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Valenza G, Citi L, Saul JP, Barbieri R. Measures of sympathetic and parasympathetic autonomic outflow from heartbeat dynamics. J Appl Physiol (1985) 2018; 125:19-39. [PMID: 29446712 DOI: 10.1152/japplphysiol.00842.2017] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Reliable and effective noninvasive measures of sympathetic and parasympathetic peripheral outflow are of crucial importance in cardiovascular physiology. Although many techniques have been proposed to take up this long-lasting challenge, none has proposed a satisfying discrimination of the dynamics of the two separate branches. Spectral analysis of heart rate variability is the most currently used technique for such assessment. Despite its widespread use, it has been demonstrated that the subdivision in the low-frequency (LF) and high-frequency (HF) bands does not fully reflect separate influences of the sympathetic and parasympathetic branches, respectively, mainly due to their simultaneous action in the LF. Two novel heartbeat-derived autonomic measures, the sympathetic activity index (SAI) and parasympathetic activity index (PAI), are proposed to separately assess the time-varying autonomic nervous system synergic functions. Their efficacy is validated in landmark autonomic maneuvers generally employed in clinical settings. The novel measures move beyond the classical frequency domain paradigm through identification of a set of coefficients associated with a proper combination of Laguerre base functions. The resulting measures were compared with the traditional LF and HF power. A total of 236 ECG recordings were analyzed for validation, including autonomic outflow changes elicited by procedures of different nature and temporal variation, such as postural changes, lower body negative pressure, and handgrip tests. The proposed SAI-PAI measures consistently outperform traditional frequency-domain indexes in tracking expected instantaneous autonomic variations, both vagal and sympathetic, and may aid clinical decision making, showing reduced intersubject variability and physiologically plausible dynamics. NEW & NOTEWORTHY While it is possible to obtain reliable estimates of parasympathetic activity from the ECG, a satisfying method to disentangle the sympathetic component from HRV has not been proposed yet. To overcome this long-lasting limitation, we propose two novel HRV-based indexes, the sympathetic and parasympathetic activity indexes.
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Affiliation(s)
- Gaetano Valenza
- Computational Physiology and Biomedical Instruments Group, Bioengineering and Robotics Research Center E. Piaggio, and Department of Information Engineering, University of Pisa , Pisa , Italy.,Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital , Boston, Massachusetts
| | - Luca Citi
- School of Computer Science and Electronic Engineering, University of Essex , Colchester , United Kingdom
| | - J Philip Saul
- Department of Pediatrics, West Virginia University School of Medicine , Morgantown, West Virginia
| | - Riccardo Barbieri
- Department of Electronics, Informatics and Bioengineering, Politecnico di Milano, Milano , Italy.,Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital , Boston, Massachusetts
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Sarabadani Tafreshi A, Klamroth-Marganska V, Nussbaumer S, Riener R. Real-Time Closed-Loop Control of Human Heart Rate and Blood Pressure. IEEE Trans Biomed Eng 2015; 62:1434-1442. [DOI: 10.1109/tbme.2015.2391234] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Giassi P, Okida S, Oliveira MG, Moraes R. Validation of the Inverse Pulse Wave Transit Time Series as Surrogate of Systolic Blood Pressure in MVAR Modeling. IEEE Trans Biomed Eng 2013; 60:3176-84. [DOI: 10.1109/tbme.2013.2270467] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Aletti F, Ferrario M, Xu D, Greaves DK, Shoemaker JK, Arbeille P, Baselli G, Hughson RL. Short-term variability of blood pressure: effects of lower-body negative pressure and long-duration bed rest. Am J Physiol Regul Integr Comp Physiol 2012; 303:R77-85. [DOI: 10.1152/ajpregu.00050.