Effect of meal content on heart rate variability and cardiovascular reactivity to mental stress

Little is known about transient effects of foods and nutrients on reactivity to mental stress. In a randomized crossover study of healthy adults (n=20), we measured heart rate variability (respiratory sinus arrhythmia), blood pressure, and other hemodynamic variables after three test meals varying in type and amount of fat. Measurements were collected at rest and during speech and cold pressor tasks. There were significant postmeal changes in resting diastolic blood pressure (-4%), cardiac output (+18%), total peripheral resistance (-17%), and interleukin-6 (-27%). Heart rate variability and hemodynamic reactivity to stress was not affected by meal content. We recommend that future studies control for time since last meal and continue to examine effects of meal content on heart rate variability.     

Consistency of heart rate and sympathovagal reactivity across different autonomic contexts

Theories that psychophysiological reactivity constitutes a risk factor for coronary artery disease assume that reactivity is a consistent individual characteristic. We tested this assumption by measuring reactivity to three psychologically challenging tasks performed by 22 healthy subjects across different autonomic contexts produced by positional change. Dependent variables included heart rate (HR), low-frequency (LF; 0.04–0.15 Hz) and high-frequency (HF; 0.15–0.50Hz) heart period variability, and the LF/HF ratio. HR (r= .44, p < .05) and LF/HF ratio (r= .48, p= .03) reactivity were modestly correlated across the different autonomic contexts, but HF and LF power reactivity were not. These findings suggest that HR reactivity to psychological challenge is a modestly consistent characteristic of individuals, despite differences in autonomic context. Although the same is true of cardiac sympathovagal balance, reactivity of HF and LF power were less consistent.     

Temporal stability of heart period variability during a resting baseline and in response to psychological challenge

Central to the psychophysiologic reactivity hypothesis of the etiology of coronary artery disease is the assumption that reactivity is an individual characteristic that is stable over time. Although heart rate (HR) and blood pressure reactivity appear to meet this criterion, temporal stability of cardiac autonomic control as measured by analysis of heart period variability (HPV) has not been assessed. In this study, we tested the stability of HPV, measured in both the time and frequency domain, during a quiet, resting baseline and in response to 5-min mental arithmetic and reaction time tasks, in 20 normal subjects measured in three testing sessions during a 9-month period. Stability, assessed by the intraclass correlation coefficient (ICC), was excellent for resting baseline measures of HR and HPV, with ICCs of 0.68–0.86. However, HR and HPV reactivity to either arithmetic or reaction time tasks generally was less stable, with ICCs of 0.17–0.73, in contrast to results of previous studies demonstrating long-term Stability of HR responses to psychological challenge. Stability of aggregated reactivity scores was only slightly improved. Whether for individual tasks or aggregated measures, reactivity of total and low-frequency measures of HPV was moderately stable but stability of high-frequency HPV reactivity was poor.     

Individual differences in the autonomic origins of heart rate reactivity: the psychometrics of respiratory sinus arrhythmia and preejection period

Heart rate reactivity has been conceptualized, at least implicitly, as a unidimensional construct ranging from low to high, reflecting individual differences in adrenergic reactivity to daily stressors. However, an individual's classification as high in heart rate reactivity ignores possible individual differences in the autonomic origins of this reactivity. Sixty-eight women were exposed to orthostatic and speech stressors to determine the psychometric properties (postural stability, convergent and discriminant validity) of heart rate, preejection period, and respiratory sinus arrhythmia. Results revealed that (a) basal, stress, simple reactivity (stress - baseline), and residualized change indices of heart rate, preejection period, and respiratory sinus arrhythmia were stable across postures and (b) heart rate reactivity was significantly related to preejection period and respiratory sinus arrhythmia reactivity, whereas the latter two measures were unrelated. Reactivity classifications may therefore be significantly improved by attention to concurrent estimates of the activity of both autonomic branches.     

