The effect of laboratory stressors on glycemic control and gastrointestinal transit time

This study compared effects of an active coping task (computerized stressors involving arithmetic, anagrams, and Atari games) and a passive coping task (cold pressor) on gastrointestinal transit time and glycemic response to an oral glucose load. Eleven normal weight males were studied; subjects participated in three counterbalanced sessions, each including a 45-minute baseline, 20-minute experimental period (active coping, passive coping, or nonstress control) and 2.5-hour recovery period. The stressors produced different cardiovascular and catecholamine responses; systolic and diastolic blood pressure were highest during cold pressor (p less than 0.001), heart rate was highest during computer stressor (p less than 0.001), and norepinephrine excretion was greatest during cold pressor (p less than 0.002). However, both stressors delayed gastrointestinal transit time compared with the control condition (p less than 0.009 and p less than 0.026 for cold pressor and computerized stressor, respectively) and both delayed the time of peak glucose response (p less than 0.002 and p less than 0.05, respectively). Implications of these findings for patients with diabetes and for effects of stress on eating behavior are discussed.     

The effect of participation in an exercise training program on cardiovascular reactivity in sedentary middle-aged males.

Exaggerated cardiovascular reactivity to mental stressors may be a risk factor for cardiovascular disease. To determine if participation in a moderate intensity aerobic exercise training program reduces cardiovascular reactivity to laboratory stressors, 40 sedentary middle-aged males were randomly assigned: training group (n = 25) and control group (n = 15). Cardiovascular reactivity during and after three mental stressors (passive responding, push-button Stroop and verbal Stroop) and mild exercise (bicycle ergometer) was assessed before and after an 8-week intervention. VO2(peak) was determined using the Balke protocol. Among 19 subjects who completed the training, VO2(peak) increased 13.7%. Also, trained compared to untrained subjects showed significant reductions in baseline and absolute heart rate responses to all stressors. Baseline adjusted heart rates were significantly lower during push-button Stroop recovery and during verbal Stroop. Blood pressure, T-wave amplitude, finger pulse amplitude and pulse transit time responses were unaffected by exercise training. It was concluded that participation in a short-term, moderate intensity aerobic exercise training program may have a cardioprotective effect by significantly reducing absolute and baseline-adjusted heart rate responses to stressors.     

The ability of active versus passive coping tasks to predict future blood pressure levels in normotensive men and women

Casual blood pressure (BP) after a 2-year follow-up interval was determined in 40 normotensive men and women (20 Blacks and 20 Whites), who had been initially tested for cardiovascular responses to a variety of active and passive coping tasks, including active speech, passive speech, reaction time, and forehead cold pressor tasks. Stepwise multiple regression analyses were used to identify the best model for predicting follow-up BP. Average systolic blood pressure (SBP) level during cold pressor stress was the single most powerful predictor of casual SBP over 2 years even after controlling for initial resting SBP. Other predictors of follow-up SBP were initial SBP, parental history of hypertension, and heart rate and SBP during passive speech (final model R(2) = .78). For follow-up diastolic blood pressure (DBP), the only significant predictors were initial DBP and male gender. These results contribute to a growing body of literature that suggests that cardiovascular measures observed during stressors have predictive validity above and beyond that of traditional predictor variables.     

Aerobic Fitness Affects Cardiovascular and Catecholamine Responses to Stressors

Subjects of varying degrees of aerobic fitness were subjected to four laboratory stressors in a test of the hypothesis that aerobic fitness is associated with decreased responsiveness to stressors other than exercise. Blood pressure, heart rate, norepinephrine, epinephrine, and psychological responses to a film of industrial accidents (passive psychological stressor), the Stroop word color task (active psychological stressor), the cold pressor test (passive physical stressor), and running to exhaustion on a treadmill (active physical stressor) were measured. Baseline systolic blood pressure and relative diastolic responses to the film, Stroop task, and exercise were smaller in fit subjects over 40 than in less fit subjects of the same age group. Heart rates were lower in fit subjects at most times, except during and after maximal exercise. Norepinephrine was lower after 9 min of exercise in fit subjects, but was much higher at exhaustion, after these subjects had accomplished more work. Norepinephrine levels fell rapidly and were not different among groups 3 and 10 min after exercise. There was no preferential generalization of the “fitness effect” to the active psychological task.     

