Attention Deficit/Hyperactivity Disorder (ADHD) Is Associated With Altered Heart Rate Asymmetry

Heartfelt Minds: Uncovering the Intricate yet Overlooked Connection Between Psychiatric Disorders and Cardiology

In recent years, there has been a notable and concerning rise in the prevalence of mental disorders, indicating a growing societal challenge that warrants attention and support for affected individuals. Psychiatric problems range on a wide spectrum from as little as work or school related stress to as big as severe depression related to the loss of a loved one, a sense of loneliness, etc. This current generation yields the highest amounts of mental disorder patients due to the newfound pressures, difficulties, and ways of life. According to the Center for Disease Control and Prevention, more than 1 in 5 US adults live with a mental illness and about 1 in 25 US adults live or lived with a serious mental illness such as schizophrenia, bipolar disorder, or major depression. A similar statistic shows us that about 695,000 people in the United States in 2021 died due to some form of heart related disease. That is 1 in every 5 deaths. More recently, it has been noticed that these psychiatric disorders and heart diseases could be correlated. In this manuscript, we review the current literature on the effect and correlation of psychiatric disorders on the cardiovascular system. We present a review on primarily the "5 major psychiatric disorders," according to the NIH: depression, autism, attention-deficit/hyperactivity disorder, bipolar disorder, and schizophrenia. We will also present a review on stress-induced cardiac diseases, especially more recently with the rise of the COVID-19 Pandemic.

An assessment of heart rate and blood pressure asymmetry in the diagnosis of vasovagal syncope in females

Introduction: Heart Rate Asymmetry (HRA) describes a phenomenon of differences between accelerations and decelerations in human heart rate. Methods used for HRA assessment can be further implemented in the evaluation of asymmetry in blood pressure variations (Blood Pressure Asymmetry-BPA). Methods: We have analyzed retrospectively the series of heartbeat intervals extracted from ECG and beat-to-beat blood pressure signals from 16 vasovagal patients (age: 32.1 ± 13.3; BMI: 21.6 ± 3.8; all female) and 19 healthy subjects (age: 34.6 ± 7.6; BMI: 22.1 ± 3.4; all female) who have undergone tilt test (70°). Asymmetry was evaluated with Poincaré plot-based methods for 5 min recordings from supine and tilt stages of the test. The analyzed biosignals were heart rate (RR), diastolic (dBP) and systolic Blood Pressure (sBP) and Pulse Pressure (PP). In the paper we explored the differences between healthy and vasovagal women. Results: The changes of HRA indicators between supine and tilt were observed only in the control group (Porta Index p = 0.026 and Guzik Index p = 0.005). No significant differences in beat-to-beat variability (i.e. spread of points across the line of identity in Poincaré plot-SD1) of dBP was noted between supine and tilt in the vasovagal group (p = 0.433 in comparison to p = 0.014 in healthy females). Moreover, in vasovagal patients the PP was significantly different (supine: 41.47; tilt: 39.27 mmHg) comparing to healthy subjects (supine: 35.87; tilt: 33.50 mmHg) in supine (p = 0.019) and in tilt (p = 0.014). Discussion: Analysis of HRA and BPA represents a promising method for the evaluation of cardiovascular response to orthostatic stressors, however currently it is difficult to determine a subject's underlying health condition based only on these parameters.

Analysis of Short-Term Heart Rate Asymmetry in High-Performance Athletes and Non-Athletes

Heart rate asymmetry (HRA) refers to how asymmetrically the acceleration and deceleration patterns in heartbeat fluctuations are distributed. There is limited evidence regarding HRA changes in athletes and their association with autonomic regulation. This study aimed to compare the short-term HRA of high-performance athletes and non-athletes during an autonomic function test by calculating relevant HRA measures. This exploratory study obtained beat-to-beat RR interval time series from 15 high-performance athletes and 12 non-athletes during a standardized autonomic function test. This test includes rest, postural change, controlled respiration, prolonged orthostatism, exercise, and recovery phases. The following HRA parameters were computed from the RR time series for both groups: asymmetric spread index (ASI), slope index (SI), Porta’s index (PI), Guzik’s index (GI), and Ehlers’ index (EI). We found significant differences (p < 0.01) in the mean value of several HRA parameters between athletes and non-athletes and across the autonomic function test phases, mainly in postural change and recovery phases. Our results indicate that high-performance athletes manifest a higher number and magnitude of cardiac decelerations than non-athletes after an orthostatic challenge, as indicated by GI and EI. In addition, lower HRA was found in athletes in the recovery phase than in non-athletes, as indicated by ASI.

