Cardiovascular indices of peripheral and central sympathetic activation

Subtyping attention-deficit/hyperactivity disorder using temperament dimensions: toward biologically based nosologic criteria

IMPORTANCE

Psychiatric nosology is limited by behavioral and biological heterogeneity within existing disorder categories. The imprecise nature of current nosologic distinctions limits both mechanistic understanding and clinical prediction. We demonstrate an approach consistent with the National Institute of Mental Health Research Domain Criteria initiative to identify superior, neurobiologically valid subgroups with better predictive capacity than existing psychiatric categories for childhood attention-deficit/hyperactivity disorder (ADHD).

OBJECTIVE

To refine subtyping of childhood ADHD by using biologically based behavioral dimensions (i.e., temperament), novel classification algorithms, and multiple external validators.

DESIGN, SETTING, AND PARTICIPANTS

A total of 437 clinically well-characterized, community-recruited children, with and without ADHD, participated in an ongoing longitudinal study. Baseline data were used to classify children into subgroups based on temperament dimensions and examine external validators including physiological and magnetic resonance imaging measures. One-year longitudinal follow-up data are reported for a subgroup of the ADHD sample to address stability and clinical prediction.

MAIN OUTCOMES AND MEASURES

Parent/guardian ratings of children on a measure of temperament were used as input features in novel community detection analyses to identify subgroups within the sample. Groups were validated using 3 widely accepted external validators: peripheral physiological characteristics (cardiac measures of respiratory sinus arrhythmia and pre-ejection period), central nervous system functioning (via resting-state functional connectivity magnetic resonance imaging), and clinical outcomes (at 1-year longitudinal follow-up).

RESULTS

The community detection algorithm suggested 3 novel types of ADHD, labeled as mild (normative emotion regulation), surgent (extreme levels of positive approach-motivation), and irritable (extreme levels of negative emotionality, anger, and poor soothability). Types were independent of existing clinical demarcations including DSM-5 presentations or symptom severity. These types showed stability over time and were distinguished by unique patterns of cardiac physiological response, resting-state functional brain connectivity, and clinical outcomes 1 year later.

CONCLUSIONS AND RELEVANCE

Results suggest that a biologically informed temperament-based typology, developed with a discovery-based community detection algorithm, provides a superior description of heterogeneity in the ADHD population than does any current clinical nosologic criteria. This demonstration sets the stage for more aggressive attempts at a tractable, biologically based nosology.

Ambulatory measurement of the ECG T-wave amplitude

Ambulatory recording of the preejection period (PEP) can be used to measure changes in cardiac sympathetic nervous system (SNS) activity under naturalistic conditions. Here, we test the ECG T-wave amplitude (TWA) as an alternative measure, using 24-h ambulatory monitoring of PEP and TWA in a sample of 564 healthy adults. The TWA showed a decrease in response to mental stress and a monotonic decrease from nighttime sleep to daytime sitting and more physically active behaviors. Within-participant changes in TWA were correlated with changes in the PEP across the standardized stressors (r = .42) and the unstandardized naturalistic conditions (mean r = .35). Partialling out changes in heart rate and vagal effects attenuated these correlations, but they remained significant. Ambulatory TWA cannot replace PEP, but simultaneous recording of TWA and PEP provides a more comprehensive picture of changes in cardiac SNS activity in real-life settings.

Nocturnal cardiac autonomic profile in young primary insomniacs and good sleepers

We investigated cardiac vagal and sympathetic activity in 13 young primary insomniacs (PI; 24.4±1.6years) and 14 good sleepers (GS; 23.3±2.5years) during nocturnal sleep. Pre-ejection period (PEP; inversely related to beta-adrenergic sympathetic activity), interval between consecutive R-waves (RR), and vagal-related indices of time- and frequency-domain heart rate variability were computed during pre-sleep wakefulness and undisturbed arousal-free sleep stages (N2, SWS, REM) as well as across the whole night irrespective of the presence of disruptive sleep events (e.g. sleep arousals/awakenings) and/or sleep stage transitions. Groups exhibited a similar vagal activity throughout each undisturbed sleep stage as well as considering the whole night, with a higher modulation during sleep compared to prior wakefulness. However, PEP was constantly shorter (higher sympathetic activity) during pre-sleep wakefulness and each sleep stage in PI compared to GS. Moreover, pre-sleep RR intervals were positively associated with sleep efficiency and negatively associated with wake after sleep onset in PI. Altogether our findings indicated a dysfunctional sympathetic activity but a normal parasympathetic modulation before and during sleep in young adults with insomnia.

Noradrenergic modulation of cognition: therapeutic implications

The noradrenaline (norepinephrine) system exerts profound influences on cognition via ascending projections to the forebrain, mostly originating from the locus coeruleus. This paper provides an overview of available infrahuman and healthy human studies, exploring the effects of specific noradrenergic manipulations on dissociable cognitive functions, including attention, working memory, cognitive flexibility, response inhibition and emotional memory. Remarkable parallels across species have been reported which may account for the mechanisms by which noradrenergic medications exert their beneficial effects in disorders such as depression and attention-deficit hyperactivity disorder (ADHD). The literature is discussed in relation to prevailing models of noradrenergic influences over cognition and novel therapeutic directions, including in relation to investigating the effects of noradrenergic manipulations on other disorders characterized by impulsivity, and dementias. Unanswered questions are also highlighted, along with key avenues for future research, both proof-of-concept and clinical.

Effects of aerobic conditioning on cardiovascular sympathetic response to and recovery from challenge

Exercise has widely documented cardioprotective effects, but the mechanisms behind these effects are still poorly understood. Here, we test the hypothesis that aerobic training lowers cardiovascular sympathetic responses to and speeds recovery from challenge. We conducted a randomized, controlled trial contrasting aerobic versus strength training on indices of cardiac (pre-ejection period, PEP) and vascular (low-frequency blood pressure variability, LF-BPV) sympathetic responses to and recovery from psychological and orthostatic challenge in 149 young, healthy, sedentary adults. Aerobic and strength training did not alter PEP or LF-BPV reactivity to or recovery from challenge. These findings, from a large randomized, controlled trial using an intent-to-treat design, show that moderate aerobic exercise training has no effect on PEP and LF-BPV reactivity to or recovery from psychological or orthostatic challenge. In healthy young adults, the cardioprotective effects of exercise training are unlikely to be mediated by changes in sympathetic activity.

