Information Processing and Cardiovascular Control

It has previously been reported that an increase in mental task load is accompanied by a decrease in heart rate variability (HRV). In most of the experiments relating mental task load to HRV, the number of signals in paced choice reaction time tasks served as the main loading factor. However, this determinant of task load confounds muscular and mental load. In the present article we scored HRV by computing the power spectrum of the cardiac interval signal. The spectrum contains power related to respiratory activity (usually between 0.20 and 0.40 Hz) and power related to non-linear processes involved in the control of body temperature and blood pressure (between 0.02 and 0.20 Hz). During performance on cognitive tasks the total power is attenuated, but the spectral power between 0.02 and 0.20 Hz (comprising about 80% of the total spectral energy, i.e. HRV) is particularly affected. Within this latter region we especially investigated the power between 0.06 and 0.14 Hz. The power in this region is believed to originate from processes involved in the dynamic control of mean arterial pressure. In Experiment 1 it was shown that this blood pressure-related spectral component was rather insensitive to considerable changes in respiratory rate and depth. In Experiments 2 and 3 we kept signal rate constant but varied the cognitive demands of a sentence comprehension task and a working memory task. These experiments indicated that the power of the 0.10 Hz vasomotor oscillations was significantly affected by the processing demands of these tasks. The evidence suggested a decreased baroreflex sensitivity (i.e. a decrease in gain) during mental loading. A method was proposed to non-invasively determine baroreflex sensitivity.     

小波变换用于从血压信号中提取呼吸及心率信息的研究

本文提供了一种新的数字信号处理工具一小波变换和小波分析程序流程图,可用于重量及其它学科科研实验研究。文中给出了利用Gauss一介导数小波变换从家兔动脉血压信号中提取呼吸频率及心率的方法。     

Cardiovascular response to Stroop: effect of verbal response and task difficulty

The purpose was to examine the effect of verbal response and task difficulty on cardiovascular response to the Stroop task. Heart rate, mean arterial blood pressure, forearm blood flow (FBF), and catecholamine response of 13 males was assessed during 3, 5-min differing versions of the Stroop task. Heart rate, epinephrine, and FBF were significantly greater during Stroop 1 (the color-word conflict task) compared to Stroop 3 (a non-verbal version of Stroop where participants responded cognitively without any oral or behavioural response), whereas mean arterial pressure was significantly greater during Stroop 1 than that of Stroop 2 (slides in monochrome without color conflict) and Stroop 3. Rating of level of difficulty and concentration was lower for Stroop 2 compared to the other two Stroop tasks. These results suggest that performance of the traditional Stroop task caused significant cardiovascular, FBF, and epinephrine reactivity. This reactivity was attenuated during reading of monochrome words and was virtually abolished when performing the Stroop without verbally responding.     

Cardiovascular reactivity in real life settings: Measurement, mechanisms and meaning

Cardiovascular reactivity to stress is most commonly studied in the laboratory. Laboratory stressors may have limited ecological validity due to the many constraints, operating in controlled environments. This paper will focus on paradigms that involve the measurement of cardiovascular reactions to stress in real life using ambulatory monitors. Probably the most commonly used paradigm in this field is to measure the response to a specific real life stressor, such as sitting an exam or public speaking. A more general approach has been to derive a measure of CV variability testing the hypothesis that more reactive participants will have more variable heart rate or blood pressure. Alternatively, self-reports of the participants’ perceived stress, emotion or demands may be linked to simultaneously collected ambulatory measures of cardiovascular parameters.This paper examines the following four questions: (1) What is the form and what are the determinants of stress-induced CV reactivity in real life? (2) What are the psychophysiological processes underlying heart rate and blood pressure reactivity in real life? (3) Does CV reactivity determined in the laboratory predict CV reactivity in real life? (4) Are ambulatory cardiovascular measures predictive of cardiovascular disease?It is concluded that the hemodynamic processes that underlie the blood pressure response can reliably be measured in real life and the psychophysiological relationships seen in the laboratory have been obtained in real life as well. Studies examining the effects of specific real life stressors show that responses obtained in real life are often larger than those obtained in the laboratory. Subjective ratings of stress, emotion and cognitive determinants of real life stress (e.g. demand, reward and control) also relate to real life CV responses. Surprisingly, ambulatory studies on real life cardiovascular reactivity to stress as a predictor of cardiovascular disease are rare. Measuring the CV response to stress in real life may provide a better measure of the stress-related process that are hypothesized to cause disease than is possible in the laboratory. In addressing these questions, below we review the studies that we believe are representative of the field. Therefore, this review is not comprehensive.     

