Effects of Isoproterenol on T-Wave Amplitude and Heart Rate: A Dose-Response Study

This report examines the hypothesis that electrocardiographic T-wave amplitude is sensitive to graded increases in beta-sympathetic stimulation of the heart. Beta-adrenergic activity was manipulated pharmacologically in 9 healthy men by bolus infusion of isoproterenol in each of six doses: 0.1, 0.25, 0.5, 1.0, 2.0, and 4.0 micrograms. Results indicated that elevations in heart rate above placebo values increased as a linear function of isoproterenol dose. In contrast, the dose-response curve for T-wave amplitude was best described by a quadratic function: an initial reduction in T-wave amplitude at low levels of isoproterenol infusion was followed by a significant reversal of this effect at higher doses. Comparison of the heart rate and T-wave amplitude data points to limitations in the use of the latter as an index of beta-adrenergic activity. One of several possible explanations for the T-wave results would entail a mechanism that preserves ventricular function at high levels of beta-sympathetic stimulation.     

Responses of the T-Wave Amplitude as a Function of Active and Passive Tasks and Beta-Adrenergic Blockade

This paper presents evidence that phasic changes in T-wave amplitude vary as a function of task conditions and beta-adrenergic drugs. Three experiments were designed to test the sensitivity of T-wave amplitude to manipulations in sympathetic arousal. In the first experiment, T-wave amplitude was recorded during an active behavioral task in which 32 subjects believed that they could control the duration of an aversive white noise and during a passive behavioral task in which another 30 subjects knew that they had no control. T-wave amplitude decreased to a greater extent in the active behavior group than in the passive group. In the second experiment, 9 subjects receiving one of two beta-adrenergic blockers and 10 subjects receiving placebo completed the active task. Task-induced reductions in T-wave amplitude were systematically blocked by the beta blockers. In the third experiment, 5 subjects received placebos and 15 received one of two different beta blockers. All subjects performed a mental arithmetic task. Subjects receiving a placebo, but not those receiving beta blockade, exhibited a significant reduction in T-wave amplitude during mental arithmetic.     

Secretory immunoglobulin A and cardiovascular reactions to mental arithmetic, cold pressor, and exercise: effects of beta-adrenergic blockade.

We investigated the influence of sympathetic nervous system processes on mucosal immunity by comparing the effects of beta-adrenoceptor blockade with 40 mg propranolol and placebo on secretory immunoglobulin A (sIgA) at rest and during paced serial arithmetic, cold pressor, and submaximal cycling. These tasks produced patterns of cardiovascular activity indicative of combined alpha- and beta-adrenergic, alpha-adrenergic, and beta-adrenergic activation, respectively. The effectiveness of the beta blockade was confirmed by the attenuation under propranolol of the shortening of the cardiac preejection period and the tachycardia elicited by mental arithmetic and exercise. The cold pressor test did not affect sIgA under either the placebo or the propranolol. Mental arithmetic increased sIgA concentration, and this increase was not blocked by propranolol. Exercise elicited increases in both sIgA concentration and sIgA secretion rate, which were not diminished by beta blockade. These data suggest that sIgA is not regulated by beta-adrenergic mechanisms.     

Differences Between ECG and Pulse When Measuring Heart Rate and Reactivity Under Two Physical and Two Psychological Stressors

To test the level of agreement of heart rate and reactivity to stressor tasks as measured via noninvasive ECG and pulse, 38 healthy subjects underwent four stressor tasks: mental arithmetic, reaction time, cold pressor, and bicycling. Data on resting and stressor heart rate were collected via ECG and photoplethysmography, and heart rate reactivity was calculated via five methods noted in the wider literature. Results indicated that, although resting heart rate values did not differ significantly across the two instruments, there were some significant differences in heart rate during certain periods of mental and physical stress reactivity. Calculation of heart rate reactivity revealed that there were few significant differences between data from the two measures but that the tasks themselves produced markedly different patterns of reactivity, questionning assumptions underlying comparison of reactivity data under different stress tasks. Implications for the assessment of reactivity are discussed.     

