggesting that the model is able to mimic physiological pressure propagation with a high degree of accuracy and can therefore be used to generate and test hypotheses. This work demonstrates that: (i) tapering in the aorta lumen radius causes supplementary amplification of the pressure pulses in the system and increases the propagation velocity; however, tapering in the aorta wall thickness generates opposite effects, (ii) increasing the wall stiffness causes a change in the natural frequency of the system and increases the propagation velocity, and (iii) inclusion of either the advective momentum correction term or the viscosity term insignificantly affects the pressure ratio. The last observation suggests that the flow pattern does not influence the pressure propagation characteristics. [Copyright &y& Elsevier]

Abstract: This paper presents a novel approach to estimate stiffness changes in airway smooth muscles due to external oscillation. Artificial neural networks are used to model the stiffness changes due to cyclic stretches of the smooth muscles. The nonlinear relationship between stiffness ratios and oscillation frequencies is modeled by a feed-forward neural network (FNN) model. The structure of the FNN is selected through the training and validation using literature data from 11 experiments with different muscle lengths, muscle masses, oscillation frequencies and amplitudes. Data pre-processing methods are used to improve the robustness of the neural network model to match the non-linearity. The validation results show that the FNN model can predict the stiffness ratio changes with a mean square error of 0.0042. [Copyright &y& Elsevier]

Excessive airway narrowing due to airway smooth muscle (ASM) hyperconstriction is a major symptom in many respiratory diseases. In vitro imposition of length oscillations similar to those produced by tidal breathing on contracted ASM have shown to reduce muscle active forces, which is usually attributed to unconfirmed disruption of actomyosin cross-bridges. This research focuses on an in vitro investigation of the effect of mechanical oscillations on ASM reactivity and actomyosin cross-bridges. A computerized organ bath system was used to test maximally precontracted bovine ASM subjected to length oscillations at frequencies in the range of 10-100 Hz superimposed on tidal breathing oscillation. Using an immunofluorescence technique, two specific antibodies against the phospho-serine19 myosin light chain and the α-smooth muscle actin were used to analyze the colocalization between these two filaments. Data were processed using the plug-in "colocalization threshold" of ImageJ 1.43m software. The results demonstrate that both tidal and superimposed length oscillations reduce the active force in contracted ASM for a relatively long term and that the latter enhances the force reduction of the former. This reduction was also found to be frequency and time dependent. Additionally colocalization analysis indicates that length oscillations cause the detachment of the actomyosin connections and that this condition is sustained even after the cessation of the length oscillations. [ABSTRACT FROM AUTHOR]

Abstract: Nasal morphology plays an important functional role in the maintenance of upper airway health. Identification of functional regions, based on morphological attributes, assists in correlating location to primary purpose. The effects of morphological variation on heat and water mass transport in congested and patent nasal airways were investigated by examining nasal cross-sectional MRI images from 8 healthy subjects. This research confirms the previous identification of functional air-conditioning regions within the nose. The first is the anterior region where the morphology prevents over-stressing of tissue heat and fluid supply near the nares. The second is the mid region where low flow velocity favours olfaction and particle deposition. The third is the posterior region which demonstrates an increase in heat and water mass flux coefficients to compensate for rising air humidity and temperature. Factors identified within the congested airway that favour enhanced mucocillary clearance were also identified. [Copyright &y& Elsevier]

Abstract: Preterm newborn infants may develop respiratory distress syndrome (RDS) due to functional and structural immaturity. A lack of surfactant promotes collapse of alveolar regions and airways such that newborns with RDS are subject to increased inspiratory effort and non-homogeneous ventilation. Pressure oscillation has been incorporated into one form of RDS treatment; however, how far it reaches various parts of the lung is still questionable. Since in-vivo measurement is very difficult if not impossible, mathematical modeling may be used as one way of assessment. Whereas many models of the respiratory system have been developed for adults, the neonatal lung remains essentially ill-described in mathematical models. A mathematical model is developed, which represents the first few generations of the tracheo-bronchial tree and the 5 lobes that make up the premature ovine lung. The elements of the model are derived using the lumped parameter approach and formulated in Simulink™ within the Matlab™ environment. The respiratory parameters at the airway opening compare well with those measured from experiments. The model demonstrates the ability to predict pressures, flows and volumes in the alveolar regions of a premature ovine lung. [Copyright &y& Elsevier]