Cardiovascular Reactivity to Psychological Stress in Healthy Children

Cardiovascular reactivity to stress has been implicated as a marker and/or mechanism in the development of cardiovascular disease. No normative data exist to classify children's reactivity to psychological stress. This investigation presents normative percentile data on the hemodynamic responses (heart rate and blood pressure) of 310 healthy, black or white, children between the ages of 6 and 18 years to the stress of a television video game. A series of three video games, played under three increasing levels of stress, elicited progressively higher values of blood pressure and heart rate. Both the child's race and gender, as well as the experimenter's race, significantly affected reactivity. Children demonstrated a wide range of interchild reactivity, thus allowing separation of individuals into high and low risk percentile groups.     

Cardiovascular autonomic responsiveness in postmenopausal women with and without hot flushes

Objectives

During menopausal transition autonomic balance is known to shift towards sympathetic dominance, but the role of vasomotor hot flushes in this phenomenon is not understood. We compared cardiovascular autonomic responsiveness between women with and without hot flushes.

Study design and main outcome measures

One hundred fifty recently postmenopausal healthy women with varying degree of hot flushes (none, mild, moderate, severe) underwent comprehensive cardiovascular autonomic nervous testing (controlled and deep breathing, active orthostatic test, Valsalva manoeuvre and handgrip test) assessing both sympathetic and parasympathetic activity. The responses of heart rate, heart rate variability and blood pressure in these tests were evaluated.

Results

Responses in heart rate showed differences between the study groups only in the Valsalva manoeuvre where the tachycardia ratio in all symptomatic women was lower (p = 0.041) than in women without hot flushes. Neither change in the heart rate variability analyses nor the blood pressure responses were affected by hot flush status. However, there was a non-significantly higher maximum systolic (140 (112–182) mmHg vs. 135 (102–208) mmHg) and diastolic blood pressure (94 (72–112) mmHg vs. 90 (66–122) mmHg) following the handgrip test in women without hot flushes vs. all the symptomatic women.

Conclusions

Menopausal hot flushes seem to be associated with a possibly increased sympathetic preponderance without an effect on parasympathetic activity in cardiovascular autonomic responses. This may imply a potentially negative impact on cardiovascular health in women experiencing hot flushes.     

One-handed load carrying — Cardiovascular,muscular and subjective indices of endurance and fatigue

Summary A group of 5 women and 11 men walked on a treadmill, each carrying a weight in the right hand. In separate experiments, the mass was varied to give total exhaustion within 3 min, 5 min, 9 min, and 13 min. In additional experiments 50% and 25% of the masses leading to exhaustion after 5 min were used, and these were stopped after 16 min. Heart rate (f _c) and systolic blood pressure (BP_s) were measured noninvasively. There was a consistent increase in (f _c) x BP_s during the experiments leading to exhaustion, while steady-states were obtained in the nonexhausting trials. An electromyogram (EMG) was recorded with cutaneous electrodes over the flexor carpi ulnaris and flexor digitorum superficialis muscles and the number of zero crossings (ZC) of the EMG signal per time unit were analysed. As the subjects approached exhaustion, the number of ZC declined exponentially, reaching approximately 50% of their initial values. In the nonexhausting experiments, however, the decline was slower and less marked, and during the second half of the experiment the number of ZC increased again. Subjectively, endurance was underestimated by all the subjects. It was concluded that cardiovascular and muscle criteria of fatigue in carrying coincided. Prolonged carrying in one hand of more than 6 kg or 10 kg for young healthy women and men respectively should not be recommended, since it could lead to cardiovascular non steady-states and EMG signs of fatigue.     

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.     

