Consistency of heart rate and sympathovagal reactivity across different autonomic contexts

Effects of Workstation Type on Mental Stress: FNIRS Study

OBJECTIVE

The purpose of this study is to examine the effect of the workstation type on the severity of mental stress by means of measuring prefrontal cortex (PFC) activation using functional near-infrared spectroscopy.

BACKGROUND

Workstation type is known to influence worker's health and performance. Despite the practical implications of ergonomic workstations, limited information is available regarding their impact on brain activity and executive functions.

METHOD

Ten healthy participants performed a Montreal imaging stress task (MIST) in ergonomic and nonergonomic workstations to investigate their effects on the severity of the induced mental stress.

RESULTS

Cortical hemodynamic changes in the PFC were observed during the MIST in both the ergonomic and nonergonomic workstations. However, the ergonomic workstation exhibited improved MIST performance, which was positively correlated with the cortical activation on the right ventrolateral and the left dorsolateral PFC, as well as a marked decrease in salivary alpha-amylase activity compared with that of the nonergonomic workstation. Further analysis using the NASA Task Load Index revealed a higher weighted workload score in the nonergonomic workstation than that in the ergonomic workstation.

CONCLUSION

The findings suggest that ergonomic workstations could significantly improve cognitive functioning and human capabilities at work compared to a nonergonomic workstation.

APPLICATION

Such a study could provide critical information on workstation design and development of mental stress that can be overlooked during traditional workstation design and mental stress assessments.

Maladaptive Cardiac Autonomic Control during a Stress Reactivity Assessment Among Primary Care Patients with Metabolic Syndrome

Metabolic syndrome (MetS) comprises a constellation of metabolic abnormalities that substantially increase risk for chronic illnesses. Autonomic dysregulation is closely linked to MetS, and while pathophysiological models often address chronic stress exposure, none have examined how such physiological contributions operate situationally, in a clinical setting. We used ambulatory impedance cardiography to examine indicators of cardiac autonomic control (CAC) in a sample of 50 adult primary care patients with and without MetS. Indices of independent sympathetic and parasympathetic cardiovascular control in primary care outpatients were measured during a brief stress reactivity assessment. We compared interdependent CAC features, including cardiac autonomic balance (i.e., sympathovagal reciprocity) and cardiac autonomic regulation (i.e., sympathovagal coactivation) and found significant differences among MetS participants as compared to healthy controls. In particular, cardiac autonomic regulation scores were higher among MetS patients when discussing medication concerns, and cardiac autonomic balance scores were lower among MetS patients when discussing daily stressors. These results suggest that patients meeting criteria for MetS demonstrate momentary variations in CAC depending on personally relevant health topics. The potential for future research is discussed with a focus on prospective data collection to enhance diagnostic procedures and treatment monitoring.

Respiratory Changes in Response to Cognitive Load: A Systematic Review

When people focus attention or carry out a demanding task, their breathing changes. But which parameters of respiration vary exactly and can respiration reliably be used as an index of cognitive load? These questions are addressed in the present systematic review of empirical studies investigating respiratory behavior in response to cognitive load. Most reviewed studies were restricted to time and volume parameters while less established, yet meaningful parameters such as respiratory variability have rarely been investigated. The available results show that respiratory behavior generally reflects cognitive processing and that distinct parameters differ in sensitivity: While mentally demanding episodes are clearly marked by faster breathing and higher minute ventilation, respiratory amplitude appears to remain rather stable. The present findings further indicate that total variability in respiratory rate is not systematically affected by cognitive load whereas the correlated fraction decreases. In addition, we found that cognitive load may lead to overbreathing as indicated by decreased end-tidal CO₂ but is also accompanied by elevated oxygen consumption and CO₂ release. However, additional research is needed to validate the findings on respiratory variability and gas exchange measures. We conclude by outlining recommendations for future research to increase the current understanding of respiration under cognitive load.

Physiological regulation in infants of women with a mood disorder: examining associations with maternal symptoms and stress

BACKGROUND

The offspring of mothers with mood disorders may evidence increased behavioral problems as early as preschool; however, no study to date has examined psychophysiological characteristics during infancy, particularly among offspring of mothers diagnosed with bipolar disorder. Elucidating psychobiological mechanisms of risk early in development is critical to inform prevention and early intervention efforts.