Phasic Cardiac Reactivity to Psychological Stress as a Function of Aerobic Fitness Level

Cardiovascular adjustments to physical exertion are known to be affected by aerobic fitness level. This raises the possibility that the cardiovascular responses associated with psychological stress may also be related to aerobic fitness. This study was undertaken to determine if phasic cardiac reactivity to stress would be affected by aerobic fitness level, and to make inferences regarding the autonomic mechanisms which might mediate such an effect. Twenty-four males were given a standard physical fitness test and then divided into high and low aerobic fitness level groups. Within two weeks of this assessment, the heart rate and electrocardiographic T-wave amplitude responses of these subjects were monitored during the performance of hard and easy versions of a mental arithmetic task. Analysis of the heart rate data revealed no aerobic fitness level effect. There was, however, greater T-wave amplitude attenuation in the low as compared to the high aerobic fitness level group on hard trials. This pattern of results suggests that psychologically-elicited sympathetic cardiac reactivity is reduced by enhanced aerobic fitness level.     

The combined effects of orthostatic and mental stress on heart rate,T-wave amplitude,and pulse transit time

The purpose of the present study was to determine whether cardiovascular reactivity to mental stress may be comparable in sitting and standing postures. Fifteen healthy males performed two 1-min mental arithmetic tasks, either while sitting or while standing, in counterbalanced order. Heart rate, pulse transit time, and T-wave amplitude were recorded in the last 10 s of the minute before, during, and after the mental arithmetic. Reactivity scores for each of the dependent measures were computed by calculating the percentage change from baseline values. Data were analyzed with multivariate and univariate repeated measures analysis of variance. Heart rate reactivity to the combination of orthostatic and mental stress was greater than to either stressor alone. Cardiac-sympathetic reactivity was greater in response to orthostatic than to mental stress as revealed by greater changes in T-wave amplitude and pulse transit time in response to the former. No additional decreases in T-wave amplitude, in response to mental stress, were observed during standing, but pulse transit time decreased in the same situation. However, no changes in pulse transit time in response to mental stress were observed in the sitting position. These results demonstrate that cardiovascular reactivity to mental stress depends on the body position in which the stressor is encountered.     

Computerized Cardiovascular Monitoring: Method and Data

This paper describes the development of a digitized, real-time, microcomputer-based signal processing system which records the following variables: systolic and diastolic blood pressure, heart rate, pulse transit time, blood volume pulse, and R-, S-, and T-wave amplitudes of EKG signals. Forty-eight healthy subjects participated in a three-task stress response study in order to gather initial data for evaluating the reliability and validity of this monitoring system. The three tasks represented replications of earlier studies: 1) reading aloud of a monotonous neutral text (Reading Only, RO); 2) mental arithmetic without vocalization (Arithmetic Quiet, AQ); and 3) mental arithmetic with vocalization (Arithmetic Aloud, AA). The findings provided support for the reliability and validity of the new monitoring system given that few data were lost, and resting values as well as differential task responses were found to be comparable with earlier data sets derived via similar experimental protocols.     

Comparative effects of two beta-blockers on cardiovascular reactivity and type A behavior in hypertensives

This study compared the effects of beta-blockers differing in degree of central nervous system penetration on Type A behavior and cardiovascular reactivity to mental stress. Forty-six male hypertensives were assigned randomly to receive either highly lipophilic and nonselective propranolol, hydrophilic and cardioselective atenolol, the diuretic hydrochlorothiazide, or placebo. Subjects were administered parallel forms of the Structured Interview (SI) and performed mental arithmetic and a cognitive task prior to and after 6 weeks of therapy. Results indicated that diuretic and placebo subjects (subsequently combined into a single control group) did not differ and that both beta-blockers reduced heart rate but not blood pressure reactivity to mental stress (p less than 0.02), an effect that was strongest during the mental arithmetic test. Analysis of SI components indicated a reduction only in explosive speech for beta-blockers versus controls (p less than 0.05). For global SI classifications, seven out of 12 subjects (58%) receiving propranolol, three of 12 (25%) receiving atenolol, and four of 22 control subjects (18%) became less Type A (p less than 0.05). These data do not replicate results of a prior study obtained with atenolol and suggest that only a subset of hypertensive individuals show reduced Type A behavior with propranolol. Central nervous system mechanisms may be important in producing these effects.     

