Autonomic nervous control of the heart rate response to dynamic incremental exercise: evaluation of the Rosenblueth-Simeone model

Summary To evaluate the validity of the Rosenblueth-Simeone model for the heart rate response to incremental dynamic exercise, 11 healthy men performed maximal exercise tests on a cycle ergometer after administration of placebo, propranolol, atropine or both propranolol and atropine. The model showed that the influence of sympathetic activity on heart rate increased at intensities up to those which resulted in a heart rate 70% maximal heart rate on placebo, and levelled off at higher intensities, while there was a progressive withdrawal of the parasympathetic activity. The ratio between heart rate predicted by the model and the recorded heart rate following placebo treatment tended to be less than 1.0 at lower exercise intensities, and approached the unit at intensities above those which resulted in a heart rate higher than 70% of maximal heart rate on placebo. There was a strong correlation (r=0.94,P<0.01) between the heart rate on placebo and the heart rate estimated by the model. Nevertheless, there was some scattering of the data around the identity line, with a standard error of the estimate for the regression line of 11 beats · min^–1. Thus, during incremental exercise, the influence of sympathetic activity on heart rate does not become progressively more important at higher exercise intensities. The application of the Rosenblueth-Simeone model shows limitations during incremental exercise, particularly at low exercise intensities.     

Autonomic nervous control of the heart rate during isometric exercise in normal man

The relative contribution of the efferent components of the autonomic nervous system to the regulation of tachycardia induced by isometric exercise was assessed in 23 normal males. The isometric exercise (handgrip) was performed at the maximum intensity tolerated by the individual over a period of 10 s (maximal voluntary contraction — MVC) and at levels equivalent to 75, 50 and 25% of MVC for 20, 40 and 10 s, respectively. The study was performed both under control conditions and after pharmacological blockade with atropine (12 individuals) or propranolol (11 individuals). Under control conditions, the heart rate (HR) responses to isometric effort were dependent on the intensity and duration of the exercise, showing a tendency towards progressive elevation with the maintenance of muscular contraction at the levels studied. The tachycardia evoked by this effort was of considerable magnitude and of rapid onset, especially at the more intense levels of activity. Parasympathetic blockade markedly decreased tachycardia, which manifested itself during the first 10 s of exercise at all levels of intensity, whereas sympathetic blockade markedly modified the HR response after 10 s of effort at the 75 and 50% MVC levels. A slight depression of the tachycardiac response could be observed already after 10 s of maximum effort after propranolol. The present results suggest that the autonomic regulation of these responses is based on a biphasic mechanism, with the initial phase depending on the rapid withdrawal of the parasympathetic influence, followed by a marked sympathetic contribution to the induction of tachycardia after 10 s of isometric contraction or even a little before at maximum exertion.     

Effect of short-term exercise training on muscle glycogen in resting conditions in rats fed a high fat diet

Summary It has been reported that exercise training increases muscle glycogen storage in rats fed a high carbohydrate (CHO) diet in resting conditions. The purpose of this study was to examine whether a 3-week swimming training programme would increase muscle glycogen stores in rats fed a high-fat (FAT) diet in resting conditions. Rats were fed either the FAT or CHO diet for 7 days ad libitum, and then were fed regularly twice a day (between 0800 and 0830 hours and 1800 and 1830 hours) for 32 days. During this period of regular feeding, half of the rats in both dietary groups had swimming training for 3 weeks and the other half were sedentary. The rats were not exercised for 48 h before sacrifice. All rats were killed 2 h after their final meal (2030 hours). The glycogen contents in red gastrocnemius muscle, heart and liver were significantly higher in sedentary rats fed the CHO diet than in those fed the FAT diet. Exercise training clearly increased glycogen content in soleus, red gastrocnemius and heart muscle in rats fed the CHO diet. In rats fed the FAT diet, however, training did not increase glycogen content in these muscles or the heart. Exercise training resulted in an 87% increase of total glycogen synthase activity in the gastrocnemius muscle of rats fed the CHO diet. However, this was not observed in rats fed the FAT diet. The total glycogen phosphorylase activity in the gastrocnemius muscle of the rats of both dietary groups was increased approximately twofold by training. These results suggested that muscle glycogen was enhanced in rats fed the CHO diet and that the glycogen content of the muscle of rats fed the FAT diet was not increased by exercise training.     

