title: Quantification of respiratory sinus arrhythmia by use of low order ARX models

authors: Han, Bo

abstract: Respiratory Sinus Arrhythmia (RSA) is a change in the heart rate that corresponds to the frequency of respiration, but its causative mechanisms in humans remain only partially determined. In this thesis, models of the human cardiovascular system have been developed to give physiologically reasonable explanations of RSA. In a normally intact system, the cardiovascular system has respiration as input and heart rate as the output, which can be used to evaluate the cardiovascular system dynamics. It is proposed that respiration oscillations play a major role in the generation of RSA in healthy humans through the action of medullary respiratory neurons, which have been shown to both control respiration itself and via a coupling to autonomic centers to modulate heart rate by varying parasympathetic and sympathetic inputs to the sinoatrial node. The Baroreflex does not play an important role in modifying the RSA response in normal conditions but does maintain arterial blood pressure within a fairly narrow range through feedback control. Based on the neural network autoregressive with exogenous input (ARX) model, sensitivity analysis has been employed to demonstrate that instantaneous lung volume (ILV) has a much higher percentage of contribution to heart rate variability (HRV) than systolic blood pressure (SBP) (typically 11.6%, 4.6%), which agrees well with our cardiovascular system model.

System identification of RSA in random, regular and spontaneous breathing patterns performed well when using an ARX model of low order, typically [4, 2, x]. In order to get a tradeoff between the accuracy of the model and an excessive number of parameters associated with that model, both the false nearest neighbors (FNN) algorithm and visual inspection of the loss function were used for model order determination. Good model qualities were proved by model validations and agreed well with the results of previous research. Studying transfer characteristics from fluctuations of ILV to HRV, the impulse response was obtained from the ARX model and it was then decomposed algebraically into two combinations of exponential decays, i.e., the fast and slow response components. The low order ARX model was tested on data acquired from a range of healthy subjects and patients.

Analysis of the data indicated that the fast response component of the impulse response corresponds to the high frequency power (HF) (0.3-0.5 Hz) of HRV fluctuations, and the slow response component corresponds to the low frequency power (LF) (0.08-0.15 Hz) of HRV fluctuation. The fast component reflects the change of HRV due to parasympathetic input and the slow component is attributed to both sympathetic and parasympathetic input.

Analysis of the model parameters, the amplitude and time constant of impulse response components, showed these can identify differences in the system response due to the shifts in autonomic balance produced by changing posture and in patients with large sympathetic inputs. Compared with HF:LF power ratio, our slow components of impulse response are more informative in quantifying the balance between the sympathetic and parasympathetic response due to respiration.

To our knowledge, this is first attempt to use an ARX model to quantify RSA for patients in uncontrolled situations where the spontaneous breathing pattern can take on a variety of forms. Our study shows that the results of this system identification to patients are reliable quantitative indexes of RSA after the data has been examined to ensure that cardiorespiratory interaction is linear and stationary.

text: Quantification of respiratory sinus arrhythmia by use of low order ARX models Respiratory Sinus Arrhythmia (RSA) is a change in the heart rate that corresponds to the frequency of respiration, but its causative mechanisms in humans remain only partially determined. In this thesis, models of the human cardiovascular system have been developed to give physiologically reasonable explanations of RSA. In a normally intact system, the cardiovascular system has respiration as input and heart rate as the output, which can be used to evaluate the cardiovascular system dynamics. It is proposed that respiration oscillations play a major role in the generation of RSA in healthy humans through the action of medullary respiratory neurons, which have been shown to both control respiration itself and via a coupling to autonomic centers to modulate heart rate by varying parasympathetic and sympathetic inputs to the sinoatrial node. The Baroreflex does not play an important role in modifying the RSA response in normal conditions but does maintain arterial blood pressure within a fairly narrow range through feedback control. Based on the neural network autoregressive with exogenous input (ARX) model, sensitivity analysis has been employed to demonstrate that instantaneous lung volume (ILV) has a much higher percentage of contribution to heart rate variability (HRV) than systolic blood pressure (SBP) (typically 11.6%, 4.6%), which agrees well with our cardiovascular system model.

System identification of RSA in random, regular and spontaneous breathing patterns performed well when using an ARX model of low order, typically [4, 2, x]. In order to get a tradeoff between the accuracy of the model and an excessive number of parameters associated with that model, both the false nearest neighbors (FNN) algorithm and visual inspection of the loss function were used for model order determination. Good model qualities were proved by model validations and agreed well with the results of previous research. Studying transfer characteristics from fluctuations of ILV to HRV, the impulse response was obtained from the ARX model and it was then decomposed algebraically into two combinations of exponential decays, i.e., the fast and slow response components. The low order ARX model was tested on data acquired from a range of healthy subjects and patients.

Analysis of the data indicated that the fast response component of the impulse response corresponds to the high frequency power (HF) (0.3-0.5 Hz) of HRV fluctuations, and the slow response component corresponds to the low frequency power (LF) (0.08-0.15 Hz) of HRV fluctuation. The fast component reflects the change of HRV due to parasympathetic input and the slow component is attributed to both sympathetic and parasympathetic input.

