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Biomedical subjects

J F Thayer

Publications and source records attributed to J F Thayer.

At least 37 records · Page 2Linked to original sources
PubMed1998

Autonomic balance revisited: panic anxiety and heart rate variability.

The analysis of heart rate variability (HRV) is becoming widely used in clinical research to provide a window into autonomic control of HR. This technique has been valuable in elucidating the autonomic underpinnings of panic disorder (PD), a condition that is marked by reports of heart palpitations. A body of research has emerged that implicates a relative reduction in HRV and cardiac vagal tone in PD, as indicated by various HRV measures. These data are consistent with the cardiac symptoms of panic attacks, as well as with developmental evidence that links high vagal tone with enhanced attention, effective emotion regulation, and organismic responsivity. Implications of these findings for nosology and pathophysiology are discussed. Reports of reduced HRV in PD contrast with portrayals of excess autonomic lability in anxiety. This contradiction is addressed in the context of traditional homeostatic models versus a systems perspective that views physiologic variability as essential to overall stability.

Anxiety Disorders↗
PubMed1998

Anxiety and autonomic flexibility: a cardiovascular approach.

Autonomic characteristics of panickers, blood phobics, and nonanxious controls were compared with a variety of cardiovascular measures, including spectral analysis of the cardiac inter-beat interval time series (derived from the electrocardiogram). Responses to laboratory stressors (shock avoidance and cold face stress) of 16 participants who reported recent occurrences of frequent severe panic attacks, 15 participants who reported strong somatic reactions and fainting to the sight of blood, and 15 controls, were recorded. Results suggested distinct autonomic patterns among the three groups. Across conditions, panickers displayed the highest heart rates (HR) coupled with the least HR variability, which indicates low levels of cardiac vagal tone. Blood phobics showed more vagally mediated HR variability than panickers, with a significant association between cardiac rate and mean arterial pressure. Controls generally showed the most HR variability and 'spectral reserve' (a quality that indicates flexible responsivity). Results are discussed in the context of traditional models of anxiety and autonomic activity in contrast to contemporary notions of stability and change in biological systems.

Adult↗
PubMed1998

The effect of autonomic nervous system activity on gastric myoelectrical activity: does the spectral reserve hypothesis hold for the stomach?

Previous studies have associated changes in gastric myoelectrical activity during motion sickness, as indexed using the electrogastrogram (EGG), with changes in autonomic nervous system (ANS) activity. Subjects who did not report nausea in a rotating optokinetic drum were characterized by normal 3 cycles per minute (cpm) gastric myoelectrical activity, strong parasympathetic nervous system (PNS) activity, and low sympathetic nervous system (SNS) activity. The goals of this study were: (1) to determine whether tasks previously shown to alter ANS activity as indexed by changes in cardiac inter-beat intervals (IBIs) would result in systematic changes in gastric myoelectrical activity in accord with the findings from motion sickness studies; and (2) to determine whether the 'spectral reserve hypothesis' applies to gastric myoelectrical activity. EGGs and IBIs were collected from 24 healthy subjects during resting/baseline, reaction time/shock-avoidance (RT) and cold face stress (CF) tasks. Tachyarrhythmia was found to be significantly greater during the RT task than during the baseline and CF tasks. It was concluded that: (1) tasks that alter ANS activity do systematically alter gastric myoelectrical activity; and (2) gastric myoelectrical activity does not follow the cardiac model of health being associated with increased spectral complexity.

Adult↗
PubMed1998

Anxiety and autonomic flexibility: a cardiovascular approach.

Autonomic characteristics of panickers, blood phobics, and nonanxious controls were compared with a variety of cardiovascular measures, including spectral analysis of the cardiac inter-beat interval time series (derived from the electrocardiogram). Responses to laboratory stressors (shock avoidance and cold face stress) of 16 participants who reported recent occurrences of frequent severe panic attacks, 15 participants who reported strong somatic reactions and fainting to the sight of blood, and 15 controls, were recorded. Results suggested distinct autonomic patterns among the three groups. Across conditions, panickers displayed the highest heart rates (HR) coupled with the least HR variability, which indicates low levels of cardiac vagal tone. Blood phobics showed more vagally mediated HR variability than panickers, with a significant association between cardiac rate and mean arterial pressure. Controls generally showed the most HR variability and 'spectral reserve' (a quality that indicates flexible responsivity). Results are discussed in the context of traditional models of anxiety and autonomic activity in contrast to contemporary notions of stability and change in biological systems.