Manipulation of arterial stiffness, wave reflections, and retrograde shear rate in the femoral artery using lower limb external compression

Exposure of the arterial wall to retrograde shear acutely leads to endothelial dysfunction and chronically contributes to a proatherogenic vascular phenotype. Arterial stiffness and increased pressure from wave reflections are known arbiters of blood flow in the systemic circulation and each related to atherosclerosis. Using distal external compression of the calf to increase upstream retrograde shear in the superficial femoral artery (SFA), we examined the hypothesis that changes in retrograde shear are correlated with changes in SFA stiffness and pressure from wave reflections. For this purpose, a pneumatic cuff was applied to the calf and inflated to 0, 35, and 70 mmHg (5 min compression, randomized order, separated by 5 min) in 16 healthy young men (23 ± 1 years of age). Doppler ultrasound and wave intensity analysis was used to measure SFA retrograde shear rate, reflected pressure wave intensity (negative area [NA]), elastic modulus (Ep), and a single-point pulse wave velocity (PWV) during acute cuff inflation. Cuff inflation resulted in stepwise increases in retrograde shear rate (P < 0.05 for main effect). There were also significant cuff pressure-dependent increases in NA, Ep, and PWV across conditions (P < 0.05 for main effects). Change in NA, but not Ep or PWV, was associated with change in retrograde shear rate across conditions (P < 0.05). In conclusion, external compression of the calf increases retrograde shear, arterial stiffness, and pressure from wave reflection in the upstream SFA in a dose-dependent manner. Wave reflection intensity, but not arterial stiffness, is correlated with changes in peripheral retrograde shear with this hemodynamic manipulation.

Aerobic exercise and strength training effects on cardiovascular sympathetic function in healthy adults: a randomized controlled trial

OBJECTIVE

Exercise has widely documented cardioprotective effects, but the mechanisms underlying these effects are not entirely known. Previously, we demonstrated that aerobic but not strength training lowered resting heart rate and increased cardiac vagal regulation, changes that were reversed by sedentary deconditioning. Here, we focus on the sympathetic nervous system and test whether aerobic training lowers levels of cardiovascular sympathetic activity in rest and that deconditioning would reverse this effect.

METHODS

We conducted a randomized controlled trial contrasting the effects of aerobic (A) versus strength (S) training on indices of cardiac (preejection period, or PEP) and vascular (low-frequency blood pressure variability, or LF BPV) sympathetic regulation in 149 young, healthy, and sedentary adults. Participants were studied before and after conditioning, as well as after 4 weeks of sedentary deconditioning.

RESULTS

As previously reported, aerobic capacity increased in response to conditioning and decreased after deconditioning in the aerobic, but not the strength, training group. Contrary to prediction, there was no differential effect of training on either PEP (A: mean [SD] -0.83 [7.8] milliseconds versus S: 1.47 [6.69] milliseconds) or LF BPV (A: mean [SD] -0.09 [0.93] ln mm Hg(2) versus S: 0.06 [0.79] ln mm Hg(2)) (both p values > .05).

CONCLUSIONS

These findings, from a large randomized controlled trial using an intent-to-treat design, show that moderate aerobic exercise training has no effect on resting state cardiovascular indices of PEP and LF BPV. These results indicate that in healthy, young adults, the cardioprotective effects of exercise training are unlikely to be mediated by changes in resting sympathetic activity.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT00358137.

Gritty people try harder: grit and effort-related cardiac autonomic activity during an active coping challenge

Grit, a recently proposed personality trait associated with persistence for long-range goals, predicts achievement in a wide range of important life outcomes. Using motivational intensity theory, the present research examined the physiological underpinnings of grit during an active coping task. Forty young adults completed the Short Grit Scale and worked on a self-paced mental effort task. Effort-related autonomic nervous system (ANS) activity was assessed using impedance cardiography, which yielded measures of sympathetic activity (pre-ejection period; PEP) and parasympathetic activity (respiratory sinus arrhythmia; RSA). Multilevel models revealed that people high on the Perseverance of Effort subscale showed autonomic coactivation: both PEP and RSA became stronger during the task, reflecting higher activity of both ANS divisions. The Consistency of Interest subscale, in contrast, predicted only weaker sympathetic activity (slower PEP). Taken together, the findings illuminate autonomic processes associated with how "gritty" people pursue goals, and they suggest that more attention should be paid to the facets' distinct effects.

Inattentive and hyperactive preschool-age boys have lower sympathetic and higher parasympathetic activity

The presented study aimed to clarify the relationship between the autonomic nervous system and disruptive behaviors among preschoolers. Possible gender differences in autonomic activity were also examined. A total of 88 preschool-age children were enrolled in this study. Autonomic activities were measured by power spectrum analysis of heart rate variability (HRV). The Swanson, Nolan and Pelham parents and teachers rating scale (SNAP-IV) was applied to evaluate each subject's severity of disruptive behavior. The relationship between the HRV results and the SNAP-IV was evaluated by correlation analysis, which disclosed that the scores for inattention, hyperactivity/impulsivity and oppositional defiant disorder showed a negative association with LF % and LF/HF. The above scales, except for the hyperactivity subscale, also showed a positive association with HF. On separating the two genders, only boys showed the above correlations. Preschool-age boys who show more inattentive and hyperactive features have lower sympathetic and higher parasympathetic activity.

