Driving can be a stressful task, especially under congestion conditions. Several studies have shown a positive correlation between stress and aggressive behaviour behind the wheel, leading to accidents. One common way to minimize stress while driving is to avoid highly congested roads. However, not all drivers show the same response towards high traffic situations or other road conditions. For instance, some drivers may prefer congested routes to longer ones to minimize travel time. Increasingly, drivers are employing Advanced Traveller Information Systems while commuting to both familiar and unfamiliar destinations, not just to obtain information on how to reach a certain endpoint, but to acquire real-time data on the state of the roads and avoid undesired traffic conditions. In this thesis, we propose an Advanced Traveller Information System that personalizes the driver’s route using their road preferences and measures their physiological signals during the trip to assess mental stress. The system then links road attributes, such as number of lanes, speed limit, and traffic severity, with the driver’s stress levels. Then, it uses machine learning to predict their stress levels on similar roads. Hence, routes that contribute to high-levels of stress can therefore be avoided in future trips. The average accuracy of the proposed stress level prediction model is 76.11%.

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Emotion regulation is processes by which individuals influence which emotions they have, when they have them, and how they experience and express those emotions. In the field of developmental psychology, there is a large literature on affect regulation focused almost exclusively on infants and young children with a focus on temperamental differences in reactivity, both affective and physiological, and accompanying regulatory strategies. The purpose of the current study was to examine the role of two dimensions of temperament, negative affect (NA) and effortful control (EC), and how these dimensions relate to physiology, self-report of emotion, and behavior during resting and stressor tasks (Stroop, video game, hand cold pressor, and delayed gratification), the latter in which emotion suppression instructions were given. Using the Adult Temperament Questionnaire (ATQ) to screen 656 subjects, 24 males and 53 females were recruited to take part in the second phase of the study, creating four groups with their screening ATQ scores: high NA/high EC, low NA/low EC, high NA/low EC, low NA/high EC. Physiological measures derived from electrocardiogram (ECG) and impedance cardiography were recorded during each task and behaviors were coded using the Emotion Expressive Behavior Coding System. EC Group and NA Group were not significant for the majority of the physiological, self-report, and behavioral variables. However, the EC subscale inhibitory control was predictive of lower resting HRV for females only, and the Extraversion/Surgency subscale Sociability was a significant predictor of cardiac sympathetic activity during the tasks, with low sociability subjects showing a stronger sympathetic response. Neither self-report of emotion nor behavioral variables show a clear group difference in response to the tasks. Future studies will examine the use of other types of regulatory tasks, such as social interactions, as well as the need for a balance between emotion expressivity and emotion regulation. / Ph. D.

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Anxiety and its cognitive component of worry have been related to exaggerated cardiovascular reactivity and delayed recovery to laboratory stressors, and to increased risk of cardiovascular disease. Previous research on the anxiety-cardiovascular system relationship, including data from Knepp and Friedman (2008), are included to support this project. Two experiments were completed during the course of this study. The first consisted of two peripheral-based body positioning tasks. The second experiment used an active versus passive sympathetic stress task paradigm (mental arithmetic, hand cold pressor). Subjects were nonsmokers free of cardiovascular and neurological disease. Trait worry was examined through the Penn State Worry Questionnaire (PSWQ). Blood pressure recordings and cardiac recordings through ECG and ICG were done in each experiment during seven epochs: an anticipatory baseline with three baselines preceding and three recovery periods following each task. Repeated measures analysis was run on all cardiovascular measures. In the first experiment, high worriers had worsened blood pressure reactivity to task. The second experiment found that high worriers had increased stroke volume across all epochs. There were mixed findings in the studies relating to subjects acclimated to the laboratory experience. Future directions of research relating anxiety, worry, and cardiovascular risk factors are discussed. / Ph. D.