METHOD

This study compared physiological and behavioral responsivity in 6-month-old infants (N = 329) of mothers with lifetime histories of bipolar disorder (BD, n = 44), major depressive disorder (MDD, n = 244), or no history of Axis I disorders (CTL, n = 41). Infant respiratory sinus arrhythmia (RSA) was measured in a laboratory stressor paradigm. Measures of infant affect and behavior during mother-infant interaction, current maternal depressive symptoms, and exposure to stressful life events were examined with respect to diagnostic group and RSA.

RESULTS

Groups did not differ in baseline RSA or infant affect measures. However, during the stressor task, infants of mothers with BD evidenced increases in RSA, while infants of MDD and CTL mothers evidenced decreases in RSA. Though levels of postnatal stress and current levels of maternal depressive symptoms differed among groups, neither of these factors predicted infant psychophysiological responses.

CONCLUSIONS

At 6 months of age, infants of mothers with BD show differences in psychophysiological regulation. These differences cannot be accounted for by perinatal outcome, current maternal depressive symptoms, or exposure to stressful life events, and thus may reflect endophenotypic markers of psychopathological risk.

Physiological responses to workload change. A test/retest examination

The purpose of this study is to examine the test/retest consistency of physiological responses induced by mental tasks. Fifteen healthy male university students were recruited as participants. They were instructed to perform a 5-min Multi-Attribute Task Battery (MATB) trial three times successively. The task difficulty level of the tracking task of the second trial was set as medium (M). The first one was set as more difficult (H) and the last trial was easiest (L). The difficulty levels of the other two tasks (resource management and system monitoring) of the MATB were identical for all three trials. The participants repeated this procedure on three different days separated by at least a 1-day interval. The order of the tasks was the same for all repeated trials, i.e., H-M-L. Tissue blood volume from the tip of the nose using a laser Doppler blood flow meter, skin potential level (SPL), ECG from three leads on the chest, systolic time intervals (pre-ejection period, left ventricular ejection time), and hemodynamic parameters (stroke volume, cardiac output) were recorded during the task trials and before and after 5-min resting periods. The participants reported their subjective workload via NASA-TLX after each task trial. Autonomic nervous system parameters derived from the above-mentioned signals, subjective workload scores, and performance indices of MATB were analyzed, and test/retest reliability was investigated. The results showed that a significant test/retest correlation was obtained for SPL for more participants than in the other parameters, although there were large individual differences.

Reduced heart rate variability and vagal tone in anxiety: trait versus state, and the effects of autogenic training

This study investigated heart rate variability (HRV) in healthy volunteers that were selected for extreme scores of trait anxiety (TA), during two opposite psychophysiological conditions of mental stress, and relaxation induced by autogenic training. R-R intervals, HF and LF powers, and LF/HF ratios were derived from short-term electrocardiographic recordings made during mental stress and relaxation by autogenic training, with respiratory rate and skin conductance being controlled for in all the analyses. The main finding was that high TA was associated with reduced R-R intervals and HF power across conditions. In comparison to mental stress, autogenic training increased HRV and facilitated the vagal control of the heart. There were no significant effects of TA or the psychophysiological conditions on LF power, or LF/HF ratio. These results support the view that TA, which is an important risk factor for anxiety disorders and predictor of cardiovascular morbidity and mortality, is associated with autonomic dysfunction that seems likely to play a pathogenetic role in the long term.

RSA fluctuation in major depressive disorder

Cardiac vagal control, as measured by indices of respiratory sinus arrhythmia (RSA), has been investigated as a marker of impaired self-regulation in mental disorders, including depression. Past work in depressed samples has focused on deficits in resting RSA levels, with mixed results. This study tested the hypothesis that depression involves abnormal RSA fluctuation. RSA was measured in depressed and healthy control participants during rest and during two reactivity tasks, each followed by a recovery period. Relative to controls, depressed persons exhibited lower resting RSA levels as well as less RSA fluctuation, primarily evidenced by a lack of task-related vagal suppression. Group differences in RSA fluctuation were not accounted for by differences in physical health or respiration, whereas group differences in resting RSA level did not survive covariate analyses. Depression may involve multiple deficits in cardiac vagal control.

Autonomic response to standardized stress predicts subsequent disease activity in ulcerative colitis

OBJECTIVES

Prospective studies of the role of psychological stress in ulcerative colitis are inconsistent or show a modest relationship. We tested the hypothesis that individual differences in autonomic function are associated with differences in the disease course of ulcerative colitis.

