Doctoral Theses
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The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.
For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.
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Browsing Doctoral Theses by Supervisor "Al-Jumaily, Ahmed"
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- ItemAirway smooth muscle dynamics(Auckland University of Technology, 2010) IJpma, GijsThe current study aims to investigate the relative contributions of each of the processes that govern airway smooth muscle mechanical behaviour. Studies have shown that breathing dynamics have a substantial effect on airway constriction in healthy and diseased subjects, yet little is known about the dynamic response of the main instigator of airway constriction, Airway Smooth Muscle (ASM). In this work several models are developed to further the understanding of ASM dynamics, particularly the roles and interactions of the three dominant processes in the muscle: contractile dynamics, length adaptation and passive dynamics. Three individual models have been developed, each describing a distinct process or structure within the muscle. The first is a contractile model which describes the contractile process and the influence of external excitation on contractile behaviour. The second model incorporates the contractile model to describe length adaptation, which includes the reorganisation and polymerisation of contractile elements in response to length changes. The third model describes the passive behaviour of the muscle, which entails the mechanical behaviour of all non-contractile components and processes. As little data on the passive dynamics of the muscle was available in the literature, a number of experiments were conducted to investigate relaxed ASM dynamics. The experimental data and mathematical modelling showed that passive dynamics plays not only a dominant role in relaxed ASM, but contributes considerably to the dynamics of contracted muscle as well. A novel theory of sequential multiplication in passive ASM is proposed and implemented in a mathematical model. Experiments and literature validated the model simulations. Further integration of the models and improved force control modelling of length adaptation is proposed for future study. It is likely that the coupling of the models presented here with models describing other airway wall components will provide a more complete picture of airway dynamics, which will be invaluable for understanding respiratory disease.
- ItemAirway smooth muscle response to vibrations(Auckland University of Technology, 2006) Du, YouhuaThe main goal of this research was the in vitro investigation of the stiffness response of contracted airway smooth muscles under different external oscillations. Living animal airway smooth muscle tissues were dissected from pig tracheas and stimulated by a chemical stimulus (acetylcholine). These tissues were then systematically excited with different external vibrations. The force change was recorded to reflect the muscle stiffness change under vibration. The static and dynamic stiffness of contracted airway smooth muscles in isometric contraction were determined before, during and after vibrations. A continuum cross-bridge dynamic model (the fading memory model) was modified to accommodate smooth muscle behaviour and dynamically describes the cross-bridge kinetics. A two-dimensional finite element model (FEM) was developed to simulate longitudinal and transverse vibrations of the tissue. An empirical equation, derived from the experiments, is incorporated into the FEM. The results indicate that the stiffness of active smooth muscles can be physically reduced using external vibrations. This reduction is caused by a certain physical position change between actin and myosin. The dynamic stiffness has the tendency of decreasing as the frequency and/or amplitude of external vibration increases. However, the static stiffness decreases with an increase in the frequency and amplitude of excitation until it reaches a critical value of frequency where no variation in stiffness is observed. It is postulated that the tissue elasticity and mass inertia are the main contributors to the dynamic stiffness while the actin-myosin cross-bridge cycling is the main contributor to the static stiffness.
- ItemAn Investigation into Using Ultrasound for Airway Humidification(Auckland University of Technology, 2023) Uddin, RiazHumidification is an essential process required in many lungs therapeutic devices to overcome the complications caused by dry air in the lungs. The humidification requirements for medical devices are quite different from those for currently available ultrasonic humidifiers. For breathing devices, humidifiers need to produce vapours with droplets of less than 1 µm in diameter, while all other ultrasonic droplet generation devices reported to date cannot consistently generate required diameter droplets. The existing humidifier mechanisms for medical devices are traditional heat transfer devices that add bulky circuitry to the system. The required vaporisation for lung therapeutic devices can be achieved through accelerated evaporation using high-intensity ultrasound impact on droplets. This study explores an alternative approach for generating a strong ultrasonic field that can facilitate the rapid evaporation of droplets, a key requirement for human airway humidification in therapeutic devices such as the Continuous Positive Airway Pressure (CPAP) device. The technique involves applying high-intensity ultrasound to droplets to accelerate their evaporation. The ultrasonic levitation mechanism uses high-intensity ultrasound that can hold droplets. By precisely controlling the frequency and intensity of the ultrasound waves, it can also be used to effectively impact droplets during evaporation if placed as the second stage ultrasonic field. Various options for high-intensity ultrasound field transducers were researched, and with the aid of theoretical investigation and CAD with FEA analysis, the design of a levitator was formed and implemented. The levitator's output was measured, and its interaction with droplets was experimented. The results provide the significant impact of the ultrasonic field on droplets accelerated evaporation. The research has proposed a novel design for an ultrasonic humidifier that can be used in human airways and will help reimagine humidifiers for CPAP systems. It will aid in decreasing the size of the humidifier, which will allow better equipment mobility and improve power efficiency. Ultrasonic humidifier studies will not be restricted to the humidification and miniaturization of the CPAP system but will also help in redesigning humidification systems for other relevant respiratory therapy equipment, such as ventilators.
