Effects of stress on heart rate complexity—A comparison between short-term and chronic stress

This study examined chronic and short-term stress effects on heart rate variability (HRV), comparing time, frequency and phase domain (complexity) measures in 50 healthy adults. The hassles frequency subscale of the combined hassles and uplifts scale (CHUS) was used to measure chronic stress. Short-term stressor reactivity was assessed with a speech task. HRV measures were determined via surface electrocardiogram (ECG). Because respiration rate decreased during the speech task (p < .001), this study assessed the influence of respiration rate changes on the effects of interest. A series of repeated-measures analyses of covariance (ANCOVA) with Bonferroni adjustment revealed that short-term stress decreased HR D2 (calculated via the pointwise correlation dimension PD2) (p < .001), but increased HR mean (p < .001), standard deviation of R–R (SD_RR) intervals (p < .001), low (LF) (p < .001) and high frequency band power (HF) (p = .009). Respiratory sinus arrhythmia (RSA) and LF/HF ratio did not change under short-term stress. Partial correlation adjusting for respiration rate showed that HR D2 was associated with chronic stress (r = −.35, p = .019). Differential effects of chronic and short-term stress were observed on several HRV measures. HR D2 decreased under both stress conditions reflecting lowered functionality of the cardiac pacemaker. The results confirm the importance of complexity metrics in modern stress research on HRV.     

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.     

Cardiovascular Variability During Periodic Leg Movements in Sleep in Children

Study Objectives:

Periodic leg movements in sleep (PLMS) are episodes of repetitive and stereotypic leg movements occurring during sleep. In adults, research indicates that PLMS affects sleep quality and duration and are associated with a shift to relatively greater sympathetic influence over cardiovascular variables. However, little research has been performed to investigate the effect of PLMS episodes on cardiac autonomic control in children. This study aimed to quantify the effect of PLMS episodes during NREM2 sleep on heart rate variability (HRV) measures of sympathovagal balance in children.

Participants:

Overnight polysomnography data from 20 children (7–12 y) referred for assessment of sleep disordered breathing (SDB) were analyzed retrospectively. Ten children with episodes of PLMS were matched for age and SDB severity with a control group of 10 children without PLMS episodes.

Results:

The LF/HF ratio was significantly higher in the PLM+ compared with both the PLM− periods from PLMS subjects (P < 0.001) and the periods from the control group (P < 0.001). However, this effect could not be parsimoniously interpreted due to the likelihood that leg movements had a direct effect on the lower frequencies. Analysis of the ratio PLM+ to PLM+ plus PLM− indicated parasympathetic inhibition during periods of periodic leg movement and the onset of individual leg movements were associated with cardiac acceleration followed by a return to pre-movement levels.

Conclusion:

This study identified vagal inhibition in association with episodes of PLMS in children. Rapid cardiac acceleration occurring concurrently with the onset of individual leg movements also suggested decreased vagal activity associated with the movements.

Citation:

Walter LM; Foster AM; Patterson RR; Anderson V; Davey MJ; Nixon GM; Trinder J; Walker AM; Horne RSC. Cardiovascular variability during periodic leg movements in sleep in children. SLEEP 2009;32(8):1093-1099.     

The relationships of impulsivity and cardiovascular responses: The role of gender and task type

The present study was conducted to assess the relationships of impulsivity with both baseline cardiovascular levels and reactivity during two laboratory stressors in both female and male young adults. Heart rate (HR), blood pressure (BP), and heart rate variability (HRV) were measured at rest and during a reaction time and speech task in one hundred and one undergraduate students. Impulsivity was measured using the Barratt Impulsiveness Scale-11 and Block's Ego-Undercontrol Scale. Males and females responded similarly to both laboratory tasks and also did not differ on the impulsivity scales. For males, higher scores on impulsivity were associated with higher systolic BP levels at rest but decreased systolic BP and HR reactivity during the preparation of the speech task; females showed no relationships of resting cardiovascular levels with impulsivity, but more impulsive females did show decreased HR response during speech preparation. No significant relationships were found between impulsivity and either HRV levels or reactivity. It is speculated that tasks involving a degree of planning may be important to find relationships between impulsivity and cardiovascular reactivity, especially in males.     

In vivo specific tension of the human quadriceps femoris muscle

It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F _t) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F _t by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 ± 5 N cm⁻²) was similar to and correlated with that of Method 2 (29 ± 5 N cm⁻²; R ² = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited.     