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mild lower-body negative pressure (LBNP) has been utilized to selectively unload cardiopulmonary baroreceptors, but there is evidence that arterial baroreceptors can be transiently unloaded after the onset of mild LBNP. In this paper, a black box mathematical model for the prediction of diastolic blood pressure (DBP) variability from multiple inputs (systolic blood pressure, R-R interval duration, and central venous pressure) was applied to interpret the dynamics of blood pressure maintenance under the challenge of LBNP and in long-duration, head-down bed rest (HDBR). Hemodynamic recordings from seven participants in the WISE (Women's International Space Simulation for Exploration) Study collected during an experiment of incremental LBNP (−10 mmHg, −20 mmHg, −30 mmHg) were analyzed before and on day 50 of a 60-day-long HDBR campaign. Autoregressive spectral analysis focused on low-frequency (LF, ∼0.1 Hz) oscillations of DBP, which are related to fluctuations in vascular resistance due to sympathetic and baroreflex regulation of vasomotor tone. The arterial baroreflex-related component explained 49 ± 13% of LF variability of DBP in spontaneous conditions, and 89 ± 9% ( P < 0.05) on day 50 of HDBR, while the cardiopulmonary baroreflex component explained 17 ± 9% and 12 ± 4%, respectively. The arterial baroreflex-related variability was significantly increased in bed rest also for LBNP equal to −20 and −30 mmHg. The proposed technique provided a model interpretation of the proportional effect of arterial baroreflex vs. cardiopulmonary baroreflex-mediated components of blood pressure control and showed that arterial baroreflex was the main player in the mediation of DBP variability. Data during bed rest suggested that cardiopulmonary baroreflex-related effects are blunted and that blood pressure maintenance in the presence of an orthostatic stimulus relies mostly on arterial control.
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Affiliation(s)
- Federico Aletti
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Manuela Ferrario
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Da Xu
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Danielle K. Greaves
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - J. Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada; and
| | - Philippe Arbeille
- Unité Médecine et Physiologie Spatiale CEntre de Recherche COeur et Maladies vasculaires, University Hospital Trousseau, Tours, France
| | - Giuseppe Baselli
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Richard L. Hughson
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
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Bolea J, Caiani EG, Pueyo E, Laguna P, Almeida R. Microgravity effects on ventricular response to heart rate changes. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2012:3424-3427. [PMID: 23366662 DOI: 10.1109/embc.2012.6346701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The effect of simulated microgravity on ventricular repolarization (VR) has been evaluated on healthy volunteers by a 5-day Head Down (-6°) Bed Rest (HDBR) maneuver. QT to RR and QT(p) (measured until the peak of the T wave) to RR hystereses have been measured during a tilt table test, and differences between them have been studied to better understand possible changes in the final part of the repolarization. To characterize the hystereses, two indices have been computed: M(90), quantifying adaptation lag in beats, and α evaluating the slope of parabolic regression fitting. Significant differences between QT and QT(p) were found before, but not after HDBR. Specifically, before HDBR was considerable lower for QT(p) than for QT, while α was significantly higher. After HDBR, M(90) and a took essentially the same values for QT and QT(p). This fact evidenced the different effect of HDBR on QT to RR and QT(p) to RR adaptations, and suggest HDBR could lead to an impairment in ventricular repolarization dispersion.
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Affiliation(s)
- Juan Bolea
- Communications Technology Group, Aragón Institute of Engineering Research (I3A), IIS Aragón, Universidad de Zaragoza, Zaragoza, Spain. jbolea@lagunaat unizar.es
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6
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Ferrario M, Aletti F, Toschi N, Canichella A, Coniglione F, Sabato E, Della Badia Giussi F, Dauri M, Sabato AF, Guerrisi M, Cerutti S. Arterial blood pressure regulation following aorta clamping and declamping during surgery. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2011; 2011:8428-8431. [PMID: 22256303 DOI: 10.1109/iembs.2011.6092079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this paper, we propose the use of black box models for the system identification of the cardiopulmonary baroreflex control of arterial resistance and of ventricular contractility and of arterial baroreflex control of heart rate (HR) from invasive, continuous measurements of arterial blood pressure (ABP) and central venous pressure (CVP), and non invasive, continuous recordings of ECG and respiration. Two crucial phases of the abdominal aortic aneurism (AAA) repair were investigated: the clamping and declamping of aorta. The objective of the present work is to evaluate and to test the ability to monitor baroreflex responses to clamping and declamping maneuvers preceding and following aneurism removal.
