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.     

摄食行为对小型猪心脏自主神经功能的影响

目的观察摄食行为对小型猪心脏自主神经功能的影响。方法利用大动物无创遥测技术观察清醒活动状态下小型猪摄食前（BI）、摄食过程中（IP）、摄食后（AI）、AI 2 h和AI 4h的心电图（ECG）和自主活动,并用HRV功率谱分析其自主神经功能。结果与摄食前比较,小型猪摄食过程中心率（HR）、自主活动和标准化低频成分（LFnu）明显增加,RR间期（RRI）、总功率（TP）、极低频成分（VLF）、高频成分（HF）明显减少,LF/HF比值明显升高;且随着摄食后恢复时间的延长,小型猪HR、自主活动、LFnu均有所降低,而RRI、TP、VLF、HF均有所升高,LF/HF比值逐渐降低,并在摄食后2 h、4 h时变化显著;相关分析显示摄食行为与TP、VLF、HF、LF和LF/HF密切相关,多元线性逐步回归分析亦显示摄食行为与VLF、LF/HF和TP密切相关,且VLF起主要作用。结论小型猪摄食行为不仅影响心脏活动;而且能引起小型猪心脏自主神经控制能力发生改变,其中VLF在摄食行为过程中占有重要作用。     

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.     

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.     

The daily pattern of heart rate, body temperature, locomotor activity, and autonomic nervous activity in congenitally bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs.

We studied the characteristics of the rhythmicity of heart rate (HR), body temperature (BT), locomotor activity (LA) and autonomic nervous activity in bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs. For this purpose, HR, BT, LA, and electrocardiogram (ECG) were recorded from conscious and unrestrained guinea pigs using a telemetry system. Autonomic nervous activity was analyzed by power spectral analysis of heart rate variability. Nocturnal patterns, in which the values in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed in HR, BT and LA in both strains of guinea pigs. The autonomic nervous activity in BHS guinea pigs showed a daily pattern, although BHR guinea pigs did not show such a rhythmicity. The high frequency (HF) power in BHS guinea pigs was higher than that in BHR guinea pigs throughout the day. Moreover, the low frequency/high frequency (LF/HF) ratio in BHS guinea pigs was lower than that in BHR guinea pigs throughout the day. These results suggest that parasympathetic nervous activity may be predominant in BHS guinea pigs.     

Associations between Diurnal 24-Hour Rhythm in Ambulatory Heart Rate Variability and the Timing and Amount of Meals during the Day Shift in Rotating Shift Workers

It has not hitherto been clarified whether there is an association between dietary behavior and circadian variation in autonomic nervous system activity among shift workers. This study examines diurnal 24-h rhythm in heart rate variability (HRV) and dietary behavior among rotating shift workers, while taking into account the sleep-wake cycle and physical activity. The subjects were 11 female and 2 male nurses or caregivers working in a rotating 2-shift system at a health care facility. All the subjects were asked to undergo 24-h electrocardiograph and step count recordings, and to record the time of each meal and the amounts of each food and beverage consumed. Coarse graining spectral analysis was used for approximately 10-min segments of HRV to derive the total power (TOT: >0.04 Hz) of the periodic components and the integrated power of periodic components in the low-frequency (LF: 0.04–0.15 Hz) and high-frequency (HF: >0.15 Hz) ranges. Then the ratio of HF power to TOT (HF nu) and the ratio of LF power to HF power (LF/HF) were calculated to assess cardiac vagal tone and cardiac sympathovagal balance, respectively. Single cosinor analysis was used to obtain 24-h period variations in both variables of HRV. Acrophases of HF nu and LF/HF expressed in time since awakening were significantly (p<0.05) delayed for subjects having breakfast at a later time after awakening. Multivariable regression analysis indicated that the timing of breakfast, the ratio of energy intake at dinner to total energy intake, and total energy intake were correlated to the acrophases of HF nu and/or LF/HF. These results suggest that the phase angle between circadian variation in cardiac autonomic nervous system activity and the sleep-wake cycle may be associated with dietary behavior in shift workers.     