Abstract: Surfactant dysfunction plays a major role in respiratory distress syndrome (RDS). This research seeks to determine whether the use of natural surfactant, Curosurf™ (Cheisi Farmaceutici, Parma, Italy), accompanied with pressure oscillations at the level of the alveoli can reduce the surface tension in the lung, thereby making it easier for infants with RDS to maintain the required level of functional residual capacity (FRC) without collapse. To simulate the alveolar environment, dynamic surface tension measurements were performed on a modified pulsating bubble surfactometer (PBS) type device and showed that introducing superimposed oscillations about the tidal volume excursion between 10 and 70Hz in a surfactant bubble lowers interfacial surface tension below values observed using tidal volume excursion alone. The specific mechanisms responsible for this improvement are yet to be established; however it is believed that one mechanism may be the rapid transient changes in the interfacial area increase the number of interfacial binding sites for surfactant molecules, increasing adsorption and diffusion to the interface, thereby decreasing interfacial surface tension. Existing mathematical models in the literature reproduce trends noticed in experiments in the range of breathing frequencies only. Thus, a modification is introduced to an existing model to both incorporate superimposed pressure oscillations and demonstrate that these may improve the dynamic surface tension in the alveoli. [ABSTRACT FROM AUTHOR]

Different characteristic points used for the evaluation of pulse wave velocity (PWV) give significantly different results. Hence, the accuracy of using these points is questionable. There is need for quantitative comparison of different techniques to determine PWV. Previous studies aimed at comparing different PWV measurement techniques have been noted, however, on a limited number of smaller animals (mice, dogs, etc.). This simulation-based study aims to compare different techniques for PWV measurement in a large representative human population. A computer model is developed for simulating the pressure wave propagation between the carotid and femoral arteries. Using relationships observed in clinical trials, the model input parameters for a statistically representative population are expressed in terms of a person's age, gender and height. The model is used to calculate the carotid-femoral pressure ratio for different individuals, which is then parameterised into a number of features, and the equivalent propagation time is calculated using the phase-slope method. Using this time, the apparent phase velocity is determined and compared with PWV determined by the foot-to-foot technique. The two velocities compare well with a difference of 0.0059±0.0904 m/s. An averaging criterion for the calculation of apparent phase velocity has been tested and shown to give good estimates compared to the foot-to-foot technique. As it does not involve the identification of characteristic points on the measured pressure waves, the phase-slope method is more suitable for implementation in PWV monitors. [ABSTRACT FROM AUTHOR]

• Vibroacoustic characteristics of circumferentially stepped transducers are studied. • Steps excite circumferential mode numbers which are the same as number of steps. • Localized higher amplitude vibration is induced at thin, stepped regions. • A design is identified with nearly doubled sound pressure at the same input power. • Increasing input excitation is found inefficient compared to stepped design. Circular cylindrical transducers have a wide range of applications in ultrasound generation. Introducing axial or circumferential stepped-thickness variations affects the performance of these transducers. This paper investigates the effect of circumferential stepped-thickness variations on the vibration and acoustic characteristics of a circular cylindrical piezoelectric shell. FEM software ANSYS is used to simulate these characteristics and experiments are performed to validate the simulations. Stress concentration levels due to these steps are observed in order to avoid exceeding the material limit. The results show that these steps can excite certain mode shapes which produce strong ultrasound fields and these modes have circumferential wave numbers commensurate with the number of stepped regions. These steps localize the vibration within the thin-walled regions leading to higher amplitude acoustic waves produced by constructive interference. Superiority of a circumferentially stepped transducer over an axially stepped one is demonstrated in this study through a much more uniform acoustic field along the length of the transducer as well as a lower frequency of operation at the intended mode shape. The effect of input excitation is also investigated and it is shown that introducing circumferential steps is more effective in terms of acoustic amplification than increasing the input excitation for the uniform-thickness transducer. [ABSTRACT FROM AUTHOR]

