Baroreceptor reflex and arterial rigidity in adolescents

The heart rate (HR) variability and pulse wave delay (PWD) in the major arteries of schoolchildren were studied. The function of ordinary coherence of the HR and PWD was used, which reflects the linear relationship between the two processes in the heart and vessels. The high tone of the sympathetic part of the autonomic nervous system (ANS) in schoolchildren causes an increase in heart performance and decreases the shift in the phase of association between HR and PWD, which leads to the appearance of a new characteristic of the system, arterial rigidity. The results of the physiological activation of the sympathetic part of ANS during passive orthostasis and pharmacological trials with blockers of ANS receptors in schoolchildren with heart arrhythmia at rest are presented.     

Changes in some indices of the cardiovascular system in different mental tasks

In order to study the effects of the type of mental activity on the function of the cardiovascular system in humans, the following indices were used: the heart rate (HR), RR interval, variation magnitude (VM), systolic wave amplitude (SWA), and pulse wave transit time (PWTT). These indices were recorded when the subjects solved verbal-logical or spatial mental tasks. The HR was substantially increased during solving of the spatial tasks as compared to solving of the verbal-logical tasks, whereas the SWA showed the opposite changes. The latencies of the performance of the tasks of various types were similar in the subjects; therefore, the changes in the autonomic indices did not depend on the difficulties of the mental tasks. They rather depended on specific features of the mental processes involved in the performance of the tasks of different types. Thus, changes in the HR and the decreased SWA, which was related to elevated blood pressure, represent the effect of the sympathetic nervous system on the heart function during solving verbal-logical tasks. Our data demonstrate that the HR and blood pressure can be used as additional indices for the development of new techniques for assessment of different types of mental processes together with the indices of electrical brain activity.     

Changes in indexes of cardiovascular system in different mental tasks

The influence of different types of mental activity on the cardiovascular system was analyzed by following indexes: the heart rate (HR), the variation magnitude (VM), the amplitude of systolic wave (SWA) and the pulse wave transit time (PWTT). A registration of these indexes was conducted when the subjects solved verbal-logical and spatial mental tasks. HR was significantly greater in the spatial tasks than in the verbal-logical tasks, while SWA had an inverse relationship. The time for solving of tasks of the both types did not differ significantly. Therefore, the observed changes in autonomic indexes were not related to a difficulty of the mental tasks, but depended on the specific cognitive processes involved in the mental tasks of different types. Thus, the observed change in HR and the decrease in SWA correlating with the blood pressure rise reflect an influence of the sympathetic nervous system on the heart work during mental tasks of the verbal-logic type. The obtained results suggest that the indexes of HR and a blood pressure may also serve as supporting criteria in a development of new technologies for a determination of different types of mental operations in addition to the rhythms of the brain electrical activity.     

Transfer function analysis between arterial pressure and renal sympathetic nerve activity at cardiac pacing frequencies in the rat.

This study examined the possible influence of changes in heart rate (HR) on the gain of the transfer function relating renal sympathetic nerve activity (RSNA) to arterial pressure (AP) at HR frequency in rats. In seven urethane-anesthetized rats, AP and RSNA were recorded under baseline conditions (spontaneous HR = 338 +/- 6 beats/min, i.e., 5.6 +/- 0.1 Hz) and during 70-s periods of cardiac pacing at 6-9 Hz applied in random order. Cardiac pacing slightly increased mean AP (0.8 +/- 0.2 mmHg/Hz) and decreased pulse pressure (-3.6 +/- 0.3 mmHg/Hz) while leaving the mean level of RSNA essentially unaltered (P = 0.680, repeated-measures ANOVA). The gain of the transfer function from AP to RSNA measured at HR frequency was always associated with a strong, significant coherence and was stable between 6 and 9 Hz (P = 0.185). The transfer function gain measured under baseline conditions [2.44 +/- 0.28 normalized units (NU)/mmHg] did not differ from that measured during cardiac pacing (2.46 +/- 0.27 NU/mmHg). On the contrary, phase decreased linearly as a function of HR, which indicated the presence of a fixed time delay (97 +/- 6 ms) between AP and RSNA. In conclusion, the dynamic properties of arterial baroreflex pathways do not affect the gain of the transfer function between AP and RSNA measured at HR frequency in the upper part of the physiological range of HR variations in the rat.     