Alternate Cardiovascular Baseline Assessment Techniques: Vanilla or Resting Baseline

The accurate evaluation of cardiovascular reactions to psychological challenge requires stable baselines against which change can be evaluated. When more than one challenge is employed, the recovery of this baseline becomes important in order to avoid carryover effects. Resting periods, even those of 20 min or more, do not guarantee baseline stability. We compared a 20-min resting condition and a new form of baseline condition in 48 college men using video tasks as the psychological challenges. The new form was a minimally demanding color detection task, termed the "vanilla" baseline condition. A 10-min version and a 20-min version of this condition were tested. Comparisons to 10-min resting baselines were made using our prior work and values from the literature. Vanilla baseline conditions were shown to be equal to or better than resting baseline conditions using criteria of between- and within-baseline stability, amplitude and significance of responsivity, and generalizability between sessions on separate days. Ten-minute resting baselines also showed acceptable stability, questioning the value of lengthy baselines. The good performance of the 10-min vanilla baseline in initial and replication samples supported its utility for estimating baselines for many purposes.     

Cardiovascular Reactivity in Borderline Hypertensives during Behavioural and Orthostatic Stress

Blood pressure and heart rate were measured in 16 borderline hypertensive and 10 normotensive subjects during mental arithmetic and reaction time tests, on standing, and during the pre-test period and instructions preceding these tests. The reliability of responses was assessed on 3 consecutive days. Increases in systolic blood pressure and heart rate during mental arithmetic instructions, increases in systolic blood pressure during the mental arithmetic test, and increases in diastolic blood pressure on standing were greater in borderline hypertensives. These differences persisted throughout the 3 experimental sessions. Apart from stress ratings for the reaction time test, other behavioural measures, including number of mental arithmetic mistakes and reaction times, did not differ between normotensives and borderline hypertensives. The possibility that the parasympathetic nervous system exerts a restraining influence on sympathetic overactivity in borderline hypertension was discussed.     

Cardiovascular effects of static and dynamic exercise

Summary The cardiovascular response to static exercise has often been quantified on the basis of a comparison between static handgrip and dynamic cycling exercise. It is then difficult to make precise comparisons because the physical units of work are not compatible. If the data from dynamic exercise can be used to predict the cardiovascular response to zero movement (static exercise) this would suggest that static exercise is not fundamentally different from dynamic exercise. Using leg extension exercise which lasted for 1 min, a set of weights was lifted repeatedly 50 times/min, through three different distances. On each occasion, the heart rate, systolic time intervals (STI) and systemic arterial blood pressure were monitored non-invasively. Regression analysis of heart rate (HR) or blood pressure (BP) against the distance moved by the weights was used to predict the heart rate or blood pressure that would be expected for static exercise. In addition the same responses were measured following 1 min of static exercise during which the weights were held up but not moved. Five subjects, trained in leg extension exercise, completed the four exercise sessions in a random order. A constant force was produced in each variant of the protocol and in the static exercise it amounted to 50% maximal voluntary contraction (MVC). The forces developed and the distance the weights were lifted were monitored. During this sustained static exercise at relatively low intensity the cardiovascular changes could be predicted from the responses induced by dynamic exercise. It is suggested that other factors are important in determining the cardiovascular response to exercise, not simply the mode.     

Cardiovascular changes during the sleep-wake cycle in spontaneous hypertensive rats and in their genetically normotensive precursors

Blood pressure and heart rate were recorded in spontaneously hypertensive rats (SH) and in their genetically normotensive precursors (WKY) during the sleep-wake cycle using a computer-assisted method. Similar results were obtained in both strains: (a) No significant difference was observed in blood pressure values between slow-wavesleep (SWS) and the last 2 min of the preceding wakefulness (W) episode within the complete cycle; blood pressure then increased duringPS. (b) Heart rate values during SWS were significantly lower than those computed for W; a further fall of heart rate was observed during paradoxical sleep (PS) only in hypertensive rats. (c) During SWS the blood pressure and heart rate variability was significantly lower than during W and PS. In addition, blood pressure variability values during the three sleep-wake states were lower in hypertensive than in normotensive rats. These data suggest that there are no qualitative differences in the mechanisms that control eirculation during sleep in normotensive and spontaneous hypertensive rats.     

