Heartbeat Counting Research Articles

Transcutaneous vagus nerve stimulation improves interoceptive accuracy

How can interoceptive accuracy, i.e. the objective ability to identify interoceptive signals, be improved? In the present study, we investigated whether non-invasive stimulation of the auricular branch of the vagus nerve (taVNS) modulates cardiac interoceptive accuracy, interoceptive sensibility, i.e. confidence in the identification of bodily signals, and interoceptive awareness, i.e. the capacity to evaluate one's ability in the objective task. Using a single-blind within-subjects design we compared participants' performance on the heartbeat counting task and on the heartbeat discrimination task during active and sham taVNS stimulation. Results revealed improved accuracy during active taVNS on the heartbeat discrimination task but not on the heartbeat counting task. Participants were also more confident during active stimulation, but interoceptive awareness was not modulated by taVNS. These findings show that taVNS can modulate interoceptive processing and suggest its potential as a tool to investigate body-brain interactions.

I feel it in my finger: Measurement device affects cardiac interoceptive accuracy

In recent years, measures of cardiac interoceptive accuracy have been heavily scrutinised. The focus has been on potentially confounding physiological and psychological factors; little research has examined whether the device used to record objective heartbeats may influence cardiac interoceptive accuracy. The present studies assessed whether the device employed influences heartbeat counting (HCT) accuracy and the location from which heartbeats are perceived. In Study One, participants completed the HCT using a hard-clip finger pulse oximeter, electrocardiogram (ECG) and a smartphone application. In Study Two, an ECG, hard-clip and soft-clip oximeter were compared. Moderate-strong correlations were observed across devices, however, mean HCT accuracy and confidence varied as a function of device. Increased sensation in the finger when using a hard-clip pulse oximeter was related to increased accuracy relative to ECG. Results suggest that the device employed can influence HCT performance, and argue against comparing, or combining, scores obtained using different devices.

Estimating the stability of heartbeat counting in middle childhood: A twin study

There is growing interest in interoception, the perception of the body’s internal state, and its relevance for health across development. Most evidence linking interoception to health has used the heartbeat counting task. However, the temporal stability of the measure, particularly during childhood, and the etiological factors that underlie stability, remain largely unexamined. Using data from the ECHO twin sample we estimated the magnitude of genetic and environmental influences on the stability of heartbeat counting across two years (age 8–10), the longest time-frame examined. Heartbeat counting accuracy was modestly correlated across time, (r = .35) and accuracy improved with age. Non-shared environmental factors accounted for the most variance at both time points and were the main contributors to temporal stability of heartbeat counting. Future research should seek to identify these non-shared environmental factors and elucidate whether this relatively modest stability reflects variability of interoception across development or unreliability of the heartbeat counting task.

Study of structural and magnetic properties of hydro/solvothermally synthesized α-Fe2O3 nanoparticles and its toxicity assessment in zebrafish embryos

Hematite (α-Fe2O3) nanoparticles with different shape and size were obtained by hydro-solvothermal technique under various conditions. The structural, morphological and magnetic properties of the synthesized α-Fe2O3 nanoparticles were characterized using XRD, FESEM with EDX, FTIR and VSM. The results revealed that the size and shape of the α-Fe2O3 nanoparticles can be modified by changing the synthetic parameters like reaction temperature, pH of the solution, and solvents used for synthesis. The zebrafish embryos exposed to different concentrations of α-Fe2O3 nanoparticles and its physical anomalies were monitored in order to study its ecological toxicity. The changes in hatching rate, survival percentage, heartbeat count, body length of zebrafish due to α-Fe2O3 nanoparticles were analyzed. Toxicity assessment in the early life stage of zebrafish shows that minor changes occurred at lower concentrations of nanoparticles and some malformations at higher concentrations compared to the control group. The results revealed that the toxicity of zebrafish was greatly depended on the size and the concentration of α-Fe2O3 nanoparticles.

Improved differential diagnosis of intracardiac and extracardiac shunts using acoustic intensity mapping of saline contrast studies.