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Affiliation(s)
- Manuela Ferrario
- Dipartimento di Bioingegneria, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
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Batzel J, Baselli G, Mukkamala R, Chon KH. Modelling and disentangling physiological mechanisms: linear and nonlinear identification techniques for analysis of cardiovascular regulation. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:1377-91. [PMID: 19324714 PMCID: PMC3268216 DOI: 10.1098/rsta.2008.0266] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Cardiovascular (CV) regulation is the result of a number of very complex control interactions. As computational power increases and new methods for collecting experimental data emerge, the potential for exploring these interactions through modelling increases as does the potential for clinical application of such models. Understanding these interactions requires the application of a diverse set of modelling techniques. Several recent mathematical modelling techniques will be described in this review paper. Starting from Granger's causality, the problem of closed-loop identification is recalled. The main aspects of linear identification and of grey-box modelling tailored to CV regulation analysis are summarized as well as basic concepts and trends for nonlinear extensions. Sensitivity analysis is presented and discussed as a potent tool for model validation and refinement. The integration of methods and models is fostered for a further physiological comprehension and for the development of more potent and robust diagnostic tools.
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Affiliation(s)
- Jerry Batzel
- Institute for Mathematics and Scientific Computing, University of Graz, 8010 Graz, Austria.
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Porta A, Aletti F, Vallais F, Baselli G. Multimodal signal processing for the analysis of cardiovascular variability. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:391-409. [PMID: 18940775 DOI: 10.1098/rsta.2008.0229] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Cardiovascular (CV) variability as a primary vital sign carrying information about CV regulation systems is reviewed by pointing out the role of the main rhythms and the various control and functional systems involved. The high complexity of the addressed phenomena fosters a multimodal approach that relies on data analysis models and deals with the ongoing interactions of many signals at a time. The importance of closed-loop identification and causal analysis is remarked upon and basic properties, application conditions and methods are recalled. The need of further integration of CV signals relevant to peripheral and systemic haemodynamics, respiratory mechanics, neural afferent and efferent pathways is also stressed.
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Affiliation(s)
- Alberto Porta
- Department of Technologies for Health, Galeazzi Orthopaedic Institute, University of Milan, 20161 Milan, Italy
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Chen X, Mukkamala R. Selective quantification of the cardiac sympathetic and parasympathetic nervous systems by multisignal analysis of cardiorespiratory variability. Am J Physiol Heart Circ Physiol 2008; 294:H362-71. [DOI: 10.1152/ajpheart.01061.2007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Heart rate (HR) power spectral indexes are limited as measures of the cardiac autonomic nervous systems (CANS) in that they neither offer an effective marker of the β-sympathetic nervous system (SNS) due to its overlap with the parasympathetic nervous system (PNS) in the low-frequency (LF) band nor afford specific measures of the CANS due to input contributions to HR [e.g., arterial blood pressure (ABP) and instantaneous lung volume (ILV)]. We derived new PNS and SNS indexes by multisignal analysis of cardiorespiratory variability. The basic idea was to identify the autonomically mediated transfer functions relating fluctuations in ILV to HR (ILV→HR) and fluctuations in ABP to HR (ABP→HR) so as to eliminate the input contributions to HR and then separate each estimated transfer function in the time domain into PNS and SNS indexes using physiological knowledge. We evaluated these indexes with respect to selective pharmacological autonomic nervous blockade in 14 humans. Our results showed that the PNS index derived from the ABP→HR transfer function was correctly decreased after vagal and double (vagal + β-sympathetic) blockade ( P < 0.01) and did not change after β-sympathetic blockade, whereas the SNS index derived from the same transfer function was correctly reduced after β-sympathetic blockade in the standing posture and double blockade ( P < 0.05) and remained the same after vagal blockade. However, this SNS index did not significantly decrease after β-sympathetic blockade in the supine posture. Overall, these predictions were better than those provided by the traditional high-frequency (HF) power, LF-to-HF ratio, and normalized LF power of HR variability.