Heart period and heart period variability during sleep on the MIR space station

The long-term acclimation of cardiac rhythms to microgravity was studied in four astronauts aboard the Russian space station MIR during wakefulness and sleep. Sleep polygraphies were obtained between the third and the 30th day in space and, in addition, prior to mission on the ground. From each of the sleep polygraphies, beat-to-beat intervals of cardiac rhythms were determined. The response of heart period and heart period variability to the stimulus microgravity was tested during sleep across sleep stages and during waking. A lengthening of heart period by about 100 ms was found in space compared to measurements on the ground. The slowing of heart rate was more pronounced for non-REM sleep than for REM sleep. A systematic change in heart period in relation to the duration of the stay in space could not be detected. An analysis of heart period variability in the high frequency (respiratory sinus arrhythmia) band supports the hypothesis that the decrease of heart rate under microgravity is produced by an increase in parasympathetic activity. Testing the response of cardiac rhythms to microgravity across distinct behavioural states seems to be a powerful tool to investigate the cardiovascular system.     

Effects of paced respiration on heart period and heart period variability

The present study investigated psychophysiological responses to paced respiration of different frequencies. Twenty men and 20 women (mean age: 24.3 years) underwent five breathing conditions (paced with 0.15 Hz, 0.20 Hz, 0.25 Hz, 0.30 Hz, and unpaced), each lasting 5 min. As dependent physiological measures heart period, and different heart period variability (HPV) parameters were assessed. Psychological variables consisted of mood estimates as well as rated accuracy and effort to follow the pacing rhythm. HPV decreased with higher breathing frequencies, under paced and unpaced conditions, whereas mood ratings did not change. Subjects indicated more effort and less accuracy in following the pacing signal, the more its frequency differed from their spontaneous breathing frequency. The comparison of a spontaneous breathing condition with a frequency-matched paced condition revealed that pacing per se provoked a reduction in heart period. Because this decrease was not accompanied by changes in any of the HPV frequency components, their validity as measures of autonomic control needs to be questioned.     

Reproducibility of blood pressure and heart rate reactivity: A meta-analysis

Reproducibilities of blood pressure and heart rule (HR) reactivity reported in studies assessing responses to the same laboratory stressors across occasions were reviewed with meta-analytic techniques. Changes in HR had the greatest reproducibility (r =.555), followed by systolic blood pressure (SBP) (.407) and diastolic blood pressure (DBF) (.348), Both SBP and HR response reproducibility was higher at shorter lest-retest intervals, whereas DBP values varied unsystematically with length of test-retest interval Older samples exhibited higher SBP and DBP reproducibility to stressors. SBP and DBP reproducibilities were better for tasks that did not make speech demands. The reliability of reactivity assessment was higher when based on three or more measurements, On the basis of able evidence, the drop in stress reproducibility, as test-retest interval increases, places limits on the viability of BP reactivity as a strong marker or risk factor for coronary heart disease.     

ECG artifacts and heart period variability: Don't miss a beat!

The impact of artifacts on estimates of heart period variability were evaluated by modeling the effects of missed R-waves and spurious R-wave detections in actual and simulated heart period series. Results revealed that even a single artifact, occurring within a 128-s interbeat interval series, can impart substantial spurious variance into all commonly analyzed frequency bands, including that associated with respiratory sinus arrhythmia. In fact, the spurious variance introduced by a single artifact may be greater than that associated with true basal heart period variability and can far exceed typical effect sizes in psychophysiological studies. The effects of artifacts are not related to a specific analytical method and are apparent in both frequency and time domain analyses. Results emphasize the importance of artifact detection and resolution for studies of heart period variability.     

The relationship between mental and physical health: Insights from the study of heart rate variability

Here we review our recent body of work on the impact of mood and comorbid anxiety disorders, alcohol dependence, and their treatments on heart rate variability (HRV), a psychophysiological marker of mental and physical wellbeing. We have shown that otherwise healthy, unmedicated patients with these disorders display reduced resting-state HRV, and that pharmacological treatments do not ameliorate these reductions. Other studies highlight that tricyclic medications and the serotonin and noradrenaline reuptake inhibitors in particular may have adverse cardiovascular consequences. Reduced HRV has important functional significance for motivation to engage social situations, social approach behaviours, self-regulation and psychological flexibility in the face of stressors. Over the longer-term, reduced HRV leads to immune dysfunction and inflammation, cardiovascular disease and mortality, attributable to the downstream effects of a poorly functioning cholinergic anti-inflammatory reflex. We place our research in the context of the broader literature base and propose a working model for the effects of mood disorders, comorbid conditions, and their treatments to help guide future research activities. Further research is urgently needed on the long-term effects of autonomic dysregulation in otherwise healthy psychiatric patients, and appropriate interventions to halt the progression of a host of conditions associated with morbidity and mortality.     