Estimated preejection period (PEP) based on the detection of the R-wave and dZ/dt-min peaks does not adequately reflect the actual PEP across a wide range of laboratory and ambulatory conditions

The current study evaluates the validity of the PEP computed from a fixed value for the Q-wave onset to R-wave peak (QR) interval and an R-wave peak to B-point (RB) interval that is estimated from the R-peak to dZ/dt-min peak (ISTI) interval. Ninety-one subjects participated in a 90min laboratory experiment in which a variety of often employed physical and mental stressors were presented and 31 further subjects participated in a structured 2hour ambulatory recording in which they partook in natural activities that induced large variation in posture and physical activity. PEP, QR interval, and ISTI were scored and rigorously checked by interactive inspection. Across the very diverse laboratory and ambulatory conditions the QR interval could be approximated by a fixed interval of 40ms but 95% confidence intervals were large (25.5 to 54.5ms). Multilevel analysis showed that 79% to 81% of the within and between-subject variation in the RB interval could be predicted by the ISTI with a simple linear regression equation. However, the optimal intercept and slope values in this equation varied significantly across subjects and study setting. Bland Altman plots revealed a large discrepancy between the estimated PEP using the R-wave peak and dZ/dt-min peak and the actual PEP based on the Q-wave onset and B-point. We conclude that the PEP estimated from a fixed QR interval and the ISTI could be a useful addition to the psychophysiologist's toolbox, but that it cannot replace the actual PEP to index cardiac sympathetic control.

Nocturnal cardiovascular activity in essential hypotension: evidence of differential autonomic regulation

OBJECTIVE

Essential hypotension represents a form of chronic low blood pressure (BP) not explained by medical or orthostatic conditions. The pathogenesis of essential hypotension may involve sympathetic hypoactivation and other forms of autonomic dysregulation. The aim of the current study was to investigate autonomic and cardiovascular activity during sleep in individuals with essential hypotension.

METHODS

A case-control study was conducted in 14 individuals with essential hypotension (mean [standard error] = 23.4 [0.6] years, all women) and 14 controls (mean [standard error] age = 22.2 [0.4] years, all women). The following measures were collected over a night of sleep: BP, heart rate (HR), stroke volume, cardiac output (CO), preejection period (PEP), total peripheral resistance, and time-domain measures of HR variability.

RESULTS

Hypotensive participants had consistently lower BP, HR, and CO than did normotensives. Cardiac autonomic variables revealed enhanced parasympathetic tone (proportion of adjacent normal-to-normal intervals that differed in length by more than 50 milliseconds = 40.8 [6.3] versus 23.4 [4.5], p = .03) and reduced sympathetic drive in hypotensives (PEP = 99.4 [3.6] versus 86.1 [4.3], p = .02). Analysis of temporal profiles showed that HR, stroke volume, and CO decreased throughout the night in both groups, whereas PEP and HR variability increased. Unlike controls, BP remained essentially unchanged in hypotensives, as the decrease in CO was counterbalanced by a parallel rise in total peripheral resistance.

CONCLUSIONS

These findings suggest that nocturnal cardiac sympathetic withdrawal combined with vagal hyperactivity is a characteristic of the autonomic regulation in essential hypotension.

Effects of antidepressants, but not psychopathology, on cardiac sympathetic control: a longitudinal study

Increased sympathetic activity has been hypothesized to have a role in the elevated somatic disease risk in persons with depressive or anxiety disorders. However, it remains unclear whether increased sympathetic activity reflects a direct effect of anxiety or depression or an indirect effect of antidepressant medication. The aim of this study was to test longitudinally whether cardiac sympathetic control, measured by pre-ejection period (PEP), was increased by depression/anxiety status and by antidepressant use. Cross-sectional and longitudinal data were from a depression and anxiety cohort: the Netherlands Study of Depression and Anxiety (NESDA). Baseline data of 2838 NESDA subjects (mean age 41.7 years, 66.7% female) and 2-year follow-up data of 2226 subjects were available for analyses. Included were subjects with and without depressive/anxiety disorders, using or not using different antidepressants at baseline or follow-up. The PEP was measured non-invasively by 1.5 h of ambulatory impedance cardiography. Cross-sectional analyses compared PEP across psychopathology and antidepressant groups. Longitudinal analyses compared 2-year changes in PEP in relation to changes in psychopathology and antidepressant use. Cross-sectional analyses showed that antidepressant-naïve depressive/anxious subjects had comparable PEP as controls, whereas subjects using tricyclic (TCA) or combined serotonergic/noradrenergic antidepressants (SNRI) had significantly shorter PEP compared with controls. In contrast, subjects using selective serotonin re-uptake inhibitors (SSRIs) had longer PEP than controls. Longitudinal results confirmed these findings: compared with 2-year change in PEP in continuous non-users (+2 ms), subjects who started TCA or SNRI treatment showed significantly shortened PEP (-11 ms, p=0.005 and p<0.001), whereas subjects who started SSRI treatment showed significant prolongation of PEP (+9 ms, p=0.002). Reversed findings were observed among those who stopped antidepressant use. These findings suggest that depressive and anxiety disorders are not associated with increased cardiac sympathetic control. However, results pose that TCA and SNRI use increases sympathetic control, whereas SSRI use decreases sympathetic control.

Small bolus of esmolol effectively prevents sodium nitroprusside-induced reflex tachycardia without adversely affecting blood pressure

PURPOSE

Hypotensive anesthesia with sodium nitroprusside (SNP) often is associated with reflex tachycardia. The purpose of this study was to investigate whether a small bolus of esmolol could counteract SNP-induced reflex tachycardia and sympathetic activation without affecting blood pressure.

MATERIALS AND METHODS

Using a time-series study design, 27 healthy young patients scheduled for mandibular osteotomy were enrolled in this study. General anesthesia was maintained with 2% sevoflurane and 67% nitrous oxide in oxygen. SNP was administered to decrease the mean arterial pressure to 55 to 65 mm Hg. When heart rate (HR) increased reflexively to higher than 95 beats/min from SNP-induced hypotension, esmolol 0.5 mg/kg was given. Blood pressure and HR were measured, and the low-frequency component (0.04 to 0.15 Hz) of systolic blood pressure variability and high-frequency component (0.15 to 0.4 Hz) of HR variability were calculated to evaluate the autonomic condition. Data were analyzed using 1-way analysis of variance after multiple comparisons or t test. P < .05 was considered statistically significant.