Adolescent↗
PubMed1998

Trajectories of adaptation in pediatric chronic illness: the importance of the individual.

This study used individual growth modeling to examine individual difference and group difference models of adaptation. The adaptation of 27 children with juvenile rheumatoid arthritis (JRA) and 40 children with insulin-dependent diabetes mellitus (IDDM) was tracked for 18 months from diagnosis. A control group of 62 healthy children was followed over the same time period. Clustering procedures indicated that child and family adaptation could be described by a number of distinct adaptation trajectories, independent of diagnostic group membership. In contrast, parental adaptation trajectory was associated with diagnostic group membership and control over disease activity for the JRA group and with diagnostic group membership for healthy controls. The observation of common patterns across trajectory sets, as well as the finding that trajectories were differentially related to a number of variables of interest, support the use of trajectories to represent adaptation to chronic disease.

Adaptation, Psychological↗
PubMed1997

Heart rate variability during exercise in the horse.

High heart rate variability (HRV) has been associated with more efficient autonomic control, allowing more responsivity and sensitivity to changing environmental demands. Previous results from spectral analysis of interbeat intervals of equine heart rate (HR) indicated increased HRV, reflecting more effective vagal control of the heart. This study focuses on characterizing equine HR and HRV during increasing then decreasing physical demand. A non-invasive ambulatory monitoring system continuously records HR and HRV as horses exercise on a high speed equine treadmill at increasing then decreasing workloads. After a 5 minute baseline, the horses walk, then trot, then canter or trot fast, return to the slower trot, then walk, and then remain quiet for a 5 minute recovery period. Results indicate a decrease of HRV and large individual differences in parasympathetic activity during exercise. Resulting patterns of HR fluctuation indicate a nonlinear dynamical approach may describe the task responses more completely than the more traditional models.

Animals↗
PubMed1997

Thermoregulation and cardiac variability: a time-frequency analysis.

High heart rate variability (HRV) has been associated with more efficient autonomic control, allowing more responsivity and sensitivity to changing environmental demands. A number of specific periodicities have been identified in the spectra of cardiac time series. A high frequency component related to respiratory sinus arrhythmia, a low frequency component related to blood pressure variability, and a very low frequency component thought to reflect thermoregulation have been reported in the literature. However, the source of the very low frequency component has not been extensively investigated in humans using non-invasive methods and analytic techniques that do not rely upon stationarity. We investigated HRV in response to both hot and cold thermal challenge in healthy adults using time-frequency analysis. This analytic technique does not rely upon signal stationarity. The results suggest that very low frequency power may reflect thermoregulation to ambient temperature changes. Implications for prediction of cardiac events are discussed.

Adult↗
PubMed1997

Heart rate variability in the horse by ambulatory monitoring.

Using a microprocessor controlled Ambulatory Monitoring System (AMS) developed by one of us (LvD), we have been studying the changes in and control of heart rate in the resting horse. The system provides us with InterBeat Intervals (IBI in milliseconds), motion sensing, and a time domain measure (mean successive differences: MSD) of heart rate variability for periods up to 72 hours. Thoracic impedance is also available but parameters for the equine chest are not currently available. The system is completely noninvasive, small, and carried on a surcingle worn by the subject. The equine subject is confined to a stall in our teaching hospital but not otherwise restrained. Recording is virtually unobtrusive. Ten horses (judged to be clinically normal) were used in this preliminary study. After collection, the data were "offloaded" to a laptop computer for additional analysis. The electrocardiogram could be recorded on each of the ten animals. Complete data, suitable for spectral analysis, were obtained from four of the animals. Spectral estimates were calculated on periods of varying lengths (3-5 minutes) with more stable spectral estimates associated with longer recording periods. Results indicated the preponderance of parasympathetic control in equid heart rate. These results provide support for the utility of this method for the study of heart rate variability in the freely behaving horse.