Heart rate complexity: A novel approach to assessing cardiac stress reactivity

Correlation dimension (D2), a measure of heart rate (HR) complexity, has been shown to decrease in response to acute mental stress and relate to adverse cardiovascular health. However, the relationship between stress‐induced changes in D2 and HR has yet to be established. The present studies aimed to assess this relationship systematically while controlling for changes in respiration and autonomic activity. In Study 1 (N = 25) D2 decreased during stress and predicted HR reactivity even after adjusting for changes in respiration rate, and cardiac vagal tone. This result was replicated in Study 2 (N = 162) and extended by including a measure of cardiac sympathetic activity; correlation dimension remained an independent predictor of HR reactivity in a hierarchical linear model containing measures of cardiac parasympathetic and sympathetic activity and their interaction. These results suggest that correlation dimension may provide additional information regarding cardiac stress reactivity above that provided by traditional measures of cardiac autonomic function.     

Exercise after heart transplantation

Exercise intolerance in heart transplant recipients (HTR) has a multifactorial origin, involving complex interactions among cardiac, neurohormonal, vascular, skeletal muscle and pulmonary abnormalities. However, the role of these abnormalities may differ as a function of time after transplantation and of many other variables. The present review is aimed at evaluating the role of cardiac, pulmonary and muscular factors in limiting maximal aerobic performance of HTR, and the benefits of chronic exercise. Whereas pulmonary function does not seem to affect gas exchange until a critical value of diffusing lung capacity is attained, cardiac and skeletal muscle function deterioration may represent relevant factors limiting maximal and submaximal aerobic performance. Cardiac function is mainly limited by chronotropic incompetence and diastolic dysfunction, whereas muscle activity seems to be limited by impaired oxygen supply as a consequence of the reduced capillary network. The latter may be due to either immunosuppressive regimen or deconditioning. Endurance and strength training may greatly improve muscle function and maximal aerobic performance of HTR, and may also reduce side effects of immunosuppressive therapy and control risk factors for cardiac allograft vasculopathy. For the above reasons exercise should be considered an important therapeutic tool in the long-term treatment of heart transplant recipients.     

Very high frequency oscillations in the heart rate and blood pressure of heart transplant patients

The authors studied the recently reported very high frequency (VHF) peaks in the heart rate (HR) and blood pressure (BP) power spectra of heart transplant (HT) patients. These VHF peaks appear at frequencies much higher than the respiratory frequency, in addition to the typical low-frequency and high-frequency peaks. Twenty-five recordings obtained from 13 male HT patients (0.5–65 months following surgery) were compared with recordings from 14 normal male subjects. The ECG, continuous BP and respiration were recorded during 45 min of supine rest. Eight recordings from HT patients were excluded owing to arrhythmias. Spectral analysis was performed on all other recordings. VHF peaks were found in the spectra of both BP and HR in nine recordings obtained from six HT patients. In some cases, the power in the VHF peaks was markedly higher than that of the high-frequency peak. No VHF peaks were observed in eight recordings obtained from four HT patients or in recording from any of the normal subjects. No correlation was found between the incidence of VHF peaks and time after transplant. It was proved that the VHF peaks were not artifactual, and their significance within the framework of the theory of communication systems is discussed. The presence of those peaks was attributed to vagal denervation.     

Heart period variability during estrogen exposure and withdrawal in female rats

Heart period, heart period variability, and an estimate of vagal tone were evaluated during estrogen exposure and withdrawal in ovariectomized, freely moving female rats. Spectral analysis was used to quantify the respiratory component of heart period variability (V?), which has been found to be sensitive to alterations of vagal tone to the heart. During estrogen withdrawal, V? decreased significantly and was accompanied by a decrease in heart period. There were no significant differences in heart period or V? between the experimental (estrogen) group and the control (no estrogen) group during estrogen exposure. Total heart period variability did not differ significantly from controls during estrogen withdrawal but it did exhibit an increase during estrogen exposure. In this experiment V? appeared to be more sensitive to changes in estrogen levels than total heart period variability. These data suggest that decreases in cardiac vagal tone and heart rate occur during estrogen withdrawal.     

