Post‐traumatic stress disorder (PTSD) has been associated with cardiovascular disease (CVD), but the mechanisms remain unclear. Autonomic dysfunction, associated with higher CVD risk, may be ...triggered by acute PTSD symptoms. We hypothesized that a laboratory‐based trauma reminder challenge, which induces acute PTSD symptoms, provokes autonomic dysfunction in a cohort of veteran twins. We investigated PTSD‐associated real‐time physiologic changes with a simulation of traumatic experiences in which the twins listened to audio recordings of a one‐minute neutral script followed by a one‐minute trauma script. We examined two heart rate variability metrics: deceleration capacity (DC) and logarithmic low frequency (log‐LF) power from beat‐to‐beat intervals extracted from ambulatory electrocardiograms. We assessed longitudinal PTSD status with a structured clinical interview and the severity with the PTSD Symptoms Scale. We used linear mixed‐effects models to examine twin dyads and account for cardiovascular and behavioral risk factors. We examined 238 male Veteran twins (age 68 ± 3 years old, 4% black). PTSD status and acute PTSD symptom severity were not associated with DC or log‐LF measured during the neutral session, but were significantly associated with lower DC and log‐LF during the traumatic script listening session. Long‐standing PTSD was associated with a 0.38 (95% confidence interval, −0.83,‐0.08) and 0.79 (−1.30,‐0.29) standardized unit lower DC and log‐LF, respectively, compared to no history of PTSD. Traumatic reminders in patients with PTSD lead to real‐time autonomic dysregulation and suggest a potential causal mechanism for increased CVD risk, based on the well‐known relationships between autonomic dysfunction and CVD mortality.
Our study employed an innovative laboratory trauma recall challenge to examine the acute impact of PTSD symptoms on autonomic physiology in male veteran twins. We found evidence that PTSD leads to real‐time pathological effects on the autonomic nervous system such as vagal withdrawal. Our findings provide direct evidence to a causal mechanism linking PTSD to heart disease by comparing PTSD discordant twin brothers.
Exposure to natural environments, whether real or virtual, has been demonstrated to have restorative effects. However, it is unclear whether these effects depend on the meanings and associations that ...individuals attribute to different environments. This study explored the restorative effects of mental imagery of nature (i.e., pure top-down processing) following cognitive stress induction. Fifty students participated in a within-subject study where they imagined the contents of nature and urban words for 5 min each. Self-rated measures indicated a stronger sense of subjective restoration following nature imagery compared to urban imagery. The heart rate was slower, and heart rate variability was larger during nature imagery than during urban imagery, suggesting a greater degree of relaxation with nature imagery. Both tonic and phasic electrodermal activity was stronger during the mental imagery of nature than urban contents. This difference was driven by a higher preference for nature over urban words, indicating that imagery of nature was associated with stronger positive arousal than urban imagery. Notably, participants’ reported connection to nature moderated some of the physiological responses. In conclusion, top-down processes and individual meanings and associations play a significant role in the positive effects of nature exposure. The results also indirectly support the inclusion of nature imagery as a cost-effective component of therapeutic techniques aimed at promoting relaxation.
•Mental imagery of nature produced subjective restoration from cognitive stress.•Heart rate variability was larger in the nature than urban imagery condition.•Skin conductance was higher in the nature than urban imagery condition.•Preference (liking) explained most of the differences between the conditions.•Imagery of nature is restorative because nature is preferred.
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•I discuss the notion of HRV with practical implications to biomedical informatics.•Sensitivity to sampling rate errors varies as to predictive performance. Combination of several, ...especially nonlinear HRV metrics can remedy sampling rate constraints.•I present methodology for comprehensive validation of the effect of sampling rate on HRV.
Sampling rate impacts the quality of HRV estimates. In the context of the recent research article by Burma et al published in JBI which systematically examined this matter, I discuss this notion more deeply with practical implications to biomedical informatics. Not all HRV metrics are created equal regarding their sensitivity to sampling rate errors when their health predictive performance is concerned. A combination of several, especially nonlinear HRV metrics can remedy these sampling rate constraints. I present methodology for comprehensive validation of the effect of sampling rate on HRV.