Animals↗
PubMed1997

Estimation of the correlation dimension of heart rate using surrogate data techniques.

Researchers have recently applied nonlinear dynamical systems theory to physiological time series data. However, the direct implementation of the deterministic equations used to estimate the correlation dimension is problematic for physiological data. Importantly, the distinction between a nonlinear process and noise is particularly difficult for experimental data. One technique that has been developed to help with this distinction is the use of surrogate data. These data preserve many of the properties of the original time series but in fact are a randomization of the original data. Whereas in a sufficiently high embedding space the estimates of the correlation dimension of a nonlinear process will plateau, such estimates for a noise process will continue to rise with increases in the embedding dimension. In the present experiment two data sets were examined. Heart period time series were collected from a female subject during spontaneous breathing and breathing paced at 15 breaths per minute. Both data sets consisted of approximately 3000 interbeat intervals and embedding dimensions of m = 2 through m = 6 were examined. Results indicate that the correlation dimension estimate for the spontaneous breathing data reached a plateau around 4, whereas the surrogate data for this series showed no such plateau. For the paced breathing data, both the original and the surrogate data failed to show evidence of a plateau in the estimates of the correlation dimension. These results suggest that caution must be used in interpreting finite values of correlation dimension as evidence of a chaotic attractor in experimental data if no test for determinism is performed.

Female↗
PubMed1996

Autonomic characteristics of generalized anxiety disorder and worry.

Autonomic characteristics of generalized anxiety disorder (GAD) and worry were examined using measures of heart period variability. The cardiorespiratory responses of 34 GAD clients and 32 nonanxious control subjects were recorded during resting baseline, relaxation, and worry periods. Results indicated differences between GAD subjects and controls as well as among baseline, relaxation, and worry periods. GAD clients exhibited shorter cardiac interbeat intervals (IBIs) and lower high frequency spectral power across all task conditions. Relative to baseline and relaxation conditions, worry was associated with (1) shorter IBIs, (2) smaller mean successive differences (MSD) of the cardiac IBIs, and (3) lower high frequency spectral power. These findings suggest that GAD and its cardinal feature (worry), are associated with lower cardiac vagal control. The findings of the present study provide evidence for the utility of further exploration of the role of autonomic nervous system activity in GAD.

Adult↗
PubMed1996

Spectral characteristics of heart period variability during cold face stress and shock avoidance in normal subjects.

Spectral analysis of heart period variability was used to examine autonomic cardiac control in several tasks used in experimental and clinical assessments of autonomic nervous system function. Cardiovascular measures were recorded in healthy humans during quiet rest, reaction time shock-avoidance, cold face stress, and combined shock-avoidance/cold face stress. Shock-avoidance was characterized by sympathetic beta-adrenergic dominance, as evidenced by (1) shorter heart periods, (2) less high-frequency spectral power, (3) elevated low-frequency power, (4) increased ratios of low- to high-frequency power, and (5) a steep regression line fitted to the log-log plot of the power spectra. Cold face stress yielded (1) longer heart periods, (2) more high-frequency power, (3) decreased low-frequency spectral power, and (4) a flat regression slope, indicating vagal dominance. Quiet rest appeared as mildly vagal, with less total spectral power, and the combination task elicited a mixed vagal-sympathetic pattern. These results are discussed in the context of (1) the autonomic underpinnings of low-frequency power, (2) the autonomic effects of facial cooling, and (3) the utility of spectral analysis of heart period variability during autonomic challenge tasks for basic research and clinical application.

Adult↗
PubMed1996

Assessment of the multiple dimensions of nausea: the Nausea Profile (NP).

Nausea, unlike emesis, is a subjective experience that is difficult to describe to others, be they clinicians or researchers. Previous research has been limited to examining the frequency, severity, and duration of nausea. The goal of this study was to design a questionnaire that would allow for the evaluation of the characteristics of nausea across individuals and situations. This study consisted of 4 stages: descriptors were generated, categorized into 3 dimensions, and reevaluated to verify their reliability; in the final stage, the developed checklist was compared to a visual-analogue-scale (VAS) report of nausea in subjects exposed to a rotating optokinetic drum to stimulate nausea. The overall nausea checklist score and the VAS score were highly correlated (r = 0.71, p < 0.01). The development and use of the nausea checklist are discussed.