Thyroid status influences baroreflex function and autonomic contributions to arterial pressure and heart rate

The effect of thyroid status on arterial baroreflex function and autonomic contributions to resting blood pressure and heart rate (HR) were evaluated in conscious rats. Rats were rendered hyperthyroid (Hyper) or hypothyroid (Hypo) with triiodothyronine and propylthiouracil treatments, respectively. Euthyroid (Eut), Hyper, and Hypo rats were chronically instrumented to measure mean arterial pressure (MAP), HR, and lumbar sympathetic nerve activity (LSNA). Baroreflex function was evaluated with the use of a logistic function that relates LSNA or HR to MAP during infusion of phenylephrine and sodium nitroprusside. Contributions of the autonomic nervous system to resting MAP and HR were assessed by blocking autonomic outflow with trimethaphan. In Hypo rats, the arterial baroreflex curve for both LSNA and HR was shifted downward. Hypo animals exhibited blunted sympathoexcitatory and tachycardic responses to decreases in MAP. Furthermore, the data suggest that in Hypo rats, the sympathetic influence on HR was predominant and the autonomic contribution to resting MAP was greater than in Eut rats. In Hyper rats, arterial baroreflex function generally was similar to that in Eut rats. The autonomic contribution to resting MAP was not different between Hyper and Eut rats, but predominant parasympathetic influence on HR was exhibited in Hyper rats. The results demonstrate baroreflex control of LSNA and HR is attenuated in Hypo but not Hyper rats. Thyroid status alters the balance of sympathetic to parasympathetic tone in the heart, and the Hypo state increases the autonomic contributions to resting blood pressure.     

Changes in cardiac rhythm of rats in dehydration

80 mongrel rats were studied for peculiarities of the heart activity regulation in dehydration, conditions of the vegetative homeostasis being different. Data of the variation pulsometry were used. A sympathetic shift of the vegetative homeostasis was a common dehydration-caused response. The shift was significant in rats with an initial equilibrium of the vegetative homeostasis and prevailing parasympathetic effects. The survival rate of this group of rats was high. In the group of rats with the initial prevalence of a sympathetic tonus a short-term sympathetic shift was replaced by an increase of parasympathetic effects. The survival rate of this group was much lower. Therefore, rats with initial prevalence of the sympathetic compartment tonus of the vegetative nervous system are more labile to the effect of the dehydration stress.     

Power spectral analysis of heart rate variability for assessment of diurnal variation of autonomic nervous activity in guinea pigs.

We established characteristics of power spectral analysis of heart rate variability, and assessed the diurnal variations of autonomic nervous function in guinea pigs. For this purpose, an electrocardiogram (ECG) was recorded for 24 hr from conscious and unrestrained guinea pigs using a telemetry system. There were two major spectral components, at low frequency (LF) and high frequency (HF) bands, in the power spectrum of HR variability. On the basis of these data, we defined two frequency bands of interest: LF (0.07-0.7 Hz) and HF (0.7-3.0 Hz). The power of LF was higher than that of HF in the normal guinea pigs. Atropine significantly reduced power at HF. Propranolol also significantly reduced power at LF. Furthermore, the decrease in the parasympathetic mechanism produced by atropine was reflected in a slight increase in the LF/HF ratio. The LF/HF ratio appeared to follow the reductions of sympathetic activity produced by propranolol. Autonomic blockade studies indicated that the HF component reflected parasympathetic activity and the LF/HF ratio seemed to be a convenient index of autonomic balance. Nocturnal patterns, in which the values of heart rate in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed. However, the HF, LF and the LF/HF ratio showed no daily pattern. These results suggest that the autonomic nervous function in guinea pigs has no clear circadian rhythmicity. Therefore, this information may be useful for future studies concerning the autonomic nervous function in this species.     