RESULTS

Of the 27 patients analyzed, 19 patients (70%) required esmolol. In these patients, SNP caused an increase in the low-frequency component of systolic blood pressure variability and a decrease in the high-frequency component of HR variability, leading to tachycardia (HR range, 95.9 ± 7.3 to 106.7 ± 7.4 beats/min; P < .001). Esmolol suppressed the effects of SNP on the low-frequency component of systolic blood pressure variability and high-frequency component of HR variability, resulting in an immediate decrease in HR to 86.9 ± 6.2 beats/min (P < .001), whereas mean arterial pressure remained unchanged.

CONCLUSIONS

A small bolus of esmolol can suppress reflex tachycardia without significantly changing mean arterial pressure. Thus, esmolol restores the autonomic imbalance induced by SNP during hypotensive anesthesia.

Effect of mild, asymptomatic obstructive sleep apnea on daytime heart rate variability and impedance cardiography measurements

Dysregulation of autonomic nervous system dynamics is important in the pathophysiology of cardiovascular risk in obstructive sleep apnea (OSA). Heart rate variability (HRV) and impedance cardiography measures can estimate autonomic activity but have not gained traction clinically. The hypothesis of this study was that even in a cohort of patients with mild, asymptomatic OSA without overt cardiovascular disease, daytime HRV metrics and impedance cardiography measurements of preejection period would demonstrate increased sympathetic and decreased parasympathetic modulation compared to matched controls. Obese subjects (body mass index ≥30 kg/m(2)) without any known cardiovascular or inflammatory co-morbidities were recruited from the community. Subjects underwent standard in-laboratory polysomnography followed by simultaneous electrocardiographic and impedance cardiographic recordings while supine, supine with paced breathing, and after standing. Seventy-four subjects were studied, and 59% had OSA (apnea-hypopnea index ≥10 events/hour), with a median apnea-hypopnea index of 25.8 events/hour. Subjects with OSA had significantly decreased daytime time- and frequency-domain HRV indexes, but not significantly different preejection periods, compared to controls. Apnea-hypopnea index was a significant independent predictor of time-domain HRV measures in all awake conditions, after controlling for age, gender, blood pressure, fasting cholesterol levels and glycosylated hemoglobin. In conclusion, these results demonstrate reductions in cardiac vagal modulation, as measured by multiple daytime time-domain markers of HRV, in patients with asymptomatic OSA compared to controls. Further prospective outcomes-based studies are needed to evaluate the applicability of these metrics for noninvasive screening of obese patients with asymptomatic OSA, before the onset of overt cardiovascular disease.

Relationship of basal heart rate variability to in vivo cytokine responses after endotoxin exposure

Autonomic inputs from the sympathetic and parasympathetic nervous systems, as measured by heart rate variability (HRV), have been reported to correlate to the severity injury and responses to infectious challenge among critically ill patients. In addition, parasympathetic/vagal activity has been shown experimentally to exert anti-inflammatory effects via attenuation of splanchnic tissue TNF-alpha production. We sought to define the influence of gender on HRV responses to in vivo endotoxin challenge in healthy humans and to determine if baseline HRV parameters correlated with endotoxin-mediated circulating cytokine responses. Young (<30 years of age), healthy subjects (n = 30) received endotoxin (2 ng/kg), and HRV and blood samples were obtained serially thereafter. Plasma cytokines were measured by enzyme-linked immunosorbent assay, and HRV parameters were determined by analysis of serial 5-min epochs of heart rate monitoring. In addition, calculation of multiscale entropy deriving from cardiac monitoring data was performed. The influence of factors such as gender, body mass index, and resting heart rate on HRV after endotoxin exposure was assessed. We found that gender, body mass index, or resting heart rate did not significantly alter the HRV response after endotoxin exposure. Using entropy analysis, we observed that females had significantly higher entropy values at 24 h after endotoxin exposure. Using a serially sampling protocol for cytokine determination, we found a significant correlation of several baseline HRV parameters (percentage of interval differences of successive interbeat intervals more than 50 ms, r = 0.42, P < 0.05; high-frequency variability, r = 0.4, P < 0.05; and low-frequency/high-frequency ratio, r = -0.43, P < 0.05) on TNF-alpha release after endotoxin exposure.

The heart contracts to reward: monetary incentives and preejection period

Wright's (1996) integration of motivational intensity theory (Brehm & Self, 1989) and Obrist's (1981) active coping approach predict that cardiovascular reactivity in active coping depends on the importance of success when task difficulty is unclear. Despite the support for this perspective, one of the basic hypotheses-the mediation of these effects by beta-adrenergic activity-has not been tested yet. To close this gap, participants worked on a delayed-matching-to-sample task and could earn either 1, 15, or 30 Swiss Francs for a successful performance. Results showed that preejection period reactivity-an indicator of beta-adrenergic impact on the heart-increased with increasing incentive value. Thus, this experiment closes a gap in the support of Wright's model by demonstrating that beta-adrenergic reactivity is associated with incentive value under conditions of unclear difficulty.

Attenuated pre-ejection period response to tyramine in patients with cardiac sympathetic denervation

Stress is a well-known factor affecting cardiac contractility through the cardiac sympathetic nerves. A positive inotropic effect of the cardiac sympathetic nerves on the myocardium is reflected by pre-ejection period (PEP) shortening. Patients with Parkinson disease (PD) and neurogenic orthostatic hypotension (NOH) (PD + NOH) or with pure autonomic failure (PAF) have markedly decreased myocardial 6-[(18)F]Fluorodopamine-derived radioactivity, reflecting cardiac sympathetic denervation. The functional effects of the cardiac sympathetic denervation have been unknown. We measured PEP and heart rate-corrected PEP (PEPI) responses to i.v. tyramine (1 mg/min) in 13 patients (9 PD + NOH and 4 PAF) with low 6-[(18)F]Fluorodopamine-derived radioactivity and in subjects with normal radioactivity (15 multiple system atrophy with NOS patients (MSA + NOS). Baseline PEP and PEPI did not differ between the groups. By 10 min after initiation of tyramine infusion, PEP and PEPI were significantly lower (P < 0.01) in MSA + NOS, compared to base line, whereas PEP and PEPI remained unchanged in the PD + NOH/PAF group. The PEP and PEPI decrease was larger in the MSA + NOS group than in the PD + NOH/PAF group (P < 0.05). One of the functional consequences of cardiac sympathetic denervation is failure to increase contractility in response to stimuli that depend on endogenous norepinephrine release.