Abstract: The heat transfer characteristics of various insulated long polygonal ducts are analyzed using one-dimensional Plane Wedge Thermal Resistance (PWTR) and Plate Thermal Resistance (PTR) models. It is found that errors generated by the PWTR model are all positive and those generated by the PTR model are all negative. Thus, the Combined Plate Wedge Thermal Resistance (CPWTR) model generated by implementing PWTR and PTR models and equating the proportion factors can neutralize the positive and negative errors and generate reasonably accurate results when compared with the two-dimensional numerical analysis. Most errors generated by the one-dimensional CPWTR model are within ±1% for practical sizes and insulated thickness for air-conditioning and refrigeration applications. Meanwhile, the PTR model can be used to estimate accurately the maximum or minimum surface temperatures, respectively, with hot or cold fluids inside an insulated triangular, rectangular or pentagonal duct. [Copyright &y& Elsevier]

Continuous positive airway pressure is the most effective long-term treatment for obstructive sleep apnoea, which is a sleeping disorder characterized by pauses in breathing during sleep. It introduces pressurized atmospheric air into the respiratory system in order to maintain open airways without blockage. Some continuous positive airway pressure devices incorporate a convective heat transfer humidifier to overcome dryness. However, many side effects, including the unacceptable excess of water droplets in the air supply line, have been reported and improvements are essential for better patient's comfort and acceptance of the therapy. The excess of water droplets is attributed to the qualitative rather than the quantitative approach of determining the rise in temperature and humidity of the inspired air. Therefore, a human upper airway mathematical model is developed to predict the heat and water transfer variation between normal breathing and continuous positive airway pressure conditions and determine the optimal input temperature and relative humidity in the continuous positive airway pressure humidifier. [ABSTRACT FROM AUTHOR]

Research indicates that deaths due to fall incidents are the second leading cause of unintentional injury deaths in the world. Death by fall due to a person texting or talking on mobile phones while walking, impaired vision, unexpected terrain changes, low balance, weakness, and chronic conditions has increased drastically over the past few decades. Particularly, unexpected terrain changes would many times lead to severe injuries and sometimes death even in healthy individuals. To tackle this problem, a warning system to alert the person of the imminent danger of a fall can be developed. This paper describes a solution for such a warning system used in our bio-inspired wearable pet robot, KiliRo. It is a terrain perception system used to classify the terrain based on visual features obtained from processing the images captured by a camera and notify the wearer of terrain changes while walking. The parrot-inspired KiliRo robot can twist its head and the camera up to 180 degrees to obtain visual feedback for classification. Feature extraction is followed by K-nearest neighbor for terrain classification. Experiments were conducted to establish the efficacy and validity of the proposed approach in classifying terrain changes. The results indicate an accuracy of over 95% across five terrain types, namely pedestrian pathway, road, grass, interior, and staircase. [ABSTRACT FROM AUTHOR]

• Acoustic radiation of cylindrical piezoelectric tubes with external, internal and internal-external axial steps is studied. • Localized higher amplitude vibration is induced at thin-walled, stepped regions. • High stress levels affect the vibration and acoustic performance of stepped tubes. • A design is identified with nearly doubled sound pressure at the same input power. • Effect of input excitation voltage on the output acoustic pressure is nonlinear. Using stepped-thickness variations, this work aims at amplifying the strength of the focused acoustic field generated inside a hollow piezoelectric cylindrical tube transducer without increasing the driving power. This requires a full understanding of the vibration and acoustic radiation characteristics of various configurations of piezoelectric tube transducers with internal and external axial stepped-thickness variations. A uniform-thickness cylindrical shell is machined at specific regions to acquire a stepped-thickness cylindrical shell with thin-walled regions. The design procedure includes determining the location and number of these thin regions. ANSYS software is used to determine the frequencies and mode shapes of various configurations of these shells. However, stress concentration, as an important design consideration, is also scrutinized at the step regions to avoid exceeding the material fatigue limit. An optimum design configuration for the stepped-thickness transducer is identified. Stronger acoustic fields are obtained using geometrical variations without any increase in the driving power. The simulations are validated experimentally with reasonable agreement. [ABSTRACT FROM AUTHOR]

