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Engineering in Medicine and Biology Magazine, IEEE

Issue 2 • Date March-April 2001

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Displaying Results 1 - 13 of 13
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  • The sympathetic nervous system's role in regulating blood pressure variability

    Page(s): 17 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    This article focuses on how sympathetic nerve activity (SNA) contributes to the variability seen in blood pressure. Specifically, it examines the following questions: why do oscillations occur at certain frequencies, why do only certain frequencies of oscillations in SNA induce oscillations in the vasculature, and what may be the functional purpose of these oscillations. View full abstract»

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  • Comparing spectral and invasive estimates of baroreflex gain

    Page(s): 43 - 52
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2920 KB) |  | HTML iconHTML  

    One of the new methods to evaluate the sensitivity of the baroreceptor-heart rate (HR) reflex involves the use of power spectral analysis to calculate the transfer function between blood pressure and HR. We assess the applicability and reproducibility of the baroreflex gain estimated by this method with traditional invasive techniques that induce ramp changes in mean arterial pressure (MAP) in conscious rabbits. Renal sympathetic nerve activity recordings are used to identify the mid-frequency band, and we also identify coherent fluctuations of MAP and HR with a 1.8 s phase delay, consistent with a baroreflex relationship and therefore appropriate to estimate the cross spectral transfer function. View full abstract»

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  • Noninvasive estimation of baroreflex sensitivity using pressure pulse amplification

    Page(s): 53 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB) |  | HTML iconHTML  

    Studies using peripheral pressure measurements have facilitated studies in identifying particular gain characteristics of baroreflex control loops. However, the baroreceptors are located in central regions of the arterial tree (aortic arch and carotid arteries) and are subjected to peak pressures that are different to those measured in peripheral locations (e.g., finger). The analysis presented shows that if the known transfer function properties between peripheral and central pressures are used to derive central pressure from peripheral measurements, the baroreflex gain characteristics can be calculated in terms of central aortic pressure changes. The results obtained by this method are markedly different than those calculated using peripheral pressure. View full abstract»

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  • Applying nonlinear noise reduction in the analysis of heart rate variability

    Page(s): 59 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    The heart rate variability (HRV) signal represents one of the most promising markers of autonomic activity. However, the significance and meaning of the many different measures of the HRV are more complex than generally appreciated. The analysis of HRV shows that the structure generating the signal is not simply linear, but also involves nonlinear contributions. This article proposes an enhancement of these HRV components through the application of a noise-reduction method in state space. The method works directly in an embedding space and corrects noisy trajectories, projecting them onto local subspaces that are a good approximation of the original surface of the system attractor. At any iteration, the procedure returns a new time series with the relevant amount of subtracted noise. An empirical criterion, originally proposed, estimates the optimum iteration number to reach a good result in terms of signal-to-noise ratio. Ultimately, our goal is to verify a possible improvement of the diagnostic and prognostic power of HRV analysis through the use of new nonlinear approaches that appear as a promising tool in the early identification of dangerous cardiovascular events. View full abstract»

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  • A mathematical model for autonomic control of heart rate variation

    Page(s): 69 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    The aim of the study presented was to develop a mathematical model that could demonstrate the characteristics of beat-to-beat fluctuations in heart rate under simultaneous sympathetic and vagal controls. By this model, we attempted to illustrate the relation between autonomic activity and HRV, and to explain those controversies in interpreting HRV under certain physiological and pharmacological conditions. View full abstract»

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  • An optimal control model of 1/f fluctuations in heart rate variability

    Page(s): 77 - 87
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4316 KB) |  | HTML iconHTML  

    We investigate the generation mechanisms underlying the 1/f fluctuations in HRV in the context of an optimal control of the cardiovascular system. First, the phenomenon is experimentally quantified for human and cat HRV. Second, the relationship between the resulting dynamics of HRV and the regulatory criteria of optimal control is investigated by using a newly proposed cardiovascular system model. Finally, an operational point of the model is hierarchically controlled to simulate changes in physiological states, including the state of consciousness. This hierarchical control mechanism is suggested to be essential for generating the 1/f HRV fluctuations, and their physiological significance is discussed. Through these analyses, a possible control strategy of the cardiovascular system is suggested. View full abstract»

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  • The complexity of heart rate in its postnatal development

    Page(s): 88 - 91
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (119 KB) |  | HTML iconHTML  