Influence of acute fluid loading on stress-induced hemoconcentration and cardiovascular reactivity

The goal of this study was to assess the possible attenuating effects of oral fluid loading on hematological and hemodynamic factors during acute psychological stress in two separate experiments: Experiment 1 assessed the effects of hypotonic fluid loading (water) and Experiment 2 assessed the effects of isotonic fluid loading (Gatorade). Twenty-eight participants were recruited for Experiment 1, and 28 participants were recruited for Experiment 2. Participants for each experiment completed two test sessions, once in a hypo-hydrated condition (following 12-h fast) and once in a fluid loaded condition (hypotonic or isotonic fluid). During each session, hematocrit (Hct), hemoglobin (Hgb), calculated plasma volume (CPV), heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), cardiac output (CO), stroke volume (SV), and total peripheral resistance (TPR) were assessed during a 10-min resting baseline period, 6-min mental arithmetic (MA) task, and a 16-min recovery period. Results for Experiment 1 revealed that the fluid load condition Hct, Hgb, and HR levels were significantly lower in comparison to the hypo-hydration condition, and that Hct, Hgb, and CPV reactivity was greater during the fluid load condition. Results for Experiment 2 revealed that Hct, Hgb, and TPR were lower and CPV, SBP, SV, and CO were higher during the fluid load condition compared to the hypo-hydration condition and that HR, CO, and TPR reactivity was greater during the fluid load condition. Finally, analytic comparisons between the two fluid types revealed that SV and CO levels were significantly greater at baseline and during MA when isotonic fluid was ingested compared to hypotonic fluid ingestion.     

Regional cerebral blood flow correlates with heart period and high-frequency heart period variability during working-memory tasks: Implications for the cortical and subcortical regulation of cardiac autonomic activity

The aim of the present study was to characterize the functional relationships between behaviorally evoked regional brain activation and cardiac autonomic activity in humans. Concurrent estimates of regional cerebral blood flow (rCBF; obtained by positron emission tomography), heart period, and high-frequency heart period variability (HF-HPV; an indicator of cardiac parasympathetic activity) were examined in 93 adults (aged 50-70 years) who performed a series of increasingly difficult working-memory tasks. Increased task difficulty resulted in decreased heart period (indicating cardioacceleration) and decreased HF-HPV (indicating decreased cardiac parasympathetic activity). Task-induced decreases in heart period and HF-HPV were associated with concurrent increases and decreases in rCBF to cortical and subcortical brain regions that are speculated to regulate cardiac autonomic activity during behavioral processes: the medial-prefrontal, insular, and anterior cingulate cortices, the amygdala-hippocampal complex, and the cerebellum. These findings replicate and extend a small number of functional neuroimaging studies that suggest an important role for both cortical and subcortical brain systems in human cardiac autonomic regulation.     

Enhancing the laboratory-to-life generalizability of cardiovascular reactivity using multiple occasions of measurement

Studies examining the association between laboratory measures of stress-related cardiovascular (CV) reactivity and responses to psychological challenges in the natural environment have yielded mixed results. Frequently, single laboratory tasks have been used to predict responses to natural stressors on a single occasion of measurement. Because aggregation broadens the range of stimuli sampled and reduces measurement error, laboratory-to-life generalizability should be more easily detected when multiple predictor and criterion observations are used. Sixty students in a public speaking course were administered multitask assessments of CV reactivity during two laboratory sessions and during two in-class public speech assignments. CV responses to the classroom speeches were greater among those who showed larger responses in the laboratory, and these associations became stronger as measures were aggregated across multiple samples of behavior. These results support the generalizability of CV reactivity as a measure of individual difference, and they help to shed light on previous inconsistent findings in this area.     