Although the negative consequences of traumatic exposure across various domains of functioning have been well-documented, gaps and discrepancies continue to exist in the understanding of the impact of complex trauma, such as interpersonal violence (IPV), and how outcomes may vary across diverse populations and identities. In this cross-sectional study investigating the impact of traumatic exposure on physiological domains of functioning, a sample of female-identifying college students completed a number of self-reported measures (assessing past and present trauma exposure, complex posttraumatic stress disorder [CPTSD] symptoms, racial-ethnic minority status, and age of onset of first traumatic exposure) and provided resting high-frequency heart rate variability (hfHRV) data, which served as a biomarker for the potential impact of trauma exposure on physiological domains. Correlational and multiple regression analyses were conducted to determine the strength of relationships between variables and the predictive value of the models. Results indicated endorsement of IPV trauma was significantly associated with earlier age of onset, more severe levels of CPTSD symptoms, and higher hfHRV, but not racial-ethnic minority status. Racial-ethnic minority status was significantly related to more severe CPTSD symptoms. Type of trauma exposure was the only variable that emerged as having predictive value for changes in hfHRV. These findings suggest that experiencing IPV may have unique implications for trauma symptomatology and functioning above and beyond other forms of traumatic exposure, but that continued research must be conducted in order to draw more robust conclusions about the effects of exposure on physiological regulation across various racial-ethnic identities. / M.S. / Research has highlighted the consequences that extremely negative, stressful experiences, also called traumatic events, can have on the way humans think, emote, behave, and physically react. It can be more difficult to draw conclusions about the effects of interpersonal violence (IPV), or violence that occurs at the hands of another (i.e., family, partner, or community violence), due to the complex, severe, and long-term nature of symptoms that survivors experience. There is also limited research about what complex trauma looks like across diverse populations. This study aimed to investigate the impact of traumatic exposure on physiology, which falls under biology and broadly includes the functions of living things. A sample of female-identifying college students completed a number of self-reported measures (assessing trauma exposure, complex posttraumatic stress disorder [CPTSD] symptoms, racial-ethnic minority status, and age of onset of first traumatic exposure) and provided resting high-frequency heart rate variability (hfHRV) data, which measures variation in time between beats and served as a measure for the potential impact of trauma exposure on physiology. Results suggested that IPV exposure was associated with earlier age of first traumatic experience, more severe levels of CPTSD symptoms, and higher hfHRV. Racial-minority status was significantly related to more severe CPTSD symptoms. Type of trauma exposure significantly predicted changes in hfHRV. Findings suggest that experiencing IPV may uniquely influence trauma symptoms and functioning above and beyond other forms of traumatic exposure. Continued research will allow for stronger conclusions about the effects of traumatic exposure on physiology across various racial-ethnic identities.

Heart rate variability (HRV) has been used to evaluate cardiac autonomic function by measuring variations in electrocardiographic R-R intervals between cardiac cycles. HRV was first used to associate decreases in autonomic nervous system (ANS) control with an increased risk of mortality in coronary heart disease and in the diagnosis of diabetes (1). Current clinical research interest has extended to investigate uses of HRV to evaluate changes in the cardiovascular system due to disease, aging, physical activity, and cardiac rehabilitation treatment (2, 5). HRV scores are derivatives of R-R intervals and these may be represented as a function of either time or frequency domain parameters. Time domain analysis is the simplest and includes: the standard deviation of R-R intervals and the number of adjacent RR intervals that differ by >50ms (dRR50). Frequency domain measures involve more elaborate calculation and have been applied in studies to evaluate sympathetic and parasympathetic autonomic balance. The latter include: Low Frequency Power (LF), High Frequency Power (HF), and LF/HF ratio. HRV has been measured in a variety of ways, the most common being a continuous 