Exercise training and resting oxygen consumption

Summary Resting oxygen consumption was measured in trained and nontrained normal, hypophysectomized and thyroidectomized rats. No training effect was found for resting oxygen consumption in any of the groups after the 10 week training program. Evidence is presented which indicates that for animals of homogeneous body size, expressing metabolism as a function of body weight is no less valid than expressing metabolism as an exponential function of body weight.This work was supported by PHS grant AM 08893-4.PHS Trainee, Department of Physiology and Biophysics.     

Conditioned heart rate response: Testing under anaesthesia in rats

Classically conditioned heart rate response was studied in anaesthetized rats. Rats were conditioned with photic stimuli followed by electric tail shocks in a conscious state and tested under anaesthesia for conditioned heart rate change. Testing photic stimuli evoked a transient bradycardia in about one-third of testing trials. Magnitude of the bradycardia was significantly greater in conditioned rats than that in untrained or control rats trained with electric tail shocks followed by photic stimuli. The difference was found to be mainly due to the difference in amplitude of individual bradycardia response rather than that in frequency of occurrence of the response. Testing stimuli also evoked a slight and sustained tachycardia, but magnitude of the tachycardia in conditioned rats did not differ significantly from that in control or untrained rats. These results suggest that effects of classical conditioning on autonomic functions can be detected and studied under anaesthesia.     

The effect of endurance training on resting heart rate variability in sedentary adult males

Eleven previously sedentary adult males, serving as the experimental (EXP) group [mean (SE) age 36.6 (1.7) years, body mass 87.2 (4.3) kg, body mass index, BMI, 28.4 (1.5) kg·m^–2] participated in a 16-week supervised exercise program (3 days·week^–1, 30 min·day^–1, at ≅80% of heart rate reserve) to determine the temporal effects of a moderate-to-vigorous-intensity exercise program on heart rate variability (HRV). Five sedentary males [mean (SD) age 36.6 (4.2 )years, body mass 83.8 (6.6) kg, BMI 22.8 (1.7) kg·m^–2] served as non-exercising controls (CON). HRV was measured every 4 weeks from a resting electrocardiogram obtained while subjects paced their breathing at 10 breaths·min^–1 (0.167 Hz). The time-domain measures of HRV recorded were the proportion of adjacent intervals differing by more than 50 ms (pNN50), the root mean square of successive differences (rMSSD), and the standard deviation of the resting interbeat interval. The frequency-domain measures recorded were high (HF) and low (LF) frequency oscillations, as determined using the fast Fourier transform technique. Aerobic capacity (i.e., peak oxygen uptake) increased by 13.8% in EXP (P<0.001), but did not change in CON. Resting heart rate did not change in either EXP or CON. In EXP, pNN50 at week 12 (P<0.01), rMSSD at weeks 12 (P<0.01) and 16 (P=0.05), and HF power at weeks 12 (P<0.01) and 16 (P=0.05) were elevated above baseline. Time- and frequency-domain measures of HRV remained unchanged in CON. It is concluded that a moderate-to-vigorous-intensity exercise program produces increases in time- and frequency-domain measures of HRV within 12 weeks. Electronic Publication     

The effects of different inspiratory muscle training intensities on exercising heart rate and perceived exertion

This study investigated the relationship between the intensity of an inspiratory muscle training programme and its effect on respiratory muscle strength, exercising heart rate, and ratings of perceived exertion. A total of 66 subjects were randomly assigned to one of three groups. One group trained at 100% of maximum inspiratory pressure (MIP) for 6 weeks (MAX, n=22). A second group performed 6 weeks of inspiratory muscle training at 80% of MIP (SUB, n=21) and a third control group received no inspiratory training (CON, n=23). Both the MAX and SUB training groups improved MIP relative to the control group [32 (19) cmH₂O, P=0.01; 37 (25) cmH₂O, P=0.001, respectively]. A significant decrease in heart rate [–6 (9) beats min^–1, P=0.02] and rating of perceived exertion [–0.5 (1.4), P=0.04] was observed for the MAX group only. It is concluded that 6 weeks of both MAX and SUB training were sufficient to improve inspiratory muscle strength. However, exercising heart rate and perceived exertion decreased with MAX training only.     