Autonomic cardiovascular control in conscious mice

Autonomic cardiovascular control was characterized in conscious, chronically catheterized mice by spectral analysis of arterial pressure (AP) and heart rate (HR) during autonomic blockade or baroreflex modulation of autonomic tone. Both spectra were similar to those obtained in humans, but at approximately 10x higher frequencies. The 1/f relation of the AP spectrum changed to a more shallow slope below 0.1-0.2 Hz. Coherence between AP and HR reached 0.5 or higher below 0.3-0.4 Hz and also above 2.5 Hz. Muscarinic blockade (atropine) or beta-adrenergic blockade (atenolol) did not significantly affect the AP spectrum. Atropine reduced HR variability at all frequencies, but this effect waned above 1 Hz. beta-Adrenergic blockade (atenolol) slightly enhanced the HR variability only above 1 Hz. alpha-Adrenergic blockade (prazosin) reduced AP variability between 0.05 and 3 Hz, most prominently at 0. 15-0.7 Hz. A shift of the autonomic nervous tone by a hypertensive stimulus (phenylephrine) enhanced, whereas a hypotensive stimulus (nitroprusside) depressed AP variability at 1-3 Hz; other frequency ranges of the AP spectrum were not affected except for a reduction below 0.4 Hz after nitroprusside. Variability of HR was enhanced after phenylephrine at all frequencies and reduced after nitroprusside. As with atropine, the reduction with nitroprusside waned above 1 Hz. In conclusion, in mice HR variability is dominated by parasympathetic tone at all frequencies, during both blockade and physiological modulation of autonomic tone. There is a limitation for further reduction but not for augmentation of HR variability from the resting state above 1 Hz. The impact of HR on AP variability in mice is confined to frequencies higher than 1 Hz. Limits between frequency ranges are proposed as 0.15 Hz between VLF (very low frequency range) and LF (low frequency range) and 1.5 Hz between LF and HF (high frequency range).     

Effect of autonomic blockers on heart period variability in calves: evaluation of the sympathovagal balance

This study was designed to validate the measures of heart period variability for assessing of autonomic nervous system control in calves. Eight calves received an injection of either 0.5 mg/kg atenolol (sympathetic tone blockade), 0.2 mg/kg atropine sulfate (parasympathetic tone blockade), 0.5 mg/kg atenolol + 0.2 mg/kg atropine sulfate (double autonomic blockade) or saline. In the time-domain, we calculated the mean instantaneous heart rate (HR), mean of RR intervals (MeanRR), standard deviation of RR intervals (SDRR) and that of the difference between adjacent intervals (RMSSD). In the frequency-domain, the power of the spectral band 0-1 Hz (TPW), the power of the 0-0.15 Hz band (LF), that of the 0.15-1 Hz band (HF), and the LF/HF ratio were considered. The net vago-sympathetic effect (VSE) was calculated as the ratio of MeanRR in a defined situation to MeanRR during the double blockade. Atenolol injection had no effect on cardiac activity, whereas atropine induced large modifications which were moderated when atenolol was administered at the same time. VSE, HR, MeanRR and RMSSD were found to be valid indicators of the parasympathetic tone of calves because of large variations due to the drug and low individual variations. No measure reflected the sympathetic tone.     

Capsaicin increases modulation of sympathetic nerve activity in rats: measurement using power spectral analysis of heart rate fluctuations

We assessed the sympatho-vagal activities of the heart after administration of capsaicin by measuring the power spectral analysis in rats. There were major two frequency components of heart rate variability, which we defined as high (1.0 Hz <, HF) and low (LF, < 1.0 Hz) frequency components. Vagal blockade by atropine abolished the high frequency component, and lowered the amplitude of the low frequency component. On the other hand, under conditions of sympathetic blockade by propranolol, the low frequency component was reduced. Combined vagal and sympathetic blockade abolished all heart rate fluctuations. We analyzed the low and high frequency components by integrating the spectrum for the respective band width. The rats administered capsaicin had a higher heart rate and sympathetic nervous system index (LF/HF) than the control group of rats. These results suggest that power spectral analysis is an effective and noninvasive method for detecting subtle changes in autonomic activity in response to the intake of foods or drugs.     