The aim of this study was to test the hypothesis that temporal patterns of saline contrast entry into, and exit from the left heart are significantly different in intra- and extra-cardiac shunts and can be used to differentiate the shunt mechanism when Valsalva manoeuvre cannot be performed, or is of uncertain quality. We propose a novel approach of mapping the temporal changes in acoustic intensity (AI) within the left and right heart to identify and define these unique patterns. We screened cases of right to left shunting on resting agitated saline contrast echocardiograms with clinical criteria that identified the origin of shunting as either a patent foramen ovale or pulmonary arteriovenous malformation. Acoustic time-intensity curves were generated from the right and left heart chambers that reflected the change in saline contrast density over time. Several novel pre-specified parameters were measured from these curves, in addition to the standard heartbeat counting method, to characterize the entrance (wash-in) and exit (wash-out) patterns of saline contrast in the left heart. Statistical analysis showed that AI mapping provided superior differentiation of the two populations than did the traditional beat counting method. Diagnosis of shunt mechanism from saline contrast studies can be improved over current methods through the use of AI mapping to define the rapidity that peak contrast effect develops, the speed that the contrast effect decays, and the contrast intensity late in the recording.

Acute cortisol response to a psychosocial stressor is associated with heartbeat perception

The aim of the present study was to examine the effect of an acute increase in cortisol in response to a psychosocial stressor on heartbeat perception, in a laboratory environment. Thirty-six participants (20 women, 16 men, mean age = 21.7 years, standard deviation = 1.7 years) completed a heartbeat counting task (Schandry paradigm) before and after exposure to an acute psychosocial stressor (Trier Social Stress Test; TSST). Heartbeat counting performance was compared between participants who exhibited strong cortisol responses (>15.5% increase in cortisol from baseline; responders) and those who did not (non-responders). Responders showed increased heartbeat counting accuracy following the TSST, which was not observed in non-responders. The two groups did not differ in their responsivity to subjective anxiety ratings or heart rate. These results indicated that acutely elevated cortisol in response to a psychosocial stressor is associated with increased interoceptive accuracy. The results provide a possible explanation for inconsistent findings on the effect of stress exposure on interoception.

Automated drosophila heartbeat counting based on image segmentation technique on optical coherence tomography

Drosophila and human cardiac genes are very similar. Biological parametric studies on drosophila cardiac have improved our understanding of human cardiovascular disease. Drosophila cardiac consist of five circular chambers: a conical chamber (CC) and four ostia sections (O1–O4). Due to noise and grayscale discontinuity on optical coherence tomography (OCT) images, previous researches used manual counting or M-mode to analyze heartbeats, which are inefficient and time-consuming. An automated drosophila heartbeat counting algorithm based on the chamber segmentation is developed for OCT in this study. This algorithm has two parts: automated chamber segmentation and heartbeat counting. In addition, this study proposes a principal components analysis (PCA)-based supervised learning method for training the chamber contours to make chamber segmentation more accurate. The mean distances between the conical, second and third chambers attained by the proposed algorithm and the corresponding manually delineated boundaries defined by two experts were 1.26 ± 0.25, 1.47 ± 1.25 and 0.84 ± 0.60 (pixels), respectively. The area overlap similarities were 0.83 ± 0.09, 0.75 ± 0.11 and 0.74 ± 0.12 (pixels), respectively. The average calculated heart rates of two-week and six-week drosophila were about 4.77 beats/s and 4.73 beats/s, respectively, which was consistent with the results of manual counting.

Death after Discharge – Every heart beat counts (probably)!

The assumption would be that patients who are discharged from an emergency or acute medicine department have been thoroughly assessed and are good to return to the safety of their own home. An unplanned death after discharge from hospital is the worst-case scenario for patients, families and indeed clinicians. In order to prevent adverse events after patients leave hospital most units have a multi-layered system to capture risk that includes triage, recording of vital signs, basic blood tests, understanding of existing past medical history and assessment by a senior clinician to add experience and intuition. Discharge decisions depend on a balanced review of all these parameters and a discussion with patients about residual risks. Only after this will patients go home. Despite this a small percentage of patients pass away unexpectedly within days after leaving hospital.