外周有关递质对疑核（AMB）调节细胞免疫机能的影响

本实验研究了三种受体拮抗剂对电刺激疑核调节细胞免疫机能的影响,并对疑核调节机体细胞免疫的机制作了探讨。实验用麻醉家兔,分3组进行。分别在静注阿托品、酚妥拉明或心得安后电刺激疑核,并分别于注射前及刺激后不同时间取外周血,测定T细胞百分率及对PHA的反应。结果:阿托品组上述免疫指标比注射前明显降低;酚妥拉明组上述免疫指标在刺激后60分钟时比注射前有所升高;心得安组上述指标在刺激后120分钟时比注射前明显降低。提示:疑核对细胞免疫机能的调节可能是通过迷走神经末梢释放乙酰胆碱,作用于免疫器官及免疫细胞上的M型胆碱能受体实现的。     

Influence of physical training,aortic constriction and exogenous anterior pituitary hormones on the heart weights of hypophysectomized rats

Summary Studies were conducted with hypophysectomized rats to determine the effects of chronic exercise (training), injections of exogenous hormones, aortic constrictions and combinations there of on the weight of the heart. In addition, the role of growth hormone on cardiac weight was reinvestigated. The hypophysectomized rats that were trained for 10 weeks or longer had significantly heavier heart weights than their nontrained counterparts. When daily injections of a single exogenous hormone of ACTH, GH, ICSH or TSH were made into trained and nontrained animals, there was no trained group that had significantly heavier heart weights than their control group. Rats having aortic constrictions or receiving DOCA injections also had significantly heavier heart weights than their controls. When various dosages of GH (0.2 mg to 6.0 mg) were injected daily for three weeks, no evidence was obtained that indicated that the presence of this hormone resulted in cardiac enlargement. It was concluded that under the experimental condition of this study, cardiac enlargement can occur in hypophysectomized rats when the work demands on the heart have been increased.Supported in part by funds provided by the Iowa Heart Association.     

运用排列熵方法分析冥想训练对心率变异性的影响

背景：冥想训练有利于保持身体与心理健康,训练过程中通过自主神经调整训练心率是一个可能的因素。两者之间关系的研究有助于加深对于心血管系统调节以及健康训练的理解。 目的：从复杂性分析的角度考察冥想训练过程中心率调整的规律。 方法：心率变异信号取自PhysioNet中冥想训练心率数据库,应用排列熵方法对中国气功以及瑜伽训练前和训练中数据分别进行分析,考察两种训练对于心率复杂性的影响。 结果与结论：冥想训练中心率变异序列的排列熵值均显著小于训练前的熵值,表明中国气功以及瑜伽均有降低心率复杂性的效果。而前期研究使用排列熵对于年轻、年老、心力衰竭患者的研究表明衰老和疾病会使排列熵值增加。因此,冥想训练通过自主神经对心率的调整可能是其帮助人体保持健康的一个重要因素。     

Identification of low and high frequency ranges for heart rate variability and blood pressure variability analyses using pharmacological autonomic blockade with atropine and propranolol in swine

Understanding autonomic nervous system functioning, which mediates behavioral and physiological responses to stress, offers great potential for assessing farm animal stress and welfare. Evaluation of heart rate variability (HRV) and blood pressure variability (BPV), using time and frequency domain analyses may provide a sensitive and reliable measure of affective states and stress-mediated changes in sympathetic and parasympathetic tones. The aim of this research was to define low (LF) and high frequency (HF) power spectral ranges using pharmacological autonomic blockade, and to examine HRV and BPV parameter changes in response to atropine and propranolol in swine. Ten, 13-week old, barrows (n = 6) and gilts (n = 4) underwent surgery to place an intra-cardiac electrode and a blood pressure catheter attached to a biotelemetric transmitter; pigs had a 3-week recovery period prior to data collection. Each pig was subjected to administration of 4 intravenous (i.v.) drug treatments: a control treatment, 3 mL of saline, and 3 blockade treatments; 0.1 mg/kg of atropine, 1.0 mg/kg of propranolol, and .1 mg/kg of atropine together with 1.0 mg/kg of propranolol. All treatments were delivered by injection in the jugular vein with a minimum of 48 h between individual treatments. Behavior, ECG and blood pressure data were recorded continuously for a total of 1 h, from 30 min pre-injection to 30 min post-injection. For data analyses, two 512-beat intervals were selected for each treatment while the pig was lying and inactive. The first interval was selected from the pre-injection period (baseline), and the second was selected between 10 and 30 min post-injection. Time and frequency domain (power spectral density) analyses were performed on each data interval. Subsequent, LF and HF bands from the power spectral densities were defined based on general linear and regression analyses. The HRV and BPV were computed with a covariate (baseline) factorial analysis of treatment by sex interaction, and day of injection, with mixed models and Tukey's post-hoc tests. The best-fit range for LF was 0.0-0.09 Hz, and HF was 0.09-2.0 Hz (r²: 0.41 and 0.43, respectively). Propranolol and saline injections led to a greater overall total power and overall higher inter-beat interval, HF and LF power. Atropine led to a dominant sympathovagal balance of the cardiac activity in pigs. In addition, atropine led to an increase in LF power of both systolic and diastolic blood pressures in gilts suggesting vagal tone mediation of BPV. The understanding of autonomic regulation of HRV and BPV in domestic swine facilitates our ability to detect and quantify stress responses, and broadens its application in assessing farm animal welfare.     