Time-variant spectral analysis of heart rate variability during parabolic flight with and without LBNP

Modifications of autonomic activity during parabolic flight were studied by a time-variant model able to estimate low (LF, 0.04-0.14 Hz) and high (HF, 0.14-0.35 Hz) frequency spectral components on a beat-to-beat basis. Ten subjects were studied with and without lower body negative pressure (LBNP). ECG and Gz load were digitized (500 Hz) and RR interval variability series extracted. Beat-to-beat mean RR, variance, LF and HF power were obtained. One-way ANOVA (p<0.01) was used to compare values obtained during starting 1Gz (I), first 1.8Gz (II), 0Gz (III), second 1.8Gz (IV), ending 1Gz (V). Without LBNP, total and LF power increased during 0Gz to 1.69 +/- 1.41 and 2.87 +/- 4.66 respectively (mean +/- SD, normalized by phase I value). With LBNP, their change during 0Gz (1.38 +/- 1.37 and 1.54 +/- l.04 respectively) reached significance only with phase II and phase V. Phase I HF power was higher than in the other phases, both without and with LBNP.     

Selective quantification of the cardiac sympathetic and parasympathetic nervous systems by multisignal analysis of cardiorespiratory variability

Heart rate (HR) power spectral indexes are limited as measures of the cardiac autonomic nervous systems (CANS) in that they neither offer an effective marker of the beta-sympathetic nervous system (SNS) due to its overlap with the parasympathetic nervous system (PNS) in the low-frequency (LF) band nor afford specific measures of the CANS due to input contributions to HR [e.g., arterial blood pressure (ABP) and instantaneous lung volume (ILV)]. We derived new PNS and SNS indexes by multisignal analysis of cardiorespiratory variability. The basic idea was to identify the autonomically mediated transfer functions relating fluctuations in ILV to HR (ILV-->HR) and fluctuations in ABP to HR (ABP-->HR) so as to eliminate the input contributions to HR and then separate each estimated transfer function in the time domain into PNS and SNS indexes using physiological knowledge. We evaluated these indexes with respect to selective pharmacological autonomic nervous blockade in 14 humans. Our results showed that the PNS index derived from the ABP-->HR transfer function was correctly decreased after vagal and double (vagal + beta-sympathetic) blockade (P < 0.01) and did not change after beta-sympathetic blockade, whereas the SNS index derived from the same transfer function was correctly reduced after beta-sympathetic blockade in the standing posture and double blockade (P < 0.05) and remained the same after vagal blockade. However, this SNS index did not significantly decrease after beta-sympathetic blockade in the supine posture. Overall, these predictions were better than those provided by the traditional high-frequency (HF) power, LF-to-HF ratio, and normalized LF power of HR variability.     

Applicability of recent methods used to estimate spontaneous baroreflex sensitivity to resting mice

Short-term blood pressure (BP) variability is limited by the arterial baroreflex. Methods for measuring the spontaneous baroreflex sensitivity (BRS) aim to quantify the gain of the transfer function between BP and pulse interval (PI) or the slope of the linear relationship between parallel BP and PI changes. These frequency-domain (spectral) and time-domain (sequence) techniques were tested in conscious mice equipped with telemetric devices. The autonomic relevance of these indexes was evaluated using pharmacological blockades. The significant changes of the spectral bandwidths resulting from the autonomic blockades were used to identify the low-frequency (LF) and high-frequency (HF) zones of interest. The LF gain was 1.45 +/- 0.14 ms/mmHg, with a PI delay of 0.5 s. For the HF gain, the average values were 2.0 +/- 0.19 ms/mmHg, with a null phase. LF and HF bands were markedly affected by atropine. On the same 51.2-s segments used for cross-spectral analysis, an average number of 26.4 +/- 2.2 slopes were detected, and the average slope in resting mice was 4.4 +/- 0.5 ms/mmHg. Atropine significantly reduced the slopes of the sequence method. BRS measurements obtained using the sequence technique were highly correlated to the spectral estimates. This study demonstrates the applicability of the recent methods used to estimate spontaneous BRS in mice. There was a vagal predominance in the baroreflex control of heart rate in conscious mice in the present conditions.     