Heart rate variability (HRV) indexes are becoming useful in various applications, from better diagnosis and prevention of diseases to predicting stress levels. Typically, HRV indexes are retrieved ...from the heart's electrical activity collected with an electrocardiographic signal (ECG). Heart-induced mechanical signals recorded from the body's surface can be utilized to record the mechanical activity of the heart and, in turn, extract HRV indexes from interbeat intervals (IBIs). Among others, accelerometers and gyroscopes can be used to register IBIs from precordial accelerations and chest wall angular velocities. However, unlike electrical signals, the morphology of mechanical ones is strongly affected by body posture. In this paper, we investigated the feasibility of estimating the most common linear and non-linear HRV indexes from accelerometer and gyroscope data collected with a wearable skin-interfaced Inertial Measurement Unit (IMU) positioned at the xiphoid level. Data were collected from 21 healthy volunteers assuming two common postures (i.e., seated and lying). Results show that using the gyroscope signal in the lying posture allows accurate results in estimating IBIs, thus allowing extracting of linear and non-linear HRV parameters that are not statistically significantly different from those extracted from reference ECG.
Recent clinical trials and real-world studies highlighted those variations in ECG waveforms and HRV recurrently occurred during hypoglycemic and hyperglycemic events in patients with diabetes. ...However, while several studies have been carried out for adult age, there is lack of evidence for paediatric patients. The main aim of the study is to identify the correlations of variations in ECG Morphology waveforms with blood glucose levels in a paediatric population. Methods: T1D paediatric patients who use CGM were enrolled. They wear an additional non-invasive wearable device for recording physiological data and respiratory rate. Glucose metrics, ECG parameters and HRV features were collected, and Wilcoxon rank-sum test and Spearman’s correlation analysis were used to explore if different levels of blood glucose were associated to ECG morphological changes. Results: Results showed that hypoglycaemic events in paediatric patients with T1D are strongly associated with variations in ECG morphology and HRV. Conclusions: Results showed the opportunity of using the ECG as a non-invasive adding instrument to monitor the hypoglycaemic events through the integration of the ECG continuous information with CGM data. This innovative approach represents a promising step forward in diabetes management, offering a more comprehensive and effective means of detecting and responding to critical changes in glucose levels.
This paper suggests a method to assess the extent to which ultra-short Heart Rate Variability (HRV) features (less than 5 min) can be considered as valid surrogates of short HRV features (nominally 5 ...min). Short term HRV analysis has been widely investigated for mental stress assessment, whereas the validity of ultra-short HRV features remains unclear. Therefore, this study proposes a method to explore the extent to which HRV excerpts can be shortened without losing their ability to automatically detect mental stress.
ECGs were acquired from 42 healthy subjects during a university examination and resting condition. 23 features were extracted from HRV excerpts of different lengths (i.e., 30 s, 1 min, 2 min, 3 min, and 5 min). Significant differences between rest and stress phases were investigated using non-parametric statistical tests at different time-scales. Features extracted from each ultra-short length were compared with the standard short HRV features, assumed as the benchmark, via Spearman's rank correlation analysis and Bland-Altman plots during rest and stress phases. Using data-driven machine learning approaches, a model aiming to detect mental stress was trained, validated and tested using short HRV features, and assessed on the ultra-short HRV features.
Six out of 23 ultra-short HRV features (MeanNN, StdNN, MeanHR, StdHR, HF, and SD2) displayed consistency across all of the excerpt lengths (i.e., from 5 to 1 min) and 3 out of those 6 ultra-short HRV features (MeanNN, StdHR, and HF) achieved good performance (accuracy above 88%) when employed in a well-dimensioned automatic classifier.
This study concluded that 6 ultra-short HRV features are valid surrogates of short HRV features for mental stress investigation.