Cardiac performance: independence of adrenergic inotropic and chronotropic effects

During right atrial pacing in open-chest anesthetized dogs, the relationships between reduction in stroke volume and rise in heart rate were identical in control experiments, during intravenous infusion of isoproterenol, and after blockade of adrenergic beta-receptors by propranolol. To examine the mechanism of this constant relationship, left ventricular volume was estimated by continuous recordings of myocardial chord length (MCL) between ultrasonic elements inserted into the anterior ventricular wall. Diastolic filling curves were curtailed by raising heart rate and end-diastolic MCL was reduced. At constant heart rate, end-diastolic MCL was not altered by isoproterenol infusion, except for a slight rise at heart rates exceeding 220 beats/min. End-systolic MCL, however, was reduced, accounting for larger stroke volume during isoproterenol than during propranolol infusion. The reduction in end-systolic MCL was constant at all heart rates examined. Hence, chronotropic changes influence end-diastolic volume and inotropic changes influence end-systolic volume; their effects on stroke volume regulation are, therefore, virtually independent.     

Caffeine effects on several indices of cardiovascular activity at rest and during stress

The effects of caffeine on cardiovascular responses to a mental arithmetic task were assessed using a between-subjects, double-blind design. Thirty-six male undergraduates were randomly assigned to either a placebo group or a group which received 250mg of caffeine. Repeated measurements of systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), digital blood volume pulse (DBVP), and finger pulse transit time (FPTT) were obtained during a predrug baseline, a postdrug resting period, and a mental arithmetic task. Significant Period (i.e., stress) effects were observed on all measures, except DBVP which revealed a marginally significant Period effect. Significant main effects of Drug were observed on DBP and DBVP. There were no significant Drug X Period interactions. These results indicate that the increases in DBP and the decreases in DBVP produced by caffeine were additive with effects produced by stress.This research was supported by a Medical Research Council of Canada Studentship awarded to the first author and by Grant (MA-9224) from the Medical Research Council of Canada awarded to the second.     

女大学生月经周期应激敏感性的生理心理评估

目的:评估女大学生在月经周期不同阶段应激敏感性的变化。方法:在经前、经后和排卵期对29名月经周期规律的女大学生进行静息、心算任务的心理生理测试。结果:心率变化最显著,排卵期的心率显著大于经前和经后;在排卵期和经后心算心率显著大于静息心率,而在经前两者之间无显著差异;在心率变异性上,仅发现低频成分在静息状态显著大于心算状态;皮肤电反应在心算状态显著大于静息状态。结论:女大学生在经前应激敏感性最高。     

Diminished pulse pressure response to psychological stress: early precursor of essential hypertension?

An excessive blood pressure response to mental stress is a widely reported characteristic of young normotensive offspring of hypertensive parents. At odds with these reports are data from a large biracial study showing that high risk adolescent offspring had diminished pulse pressure under mental stress and no evidence of greater blood pressure reactivity. We examined this apparent contradiction in a similar but larger sample of 213 normotensive adolescents, comparing blood pressure and heart rate responses to video game, mirror drawing, mental arithmetic, interview, and physical exercise in high- and low-risk offspring. Results replicated the diminished pulse pressure finding, suggesting it is characteristic of African Americans and is evoked by behavioral tasks that entail skeletal-motor inhibition. Submaximal physical exercise failed to discriminate between offspring groups. Possible biologic correlates of diminished pulse pressure in black adolescents with "high normal" blood pressure warrant further investigation.     

