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.     

Work pressure and the type A behavior pattern exam stress in male medical students

The psychologic and physiologic effects of variations in occupational stress on Type A (coronary-prone) and Type B men have not previously been examined. Accordingly, 58 male medical students in two successive first-year classes (32 As, 26 Bs defined by interview) were tested for mood states, perception of work pressure, and for pituitary-adrenal and cardiovascular function during a period of minimal work pressure (no exams for 1 week) and during maximal work pressure (final exam week). All observations were made at the beginning of the school day, while the students were studying course material in the building where classes were held and study modules were located. Perceived stress and self-ratings of dysphoric moods increased significantly (ps less than 0.0005) for both groups during exams compared to no exams. Plasma cortisol concentrations increased significantly (+20%) from no exams to exams for both As and Bs. Heart rate increased significantly to exams (+8%) and did so slightly more for As (+9%) than for Bs (+7%), with As showing significantly higher rates in the work setting at both times. Systolic blood pressure increased nonsignificantly for both groups. The effect of the higher heart rate and the slight systolic blood pressure rise produced a significantly greater rate-pressure product for As than for Bs at both exams and no exams (p less than 0.005), with As showing a larger rise to exams than did Bs (+11% vs. +8%). Results indicate that the As had a higher level of tonic cardiovascular activation in the work place than the Bs, and that this was additive with the effects of increased work pressure.     

Exaggerated pressure response to exercise in men at risk for systemic hypertension

Normotensive persons at high risk of developing systemic hypertension have greater cardiovascular reactivity to mental and physical stressors. This study compared cardiovascular responses to exercise in normotensive men (aged 28 +/- 0.8 years [mean +/- standard error of the mean]) at high risk (positive parental history and high normal resting blood pressure [BP], n = 20) and at low risk (negative history, low normal BP, n = 15) of hypertension. All men had normal body weight and exercise tolerance. During graded supine bicycle exercise, 35% (7 of 20) of high-risk men had exaggerated BP responses (greater than or equal to 230/100 mm Hg) versus 0% of low-risk men, thus forming 3 groups (low risk, high-risk normal BP response, high-risk exaggerated response). Cardiac function was measured by nuclear cardiography. Cardiac index, peripheral resistance index, left ventricular ejection fraction and contractility index were measured at rest and during each exercise work load. High-risk exaggerated responders could not be distinguished from their high-risk normal-responding counterparts using resting BP or other cardiovascular variables. During exercise all 3 groups had equivalent increases in cardiac output. However, the high-risk exaggerated responders had blunting in peripheral resistance decline, resulting in excessive BP increases. This finding suggests an impaired capacity for exercise-induced vasodilation, indicating that the exaggerated response group may be at highest risk for future hypertension in these 3 groups.     

Caffeine, extended stress, and blood pressure in borderline hypertensive men

Caffeine increases blood pressure (BP), and its pressor effects are larger in borderline hypertensive (BH) men than in controls. This article extends findings of larger caffeine effects on BP at rest and to brief mental stress in BH to a new analysis of caffeine and prolonged mental stress in BH. In a double-blind, crossover study, 24 male BH (140/90 mmHg < BP < 160/95 mmHg) and 23 normotensive controls who were habitual caffeine consumers (NT; BP < 135/85 mmHg; negative parental history) worked on alternating mental stressors for 35 min after placebo or caffeine (3.3 mg/kg). Caffeine raised systolic blood pressure (SBP) and diastolic blood pressure (DBP) alone and during the extended tasks (all ps < .00001/.00001). BH had larger SBP and DBP increases over all postcaffeine periods (ps < .04/04) and larger DBP rises to the extended tasks after caffeine (p = .007). These combined effects led to undesirably high BPs (> 140/82 mmHg) relative to controls (< 130/75) during the 100 min after caffeine intake. Caffeine taken by BH at times of extended behavioral stress may elevate BP to a clinically meaningful degree. This research was supported by the Medical Research Service of the Department of Veterans Affairs and the National Heart Lung and Blood Institute of the National Institutes of Health, grant numbers HL32050 and HL07640. We thank Barbara McKey and Judith Silverstein for their efforts in data collection and Terrie Thomas for her valuable comments on an earlier version of this article.     

Simultaneous measurement of stroke volume by impedance cardiography and nuclear ventriculography: Comparisons at rest and exercise

We have conducted four major impedance cardiography (ZCG) studies to provide data on validity, reproducibility, and sensitivity of response to interventions. The reference technique was quantitative nuclear ventriculography (NVG). Subjects were healthy young men in situations where minimally invasive and unobtrusive techniques were preferred. Interventions used included caffeine ingestion and exercise. Validity of ZCG estimates of stroke volume index (SVI, ml/m²) was tested in 35 men at rest. SVI was 49±9 by ZCG and 46±7 by NVG (r=0.82). Measurements of SVI during bicycle exercise showed no overall difference by the two methods (F=0.26, P=NS). Vascular resistance index (mean BP/CI) increased comparably by both techniques (+9.6% by ZCG and +9.7% by NVG) following caffeine (3.3 mg/kg). The reproducibility of ZCG was demonstrated in the day-to-day consistency of caffeine's effect on vascular resistance in 3 other studies (+11.9%, 12%, and 8.9%). Reliability across and within days was shown by repeated tests in the same subjects (SVI, r's=.96, .92). Conclusion: Impedance cardiography was shown to be a useful noninvasive technique for evaluation of cardiodynamics in biomedical research since it was highly reproducible and yielded equivalent results of relative changes produced by pharmacological and physical challenge. In addition, there was good agreement with NVG in absolute values for grouped data. Supported by funds from the National Heart, Lung, and Blood Institute, HL32050; and the Medical Research Service, Department of the Veterans Affairs.     