METHODS

The spectral power of heart rate variability, an indirect marker of autonomic function, was measured during a standardized stress protocol in 93 ulcerative colitis patients. Patients were categorized as typical or atypical by an increase or decrease, respectively, in the high frequency band of heart rate variability from a period of acute stress to recovery 5 min later. Disease activity was measured at baseline (time 1) and a second time point (time 2) 7-37 months later.

RESULTS

An atypical pattern of heart rate variability at time 1, present in 29% of patients, was associated with lower mean disease activity at time 2 (atypical, 0.56+/-0.93; typical, 2.27+/-2.56, P=0.001). The contribution of heart rate variability pattern to explaining time 2 disease activity was independent of the contributions of other factors that differed between groups, including time 1 disease activity and lifetime corticosteroid use.

DISCUSSION

An atypical pattern of autonomic reactivity may be a marker of individual differences in stress regulation that has prognostic significance in ulcerative colitis.

The influence of hostility and family history of cardiovascular disease on autonomic activation in response to controllable versus noncontrollable stress, anger imagery induction, and relaxation imagery

Autonomic activation in response to controllable versus noncontrollable stress, anger imagery induction, and relaxation imagery was studied among 80 participants between the ages of 18 and 34 years. Participants differed in level of trait hostility and family history of cardiovascular disease. Results were obtained through power spectral analyses of electrocardiograph R-R intervals, which produced an index of autonomic nervous system activation. For both male and female populations, parasympathetic regulation was diminished during anger induction for individuals with high levels of trait hostility and having a family history of cardiovascular disease. Similar results were obtained for women during the uncontrolled stress condition. Based on family history of cardiovascular disease and trait hostility, men responded differentially to relaxation imagery induction, whereas no differences were found among females.

Socioeconomic status and health: is parasympathetic nervous system activity an intervening mechanism?

BACKGROUND

The link between socioeconomic status (SES) and health is widely recognized but the pathophysiologic mechanisms are not well understood. We tested the hypothesis that parasympathetic nervous system (PNS) regulation is one such mechanism.

METHODS

In a cross-sectional study, electrocardiogram-derived RR interval variability (RRV), a non-invasive index of cardiac PNS regulation, and SES, measured as educational attainment and income, were collected in 756 subjects in the CARDIA study of heart disease in young adults.

RESULTS

Relative to those with less than a high school education, those with high school to college and post-college education had 26% (beta = 0.233) and 43% (beta = 0.355) greater low frequency (LF) RRV, respectively, adjusted for age, sex, and race. For high frequency (HF) RRV, race interacted with income: relative to low income whites, intermediate and high income whites had 133 and 191% greater HF power, respectively, while intermediate and high income blacks had 32 and 44% greater HF RRV, respectively, relative to low income blacks.

CONCLUSIONS

Numerous studies demonstrate that psychosocial stressors reduce cardiac parasympathetic regulation and that SES disparities are associated with increasing social stress proportional to the degree of disparity. Data from the current study suggest that PNS regulation may be a mechanism linking the stressful effects of low SES to increased morbidity and mortality.

Respiratory Sinus Arrhythmia During Stress Predicts Resting Respiratory Sinus Arrhythmia 3 Years Later in a Pediatric Sample

The author examined whether respiratory sinus arrhythmia (RSA) responses to stress predicted resting RSA approximately 3 years later in children and adolescents. A total of 149 children and adolescents (49% girls and women, 44% African Americans) participated in 2 laboratory protocols approximately 3 years apart. RSA reactivity during tasks was consistent within participants across tasks during each session. Resting RSA at Visit 1 explained 17% of the variance in resting RSA at Visit 2 when body mass index, duration between visits, race, gender, and age were controlled for. Visit 1 RSA reactivity explained an additional 5% of the variance in resting RSA at Visit 2. The positive relationship between Visit 1 reactivity and Visit 2 resting levels suggests that larger decreases in RSA during stress predicted lower resting RSA. Conversely, increases in RSA during stress were associated with higher resting RSA an average of 3 years later.

