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: Making sense of children's sexuality: Understanding sexual development and activity in education contexts.

authors: Flanagan, Paul G.

subjects: child sexuality

abstract: Most adults find that responding to sexual activity by children and between children is challenging. This is especially so for teachers in early childhood and primary education contexts. One common view is that children should not be sexual or, if they are, that there is something wrong. These concerns are strengthened by popular adult discourses of sexuality and accompanying ideas of sexual privacy. Among discourses of child development sit ideas of childhood innocence and natural curiosity. However, assumptions of abuse arise when children's sexual curiosity extends beyond what is considered appropriate or "normal". This article examines pre-adolescent child sexual development. It scans some of the ideas and practices that shape adults' understandings in the construction of children's sexual identities. These ideas and practices also shape children's knowledges. Adult responses to children's sexual actions often portray children as abused, abusive or deviant. Using a social constructionist lens, this paper offers educators an exploration of a range of understandings and alternative thinking about sexuality in the worlds of children-yet also critiques ideas of normative behaviour and development. The reader is invited to think about how children can be encouraged to share their subjective meanings and understandings.

text: Making sense of children's sexuality: Understanding sexual development and activity in education contexts. Most adults find that responding to sexual activity by children and between children is challenging. This is especially so for teachers in early childhood and primary education contexts. One common view is that children should not be sexual or, if they are, that there is something wrong. These concerns are strengthened by popular adult discourses of sexuality and accompanying ideas of sexual privacy. Among discourses of child development sit ideas of childhood innocence and natural curiosity. However, assumptions of abuse arise when children's sexual curiosity extends beyond what is considered appropriate or "normal". This article examines pre-adolescent child sexual development. It scans some of the ideas and practices that shape adults' understandings in the construction of children's sexual identities. These ideas and practices also shape children's knowledges. Adult responses to children's sexual actions often portray children as abused, abusive or deviant. Using a social constructionist lens, this paper offers educators an exploration of a range of understandings and alternative thinking about sexuality in the worlds of children-yet also critiques ideas of normative behaviour and development. The reader is invited to think about how children can be encouraged to share their subjective meanings and understandings.

year: 2011

title: Indigenous perspectives and gene editing in Aotearoa New Zealand

authors: Hudson, Maui

subjects: Science & Technology

abstract: Gene editing is arguably the most significant recent addition to the modern biotechnology toolbox, bringing both profoundly challenging and enabling opportunities. From a technical point of view the specificity and relative simplicity of these new tools has broadened the potential applications. However, from an ethical point of view it has re-ignited the debates generated by earlier forms of genetic modification. In New Zealand gene editing is currently considered genetic modification and is subject to approval processes under the Environmental Protection Authority (EPA). This process requires decision makers to take into account Māori perspectives. This article outlines previously articulated Māori perspectives on genetic modification and considers the continuing influence of those cultural and ethical arguments within the new context of gene editing. It also explores the range of ways cultural values might be used to analyse the risks and benefits of gene editing in the Aotearoa New Zealand context. Methods used to obtain these perspectives consisted of (a) review of relevant literature regarding lessons learned from the responses of Maori to genetic modification, (b) interviews of selected ‘key Maori informants’ and (c) surveys of self-selected individuals from groups with interests in either genetics or environmental management. The outcomes of this pilot study identified that while Māori informants were not categorically opposed to new and emerging gene editing technologies a priori, they suggest a dynamic approach to regulation is required where specific uses or types of uses are approved on a case by case basis. This study demonstrates how the cultural cues that Māori referenced in the genetic modification debate continue to be relevant in the context of gene editing but that further work is required to characterize the strength of various positions across the broader community.

text: Indigenous perspectives and gene editing in Aotearoa New Zealand Gene editing is arguably the most significant recent addition to the modern biotechnology toolbox, bringing both profoundly challenging and enabling opportunities. From a technical point of view the specificity and relative simplicity of these new tools has broadened the potential applications. However, from an ethical point of view it has re-ignited the debates generated by earlier forms of genetic modification. In New Zealand gene editing is currently considered genetic modification and is subject to approval processes under the Environmental Protection Authority (EPA). This process requires decision makers to take into account Māori perspectives. This article outlines previously articulated Māori perspectives on genetic modification and considers the continuing influence of those cultural and ethical arguments within the new context of gene editing. It also explores the range of ways cultural values might be used to analyse the risks and benefits of gene editing in the Aotearoa New Zealand context. Methods used to obtain these perspectives consisted of (a) review of relevant literature regarding lessons learned from the responses of Maori to genetic modification, (b) interviews of selected ‘key Maori informants’ and (c) surveys of self-selected individuals from groups with interests in either genetics or environmental management. The outcomes of this pilot study identified that while Māori informants were not categorically opposed to new and emerging gene editing technologies a priori, they suggest a dynamic approach to regulation is required where specific uses or types of uses are approved on a case by case basis. This study demonstrates how the cultural cues that Māori referenced in the genetic modification debate continue to be relevant in the context of gene editing but that further work is required to characterize the strength of various positions across the broader community.

year: 2019