Time-Reversibility, Causality and Compression-Complexity

Detection of the temporal reversibility of a given process is an interesting time series analysis scheme that enables the useful characterisation of processes and offers an insight into the underlying processes generating the time series. Reversibility detection measures have been widely employed in the study of ecological, epidemiological and physiological time series. Further, the time reversal of given data provides a promising tool for analysis of causality measures as well as studying the causal properties of processes. In this work, the recently proposed Compression-Complexity Causality (CCC) measure (by the authors) is shown to be free of the assumption that the "cause precedes the effect", making it a promising tool for causal analysis of reversible processes. CCC is a data-driven interventional measure of causality (second rung on the Ladder of Causation) that is based on Effort-to-Compress (ETC), a well-established robust method to characterize the complexity of time series for analysis and classification. For the detection of the temporal reversibility of processes, we propose a novel measure called the Compressive Potential based Asymmetry Measure. This asymmetry measure compares the probability of the occurrence of patterns at different scales between the forward-time and time-reversed process using ETC. We test the performance of the measure on a number of simulated processes and demonstrate its effectiveness in determining the asymmetry of real-world time series of sunspot numbers, digits of the transcedental number π and heart interbeat interval variability.

Lack of association between heart period variability asymmetry and respiratory sinus arrhythmia in healthy and chronic heart failure individuals

Temporal asymmetry is a peculiar aspect of heart period (HP) variability (HPV). HPV asymmetry (HPVA) is reduced with aging and pathology, but its origin is not fully elucidated. Given the impact of respiration on HPV resulting in the respiratory sinus arrhythmia (RSA) and the asymmetric shape of the respiratory pattern, a possible link between HPVA and RSA might be expected. In this study we tested the hypothesis that HPVA is significantly associated with RSA and asymmetry of the respiratory rhythm. We studied 42 middle-aged healthy (H) subjects, and 56 chronic heart failure (CHF) patients of whom 26 assigned to the New York Heart Association (NYHA) class II (CHF-II) and 30 to NYHA class III (CHF-III). Electrocardiogram and lung volume were monitored for 8 minutes during spontaneous breathing (SB) and controlled breathing (CB) at 15 breaths/minute. The ratio of inspiratory (INSP) to expiratory (EXP) phases, namely the I/E ratio, and RSA were calculated. HPVA was estimated as the percentage of negative HP variations, traditionally measured via the Porta’s index (PI). Departures of PI from 50% indicated HPVA and its significance was tested via surrogate data. We found that RSA increased during CB and I/E ratio was smaller than 1 in all groups and experimental conditions. In H subjects the PI was about 50% during SB and it increased significantly during CB. In both CHF-II and CHF-III groups the PI was about 50% during SB and remained unmodified during CB. The PI was uncorrelated with RSA and I/E ratio regardless of the experimental condition and group. Pooling together data of different experimental conditions did not affect conclusions. Therefore, we conclude that the HPVA cannot be explained by RSA and/or I/E ratio, thus representing a peculiar feature of the cardiac control that can be aroused in middle-aged H individuals via CB.

Central autonomic regulation assessed by pupillary light reflex is impaired in children with attention deficit hyperactivity disorder

It is assumed that the Attention Deficit Hyperactivity Disorder is associated with the central autonomic dysregulation, however, the studies are rare. Analysis of pupillary light reflex represents a non-invasive tool to provide information related to the central autonomic regulation; thus, we aimed to evaluate potential disturbances in the central autonomic integrity using pupillary light reflex examination in Attention Deficit Hyperactivity Disorder. We have examined 20 children with Attention Deficit Hyperactivity Disorder (10 boys, 13.0+/-2.3 years) and 20 age/gender-matched healthy subjects. Pupillary light reflex was examined at rest for both eyes using Pupillometer PLR-2000 (NeurOptics, USA). Evaluated parameters were: diameter of the pupil before the application of light stimulus and after illumination at the peak of the constriction, the percentual change of the pupil diameter during constriction, average constriction velocity, maximum constriction velocity and average dilation velocity. We found significantly lower percentual change of the pupil diameter during constriction for both eyes in Attention Deficit Hyperactivity Disorder group compared to controls (right eye: -25.81+/-1.23 % vs. -30.32+/-1.31 %, p<0.05, left eye: -25.44+/-1.65 % vs. -30.35+/-0.98 %, p<0.05). The average constriction velocity and maximum constriction velocity were significantly shortened in left eye in Attention Deficit Hyperactivity Disorder group compared to controls (p<0.05). Our findings revealed altered pupillary light reflex indicating abnormal centrally-mediated autonomic regulation characterized by parasympathetic underactivity associated with relative sympathetic predominance in children suffering from Attention Deficit Hyperactivity Disorder.