Heart Rate Reactivity and Type A Behavior as Modifiers of Physiological Response to Active and Passive Coping

We examined the long term predictivity of heart rate reactivity (HRR) and its relation to cardiovascular and biochemical activity during rest and during tasks requiring active and passive coping. HRR was determined in 28 young men by measuring peak heart rate change to cold pressor one year after performing tasks eliciting active and passive coping. Heart rate change to cold pressor was significantly correlated with change to active coping (r= .65, p<.01) and to passive coping (r= .53, p<.01). Responses to the tasks were equivalent for Type A and B subjects. On the other hand, high HRRs were significantly more reactive than low HRRs with the effect being most apparent during active coping. HRR appeared to be a trait stable over one year which predicted enhanced cardiac, neuroendocrine, and neuromuscular response.     

Airflow and autonomic responses to stress and relaxation in asthma: the impact of stressor type.

The impact of stress on respiratory airflow in asthmatics is unclear. Part of the uncertainty may spring from the different physiological effects of different stressors. Given their potential to elicit increases in parasympathetic vagal activity, stressful situations that present few opportunities for coping (passive coping stressors) may be particularly problematic for people with asthma. Thirty-one adult asthmatics participated in a protocol including a widely used passive coping stressor (the cold pressor test), an active coping stressor (mental arithmetic), an interview about an upsetting asthma-related incident (viewed as a potential passive coping stressor given the exposure to unpleasant memories), and progressive muscle relaxation. Repeated measurements of airflow (via peak expiratory flow), vagal tone (via heart rate variability), and other variables were obtained. The cold pressor test, asthma interview and progressive muscle relaxation produced significant decreases in airflow compared to the baseline period. The cold pressor test and progressive muscle relaxation produced significant, complementary increases in vagal tone. These results suggest that passive coping stressors and other stimuli (e.g., certain forms of relaxation) that elicit increased vagal tone may be associated with poorer asthma control, a view consistent with a significant negative correlation between the participant's mean vagal tone response to the tasks and score on a measure of asthma self-efficacy.     

Cardiovascular Responses to the Combination of Caffeine and Mental Arithmetic, Cold Pressor, and Static Exercise Stressors

The present study examined cardiovascular responses to the combination of caffeine (250mg) and mental arithmetic, cold pressor, and static exercise stressors in 48 healthy males. Subjects were tested in a within-subject, placebo-controlled, double-blind design. Repeated measurements of heart rate, finger temperature, respiratory sinus arrhythmia, forearm blood flow, and blood pressure were obtained during a pre-drug resting baseline, a post-drug resting baseline, the three stressor tasks, and a recovery baseline. The primary analyses were 2(Drug) x 5(Period) x 6(Stress Order) MANCOVAs using pre-drug baseline values as covariates. Significant period main effects were observed for all measures. Significant drug main effects were observed for blood pressure, finger temperature, respiratory sinus arrhythmia, and forearm blood flow. The significant changes in blood pressure and finger temperature produced by caffeine combined in an additive fashion with the effects produced by the stressors. Significantly greater increases in forearm blood flow and heart rate during mental arithmetic on the caffeine day suggested a potentiation of sympathetic, beta-adrenergic activity. Questionnaires administered during baseline periods to assess psychological responses to stress and caffeine revealed a potentiation of anxiety and anger responses to stress on the caffeine day.     

Cardiovascular Responses to Effortful Active Coping: Implications for the Role of Stress in Hypertension Development

Recent contributions to the literature on stress and hypertension are discussed. The significance of effortful active coping in evoking sympathetically-mediated heart rate and blood pressure increases is supported by results of studies involving both aversive and appetitive task incentives. Young healthy males who are above-average in heart rate during coping tasks show consistently higher heart rates and systolic pressures during other stresses as well, but are indistinguishable from less reactive persons when relaxed. Studies involving beta-blockade indicate that these above-average cardiovascular increases are partly due to a greater beta-adrenergic response among the high heart rate reactors. In addition, the parents of these high heart rate reactors report a greater incidence of hypertension than parents of low reactors, suggesting that high cardiovascular responses during active coping stress may reflect a high degree of susceptibility to later hypertension.     

Heart rate variability during manual restraint in chicks from high- and low-feather pecking lines of laying hens

The purpose of this investigation was to determine whether there is a difference in coping style in chicks from a high (HFP)- and low-feather pecking (HFP) line of laying hens. Active and passive coping styles can be distinguished by differences in sympathetic and parasympathetic activities on the heart. We studied heart rate during baseline conditions and during manual restraint in HFP and LFP hens. Heart rate and locomotor activity were successfully monitored around the clock with a biotelemetric implant. During the light period, the values for locomotor activity and heart rate were highest, whereas during the dark period they were the lowest. These values did not differ in LFP and HFP hens. However, during manual restraint (restraining the bird on its side by hand for 8 min) HFP birds had somewhat faster heart rate than LFP birds (at 4 min, p = 0.066). Studying heart rate variability during manual restraint showed that LFP chickens had a significant higher parasympathetic activity at 5 min (p = 0.023) and at 6 min (p = 0.002) as compared to HFP hens. The results showed that in terms of coping style, LFP chickens are passive, whereas HFP birds are active.     