Effects of body weight-supported treadmill training on heart rate variability and blood pressure variability in individuals with spinal cord injury.

Individuals with spinal cord injury are prone to cardiovascular dysfunction and an increased risk of cardiovascular disease. Body weight-supported treadmill training (BWSTT) may enhance ambulation in individuals with incomplete spinal cord injury; however, its effects on cardiovascular regulation have not been investigated. The purpose of this study was to examine the effects of 6-mo of BWSTT on the autonomic regulation of heart rate (HR) and blood pressure (BP) in individuals with incomplete tetraplegia. Eight individuals [age 27.6 yr (SD 5.2)] with spinal cord injury [C4-C5; American Spinal Injury Association B-C; 9.6 yr (SD 7.5) postinjury] participated. Ten-minute HR and finger arterial pressure (Finapres) recordings were collected during 1) supine rest and 2) an orthostatic stress (60 degrees head-up tilt) before and after 6 mo of BWSTT. Frequency domain measures of HR variability [low-frequency (LF) power, high-frequency (HF) power, and LF-to-HF ratio] and BP variability (systolic and diastolic LF power) were used as clinically valuable indexes of neurocardiac and neurovascular control, respectively. There was a significant reduction in HR [61.9 (SD 6.9) vs. 55.7 beats/min (SD 7.7); P=0.05] and LF-to-HF ratio [1.23 (SD 0.47) vs. 0.99 (SD 0.40); P < 0.05] after BWSTT. There was a significant reduction in LF systolic BP [183.1 (SD 46.8) vs. 158.4 mmHg2 (SD 45.2); P < 0.01] but no change in BP. There were no significant effects of training on HR variability or BP variability during 60 degrees head-up tilt. In conclusion, individuals with incomplete tetraplegia retain the ability to make positive changes in cardiovascular autonomic regulation with BWSTT without worsening orthostatic intolerance.     

Sleep-related sympathovagal imbalance in SHR

The role of the autonomic nervous system in spontaneous hypertension during each stage of the sleep-wake cycle remains unclear. The present study attempted to evaluate the differences in cardiac autonomic modulations among spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD) across sleep-wake cycles. Continuous power spectral analysis of electroencephalogram, electromyogram, and heart rate variability was performed in unanesthetized free moving rats during daytime sleep. Frequency-domain analysis of the stationary R-R intervals (RR) was performed to quantify the high-frequency power (HF), low-frequency power (LF)-to-HF ratio (LF/HF), and normalized LF (LF%) of heart rate variability. WKY and SD had similar mean arterial pressure, which is significantly lower than that of SHR during active waking, quiet sleep, and paradoxical sleep. Compared with WKY and SD, SHR had lower HF but similar RR, LF/HF, and LF% during active waking. During quiet sleep, SHR developed higher LF/HF and LF% in addition to lower HF. SHR ultimately exhibited significantly lower RR accompanied with higher LF/HF and LF% and lower HF during paradoxical sleep compared with WKY. We concluded that significant cardiac sympathovagal imbalance with an increased sympathetic modulation occurred in SHR during sleep, although it was less evident during waking.     