Cardiac Autonomic Activity During Human Sleep: Analysis of Sleep Stages and Sleep Cycles

In this study characteristics of cardiac functioning were investigated in nine subjects during their nocturnal sleep. The pre-ejection period and the high frequency component of heart rate variability were used as indices of cardiac sympathetic and parasympathetic activity of the autonomic nervous system respectively. Heart rate and the autonomic indices were assessed across physiological determined sleep stages and consecutive temporal sleep cycles. Repeated measures ANOVA analyses indicated a significant pattern of heart rate as a function of sleep stages, which was mirrored by parasympathetic activity. Further, a significant decrease of heart rate as a function of sleep cycles was mirrored by an increase of sympathetic activity. Moreover, non-REM/REM differences revealed a dominant role of parasympathetic activity during sleep stages as well as sleep cycles. These findings demonstrate that sympathetic activity is influenced by time asleep, whereas parasympathetic activity is influenced by the depth of sleep.     

Cardiac Autonomic Activity During Human Sleep: Analysis of Sleep Stages and Sleep Cycles

In this study characteristics of cardiac functioning were investigated in nine subjects during their nocturnal sleep. The pre-ejection period and the high frequency component of heart rate variability were used as indices of cardiac sympathetic and parasympathetic activity of the autonomic nervous system respectively. Heart rate and the autonomic indices were assessed across physiological determined sleep stages and consecutive temporal sleep cycles. Repeated measures ANOVA analyses indicated a significant pattern of heart rate as a function of sleep stages, which was mirrored by parasympathetic activity. Further, a significant decrease of heart rate as a function of sleep cycles was mirrored by an increase of sympathetic activity. Moreover, non-REM/REM differences revealed a dominant role of parasympathetic activity during sleep stages as well as sleep cycles. These findings demonstrate that sympathetic activity is influenced by time asleep, whereas parasympathetic activity is influenced by the depth of sleep.     

Evidence for fractal correlation properties in variations of peripheral arterial tone during REM sleep

Previous studies utilizing detrended fluctuation analysis (DFA) of heart rate variability during sleep revealed a higher fractal exponent during rapid eye movement (REM) sleep than non-REM sleep. The aim of this study was to determine whether the same difference exists in the variations of peripheral arterial tone (PAT). Finger pulse wave measured by a novel plethysmographic technique was monitored during sleep in 12 chronic heart failure patients, 8 heavy snorers, and 12 healthy volunteers. For each subject, at least two 15-min time series were constructed from the interpulse intervals and from pulse wave amplitudes during REM and non-REM sleep. Fractal scaling exponents of both types of time series were significantly higher for REM than non-REM sleep in all groups. In each of the groups and in both sleep stages, the fractal scaling exponents based on pulse wave amplitude were significantly higher than those based on pulse rate variability. A repeat of the analysis for short-, intermediate-, and long-term intervals revealed that the fractal-like exponents were evident only in the short- and intermediate-term intervals. Because PAT is a surrogate of sympathetic activation, our results indicate that variations in sympathetic activation during REM sleep have a fractal-like behavior.     

Effects of psychological stress on autonomic control of heart in rats.

The aim of this study was to examine the effects of psychological stress on autonomic control of the heart in rats. For this purpose, we evoked anxiety-like or fear-like states in rats by means of classical conditioning and examined changes in autonomic nervous activity using an implanted telemetry system and power spectral analysis of heart rate variability. Anxiety-like states resulted in a significant increase in heart rate (HR), low frequency (LF) power, and LF/HF ratio, with no change in high frequency (HF) power. Fear-like states resulted in a significant increase in HR and a significant decrease in HF power with no significant change in both LF power and LF/HF ratio, although LF/HF ratio increased slightly. These results suggest that autonomic balance becomes predominant in sympathetic nervous activity in both anxiety-like and fear-like states. These changes in rats correspond to changes which are relevant to cardiovascular diseases in humans under many kinds of psychological stress. Therefore, the experimental design of this study is a useful experimental model for investigating the effects of psychological stress on autonomic control of the heart in humans.     