24-hour collection of R-R data. In recent years, several investigators have sought to assess HRV by utilizing brief collection periods. Controversy exists about the potential of these short-term sampling intervals to yield reproducible and meaningful measurements of HRV. Many confounders such as respiration, stress, and body positioning can influence HRV, which is why a longer collection period has been accepted as the standard for providing a stable index of ANS function. However, short sampling periods would be useful to evaluate HRV when faced with time constraints. The purpose of the current study was to evaluate the reproducibility of HRV using 8-hour daytime measures with the Polar R-R RecorderTM (Polar Electro Oy, Kempele, Finland) and with short sampling duration of 512 cardiac cycles, using the Schiller AT-10TM device (Schiller AG, Baar, Switzerland). Methods: 10 apparently healthy adult volunteers participated in the study, which was conducted at the Sleep Disorders Clinic in Christiansburg, VA. Each subject performed two HRV trials with the Cardiovit AT-10TM device using recordings of 512 cardiac cycles. Within one or two days following the Schiller, the same subjects wore a Polar R-R RecorderTM device to obtain an 8-hour recording of HRV during waking hours; 24-hour urine samples were collected on the same day. Urine was analyzed for catecholamine levels, including norepinephrine and epinephrine in order to evaluate sympathetic nervous system globally. Each subject recorded their personal impressions of unavoidable physical activity and daytime stress demands on the day of the 8-hour recording and urine collection. This entire protocol was repeated one week later. On one of the days of the short sampling recording, VO2pk also was evaluated for each subject using a ramp protocol on the cycle ergometer and a metabolic cart. Results: The correlation analysis for the HRV response variables using the Schiller method indicated a high-to-very high correlation between trials within a day for the time domain measures (r = 0.75-0.99). The frequency domain measures, however, were low-to-moderately correlated (r = 0.24-0.66) between trials within a day for the Schiller method. Correlations between days for HRV response variables using the Schiller method were similarly low for both time (r < 0.5) and (r < 0.4) frequency domain measures. Correlation coefficients between days for the HRV response variables using the Polar method were moderate (r = 0.59-0.67) for the time domain and only low-moderate for the frequency domain measures (r = 0.37-0.69). However, an important finding was that Polar R-R data for two of the subjects contained excessive signal artifact, which affected the fidelity of the HRV scores. When these two cases were excluded from the group analyses, the resulting correlations were high-very high for all time and frequency domain measures (r = 0.70-0.93). The means for each response HRV time and frequency domain variable between the Polar method and Schiller method were significantly different (P < 0.05). Additional correlational analyses did not reveal any systematic associations between HRV measures and simple markers of sympathetic activity (urinary NE or E) and aerobic fitness (VO2pk) in this small sample of subjects. Conclusions: Due to this important change in reproducibility with the Polar method, the consequence of artifact-free recordings is unmistakable. Within the limitations of this small study sample it is concluded that, while HRV in apparently healthy adults may not be measured reliably with brief data collection periods, longer daytime sampling periods of 8 hours (e.g. Polar device) yields acceptable reliability for both time and frequency domain parameters of HRV. / Master of Science

The purpose of this study was to assess heart rate variability (HRV) in patients with coronary artery disease (CAD): reproducibility, circadian variability and the effects of stress (coronary angiogram). Sixty-one patients who had a coronary angiogram underwent 48-hour Holter monitoring during a period of high stress beginning 4-hours post-angiography (Day 1 and 2), and again two weeks later during a period of low stress (Day 3 and 4); both 24-hour time domain and power spectral measures were computed. To determine reproducibility, intraclass correlation coefficients were calculated for both time and frequency domain indices on Days 3 and 4. The intraclass correlation coefficient for the standard deviation of normal RR-intervals over 24-hours (SDNN) was 0.91, while the standard deviation of the mean of all 5-minute segments of normal RR-intervals for 24-hours (SDANN) was 0.85. The most reproducible time domain measure was pNN50 (defined as the percentage of differences