- ItemBiodegradable Polymer Blends/Composites, With High Performance Characteristics, for Packaging Application(Auckland University of Technology, 2021) Govindan, SrinivasanThis research project focuses on developing biodegradable polymer films for flexible packaging applications with high-performance characteristics. During this research, three biodegradable polymers, namely, Polybutylene succinate (PBS), Polyhydroxybutyrate (PHB), and Polylactic acid (PLA), were selected and investigated to improve their performance. Three strategies were adopted for improvement; namely, i) by blending with Polycaprolactone (PCL), a highly biodegradable polymer, ii) by plasticization with three plasticizers, and iii) by the fabrication of nanocomposites/ by incorporating nanomaterials such as nano-cellulose and nano-clay. Polymer films of various compositions were fabricated by injection molding, followed by hot-pressing and carried out an investigation of the tensile properties, water vapor transmission rate (WVTR)/ barrier properties, and biodegradability characteristics (in-home compost & seawater medium) of polymer films, and analyzed the effect of blending, plasticization, and nanomaterials. The investigation carried out on blending of PBS, PHB, and PLA with PCL (with 10, 20, 30, and 40 wt% PCL) demonstrated enhancement of tensile elongation (ε), improvement in water vapor barrier property (decrease in WVTR), and increase in the biodegradation rate (in-home compost and seawater), with the addition of PCL, though with a slight decrease in tensile strength (σ). It was concluded from the studies on blending that polymer blending with approximately 10-20wt % PCL offer overall enhancement of polymer properties. Studies carried out on plasticization of PBS-PCL20, PHB-PCL20, and PLA-PCL20 blends, with three plasticizers, [GTA, a monomeric plasticizer P1; Ultramoll, a polymeric plasticizer P2; and mixed plasticizer P3 ( 1: 1 mix of P1 and P2)], with 5 wt% plasticizer loading, indicated, a substantial increase in elongation at break and biodegradability, with the addition of all the three plasticizers, though with a decrease in tensile strength (σ) and water vapor barrier property. It was concluded from the plasticization study that mixed plasticizer P3 offers the best overall performance enhancement. An investigation carried out on nanocomposites of PBS, PHB and PLA, prepared by incorporating nano cellulose and nano clay ( 1, 3, and 6 wt%) in plasticized blends, ( PBS-PCL20-P3, PHB-PCL20-P3, and PLA-PCL20-P3) demonstrated improved water vapor barrier properties (decrease in WVTR), improved tensile strength (except for PLA), and higher biodegradation rate with the addition of both nano cellulose and nano clay. Though a decrease in elongation at break was observed with nanomaterials' addition to the plasticized blends, the cumulative improvement was observed for neat polymers. Studies on nanomaterial content's effect indicated that the best performance was obtained with 1wt % nano cellulose and 6% nano clay, which differ only slightly in properties. The nanocomposites with nano cellulose (1wt%), namely PBS-PCL20-P3-nCell1, PHB-PCL20-P3- nCell1, and PLA-PCL20-P3- nCell1 was found to have improved properties, such as higher tensile elongation by 50%, 168%, and 494%; higher water vapor barrier properties (lesser WVTR) by 59%, 46% and 48%; higher biodegradation rate in home compost media by 56%, 13%, and 93%; and higher biodegradation rate in seawater media (after 180 days) by 79%, 10%, and 92% respectively, compared to neat PBS, PHB and PLA. The nanocomposites with 6 wt% nano clay were found to have slightly higher tensile strength and water vapor barrier properties, though slightly lower ductility and biodegradability. Hence nanocomposites with 1% nano cellulose or 6% nano clay may be used depending on the application requirement. The present investigation thus demonstrated the overall performance improvement of PBS, PHB, and PLA polymers through blending, plasticization, and nanomaterials. The present investigation has also generated valuable data on biodegradation of PBS, PHB and PLA polymers, PCL blends, plasticized blends, and nanocomposites under ambient temperature/ home composting conditions and marine environment, which will be of great help for future researchers.
- ItemComputational fluid dynamic modelling for arterial diseases assessment(Auckland University of Technology, 2012) Al-Rawi, MohammadOne of the leading causes of death is cardiovascular disease, being 30% of all deaths worldwide and 40% of those in New Zealand. In other words, every 90 minutes a New Zealander dies due to cardiovascular disease. Cardiovascular mortality is higher in New Zealand than Australia, but the reasons for this are not clear. Although Australia and New Zealand are similar politically, culturally, and socioeconomically, mortality from cardiovascular disease is about 25% higher in New Zealand than in Australia. In recent years, engineers and scientists have collaborated with the medical community to find new methods and approaches for assessing and investigating the development of cardiovascular diseases such as abdominal aortic aneurysm and atherosclerosis. In this thesis, atherosclerosis and aneurysm diseases are investigated and analysed using computational fluid dynamic/finite element (CFD/FE) methods. These models are validated against the in vivo and in vitro experiments performed on animals. The experimental models are also investigated; the assessment of arterial blockages using blood pressure waveforms obtained invasively at the right femoral artery. The animal experiments are performed following appropriate ethical protocols (R915) on Wistar rats weighing between 250-350g. An arterial blockage is created surgically within the abdominal aorta of healthy animals to create an unhealthy condition. Blood pressure waveforms are measured by injecting catheter into the right femoral artery of the rat. These measurements are taken at the baseline (healthy condition) and at four different severities of arterial blockage of the abdominal aorta for the same specimen. In vivo and in vitro measurements of the arterial diameter and wall thickness are also taken using Magnetic Resonance Imaging (MRI) and microscopic techniques, respectively. These data are then input onto CFD/FE models in order to develop a new, non-invasive method of assessing arterial blockage. The experimental and computational results indicate that arterial blockages occurring within the abdominal aorta could be assessed, and the development of the disease diagnosed, very clearly and non-invasively at the right femoral artery. The findings of the animal model are then implemented in the human model for screening atherosclerosis and aneurysm at the brachial artery. These diseases are modelled and simulated in a 3D CFD/FE aorta geometry using the fluid–structure interaction (FSI) approach on the commercial software ANSYS®14.0. Literature blood flow waveform datum is assumed at the inlet and invasive catheter pulsatile pressure waveforms data is imposed at the four outlets of the aorta (provided by Green Lane Hospital under ethic approval number NTX/09/11/109). Correlations between the stress phase angle (SPA), augmentation index (AI), lumen diameter and blood pressure waveforms for various scenarios of diseased models are made and compared to the control model. The results show that CFD/FE models with different radii and thicknesses at the abdominal aorta significantly influence blood pressure waveforms, high negative SPA values, and high AI detected at the brachial artery.