Analysis of the model parameters, the amplitude and time constant of impulse response components, showed these can identify differences in the system response due to the shifts in autonomic balance produced by changing posture and in patients with large sympathetic inputs. Compared with HF:LF power ratio, our slow components of impulse response are more informative in quantifying the balance between the sympathetic and parasympathetic response due to respiration.

To our knowledge, this is first attempt to use an ARX model to quantify RSA for patients in uncontrolled situations where the spontaneous breathing pattern can take on a variety of forms. Our study shows that the results of this system identification to patients are reliable quantitative indexes of RSA after the data has been examined to ensure that cardiorespiratory interaction is linear and stationary.

year: 1999

title: How structural and symbolic violence during resettlement impacts the social and mental wellbeing of forced migrant women: the lived experiences of Arabic speaking survivors of IPV resettled in Melbourne, Australia.

authors: Hourani, Jeanine

subjects: Forced migrant

abstract: Forced migrant women experience high levels of violence across their journeys and violence can be characterised as having three overarching forms: structural, symbolic, and interpersonal. It is important to understand the intersecting nature of gendered forms of symbolic, structural and interpersonal violence, and their impact on the mental health of forced migrant women in order to develop holistic IPV and resettlement programs and interventions. This article adopts an ecological framework of violence and qualitative methods with mental health service providers and survivors of IPV to understand the intersections of different forms of violence and their impact on mental health as they relate to the lived experiences of Arabic-speaking forced migrant survivors currently residing in Melbourne, Australia. Our research has three key findings: (1) that forced migrant women living in Melbourne, Australia experience intersecting forms of violence during resettlement (2) Structural and symbolic violence against forced migrant women persists regardless of marital status (3) Autonomy and independence plays a vital role in the mental health and wellbeing of forced migrant women. Our findings reveal that structural and symbolic violence increase the risk of IPV for forced migrant women during resettlement and that even when forced migrant women leave IPV situations, structural and symbolic violence persist and exacerbate mental ill-health. This article also reveals the importance autonomy and independence in both the perpetration of violence and in healing and recovery.

text: How structural and symbolic violence during resettlement impacts the social and mental wellbeing of forced migrant women: the lived experiences of Arabic speaking survivors of IPV resettled in Melbourne, Australia. Forced migrant women experience high levels of violence across their journeys and violence can be characterised as having three overarching forms: structural, symbolic, and interpersonal. It is important to understand the intersecting nature of gendered forms of symbolic, structural and interpersonal violence, and their impact on the mental health of forced migrant women in order to develop holistic IPV and resettlement programs and interventions. This article adopts an ecological framework of violence and qualitative methods with mental health service providers and survivors of IPV to understand the intersections of different forms of violence and their impact on mental health as they relate to the lived experiences of Arabic-speaking forced migrant survivors currently residing in Melbourne, Australia. Our research has three key findings: (1) that forced migrant women living in Melbourne, Australia experience intersecting forms of violence during resettlement (2) Structural and symbolic violence against forced migrant women persists regardless of marital status (3) Autonomy and independence plays a vital role in the mental health and wellbeing of forced migrant women. Our findings reveal that structural and symbolic violence increase the risk of IPV for forced migrant women during resettlement and that even when forced migrant women leave IPV situations, structural and symbolic violence persist and exacerbate mental ill-health. This article also reveals the importance autonomy and independence in both the perpetration of violence and in healing and recovery.

year: 2022-11-11

title: Incentivising change in the Lake Rotorua catchment

authors: Grayling, Anna

abstract: Anna Grayling is the Rotorua Lakes Business Manager for Bay of Plenty Regional Council. After completing a Bachelor of Law and a Bachelor of Sciences at the University of Waikato, Anna’s career began as an ecological consultant. Following this role, Anna spent five years in planning and policy for both the district and regional councils. For the last five years Anna has been dedicated to the Rotorua Te Arawa Lakes Programme. She is now the project lead for the Incentive Fund Development for land-use change in the Lake Rotorua catchment.
Alastair MacCormick has worked as a Lakes Restoration Officer with the Bay of Plenty Regional Council since 2007. His primary function has been the implementation of nutrient discharge limits under Rule 11. An experienced user of the Overseer nutrient budgeting software, and with broad knowledge of farming systems in the catchment, he also provides information and advice on the issues and complications associated with nutrient accounting.

text: Incentivising change in the Lake Rotorua catchment Anna Grayling is the Rotorua Lakes Business Manager for Bay of Plenty Regional Council. After completing a Bachelor of Law and a Bachelor of Sciences at the University of Waikato, Anna’s career began as an ecological consultant. Following this role, Anna spent five years in planning and policy for both the district and regional councils. For the last five years Anna has been dedicated to the Rotorua Te Arawa Lakes Programme. She is now the project lead for the Incentive Fund Development for land-use change in the Lake Rotorua catchment.
Alastair MacCormick has worked as a Lakes Restoration Officer with the Bay of Plenty Regional Council since 2007. His primary function has been the implementation of nutrient discharge limits under Rule 11. An experienced user of the Overseer nutrient budgeting software, and with broad knowledge of farming systems in the catchment, he also provides information and advice on the issues and complications associated with nutrient accounting.

year: 2013