Influence of sound and light on heart rate variability

The effects of acoustic and visual stimuli and their synergistic effects on heart rate variability including gender differences were investigated. Of particular interest was the influence of visual stimulus on heart rate variability during listening to simple sounds of different characters. Twelve male and 12 female university students were selected as subjects. The subjects listened at rest to 7 different figures of sound at loudness levels averaging 60 dB. Beat-to-beat R-R intervals were continuously recorded under the closed-eye condition (CEC) and the open-eye condition (OEC) prior to, during, and immediately after the exposure to acoustic stimuli. Low frequency (LF) power was defined over 0.04-0.15 Hz and high frequency (HF) power over 0.15-0.40 Hz. Cardiac autonomic function was estimated by plotting LF/HF in standard measure against HF in standard measure and by plotting LF/HF (%) against HF (%), accompanied by a demarcated central area. Values of LF/HF tended to be smaller under CEC than under OEC. Values of HF while listening to a 110 Hz sine wave under CEC were significantly greater than values for 880 Hz and 3520 Hz sine waves, or for 110 Hz or 880 Hz sawtooth waves, under OEC. Under CEC, values of HF for 7 figures of sound were greater in females than in males. The value of HF of sine wave for 110 Hz under CEC and OEC was significantly greater than that for white noise under the OEC. The results suggest that the cardiac parasympathetic nervous activity during auditory excitation increases with elimination of visual stimuli and tends to be greater in females than in males.     

Cardiovascular Variability Analysis and Baroreflex Estimation in Patients with Type 2 Diabetes in Absence of Any Manifest Neuropathy

Introduction

Indexes derived from spontaneous heart period (HP) and systolic arterial pressure (SAP) fluctuations can detect autonomic dysfunction in individuals with type 2 diabetes mellitus (DM) associated to cardiovascular autonomic neuropathy (CAN) or other neuropathies. It is unknown whether HP and SAP variability indexes are sensitive enough to detect the autonomic dysfunction in DM patients without CAN and other neuropathies.

Methods

We evaluated 68 males aged between 40 and 65 years. The group was composed by DM type 2 DM with no manifest neuropathy (n = 34) and healthy (H) subjects (n = 34). The protocol consisted of 15 minutes of recording of HP and SAP variabilities at rest in supine position (REST) and after active standing (STAND). The HP power in the high frequency band (HF, from 0.15 to 0.5 Hz), the SAP power in the low frequency band (LF, from 0.04 to 0.15 Hz) and BRS estimated via spectral approach and sequence method were computed.

Results

The HF power of HP was lower in DM patients than in H subjects, while the two groups exhibited comparable HF power of HP during STAND. The LF power of SAP was similar in DM and H groups at REST and increased during STAND in both groups. BRSs estimated in the HF band and via baroreflex sequence method were lower in DM than in H and they decreased further during STAND in both populations.

Conclusion

Results suggest that vagal control of heart rate and cardiac baroreflex control was impaired in type 2 DM, while sympathetic control directed to vessels, sympathetic and baroreflex response to STAND were preserved. Cardiovascular variability indexes are sensitive enough to typify the early, peculiar signs of autonomic dysfunction in type-2 DM patients well before CAN becomes manifest.     

Loss of Breathing Modulation of Heart Rate Variability in Patients with Recent and Long Standing Diabetes Mellitus Type II

Healthy subjects under rhythmic breathing have heart interbeat intervals with a respiratory band in the frequency domain that can be an index of vagal activity. Diabetes Mellitus Type II (DM) affects the autonomic nervous system of patients, thus it can be expected changes on the vagal activity. Here, the influence of DM on the breathing modulation of the heart rate is evaluated by analyzing in the frequency domain heart interbeat interval (IBI) records obtained from 30 recently diagnosed, 15 long standing DM patients, and 30 control subjects during standardized clinical tests of controlled breathing at 0.1 Hz, supine rest and standing upright. Fourier spectral analysis of IBI records quantifies heart rate variability in different regions: low-frequencies (LF, 0.04–0.15 Hz), high-frequencies (HF, 0.15–0.4 Hz), and a controlled breathing peak (RP, centered around 0.1 Hz). Two new parameters are introduced: the frequency radius r_f (square root of the sum of LF and HF squared) and β (power of RP divided by the sum of LF and HF). As diabetes evolves, the controlled breathing peak loses power and shifts to smaller frequencies, indicating that heart rate modulation is slower in diabetic patients than in controls. In contrast to the traditional parameters LF, HF and LF/HF, which do not show significant differences between the three populations in neither of the clinical tests, the new parameters r_f and β, distinguish between control and diabetic subjects in the case of controlled breathing. Sympathetic activity that is driven by the baroreceptor reflex associated with the 0.1 Hz breathing modulations is affected in DM patients. Diabetes produces not only a rigid heartbeat with less autonomic induced variability (r_f diminishes), but also alters the coupling between breathing and heart rate (reduced β), due to a progressive decline of vagal and sympathetic activity.     