- ItemThe effect of pressure oscillations on respiratory performance(Auckland University of Technology, 2009) Reddy, Prasika InderjeethThis thesis is aimed at understanding the effective operation of the Bubble CPAP System when treating neonates with respiratory distress syndrome (RDS). It is also aimed at determining the effect that pressure oscillations have on respiratory performance in terms of the work of breath (WOB) and surfactant dynamics. The principle objectives were to: • Create an original multi-compartmental model of the neonatal lung that includes compartment-specific inertance and viscoelasticity for 128 day (premature) and 142 day (near-term) gestation lambs. • Validate the model with experimental data obtained from clinical trials. • Use the model to determine the effect of pressure oscillations as produced by the Bubble CPAP System on respiratory performance. • Determine the frequencies of oscillation that provide the optimal respiratory support. • Build a surface tension model that simulates surface tension dynamics in an alveolus exposed to pressure oscillation frequencies in the range typically produced by the Bubble CPAP System. • Validate the surface tension model with experiments conducted on a custom-built pulsating bubble surfactometer (PBS). To fulfill the first four objectives, a mathematical model of the neonatal ovine lung was developed in Simulink within the Matlab environment. Mechanical and physical parameters that were required for the model were either empirically determined from measurements on preterm lamb lungs or derived from the literature. Simulations were then performed to determine the effectiveness of Bubble CPAP and the use of ‘optimal frequencies’ in neonatal respiration. To study the surface tension dynamics, a PBS was constructed to study the effect of frequencies on a surfactant bubble which simulated an alveolus. Modulated frequencies (10-70 Hz) were superimposed on the breath cycle at 3 different amplitudes expressed as a percentage of the tidal volume (TV) excursion (15%TV, 22.5%TV and 30%TV). A numerical model was also built in Matlab to characterize the surfactant behaviour and help determine the mechanisms responsible for any observed changes in surface tension. The experimental results and computer simulations resulted in the following conclusions: • The model is able to accurately predict the respiratory parameters at the airway opening during CPAP and Bubble CPAP operation. • The model shows the ability to predict the uneven ventilation profiles in the neonatal lung. • Both model predictions and experimental measurements show the trend that the mechanical WOB is greater (improved) during ventilation under Bubble CPAP when compared to CPAP. • Pressure oscillation frequencies which show improved WOB measures in the 128 day gestation lamb lung were identified as 19, 23, 28, 33, 44, 49, 54, 81, 88, 99, 111 and 113 Hz. • Model predictions showed that the improvement in WOB (due to mechanical effects) relative to CPAP-only treatment was 1-2% when introducing single frequencies at the generator, but increased to 4-6% when introducing ‘mixed frequencies’ at the generator and 4-10% when introducing ‘mixed frequencies’ at the patient interface. • It was shown that the Bubble CPAP System delivers frequencies similar to the identified optimal frequencies of the 128 day gestation lung (17 and 23 Hz) which contribute to the noticed improvement in WOB. • The average trends of all the experiments on a PBS and results from the numerical model revealed that the minimum and maximum surface tension in an alveolus decreases with increasing frequency and increasing amplitude. • The mechanism of improvement of surface tension in the alveolus with frequency and amplitude is due to the increased diffusion and adsorption of surfactant molecules to the air-liquid interface, increasing the interfacial surface concentration and decreasing the surface tension.
- ItemElimination of Skin-stretch Induced Motion Artefacts from Electrocardiogram Signals(Auckland University of Technology, 2017) Kalra, AnubhaElectrocardiography (ECG) is widely used in clinical practice, for example to diagnose coronary artery disease or the cause of chest pain during a stress test, while the patient is running on a treadmill. Ambulatory ECG monitoring is used for long term recording of ECG signals, while the patient carries out his/her daily activities. Artefacts in ECG are caused by the patient’s movement, moving cables, interference from outside sources, electromyography (EMG) interference and electrical contact from elsewhere on the body. Most of these artefacts can be minimised by using proper electrode design and ECG circuitry. However, artefacts due to subject’s movement are hard to identify and eliminate and can be easily mistaken for symptoms of arrhythmia and the physiological effects of exercise, leading to misdiagnosis and false alarms. Skin stretch has been identified as a major source of motion artefacts in ECG signals, which arise due to the flow of current, called the ‘injury current’ across the epidermis. Thus, the skin is generally abraded or punctured to minimize variations in injury current. This is unpleasant and not useful for long term monitoring, as the skin regrows after 24 hours. Present motion sensing approaches to artefact reduction in ECG do not measure motion in terms of skin stretch. The main goal of this study is to quantify and eliminate motion artefacts from ECG pertaining to skin stretch. A polymer patch electrode with Young’s modulus lower than of skin has been developed to simultaneously measure ECG and skin stretch using an optical sensing technique. These signals were combined with infinitesimal strain theory to quantify skin stretch as two dimensional strains. Principal component analysis (PCA) and independent component analysis (ICA) were utilised for motion artefact removal from ECG signals. A motion Artefact Rejection (AR) system has been developed to validate the approach implemented in this study. As this study mainly focuses on skin stretch induced artefacts, a plastic tube has been used to stretch the forearm skin of 7 subjects across the following age groups: 18–35 years (3 subjects), 36–55 years (2 subjects), and 56 years and above (2 subjects). ECG with motion artefacts were measured using CNT/PDMS electrodes and dry Ag electrodes. The reference ECG (ECG at rest) was measured from the chest using conventional Ag/AgCl electrodes. The average improvements in SNRs using PCA and ICA algorithms were found to be 4.249 dB and 9.586 dB respectively, while the average of maximum deviation from rest/reference ECG was 0.0843 for ECG with motion artefacts, 0.0702 for ECG after PCA and 0.0442 for ECG after ICA. Both PCA and ICA algorithms also aided in removing baseline wander and high frequency noises in the cases of less or no motion artefact. The system performed well in removing artefacts generated due to EMG interference and stretching the skin perpendicular, diagonal and parallel to Langer’s lines. Higher SNRs were achieved when PCA and ICA were performed by using 2D strains as motion information than when no motion information was used. In conclusion, ICA used for motion artefact reduction in ECG signals shows better performance than other techniques employing adaptive filtering, PCA and ICA. A novel, state-of-the-art technique to identify and eliminate motion artefacts from ECG signals has been developed through this study which is feasible for practical implementations.