Melatonin reduces arousal and startle responsiveness without influencing startle habituation or affective startle modulation in young women

Melatonin has been suggested to affect human emotion, but conflicting evidence exists. Therefore, we tested the effect of a single dose of a 4 mg prolonged release formulation of melatonin on a biologically based model of emotional processing. Affective modulation of acoustic white noise startle (103 dB) by emotional slides selected from the International Affective Picture System (IAPS) was assessed in 16 healthy young women twice, in a double-blind, placebo-controlled, balanced cross-over design. Melatonin significantly reduced startle responsiveness, but did not impact affective startle modulation, nor startle habituation. Melatonin significantly reduced arousal ratings and induced a parasympathetically dominated heart rate variability pattern indicative of a non-aroused state. We conclude that melatonin reduces arousal and startle responsiveness. However, no evidence for a direct emotion-modulating effect of melatonin was found in this healthy cohort.

Task difficulty effects on cardiac activity

An experiment with 64 participants manipulated task difficulty and assessed cardiac reactivity in active coping over four levels of demand. Participants performed a memory task while preejection period, heart rate, and blood pressure were assessed. In accordance with the theoretical predictions of R. A. Wright's (1996) integration of motivational intensity theory (J. W. Brehm & E. A. Self, 1989) with Obrist's active coping approach (P. A. Obrist, 1981), preejection period and systolic blood pressure reactivity increased with task difficulty across the first three difficulty levels. On the fourth difficulty level-where success was impossible-reactivity of both preejection period and systolic blood pressure were low. These findings provide the first clear evidence for the notion of Wright's integrative model that energy mobilization in active coping is mediated by beta-adrenergic impact on the heart.

Method to measure autonomic control of cardiac function using time interval parameters from impedance cardiography

The time difference between the electrocardiogram and impedance cardiogram can be considered as a measure for the time delay between the electrical and mechanical activities of the heart. This time interval, characterized by the pre-ejection period (PEP), is related to the sympathetic autonomous nervous control of cardiac activity. PEP, however, is difficult to measure in practice. Therefore, a novel parameter, the initial systolic time interval (ISTI), is introduced to provide a more practical measure. The use of ISTI instead of PEP was evaluated in three groups: young healthy subjects, patients with Parkinson's disease, and a group of elderly, healthy subjects of comparable age. PEP and ISTI were studied under two conditions: at rest and after an exercise stimulus. Under both conditions, PEP and ISTI behaved largely similarly in the three groups and were significantly correlated. It is concluded that ISTI can be used as a substitute for PEP and, therefore, to evaluate autonomic neuropathy both in clinical and extramural settings. Measurement of ISTI can also be used to non-invasively monitor the electromechanical cardiac time interval, and the associated autonomic activity, under physiological circumstances.

Functional effects of cardiac sympathetic denervation in neurogenic orthostatic hypotension

BACKGROUND

Diseases characterized by neurogenic orthostatic hypotension (NOH), such as Parkinson disease (PD) and pure autonomic failure (PAF), are associated with cardiac sympathetic denervation, as reflected by low myocardial concentrations of 6-[(18)F]fluorodopamine-derived radioactivity. We studied the impact of such denervation on cardiac chronotropic and inotropic function.

METHODS

Cardiac inotropic function was assessed by the pre-ejection period index and the systolic time ratio index in response to the directly acting beta-adrenoceptor agonist, isoproterenol, and to the indirectly acting sympathomimetic amine, tyramine, in patients with PD+NOH or PAF (PD+NOH/PAF group, N=13). We compared the results to those in patients with multiple system atrophy, which usually entails NOH with normal cardiac sympathetic innervation (MSA, N=15), and in normal control subjects (N=5).

RESULTS

The innervated and denervated groups did not differ in baseline mean pre-ejection period index or systolic time ratio index. Tyramine increased cardiac contractility in the MSA patients and controls but not in the PD+NOH/PAF group. For similar heart rate responses, the PD+NOH/PAF group required less isoproterenol (p<0.01) and had lower plasma isoproterenol levels (p<0.01) than did the MSA group.

CONCLUSIONS

Among patients with NOH those with cardiac sympathetic denervation have an impaired inotropic response to tyramine and exaggerated responses to isoproterenol. This pattern suggests that cardiac denervation is associated with decreased ability to release endogenous norepinephrine from sympathetic nerves and with supersensitivity of cardiac beta-adrenoreceptors.

Salt-sensitive men show reduced heart rate variability, lower norepinephrine and enhanced cortisol during mental stress

Salt sensitivity (SS) represents a risk factor for essential hypertension, which has been related to enhanced cardiovascular stress reactivity possibly mediated by increased noradrenergic susceptibility. We investigated biophysiological responses to mental stress in salt-sensitive (ss) and salt-resistant (sr) subjects, hypothesizing lower heart rate variability (HRV) and higher cortisol in the ss. A total of 48 healthy normotensive Caucasian men (age 25.6+/-2.6, body mass index 22.9+/-2.3) were phenotyped for SS (defined as significant drop in mean arterial pressure>3 mm Hg under the low-salt diet) by a 2-week high- versus low-salt diet. Subjects underwent a standardized mental stress task with continuous cardiovascular monitoring before, during and after the test (Finapres; Ohmeda, Louisville, CO, USA). Blood samples were drawn to examine cortisol and catecholamines before, after and 20 min after stress. The task elicited significant increases of systolic blood pressure (SBP), diastolic BP (DBP) and heart rate (HR) and a significant decrease of HRV (all time effects P<0.0001). The ss subjects showed lower norepinephrine (NE) and higher cortisol, indicated by significant group effects (P=0.009 and 0.025, respectively). HR increased and HRV decreased more in the ss under the stress, shown by significant time by group interactions (P=0.045 and 0.003, respectively). The observation of a more pronounced HR rise coupled with a greater decrease of HRV in healthy ss men under the influence of brief mental stress confirms their enhanced physiological stress reactivity. The lower peripheral NE may represent an effort to compensate for increased noradrenergic receptor sensitivity. The enhanced cortisol levels are backed by recent genetic findings on HSD11B2 polymorphisms and may promote hypertension.