Hemodynamics of Blood Pressure Responses During Active and Passive Coping

This laboratory study was designed to address a number of interrelated issues regarding cardiovascular reactivity to psychological stress. One objective was to extend the previous research comparing cardiovascular responses during active versus passive coping, by comparing responses to two task conditions designed to be similar in all ways except the opportunity to make a response influencing the task's outcome. A second objective was to compare responses to two different passive film tasks, which differed in outcome uncertainty and the degree of vicarious active coping achieved through identification with the role portrayed by the actors. A third objective was to evaluate whether individuals are predisposed to exhibit a particular hemodynamic pattern underlying their blood pressure adjustments, independently of the task demands imposed. Ninety healthy young adult male subjects were tested in pairs on a series of tasks that included a competitive reaction-time task, an active as well as a passive phase of a team reaction-time task, and passive viewing of two film segments. The tasks demanding active coping responses tended to raise blood pressure due primarily to an increase in cardiac output, while vascular resistance fell. During passive coping demands cardiac output increased to a lesser extent, but vascular resistance also tended to increase, thereby raising blood pressure by their synergistic effects. However, these patterns were not typical of all participating subjects. On the basis of their cardiac output and vascular resistance responses to the competitive reaction-time task, one third of the subjects were categorized as being high myocardial reactors (n = 30) and another third high vascular reactors (n = 31). Post-hoc analyses of responses to the other tasks, based on these categorizations, indicated that the hemodynamic basis of reactivity is an individual characteristic only partially modified by coping demands. The active/passive coping dimension is discussed both conceptually and in relation to the role of stress in the etiology of hypertension.     

Influences of sex and age on cardiovascular responses during stress

The present investigation examined the influence of sex and age on blood pressure and heart rate responses in 125 women, 93 men, 121 girls, and 96 boys to three standardized stressors: serial subtraction, mirror-image tracing, and isometric handgrip. With baseline measures and body mass index controlled for, analyses of covariance showed that adults had greater systolic blood pressure responses than did children; men had greater blood pressure responses to all stressors than did women; and high school boys had greater systolic blood pressure responses than did high school girls. In addition, adults had smaller heart rate responses during isometric handgrip than did children, and high school students had smaller heart rate responses during all tasks than did the remaining, younger students. These results show that sex and age are important determinants of the magnitude of cardiovascular adjustments during stressors. The implications of these results are discussed in light of sex differences in coronary heart disease morbidity and mortality.     

For Distinguished Early Career Contribution to Psychophysiology: Award Address, 1988

This program of experiments examined heart rate responses to mental arithmetic and a video game. Attention first focused on their metabolic relevance. Comparison with heart rate/oxygen consumption regression equations generated from isotonic exercise data revealed that the heart rate increases of certain individuals were considerably in excess of those necessitated by contemporary metabolic demand. Both temporal and intertask consistency of reaction were explored, and supportive evidence was obtained. The relationship between laboratory and real-world reactions was investigated, and preliminary evidence found suggesting that in-laboratory responses are indicative of responses to more naturalistic stressors. Finally, twin studies examining the genetic and environmental determinants of individual differences in heart rate change during the tasks revealed a substantial genetic component for these responses.     

Cardiovascular reactivity, anxiety and anger during perceived controllability

The purpose of this study was to investigate the relationship between emotional and cardiovascular responses in an aversive active coping situation. A letter detection task was presented to 64 male students. From a stream of letters scrolling over a screen, subjects were required to eliminate specific letters. Task difficulty was varied by changing the speed with which the stream moved along on the screen. Perceived control over an aversive loud tone was manipulated by instruction. While blood pressure differences in the experimental conditions could not be found, the group with perceived control displayed greater increases in heart rate and greater shortening of pulse transit time. In subjects low in trait anger, belief of control over aversive tones led to heightened cardiovascular reactivity compared with subjects high in trait anger. The results are discussed with respect to suppression of anger and a possibly opposite effect of emotion and mental effort in aversive active coping situations.     