Heart Rate Variability in Outbred White Rats upon Periodical α-Tocopherol Administration

Effect of α-tocopherol (vitamin E) periodical administration on heart rhythm regulation was investigated in outbred white rats. α-Tocopherol administration to males was followed by reduction of sympathetic neural influence on heart rhythm and also by the increase of the number of individuals with high activity of autonomic regulation loop. In female rats α-tocopherol administration modulates the activity of humoral control circuit and promotes heart rate reduction, however upon that the percent of females with high centralization of heart rate regulation was increased. Translated from Byulleten’ Experimental’noi Biologii i Meditsiny, Vol. 147, No 2, pp. 130–133, February, 2009     

Heart Rate Variability in Rats with Experimental Chronic Heart Failure and Long-Term Exposure to β-Adrenoblockers

Simulation of chronic heart failure in rats led to an increase in heart rate variability and decrease in heart rate. All β-blockers also promoted the heart rate variability augmentation in ill animals. The most potent effects on heart rate variability were produced by pindolol, atenolol, and propranolol. Bisoprolol and metoprolol affected heart rate and heart rate variability in less extent, and nebivolol normalized a part of heart rate variability parameters. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 147, No. 2, pp. 139–143, February, 2009     

Review of the Lynch syndrome: history, molecular genetics, screening, differential diagnosis, and medicolegal ramifications

Platelets have a central role in the development of arterial thrombosis and subsequent cardiovascular events. An appreciation of this complex process has made antiplatelet therapy the cornerstone of cardiovascular disease management. However, numerous patients will experience a recurrent atherothrombotic vascular event despite adequate antiplatelet therapy. Individual differences in the rate of platelet activation and reactivity markedly influence normal hemostasis and the pathological outcome of thrombosis. Such an individual variability is largely determined by environmental and genetic factors. These are known to either hamper platelets' response to agonists, and thereby mimic the pharmacological modulation of platelet function or mask therapy effect and sensitize platelets. In this article, we reviewed the antiplatelet mechanisms of aspirin and clopidogrel and the possible role of different polymorphisms, which may affect the efficacy of antiplatelet therapy. Heterogeneity in the way patients respond to aspirin and clopidogrel may in part reflect variation in cyclooxygenase (COX)-1, COX-2, glycoprotein (GP) Ib alpha, GP Ia/IIa, GP IIb/IIIa, UGT1A6*2, P2Y₁, P2Y₁₂, CYP2C9, CYP3A4 and CYP3A5 genotypes.     

Recovery of motor and cognitive function after cerebellar lesions in a songbird – role of estrogens

In addition to its key role in complex motor function, the cerebellum is increasingly recognized to have a role in cognition. Songbirds are particularly good models for the investigation of motor and cognitive processes but little is known about the role of the songbird cerebellum in these processes. To explore cerebellar function in a songbird, we lesioned the cerebellum of adult female zebra finches and examined the effects on a spatial working memory task and on motor function during this task. There is evidence for steroid synthesis in the songbird brain and neurosteroids may have an impact on some forms of neural plasticity in adult songbirds. We therefore hypothesized that neurosteroids would affect motor and cognitive function after a cerebellar injury. We found that cerebellar lesions produced deficits in motor and cognitive aspects of a spatial task. In line with our prediction, birds in which estrogen synthesis was blocked had impaired performance in our spatial task compared with those that had estrogen synthesis blocked but estrogen replaced. There was no clear effect of estrogen replacement on motor function. We also found that lesions induced expression of the estrogen synthetic enzyme aromatase in reactive astrocytes and Bergmann glia around a cerebellar lesion. These data suggest that the cerebellum of songbirds mediates both motor and cognitive function and that estrogens may improve the recovery of cognitive aspects of cerebellar function after injury.     

Impulsive choice in hippocampal but not orbitofrontal cortex-lesioned rats on a nonspatial decision-making maze task

Orbitofrontal cortical (OFC) and hippocampal (HPC) lesions in primates and rodents have been associated with impulsive behaviour. We showed previously that OFC- or HPC-lesioned rats chose the immediate low-reward (LR) option in preference to the delayed high-reward (HR) option, where LR and HR were associated with different spatial responses in a uniform grey T-maze. We now report that on a novel nonspatial T-maze task in which the HR and LR options are associated with patterned goal arms (black-and-white stripes vs. gray), OFC-lesioned rats did not show impulsive behaviour, choosing the delayed HR option, and were indistinguishable from controls. In contrast, HPC-lesioned rats exhibited impulsive choice in the nonspatial decision-making task, although they chose the HR option on the majority of trials when there was a 10-s delay associated with both goal arms. The previously reported impairment in OFC-lesioned rats on the spatial version of the intertemporal choice task is unlikely to reflect a general problem with spatial learning, because OFC lesions were without effect on acquisition of the standard reference memory water-maze task and spatial working memory performance (nonmatching-to-place) on the T-maze. The differential effect of OFC lesions on the two versions of the intertemporal choice task may be explained instead in terms of the putative role of OFC in using associative information to represent expected outcomes and generate predictions. The impulsivity in HPC-lesioned rats may reflect impaired temporal information processing, and emphasizes a role for the hippocampus beyond the spatial domain.