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Xiao X, Mukkamala R, Cohen R. Quantifying cardiac parasympathetic and sympathetic function based on a weighted-principal component regression method. CONFERENCE PROCEEDINGS : ... ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL CONFERENCE 2007; 2004:3945-8. [PMID: 17271160 DOI: 10.1109/iembs.2004.1404102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
A quantitative evaluation of autonomic cardiovascular control is important in understanding basic pathophysiological mechanisms or for patient monitoring, treatment design and follow-up. Noninvasive techniques for this purpose have been the focus of many research endeavors. We previously proposed a method to extract pure parasympathetic and pure sympathetic indices based on the impulse response between instantaneous lung volume and heart rate. Identification of this impulse response involves a dual-input, single-output system in which one input interacts with the output in closed-loop. To identify this relatively complicated system, we propose here a new system identification technique based on a weighted-principal component regression method. Asymptotically, this technique implements model selection in the frequency domain. Therefore, in contrast to the conventional methods, it allows the data to play a significant role in determining candidate models. Moreover, the estimated model parameters reflect a trade-off between bias and variance to reach a relatively small mean squared prediction error. We employ experimental data to demonstrate that this technique is superior to a more traditional technique in terms of measuring cardiac autonomic indices.
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Affiliation(s)
- X Xiao
- Division of Health Science and Technology, Harvard-MIT, Cambridge, MA, USA
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11
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Lee YB, Park JT, Lim HK, Choi JC, Kim SY, Cho JH, Lee KH. Cardiovascular Effects of Hind-limb Unweighing in Mice. Korean J Anesthesiol 2007. [DOI: 10.4097/kjae.2007.53.2.222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- Young Bok Lee
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Jong Taek Park
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Hyun Kyo Lim
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Jae Chan Choi
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Soon Yul Kim
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Jun Hyun Cho
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Kwang Ho Lee
- Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
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12
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Grenon SM, Xiao X, Hurwitz S, Sheynberg N, Kim C, Seely EW, Cohen RJ, Williams GH. Why is orthostatic tolerance lower in women than in men? Renal and cardiovascular responses to simulated microgravity and the role of midodrine. J Investig Med 2006; 54:180-90. [PMID: 17152857 DOI: 10.2310/6650.2006.05064] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
BACKGROUND Exposure to microgravity induces cardiovascular deconditioning, manifested by orthostatic intolerance (OI). We assessed the renal, cardioendocrine, and cardiovascular responses of women and men to simulated microgravity to examine the impact of gender on OI. METHODS Fifteen healthy female and 14 healthy male subjects were given a constant diet for 3 to 5 days, after which they underwent a tilt-stand test (pre-TST) and began 14 to 16 days of head-down tilt bed rest (HDTB), followed by a repeat tilt-stand test (post-TST). Female subjects began HDTB so that the post-TST was at the same time in their menstrual cycle as their pre-TST. Twenty-four-hour urine collections (daily), hormonal measurements, plethysmography, and cardiovascular system identification were performed. RESULTS The times to presyncope were significantly different for men and women before (p= .005) and after HDTB (p= .001), with all of the women but only 50% of the men experiencing presyncope during the pre-TST (p= .002) and all of the women but only 64% of the men experiencing presyncope during the post-TST. At baseline, the following differences between women and men were observed: women had higher serum aldosterone levels (p = .02), higher parasympathetic responsiveness (p = .01), lower sympathetic responsiveness (p = .05), and lower venous compliance (p = .05). Several parameters changed with HDTB in both men and women. In a double-blinded randomized trial, midodrine (5 mg orally) or placebo given to female subjects 1 hour before post-TST was ineffective in preventing 01. CONCLUSION In conclusion, the frequency of OI is higher in women than in men and is not modified by midodrine at the dose used. This increased susceptibility is likely secondary to intrinsic basal differences in the activity of volume-mediated parasympathetic and adrenergic systems and in venous tone. Thus, approaches to reduce OI in women are likely to differ from those effective in men.
