Changes in heart beat timing: reactivity, resetting, or perturbation?

Model-free Cardiorespiratory Motion Prediction from X-ray Angiography Sequence with LSTM Network

We present a novel model-free approach for cardiorespiratory motion prediction from X-ray angiography time series based on Long Short-Term Memory Recurrent Neural Networks (LSTM-RNN). Cardiorespiratory motion prediction is defined as a problem of estimating the future displacement of the coronary vessels in the next image frame in an X-ray angiography sequence. The displacement of the vessels is represented as a sequence of 2D affine transformation matrices allowing 2D X-ray registrations in a sequence. The new displacement parameters from a sequence of transformation matrices are predicted using an LSTM model. LSTM is a particular form of Recurrent Neural Network (RNN) architecture suitable for learning sequential data and predicting time series. The method was developed and validated by simulated data using a realistic cardiorespiratory motion simulator (XCAT). The results show that this method converges quickly and can predict the complex motion in the angiography sequences with irregularities. The mean values of prediction error over all the patients are approximately 0.29 mm (2 pixels) difference for the combination of both motions, 0.51 mm (3.5 pixels) difference for cardiac motion and 0.44 mm (3 pixels) difference for respiratory motion.

Emotion Dysregulation Across Emotion Systems in Attention Deficit/Hyperactivity Disorder

Children with attention deficit/hyperactivity disorder (ADHD) display alterations in both emotion reactivity and regulation. One mechanism underlying such alternations may be reduced coherence among emotion systems (i.e., autonomic, facial affect). The present study sought to examine this. One hundred children (50 with ADHD combined presentation), 7-11 years of age (62% male, 78% White), completed an emotion induction and suppression task. This task was coded for facial affect behavior across both negative and positive emotion eliciting task conditions. Electrocardiogram and impedance cardiography data were acquired throughout the task. Time-linked coherence of facial affect behavior and autonomic reactivity and regulation were examined during the induction conditions using hierarchical linear modeling. Although ADHD and typically developing children did not differ with respect to rates of facial affect behavior displayed (all Fs < 2.09, ps > .29), the ADHD group exhibited reduced coherence between facial affect behavior and an index of parasympathetic functioning (i.e., respiratory sinus arrhythmia), γ₁₀ = -0.03, SE = 0.02, t(138) = -1.96, p = .05. In contrast, children in the control group displayed a significant, positive, γ₁₀ = 0.06, SE = 0.01, t(138) = 4.07, p < .001, association between facial affect behavior and respiratory sinus arrhythmia. Children with ADHD may receive conflicting emotional signals at the levels of facial affective behavior and parasympathetic functioning when compared to typically developing youth. Weakened coherence among these emotion systems may be an underlying mechanism of emotion dysregulation in ADHD. Implications for etiology and treatment are discussed.

Heart rate variability characteristics in a large group of active-duty marines and relationship to posttraumatic stress

OBJECTIVE

Heart rate variability (HRV), thought to reflect autonomic nervous system function, is lowered under conditions such as posttraumatic stress disorder (PTSD). The potential confounding effects of traumatic brain injury (TBI) and depression in the relationship between HRV and PTSD have not been elucidated in a large cohort of military service members. Here we describe HRV associations with stress disorder symptoms in a large study of Marines while accounting for well-known covariates of HRV and PTSD including TBI and depression.

METHODS

Four battalions of male active-duty Marines (n = 2430) were assessed 1 to 2 months before a combat deployment. HRV was measured during a 5-minute rest. Depression and PTSD were assessed using the Beck Depression Inventory and Clinician-Administered PTSD Scale, respectively.

RESULTS

When adjusting for covariates, including TBI, regression analyses showed that lower levels of high-frequency HRV were associated with a diagnosis of PTSD (β = -0.20, p = .035). Depression and PTSD severity were correlated (r = 0.49, p < .001); however, participants with PTSD but relatively low depression scores exhibited reduced high frequency compared with controls (p = .012). Marines with deployment experience (n = 1254) had lower HRV than did those with no experience (p = .033).

