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.     

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.     

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.     

Cardiovascular responses to occupational stress and caffeine in telemarketing employees

Cardiovascular responses to the combination of caffeine and a challenging occupational activity were examined using a within-subject, double-blind design. Seventeen female and 11 male telemarketing employees received drinks that did and did not contain 250 mg of caffeine on two consecutive days, with order of presentation counterbalanced across subjects. Repeated measurements of systolic and diastolic blood pressure, heart rate, and digital blood volume pulse were obtained during a pre-drug resting baseline and a post-drug working period on each day. Repeated measures analyses of variance revealed significant main effects of Period on all measures of cardiovascular activity, indicating that occupational demands elicited significant cardiovascular adjustments. Only systolic blood pressure revealed a significant Drug X Period effect, indicating that responses were significantly greater on the caffeine versus placebo day. The changes in diastolic blood pressure and heart rate, although not significant, were consistent in direction with the results from previous laboratory studies. There were no significant differences between males and females in cardiovascular response to the combination of stress and caffeine.     

Familial influences on heart rate, blood pressure, and self-report anxiety responses to stress: Results from 100 twin pairs

Two hundred healthy adolescent to middle-aged individuals (12–44 years, M= 20 years) were tested in a standardized stress protocol. These individuals comprised 20 monozygotic female, 20 monozygotic male, 20 samesex dizygotic female, 20 same-sex dizygotic male, and 20 opposite-sex dizygotic twin pairs. Familial influences on heart rate, blood pressure, and self-report anxiety responses to four different kinds of stressors (Visual-Verbal Test for Conceptual Thought, mental arithmetic, isometric handgrip, cold pressor) were assessed using biometrical genetic model fitting. Evidence of significant genetic effects on resting heart rate and blood pressure was obtained, providing heritability estimates of .65, .63, and .58 for resting heart rate and systolic and diastolic blood pressure, respectively. Cardiovascular reactivity to the Visual-Verbal Test, mental arithmetic, and the cold pressor test appeared to be primarily influenced by genetic and idiosyncratic (nonfamilial) environmental factors, whereas reactivity to handgrip was more related to effects of the family environment. The results of multivariate model fitting suggested that the genetic effects on reactivity were relatively independent of those affecting resting heart rate and blood pressure and that there was significant overlap of genetic influences on heart rate and blood pressure responses to the two active coping tasks.     

Race, Parental History of Hypertension, and Patterns of Cardiovascular Reactivity in Women

This study examined the interaction of race and parental history of hypertension on patterns of cardiovascular responses among women. Two stressors were used that produce different patterns of cardiovascular reactivity: mental arithmetic, primarily a beta-adrenergic stimulus, and the cold face stimulus, which evokes alpha-adrenergic (i.e. vascular) activity. Systolic and diastolic blood pressure, heart rate, forearm blood flow, and forearm vascular resistance were assessed before, during, and after arithmetic and cold face stimulus. Both tasks produced the expected patterns of cardiovascular adjustment, although no Black-White differences occurred during arithmetic. However, Black subjects did show a slower recovery of diastolic blood pressure following arithmetic. The cold face stimulus produced significantly greater changes in systolic blood pressure in the Black than in the White women. Parental history of hypertension did not relate significantly to reactivity. The results provide limited support for the idea that Black females exhibit a greater pressor response than White females to a stimulus that produces primarily vascular rather than cardiac changes. These findings are discussed in relation to previous findings with males and with respect to their implications for the role of reactivity in Black-White differences in hypertension prevalence.     

Psychophysiological Response Patterns to Single, Double, and Triple Stressors

Synergistic activation elicited by multiple stressors as compared to single stressors has received little attention in the literature. In the present study, mental arithmetic, cold pressor, and physical exercise tasks were administered to 54 male subjects alone and in all possible simultaneous combinations. The dependent variables measured were heart rate, cardiac output, RZ-time, blood pressure, respiration rate, tidal volume, respiratory minute volume, oxygen uptake, oxygen equivalent, self-report data of psychological and somatic tension, pain ratings during the cold pressor test, and performance on mental arithmetic. Results for physiological variables indicate synergistic effects for stressor combinations as compared to single stressors, depending on the respective combination or variable. Contrary to this finding, psychological variables revealed ceiling and depressor effects. Response patterns to the different stressors showed only moderate similarity and exhibited stimulus-specific effects. Heart rate, diastolic blood pressure, and respiration rate were most appropriate in describing various response patterns.     