Hemodynamic responses during simulated automobile driving in a monotonous situation

Long hours of automobile driving under monotonous situations may cause the lowering of what we term a driver's activation state (DAS) or in other words the production of drowsiness, resulting in an increased risk of a traffic accident. There is therefore a need to create a newly advanced system focused on the DAS in-car, hopefully thus avoiding potentially dangerous situations. In order to develop such a system as a final goal, we have firstly set out to acquire such cardiovascular variables as beat-by-beat blood pressure (BP), RR interval from ECG and normalized pulse volume (NPV) used as a peripheral vascular tone of alpha-adrenergic sympathetic activity, during presentation to the driver of a screen movie simulating monotonous travel at constant speed on a test-course. Subsequently, we have investigated the reactivity in terms of the driver's cardiovascular hemodynamics. Through the successful monitoring of cardiovascular parameters during the movie presentation obtained in 11 healthy male subjects, the following results were obtained: The monotonous driving produces a statistically significant gradual rise in BP following drowsiness, which could be explained by enhancement of sympathetic activity using a time-frequency analysis of BP and RR. This finding strongly indicates that continuous driving in such monotonous situations can make a driver considerably stressful and thus may cause a gradual increase in BP, and that this gradual BP increase may be used as a possible index relevant to the DAS. This finding was also confirmed by the analysis of NPV, suggesting that the gradual increase in BP during the monotonous driving would be rather caused by a regulation of peripheral vasomotor constriction.

No Effect of Training State on Ambulatory Measures of Cardiac Autonomic Control

We examined the effect of training state on cardiac autonomic control in a naturalistic setting. Twenty-four vigorous exercisers were compared to age- and sex-matched sedentary controls. The regular exercisers were subjected to a 6-week training program after which they were randomized to 2 weeks of continued training or 2 weeks of detraining. Cardiac autonomic control was measured over a 24-h period by ambulatory recording, using the preejection period (PEP) and respiratory sinus arrhythmia (RSA). Nonexercising controls had a significantly higher ambulatory heart rate (HR) compared to the regular exercisers but comparable 24-h levels of PEP and RSA. In regular exercisers, 2 weeks of detraining did not significantly change the 24-h levels of HR, PEP, or RSA. We conclude that the bradycardia in healthy regular exercisers is the result of a lower intrinsic heart rate rather than a shift in cardiac autonomic balance from sympathetic to vagal control.

Heart-rate and blood-pressure variability during psychophysiological tasks involving speech: influence of respiration

Changes in heart-rate and systolic arterial pressure variability (HRV and SAPV) indexes have been used in psychophysiology to assess autonomic activation, including during tasks involving speech. The current article clearly demonstrates in a sample of 25 adult subjects that the erratic and broadband respiratory patterns during such tasks violate the usual assumption that respiration is limited to the high-frequency band (0.15-0.4 Hz). For these tasks, interindividual differences and rest-task changes in HRV and SAPV in the low-frequency band (0.04-0.15 Hz) can be explained, to a large extent, by variations in the respiratory volume signal. This makes the use of HRV and SAPV as markers of autonomic function during these tasks highly questionable. Furthermore, a number of subjects with long respiratory period at rest were identified, whose presence in the sample can bias the estimation of baseline rest values.

Assessing the Effectiveness of Increased F<inf>I</inf>O<inf>2</inf>for Enhancing Driver's Activation State Using Simulated Monotonous Driving

Lowering of what we term a driver's Activation State (AS) during monotonous driving conditions may increase the risk of an accident. To develop an in-car environment that allows active driving - "Biofee dforward System" - we have investigated the effects of applying a stimulus of increased inspired oxygen fraction (F<inf>I</inf>O<inf>2</inf>) supply on a driver's AS, using simulated monotonous driving. We used our previously substantiated index of As derived from beat-by-beat blood pressure (BP) response following an electrical stimulus. We have made physiological measurements including BP and found that the increased F<inf>I</inf>O<inf>2</inf>stimulus is effective in enhancing the AS. This finding was also confirmed in terms of the autonomic activity balance as well as the lengthening in time for active, safer, driving.

Toward understanding respiratory sinus arrhythmia: relations to cardiac vagal tone, evolution and biobehavioral functions

Respiratory sinus arrhythmia (RSA, or high-frequency heart-rate variability) is frequently employed as an index of cardiac vagal tone or even believed to be a direct measure of vagal tone. However, there are many significant caveats regarding vagal tone interpretation: 1. Respiratory parameters can confound relations between RSA and cardiac vagal tone.2. Although intraindividual relations between RSA and cardiac vagal control are often strong, interindividual associations may be modest.3. RSA measurement is profoundly influenced by concurrent levels of momentary physical activity, which can bias estimation of individual differences in vagal tone.4. RSA magnitude is affected by beta-adrenergic tone.5. RSA and cardiac vagal tone can dissociate under certain circumstances.6. The polyvagal theory contains evolution-based speculations that relate RSA, vagal tone and behavioral phenomena. We present evidence that the polyvagal theory does not accurately depict evolution of vagal control of heart-rate variability, and that it ignores the phenomenon of cardiac aliasing and disregards the evolution of a functional role for vagal control of the heart, from cardiorespiratory synchrony in fish to RSA in mammals. Unawareness of these issues can lead to misinterpretation of cardiovascular autonomic mechanisms. On the other hand, RSA has been shown to often provide a reasonable reflection of cardiac vagal tone when the above-mentioned complexities are considered. Finally, a recent hypothesis is expanded upon, in which RSA plays a primary role in regulation of energy exchange by means of synchronizing respiratory and cardiovascular processes during metabolic and behavioral change.