Cardiac parasympathetic activity may be non-invasively investigated using heart rate variability (HRV), although HRV is not widely accepted to reflect sympathetic activity. Instead, cardiac ...sympathetic activity may be investigated using systolic time intervals (STI), such as the pre-ejection period. Although these autonomic indices are typically measured during rest, the "reactivity hypothesis" suggests that investigating responses to a stressor (e.g., exercise) may be a valuable monitoring approach in clinical and high-performance settings. However, when interpreting these indices it is important to consider how the exercise dose itself (i.e., intensity, duration, and modality) may influence the response. Therefore, the purpose of this investigation was to review the literature regarding how the exercise dosage influences these autonomic indices during exercise and acute post-exercise recovery. There are substantial methodological variations throughout the literature regarding HRV responses to exercise, in terms of exercise protocols and HRV analysis techniques. Exercise intensity is the primary factor influencing HRV, with a greater intensity eliciting a lower HRV during exercise up to moderate-high intensity, with minimal change observed as intensity is increased further. Post-exercise, a greater preceding intensity is associated with a slower HRV recovery, although the dose-response remains unclear. A longer exercise duration has been reported to elicit a lower HRV only during low-moderate intensity and when accompanied by cardiovascular drift, while a small number of studies have reported conflicting results regarding whether a longer duration delays HRV recovery. "Modality" has been defined multiple ways, with limited evidence suggesting exercise of a greater muscle mass and/or energy expenditure may delay HRV recovery. STI responses during exercise and recovery have seldom been reported, although limited data suggests that intensity is a key determining factor. Concurrent monitoring of HRV and STI may be a valuable non-invasive approach to investigate autonomic stress reactivity; however, this integrative approach has not yet been applied with regards to exercise stressors.
Autonomic nervous system (ANS) dysfunction is frequently seen in people living with multiple sclerosis (MS). Heart rate variability (HRV) is an easy and objective index for evaluating ANS ...functioning, and it has been previously used to explore the association between ANS and the experience of symptom burden in other chronic diseases. Given ANS functioning can be influenced by physical and psychological factors, this study investigated whether emotional distress and/or the presence of ANS dysfunction is associated with symptom severity in people living with MS.
Participants with MS and healthy controls (HC) with no history of cardiac conditions were recruited to self-collect HR data sampled from a chest strap HR monitor (PolarH10). Short-term HR signal was collected for five minutes, and time and frequency HRV analyses were performed and compared between groups. HRV values were then compared to self-reported distress (Kessler Psychological Distress Scale) and MS participants’ self-reported measures of symptom burden (SymptoMScreen).
A total of n = 23 adults with MS (51 ± 12 years, 65 % female, median Patient Determined Disease Steps PDDS: 3.0) and n = 23 HCs (43 ± 18 years, 40 % female) completed the study procedures. All participants were able to complete the chest strap placement and HR data capture independently. Participants with MS, compared to the HC participants, had a significantly lower parasympathetic activation as shown by lower values of the root mean square of successive differences between normal heartbeats (RMSSD: 21.86 ± 9.84 vs. 43.13 ± 20.98 ms, p = 0.002) and of high-frequency (HF) power band (HF-HRV: 32.69 ± 12.01 vs. 42.39 ± 7.96 nu, p = 0.016), indicating an overall lower HRV in the MS group. Among individuals with MS, HF-HRV was significantly correlated with the severity of self-reported MS symptoms (r = -0.548, p = 0.010). Participants with MS also reported higher levels of distress compared to HC participants (18.32 ± 6.05 vs. 15.00 ± 4.61, p = 0.050), and HRV correlated with the severity of distress in MS participants (r = -0.569, p = 0.007). A significant mediation effect was also observed, with emotional distress fully mediating the association between HRV and symptom burden.
These findings suggest the potential for ANS dysfunction, as measured by HRV (i.e., lower value of HF power), to be utilized as an objective marker of symptom burden in people living with MS. Moreover, it is apparent that the relationship between HRV and symptom burden is mediated by emotional distress.
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