- ItemHolographic microwave imaging for lesion detection(Auckland University of Technology, 2013) Wang, LuluThis thesis presents the preliminary analysis and development of a novel technique to detect inclusion in a dielectric object that is based on holographic microwave imaging array (HMIA) and aperture synthesis far-field imaging techniques. This new microwave based approach may have a potential to become an imaging tool for breast lesion detection in the future. The two dimensional (2D) and three dimensional (3D) computer simulation models have been developed using MATLAB to demonstrate the 2D and 3D HMIA image reconstruction algorithms. A suitable antenna for experimental implementation using HMIA techniques is designed, and the spiral and random antenna array configurations are developed to significantly improve the quality of the images. The proposed technique has been validated through simulation and measurements on multiple dielectric objects (breast phantoms). Results have demonstrated the feasibility and superiority of detecting small inclusions (lesions) in the breast model using the HMIA imaging algorithms. The achieved simulation and experimental images using different antenna array configurations have been evaluated using visual inspection and quantitative analysis methods. Results show that the spiral and random antenna array configurations have the ability to produce better quality images compare to the most widely used regularly spaced array. Finally, the 2D HMIA technique has been applied on 2D and 3D head models for brain stroke detection. The Method of Moments (MoM) and Born approximation approaches are employed to solve the scattering electric field of 2D and 3D head models respectively. The simulation results indicate that the HMIA technique has a potential for other medical imaging applications, such as brain stroke detection.
- ItemAn investigation into Abdominal Aortic Aneurysm (AAA) rupture prediction(Auckland University of Technology, 2014) Embong, Abd HalimCardiovascular Disease (CVD) is one of the leading causes of death and disability in the world. The mortality rate between 1993 -1997 in New Zealand was about 46% and 32% worldwide. CVDs such as Abdominal Aortic Aneurysm (AAA) is life threatening and poses a very high risk for aneurysm patients with particular aneurysm diameter. AAA rupture is a patient-specific problem with evolving structures and on-going growth. Current ultrasound methods are used to probe for and diagnose instantaneous AAA by analysing arterial tissue deformation. However, tracking the progression of potential aneurysms, and predicting their risk of rupturing based on the diameter of the aneurysm is still an insufficient method. AAA image segmentation and analysis using the Patient-Specific Aneurysm Rupture Predictor (P-SARP) protocol is proposed to identify dependent elements that lead to a three-dimensional (3-D) aneurysm reconstructive model. Models of the patient-specific aneurysm images were designed along with biomechanical characterization and specific material properties to be incorporated. Fluid Structure Interaction (FSI) is used to mathematically establish the oscillations of patient-specific cyclic pressure loading in order to visualize the impact of potential pressure distributions on the deformed arterial wall over time. The correlation between the geometric elements and the models’ potential for rupture are extensively investigated to produce a possible AAA rupture mechanism. This research presents a new Computational Fluid Dynamics (CFD) of Patient-Specific Aneurysm Model (PSAM) which is based on the energy strain function combined with the dilated vessel wall stress-strain relationship to predict aneurysm rupture. This thesis focuses on investigating how computer simulation can be incorporated to predict AAA rupture. The personalized model is developed based on instantaneous arterial deformations obtained from ultrasound images using a 6-9 MHz doppler transducer. The PSAM relies on available vii mechanical properties and parameters obtained from the personalised model. Using the strain energy function based on historical stress-strain relationship to extrapolate cyclic loading on the PSAM along with patient-specific pressure, multi variant factors are proposed and considered to predict the actual location of the weakening points to reach rupture. The material properties of the wall are calculated using biaxial tensile tests to observe the time dependency of the material response and formation of the aneurysm wall rupture. The outcomes indicate that the proposed technique of the PSAM model has the ability correlate the wall deformation and tissue failure mode with predicting rupture. Thus, this method can positively be integrated with already established ultrasound techniques for improvements in the accuracy of future diagnoses of potential AAA ruptures.