Investigations on the in-vivo toxicity analysis of reduced graphene oxide/TiO2 nanocomposite in zebrafish embryo and larvae (Danio rerio)

The growing production and widespread use of nanomaterials are a severe concern to human health. Typically, titanium dioxide (TiO2) incorporated reduced graphene oxide (RGO), and graphene oxide (GO) has grown considerably due to their wide range of applications in nanomedicine. They are used in wound healing, drug delivery, tissue engineering and biosensor. In this work, RGO/TiO2 nanocomposite was synthesized by varying the TiO2 concentration, and the toxicity assessment was done using the zebrafish embryo model. Further, the obtained RGO/TiO2 nanocomposites were characterized through SEM, TEM, XRD, XPS, FTIR, UV and Raman analysis. The RGO/TiO2 nanocomposite is found to be biocompatible. Zebrafish body length, heartbeat count and survival percentage were carefully measured in sets of controlled experiments. Especially, the RGO/TiO2 nanocomposite showed very low toxicity to the zebra fish embryos at lower concentration of 30 μg ml. Also, the toxicity of the nanocomposites increases with increase in the concentration up to 1.0 mg mL−1. RGO/TiO2 nanocomposite at higher concentration generates reactive oxygen species (ROS) and causes teratogenicity and cardiotoxicity. The results showed that the toxicity effect of RGO/TiO2 is concentration dependent. The outcomes of present work contribute to the use of the RGO/TiO2 composites in nanomedicine.

Does it help to feel your body? Evidence is inconclusive that interoceptive accuracy and sensibility help cope with negative experiences

ABSTRACTIn four studies (total N = 534), we examined the moderating impact of Interoceptive Accuracy (i.e. IAcc, as measured with the heartbeat counting task) and Interoceptive Sensibility (IS, assessed via questionnaire) on negative affect, following social exclusion or after receiving negative feedback. Results from an integrative data analysis combining the four studies confirmed that the manipulations were successful at inducing negative affect. However, no significant interaction between mood induction (control versus negative affect induction) and interoception on mood measures was observed, and this was true both for objective (i.e. IAcc) and subjective (i.e. IS) measures of interoception. Hence, previous conclusions on the moderating impact of interoception in the relationship between mood induction and self-reported mood were neither replicated nor generalised to this larger sample. We discuss these findings in light of theories of emotion regulation as well as recent concerns raised about the validity of the heartbeat counting task.

Interoception and respiratory sinus arrhythmia in gambling disorder.

Gambling has longstanding links with excitement and physiological arousal, but prior research has not considered (a) gamblers' ability to detect internal physiological signals, or (b) markers of parasympathetic functioning. The present study measured interoception in individuals with gambling disorder, using self-report measures and a heartbeat counting task administered at rest. Resting state respiratory sinus arrhythmia (RSA), an index of heart rate variability, was measured as a proxy for parasympathetic control and emotional regulation capacity. In a case-control design, 50 individuals with gambling disorder were compared against 35 controls without gambling problems. Participants completed two self-report measures of bodily awareness and a behavioral test of heartbeat counting. A resting state electrocardiogram (5min) was used to calculate RSA. There were no significant differences on the self-report or behavioral interoception probes. The group with gambling disorder displayed significantly reduced RSA, which at face value is consistent with reduced parasympathetic control. However, the group difference in RSA did not survive controlling for age and smoking status, as established predictors of heart rate variability. Our findings do not support any changes in interoceptive processing in people with gambling disorder, at least under resting conditions. Our observation that group differences in RSA are partly explained by smoking behavior highlights the importance of controlling for nicotine use in future research characterizing physiological functioning and emotional regulation in disordered gambling.

Relationship between interoception and emotion regulation: New evidence from mixed methods.

Interoception is the ability to perceive one's inner bodily feelings and is thought to be associated with the capacity of recognising and experiencing emotions. Previous research on interoception and emotion regulation has presented limitations arising from the low reliability of the interoceptive measurement and provided inconsistent results. The current study used a mixed method approach to investigate this relationship from the individuals' perspective. In the first phase (quantitative), questionnaires assessing interoceptive sensibility, the subjective, self-reported ability to perceive internal states, were administered to 100 healthy participants. In the second phase (qualitative), individual semi-structured interviews were conducted with nine participants. The interviews were analysed using the Interpretative Phenomenological Analysis. Three main dimensions were explored with open questions: 1) Perception of internal bodily states; 2) Emotion regulation; 3) Potential relationship between bodily states perception and emotion recognition and regulation. Findings revealed that people with low interoceptive abilities show more difficulties in verbalizing their feelings and in decreasing the impact of emotions generated by negative experiences in daily life LIMITATIONS: The generalization of the results is limited by the specific age and gender of the recruited sample. Responses of the participants supported recent evidence regarding the lack of reliability of the heartbeat counting task as a measure of interoceptive accuracy, however interviews sustained the importance of recognising the bodily states in order to be able to understand and regulate emotions.

