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    Mathematical modelling of the cardiovascular system to study the effects of respiratory sinus arrhythmia and heart failure : this dissertation is submitted for the degree of Doctor of Philosophy, School of Natural and Computational Science, Massey University
    (Massey University, 2021) Noreen, Shumaila
    This thesis presents the development of lumped parameter models of the cardiovascular system with a specific aim of simulating the system dynamics over a range of heart rates. The models contain several new modelling features that have been introduced progressively throughout the thesis starting with isolated models and continuing with closed loop models of the circulation. Specifically, the contraction of the cardiac chambers is modelled using a time-dependent muscle force with constant elasticity instead of time dependent elasticity. A new hypothesis about the mechanical contraction of the atria generates realistic pressure volume loops. The inter-ventricular interaction is modelled as well. Additionally, hysteresis is incorporated in the aortic valve to produce an end-systolic reverse (negative) flow. Most of the model parameters were taken from the literature and experimental data. Sensitivity analysis was performed on one of the models outputs by changing one parameter at a time; this analysis indicated that the total blood volume is the most influential parameter in the model. The developed models were used to study the effects of Respiratory Sinus Arrhythmia (RSA), variability in heart rate at the frequency of breathing. RSA is an indicator of good health but the mechanism that gives rise to RSA and its function are still debatable. Two potential sources of RSA were incorporated: periodic heart rate that mimics the central regulation of heart rate which originates in the brainstem, and periodic systemic veins resistance that mimics one possible effect of the pleural pressure which drives breathing. The effects of RSA on cardiac output were then studied. The simulations suggest that the mean cardiac output does not change significantly due to RSA at either low or high heart rates. Two types of heart failure were simulated using the new models by changing certain model parameters: systolic and diastolic. Both the systolic and diastolic heart failures caused an accumulation of blood in the lungs. The ejection fraction for diastolic heart failure remained within the normal physiological range while in the case of systolic heart failure the ejection fraction reduced rapidly. These results are consistent with physiological observations.
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    Heart to heart - He ngākau māhaki : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Public Health, Massey University, Wellington, New Zealand
    (Massey University, 2019) Hoerara, Roy
    This research investigates the patient experiences of Indigenous men from Australia and New Zealand who have accessed specialist treatment for heart disease. Using mixed methods – qualitative interviews and a quantitative survey – this research aims to understand the relationship between their patient experience and their patient journey. Twenty men - 10 Indigenous Australian and 10 Māori (Indigenous people of Aotearoa New Zealand) were recruited through health services. A series of semi-structured interviews was used to generate a grounded theory which describes their patient engagement and on- going patient journey. Ethical review in two countries was a particular challenge. Each country required both mainstream and Indigenous reviews, as well as locality assessments in each of the health services. Through this research I extrapolated a theory that Indigenous men co- construct their patient journey. They rely on others (clinicians, partners, family/whānau) to recall events and comprehend health information for their journey going forward. Underpinning the theory of co-construction were themes which demonstrate both similarites and differences for the cohorts. Demographics, health status, socio-economic status and historically poor access to heart healthcare were factors in common. Healthcare systems within each country explained many of the differences. The Australian cohort was based within a large city, whereas the New Zealand cohort resided in a smaller province, dependant upon more distant services. There was strong evidence of positive behavioural change, growing trust and confidence with clinicans, effective support from community groups and improving health literacy. An innovative feature of this study is a comparative Indigenous analysis which seeks to explain the findings. The main limitations of this research is related to the setting. All respondents were male, and they were recruited by the health agencies they engaged with, which will have resulted in some biases. The sample size was relatively small, especially for the survey – however this aspect was intended to be more exploratory. Future research is needed to develop Indigenous-specific patient experience measurement tools.