Examination of normalized pulse volume-blood volume relationship: toward a more valid estimation of the finger sympathetic tone

The pulsatile ac component (DeltaI) superimposed on the transmitted dc components (I: tissue plus blood) are obtained from a near-infrared finger photoplethysmogram using a wavelength of 810 nm. Only the dc component is given in an ischaemic circulatory state (I(t): tissue only). Based on Lambert-Beer's law, normalized pulse volume (NPV; =DeltaI/I) and blood volume [BV; =ln(I(t)/I)] have recently been advocated as quantitative measures. In this study, the NPV-BV relationship was examined using the finger occlusion method during rest and mental arithmetic in 16 female undergraduates. Finger vascular tone during stress was evaluated by the distance of the linear and parallel NPV-BV regression lines (D(NB)) between rest and stress conditions. A reference standard was provided by the linear regression lines of compliance index (CI=NPV/pulse pressure) and BV to the transmural pressure. The estimates at 40 mmHg of transmural pressure, as an arbitrarily chosen reference point, were calculated (CI40 and BV40). D(NB) correlated well with them (r=0.81 and 0.94, respectively). The multiple regression with mean blood pressure indicated that the combination of D(NB) and the reactivities in heart period could explain approximately 50% of valiance in pressor response. In conclusion, D(NB) is easily obtainable from the NPV-BV function and seems to be more specific and valid than NPV as an index of finger sympathetic tone, since it adjusts the mechanical effect of arterial distending pressure.

Gastric meal accommodation studied by ultrasound in diabetes. Relation to vagal tone

BACKGROUND

Disturbed gastric meal accommodation may cause abdominal symptoms in patients with functional dyspepsia and diabetes mellitus who have poor vagal control of gastric motility. In the present study we aimed to explore the relation between gastric meal accommodation and vagal tone in diabetic patients with vagal neuropathy.

METHODS

Twenty patients with diabetes (DM) (insulin-dependent type; 10 men and 10 women, aged 35.3 +/- 7.6 years) and 20 healthy controls (HC) (10 men and 10 women; aged 34.7 +/- 10.7 years) were studied. Proximal gastric size was assessed with ultrasound in a sagittal area and a frontal diameter. Distal gastric (antrum) size was assessed in a sagittal area. Vagal tone was assessed non-invasively by recording of respiratory sinus arrhythmia (RSA) in beats per minute.

RESULTS

Proximal sagittal area was significantly (P = 0.03) smaller in DM (18.5 +/- 5.5 cm2) than in HC (22.2 +/- 4.6 cm2). Proximal frontal diameter did not differ significantly (P = 0.60) between DM and HC (5.9 +/- 1.1 cm versus 5.7 +/- 0.8 cm). Antral area, too, did not differ significantly (P = 0.59) between DM and HC (14.5 +/- 4.1 cm2 versus 13.6 +/- 5.8 cm2). Proximal/distal meal distribution ratio, defined as proximal sagittal area/distal sagittal area, was significantly (P = 0.05) smaller in DM (6.8 +/- 0.6) than in HC (9.9 +/- 5.5). Vagal tone was significantly (P = 0.03) lower in DM (4.5 +/- 1.9 beats/min) than in HC (6.3 +/- 2.7 beats/min). Vagal tone tended (r = 0.33, P = 0.06) to correlate with proximal sagittal area in DM and HC pooled. Vagal tone correlated (r = 0.34, P = 0.05) with proximal frontal diameter in DM and HC pooled. A significant negative correlation (r = -0.39, P = 0.03) was observed between vagal tone and antral area in DM and HC pooled.

CONCLUSIONS

Patients with diabetes and low vagal tone have an impaired postprandial gastric meal distribution characterized by a small proximal stomach and a small proximal/distal meal distribution ratio.

Inferential and descriptive influences on measures of respiratory sinus arrhythmia: sampling rate, R-wave trigger accuracy, and variance estimates

The use of respiratory sinus arrhythmia (RSA) is dependent on several quantification factors. The statistical consequences of sampling rate, R-wave trigger accuracy, and the data structure of RSA estimates were evaluated via simulations and simulated modifications. Simulations demonstrated that sampling rate determined the amplitude of the smallest oscillation that could be accurately described. When the amplitude of the oscillation was smaller in milliseconds than the sampling interval, all smaller oscillations, regardless of amplitude, were indiscriminately assigned a default value defined as 50% of the sampling interval. Also, reduced R-wave peak detection accuracy was demonstrated to influence statistical analyses. The distributional characteristics of several common methods of structuring RSA estimates were investigated, and results indicated that several methods results in asymmetrical distributions. We recommend using rapid sampling rates (i.e., 1 kHz), accurate R-wave peak detectors, and avoiding statistical trouble.