Phenotypic screening for heart rate variability in the mouse

We developed a technology for heart rate (HR) variability (HRV) analysis in the mouse for characterization of HR dynamics, modulated by vagal and sympathetic activity. The mouse is the principal animal model for studying biological processes. Mouse strains are now available harboring gene mutations providing fundamental insights into molecular mechanisms underlying cardiac electrical diseases. Future progress depends on enhanced understanding of these fundamental mechanisms and the implementation of methods for the functional analysis of mouse cardiovascular physiology. By telemetric techniques, standard time and frequency-domain measures of HRV were computed with and without autonomic blockade, and baroreflex sensitivity testing was performed. HR modulation in the high-frequency component is predominantly mediated by the parasympathetic nervous system, whereas the low-frequency component is under the influence of both the parasympathetic and sympathetic systems. The presented technology and protocol allow for assessment of autonomic regulation of the murine HR. Phenotypic screening for HR regulation in mice will further enhance the value of the mouse as a model of heritable electrophysiological human disease.     

Characteristics of autonomic nervous function in Zucker-fatty rats: investigation by power spectral analysis of heart rate variability.

We investigated the characteristics of autonomic nervous function in Zucker-fatty and Zucker-lean rats. For this purpose, a long-term electrocardiogram (ECG) was recorded from conscious and unrestrained rats using a telemetry system, and the autonomic nervous function was investigated by power spectral analysis of heart rate variability (HRV). Although heart rate (HR) in Zucker-fatty rats was lower than that in Zucker-lean rats throughout 24 h, apparent diurnal variation in HR was observed in both strains and HR during the dark period was significantly higher than that in light period. Diurnal variation in locomotor activity (LA) in Zucker-fatty rats was also observed, but LA was lower than that in Zucker lean rats, especially during the dark period. There were no significant differences, however, in high-frequency (HF) power, low-frequency (LF) power, and the LF/HF ratio between Zucker-fatty and Zucker-lean rats. The circadian rhythm of these parameters was mostly preserved in both strains of rats. Moreover, the effect of autonomic blockades on HRV was nearly the same in Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal, from the aspect of power spectral analysis of HRV.     

Changes in the Heart Rate Parameters under the Influence of Academic School Activities in Adolescents with Mental Retardation

Examination of seventh-grade schoolchildren revealed that changes in the heart rate parameters observed during a day or a week in mentally retarded (MR) adolescents have some specific features as compared with values in healthy children of the same age. Appreciable variations of power in all frequency bands and a pronounced decrease in the low-frequency spectrum power at the end of the day were characteristic of MR schoolchildren. In the middle of the week, the tone of the sympathetic nervous system dropped, while adaptive changes in the level of psychoemotional tension were not observed. In healthy adolescents, the heart rate parameters were stable throughout a school day or week, whereas psychoemotional tension rose in the middle of the week. These results provide a basis for modification of the learning regimen in correctional schools. Heart rate analysis may be used for assessing the efficiency of the academic process in children with learning problems.     

Effect of stellate ganglionectomy on basal cardiovascular function and responses to beta1-adrenoceptor blockade in the rat

Cardiac sympathetic nerve activity is an important short-term controller of cardiac function and arterial pressure. Studies also suggest that long-term increases in cardiac sympathetic nerve activity may contribute to hypertension, coronary artery disease, and cardiac remodeling in heart failure. However, our understanding of the role of cardiac sympathetic nerves in chronic models of cardiovascular disease has been limited by inadequate experimental approaches. The present study was conducted to develop a surgical method to surgically denervate the sympathetic nerves of the rat heart for long-term cardiovascular studies. We characterized the effect of cardiac sympathetic denervation on basal levels of mean arterial pressure (MAP) and heart rate (HR) and the responses to a chronic administration of atenolol, a beta1-adrenoceptor antagonist. Rats were instrumented with telemetry transmitters for continuous recording of MAP and HR. After a 4-day baseline period, the rats were subjected to bilateral stellate ganglionectomy (SGX; n=9) or sham surgery (Sham; n=8). Seven days following SGX or Sham, the rats were administered atenolol for 5 days, followed by a 7-day recovery period. Following a transient decrease, SGX had no effect on basal MAP but decreased HR compared with baseline and Sham rats. Five days of atenolol treatment decreased MAP similarly in SGX and Sham rats. Atenolol resulted in a marked bradycardia in Sham rats but had a neglible effects on HR in SGX rats. The measurement of the content of cardiac catecholamines in all cardiac chambers at the end of the study verified a successful sympathetic denervation. This study confirms that bilateral SGX is a useful method to study the contribution of cardiac sympathetic nerves on the regulation of cardiac function. Moreover, these results suggest that cardiac sympathetic nerves are relatively unimportant in maintaining the basal level of MAP or the depressor response to atenolol in conscious, unrestrained rats.     