Adult↗
PubMed1996

A hybrid approach to clustering biomedical data.

Cluster analysis is often used in an attempt to determine the number and characteristics of patterns present in vectors of biomedical response parameters. An iterative clustering procedure based upon the combined supervised and unsupervised learning algorithm of Pao is described. The present paper illustrates this procedure using growth curves of indices of family functioning in adaptation to pediatric chronic illness. This clustering procedure is based upon neural network approaches to supervised (discriminant analysis) and unsupervised (cluster analysis) learning and is similar to fuzzy set algorithms developed to assess the degree of relatedness among a number of discrete units.

Cluster Analysis↗
PubMed1996

Estimation of respiratory frequency from autoregressive spectral analysis of heart period.

Variability in heart period is modulated by respiration. Using an autoregressive spectral analytic approach on the heart period time series produces a components analysis. The central frequency of the heart period spectral component in the frequency of respiration (HFFreq) has been suggested as an index of respiratory frequency. The present experiment measured heart period variability (HPV) using an autoregressive algorithm and respiratory frequency using a mercury strain gauge (SGResp) to assess the relationship between the respiratory frequency indexed by the two methods. Twenty human participants were studied during resting baseline, relaxation, and mental effort conditions. Within- and between-person Pearson correlations and t-tests were used to assess the concordance between HFFreq and SGResp. Both within-person and between-person correlations indicated good concordance among the two methods. Moreover, t-tests, corrected for Type I error, indicated no significant differences between the respiratory frequency estimates derived from the two methods. The resolution of the estimates was approximately 1 breath per minute. These results suggest that the HFFreq may be a useful index of respiratory frequency.

Electrocardiography↗
PubMed1995

Assessment of neural network models using prediction analysis.

Examination of classification or confusion matrices in neural network models is often advocated as a way to investigate the effects of network architecture on classification rules and to understand the topography of the classification space. In addition, for model comparison purposes it is useful to be able to make statements concerning the statistical reliability of these patterns of hit and error cells. Prediction analysis provides a number of descriptive and inferential measures for the evaluation of hypotheses about patterns of hit and error cells. The present paper applied recent advances in prediction analysis to the examination of neural network classification matrices. Results of the application of prediction analysis to the generalized XOR problem and to data from classification of cardiovascular responses of human subjects were used to illustrate the determination of absolute and relative fit of omnibus models as well as the evaluation of specific hypotheses within these models.

Cardiovascular System↗
PubMed1993

Autonomic characteristics of nonclinical panic and blood phobia.

Autonomic characteristics of nonclinical panic and blood phobia were compared using spectral analysis of the electrocardiogram (EKG), as well as more conventional cardiovascular measures. The cardiovascular responses of 11 subjects who reported recent occurrence of frequent severe panic attacks, and 10 subjects who reported intense somatic reactions to the sight of blood (including episodes of syncope) were recorded during a variety of laboratory tasks (quiet rest, reaction time/shock avoidance, face immersion, and combined reaction time/face immersion). Results suggest distinct autonomic patterns in the groups. Panickers showed (a) higher heart rate and reduced heart-rate variability (b) aberrant associations among cardiovascular measures, and (c) dominant sympathetic control of heart rate coupled with diminished vagal tone. Blood phobics generally displayed an opposite pattern. The relevance of these findings to the etiology of panic and blood phobia, as well as to biological models of anxiety disorders in general, is discussed.

Adult↗
PubMed1991

Facial muscle activity and EEG recordings: redundancy analysis.

The present study explored the use of redundancy analysis, a multivariate technique for assessment of interset association, to examine facial muscle contamination of EEG recordings in studies involving covert levels of emotional expression. Redundancy analyses were performed on simultaneously recorded EEG and facial EMG data obtained in an emotion induction paradigm. Redundancy indices obtained suggest that (1) the amount of variance in EEG activity that can be explained by facial muscle activity under such conditions is minimal, and (2) the EEG alpha band may be at least as or even more susceptible to muscle contamination as the beta band.

Adult↗