Modulating interoception by insula stimulation: A double-blinded tDCS study

Interoception consists in the perception and processing of internal body signals, such as heartbeat. Previous neuroimaging studies revealed that attention to heartbeat activated bilateral insula and premotor regions.In the present double-blind study, we aimed at testing the role of insula in interoception by means of transcranial direct current stimulation (tDCS) interfering with its activity.Sixteen healthy participants responded to a questionnaire to evaluate the tendency to be internally focused and performed a heartbeat counting task before and after tDCS in three sessions (left insula stimulation, right insula stimulation, sham stimulation). Real and reported heartbeat were recorded and used to calculate the accuracy scores.A significant interaction between stimulation condition and time (pre- and post-stimulation) was found due to a significant improvement of the interoceptive accuracy in the sham condition only.Our results demonstrated that stimulation over the insula reduced the possibility to improve the precision with which individuals detect internal signals.

Contingent biofeedback outperforms other methods to enhance the accuracy of cardiac interoception: A comparison of short interventions

Background and objectivesDeviations in interoception might contribute to the development and maintenance of mental disorders. The improvement of interoceptive accuracy (IA) is desirable but assessment and training methods remain controversial. For instance, it was assumed that performance increases in heartbeat counting paradigms after cardiac feedback were due to an improvement of knowledge with regard to heart rate rather than due to an actual improvement in IA. MethodsHere, we examined effects of contingent cardiac feedback training, non-contingent cardiac feedback, mindfulness practice, and a waiting period with external attentional focus on IA. 100 healthy participants underwent a mental tracking paradigm before and after 20 min of training or waiting. ResultsResults revealed a significant increase of IA in the contingent feedback condition (d = 1.21, p ≤ .001) and no significant changes after non-contingent feedback, mindfulness practice or waiting (d ≤ 0.37; p ≥ .06). Furthermore, IA increase was significantly higher after the contingent feedback training compared to all other conditions, including non-contingent feedback. LimitationsFuture studies need to replicate these findings in clinical samples and examine time dependent effects. ConclusionsThe results provide evidence for the trainability of heartbeat perception. IA improvements may reduce the symptom burden in people suffering from mental disorders and psychophysiological conditions that have been linked to lower interoceptive accuracy such as depression, somatic symptom disorder, chronic pain, and functional somatic syndromes. Consequently, exploration of biofeedback training procedures shall be continued with the aim of identifying relevant mediators of beneficial effects and future implementation in clinical practice.

The heartbeat counting task largely involves non-interoceptive processes: Evidence from both the original and an adapted counting task

The heartbeat counting task (HCT) is among the most frequently used measures of interoceptive accuracy (i.e., IAcc). Growing concerns, however, have been raised regarding the validity of this task, as well as the validity of the IAcc scores that are derived from it. In the present study, healthy participants (N = 123) performed both the original task and an adapted version of it that stressed the importance of reporting only their perceptually felt heartbeats. In the original task, we found that participants report relying on three different strategies (i.e., detection of heartbeats in a specific body location, detection of heartbeats in a diffuse way and heart rate estimation) to complete the task. In the adapted task, we found that IAcc scores are drastically reduced (about 50%) when asking participants to avoid relying on non-interoceptive signals and to only report the heartbeats they perceive. These findings confirm that the HCT task is largely contaminated by the influence of non-interoceptive processes. Implications of these findings for research on interoception are discussed.

Interoceptive accuracy scores from the heartbeat counting task are problematic: Evidence from simple bivariate correlations

Interoception, the capacity to perceive internal bodily states, is thought to influence cognitive, affective and interpersonal functioning. It is frequently assessed using the heartbeat counting task, introduced recently in interoceptive research. In this task participants are requested to count their heartbeats without relying on external cues. Interoceptive Accuracy (i.e., IAcc) scores are then computed based on absolute comparisons between actual and reported heartbeats. In a large sample of participants (N = 572), we observed that, whereas IAcc scores are meant to be theoretically agnostic to error type (i.e., over- or underestimation of heartbeats), these scores massively (i.e., > 95%) reflect under-reports. Of concern too, the correlation between actual and reported heartbeats is low overall (r = .16), varies non-linearly across IAcc score quantiles, and suggests undistinguishable interoceptive capacities within the top 60% IAcc scorers. We also found that IAcc scores, which are conceptually independent from actual heart rates, are structurally bound to them. Finally, we show that IAcc scores vary across the time intervals used in the task. We encourage researchers using this score for studying cognitive and emotional processes to reconsider its meaning.