The effect of exercise training on restraint ulcers in rats

The effect of chronic treadmill running on susceptibility to restraint-cold-induced ulcers was studied in two strains of rats: Long-Evans and Sprague-Dawley. Runners were progressively trained for 8 weeks, reaching a rate of 1 mph for 1 hr daily, 5 days per week after the 4th week. Walkers were exposed to the treadmill environment 3 days per week (0.2 mph for 10 min). Sedentary groups remained in their home cages. After 8 weeks the rats were starved for 24 hrs, immobilized in restraint cages and placed in the refrigerator (5° C) for 4 hrs. Animals were then sacrificed and their stomachs examined for ulcerative lesions. No significant differences in number of ulcers or ulcer indexes per stomach were found between groups within each rat strain or between strains. These results suggest that treadmill running provides no protection against gastric ulceration induced by restraint-cold stress. The complex variables involved in ulcer research are discussed and suggestions presented for future work on the anti-ulcer effect of exercise.Supported in part by the University of Nebraska Research Council Summer Fellowship.     

Changes in resting heart rate variability across the menstrual cycle

Heart rate variability (HRV) is a noninvasive indicator of autonomic control. This study examines HRV changes across a normal menstrual cycle and proposes a novel piecewise function controlling for the effects of breathing on HRV spectral parameters. A resting ECG was collected from 13 women at five points in their menstrual cycle. Both heart rate and breathing rate increased across the cycle (p < .01) while time‐domain variability decreased (p = .04). Use of the piecewise function for breathing rate in HRV spectral analysis was confirmed by a substantial increase in model goodness‐of‐fit. HRV spectral parameters, controlled for breathing with the piecewise function, confirm that the decrease in variability is likely due to a parasympathetic withdrawal, since high frequency HRV decreases (p = .02).     

Effect of enflurane on the baroreflex control of heart rate in decerebrate rats

Volatile anesthetics alter the arterial baroreflex (BRX) but its mechanisms are poorly understood. This study was designed to determine the effect of 1 and 2 minimal alveolar concentrations (MAC) of enflurane on the BRX parameters in unanesthetized brain stem-intact and decerebrate rats. Under enflurane anesthesia, the femoral artery and both femoral vein were catheterized for pressor (phenylephrine) and depressor (nitroprusside) drug delivery and continuous blood pressure measurements. Decerebration was performed at midcollicular level. BRX tests were performed in 3 time periods; before enflurane (conscious brain-intact), during 1 or 2 MAC enflurane exposure 1 hour after a sham operation or a decerebration operation, and 2 hours after the termination of enflurane (zero enflurane). Mean arterial pressure (MAP) and heart rate (HR) were fitted to a sigmoid logistic equation, the Boltzman equation. The curve of best fit was obtained with a computer program. 1 MAC and 2 MAC of enflurane shifted MAP-HR baroreflex curves to the left in the all groups and significantly attenuated the baroreflex range. The slope of conscious intact period and zero enflurane period of each group did not change significantly, but during the enflurane period the slope was significantly lowered. Enflurane depressed the baroreflex sensitivity (slope) and the HR range in a similar dose-dependent manner in both brain stem-intact and decerebrate rats. Such results draw into question whether the suprapontine sites contribute to enflurane's actions on cardiovascular autonomic regulation.     