This work investigates the effect of focused acoustic field on a stream of polydisperse micro water droplets generated by a nebulizer. The acoustic field is induced by a customized axially stepped-thickness piezoelectric circular cylindrical transducer. Exposure of the droplets to the acoustic field while passing through the transducer improves the relative movement between the air and droplets, which results in an enhanced heat transfer and facilitates evaporation. Larger droplets in the stream are affected more than small ones by the acoustic field. A noticeable reduction in the size of 90% of droplets has been observed. This improves and narrows the droplet size distribution in the stream, which is of practical importance for some drug delivery applications or humidification in lung supportive devices. • Acoustically enhanced evaporation of a polydisperse micro droplet stream was studied. • A noticeable reduction in the size of 90% of droplets has been observed. • Acoustic field improved relative movement between air and droplets. • Acoustic SPLs way above 160 dB affected droplet size distribution more efficiently. • Large droplets were affected more due to higher relative movement and heat transfer. [ABSTRACT FROM AUTHOR]

Abstract Phantoms, or physical simulants of biological specimens are useful for research and development due to the unavailability of real tissues. One such example is human blood, which is a precious resource in healthcare and is not normally available for research purposes, unless it is no longer fit for human use. This work focusses on the considerations for developing a human forearm phantom specifically to exhibit the dielectric properties of fat, muscle and blood tissue domains, for bioimpedance analysis. The behavior for the tissue simulants were identified based on the conductivity and permittivity values within the β dispersion frequency range (1 kHz–2 MHz). A mixture of 80% propylene glycol and 20% 4 M saline solution was found to replicate the properties of blood within acceptable tolerances in the β dispersion frequency range. A 5% agar with 0.05% saline mixture was found to mimic the properties of fat, whereas the muscle properties were mimicked through a suspension of agar, gelatine, saline and propylene glycol. This was followed by construction of the forearm phantom with three geometries to simulate the three arterial diameter instances due to blood flow. The measurements were performed using the Quadra® Impedance Spectroscopy device within 1 kHz–349 kHz which were fitted to a Cole model to estimate the entire frequency spectrum within 1 kHz–2 MHz and compared with a previously performed simulation study. This methodology can provide a very economical, reproducible and robust means for investigating the dielectric response of tissues across several research and training platforms, and more importantly bioimpedance applications. Highlights • Electrical response of tissues is the basis of bioimpedance applications. • Dielectric phantoms provide better alternatives to real tissues. • Fat, muscle and blood tissues within a human forearm were considered. • A mixture of saline and propylene glycol mimicked the dielectric response of blood. • Gelatine and agar suspensions were found to mimic muscle and fat tissues. [ABSTRACT FROM AUTHOR]

In recent years, the increasing demand for flexible and wearable devices requires the synthesis of novel stretchable and piezoresistive materials. Piezoresistive polymer composites are popular due to their excellent piezoresistivity and high stretchability, which can readily be attached to clothes or human body. In this study, a stretchable and sensitive strain sensor based on multi-wall carbon nanotube (MWCNT)/polydimethylsiloxane (PDMS) composite with an excellent overall performance was fabricated in a facile and effective way. The composite with 7% MWCNTs is ideal for strain sensor compared to those with 5% and 9% MWCNTs. Not only can the gauge factor reach 5-9 under 10-40% strain, but also the curve of relative change in resistance versus strain is almost linear. The strain sensor can respond immediately with low hysteresis. The strain sensor also exhibits great stability under 1000 cycles of stretching/releasing, demonstrating the desirable long-term endurance to mechanical stimuli as well. The strain sensor was then implemented to monitor human motions (finger and wrist bending), precisely sensing the motion deformation and states. In conclusion, the reported sensor based on MWCNT/PDMS composite possesses numerous favorable characteristics including high sensitivity, good stretchability, ease of fabrication, and promising practical application in the field of biomedical system and wearable electronic devices. [ABSTRACT FROM AUTHOR]

