Gustavo A. Reyes del Paso

The utility of low frequency heart rate variability as an index of sympathetic cardiac tone: A review with emphasis on a reanalysis of previous studies

This article evaluates the suitability of low frequency (LF) heart rate variability (HRV) as an index of sympathetic cardiac control and the LF/high frequency (HF) ratio as an index of autonomic balance. It includes a comprehensive literature review and a reanalysis of some previous studies on autonomic cardiovascular regulation. The following sources of evidence are addressed: effects of manipulations affecting sympathetic and vagal activity on HRV, predictions of group differences in cardiac autonomic regulation from HRV, relationships between HRV and other cardiac parameters, and the theoretical and mathematical bases of the concept of autonomic balance. Available data challenge the interpretation of the LF and LF/HF ratio as indices of sympathetic cardiac control and autonomic balance, respectively, and suggest that the HRV power spectrum, including its LF component, is mainly determined by the parasympathetic system.

Relationships between features of autonomic cardiovascular control and cognitive performance.

The study investigated relationships between autonomic cardiovascular control and attentional performance. In 60 healthy subjects R-wave to pulse interval (RPI), respiratory sinus arrhythmia (RSA), heart rate variability in the mid-frequency (MF) band and sensitivity of the cardiac baroreflex (BRS) were assessed at rest and during a visual attention test. All parameters decreased markedly during test execution. Lower values of resting BRS predicted increased performance. On-task RPI, RSA, MF power and BRS were inversely related to attentional functioning, with RSA accounting for the largest portion of test score variance. The inverse association between resting BRS and performance is discussed as reflecting the bottom-up modulation of cerebral function by baroreceptor activity. The results concerning the on-task measures suggest that a pattern of cardiovascular adjustment including enhanced sympathetic and reduced vagal cardiovascular influences, as well as baroreflex inhibition may induce an adaptive state associated with improved cognitive-attentional functioning.

Autonomic cardiovascular control and responses to experimental pain stimulation in fibromyalgia syndrome

OBJECTIVE This study involves a comprehensive investigation of autonomic cardiovascular regulation in fibromyalgia syndrome (FMS) at rest and during painful stimulation and its association with pain indices. METHODS In 35 patients and 29 healthy controls, electrocardiography, impedance cardiography, and finger continuous blood pressure measurements were conducted. For the purpose of experimental pain induction, a cold pressor test was applied. RESULTS FMS patients showed lower pain threshold and tolerance, as well as higher ratings of pain intensity and unpleasantness on visual analogue scales. Resting stroke volume, myocardial contractility, R-R interval, heart rate variability, and sensitivity of the cardiac baroreflex were reduced in the patients, and increases in stroke volume and myocardial contractility during cold pressor stimulation were less pronounced. In the whole sample as well as in the FMS group, baroreflex sensitivity was inversely associated with subjective pain intensity, and a higher number of baroreflex operations per unit of time predicted higher pain tolerance. CONCLUSIONS The data suggest impaired autonomic cardiovascular regulation in FMS in terms of reduced sympathetic and parasympathetic influences, as well as blunted sympathetic reactivity to acute stress. The association between baroreflex function and pain experience reflects the pain inhibition mediated by the baroreceptor system. Given the reduced baroreflex sensitivity in FMS, one may assume deficient ascending pain inhibition arising from the cardiovascular system, which may contribute to the exaggerated pain sensitivity of FMS.

Treating chronic worry: Psychological and physiological effects of a training programme based on mindfulness.

The present study examines psychological and physiological indices of emotional regulation in non-clinical high worriers after a mindfulness-based training programme aimed at reducing worry. Thirty-six female university students with high Penn State Worry Questionnaire scores were split into two equal intervention groups: (a) mindfulness, and (b) progressive muscle relaxation plus self-instruction to postpone worrying to a specific time of the day. Assessment included clinical questionnaires, daily self-report of number/duration of worry episodes and indices of emotional meta-cognition. A set of somatic and autonomic measures was recorded (a) during resting, mindfulness/relaxation and worrying periods, and (b) during cued and non-cued affective modulation of defence reactions (cardiac defence and eye-blink startle). Both groups showed equal post-treatment improvement in the clinical and daily self-report measures. However, mindfulness participants reported better emotional meta-cognition (emotional comprehension) and showed improved indices of somatic and autonomic regulation (reduced breathing pattern and increased vagal reactivity during evocation of cardiac defense). These findings suggest that mindfulness reduces chronic worry by promoting emotional and physiological regulatory mechanisms contrary to those maintaining chronic worry.