The effects of stress and caffeine on hypertensives

Eighteen male hypertensives on diuretic medication between the ages of 37 and 60 were studied in a double-blind, randomized, crossover design under three conditions: 200 mg of caffeine and mental arithmetic; placebo and mental arithmetic; and 200 mg of caffeine alone. Systolic and diastolic blood pressure, heart rate, and skin conductance were recorded. During rest, caffeine compared to placebo increased blood pressure by 8/6 mm Hg, but had no effect on heart rate or skin conductance. During mental arithmetic, the combined effect of mental stress and caffeine led to a further increase of 17/7 mm Hg, reaching a pressure level of 163/100 mm Hg. Heart rate and skin conductance were increased above their prior caffeine levels. There were no significant differences between the blood pressure response to mental arithmetic with caffeine and that response to mental arithmetic with a placebo, which may have been due to the fact that the hypertensives were already responding at ceiling level during the mental stressor.     

Electrocardiographic T-wave changes are more pronounced in type A than in type B men during mental work

Phasic changes in heart rate (HR) and electrocardiographic T-wave amplitude (TWA) were monitored in healthy Type A (coronary-prone) and Type B (non-coronary-prone) men during the performance of a difficult arithmetic task. Type As showed significantly greater reductions in TWA as compared to Type Bs, though no group differences were present in HR change. This pattern of results, wherein a significant Type A-B difference was observed in a phasic measure of ventricular performance (TWA), but not in one of supraventricular performance (HR), suggests that Type As experience excessive neurally mediated sympathetic stimulation of the myocardium during mental work.     

Caffeine Affects Cardiovascular Responses to Stress

The effects of caffeine on cardiovascular activity at rest and during psychological stress were examined in 33 healthy male college students who did not normally ingest caffeinated products. Caffeine (250 mg) and placebo were administered double-blind in separate sessions. Heart rate, blood pressure, and forearm blood flow and vascular resistance were assessed at rest and during the stressful, competitive performance of a mental arithmetic task. Comparisons of caffeine and placebo sessions revealed that caffeine elevated resting blood pressure 4–6 mmHg, an effect which added to the elevation produced by stress. Caffeine did not affect resting forearm blood flow but potentiated the forearm blood flow response to stress and led to higher levels of flow during stress. No caffeine effects appeared in heart rate or in task performance. Family history of hypertension and Type A behavior were examined as potential modulating factors of caffeine effects but results were generally negative. These results suggest possible mechanisms through which caffeine could enhance the pathogenic effects of stress on the cardiovascular system.     

Secretory immunoglobulin A and cardiovascular reactions to mental arithmetic, cold pressor, and exercise: effects of alpha-adrenergic blockade

The mechanism underlying acute changes in secretory immunoglobulin A (sIgA) remains to be determined. In this experiment, sIgA and cardiovascular activity were monitored at rest and while participants performed a mental arithmetic task, cold pressor, and submaximal cycle exercise following placebo or 1 mg of the alpha-adrenergic blocker, doxazosin. Under placebo, the tasks produced patterns of cardiovascular activity indicative of combined alpha- and beta-adrenergic, alpha-adrenergic, and beta-adrenergic activation, respectively. Doxazosin was associated with reduced blood pressure during cold pressor, but not during arithmetic or exercise. Mental arithmetic elicited increases in sIgA concentration and exercise produced increases in both sIgA concentration and secretion rate; these changes were unaffected by alpha blockade. In contrast, the cold pressor was associated with decreases in both sIgA concentration and secretion rate, which were blocked by doxazosin. These data suggest that acute decreases, but not increases, in sIgA are mediated by alpha-adrenergic mechanisms.     