Noradrenergic modulation of working memory and emotional memory in humans

RATIONALE

Noradrenaline (NA) is implicated in arousal. Working memory is dependent upon prefrontal cortex, and moderate levels of NA are thought to facilitate working memory whereas higher levels during extreme stress may impair working memory and engage more posterior cortical and sub-cortical circuitry. The NA system also influences emotional memory via modulation of the amygdalae and related mediotemporal structures. NA dysfunction and abnormalities in arousal-dependent memory functions are evident in a variety of neuropsychiatric illnesses.

OBJECTIVES

The authors provide a concise overview of pharmacological studies that have investigated effects of selective NA manipulations on working memory and emotional memory functions in healthy human volunteers.

MATERIALS AND METHODS

Selection of relevant peer-reviewed publications was based on a PubMed search.

RESULTS

Studies to date indicate that: (1) the beta-blocker propranolol impaired working and emotional memory, (2) clonidine frequently impaired working memory, and (3) reboxetine, a selective noradrenaline reuptake inhibitor, enhanced emotional memory for positive material.

CONCLUSIONS

Improved understanding of coupling between NA, cortico-subcortical circuitry and human mnemonic functions will suggest novel therapeutic directions for the treatment of neuropsychiatric conditions, such as attention deficit hyperactivity disorder and post-traumatic stress disorder. Future research directions are discussed in relation to neuroimaging techniques, functional central nervous system polymorphisms and study designs.

Implementation and interpretation of respiratory sinus arrhythmia measures in psychosomatic medicine: practice against better evidence?

Respiratory sinus arrhythmia (RSA) or high-frequency heart rate variability has been widely used as a noninvasive measure of cardiac vagal tone. However, their dependency on both respiration rate and tidal volume is largely ignored. Only a minority of studies published in Psychosomatic Medicine in recent years has implemented precautions for controlling respiration rate in RSA measures, and tidal volume effects were only rarely addressed. We discuss methodologic issues related to respiratory control methods and present data that demonstrate that both respiration rate and tidal volume contribute substantially to the within-individual RSA variance under conditions of variable breathing, with tidal volume contributing up to one third beyond respiration rate. Finally, we outline a respiratory control method for the time-domain index of RSA and review research pertaining to its reliability, validity, and experimental application.

Organisational injustice and impaired cardiovascular regulation among female employees

OBJECTIVES

To examine the relation between perceived organisational justice and cardiovascular reactivity in women.

METHODS

The participants were 57 women working in long term care homes. Heart rate variability and systolic arterial pressure variability were used as markers of autonomic function. Organisational justice was measured using the scale of Moorman. Data on other risk factors were also collected.

RESULTS

Results from logistic regression models showed that the risk for increased low frequency band systolic arterial pressure variability was 3.8-5.8 times higher in employees with low justice than in employees with high justice. Low perceived justice was also related to an 80% excess risk of reduced high frequency heart rate variability compared to high perceived justice, but this association was not statistically significant.

CONCLUSIONS

These findings are consistent with the hypothesis that cardiac dysregulation is one stress mechanism through which a low perceived justice of decision making procedures and interpersonal treatment increases the risk of health problems in personnel.

Evidence that baroreflex feedback influences long-term incidental visual memory in men

Sympathetic nervous system (SNS) activity at the time of acquisition is associated with human memory. However, rather than SNS activity per se, it may be afferent baroreflex feedback that is responsible for this effect. A pharmacological design was employed to unload (SNP, sodium nitro-prusside) and load (norepinephrine) baroreceptors. In addition to two placebo periods, epinephrine and esmolol (a peripherally acting beta1-blocker) served as control conditions for altered cardiac perception. During drug infusion blood pressure, heart rate, and perception of heartbeat were tested. Twenty-four healthy men were participated. The participants viewed emotional slides while their electromyographic eye blink responses to random noise bursts were measured (affective startle modulation paradigm) to determine potential drug impact on emotional processing. Subjects were not informed that memory testing would take place after 4 weeks. Drugs did not impact startle, thus indicating unbiased emotional processing at the time of acquisition. Norepinephrine had no effect on heartbeat perception, but improved (p = .002) recognition memory. SNP (p = .0001) increased heartbeat perception but impaired (p = .038) recognition memory. Epinephrine, on the other hand, increased heartbeat perception (p = .0001) yet did not impair but partially improve memory (effect on high arousing pictures only: p = .05). Heartbeat perception in the placebo condition did not correlate with recognition memory (p's > .5). We suggest that baroreflex unloading, with subsequent feedback activation of the SNS, impairs long-term incidental visual recognition memory in humans while baroreflex loading enhances it. Further, we propose that these memory effects are neither secondary to cardiac sensations that accompany SNS activation nor to altered emotional picture processing at the time of acquisition.

Overcommitment to work is associated with changes in cardiac sympathetic regulation

OBJECTIVE

Work stress is associated with an increased risk for cardiovascular disease (CVD). Exaggerated cardiovascular reactivity to work-related stressors or incomplete recovery after work is a proposed mechanism underlying this increase in risk. This study examined the effects of work stress on 24-hour profiles of the pre-ejection period (PEP), a measure of cardiac sympathetic activity, obtained from ambulatory measurement of the impedance cardiogram.

METHODS

A total of 67 male white-collar workers (age 47.1 +/- 5.2) underwent ambulatory monitoring on 2 workdays and 1 non-workday. Work stress was defined according to Siegrist's model as 1) a combination of high effort and low reward at work (high imbalance) or 2) an exhaustive work-related coping style (high overcommitment).

RESULTS

High overcommitment was associated with shorter absolute PEP levels during all periods on all 3 measurement days, reduced wake-to-sleep PEP differences and reduced PEP variability, as indexed by the SD.

CONCLUSIONS

Overcommitment to work was associated with an increase in basal sympathetic drive and a reduction in the dynamic range of cardiac sympathetic regulation. Both findings are compatible with the hypothesis that overcommitment induces beta-receptor down-regulation.