Proven cardiac changes during death-feigning (tonic immobility) in rabbits (Oryctolagus cuniculus)

Tonic immobility (TI) is a response to fear or threat by remaining motionless, principally when attacked by predators from which there is no possibility of escape. Thus, here we demonstrate a way of easily reproducing this phenomenon in a laboratory setting and characterize the cardiac electromechanical alterations during TI. We observed a significant decrease in heart rate (HR) and changes of rhythm in electrocardiogram during TI in rabbits. Echocardiogram showed a significant increase in the left ventricle chamber diameter during systole and a consequent decrease in fractional shortening and ejection fraction, in addition to the HR and rhythm changes. There was also a significant decrease in aortic and pulmonary artery blood flow. Diastolic functional changes included a significant decrease of the peak atrial contraction velocity (A peak) and consequent increase in the ratio of peak early diastolic velocity to A peak and increased isovolumetric relaxation time. We were able to prove that TI changes the cardiac function considerably. Although the “fight-or-flight” response is the most common response to fear, which is characterized by the action of sympathetic nervous system with tachycardia and increased physical activity, TI is an alternative anti-predator behavior causing cardiac changes opposite to the “fight-or-flight” phenomenon.     

Hyperinsulinemic rats are normotensive but sensitized to angiotensin II

The effect of insulin on blood pressure (BP) is debated, and an involvement of an activated renin-angiotensin aldosterone system (RAAS) has been suggested. We studied the effect of chronic insulin infusion on telemetry BP and assessed sympathetic activity and dependence of the RAAS. Female Sprague-Dawley rats received insulin (2 units/day, INS group, n = 12) or insulin combined with losartan (30 mg.kg(-1).day(-1), INS+LOS group, n = 10), the angiotensin II receptor antagonist, for 6 wk. Losartan-treated (LOS group, n = 10) and untreated rats served as controls (n = 11). We used telemetry to measure BP and heart rate (HR), and acute ganglion blockade and air-jet stress to investigate possible control of BP by the sympathetic nervous system. In addition, we used myograph technique to study vascular function ex vivo. The INS and INS+LOS groups developed euglycemic hyperinsulinemia. Insulin did not affect BP but increased HR (27 beats/min on average). Ganglion blockade reduced mean arterial pressure (MAP) similarly in all groups. Air-jet stress did not increase sympathetic reactivity but rather revealed possible blunting of the stress response in hyperinsulinemia. Chronic losartan markedly reduced 24-h-MAP in the INS+LOS group (-38 +/- 1 mmHg P < 0.001) compared with the LOS group (-18 +/- 1 mmHg, P 相似文献   

Cardiac sympathetic nerve stimulation does not attenuate dynamic vagal control of heart rate via alpha-adrenergic mechanism