Comparison of cardiac versus vascular reactors and ethnic groups in plasma epinephrine and norepinephrine responses to stress

This study examined differences in plasma epinephrine (EPI) and norepinephrine (NOREPI) responses to stressors in 67 healthy African-American and Caucasian American men and women of the ages 18 to 49. Subjects were divided into three groups: (a) those who showed high blood pressure (BPI responses to stress associated with consistently high cardiac output (CO) increases with no substantial increases in total peripheral resistance (TPR), labeled cardiac reactors: (b) those with equally high BP increases associated with consistently higher TPR increases and lesser CO increases. labeled vascular reactors; (c) those who showed mixed hemodynamic responses or were low BP reactors. Ethnic and gender group differences in EPI and NOREPI responses were also examined. Cardiac reactors, vascular reactors and mixed + low reactors did not differ in EPI or NOREPI levels at baseline. During stressors, cardiac reactors showed greater increases in plasma EPI than vascular reactors or others during math, reaction time, and passive and active speech tasks: they also showed a weak trend toward greater NOREPI increases during these challenges as well. No differences were seen during the cold pressor: this stressor evoked the least change in EPI of all tasks, whereas the active speech elicited the greatest increases in both EPI and NOREPI of all tasks. Vascular reactors did not differ from mixed + low reactors in EPI or NOREPI reactivity, and men and women did not differ in EPI or NOREPI reactivity to any task. In contrast, Black subjects showed greater increases in NOREPI levels across all stressors compared to White subjects. These findings have implications for investigations of the role of sympathetic nervous system activity in the pathogenesis of hypertension in both African-American and Caucasian American populations.     

Patterns of Autonomic Response During Laboratory Stressors

The present study was designed to include an index reflecting the influence of parasympathetic nervous system activity on the heart, respiratory sinus arrhythmia, in addition to measures reflecting primarily sympathetic nervous system activity. The inclusion of the parasympathetic index was considered important for two reasons:(a) Past studies have suggested different patterns of autonomic response to qualitatively different laboratory stressors but have had to infer parasympathetic influences more indirectly, and (b) there is evidence that borderline hypertensives may have reduced vagal tone at rest when compared to normotensives. This last point is important for the study of individual differences in cardiovascular reactivity because excessive responsiveness in young normotensives (beta-adrenergic reactors) has been suggested as a model for studying the precursors of some types of hypertension. Fifty-one male college students were given a reaction time task, a mental arithmetic task, a cold pressor task, and graded bicycle exercise. A variety of cardiovascular and respiratory measures were collected on each subject. Results indicated significant differences in levels of respiratory sinus arrhythmia during the three tasks and the rest period, giving additional evidence for parasympathetic differences (along with sympathetic differences) in these conditions. Additionally, high beta-adrenergic reactors did not differ in mean level of respiratory sinus arrhythmia from low reactors either at rest or during the task periods. These results are discussed in the context of previous research.     

Respiratory Sinus Arrhythmia as an Index of Parasympathetic Cardiac Control During Active Coping

Psychophysiological studies concerning tonic cardiac responses to stressor tasks have tended to emphasize beta-adrenergic effects and to neglect parasympathetic influences and sympathetic-parasympathetic interactions. Much recent evidence indicates that both within- and between-individual variations in cardiac parasympathetic heart rate (HR) control can be easily and reliably assessed by measuring the magnitude of respiratory sinus arrhythmia (RSA). Therefore, we used RSA to index cardiac vagal responses to two active coping tasks. Both tasks consisted of the same video game, in one condition with threat of shock for inferior performance, and in the other without such threat. Twenty subjects underwent both tasks (counterbalanced over subjects), plus a preceding resting baseline period. HR and RSA were continuously measured. Results suggested that cardiac parasympathetic activity was diminished from rest to task, contributing to heart rate responses. Exaggerated HR responses were also associated with extreme parasympathetic withdrawal. Furthermore, task condition X sequence of presentation interaction effects showed that threat of shock was particularly effective in elevating HR and reducing RSA when the threat was presented during the first task condition. A repeated-measures analysis of covariance of HR, attempting to remove the effects of parasympathetic influences upon HR, suggested that sympathetic influences upon HR exceeded any reciprocal vagal effects during the threat condition for those subjects exposed to the threat task first. The findings indicate the importance of considering stress-related parasympathetic effects upon HR as well as sympathetic-vagal interactions.     