Evaluation of Myocardial and Peripheral Vascular Responses During Reaction Time, Mental Arithmetic, and Cold Pressor Tasks

The primary purpose of this study was to examine the covariation of cardiac output and forearm blood flow during reaction time, mental arithmetic, and cold pressor tasks. Cardiac output was indexed using impedance cardiography, whereas impedance venous occlusion plethysmography was used lo index forearm blood flow. Cardiac output increased significantly over resting values in all three tasks, hut the pattern of these increases differed. Large heart rate increases during mental arithmetic and cold pressor tasks more than offset stroke volume decreases; the increases in the reaction time task were due to relatively smaller heart rate increases with stroke volume augmentation. For forearm blood flow, all task levels were higher than resting levels, but only mental arithmetic levels were statistically higher. The correlation between cardiac output and forearm blood flow change was significant for the reaction time task, but not for the mental arithmetic or cold pressor tasks.     

Comparison of hemodynamic responses to social and nonsocial stress: evaluation of an anger interview

Hemodynamic responses to an anger interview and cognitive and physical stressors were compared, and the stability of associated hemodynamic reactions examined. Participants experienced control, handgrip, counting, and mental arithmetic tests and an anger interview on two occasions. Systolic and diastolic blood pressure, heart rate, stroke volume, and cardiac output were measured. Total peripheral resistance was also derived. The anger interview produced larger, more sustained changes in blood pressure in both sessions than the other stressors. These changes were largely a consequence of increased peripheral resistance. Consistent with previous findings, handgrip was associated with a resistance-type reaction whereas arithmetic was associated with a cardiac output-type reaction. There was low-to-modest stability of hemodynamic reactions to the interview. Further research is necessary to optimize its utility in studies of cardiovascular function. Nevertheless, the findings underscore the ability of ecologically relevant stressors to provoke unique configurations of cardiovascular activity.     

Heart Rate and Oxygen Consumption during Mental Arithmetic,a Video Game,and Graded Exercise: Further Evidence of Metabolically-Exaggerated Cardiac Adjustments?

Heart rate, plus various metabolic and ventilatory indices, were monitored while 20 young male subjects were exposed to a video game and a stressful mental arithmetic task. Measurements were also made while subjects undertook graded isotonic exercise. All measures changed as a function of psychological challenge, and during exercise physiological activity increased as an orderly function of workload. For each subject, heart rate was plotted against oxygen consumption over the various exercise loads. For the majority of subjects the analogous data points for the video game and mental arithmetic lay reliably above the exercise heart rate-oxygen consumption regression lines. When these regression lines were used to predict heart rate values during psychological challenge, the predicted values were significantly less than the values actually recorded for both tasks; although the discrepancy between predicted and actual values was on average greater with mental arithmetic, the difference was not statistically reliable. Pre-stressor baseline conditions were also associated with heart rate levels greater than predicted, albeit to a lesser extent. Finally, while both stressors produced heart rate adjustments additional to expectancies, inter-task consistency was low.     

T-wave amplitude utility revisited: some physiological and psychophysiological considerations.

The last decade has seen some quite polemicized discussions concerning the utility of T-wave amplitude as a psychophysiological measure, but more recent reports indicate that we are now moving into a more empirically oriented and analytic examination of this topic. Such a report is one by Contrada et al. (1989), who manipulated sympathetic (beta-adrenergic) influences both pharmacologically and behaviorally, and whose main conclusion was that their results "support the hypothesis that T-wave is significantly affected by beta-sympathetic influence on the heart". However, we question their other conclusion that "a nonspecific effect of heart rate change on T-wave amplitude would also account for these results", and also suggest that their discussion of the "implications for the utility of T-wave amplitude in psychophysiological research" bears further consideration. In particular, for psychophysiologists, of fundamental importance is the distinction between T-wave amplitude's utility as a physiological index and its utility as a psychophysiological index. Concerning the former issue, we consider: (a) the alpha/beta adrenergic distinction, (b) inappropriate T-wave amplitude augmentation effects to sympathomimetic stimulation, (c) the nonspecific-response-to-tachycardia argument, and (d) the view of pulse transit time as a criterial standard, rather than as a candidate index. Regarding the issue of psychophysiological index utility, we consider: (a) dependent-variable sensitivity, drawing a further distinction between reactive and specific sensitivity, and (b) independent-variable-manipulation effectiveness.