Keri J. Heilman

Accuracy of the LifeShirt® (Vivometrics) in the detection of cardiac rhythms

The use of heart rate measures in research requires accurate detection and timing of beat-to-beat values. Numerous technologies are available to researchers; however, benchmarking of a specific apparatus is seldom conducted. Since heart rate variability provides a portal to the neural regulation of the heart, accurate detection and timing of beat-to-beat values is essential to both basic physiological research and the clinical application of heart rate variability measures. The current study evaluated the accuracy of an ambulatory system, the LifeShirt (Vivometrics), relative to a standard laboratory-based heart rate monitoring equipment (Biopac), during baseline and exercise conditions. LifeShirt performed equivalently to the Biopac during both conditions, experienced few errors of detection, generated similar times between sequential heart periods, and produced similar summary indices of heart rate and heart rate variability.

Respiratory sinus arrhythmia and auditory processing in autism: Modifiable deficits of an integrated social engagement system?

The current study evaluated processes underlying two common symptoms (i.e., state regulation problems and deficits in auditory processing) associated with a diagnosis of autism spectrum disorders. Although these symptoms have been treated in the literature as unrelated, when informed by the Polyvagal Theory, these symptoms may be viewed as the predictable consequences of depressed neural regulation of an integrated social engagement system, in which there is down regulation of neural influences to the heart (i.e., via the vagus) and to the middle ear muscles (i.e., via the facial and trigeminal cranial nerves). Respiratory sinus arrhythmia (RSA) and heart period were monitored to evaluate state regulation during a baseline and two auditory processing tasks (i.e., the SCAN tests for Filtered Words and Competing Words), which were used to evaluate auditory processing performance. Children with a diagnosis of autism spectrum disorders (ASD) were contrasted with aged matched typically developing children. The current study identified three features that distinguished the ASD group from a group of typically developing children: 1) baseline RSA, 2) direction of RSA reactivity, and 3) auditory processing performance. In the ASD group, the pattern of change in RSA during the attention demanding SCAN tests moderated the relation between performance on the Competing Words test and IQ. In addition, in a subset of ASD participants, auditory processing performance improved and RSA increased following an intervention designed to improve auditory processing.

Autonomic regulation in fragile X syndrome

Autonomic reactivity was studied in individuals with fragile X syndrome (FXS), a genetic disorder partially characterized by abnormal social behavior. Relative to age-matched controls, the FXS group had faster baseline heart rate and lower amplitude respiratory sinus arrhythmia (RSA). In contrast to the typically developing controls, there was a decrease in RSA with age within the FXS group. Moreover, within the FXS group heart rate did not slow with age. The FXS group also responded with an atypical increase in RSA to the social challenge, while the control group reduced RSA. In a subset of the FXS group, the autonomic profile did not change following 2 months and 1 year of lithium treatment. The observed indices of atypical autonomic regulation, consistent with the Polyvagal Theory, may contribute to the deficits in social behavior and social communication observed in FXS.

Physiological responses to social and physical challenges in children: Quantifying mechanisms supporting social engagement and mobilization behaviors.

Physiological response patterns to laboratory-based social and physical challenges were investigated in 37 typically-developing 3- to 5-year-old children. The study was conducted to determine whether the response profiles during each challenge were similar and whether individual differences in the response profiles to the challenges were correlated. Results demonstrated challenge specific physiological response strategies. In response to the social challenge, respiratory sinus arrhythmia and heart period increased and motor activity decreased. In contrast, in response to the physical challenge, respiratory sinus arrhythmia and heart period decreased and motor activity increased. Neither challenge reliably elicited changes in salivary cortisol. Only heart period responses were correlated between the challenges.

The covariation of acoustic features of infant cries and autonomic state.

The evolution of the autonomic nervous system provides an organizing principle to interpret the adaptive significance of physiological systems in promoting social behavior and responding to social challenges. This phylogenetic shift in neural regulation of the autonomic nervous system in mammals has produced a neuroanatomically integrated social engagement system, including neural mechanisms that regulate both cardiac vagal tone and muscles involved in vocalization. Mammalian vocalizations are part of a conspecific social communication system, with several mammalian species modulating acoustic features of vocalizations to signal affective state. Prosody, defined by variations in rhythm and pitch, is a feature of mammalian vocalizations that communicate emotion and affective state. While the covariation between physiological state and the acoustic frequencies of vocalizations is neurophysiologically based, few studies have investigated the covariation between vocal prosody and autonomic state. In response to this paucity of scientific evidence, the current study explored the utility of vocal prosody as a sensitive index of autonomic activity in human infants during the Still Face challenge. Overall, significant correlations were observed between several acoustic features of the infant vocalizations and autonomic state, demonstrating an association between shorter heart period and reductions in heart period and respiratory sinus arrhythmia following the challenge with the dampening of the modulation of acoustic features (fundamental frequency, variance, 50% bandwidth, and duration) that are perceived as prosody.