    In a previous article, we have shown that heart rate after birth depends strongly on age. This finding indicates significant changes in function or in postnatal maturation of heart rate control during the first half year of life. In the present work, we address the question as to whether the development of heart rate changes during sleep is associated with changes in its complexity and, thus, of the nonlinear components of the regulatory system. Heart rate parameters are modulated by sleep stages. Therefore we also determined how, and to what extent, sleep stages modulate the complexity of heart rate. View full abstract»

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  • Modeling of Mayer waves generation mechanisms

    Page(s): 92 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB) |  | HTML iconHTML  

    The observed fluctuations in heart rate and blood pressure are meaningful rhythmical fluctuations that reflect useful information about autonomic regulation. These rhythmical fluctuations, known as heart rate variability (HRV) and blood pressure variation (BPV), are normally grouped into three major components: (i) the HF component, around 0.25 Hz, in synchrony with respiratory rate; (ii) the LF component, generally centered around 0.1 Hz, which is attributed to the sympathetic activity and the closed-loop controlling action of cardiovascular regulation; (iii) the VLF component, around 0.04 Hz, which is probably due to the vasorhythmicity thermoregulatory system or to humoral regulations. Unlike the HF component, there is still considerable controversy with regard to the origin of LF and VLF components, the so-called Mayer waves. Finding a model to represent the LF and VLF components in an appropriate manner, compatible with the relevant physiology, is the objective of this article. For this purpose, we first briefly review the underlying physiological mechanisms. Then, an appropriate mathematical representation for each mechanism is demonstrated and its performance within a comprehensive model of the cardiovascular regulatory system is considered. Finally, by comparing with the experimental results, we evaluate the closeness of the proposed representations to the actual observations. View full abstract»

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  • Validating phase relations between cardiac and breathing cycles during sleep

    Page(s): 101 - 106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1434 KB) |  | HTML iconHTML  

    The objective of this article is to investigate phase relations between heart beat and breathing cycles and their dependence on sleep states. Furthermore, the appearance of phase synchronizations between these signals is proved statistically by analyzing the phase relations between breathing and heart beat periods. The phase synchronizations between these signals are searched for by testing appropriate parameters of surrogate data with similar power spectra but randomly shuffled phase relations. View full abstract»

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  • Robo sapience: evolution of a new species [Book Review]

    Page(s): 123
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    Freely Available from IEEE
  • Advancements in estimating baroreflex function

    Page(s): 25 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    Among the modern approaches for evaluating the baroreflex sensitivity (BRS), one of the most frequently employed is the sequence technique. This method is based on the computerized scanning of beat-to-beat series of systolic (S)BP and RRI values in search of spontaneous sequences of three or more consecutive heart beats in which SBP progressively increases and, usually with a one-beat delay, RRI progressively lengthens (RRI+/SBP+ sequences) or, vice-versa, SBP progressively decreases and RRI shortens (RRI-/SBP- sequences). The slope of the regression line between the SBP and RRI values included in each sequence is traditionally taken as a measure of BRS. A large number of these baroreflex sequences spontaneously occurs during daily life activities, thus providing a detailed profile of BRS modulation over time. In this article, we focus on the methodological basis of this technique. In particular, by taking advantage of experimental data collected over the years, we explore the characteristics of the SBP and RRI patterns within each spontaneous sequence. This analysis is followed by methodological considerations aimed at clarifying the perspective from which the sequence technique evaluates BRS, as compared with other techniques. Finally, the latest enhancements of the sequence technique, leading to the quantification of other aspects of baroreflex function apart from BRS, are also described View full abstract»

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  • Closed- versus open-loop assessment of heart rate baroreflex

    Page(s): 33 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB) |  | HTML iconHTML  

    The autoregressive multivariate techniques described are based on simplified models of the entire cardiovascular system and satisfy both the requirements of not perturbing the system and providing a closed-loop evaluation of the interactions between R-R interval and arterial blood pressure. The closed-loop analysis is also able to calculate some of the indices previously used for baroreflex quantification, allowing for a direct comparison of the different approaches View full abstract»

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IEEE Engineering in Medicine and Biology Magazine contains articles on current technologies and methods used in biomedical and clinical engineering.

 

This Magazine ceased publication in 2010. The current retitled publication is IEEE Pulse.

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