Acute exercise improves endothelial function despite increasing vascular resistance during stress in smokers and nonsmokers

The present study examined the effect of acute exercise on flow mediated dilation (FMD) and reactivity to neurovascular challenges among female smokers and nonsmokers. FMD was determined by arterial diameter, velocity, and blood flow measured by Doppler ultrasonography after forearm occlusion. Those measures and blood pressure and heart rate were also assessed in response to forehead cold and the Stroop Color‐Word Conflict Test (CWT) before and after 30 min of rest or an acute bout of cycling exercise (～50% VO₂peak). Baseline FMD and stress responses were not different between smokers and nonsmokers. Compared to passive rest, exercise increased FMD and decreased arterial velocity and blood flow responses during the Stroop CWT and forehead cold in both groups. Overall, acute exercise improved endothelial function among smokers and nonsmokers despite increasing vascular resistance and reducing limb blood flow during neurovascular stress.     

Existing and Training Induced Differences in Aerobic Fitness: Their Relationship to Physiological Response Patterns During Different Types of Stress

Aerobic fitness has been associated with various desirable psychological and physiological characteristies. Recently, attenuation of physiological reactivity during stressful situations was added to this list, although comparison of the stress responses of sportsmen and sedentary subjects has yielded equivocal results. The present study examined cardiovascular patterns rather than single variables, and tried to clarify these matters. Tasks were used that were known to increase blood pressure through different combinations of changes in cardiac output and vascular resistance. Autonomic nervous system dynamics underlying these response patterns were studied using preejection period as an index of β-adrenergic activity, and respiratory sinus arrhythmia as an index of vagal activity. Pre-existing differences in aerobic fitness in a sample of sedentary subjects were related to their responses during the stressful tasks and the recovery periods afterwards. This approach prevented confounding of the relationship between fitness and stress-reactivity with the psychological effects of regular exercise. Furthermore, it excluded the bias in psychological makeup that is introduced when subjects spontaneously engaged in sports are compared to non-exercising persons. To rule out a third (hereditary?) factor underlying both stress-reactivity and fitness, physiological responses before and after a seven-week training program were compared to those of subjects in a waiting list control group. Substantial individual differences in aerobic fitness were found in spite of the fact that all subjects reported low levels of habitual activity. During two active coping tasks, diastolic blood pressure reactivity and vagal withdrawal were negatively related to these pre-existing differences in fitness. No such relation was seen during a cold pressor test or during recovery from the tasks. Neither β-adrenergic cardiac reactivity nor heart rate responses were related to fitness, but the absolute heart rate during the tasks was lower in the more fit subjects. Seven weeks of training were not effective in changing either reactivity or recovery of any of the variables. The discrepancy between cross-sectional and longitudinal results in the present study suggests that training of longer duration is necessary to induce the psychological or physiological changes underlying reduced reactivity. The latter may include changes in cardiac vagal/sympathetic balance or in adrenoceptor sensitivity. Alternatively, both psychological and physiological determinants of stress-reactivity may be related to aerobic fitness at a dispositional level.     

A generalized physiological hyperreactivity to acute stressors in hypertensives

Hypertensives have consistently been found to have a more reactive cardiovascular system than normotensives. In the present study, it was examined whether this enhanced cardiovascular stress reactivity generalizes to the hypothalamus-pituitary-adrenal (HPA) axis and the immune system. Forty-two unmedicated hypertensives and 21 normotensive controls performed five passive coping and active coping stressful tasks in the laboratory. In addition to the expected greater mean diastolic blood pressure reactivity to the tasks, hypertensives exhibited enhanced (baseline corrected) task salivary cortisol and secretory immunoglobulin A (S-IgA) levels. Moreover, correlations were found between blood pressure responses and task related cortisol activity and between baseline blood pressure levels and task-induced S-IgA levels. These results indicate that hypertensives not only have a hyperreactive cardiovascular system, but also an enhanced HPA axis and immune system reactivity to stress. A central stress mechanism may be responsible for the heightened generalized stress response in hypertensives.     

Active and passive coping under different degrees of stress; effects on urinary and plasma catecholamines and ECG T-wave

Cardiac sympathetic, urinary and plasma catecholamine effects of active and passive coping were investigated during both low and high stress. Stress intensity was manipulated by varying the work load on a bicycle ergometer. As predicted, T-wave flattening of the ECG - an index of cardiac sympathetic activity - was significantly more pronounced during active coping than during passive coping. This effect did not depend upon the degree of stress. A significant increase in both adrenaline and noradrenaline levels depended upon the combined effects of active coping and high stress. Because high concentrations of circulating catecholamines are thought to be related to cardiovascular pathology, the results suggest that active coping during high stress might involve the highest cardiovascular risks.