Sluggish vagal brake reactivity to physical exercise challenge in children with selective mutism

Cardiovascular response patterns to laboratory-based social and physical exercise challenges were evaluated in 69 children and adolescents, 20 with selective mutism (SM), to identify possible neurophysiological mechanisms that may mediate the behavioral features of SM. Results suggest that SM is associated with a dampened response of the vagal brake to physical exercise that is manifested as reduced reactivity in heart rate and respiration. Polyvagal theory proposes that the regulation of the vagal brake is a neurophysiological component of an integrated social engagement system that includes the neural regulation of the laryngeal and pharyngeal muscles. Within this theoretical framework, sluggish vagal brake reactivity may parallel an inability to recruit efficiently the structures involved in speech. Thus, the findings suggest that dampened autonomic reactivity during mobilization behaviors may be a biomarker of SM that can be assessed independent of the social stimuli that elicit mutism.

Multiscale analysis of heart rate variability in non-stationary environments

Heart rate variability (HRV) is highly non-stationary, even if no perturbing influences can be identified during the recording of the data. The non-stationarity becomes more profound when HRV data are measured in intrinsically non-stationary environments, such as social stress. In general, HRV data measured in such situations are more difficult to analyze than those measured in constant environments. In this paper, we analyze HRV data measured during a social stress test using two multiscale approaches, the adaptive fractal analysis (AFA) and scale-dependent Lyapunov exponent (SDLE), for the purpose of uncovering differences in HRV between chronic fatigue syndrome (CFS) patients and their matched-controls. CFS is a debilitating, heterogeneous illness with no known biomarker. HRV has shown some promise recently as a non-invasive measure of subtle physiological disturbances and trauma that are otherwise difficult to assess. If the HRV in persons with CFS are significantly different from their healthy controls, then certain cardiac irregularities may constitute good candidate biomarkers for CFS. Our multiscale analyses show that there are notable differences in HRV between CFS and their matched controls before a social stress test, but these differences seem to diminish during the test. These analyses illustrate that the two employed multiscale approaches could be useful for the analysis of HRV measured in various environments, both stationary and non-stationary.

Atypical autonomic regulation, auditory processing, and affect recognition in women with HIV

This study examined the effect of HIV on visceromotor (i.e., heart rate and heart rate variability) and somatomotor (i.e., auditory processing and affect recognition) components of a Social Engagement System defined by the Polyvagal Theory (Porges, 1995) that links vagal regulation of the heart with brainstem regulation of the striated muscles of the face and head. Relative to at risk HIV-seronegative women, HIV-seropositive women had less heart rate variability (i.e., respiratory sinus arrhythmia) and had poorer performance on auditory processing and affect recognition tasks. CD4 was negatively correlated with the accuracy to detect specific emotions. The observed indices of atypical autonomic and behavioral regulation may contribute to greater difficulties in social behavior and social communication between HIV-infected women and other individuals in their social network.

Sensory Difficulties in Children With an FMR1 Premutation

Abnormal sensory processing is one of the core characteristics of the fragile X phenotype. Studies of young children with fragile X syndrome (FXS) and the FMR1 premutation have shown sensory challenges as early as infancy and into early childhood. This study sought to examine differences in sensory difficulties in children with an FMR1 premutation compared with children with FXS and typically developing children. We conducted an online survey of 176 parents of affected children (FXS or FMR1 premutation). Most respondents were mothers who are Caucasian (86%), have a 4-year college or graduate degree (68%), and are married (92%). Children ranged in age from 5 to 18, with a mean age of 13.0 years (3.3 SD). Participants completed the BBC Sensory Scales, a 50-item Likert-type scale (1 = Almost Always, 4 = Almost Never) comprised of 8 subscales that assessed auditory processing, visual processing, tactile processing, and eating and feeding behaviors. Mean scores were calculated for the items and each of the subscales. Non-parametric tests examined differences in child and family-level variables. Across all BBCSS subscales, children with an FMR1 premutation displayed more sensory challenges than typically developing children. For six out of the eight subscales, children with the full mutation had the lowest scores indicating more sensory challenges, but this was closely followed by children with an FMR1 premutation. Fragile X status was associated with seven of the eight subscales; children with an FMR1 premutation did not differ from children with FXS on any of the subscales but had more digestive problems than children with no fragile X. Gender, autism status, and family income were also related to sensory sensitivities. In conclusion, these data provide further evidence that some children with an FMR1 premutation experience sensory difficulties that are similar to children with FXS but different than typically developing children.