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Affiliation(s)
- S Marlene Grenon
- Division of Endocrinology, Hypertension and Diabetes, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA
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13
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Xiao X, Mukkamala R, Cohen RJ. A weighted-principal component regression method for the identification of physiologic systems. IEEE Trans Biomed Eng 2006; 53:1521-30. [PMID: 16916086 DOI: 10.1109/tbme.2006.876623] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We introduce a system identification method based on weighted-principal component regression (WPCR). This approach aims to identify the dynamics in a linear time-invariant (LTI) model which may represent a resting physiologic system. It tackles the time-domain system identification problem by considering, asymptotically, frequency information inherent in the given data. By including in the model only dominant frequency components of the input signal(s), this method enables construction of candidate models that are specific to the data and facilitates a reduction in parameter estimation error when the signals are colored (as are most physiologic signals). Additionally, this method allows incorporation of preknowledge about the system through a weighting scheme. We present the method in the context of single-input and multi-input single-output systems operating in open-loop and closed-loop. In each scenario, we compare the WPCR method with conventional approaches and approaches that also build data-specific candidate models. Through both simulated and experimental data, we show that the WPCR method enables more accurate identification of the system impulse response function than the other methods when the input signal(s) is colored.
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Affiliation(s)
- Xinshu Xiao
- Department of Biology, MIT, Cambridge, MA 02139, USA.
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14
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Grenon SM, Xiao X, Hurwitz S, Ramsdell CD, Sheynberg N, Kim C, Williams GH, Cohen RJ. Simulated microgravity induces microvolt T wave alternans. Ann Noninvasive Electrocardiol 2005; 10:363-70. [PMID: 16029389 PMCID: PMC6932198 DOI: 10.1111/j.1542-474x.2005.00654.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND There are numerous anecdotal reports of ventricular arrhythmias during spaceflight; however, it is not known whether spaceflight or microgravity systematically increases the risk of cardiac dysrhythmias. Microvolt T wave alternans (MTWA) testing compares favorably with other noninvasive risk stratifiers and invasive electrophysiological testing in patients as a predictor of sudden cardiac death, ventricular tachycardia, and ventricular fibrillation. We hypothesized that simulated microgravity leads to an increase in MTWA. METHODS Twenty-four healthy male subjects underwent 9 to 16 days of head-down tilt bed rest (HDTB). MTWA was measured before and after the bed rest period during bicycle exercise stress. For the purposes of this study, we defined MTWA outcome to be positive if sustained MTWA was present with an onset heart rate<or=125 bpm. During various phases of HDTB, the following were also performed: daily 24-hour urine collections, serum electrolytes and catecholamines, and cardiovascular system identification (measure of autonomic function). RESULTS Before HDTB, 17% of the subjects were MTWA positive [95%CI: (0.6%, 37%)]; after HDTB, 42% of the subjects were MTWA positive [95%CI: (23%, 63%)] (P=0.03). The subjects who were MTWA positive after HDTB compared with MTWA negative subjects had an increased versus decreased sympathetic responsiveness (P=0.03) and serum norepinephrine levels (P=0.05), and a trend toward higher potassium excretion (P=0.06) after bed rest compared to baseline. CONCLUSIONS HDTB leads to an increase in MTWA, providing the first evidence that simulated microgravity has a measurable effect on electrical repolarization processes. Possible contributing factors include loss in potassium and changes in sympathetic function.