- ItemAn Investigation Into Acoustics and Vibration Characteristics of CPAP Devices(Auckland University of Technology, 2014) Vuong, Tung XuanHigh demand for lower noise generation in the CPAP device industries necessitates the need to have a computational modelling for obtaining in-depth understanding of internal aerodynamic flows and aero-acoustic characteristics that can be used during the product development process. In this thesis, a comprehensive numerical study is conducted to investigate flow-induced noise and vibration of the CPAP devices with supports of experimental investigations for validations. A 3-D flow system of a CPAP device is originally developed and then re-constructed and simplified for numerical simulation purposes. The CPAP flow system consists of inlet and outlet ducts, a centrifugal fan and a humidifier. A numerical simulation, which is a combination of well-established computational fluid dynamics (CFD) techniques with acoustic analogies (AA) and finite element analysis (FEA), is adopted and applied to each primary component of the CPAP devices to investigate noise and vibration generated by internal turbulent flows. The numerical results are compared with the experimental data for validations. Significant insights into the noise and vibration characteristics of the CPAP components are obtained and compared with each other to identify the noise source power and its locations. The contribution of each element to the overall noise generation level is estimated. Prior to the numerical studies, a thorough experimental investigation was conducted to investigate the flow performances, noise radiations and surfaces vibration of the CPAP devices and its main components. The results from the experimental investigation can be used for validation purposes as well as the boundary conditions for numerical studies. Numerical results has found that the uneven flow structure or asymmetric internal flow is identified as the main cause of the noise generation. The specific geometry designed for the CPAP flow system has created flow patterns which contain many aerodynamic characteristics that are related to the aerodynamic noise generation such as flow attachment and separation, flow recirculation or rotation, etc. Furthermore, individual noise power level at each components are estimated and compared with each other. It is found that the noise power generated from the centrifugal fan is the most contributed source to the overall noise level radiated from the CPAP device.
- ItemAn investigation into ambulatory blood pressure measurement(Auckland University of Technology, 2012) Hai, LanHypertension is one of the most common cardiovascular diseases threatening people's health worldwide. Although, hypertension itself is rarely an acute problem, it increases the risk of cardiovascular events and kidney diseases. Recent studies have shown that the end-organ damage associated with hypertension is more strongly correlated with ambulatory blood pressure monitoring (ABPM) than with traditional clinic BP measurements. Currently, the ambulatory, cuff-based devices are predominantly based on automatic techniques which are inherently motion-sensitive. The other devices which claim to compensate for motion artefacts measure the arterial pressure at the wrist and are less accurate than cuff-based measurement. This research aims to develop a cuff-based ABPM technique which can measure BP accurately during their daily lives. The primary objective of this research is to investigate two major issues related to ABPM technique: (1) the theory of oscillometric BP measurement method used in most of ABPM device; (2) the method to compensate for the noises during the measurement. This thesis introduces for the first time a 3D finite element (FE) model which simulates the entire oscillometric BP measurement process. The model is validated by both arm simulator and clinical results. The brachial artery closure process and the factors of arm material properties in BP measurement are discussed. The model indicates that the nonlinearity of brachial artery plays the key role in oscillometric BP measurement. It also offers a new explanation of the common phenomenon: overestimation in the elderly and underestimation in the younger. Since BP pulse, arm motion and environmental tremors all lead to the upper arm skin stretches, it is anticipated that the strain distribution due to these causes is unique for different arm motion. This thesis also describes the design of a piezoelectric strain sensor array and the relevant method for eliminating the noises and determining the subject’s BP. A FE model, whose geometry is obtained from Visible Human Body dataset, is established to study surface strain distribution during different arm motions. Referring to its results, the piezoelectric sensor array is designed and used in the clinical experiments. Using the obtained signals, a generalized input-output configuration of the designed measurement system is developed. The transfer functions of the system are determined through empirical equations. Using the developed method, the device is able to detect the arm motions, compensate for the noises and determine patients’ BP. The results can be used as a guide for developing a new type of ABPM device insensitive to artefacts.
- ItemAn investigation into bicycle performance and design(Auckland University of Technology, 2014) Prince, JohnThe main hypothesis of this thesis was to determine to what extent mathematical modelling can influence the dynamics of the bicycle and improve handling performance. Hence a key objective was to develop effective and valid design tools that bicycle manufacturers could use to optimise their designs. To do this equations of motion for a bicycle were developed and solved using Simulink in a Matlab environment. A design methodology consisting of four design charts was then developed for manufacturers and designers. The validity of these design charts was confirmed by comparing them to historical design practices and then to elite riders and bicycles from the 2013 Tour de France bicycle race.