between adjacent normal RR-intervals that are greater than 50 ms computed over 24-hours) with an intraclass correlation coefficient of 0.95. As for the frequency domain measures including low frequency (LF) area, high frequency (HF) area, low frequency to high frequency area ratio (LF:HF area), LF central frequency (cf), and total area (TA), intraclass correlations were found to be the best at 0300-hours and the worst at 1500-hours. Circadian pattern was determined on Day 4 of Holter monitoring. A main effect for time was found for heart rate (HR), LF area, HF area, and TA of the power spectra. Over a 24-hour period, HR, LF area, HF area and TA were the lowest at 0300-hours compared to all other times. There was also a main effect for myocardial infarction (MI) for the frequency domain indices LF area, HF area, LF:HF area ratio, and LFcf. Low frequency area and LF:HF area ratio were significantly elevated (both p<0.05), while both HF area (p<0.05) and LFcf (p<0.01) were reduced in patients with a prior Ml compared to those with no MI. As well, a significant interaction between time of day and Ml, and time of day and beta-blocker therapy was observed. Patients with coronary artery disease and a prior Ml demonstrated a reduced circadian pattern over 24-hours for HR. Likewise, the circadian pattern of HR for those on beta-blockers was also attenuated. The effects of stress was determined by comparing Day 1 to Day 4 of ambulatory Holter monitoring. The time domain measure SDNN was found to be significantly reduced during Day 1 (mean ± SEM; 111.67 ± 6.13 ms) compared to Day 4 (121.54 ± 6.94 ms; p<0.05). Patients with normal left ventricular function (LVF) showed a significant increase from Day 1 to 4 for both SDNN (p<0.01) and SDANN (p<0.05). In contrast, those with LV dysfunction had an attenuated response. Similarly, those CAD patients on beta-blockers demonstrated a significant increase for the time domain measure SDNN (p<0.05), unlike those not on beta-blockers. In the frequency domain, LF:HF area was significantly greater on Day 1 (1.74 ± 0.09) compared to Day 4 (1.64 ± 0.09; p<0.05). These findings suggest that HRV measures are reproducible, that a circadian pattern for HRV exists in patients with CAD, and that stress induced by an invasive procedure such as a coronary angiogram enhances sympathetic input to the SA node in the heart and thereby alters the sympathovagal balance, which is restored two weeks later. / Thesis / Master of Science (MSc)

Through a series of original research articles, this thesis explores the characteristics of autonomic cardiac regulation and respiratory function during sleep in association with depression and antidepressant medication use and validates a novel diagnostic biomarker of depression. Cardiorespiratory dysfunction during sleep may contribute to the increased risk of developing cardiovascular disease amongst individuals with depression. Sleep represents a unique physiological state shielded from many external confounding factors and may be a more relevant window to observe the effects of depression on cardiorespiratory function. In a first study, we found that depression was associated with abnormal autonomic modulation of cardiac activity during sleep. Specifically, depression was associated with reduced heart rate variability compared to healthy controls, and this difference was most prominent during sleep as compared to wake, which may indicate impairments in the parasympathetic modulation of the cardiac sinoatrial node. Secondly, we validated a machine-learning algorithm that uses patterns of heart rate during sleep to identify depression. This algorithm was found to have 79.9% classification accuracy, based on the differences in autonomic modulation associated with distinct mental states. The algorithm was highly generalizable across different depression subgroups and thus may be useful as an adjunct diagnostic tool. Finally, we found that the use of antidepressants, particularly serotonergic agents, was associated with worse sleep-related respiratory disturbances compared to non-medicated individuals with depression and those using non-serotonergic antidepressants. We proposed that depression-related alterations in serotonin receptor expression and binding may shape the response of the respiratory system to the use of serotonergic agents. Considering the high comorbidity between depression and sleep-related breathing disturbances and their impact on cardiovascular health, this has great clinical implications for the management of depression. Taken together, these results show that depression is associated with several sleep-related abnormalities in terms of cardiorespiratory function, which may represent a valid biomarker of depression.