The effect of noise interference, type of cognitive stressor, and order of task on cardiovascular activity

In the search for reliable, easily applicable mental stressors many researchers have investigated the propensity of mental arithmetic and Stroop color discrimination tasks to elicit a physiological stress response; some researchers have added noise interference with the expectation of larger response magnitudes. The present study investigates a number of previously untested questions by directly comparing cardiovascular responses to mental arithmetic or the Stroop task with and without noise interference in a sample of 66 young adults. Half of all subjects were exposed to the additional noise interference, all subjects responded to both types of mental stressors. Blood pressure responses did not discriminate among the stressors but noise interference consistently augmented heart rate responses during mental arithmetic. Response to the second, repeated stressor was associated with highly significant response habituation effects for blood pressure. Furthermore, when mental arithmetic was presented first, both tasks elicited comparable and large responses; when the Stroop test was presented first both tasks triggered smaller responses but of comparable magnitude. Subjective evaluations of the stressors were not predictive of overall physiological response.     

Cardiovascular Effects of Caffeine and Stress in Regular Coffee Drinkers

The effects of caffeine on cardiovascular activity at rest and in response to psychological stress were studied in a group of 30 healthy males who were regular coffee drinkers to replicate caffeine-stress interactions found previously in caffeine-naive subjects. Measures of heart rate, blood pressure, and forearm blood flow were recorded at rest and during the performance of a stressful mental task in two separate sessions. Caffeine (250 mg) or placebo was administered double-blind in a within-subject design. Relative to placebo, caffeine had a pressor effect at rest which persisted during stress and recovery such that blood pressure during stress was higher if caffeine had been consumed. Caffeine also magnified the forearm blood flow and forearm vascular resistance responses to stress, suggestive of a synergistic interaction of caffeine and stress. Analysis of individual difference variables suggested that caffeine effects on the forearm vascular variables were greatest in subjects who were Type B and had a positive family history of hypertension. Results suggest that regular caffeine use does not necessarily lead to tolerance for caffeine-stress interactions and that certain characteristics may be associated with greater sensitivity to caffeine's effects.     

The Effects of Caffeine and Stress on Blood Pressure in Individuals with and without a Family History of Hypertension

The effects of two doses of caffeine (125 mg, 250 mg) were compared to a placebo dose (3 mg) in a randomized double-blind cross-over design in 36 male caffeine users, half with and half without a family history of hypertension. Systolic blood pressure, heart rate, and respiration were recorded during rest, a mental arithmetic task, and recovery periods. I inter both resting and mental stress conditions, the two doses of caffeine on the average increased systolic pressure by 6.7 mini In compared to the placebo. The effects for the 125 me and 250 mg doses did not differ significantly. The pressor effects of caffeine and mental stress combined in an additive fashion. Systolic blood pressure levels were significantly greater in individuals with a family history of hypertension across all conditions, but not specifically in response to caffeine. The results arc comparable to those previously reported in caffeine-naive subjects.     

Vascular responses to fear-induced stress in humans

The information about the effect of mental activities on detailed cardiovascular responses is limited, though strong and chronic psychological stressors are risk factors of cardiovascular morbidity and mortality in humans. The responses of vascular resistance (VR) during fear-induced stress was studied by measuring the mean arterial pressure (MAP), heart rate (HR), skin blood flow in the index finger and forehead, limb blood flow in the calf and forearm, and blood flow in the renal and superior mesenteric arteries before, during, and after a period of induced fear. After 2 min of rest, baseline data were acquired from eight subjects, after which they watched a 3-min video that was considered to be frightening. Minute-by-minute data were calculated. The MAP was divided by the blood flow to attain the VR. While a clear steady state was not evident in the stress-induced vascular response, stress significantly increased the MAP and HR (e.g., by 10 ± 3 mm Hg and 8 ± 3 bpm, respectively, at the 2nd min; mean ± SEM), and the VR of the forearm and finger skin (e.g., by 80 ± 26% and 79 ± 28%, respectively, at the 2nd min). The VR increased slightly in the calf and visceral arteries but not in the forehead throughout the stimulation. The variables returned to baseline levels by the 1st min after cessation of the fearful stimulation. These results suggest that fear-induced stress causes vasoconstriction in the forearm and finger.     

Cardiovascular reactivity to stress in black male offspring of hypertensive parents

The forearm blood flow (FABF) and other cardiovascular responses of 20 black men with a parental history of hypertension were compared with the responses of 18 black men without a parental history of hypertension. The results showed that sons of hypertensive parents had higher systolic (SBP) and diastolic (DBP) blood pressure than sons of normotensive parents during the initial assessment as well as significantly higher self-determined home SBP. Sons of hypertensive parents had higher SBP responses than sons of normotensive parents during mental challenge and the cold pressor, but there were no group differences in DBP, heart rate (HR), (FABF), or forearm vascular resistance (FAVR) responses to the stressors. Significant positive correlations between HR and FABF responses to the stressors were observed for sons of hypertensive parents. Finally, the results showed that the BP and FAVR responses to the cold pressor (a painful task that elicits alpha-adrenergic activity) were significantly higher than responses to mental challenge (a task that elicits beta-adrenergic activity) for both groups. The implications of these results are discussed in light of current research suggesting that blacks may have a greater tendency toward BP responses mediated by alpha-adrenergic increases in vascular resistance.     