Cardiovascular effects of septal,thalamic, hypothalamic and midbrain self-stimulation

A positive correlation was found between the lever-pressing rate and the variability in the cardiovascular and respiratory effects elicited by septal, thalamic, hypothalamic and midbrain self-stimulation in cats. This correlation showed that all electrode placements which support self-stimulation are also capable of eliciting appropriate cardiovascular effects. The common characteristic of these effects was an increase in blood pressure, average respiratory and heart rates, and a decrease in pulse pressure during stimulation. Up to an unfavourably high level in the cardiovascular functions, self-stimulation at high rates was regularly assocaited with higher amplitude cardiovascular effects as compared to self-stimulation at low rates. Nonrewarding stimulation sites failed to evoke statistically significant changes in the cardiovascular responses. The instrumental alimentary behaviour was accompanied by an increase in blood pressure of about the same magnitude as self-stimulation at high rates. It was concluded that the cardiovascular effects are essential components of the behavioural pattern elicited by self-stimulation.     

Coronary-Prone Behavior Pattern, Task Incentive, and Cardiovascular Response

In this experiment it was predicted that the presence or absence of a performance-contingent incentive (monetary reward) would mediate effects of the coronary-prone behavior pattern on behavioral and cardiovascular responses to a difficult cognitive task. Accordingly, 44 subjects of the Type A (coronary-prone) and Type B (non-coronary-prone) behavior patterns were assigned to one of two task conditions, labelled Incentive and No Incentive. Results indicated that under No Incentive Type As performed better at the experimental task and reported less state anxiety than Type Bs, whereas in the Incentive condition, Type A and B subjects showed no differences in task performance or self-report of anxiety. Concerning cardiovascular measures, analysis of variance revealed significantly greater systolic blood pressure and pulse pressure elevations for Type A than Type B subjects, but showed no reliable interactions of the Type A, B and Incentive factors nor any related effects regarding heart rate or diastolic blood pressure. Individual differences in subjects' scores on the inventory for coronary-prone behavior pattern, however, correlated positively with heart rate accelerations in the No Incentive condition, but did not covary with heart rate changes under Incentive. With respect to subjects' perceptions of the task, self-report data suggested that Type As responded in a more active and involved manner and resisted feelings of helplessness to a greater extent than their Type B counterparts.     

Cardiovascular Changes During Classical Conditioning in the Squirrel Monkey

Changes in blood pressure (BP) and heart rate (HR) were classically conditioned in squirrel monkeys using light as the conditional stimulus, and electric shock as the unconditional stimulus. The transient (lasting less than 5 min) and sustained (maintained for a half-hour or more) changes in BP and HR in response to light-shock (LS) pairs and light alone (L) were measured while varying rates of presentation and shock intensity. LS presentation produced transient increases in both BP and HR. The magnitude of the change increased with shock intensity and decreased as stimulation rate increased. Transient changes in BP and HR in response to L presentation were induced by conditioning with LS. The conditioned transient response to L alone was greater when the LS conditioning period preceding it had greater shock intensity or slower presentation rate. Sustained changes in BP and HR were also produced by LS, the magnitude of which were directly related to the frequency of aversive stimulus presentation. Transient changes, in contrast, decreased in magnitude with more frequent presentation.     

Neuroendocrine and Cardiovascular Stress Reactivity in Middle-Aged Normotensive Adults with Parental History of Cardiovascular Disease

Neuroendocrine and cardiovascular stress reactivity was studied in healthy middle-aged individuals whose parental history included essential hypertension and/or myocardial infarction and a control group without parental history of cardiovascular disease. All subjects completed a rest session (1 hour) and a stress session (1 hour). The stress session included behavioral (mirror image tracing, mental arithmetic, and the Stroop color word conflict test) and physical stressors (the cold pressor test and isometric exercise). Systolic and diastolic blood pressures and heart rate were recorded at baseline before and during all stressors. Specimens for determination of urinary catecholamines and cortisol were sampled after the rest and stress sessions respectively. Generally, a parental history of hypertension but not of myocardial infarction influenced neuroendocrine and cardiovascular stress reactivity. A family history of hypertension was associated with exaggerated epinephrine, norepinephrine, and cortisol excretion during stress and with enhanced heart-rate reactivity to behavioral (mental arithmetic and mirror image tracing) but not to physical stressors (isometric exercise or the cold pressor test). We conclude that individuals with a family history of hypertension tend to display exaggerated cardiovascular and neuroendocrine reactivity to stress.     