Adiposity, leptin and stress reactivity in humans

Evidence suggests that individuals who are more obese may be more responsive to stress. Stress activates the sympathetic nervous system (SNS) and the adipose-tissue cytokine leptin stimulates SNS activity in animals. We examined the relationship between adiposity, leptin and physiological responses to acute laboratory stress in 67 women. We predicted that individuals with greater adiposity and/or higher plasma leptin would be more stress-responsive. Adiposity was unrelated to cardiovascular or neuroendocrine stress reactivity. However, women with larger waists had greater stress-induced increases in plasma leptin and interleukin-1 receptor antagonist (IL-1Ra). Similarly, women with higher basal leptin displayed greater stress-induced increases in heart rate and plasma interleukin-6, and larger decreases in heart rate variability and cardiac pre-ejection period. Heightened cardiovascular and inflammatory stress responses are predictive of future cardiovascular risk. Our findings suggest that the cytokines leptin and IL-1Ra may play a role in the association between obesity, stress and cardiovascular health.     

Heart rate and heart rate variability during a novel object test and a handling test in young horses

Forty-one Dutch Warmblood immature horses were used in a study to quantify temperamental traits on the basis of heart rate (HR) and heart rate variability (HRV) measures. Half of the horses received additional training from the age of 5 months onwards; the other half did not. Horses were tested at 9, 10, 21 and 22 months of age in a novel object and a handling test. During the tests, mean HR and two heart variability indices, e.g. standard deviation of beat-to-beat intervals (SDRR) and root mean square of successive beat-to-beat differences (rMSSD), were calculated and expressed as response values to baseline measures. In both tests, horses showed at all ages a significant increase in mean HR and decrease in HRV measures, which suggests a marked shift of the balance of the autonomic nervous system towards a sympathetic dominance. In the novel object test, this shift was more pronounced in horses that had not been trained. Furthermore, statistical analysis showed that the increase in mean HR could not be entirely explained by the physical activity. The additional increase in HR, the nonmotor HR, was more pronounced in the untrained horses compared to the trained. Hence, it is suggested that this nonmotor HR might be due to the level of emotionality. HR variables showed consistency between years, as well as within the second year. These tests bring about a HR response in horses, part of which may indicate a higher level of emotionality; and horses show individual consistency of these HR variables over ages. Therefore, it is concluded that mean HR and HRV measures used with these tests quantify certain aspects of a horse's temperament.     

低体温与心率变异性和血压变异性的关系

目的: 研究低体温与自主神经功能变化的关系。方法: 采用体表物理降温法逐步降低直肠温度,直肠温度变化范围为19-37 ℃。分别记录不同直肠温度下大鼠动态心电和血压信号。应用心率变异性和血压变异性分析系统评价低体温对心率变异性和收缩压变异性的影响。结果: 心率变异分析表明，直肠温度下降到29 ℃以下,R-R间期均延长（P<0.01）,提示心率明显降低;当直肠温度下降到19-21 ℃时,心率变异归一化低频功率降低（P<0.05）和归一化高频功率增加（P<0.05），而且自主神经的平衡向心迷走神经张力增强的方向发生了转移（P<0.05）。血压变异性分析表明，体温下降到31℃时与呼吸有关的归一化高频功率开始增加（P<0.01）；直肠温度下降到29 ℃以下(除27 ℃外),与呼吸有关的归一化高频功率增加（P<0.05或P<0.01），同时自主神经的平衡也发生了改变（P<0.05）。结论： 随着体温的降低，心血管迷走神经活性增加，自主神经的平衡向迷走神经张力增强的方向转移。低体温对血压变异性的影响敏感于心率变异性。     

Causal relationship between heart rate and arterial blood pressure variability signals

A method is described which allows the determination of the causal relationship existing between two biological signals (heart rate and arterial blood pressure variability signals) which carry information about the role of control elicited by the autonomic nervous system. This method assumes an autoregressive (AR) model for the two signals to check the cross-correlation of the two residuals after AR identification. This information, together with the classical parameters of the spectral analysis (mean, variance, frequency and power in two typical bands, gain, phase and coherence) may provide a more precise evaluation of the complex mechanisms involved in the control of heart rate and blood pressure in numerous physiopathological situations.