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Affiliation(s)
- S. Marlene Grenon
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
- Harvard‐MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
- Department of Cardio‐Thoracic Surgery, McGill University, Montreal, Quebec
| | - Xinshu Xiao
- Harvard‐MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
| | - Shelley Hurwitz
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
| | - Craig D. Ramsdell
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
| | - Natalie Sheynberg
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
| | - Christine Kim
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
| | - Gordon H. Williams
- Division of Endocrinology, Hypertension, and Diabetes, Brigham and Women's Hospital, Boston, MA
| | - Richard J. Cohen
- Harvard‐MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
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15
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Xiao X, Mullen TJ, Mukkamala R. System identification: a multi-signal approach for probing neural cardiovascular regulation. Physiol Meas 2005; 26:R41-71. [PMID: 15798289 DOI: 10.1088/0967-3334/26/3/r01] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Short-term, beat-to-beat cardiovascular variability reflects the dynamic interplay between ongoing perturbations to the circulation and the compensatory response of neurally mediated regulatory mechanisms. This physiologic information may be deciphered from the subtle, beat-to-beat variations by using digital signal processing techniques. While single signal analysis techniques (e.g., power spectral analysis) may be employed to quantify the variability itself, the multi-signal approach of system identification permits the dynamic characterization of the neural regulatory mechanisms responsible for coupling the variability between signals. In this review, we provide an overview of applications of system identification to beat-to-beat variability for the quantitative characterization of cardiovascular regulatory mechanisms. After briefly summarizing the history of the field and basic principles, we take a didactic approach to describe the practice of system identification in the context of probing neural cardiovascular regulation. We then review studies in the literature over the past two decades that have applied system identification for characterizing the dynamical properties of the sinoatrial node, respiratory sinus arrhythmia, and the baroreflex control of sympathetic nerve activity, heart rate and total peripheral resistance. Based on this literature review, we conclude by advocating specific methods of practice and that future research should focus on nonlinear and time-varying behaviors, validation of identification methods, and less understood neural regulatory mechanisms. Ultimately, we hope that this review stimulates such future investigations by both new and experienced system identification researchers.
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Affiliation(s)
- Xinshu Xiao
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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16
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Grenon SM, Hurwitz S, Sheynberg N, Xiao X, Ramsdell CD, Mai CL, Kim C, Cohen RJ, Williams GH. Role of individual predisposition in orthostatic intolerance before and after simulated microgravity. J Appl Physiol (1985) 2004; 96:1714-22. [PMID: 15075309 DOI: 10.1152/japplphysiol.01274.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Orthostatic intolerance (OI) is a major problem after spaceflight. Its etiology remains uncertain, but reports have pointed toward an individual susceptibility to OI. We hypothesized that individual predisposition plays an important role in post-bed rest OI. Twenty-four healthy male subjects were equilibrated on a constant diet, after which they underwent tilt-stand test (pre-TST). They then completed 14-16 days of head-down-tilt bed rest, and 14 of the subjects underwent repeat tilt-stand test (post-TST). During various phases, the following were performed: 24-h urine collections and hormonal measurements, plethysmography, and cardiovascular system identification (a noninvasive method to assess autonomic function and separately quantify parasympathetic and sympathetic responsiveness). Development of presyncope or syncope defined OI. During pre-TST, 11 subjects were intolerant and 13 were tolerant. At baseline, intolerant subjects had lower serum aldosterone (P < 0.01), higher excretion of potassium (P = 0.01), lower leg venous compliance (P = 0.03), higher supine parasympathetic responsiveness (P = 0.02), and lower standing sympathetic responsiveness (P = 0.048). Of the 14 subjects who completed post-TST, 9 were intolerant and 5 were tolerant. Intolerant subjects had lower baseline serum cortisol (P = 0.03) and a higher sodium level (P = 0.02) compared with tolerant subjects. Thus several physiological characteristics were associated with increased susceptibility to OI. We propose a new model for OI, whereby individuals with greater leg venous compliance recruit compensatory mechanisms (activation of the renin-angiotensin-aldosterone system and sympathetic nervous system, and withdrawal of the parasympathetic nervous system) in the face of daily postural challenges, which places them at an advantage to face orthostatic stress. With head-down-tilt bed rest, the stimulus to recruit compensatory mechanisms disappears, and differences between the two subgroups attenuate.