Assessment of Cardiac Autonomic Modulation during Adolescent Obesity

Objective: To investigate the cardiovascular autonomic function in pediatric obesity of different duration by using standard time domain, spectral heart rate variability (HRV), and nonlinear methods. Research Methods and Procedures: Fifty obese children (13.9 ± 1.7 years) were compared with 12 lean subjects (12.9 ± 1.6 years). Obese children were classified as recent obese (ROB) (<4 years), intermediate obese (IOB) (4 to 7 years), and long‐term obese (OB) (>7 years). In all participants, we performed blood pressure (BP) measurements, laboratory tests, and 24‐hour electrocardiogram/ambulatory BP monitoring. The spectral power was quantified in total power, very low‐frequency (LF) power, high‐frequency (HF) power, and LF to HF ratio. Total, long‐term, and short‐term time domain HRV were calculated. Poincaré plot and quadrant methods were used as nonlinear techniques. Results: All obese groups had higher casual and ambulatory BP and higher glucose, homeostasis model assessment, and triglyceride levels. All parameters reflecting parasympathetic tone (HF band, root mean square successive difference, proportion of successive normal‐to‐normal intervals, and scatterplot width) were significantly and persistently reduced in all obese groups in comparison with lean controls. LF normalized units, LF/HF, and cardiac acceleration (reflecting sympathetic activation) were significantly increased in the ROB group. In IOB and OB groups, LF, but not nonlinear, measures were similar to lean controls, suggesting biphasic behavior of sympathetic tone, whereas nonlinear analysis showed a decreasing trend with the duration of obesity. Long‐term HRV measures were significantly reduced in ROB and IOB. Discussion: Autonomic nervous system changes in adolescent obesity seem to be related to its duration. Nonlinear methods of scatterplot and quadrant analysis permit assessment of autonomic balance, despite measuring different aspects of HRV.     

Capsaicin Increases Modulation of Sympathetic Nerve Activity in Rats: Measurement Using Power Spectral Analysis of Heart Rate Fluctuations

We assessed the sympatho-vagal activities of the heart after administration of capsaicin by measuring the power spectral analysis in rats. There were major two frequency components of heart rate variability, which we defined as high (1.0 Hz<, HF) and low (LF, <1.0 Hz) frequency components. Vagal blockade by atropine abolished the high frequency component, and lowered the amplitude of the low frequency component. On the other hand, under conditions of sympathetic blockade by propranolol, the low frequency component was reduced. Combined vagal and sympathetic blockade abolished all heart rate fluctuations. We analyzed the low and high frequency components by integrating the spectrum for the respective band width. The rats administered capsaicin had a higher heart rate and sympathetic nervous system index (LF/HF) than the control group of rats. These results suggest that power spectral analysis is an effective and noninvasive method for detecting subtle changes in autonomic activity in response to the intake of foods or drugs.     

Assessment of Heart Autonomic Control on the Basis of Spectral Analysis of Heart Rate Variability

An orthostatic test with frequency-controlled breathing (with a respiration period of 10 s) or spontaneous breathing was used to analyze frequency estimates of the heart rate variability (HRV) in the low-frequency (LF) and high-frequency (HF) ranges in young men and women. It was demonstrated that the spectral components of HRV bear no signs of sex differentiation, suggesting a uniform structural organization of the system of autonomic nervous control of the heart (SANCH) in humans. The LF component of the HRV spectrum is a marker of the functional state of the SANCH; it should be studied under conditions of controlled breathing at a frequency of 0.1 Hz. The HF and LF components of the HRV characterize the state of the SANCH at a given moment and do not reflect directly its adaptation reserve. The HF component of the HRV is interesting as a parameter that may be used for estimating the changes in the adaptation reserve of heart autonomic control. It is preferable to analyze this component in the absence of external disturbances in the LF range of the spectrum.