CONCLUSIONS

This cross-sectional analysis of a large cohort supports associations between PTSD and reduced HRV when accounting for TBI and depression symptoms. Future postdeployment assessments will be used to determine whether predeployment HRV can predict vulnerability and resilience to the serious psychological and physiological consequences of combat exposure.

Emotion regulation via the autonomic nervous system in children with attention-deficit/hyperactivity disorder (ADHD)

Despite growing interest in conceptualizing ADHD as involving disrupted emotion regulation, few studies have examined the physiological mechanisms related to emotion regulation in children with this disorder. This study examined parasympathetic and sympathetic nervous system reactivity via measures of respiratory sinus arrhythmia (RSA) and cardiac pre-ejection period (PEP) in children with ADHD (n=32) and typically developing controls (n=34), using a novel emotion task with four conditions: negative induction, negative suppression, positive induction, and positive suppression of affect. Both groups showed strong task-response effects in RSA. However, typically developing children showed systematic variation in parasympathetic activity (RSA) depending on both emotion valence (more activation for negative emotion, reduced activation for positive emotion) and task demand (more activation for suppression than induction). In contrast, children with ADHD displayed a stable pattern of elevated parasympathetic activity (RSA) across all task conditions compared to baseline. No group differences in sympathetic activity (PEP) were observed. It is concluded ADHD in childhood is associated with abnormal parasympathetic mechanisms involved in emotion regulation.

Sympathetic nerve and cardiovascular responses to auditory startle and prepulse inhibition

While sudden (startling) sensory stimuli are generally thought of as inducing sympathetic excitation, in humans there is a short-lasting inhibition of limb muscle sympathetic nerve activity (MSNA). This study is the first to examine and contrast the effects of acoustic startle and the prepulse inhibition of startle (PPI) on MSNA, blood pressure, heart rate, and eye blinks. Startle elicited a two-component withdrawal of MSNA: an early inhibition of one sympathetic burst followed by a second inhibition. PPI abolished the early, but not the late MSNA inhibition. Prepulse stimuli alone had no early inhibitory effects on MSNA. Early MSNA inhibition, which may occur at latencies of approximately 100 ms, appears to be part of a CNS-generated startle reflex which subserves automatic defensive responses to potential threats. The late MSNA inhibition coincided with the stimulus-induced blood pressure increase and is probably an inhibitory reflex response.

On the importance of inhibition: central and peripheral manifestations of nonlinear inhibitory processes in neural systems

Inhibitory processes provide for the sculpting of neural action at all levels of the neuraxis. Importantly, it appears that this inhibitory function may be decidedly nonlinear in nature such that a little inhibition goes a long way in guiding the behavior of neural systems. The neural control of the heart is used as a model system to illustrate the nature of this nonlinear inhibitory control. Similar inhibitory processes function in the prefrontal cortex, in the amygdala, and between the prefrontal cortex and the amygdala in the service of organism flexibility, adaptability, and health. It is suggested that a dynamical systems perspective of neural regulation involving nonlinear inhibitory processes may be a useful framework within which to investigate the complex behavior associated with health and disease.

Idiodynamic profiles of cardiovascular activity: A P-technique approach

A study was conducted to expand the conventional view of cardiovascular (CV) reactivity by using the idiodynamic paradigm for investigation of individuals. Patterns of autonomic CV regulation were assessed in six subjects across diverse laboratory tasks on three separate occasions. Individual CV profiles were derived from these data with P-technique factor analysis, and then group aggregated with chain P-technique. The composite pattern suggested a three-component solution consisting of cardiac rate, cardiac contractility, and peripheral resistance factors. Individual profiles were compared to the composite pattern; these profiles differed in the number of components derived, percentage variance explained by these components, and relative dominance of specific CV components. A hypothesis that emerged is that the subjects differed in the complexity of CV control. It appears that the idiodynamic framework, combined with novel research designs and statistical methods, may help expand the view of CV reactivity beyond the traditional unitary view as response magnitude.