Immigration and epidemiological studies provide evidence indicating the correlation of high ultraviolet exposure during childhood and increased risks of melanoma in later life. While the explanation of this phenomenon has not been found in the skin, a class of hair has been hypothesized to be involved in this process by transmitting sufficient ultraviolet rays along the hair shaft to possibly cause damage to the stem cells in the hair follicle, ultimately resulting in melanoma in later life. First, the anatomy of hair and its possible contribution to melanoma development, and the tissue optical properties are briefly introduced to provide the necessary background. This paper emphasizes on the review of the experimental studies of the optical properties of human hair, which include the sample preparation, measurement techniques, results, and statistical analysis. The Monte Carlo photon simulation of human hair is next outlined. Finally, current knowledge of the optical studies of hair is discussed in the light of their possible contribution to melanoma development; the necessary future work needed to support this hypothesis is suggested. [ABSTRACT FROM AUTHOR]

Abdominal aortic aneurysms (AAA) continue to pose a high mortality risk despite advances in medical imaging and surgery. Intraluminal thrombus (ILT) is detected in most AAAs and may critically impact their development. Therefore, understanding ILT deposition and growth is of practical importance. To assist in managing these patients, the scientific community has been researching the relationship between intraluminal thrombus (ILT) and hemodynamic parameters wall shear stress (WSS) derivatives. This study analyzed three patient-specific AAA models reconstructed from CT scans using computational fluid dynamics (CFD) simulations and a pulsatile non-Newtonian blood flow model. The co-localization and relationship between WSS-based hemodynamic parameters and ILT deposition were examined. The results show that ILT tends to occur in regions of low velocity and time-averaged WSS (TAWSS) and high oscillation shear index (OSI), endothelial cell activation potential (ECAP), and relative residence time (RRT) values. ILT deposition areas were found in regions of low TAWSS and high OSI independently of the nature of flow near the wall characterized by transversal WSS (TransWSS). A new approach is suggested which is based on the estimation of CFD-based WSS indices specifically in the thinnest and thickest ILT areas of AAA patients; this approach is promising and supports the effectiveness of CFD as a decision-making tool for clinicians. Further research with a larger patient cohort and follow-up data are needed to confirm these findings. [ABSTRACT FROM AUTHOR]

This work presents a simulation analysis of the bioimpedance measurements at the human forearm. The Ansys® High Frequency Structure Simulator (HFSS) has been used to analyze the electrical response of a section of human forearm with three domains of dielectric behavior - fat, muscle and artery (blood). The impedance values were calculated as the ratio of the output voltage at the electrodes to the applied known current (1 mA). A model was developed and was simulated for impedance values obtained within a frequency range of 1 kHz to 2 MHz. The measurements were done at three instances of radial artery diameter. The maximum resistance and reactance values were calculated as 445 Ω and 178.5 Ω 356 Ω and 138 Ω and 368 Ω and 144.3 Ω for diameters 2.3 mm, 2.35 mm, and 2.4 mm respectively. The set of impedance values obtained followed the Cole-plot trend. The results obtained were found to be in excellent agreement with the Cole modelling. The set of values obtained at three different diameters reflected the effect of blood flow on impedance values. [ABSTRACT FROM AUTHOR]

This paper presents a study on the synthesis of porous polymers with an application to microneedles. A range of Poly (ethylene glycol-co-methacrylic acid) polymers are synthesised using bulk polymerisation techniques to produce porous polymers with various strength and fluid transport characteristics. The synthesised materials are morphologically and mechanically characterised. Using different porogens in the polymer synthesis results in different mechanical strength and fluid flow characteristics. The results indicate that the fluid flow characteristics of the polymers can be sacrificed to improve strength. Optimum polymer strength can be attained by synthesising polymers with macropores that are interconnected via nanopores using the minimum amount of porogenic solvents. [ABSTRACT FROM AUTHOR]