Respiratory Sinus Arrhythmia and Cardiovascular Responses to Stress

The parasympathetic nervous system provides mechanisms that could attenuate sympathetically mediated heart rate stress responses and might have even more general antagonistic actions on stress reactivity. Individuals characterized by higher levels of parasympathetic tone might, through such mechanisms, be less reactive when stimuli elicit sympathetically mediated responses. Respiratory sinus arrhythmia (RSA) is considered to be a noninvasive index of cardiac parasympathetic (vagal) tone. The present study investigated whether individual differences in RSA level at rest could predict variations among individuals in the magnitude of cardiovascular responses to psychological stress. None of the measures of resting respiratory sinus arrhythmia, derived from spectral analysis of beat-to-beat changes in resting heart rate, predicted the observed variations in cardiovascular task reactivity. However, scores reflecting respiratory sinus arrhythmia as the percentage of total heart rate variability (RSAnorm) were negatively correlated with blood pressure levels, both at rest and during the task. Furthermore, subjects with higher scores for RSAnorm demonstrated a faster adaptation of heart rate responses during stress, which suggests the development of parasympathetic antagonism to ongoing sympathetic arousal. Although a simple relationship between respiratory sinus arrhythmia and reactivity was not observed, these results encourage further investigation of RSA measures as psychophysiological indices of individual differences in parasympathetic (vagal) cardiac tone, or perhaps of general parasympathetic/sympathetic balance, which could modulate the expression of potentially pathogenic stress responses.     

Short-term effects of alcohol on peripheral blood flow, platelet aggregation and noradrenaline output in normal man

The effects of acute oral administration of alcohol on finger and forearm blood flow, platelet aggregation and plasma noradrenaline were examined over a three-hour period in a group of healthy male volunteers. Finger blood flow was increased at 15, 30 and 60 min and skin temperature was raised at 30 and 60 min. Digital systolic blood pressure was decreased at 15 and 30 min. No change in forearm blood flow was observed. A linear correlation was observed between finger blood flow, skin temperature and plasma alcohol concentrations. No significant changes were observed in platelet aggregation nor in plasma noradrenaline levels. Alcohol appears to have a greater effect on digital and skin blood flow as compared with muscle blood flow.     

Psychophysiological Reactivity in Cardiac Transplant Recipients

To assess the contribution of the heart's autonomic innervation to reactivity to psychological stressors, hemodynamic responsiveness of the denervated human heart was examined in two studies. In Study 1, cardiac output measured by thermodilution. heart rate, and systolic and diastolic blood pressure responses to a 4-min mental arithmetic task were studied in 7 cardiac transplant patients during routine post-transplant cardiac catheterization. In Study II, 6 cardiac transplant patients, 5 normal controls, and 5 renal transplant patients participated in a 78-min psychophysiological stress protocol during which heart rate, systolic and diastolic pressure, and cardiac output (measured noninvasively by impedance cardiography) as well as serum epinephrine and norepinephrine were measured at baseline and while subjects performed mental arithmetic and reaction time tasks. In Study I, transplant patients showed significant increases, relative to baseline, in heart rate, systolic blood pressure, and cardiac output in response to mental arithmetic. The diastolic blood pressure response was marginally significant. In Study II, mental arithmetic produced significant reactivity in systolic blood pressure and marginally significant increases in heart rate and diastolic blood pressure in cardiac transplant patients. Reaction time produced only marginally significant diastolic blood pressure reactivity. Hemodynamic reactivity of the cardiac transplant group generally was lower than that of the two innervated groups, which generally were similar to each other. Although the small number of subjects makes conclusions tentative, these data suggest that: 1) Cardiac transplant patients are capable of significant reactivity to psychological stressors despite the absence of innervation of the heart, and 2) reactivity to these stressors is diminished relative to innervated control subjects. In the absence of cardiac innervation, reactivity is due to the vascular system and cardiac effects mediated by humoral factors.     