- ItemAn Investigation into Improving the CPAP and the Electrical Stimulation for the OSA Treatment(Auckland University of Technology, 2019) Ali, Ali AdilObstructive sleep apnea (OSA) is considered a worldwide public health problem. It is characterised by the repetitive episodes of partial (hypopnea) or complete collapse (apnea) within the upper airway during sleep of OSA patients despite their continuous breathing efforts. From a pathophysiological point of view, OSA is a multifactorial disease and the mechanism underlying OSA is not fully understood. However, it is reported that it is related to the progressive loss of lingual and pharyngeal tone in the upper airway during sleep compared to wakefulness in patients with OSA. Studies have confirmed that OSA may lead to Cardiovascular diseases, Diabetes, Morbidity and high mortality rate. Current OSA treatment include many modalities. Some are non-invasive such as the continuous positive airway pressure (CPAP), which is considered as the primary choice to manage OSA patients. While others are invasive such as the electrical stimulation techniques. However, both treatment techniques have many drawbacks. For example, the use of CPAP may be associated with numerous side effects including upper airway congestion, and significant dryness. On the other hand, electrical stimulation is associated with inflammation due to biocompatibility issue of the electrode with human tissue. As both of the above two modalities are widely used and expanding, this thesis is focus on quantifying the damage caused by both of them and suggest possible scenarios to overcome these damages. To do so, this is a two-fold thesis. First to quantify humidification within upper airway (UAW) during application of CPAP. The study also aims to determine the impact of applying pressure oscillation (PO) waves superimposed on CPAP on humidification parameters of the UAW. Another important aspect of this research is to improve electrical stimulation therapy as an alternative to CPAP. To address the first part, an ex vivo experimental setup was developed to quantify the air humidification at different CPAP operating conditions. While the in vivo tests were conducted using a proper clinical trial. Results from ex vivo studies have confirmed that at normal breathing, the reconditioning of inhaled tidal volume may lead to a fluid depletion within the depth of airway surface liquid that equal to 2.17 µL/cm2.min. However, applying the CPAP at different pressure of (5,10 and 20 cmH2O may affect this value, significantly. Results of ex vivo studies have confirmed that a reduction percentage within tracheal Fluid depletion can be 38.4 % up to 75.8 %. The highest reduction percentages were associated with applying CPAP at 20 cmH2O, and the lowest effect was associated with applying CPAP at 5 cmH2O. Data suggest a backward relationship between CPAP and TWC values of the processed air and the Tracheal Fluid depletion By applying the Pressure oscillation at different frequencies of (5, 20 and 30) Hz, results shows a remarkable improvement within the tracheal Fluid depletion at any pressure value of CPAP. However, the highest improvement percentage of 78.8 % was achieved at applying PO at 30 Hz, in conjunction with the CPAP at 5 cmH2O. Result suggests the efficacy and reliability of applying PO as alternative to address issues associated with the CPAP. Results obtained from clinical trial supports findings of ex vivo studies. As per data, applying full session treatment using CPAP, saliva samples collected from participants have witnessed a drastic reduction in their salivary flow rate, which was already considered as low. Reduction percentage values were ranged from 5.81 % to 70.15 %. The highest decreasing percentages within the salivary flow rates were found with participants of BMI higher than 34.4 kg/m2. The lowest percentages were found within participants with BMI of equal to or lower than 32.8 kg/m2. However, a major improvement in the salivary flow rate recorded from participants after CPAP and PO treatment sessions. Improvement percentages are in the range of 0.49 to 1.39 mL/min, representing an increasing percentage between 9.4 % up to 129 %. The highest improvement was recorded within the salivary flow rate of the participants with a BMI of 29.9 kg/m2, whereas the lowest was obtained with participants of 49.1 kg/m2. Results may confirm the efficacy of applying the PO in conjunction with the CPAP to improve dryness symptoms that mainly associate with the use of the CPAP. To address the inflammation and poor performance caused by inflammation developed by the Electrical stimulation technique, a biocompatible electrode have been developed, Morphological studies have confirmed the capturing of cell’s feature on the surfaces of electrode. Also, the implant was electrically-conductive, and results obtained from the test confirmed that both PPy/APS/ Kolliphor P188 nanocomposites and implants are electrically-conductive. Biocompatibility of implant surfaces was tested, and results obtained from corresponding tests have confirmed its non-toxicity. Furthermore, applying electrical stimulation to the attached cells has confirmed that a signal lower than 150 mV/mm can be tolerated by the attached cell population. Collectively, result may suggest the efficacy of our innovative technique to enhance electrode biocompatibility.
- ItemInvestigation into the Development of a Parrot-inspired Therapeutic Robot to Improve Learning and Social Interaction of Children with Autism Spectrum Disorder(Auckland University of Technology, 2018) Bharatharaj, JaishankarThis research reports on the design and development of a parrot-inspired therapeutic robot to improve learning and social interaction abilities of children with autism spectrum disorder. The research also aims to reduce stress levels of participants through robot-assisted therapy. The increasing deployment of robots in recent decades has inspired new boundaries for human-robot interactions from manufacturing to health industries. Particularly, assistive robotics has found new directions in recent years and been used in numerous applications, including, elderly care, and autism therapy. With inspiration from nature, bio-inspired robots can provide solutions to various problems, which have been applied successfully in real-world situations. Specifically, animal-inspired robots have received notable acceptance in therapeutic settings, such as therapy for the elderly, children with autism spectrum disorder, and patients with dementia. A number of animal-like robots are developed to provide the benefits of animal-assisted therapy, while overcoming shortfalls, such as biting, allergies, and animal-spread diseases. Autism therapy is one such area for the deployment of animal-inspired robots to improve the lifestyle of children with autism spectrum disorder. Through an extensive review of the literature and reported benefits, the morphological form for the robot was determined to be parrots for their significant companionship contributed by their living counterparts in various disorders. In this research, a parrot-inspired therapeutic robot is designed to provide therapeutic benefits. The novelty of the research also lies in the fact that there is a complete absence of any robotic study involving the design and development of a parrot-like robot. The research is set to target improvement in learning and social interaction abilities of children with autism spectrum disorder through engaging a parrot-inspired robot, which represents a common and significant procedure for individuals with limited cognitive capabilities. The research also investigates the psychological and physiological changes in children before and after interacting with the robot. Several short-term and long-term user studies conducted to validate the effects of robot among children report a positive influence in improvement of learning and social interaction in participants. Salivary and urinary tests indicated reduction in stress levels of children with ASD after interacting with the robot. The research investigating participants’ blood pressure, heart rate, and oxygen saturation levels in blood and reported no abnormality in readings during and after interacting with the robot.