Complex sympathovagal interactions govern heart rate (HR). Activation of the postjunctional beta-adrenergic receptors on the sinus nodal cells augments the HR response to vagal stimulation, whereas exogenous activation of the presynaptic alpha-adrenergic receptors on the vagal nerve terminals attenuates vagal control of HR. Whether the alpha-adrenergic mechanism associated with cardiac postganglionic sympathetic nerve activation plays a significant role in modulation of the dynamic vagal control of HR remains unknown. The right vagal nerve was stimulated in seven anesthetized rabbits that had undergone sinoaortic denervation and vagotomy according to a binary white-noise signal (0-10 Hz) for 10 min; subsequently, the transfer function from vagal stimulation to HR was estimated. The effects of beta-adrenergic blockade with propranolol (1 mg/kg i.v.) and the combined effects of beta-adrenergic blockade and tonic cardiac sympathetic nerve stimulation at 5 Hz were examined. The transfer function from vagal stimulation to HR approximated a first-order, low-pass filter with pure delay. beta-Adrenergic blockade decreased the dynamic gain from 6.0 +/- 0.4 to 3.7 +/- 0.6 beats x min(-1) x Hz(-1) (P < 0.01) with no alteration of the corner frequency or pure delay. Under beta-adrenergic blockade conditions, tonic sympathetic stimulation did not further change the dynamic gain (3.8 +/- 0.5 beats x min(-1) x Hz(-1)). In conclusion, cardiac postganglionic sympathetic nerve stimulation did not affect the dynamic HR response to vagal stimulation via the alpha-adrenergic mechanism.     

Insulin-mediated increase in sympathetic nerve activity is attenuated by C-peptide in diabetic rats

Connecting peptide (C-peptide) is secreted along with insulin in equimolar amounts into portal circulation in response to beta cell stimulation. The biological function of C-peptide had been mostly limited to establishing the secondary and tertiary structure of proinsulin. Recent studies have suggested that C-peptide can impact several functions, such as autonomic and sensory nerve function, insulin secretion, and microvascular blood flow. In this study we examined the effects of C-peptide in the presence or absence of insulin on cardiovascular and sympathetic nerve activity in both normal and streptozotocin (STZ)-induced diabetic Wistar rats. Animals were made diabetic by a single intravenous injection of STZ (50 mg/kg) and maintained for 6 weeks. The diabetic animals had higher plasma glucose, lower plasma insulin, and C-peptide, compared with the normal animals. To characterize cardiovascular and autonomic nervous responses, the animals were anesthetized with urethane/alpha-chloralose and instrumented for the recording of mean arterial pressure (MAP), heart rate (HR), and lumbar sympathetic nerve activity (LSNA). A bolus administration of C-peptide alone did not alter MAP, HR, or LSNA in normal or diabetic animals. The bolus administration of insulin alone increased HR and LSNA in normal and diabetic animals. However, the administration of insulin plus C-peptide attenuated the increase in HR in normals and the increase in LSNA in diabetic rats. We concluded that the C-peptides play a role in modulating the insulin-stimulated sympathetic nerve response.     

Ghrelin modulates baroreflex-regulation of sympathetic vasomotor tone in healthy humans

Ghrelin, a neuropeptide originally known for its growth hormone-releasing and orexigenic properties, exerts important pleiotropic effects on the cardiovascular system. Growing evidence suggests that these effects are mediated by the sympathetic nervous system. The present study aimed at elucidating the acute effect of ghrelin on sympathetic outflow to the muscle vascular bed (muscle sympathetic nerve activity, MSNA) and on baroreflex-mediated arterial blood pressure (BP) regulation in healthy humans. In a randomized double-blind cross-over design, 12 lean young men were treated with a single dose of either ghrelin 2 μg/kg iv or placebo (isotonic saline). MSNA, heart rate (HR), and BP were recorded continuously from 30 min before until 90 min after substance administration. Sensitivity of arterial baroreflex was repeatedly tested by injection of vasoactive substances based on the modified Oxford protocol. Early, i.e., during the initial 30 min after ghrelin injection, BP significantly decreased together with a transient increase of MSNA and HR. In the course of the experiment (>30 min), BP approached placebo level, while MSNA and HR were significantly lower compared with placebo. The sensitivity of vascular arterial baroreflex significantly increased at 30-60 min after intravenous ghrelin compared with placebo, while HR response to vasoactive drugs was unaltered. Our findings suggest two distinct phases of ghrelin action: In the immediate phase, BP is decreased presumably due to its vasodilating effects, which trigger baroreflex-mediated counter-regulation with increases of HR and MSNA. In the delayed phase, central nervous sympathetic activity is suppressed, accompanied by an increase of baroreflex sensitivity.