Where to Q in PEP

The onset of ventricular depolarization defines the start of the preejection period (PEP), which is commonly used as an index of myocardial contractility and sympathetic control of the heart. Although the fiducial point for this onset has traditionally been the onset of the Q wave of the electrocardiogram, other measurement points have also been used in the literature, including the peak of the Q wave (i.e., the onset of the R wave). Conceptual, physiological, and empirical considerations addressing the reliability and validity of these alternative metrics support the application of the Q-wave peak/R-wave onset as the fiducial point for PEP measures.

Estimating cardiac autonomic activity during sleep: impedance cardiography, spectral analysis, and Poincaré plots

OBJECTIVE

To compare noninvasive measures of cardiac autonomic activity during sleep.

METHODS

The absolute and normalized (n.u.) high and low frequency peaks from the spectral analysis of R-R intervals (HF, LF, HFn.u., LFn.u.), LF/HF ratio, pre-ejection period (PEP) from impedance cardiography, and the autocorrelation coefficient (rRR) as illustrated in Poincaré plots were measured during night-time sleep in 9 young healthy subjects. Heart rate and blood pressure were also recorded.

RESULTS

Heart rate was significantly associated with cardiac sympathetic activity (PEP, average r=-0.46), but not with cardiac parasympathetic activity (HF, average r=-0.17). rRR was significantly associated with heart rate (average r=0.41), and LF/HF (average r=0.69), but not with PEP or HF. From NREM to REM sleep, heart rate, LFn.u., LF and rRR significantly increased, HFn.u. significantly decreased, LF/HF showed an increasing trend (P=0.07) and PEP showed a decreasing trend (P=0.06). Blood pressure and HF were highly variable without significant changes from NREM to REM sleep.

CONCLUSIONS

Cardiac parasympathetic activity (HF) does not vary greatly between sleep stages. Cardiac sympathetic activity (PEP) decreases linearly during sleep. rRR and LF/HF can track sympathovagal changes during sleep, but cannot differentiate between changes in cardiac parasympathetic and sympathetic activity. The relative advantages and disadvantages of the different measures are discussed.

Anxiety and hostility are associated with reduced baroreflex sensitivity and increased beat-to-beat blood pressure variability

OBJECTIVE

The purpose of this study was to determine whether psychological factors are associated with heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) among healthy middle-aged men and women.

METHODS

A population-based sample of 71 men and 79 women (35-64 years of age) was studied. Five-minute supine recordings of ECG and beat-to-beat photoplethysmographic finger systolic arterial pressure and diastolic arterial pressure were obtained during paced breathing. Power spectra were computed using a fast Fourier transform for low-frequency (0.04-0.15 Hz) and high-frequency (0.15-0.40 Hz) powers. BRS was calculated by cross-spectral analysis of R-R interval and systolic arterial pressure variabilities. Psychological factors were evaluated by three self-report questionnaires: the Brief Symptom Inventory, the shortened version of the Spielberger State-Trait Anger Expression Inventory, and the Toronto Alexithymia Scale.

RESULTS

Psychological factors were not related to HRV. Anxiety was associated with decreased BRS (p = 0.001) and higher low-frequency (p = 0.002) power of systolic arterial pressure variability. These associations were independent of age, gender, other psychological factors, heart rate, and systolic and diastolic blood pressures. Hostility was an independent correlate of increased low-frequency power of diastolic arterial pressure (p = 0.001) and increased high-frequency power of systolic arterial pressure (p = 0.033) variability.

CONCLUSIONS

Anxiety and hostility are related to reduced BRS and increased low-frequency power of BPV. Reduced BRS reflects decreased parasympathetic outflow to the heart and may increase BPV through an increased sympathetic predominance.

Rate response of a closed-loop stimulation pacing system to changing preload and afterload conditions

Closed-loop stimulation (CLS) is a new sensor concept for rate adaptive pacing measuring changes in the unipolar right ventricular impedance, which correlates to changes of the right ventricular contractility and reflects the autonomic nervous innervation of the heart. Some patients do not tolerate the CLS mode because of inappropriate tachycardia, mainly related to postural changes. This study tested if the rate response of the CLS sensor is influenced not only by myocardial contractility but also by rapid changes in right ventricular filling. In 12 patients (10 men, median age 77 years) with a Biotronik Inos(2)-CLS DDDR pacemaker and 14 controls (13 men, median age 59 years) head-up tilt and handgrip testing was performed to provoke rapid changes in pre- and afterload. Tilting the pacemaker patients resulted in a nonphysiological steep increase of the sensor rate (increase >20 beats/min, peak after 1 minute, return to baseline within 2-3 minutes), which was significantly different from the control group, showing only a slight rise in intrinsic heart rate immediately after tilting. Simultaneously to the rapid increase in sensor rate, the pacemaker patients showed a marked orthostatic decline of systolic blood pressure. During handgripping, heart rate and blood pressure curves were similar in both groups. In patients with this CLS pacemaker, rapid preload reduction during head-up tilting caused an overshooting sensor rate increase, reproducing the authors' clinical observation of postural pacemaker tachycardia in some patients. Consequently, they concluded that the rate response of the CLS pacing system can be inappropriately influenced by rapid shifts of blood volume, affecting right ventricular filling.

Hopelessness is associated with decreased heart rate variability during championship chess games

OBJECTIVE

Clinical observations suggest that negative affects such as helplessness/hopelessness (HE/HO) may induce autonomic duration; affects were assessed for every move after reconstruction of the games. In all games compiled, 18 situation of intense confidence/optimism and 20 of intense helplessness/hopelessness were observed.

RESULTS

Intense affects of HE/HO were associated with decreasing HF-HRV (Fisher exact test, p =.003), increasing "nervousness" (p =.0005), decreasing "optimism" (p =.0005), and decreasing "calmness" (p =.0005).

CONCLUSIONS

Investigation of championship chess game players with an ELO strength > or = 2300 in a natural field setting revealed increasing HE/HO being associated with reduced HF-HRV suggestive of vagal withdrawal. Thus, our data may help link negative mood states, autonomic nervous system disturbances, and cardiac events.