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Affiliation(s)
- S M Grenon
- Division of Endocrinology, Hypertension and Diabetes, Brigham and Women's Hospital, Boston, MA 02115, USA
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Grenon SM, Hurwitz S, Sheynberg N, Xiao X, Judson B, Ramsdell CD, Kim C, Cohen RJ, Williams GH. Sleep restriction does not affect orthostatic tolerance in the simulated microgravity environment. J Appl Physiol (1985) 2004; 97:1660-6. [PMID: 15234956 DOI: 10.1152/japplphysiol.00328.2004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Orthostatic intolerance (OI) is a major problem following spaceflight, and, during flight, astronauts also experience sleep restriction. We hypothesized that sleep restriction will compound the risk and severity of OI following simulated microgravity and exaggerate the renal, cardioendocrine, and cardiovascular adaptive responses to it. Nineteen healthy men were equilibrated on a constant diet, after which they underwent a tilt-stand test. They then completed 14–16 days of simulated microgravity [head-down tilt bed rest (HDTB)], followed by repeat tilt-stand test. During HDTB, 11 subjects were assigned to an 8-h sleep protocol (non-sleep restricted), and 8 were assigned to a sleep-restricted protocol with 6 h of sleep per night. During various phases, the following were performed: 24-h urine collections, hormonal measurements, and cardiovascular system identification. Development of presyncope or syncope defined OI. There was a significant decrease in time free of OI ( P = 0.02) and an increase in OI occurrence ( P = 0.06) after HDTB among all subjects. However, the increase in OI occurrence did not differ significantly between the two groups ( P = 0.60). The two groups also experienced similar physiological changes with HDTB (initial increase in sodium excretion; increased excretion of potassium at the end of HDTB; increase in plasma renin activity secretion without a change in serum or urine aldosterone). No significant change in autonomic function or catecholamines was noted. Simulated microgravity leads to increased OI, and sleep restriction does not additively worsen OI in simulated microgravity. Furthermore, conditions of sleep restriction and nonsleep restriction are similar with respect to renal, cardioendocrine, and cardiovascular responses to simulated microgravity.
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Affiliation(s)
- S Marlene Grenon
- Division of Endocrinology, Hypertension and Diabetes, Brigham and Women's Hospital, 221 Longwood Ave., Boston, MA 02115, USA
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Grenon SM, Sheynberg N, Hurwitz S, Xiao G, Ramsdell CD, Ehrman MD, Mai CL, Kristjansson SR, Sundby GH, Cohen RJ, Williams GH. Renal, Endocrine, and Cardiovascular Responses to Bed Rest in Male Subjects on a Constant Diet. J Investig Med 2004. [DOI: 10.1177/108155890405200221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/15/2023]
Abstract
Background Exposure to actual and simulated microgravity induces cardiovascular deconditioning through a variety of factors. Although the mechanisms involved remain uncertain, one involves alterations in volume-regulating systems—the hypothesis being tested in this study. To maximize our ability to detect subtle changes in the volume-regulating systems, subjects were studied on a high-average salt intake to maximally suppress these systems basally. Methods Fourteen healthy male subjects underwent 14-day head-down tilt bed rest (HDTB) during which a constant 200 mEq sodium, 100 mEq potassium diet was maintained. Daily 24-hour urine collection was performed; plasma renin activity, serum aldosterone, plethysmography, and cardiovascular system identification were performed during a control period (pre-HDTB) and at the end of HDTB (end HDTB). Results Sodium excretion increased initially (pre-HDTB = 182.8 ± 10.4 mEq/total volume; early HDTB = 236.4 ± 13.0; p = .002) and then returned to baseline values. Potassium excretion increased 4 days after the initiation of HDTB and remained elevated thereafter (pre-HDTB = 82.2 ± 2.4/total volume; mid- to late HDTB = 89.4 ± 2.1; p = .02). Plasma renin activity increased significantly with HDTB (pre-HDTB = 1.28 ± 0.21 ng/mL/h; end HDTB = 1.69 ± 0.18; p = .01), but serum aldosterone did not change. A significant decrease in autonomic responsiveness and an increase in leg compliance were observed. Conclusions We conclude that even in the presence of a high-average salt intake diet, simulated microgravity leads to renal, cardioendocrine, and cardiovascular system alterations that likely contribute to cardiovascular deconditioning.
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Affiliation(s)
- S. Marlene Grenon
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
| | - Natalie Sheynberg
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | - Shelley Hurwitz
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | - Grace Xiao
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
| | - Craig D. Ramsdell
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | - Michael D. Ehrman
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | - C. Lan Mai
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | | | - Grete H. Sundby
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
| | - Richard J. Cohen
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA
| | - Gordon H. Williams
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA
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