- ItemAn Investigation Into the Effects of Pressure Oscillations on Airway Smooth Muscle in Chronic Asthma(Auckland University of Technology, 2018) Roos, Kevin Lamar TurepuThe hyperconstriction of airway smooth muscle (ASM) is the main driving mechanism during an asthmatic attack. The airway lumen is reduced, resistance to airflow increases, and normal breathing becomes more difficult. The tissue contraction can be temporarily relieved by using bronchodilator drugs which induce relaxation of the constricted airways. With one of the highest prevalence rates in the world, New Zealand’s costs for asthma treatments total an estimated NZD$825 million per year. While widely used in asthma therapies, pharmacological treatments vary in their effectiveness from one subject to another, as do the side effects of long-term usage. Studies have shown that application of mechanical oscillations which are equivalent to the physiological patterns of normal breathing and deep inspirations in healthy airways can induce airway relaxation. This type of relaxation response is not observed in asthmatics. Utilizing length oscillations (arising from positive pressure) in association with breathing patterns provides non-pharmacological options for augmenting treatment of the ASM hyperconstriction which is present in many respiratory diseases such as asthma. There is currently little known about the effects of applying superimposed pressure oscillations in combination with breathing patterns to healthy and asthmatic airways during an asthmatic attack. Results from in vivo studies of a chronic murine asthmatic model indicate that the use of superimposed pressure oscillations (SIPO) over normal breathing patterns facilitates relaxation during an induced asthmatic attack in healthy and asthmatic subjects. Oscillation patterns, physiological pressure equivalents, and their effects on key respiratory parameters are presented. Comparisons of healthy and asthmatic lung resistance (RL) and dynamic compliance (Cdyn) values are used as assessments of the changes in airway responses to applied mechanical pressure oscillations. Additionally, a standard respiratory constant is used to normalize acute and chronic asthmatic models’ data. Use of the constant assists in modeling the effects of SIPO by transforming RL and Cdyn data into Work and Power equivalents for use in interpreting ASM mechanics.
- ItemAn Investigation into the Human Upper Airways Humidification(Auckland University of Technology, 2019) Grau Bartual, SandraThis research focuses on the analysis of the human upper airway humidification looking on one hand at the natural humidification or air conditioning process and on the other hand at the external humidification. Lung supportive devices are widely used to restore the breathing cycle and provide proper ventilation to patients. These devices introduce compressed room air into the respiratory system and generate a positive pressure inside the respiratory system and a turbulent effect to keep the airways open which distorts the natural lubrication and humidification. Hence, lung supportive devices incorporate a convective heated humidifier which provides external humidification to the patients to alleviate the upper airway dryness produced by the compressed airflow. However, the humidifier makes the devices bulky and patients are still reporting side effects after the therapy. Therefore, the purpose of this research is to investigate the effect of the positive airway pressure on the human upper airway epithelium, extrapolate the results to the entire human upper airways and develop a miniaturized, eco-friendly and affordable selfhumidifying device able to overcome the dryness side effect and replace the actual convective heated humidifier.
- ItemAn Investigation Into the Improvement of Obstructive Sleep Apnea Therapy(Auckland University of Technology, 2021) Al-Mohamadamin, Dalya Faiz HashimThe upper airway (UA) patency is a critical element of the breathing cycle. Narrowing of the UA causes breathing difficulties that may cause sudden death. Repeated closure of the UA, and subsequent physiological consequences during sleep, lead to what is called “obstructive sleep apnea” (OSA) syndrome. OSA occurs because of the excessive relaxation in the UA soft tissue. Continuous positive air pressure (CPAP) is the gold standard treatment for OSA. Generally, high pressures of CPAP are needed to be effective in treating OSA. However, this high pressure has many negative side effects, such as dryness of the upper airway, nose soreness, and irritation of the throat. Furthermore, a prospective observational study has shown that CPAP treatment resulted in a significant reduction in intima-media thickness (IMT) of the carotid artery, which may increase the risk of cerebrovascular events or stroke. Reducing CPAP pressure and the AHI is one of the main goals of this research. To reduce CPAP pressure, superimposed pressure oscillations were used in recent studies and the results were promising. Pressure oscillations is a pressurised air pulse with certain frequencies that can trigger the augmentation of the UA muscles to contract, which leads to fewer OSA events. This is a two-fold thesis. First, it focuses on the clinical trials to reinforce previous findings and obtain statistical assurance. The second objective of this research is to develop a mathematical model to simulate the UA collapse and observe UA modulation due to pressure oscillations. The clinical trials were conducted at Fisher & Paykel Healthcare. In total, 19 participants were recruited along with 14 previous participants recruited in Switzerland. Each trial lasted two nights and consisted of patients monitored using a polysomnography (PSG) during sleep. A reduced pressure of CPAP (70% titration pressure) without a humidifier was applied on the first night, and this trial was considered to be the reference point. The same reduced value of CPAP pressure combined with the PO was used on the second night. A random allocation of the order of testing was done. The main two endpoints analysed on completion of the trials were the number of arousals (AHI) and UA dryness. This work enhances the efficacy of CPAP therapy among OSA patients as well as reducing its running cost. The developed computer modelling predicted the apnea hypopnea (AHI) index using MRI images of OSA patients’ upper airways, and by calculating the lateral pharyngeal wall thickness, it can be used for future estimations of the apnea hypopnea index to achieve UA opening at lower CPAP titration pressure with superimposed pressure oscillations.