Is alexithymia characterised by impaired interoception? Further evidence, the importance of control variables, and the problems with the Heartbeat Counting Task

Interoception, the perception of one’s internal state, is commonly quantified using the heartbeat counting task (HCT) – which is thought to be a measure of cardiac interoceptive sensitivity (accuracy). Interoceptive sensitivity has been associated with a number of clinical traits and aspects of higher order cognition, including emotion processing and decision-making. It has been proposed that alexithymia (difficulties identifying and describing one’s own emotions) is associated with impaired interoceptive sensitivity, but new research questions this association. Problematically, much evidence attesting to the absence of this association has been conducted using the HCT, a measure affected by various physiological and psychological factors. Here, we present novel data (N = 287) examining the relationship between alexithymia and HCT performance, controlling for a number of potential confounds. Inclusion of these control measures reveals the predicted negative relationship between alexithymia and HCT performance. Results are discussed with regard to difficulties quantifying interoceptive sensitivity using the HCT.

Interoceptive influences on peripersonal space boundary

Integration of body-related signals within the peripersonal space (PPS) contributes to bodily self-awareness. Whereas several studies have shown how individual PPS extension is shaped by external factors, e.g. during interactions with people and objects, no studies have looked at interoceptive influences on PPS extension. We exposed participants to an audio-tactile interaction task, to measure their PPS boundary (Session 1), and to a heartbeat counting task and a time estimation task, to specifically assess their interoceptive accuracy (Session 2). Participants’ traits of private self-consciousness and social anxiety were also evaluated, to account for their possible effect on the relation between interoception and PPS representation. We found that higher interoceptive accuracy specifically predicts narrower PPS boundary. Moreover, this relation is moderated by individual traits of private self-consciousness, but not social anxiety. Extending the concept of interoceptive influences on exteroceptive body representations to PPS, our results, first, support the idea that a dynamic balance between intero-exteroceptive processing might represent a general principle underlying bodily self-awareness; second, they shed light on how interoception may affect also the way we interface with the external world. Finally, showing that, in order for interoceptive accuracy to be effective on the intero-exteroceptive balance, it is important that individuals tend to focus on inner sensations and feelings, our results suggest that a comprehensive intero-exteroceptive model of bodily self-awareness should be (at least) a three-dimensional model that includes individual self-consciousness traits.

Knowledge of resting heart rate mediates the relationship between intelligence and the heartbeat counting task

Evidence suggests that intelligence is positively associated with performance on the heartbeat counting task (HCT). The HCT is often employed as measure of interoception – the ability to perceive the internal state of one’s body – however it’s use remains controversial as performance on the HCT is strongly influenced by knowledge of resting heart rate. This raises the possibility that heart rate knowledge may mediate the previously-observed association between intelligence and HCT performance. Study One demonstrates an association between intelligence and HCT performance (N = 94), and Study Two demonstrates that this relationship is mediated by knowledge of the average resting heart rate (N = 134). These data underscore the need to account for the influence of prior knowledge and beliefs when examining individual differences in cardiac interoceptive accuracy using the HCT.

A latent state-trait analysis of interoceptive accuracy.

Interoceptive accuracy (IAc), that is, the ability to accurately perceive one's own bodily signals, is widely assumed to be a trait, although experimental manipulations such as stress may affect IAc. We used structural equation modeling to estimate the reliability of IAc, and the proportions of individual differences in IAc, explained by a trait and occasion-specific effects of situation and person-situation interactions. We assessed IAc in 59 healthy participants (40 women, MAge = 23.4 years) on three consecutive measurement occasions, approximately 1 week apart, in a rest and poststress condition, using a heartbeat counting and a heartbeat discrimination task. The results showed fair temporal stability (intraclass correlation coefficients ≥ 0.38) and good reliability (Mdn = .63; range .49-.83) for both methods. While around 40% of the variance of a single IAc measurement could be explained by a trait, approximately 27% was accounted for by occasion-specific effects of situation and person-situation interaction. These results suggest that IAc measures are relatively consistent and that situations and person-situation interactions impact IAc as measured at a certain point in time. An aggregation across at least two measurements is recommended when using IAc as a trait variable.