Aberrances in Autonomic Cardiovascular Regulation in Fibromyalgia Syndrome and Their Relevance for Clinical Pain Reports

Objective: To investigate autonomic cardiovascular regulation in fibromyalgia syndrome (FMS). Methods: In 35 patients and 29 healthy controls, electrocardiography, impedance cardiography, and finger continuous blood pressure measurements were conducted. Assessed parameters comprised blood pressure, R-R interval (RRI), heart rate variability, baroreflex sensitivity (BRS), stroke volume, and left ventricular ejection time (LVET). To evaluate cardiovascular autonomic reactivity to mental stress, parameters were obtained at rest and during an arithmetic task. As an estimate of clinical pain severity, participants completed the McGill Pain Inventory. Results: Patients exhibited lower power in all heart rate variability frequency bands (p < .05), lower BRS (7.13 ± 3.45 versus 10.73 ± 5.72 ms/mmHg), as well as reduced stroke volume, LVET, and RRI (p < .05). Stress-induced modulations were less pronounced in BRS, LVET, blood pressure, and RRI (all p < .05). Across the whole sample and in both subgroups, BRS (r = −.40) and blood pressure (r = −.39) correlated negatively with pain severity. Conclusions: The data suggest that autonomic cardiovascular regulation in FMS is impaired in terms of reduced sympathetic and parasympathetic influences, as well as baroreflex malfunctioning. Furthermore, autonomic cardiovascular adjustment to acute stress is blunted. The inverse association between BRS and pain severity reflects the well-documented pain inhibition through the baroreceptor system. On account of this and the reduced baroreflex function in FMS, one may assume deficient ascending pain inhibition arising from the cardiovascular system, which may contribute to hyperalgesia that is characteristic of the disorder. FMS = fibromyalgia syndrome; HRV = heart rate variability; HF = high frequency; LF = low frequency; ICG = impedance cardiography; SV = stroke volume; TPR = total peripheral resistance; BRS = baroreflex sensitivity; SBP = systolic blood pressure; RRI = RR interval; ECG = electrocardiography; DBP = diastolic blood pressure; LVET = left ventricular ejection time; CO = cardiac output; DV = end-diastolic volume; CI = contractility index; SPD = spectral power density.

A between-subjects comparison of respiratory sinus arrhythmia and baroreceptor cardiac reflex sensitivity as non-invasive measures of tonic parasympathetic cardiac control

Respiratory sinus arrhythmia (RSA) has been used as an index of parasympathetic cardiac control. However, recent psychophysiological research casts serious doubts upon the usefulness of RSA as an index of vagal influences upon the heart in psychophysiological as well as in clinical studies. It suggests the need to look for another measure. In this exploratory study we investigated whether the baroreflex sensitivity (BRS) could serve as an alternative tool to investigate between-subject tonic parasympathetic influences on the heart. In nine healthy subjects we examined the effects of intravenous atropine (0.03 mg/kg i.v.), intravenous metoprolol (10-15 mg i.v.), and of saline as a placebo condition upon RSA, BRS, and related cardiovascular and respiratory variables, both under resting and under mental task conditions. After parasympathetic blockade, RSA and BRS display values near zero, showing their vagal origin. After beta-adrenergic blockade, when heart period is predominantly under vagal control, RSA fails to predict heart period variability. Using BRS, however, it is possible to predict more than 97% of heart period variance during beta-blockade. Finally, both the vagal and beta-adrenergic blockade show that BRS is a better predictor of parasympathetic cardiac control during blood pressure increases than during blood pressure decreases.