Relationship between heart rate and ventricular ectopic rhythm in acute myocardial infarction

Summary The study of 1313 time intervals from 146 patients with acute myocardial infarction showed that a linear relationship exists between the occurrence of ventricular ectopic beats or runs of ventricular ectopic beats and the heart rate. With faster heart rates, the percentage of these arrhythmias is decreased. Ventricular tachycardias and ventricular fibrillation or flutter were also seen most commonly in bradycardia, but there was a second maximum in frequencies exceeding 110/min. It is supposed that in cases with such tachycardial heart action severe heart failure and myocardial hypoxia are often present and that under these circumstances, only relatively few ventricular ectopic beats are necessary to trigger ventricular tachycardias or ventricular flutter/fibrillation.These results underscore in clinical practice that acceleration of heart frequency is a reliable measure to suppress ventricular ectopic rhythm. Electrostimulation of the right atrium is recommended for this purpose, although a stable position for the electrode catheter within the atrium may be difficult to achieve.     

Effect of high intensity intermittent training on heart rate variability in prepubescent children

The purpose of this study was to observe the effect of high intermittent exercise training on children’s heart rate variability (HRV). Thirty-eight children (age 9.6 ± 1.2 years) were divided into an intermittent (IT, n = 22) and a control group (CON, n = 16). At baseline and after a 7-week training period, HRV parameters, peak oxygen consumption and maximal aerobic velocity (MAV) were assessed. Training consisted of three 30-min sessions composed by short maximal and supramaximal runs at velocities ranging from 100 up to 190% of MAV. HRV was computed in time and frequency domains. Training resulted in a significant increase in MAV and in IT (P < 0.05) only without any significant change in HRV parameters for the two groups. Thus, 7 weeks of high intermittent exercise training allows to improve aerobic fitness. However, this modality of training was not sufficient enough to underline a possible effect on the heart rate autonomic regulation in children.     

Moderate endurance training has no effect on the parathyroid function of heart transplant patients

The benefit of retraining for heart transplant recipients (HTR) is now well established. The rehabilitation of these patients can be compromised by osteopenia and bone fractures. The resting levels of parathyroid hormone (PTH) and exercise-induced increases are higher in HTR than in healthy controls. To evaluate the effect of a moderate endurance training programme on parathyroid activity, six HTR, an average of 18 months after transplant, and seven healthy sedentary controls have been studied. None of the subjects had a history of bone disease. Two exercise tests (square wave endurance exercise tests, SWEET) with identical work rates were performed before and after training. Intact PTH, ionized calcium (Ca²⁺), phosphorus (Pi) and pH were measured at rest, during exercise and in the recovery periods. Training consisted of a 45-min SWEET three times a week for 6 weeks. Levels of Ca²⁺, Pi and PTH showed a significant increase during the exercise session in both groups. Ca²⁺ and Pi levels decreased rapidly after the cessation of exercise whereas PTH reached a peak at the 10th min of the recovery in both groups. This increase in PTH was significantly higher in HTR than in controls. However, despite a significant improvement of total endurance work (+28% in HTR, +29% in controls) this endurance training had no effect on resting levels of PTH, plasma Ca²⁺ or Pi, nor on their exercise-induced variations. The exercise-induced decrease in pH was less pronounced after training which is evidence of training. We conclude that a short endurance training programme does not alter the moderate hyperparathyroidism of HTR. The effect of such a training programme on bone mass and bone mineral density needs now to be evaluated. Accepted: 4 February 1997     

Cortical thickness,resting state heart rate,and heart rate variability in female adolescents

Resting state heart rate variability (HRV) is a psychophysiological marker that has gained increasing research interest, in particular in developmental neuroscience. HRV has been shown to be associated with mental and physical health, beyond simple measures of heart rate (HR) and shows inter‐ and intraindividual variance across aging. Recently, three studies reported on a positive correlation between resting state HRV and cortical thickness in selected regions of interest (ROIs) in adult samples. Structural thickness, HRV, and HR change during the sensitive period of adolescence. Previously, no study has addressed the structural concomitants of resting HR and HRV in adolescents. Cortical thickness (3‐T MRI), HR, and HRV were recorded in 20 healthy, female adolescents (mean age: 15.92 years; SD = 1.06; range: 14–17). In line with existing research in adults, cortical thickness in a number of ROIs was associated with resting state HRV but not HR. The comparison of regression analyses using the Bayes factor revealed evidence for a correlation between HRV and cortical thickness of the bilateral rostral anterior cingulate cortex. However, unlike in adults, greater cortical thickness was associated with reduced HRV in female adolescents. Analyses on HR showed no superior model fit. Results suggest that greater HRV might be beneficial for cortical development during adolescence (cortical thinning). On the other hand, cortical development might determine changes in autonomic nervous system function in adolescents. Future studies are needed to replicate these findings in larger samples including boys and to test these hypotheses in longitudinal designs.