Heart rate reactivity as a predictor of neuroendocrine responses to aversive and appetitive challenges

The present paper examines the neuroendocrine influences of aversive and reward incentives (noise and shock versus monetary bonuses) presented during reaction time tasks administered to 71 healthy men (ages 21 to 35) classified as being high (N = 30) or low (N = 41) in heart rate reactivity. High heart rate reactivity was defined as a peak heart rate increase or greater than 19 bpm to a cold pressor test administered on a different day. Independent groups of subjects worked on one of two visual reaction time tasks: either to avoid exposure to noise (115-dBA bursts) and shock (3.5 mV, 2 sec), or to earn monetary bonuses ($0.50). High heart rate reactors showed significant plasma norepinephrine rises from baseline both to aversive incentives and to reward, although they showed significant cortisol responses only during aversive incentives. In contrast, the low heart rate reactors were unresponsive in cortisol and norepinephrine during either type of incentive. These results support psychoendocrine models which view the norepinephrine response as being nonspecifically related to expenditure of effort regardless of the emotional connotations of the challenge, while cortisol is seen as being secreted primarily during periods of distress. The present data further suggest that cardiovascular reactivity is linked to neuroendocrine reactivity, possibly within the central nervous system.     

Caffeine may potentiate adrenocortical stress responses in hypertension-prone men

The effect of caffeine on blood cortisol levels and blood pressures was examined during rest and in response to a challenging psychomotor task in men with a low versus high risk of essential hypertension. Thirty-four healthy men ages 21-35 years were selected such that 17 were at high risk for hypertension (positive parental history and screening blood pressures of 135/85-155/95 mm Hg) and 17 were at low risk (negative parental history and no pressures above 132/84 mm Hg). Testing consisted of quiet rest (20 minutes); oral placebo (grapefruit juice) or caffeine administration (3.3 mg/kg in grapefruit juice); rest during a postdrug absorption period (40 minutes); work on an unsignalled simple reaction time task (15 minutes); and quiet rest (20 minutes). Blood pressures were recorded at 2-minute intervals, and blood samples were withdrawn via an indwelling catheter at the end of the baseline, drug absorption, task, and recovery periods. The combination of task plus caffeine produced the highest blood pressures in men at risk for hypertension. Cortisol levels were found to be sustained during rest in members of the high risk group after they had consumed caffeine, whereas members of the low risk group showed a modest decline. The high risk subjects also showed a significant rise in cortisol during (+3.7 micrograms/dl) and after (+4.0 micrograms/dl) work on the reaction time task after caffeine consumption.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of caffeine on vascular resistance, cardiac output and myocardial contractility in young men

The mechanisms by which caffeine typically elevates blood pressure (BP) in humans have not been previously examined using a placebo-controlled design. Accordingly, oral caffeine (3.3 mg/kg body weight, equivalent to 2 to 3 cups of coffee) was given on 2 days and a placebo was given on 1 day to 15 healthy young men using a double-blind, crossover procedure. All 3 test sessions were held during a week of caffeine abstinence. Multiple measurements were made on subjects at rest (baseline values) and over a 45-minute interval after ingestion of caffeine for BP, heart rate, systolic time intervals and thoracic impedance measures of ventricular function. Baseline measurements were highly reliable for each subject across all sessions and yielded means for placebo vs caffeine days that were not different. Caffeine increased systolic and diastolic BP (p less than 0.01) and decreased heart rate (p less than 0.05). The pressor effect was due to progressively increased systemic vascular resistance and resulted in greater stroke work (p less than 0.01). There was no indication that caffeine increased cardiac output or contractility. These actions of caffeine were replicable when each caffeine day was tested separately against the placebo day. These results suggest that caffeine use by persons with cardiovascular diseases should be examined to determine whether caffeine's enhancement of vascular resistance may contribute to systematic hypertension and/or create excessive demands for cardiac work.     

Predicting Response to a Reaction Time Task: Heart Rate Reactivity Compared with Type A Behavior

The present study measured somatic muscle, cardiovascular, and endocrine responses to an unsignalled, rewarded reaction time task and examined the relative contributions of heart rate reactivity and Type A behavior in accounting for variability in response to the task. Task responses were characterized by significant changes in muscle tension, heart rate, blood pressure, cardiac output, and plasma norepinephrine concentration. Subjects shown to be high heart rate reactors during an independent cold pressor test were found to produce the greatest changes in heart rate, systolic and diastolic blood pressures, ventricular ejection time, cardiac output, and rate-pressure product during the reaction time task. In contrast, Type As did not respond differently from Type Bs. The results indicate that heart rate reactivity is a relatively stable trait which generalizes from cold pressor to a nonaversive task and which accounts for much of the between-subject variability in cardiovascular response.