The behavioral impact of baroreflex function: A review

The baroreflex consists of a negative feedback loop adjusting heart activity to blood pressure fluctuations. This review is concerned with interactions between baroreflex function and behavior. In addition to changes in baroreflex cardiac control subject to behavioral manipulations, interindividual differences in reflex function predicted psychological and central nervous features. The sensitivity of the reflex was inversely related to cognitive performance, evoked potential amplitudes, experimental pain sensitivity, and the severity of clinical pain. Possible variables moderating the strength of the associations are tonic blood pressure, gender, and psychiatric disease. It is suggested that these observations reflect inhibition of higher brain function by baroreceptor afferents. While in many cases increased baroreflex function implies stronger inhibition, individual and situational factors modulate the behavioral impact of cardiac regulation.

Respiratory sinus arrhythmia as an index of parasympathetic cardiac control during the cardiac defense response

The respiratory sinus arrhythmia (RSA) is being used by psychophysiologists as an index of parasympathetic cardiac control mainly in tasks within a tonic response paradigm. In procedures which engender phasic responses the belief exists that the RSA could be contaminated by slower nonrhythmic trends in the data. In the present paper two experiments are reported. The first experiment valuates, through beta-adrenergic blocking, the validity of the RSA as an index of phasic changes in parasympathetic cardiac control during phasic changes in sympathetic activation: the cardiac defense response (CDR) to intense auditory stimulation. The second experiment examines the RSA response pattern associated with the CDR. The results of the first experiment, that the RSA response pattern is not significantly influenced by the beta-adrenergic block, suggest that RSA may index phasic changes in parasympathetic cardiac control during phasic response procedures such as those which elicit the CDR. The results of the second study indicate that the CDR is associated with a pattern of changes in RSA made up of four components--reduction, increase, reduction and increase--which run parallel, but in opposite direction, to the heart rate changes. The results of both studies are consistent with a parasympathetic mediation of the first two components of the CDR and a sympathetic-parasympathetic interactive mediation of the last two components.

Increased sensitivity to heat pain in chronic low blood pressure

While in elevated blood pressure reduced sensitivity to acute pain has been well established, little is known about possible alterations in pain perception within the lower range of blood pressure. In this study, sensitivity to heat pain was assessed in 40 subjects with chronic hypotension (mean blood pressure 96.5/57.7mmHg) and 40 normotensive control persons (mean blood pressure 121.8/77.2mmHg). Employing a contact thermode, heat stimuli were applied to the forearm. Pain threshold and tolerance were determined. Participants furthermore rated subjective intensities and unpleasantness of tonic heat stimuli (45.5–47.5°C) on visual analogue scales and in a questionnaire. Possible confounding of sensitivity to heat pain with skin temperature, temperature sensitivity and mood was controlled for. In addition to blood pressure, functional features of the arterial baroreceptor system were related to pain experience. Therefore, estimates for the input on the baroreceptors, as well as baroreflex sensitivity were obtained. Hypotensive individuals exhibited markedly reduced pain threshold and pain tolerance, as well as increased sensory and affective pain experience. The measures related to the baroreceptor system were not associated with pain experience, suggesting that no significant modulation of heat pain occurs through this system. The results of this study complete the findings on hypertension‐related hypoalgesia and suggest an inverse relationship between blood pressure and pain sensitivity across the whole blood pressure spectrum. Furthermore, increased proneness of hypotensive individuals to clinical pain may be discussed.

Patterns of Cerebral Blood Flow and Systemic Hemodynamics During Arithmetic Processing

The present study explored modulations in cerebral blood flow and systemic hemodynamics during the execution of a mental calculation task in 41 healthy subjects. Time course and lateralization of blood flow velocities in the medial cerebral arteries of both hemispheres were assessed using functional transcranial Doppler sonography. Indices of systemic hemodynamics were obtained using continuous blood pressure recordings. Doppler sonography revealed a biphasic left dominant rise in cerebral blood flow velocities during task execution. Systemic blood pressure increased, whereas heart period, heart period variability, and baroreflex sensitivity declined. Blood pressure and heart period proved predictive of the magnitude of the cerebral blood flow response, particularly of its initial component. Various physiological mechanisms may be assumed to be involved in cardiovascular adjustment to cognitive demands. While specific contributions of the sympathetic and parasympathetic systems may account for the observe...