Cardiac baroreflex hysteresis is one of the determinants of the heart period variability asymmetry

In heart period (HP) variability (HPV) recordings the percentage of negative HP variations tends to be greater than that of positive ones and this pattern is referred to as HPV asymmetry (HPVA). HPVA has been studied in several experimental conditions in healthy and pathological populations, but its origin is unclear. The baroreflex (BR) exhibits an asymmetric behavior as well given that it reacts more importantly to positive than negative arterial pressure (AP) variations. We tested the hypothesis that the BR asymmetry (BRA) is a HPVA determinant over spontaneous fluctuations of HP and systolic AP (SAP). We studied 100 healthy subjects (age from 21 to 70 yr, 54 men) comprising 20 subjects in each age decade. Electrocardiogram and noninvasive AP were recorded for 15 min at rest in supine position (REST) and during active standing (STAND). The HPVA was evaluated via Porta's index and Guzik's index, while the BRA was assessed as the difference, and normalized difference, between BR sensitivities computed over positive and negative SAP variations via the sequence method applied to HP and SAP variability. HPVA significantly increased during STAND and decreased progressively with age. BRA was not significantly detected both at REST and during STAND. However, we found a significant positive association between BRA and HPVA markers during STAND persisting even within the age groups. This study supports the use of HPVA indexes as descriptors of BRA and identified a challenge soliciting the BR response like STAND to maximize the association between HPVA and BRA markers.

Pupillary Light Reflex in Children with ADHD

Attention deficit/hyperactivity disorder (ADHD) is one of the most frequently seen mental disorders in children with an increasing risk for other mental disorders. ADHD represents a primary biological dysfunction of the central nervous system, such as dysregulation of frontal-subcortical-cerebellar catecholaminergic circuits and imbalances in the dopaminergic system. However, autonomic nervous system, comprised of two primary branches - sympathetic and parasympathetic nervous systems that are normally in dynamic balance, plays an essential role in the regulation of body functions. Although it is generally assumed that the autonomic regulation is impaired during ADHD the information related to this dysregulation is limited. One of the options to observe changes of autonomic balance in ADHD is pupillary light reflex (PLR). Pupillometric evaluation can be used for the assessment of functioning of both autonomic nervous system branches and certain parameters of pupil responsivity can be helpful as a tool for medical diagnostic and treatment. In conclusion, these findings suggest the pupillometry as a non-invasive method that can indicate abnormalities in the complex central autonomic network regulating PLR.

The complexity of electrodermal activity is altered in mental cognitive stressors

The aim of this study was to evaluate potential changes in the electrodermal activity (EDA) to enable the detection of variations in the sympathetic nervous system during mental load and recovery period. Several EDA parameters were used: SCA (skin conductance amplitude), frequency of NS-EDR (nonspecific electrodermal responses), SIE (symbolic information entropy), and ApEn (approximate entropy). The cohort consisted of 50 healthy students (average age: 23.33±0.24yr., 25 women). The stress profile consisted of five phases: baseline (P1), Stroop test (P2), recovery (P3), mental arithmetic test (P4), and recovery (P5). All phases of the stress profile lasted six minutes. The results indicate that the three EDA indices have sufficient sensitivity to detect changes in the sympathetic nervous system. The SCA, SIE and ApEn were significantly increased during mental loads and decreased during recovery periods. However, SCA remained significantly elevated during recovery periods versus baseline, and SIE and ApEn decreased significantly during recovery versus baseline. The frequency of NS-EDR had no significant changes during stress. The EDA is a sensitive marker for evaluation of changes during the activation of sympathetic nervous system under the influence of a load. Detailed knowledge of EDA regulatory mechanisms associated with stress could provide important information associated with autonomic dysregulation.

Symbolic dynamics of heart rate variability — a promising tool to investigate cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD)?

We aimed to evaluate complex cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD) by using heart rate variability (HRV) nonlinear analysis — symbolic dynamics. We examined 29 boys with untreated ADHD and 25 healthy boys (age 8–13 years). ADHD symptoms were evaluated by ADHD-RS-IV scale. ECG was recorded in 3 positions: baseline supine position, orthostasis, and clinostasis. Symbolic dynamics indices were used for the assessment of complex cardiac sympathovagal regulation: normalised complexity index (NCI), normalised unpredictability index (NUPI), and pattern classification measures (0V%, 1V%, 2LV%, 2UV%). The results showed that HRV complexity was significantly reduced at rest (NUPI) and during standing position (NCI, NUPI) in ADHD group compared to controls. Cardiac-linked sympathetic index 0V% was significantly higher during all posture positions and cardiovagal index 2LV% was significantly lower to standing in boys suffering from ADHD. Importantly, ADHD symptom inattention positively correlated with 0V%, and negatively correlated with NCI, NUPI. Concluding, symbolic dynamics revealed impaired complex neurocardiac control characterised by potential cardiac beta-adrenergic overactivity and vagal deficiency at rest and to posture changes in boys suffering from ADHD that is correlated with inattention. We suggest that symbolic dynamics indices could represent promising cardiac biomarkers in ADHD.