Microwave ablation (MWA) is a minimally invasive thermal treatment modality that has already evolved as a promising alternative to radiofrequency ablation for treating different types of malignant and benign tumors, especially ≥3 cm in diameter. The efficacy of thermal ablative therapies is mainly judged by the ablation volume attained post‐ablation. In this regards, the present study aims at analyzing the influence of six critical parameters, as follows, relative permittivity, electrical conductivity, volumetric heat capacity, thermal conductivity, blood perfusion rate, and applied power on the ablation volume attained during MWA. Taguchi's L27 orthogonal array has been adopted for the current problem with six input variables having three levels each. The electric and thermophysical properties considered in the study have been derived from liver, lung, breast, and kidney. Finite element method (FEM) based numerical simulations of MWA have been conducted on three‐dimensional homogeneous model of biological tissue using coaxial single slot microwave antenna. Further, the ranking and the contribution of each parameter on the ablation volume attained during MWA have been quantified using analysis of variance. The corollaries drawn from the study would be useful to the clinical practitioners during the treatment planning stage of the MWA. [ABSTRACT FROM AUTHOR]

Background: Hypertension (HTN) is the single greatest cardiovascular risk factor worldwide. HTN management is usually guided by brachial cuff blood pressure (BP), but questions have been raised regarding accuracy.Objectives: This comprehensive analysis determined the accuracy of cuff BP and the consequent effect on BP classification compared with intra-arterial BP reference standards.Methods: Three individual participant data meta-analyses were conducted among studies (from the 1950s to 2016) that measured intra-arterial aortic BP, intra-arterial brachial BP, and cuff BP.Results: A total of 74 studies with 3,073 participants were included. Intra-arterial brachial systolic blood pressure (SBP) was higher than aortic values (8.0 mm Hg; 95% confidence interval [CI]: 5.9 to 10.1 mm Hg; p < 0.0001) and intra-arterial brachial diastolic BP was lower than aortic values (-1.0 mm Hg; 95% CI: -2.0 to -0.1 mm Hg; p = 0.038). Cuff BP underestimated intra-arterial brachial SBP (-5.7 mm Hg; 95% CI: -8.0 to -3.5 mm Hg; p < 0.0001) but overestimated intra-arterial diastolic BP (5.5 mm Hg; 95% CI: 3.5 to 7.5 mm Hg; p < 0.0001). Cuff and intra-arterial aortic SBP showed a small mean difference (0.3 mm Hg; 95% CI: -1.5 to 2.1 mm Hg; p = 0.77) but poor agreement (mean absolute difference 8.0 mm Hg; 95% CI: 7.1 to 8.9 mm Hg). Concordance between BP classification using the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure cuff BP (normal, pre-HTN, and HTN stages 1 and 2) compared with intra-arterial brachial BP was 60%, 50%, 53%, and 80%, and using intra-arterial aortic BP was 79%, 57%, 52%, and 76%, respectively. Using revised intra-arterial thresholds based on cuff BP percentile rank, concordance between BP classification using cuff BP compared with intra-arterial brachial BP was 71%, 66%, 52%, and 76%, and using intra-arterial aortic BP was 74%, 61%, 56%, and 65%, respectively.Conclusions: Cuff BP has variable accuracy for measuring either brachial or aortic intra-arterial BP, and this adversely influences correct BP classification. These findings indicate that stronger accuracy standards for BP devices may improve cardiovascular risk management. [ABSTRACT FROM AUTHOR]

The conventional gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells incorporates a carbon-based substrate, which suffers from electrochemical oxidation as well as mechanical degradation, resulting in reduced durability and performance. In addition, it involves a complex manufacturing process to produce it. The proposed technique aims to resolve both these issues by an advanced 3D printing technique, namely selective laser sintering (SLS). In the proposed work, polyamide (PA) is used as the base powder and titanium metal powder is added at an optimised level to enhance the electrical conductivity, thermal, and mechanical properties. The application of selective laser sintering to fabricate a robust gas diffusion substrate for PEM fuel cell applications is quite novel and is attempted here for the first time. [ABSTRACT FROM AUTHOR]

Direct-ethanol fuel cells (DEFCs) hold a promising future owing to its simple balance of plant operation and potential high-energy density. The significant challenges associated with it is the fuel crossover, which limits its performance and durability. In the present work, Pt-Pd nanocomposites were fused so as to find its impact on the anode design of DEFC. The current paper aimed to address these issues optimally and it also investigated the ethanol crossover by various electrochemical characterization techniques. [ABSTRACT FROM AUTHOR]