Cardiovascular and Electrodermal Response Patterns in Heart Rate Reactive Individuals During Psychological Stress

The goal of this research was to examine the cardiovascular and electrodermal response patterns of heart rate reactive and nonreactive individuals to psychological stress. Sixty males were tested while resting, listening to tones, identifying tone patterns, and performing mental arithmetic. Dependent variables were blood pressure, heart rate (HR), and skin conductance responses. Based on the change in HR from baseline to the first minute of mental arithmetic, two extreme reactivity groups of 15 subjects each were formed. Results indicated that HR reactive subjects had higher systolic blood pressure and HR than nonreactives. Reactives showed greater HR lability during all the tasks and a phasic acceleration to tones, while nonreactives showed a deceleration. Finally, comparisons of skin conductance responses indicated that subjects who were nonreactive when measuring HR were more reactive when measuring skin conductance. The HR reactivity seen in these subjects has been linked to predisposition to psychosomatic illness, and the current findings are discussed in that light.     

Task Difficulty, Type A Behavior Pattern, and Cardiovascular Response

Forty-one young male subjects performed either an easy or moderately difficult arithmetic task with the opportunity to earn a monetary incentive if they did well. Cardiovascular (heart rate, systolic and diastolic blood pressure) and subjective responses were assessed immediately prior to and 5 min following task performance. Results indicated greater systolic (SBP) responses during the Pre-task period for subjects expecting to perform the difficult task. Behavior pattern classifications based on the Jenkins Activity Survey revealed Higher Pre-task heart rate (HR) elevations among Type As compared to Bs in the Difficult task condition, and greater Pre-task SBP responses in As compared to Bs irrespective of task difficulty. There also was some evidence of an association between SBP reactivity and scores on the Thurstone Activity scale. Change-scores reflecting SBP and HR reactivity were correlated in the Pre-task period of the Difficult but not the Easy condition. Predictions regarding the impact of motivational arousal upon goal attractiveness were not supported, possibly for methodological reasons.     

Aerobic Fitness and Opioidergic Inhibition of Cardiovascular Stress Reactivity

The role of endogenous opioids in aerobic fitness-induced decrements in cardiovascular stress reactivity was examined by comparing the effects of opioid antagonism with naltrexone on responses to stress in young adults with high versus low levels of aerobic fitness. Two hundred forty subjects were given an activity questionnaire and males with the highest (Fit) and lowest (Nonfit) aerobic activity profiles were recruited for maximal oxygen consumption (VO2max) treadmill testing and psychological stress testing (final sample N = 28). Heart rate and blood pressures were measured during performance on a computer-controlled arithmetic task after pretreatment with either naltrexone (Trexan, DuPont) or a placebo. During placebo challenges, Fit subjects, compared with Nonfit, showed lower heart rate reactivity during stress and lower mean arterial blood pressures immediately before and during recovery from stress. Naltrexone eliminated these reactivity differences by increasing heart rate reactivity and raising mean arterial blood pressure in Fit subjects. These data suggest that aerobic fitness is associated with enhanced opioidergic inhibition of circulatory stress reactivity. Opioidergic modulatory effects on stress reactivity may comprise an important mechanism in fitness-associated risk reduction for cardiovascular disease.     

Cardiovascular responses of rabbits to ESB: Effects of anesthetization,stimulus frequency and pulse-train duration

Chronically prepared rabbits received short (1.0 sec) or long (10 sec) pulse-trains of electrical stimulation in septal region or hypothalamus. One sec trains of 50-, 100-, and 200-pulse pairs per sec (p.p.p.s.) elicited equivalent cardiovascular responses (i.e., an increase in mean systemic arterial blood pressure accompanied by bradycardia) provided current-intensity was increased as pulse-frequency was decreased; whereas, cardiovascular responses were attenuated or abolished by 12–25 p.p.p.s. stimulation. Anesthetization (25 mg/kg sodium pentobarbital) attenuated cardiovascular responses to stimulation and converted the pressor increase elicited by the 1.0 sec pulse-train into a depressor response. In contrast to the single cardiovascular pattern elicited by the 1.0 sec train at all electrode sites, several cardiovascular patterns were obtained by stimulating different sites in unanesthetized rabbits with a 10 sec train. The differences in result following stimulation with 1.0 and 10 sec pulse-trains were discussed in terms of (a) higher current-intensity required to elicit cardiovascular responses with a 1.0 sec train, and (b) possible modulation of baroreceptor responses occurring during the longer train.