Cluster analyses of cardiovascular responsivity to three laboratory stressors

Seventy-three young normotensive male subjects were tested with an experimental protocol that included a reaction time, a mental arithmetic, and a cold pressor task. Physiological variables that were recorded included heart rate, stroke volume, pre-ejection period, blood pressure, total peripheral resistance, and respiratory sinus arrhythmia. In order to identify subgroups of subjects who differed in their pattern of autonomic responses to the tasks, the physiological change scores from baseline to the tasks for each subject were entered into a cluster analysis for each task. Ward's method was used as the clustering algorithm. The cluster analyses identified four clusters for the reaction time and mental arithmetic tasks, and five clusters for the cold pressor task. Although there was a wide range of patterns exhibited by cluster subgroups, most subjects who were reactive to the tasks showed response patterns that were qualitatively similar to the pattern of overall mean response by all subjects, albeit varying considerably in terms of quantitative response. Little evidence was generated for the consistency of extreme beta-adrenergic response from one task to another, although significant consistency was noted when milder beta-responders were included in the comparisons. Some consistency of alpha-adrenergic response noted across tasks, as well as significant consistency of being relatively nonreactive to the tasks.     

Resting parasympathetic status and cardiovascular response to orthostatic and behavioral challenges in type I insulin-dependent diabetes mellitus

Alterations in cardiac autonomic innervation are commonly seen in individuals with diabetes mellitus. In this study, we used a cluster analysis to quantitatively separate individuals with Type I insulin-dependent diabetes mellitus (1DDM) on the basis of assessment of autonomic mediation of resting cardiac function and compared these two IDDM groups with nondiabetic control subjects. One group, termed IDDM-1, exhibited respiratory sinus arrhythmia and resting heart rale (HR) at the same level as controls. A second group, termed IDDM-2, displayed significantly reduced respiratory sinus arrhythmia and elevated resting HR, indicating reduced parasympathetic cardiac input. Noninvasive physiological assessment of the subjects’ response to orthostatic maneuvers (supine, seated, upright tilt) and behavioral stressors (speech preparation, speech talking, mirror tracing, cold pressor) revealed abnormalities in cardiovascular regulation in the IDDM groups. Specifically, under supine resting conditions the IDDM-2 group exhibited reduced myocardial contractility and stroke volume. HR was accelerated in these subjects but not enough to compensate for the decreased stroke volume, and therefore cardiac output was not maintained at normal levels. Consequently, total peripheral resistance and hlood pressure were elevated in thcse subjects. Thus. for the IDDM-2 subjects, these data sugges that blood flow to the periphery is being sacrificed In maintain flow to the heart, lungs, and brain, which cannot sustain themselves anaerobically. The IDDM subjects, when compared with the control subjects, responded with similar magnitude and pattern of cardiovascular response to the behavioral stressors that selectively challenged the heart, vasculature, or both. However, the cardiovascular pattern produced by the IDDM subjects to the seated and uprigh postural challenges suggests that the IDDM-1, and to a certain extent the IDDM-2 subjects, evidenced difficulty in regulating vasomotor and/or venomotor tone to maintain blood pressure levels. Therefore, this study demonstrates a quantitative method for assessing resting parasympathetic status that distinguishes a group of IDDM subjects with abnormal resting cardiovascular regulation and response to challenge. This work was supported by Grants POI-HL36588 and T32-HL07426 from the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Public Health Service     

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.     

Neuroendocrine and cardiovascular reactivity to stress in mid-aged and older women: long-term temporal consistency of individual differences

We report long-term temporal consistency of stress-related neuroendocrine and cardiovascular variables in mid-aged and older women who performed mental math and speech stress tasks two times approximately 1 year apart. Epinephrine, norepinephrine, ACTH, cortisol, cardiac preejection period (PEP), respiratory sinus arrhythmia, heart rate (HR), blood pressure, and respiration rate were measured at baseline, after or during stressors, and 30 min posttask. Although there were exceptions, year-to-year Spearman coefficients showed mostly moderate to high consistency (rs approximately equal to .5-.8) for baseline, stressor, and posttask values. For reactivity, HR and PEP were most consistent (rs approximately equal to .65); consistency for other variables was moderate to low (rs approximately equal to .1-.4). Means of most variables changed from year to year. Results support the use of baseline, stressor, and posttask values in longitudinal studies.     

Fatness is related to blunted vascular stress responsivity, independent of cardiorespiratory fitness in normal and overweight men.

Obesity is associated with disturbed cardiovascular responsivity to mental stress, which may mediate psychosocial disease pathways. Whether being aerobically fit is protective against psychophysiological dysfunction in the presence of overweight or obesity is undetermined. Peripheral blood flow, blood pressure, and cardiac responses were measured during a 2-min mental stress task in 48 healthy men (aged 18-32 years). Mental stress-evoked increases in mean arterial pressure and heart rate, forearm vasodilatation, and cardiac parasympathetic withdrawal. Multiple linear regression analyses adjusted for age, peak oxygen uptake, and baseline forearm vascular resistance, revealed that greater fatness was related to a blunted vasodilatation response to mental stress (beta=-.31, p<.05). There were no interactive effects of fitness and fatness. Fitness does not appear to moderate the association between fatness and impaired vascular stress responsivity in normal and overweight men.