- ItemInvestigation into the Mechanism of UV Transmission to Follicular Stem Cells and Implications for Melanoma Development(Auckland University of Technology, 2019) Huang, XiyongChildren are particularly vulnerable to sun exposure; excessive sun exposure during their childhood can result in increased melanoma incidence in later life. It is hypothesized that the reasons for the vulnerability of children to sun exposure is related to their hair follicles. The melanocyte stem cells (McSCs) in hair follicles have been identified as a possible origin of melanoma upon exposure to ultraviolet radiation (UVR). Those cells in the vellus hairs (predominant type of hair before puberty) are much shallower than in the terminal hairs (predominant type of hair after puberty). Using the Monte Carlo (MC) method for photon transport in skin alone, we have shown that the McSCs in vellus hair follicles (VHF) would receive and absorb significantly higher UV than those in the terminal hair follicles (THF). Furthermore, as a consequence of the thinner epidermis in children, the cells would absorb about 1.9- and 3.2-times greater UVA and UVB respectively compared to adult skin. Due to the unique morphologies of vellus hairs, it is also hypothesized that they contribute to the solar UV transmission in the skin to the McSCs. To validate this, Caucasian scalp and body hairs have been used to measure their transmission properties in the UV wavelength range, using a CRAIC™ microspectrophotometer. The measured properties are then implemented into realistic skin-hair models. The simulated results show that a higher level of UV is delivered to the McSCs in the skin model with vellus hairs, as compared to hairless skin. The relative increase in energy absorbed in the stem cells when vellus hair is present to hairless skin varies from 4.6% to 52.0% over the UVA – UVB wavelength ranges. For skin with terminal hair, this relative increase in energy absorbed varies from 16.7% to 55.6% over the same wavelength range. Skin with shaved vellus hair will further enhance the UV transmission into the skin. In conclusion, this research provides possible explanations as to why children are particularly vulnerable to sun exposure: 1) the shallower depth of McSCs in the VHF than in the THF result in significantly higher UV absorption; 2) relatively thinner epidermis of child’s skin increases the UV absorption even more; 3) the presence of vellus hair provides an additional optical pathway, contributing to the overall solar UV transmission into the skin. These findings also explain the positive correlation between the incidence of melanoma in adults’ bodies and the number of vellus hair in these areas. This research may lead to the improvement of melanoma prevention, e.g. improvement of the efficacy of sunscreens.
- ItemAn Investigation Into Using Regenerated Cellulose-based Electro-conductive Composites for Actuation and Drug Delivery(Auckland University of Technology, 2014) Chowdhury, Nargis AfrojUnder the influence of an electric field, ionic electro-active polymers generally bend or deswell, depending on the shape of the polymer matrices and its position relative to the electrodes. In this study, we investigate the bending behaviour of regenerated cellulose-based ionic electro-active composites for the fabrication of soft actuators with improved actuation force and durability. This research also focuses on the externally induced (electrically and magnetically) matrices deswelling and other responses, which affect the release of drug from the matrices. For actuation studies, we prepared matrices by combining carbon nanofibers, conducting polymers, and ionic liquids (through blending, doping, or coating) into the regenerated cellulose. We observed that actuators coated by polypyrrole doped with anthraquinone-2-sulfonic acid sodium salt monohydrate showed improved electrical conductivity and durability compared to that of using perchlorate ion as the dopant. This is due to the preparation process and the effect of dopants that play an important role to improve the performance of the regenerated cellulose-based ionic electro-active actuators. In addition, we investigated the influence of electrode design (layer-by-layer structure) on the properties of the actuators. Further, in this study, we developed three types of matrices consisting of regenerated cellulose/functionalized carbon nanofibers, regenerated cellulose/functionalized carbon nanofibers/polypyrrole, and regenerated cellulose/γ-ferric oxide/polypyrrole. We investigated the effects of electric field strength and electrode polarity on the release rate of sulfosalicylic acid (drug) in an acetate buffer solution with pH 5.5 and temperature 37 ᵒC during a period of 5 h. Drug release rate from the matrices containing carbon nanofibers (additives) increased effectively with increasing applied electric field. The mechanism of drug release from drug-doped polypyrrole coated matrices includes expansion of conductive polymer chain and the electrostatic force between electron and drug. The novelty of the work is- the matrices can also work under magnetic field and consequently, one can be beneficial from a contactless actuation. In this study, we also investigated electrical conductivity, morphology, swelling behaviour of the composite matrices, electro-active composite-drug interaction, and in vitro drug release behaviour of the matrices. Further, a comparative study was performed on the rate of drug release from the matrices induced by electric and magnetic field.
- ItemAn investigation of droplet evaporation characteristics in an ultrasound environment(Auckland University of Technology, 2014) Protheroe, Michael DesmondThis study investigates and quantifies the effect of an imposed ultrasound field on the evaporation of water droplets in, for example, humidifiers used in medical respiratory treatments. The purpose of the ultrasound field is to accelerate the droplet evaporation process. This would have benefits in terms of improved efficiencies, more compact equipment sizes and better process controllability. A preliminary investigation was carried out to identify the most promising mechanisms for the effect of the imposed ultrasound field on the evaporating droplets – this being the enhancement of the normal mass and heat transfer processes involved. From this, theoretical models of normal and ultrasound enhanced droplet evaporation were developed to predict the rates of water evaporation and also changes to the droplet size distribution during evaporation. An experimental investigation was carried out to measure water droplet evaporation rates and changes to the droplet size distribution under normal and ultrasound enhanced conditions. It was found that the ultrasound field improved droplet evaporation rates in all cases tested, even at very low power levels. Improvements varied from 1 – 30%. An increase in the strength of the ultrasound field increased the improvement in evaporation rate. However, air flow above a certain threshold diminished this improvement by disrupting the ultrasound field. Investigation of the changes to the droplet size distribution indicated that at high ultrasound power levels and low air flow rates a significant amount of droplet coalescence occurred which caused the droplet distribution for the remaining droplets to shift to much larger droplet sizes. Results from theoretical models compared well to the experimental results for most experimental conditions. Differences between model and experiment occurred for the very small droplet sizes and where the effect of the ultrasound field caused maximum droplet coalescence and heating of the air and these areas warrant further future investigation. It was concluded that the ultrasound enhancement of water droplet evaporation does occur by enhancing the heat and mass transfer processes involved, that improvements in evaporation rate up to 30% could be achieved and that this could be applied to medical respiratory equipment to improve its operation and efficiency.