LF Component Research Articles

Integrated central-autonomic multifractal complexity in the heart rate variability of healthy humans.

Purpose of Study: The aim of this study was to characterize the central-autonomic interaction underlying the multifractality in heart rate variability (HRV) of healthy humans. Materials and Methods: Eleven young healthy subjects participated in two separate ~40 min experimental sessions, one in supine (SUP) and one in, head-up-tilt (HUT), upright (UPR) body positions. Surface scalp electroencephalography (EEG) and electrocardiogram (ECG) were collected and fractal correlation of brain and heart rate data was analyzed based on the idea of relative multifractality. The fractal correlation was further examined with the EEG, HRV spectral measures using linear regression of two variables and principal component analysis (PCA) to find clues for the physiological processing underlying the central influence in fractal HRV. Results: We report evidence of a central-autonomic fractal correlation (CAFC) where the HRV multifractal complexity varies significantly with the fractal correlation between the heart rate and brain data (P = 0.003). The linear regression shows significant correlation between CAFC measure and EEG Beta band spectral component (P = 0.01 for SUP and P = 0.002 for UPR positions). There is significant correlation between CAFC measure and HRV LF component in the SUP position (P = 0.04), whereas the correlation with the HRV HF component approaches significance (P = 0.07). The correlation between CAFC measure and HRV spectral measures in the UPR position is weak. The PCA results confirm these findings and further imply multiple physiological processes underlying CAFC, highlighting the importance of the EEG Alpha, Beta band, and the HRV LF, HF spectral measures in the supine position. Discussion and Conclusion: The findings of this work can be summarized into three points: (i) Similar fractal characteristics exist in the brain and heart rate fluctuation and the change toward stronger fractal correlation implies the change toward more complex HRV multifractality. (ii) CAFC is likely contributed by multiple physiological mechanisms, with its central elements mainly derived from the EEG Alpha, Beta band dynamics. (iii) The CAFC in SUP and UPR positions is qualitatively different, with a more predominant central influence in the fractal HRV of the UPR position.

Immunohistochemical studies in the experimental diabetic hippocampus in relation with cognitive impairments

We have previously shown that the elevated plasma ghrelin accelerate emptying in the early stage of diabetes in rats. However, it remains unknown whether plasma ghrelin levels are still elevated in the late stage of diabetes. We studied whether solid gastric emptying and plasma ghrelin levels are altered 2–8 weeks after streptozotocin (STZ) injection. The development of autonomic neuropathy was evaluated by spectral analysis of heart rate variability (HRV). Gastric emptying was not different between control and diabetic rats at 4 weeks and 6 weeks, while it delayed at 8 weeks in STZ rats. The pre-prandial ghrelin levels were not significantly different between control and diabetic rats at 4–8 weeks. In control rats, the plasma ghrelin levels were significantly reduced 30 min after the feeding at 4–8 weeks. In contrast, there was no significant reduction of ghrelin levels observed in diabetic rats at 4–8 weeks. Plasma insulin levels were significantly increased 30 min after feeding in control rats, but not STZ rats, at 4–8 weeks. Both HF (parasympathetic activity) and LF (sympathetic activity) component were gradually reduced 6–8 weeks after STZ injection. It is suggested that hypoinsulinemia associated with diabetes increases plasma ghrelin levels. At the late stage of diabetes, gastric emptying is delayed despite increased plasma ghrelin levels. The delayed gastric emptying is mainly due to impaired activity of autonomic nerves at the late stage of diabetes.

Improvement of Heart Rate Variability by Eurythmy Therapy After a 6-Week Eurythmy Therapy Training

Eurythmy therapy (EYT) is a mind-body therapy used in anthroposophic medicine. Recently, the authors were able to show that at comparable workloads, EYT stimulated heart rate variability (HRV) whereas conventional ergometer training attenuated HRV. Furthermore, a long-term improvement of quality of life (QoL) and stress coping strategies by EYT could be shown. This study aimed to evaluate the long-term effects of EYT training on HRV. A total of 23 healthy women (mean age = 44.57 ± 8.04 years) performed 10 hours of EYT over a period of 6 weeks. Electrocardiograms were recorded before and after the EYT trial. HRV was quantified by the extent of high (HF), low (LF), very low (VLF), and ultra low frequency (ULF) oscillations of heart rate. Autonomic regulation was significantly changed following the EYT training compared with baseline. Especially the proportion referring to the total power (P) of HF/P and LF/P increased, whereas ULF/P and (ULF+VLF)/P decreased after the training period. EYT shifted the autonomic regulation proportionally referring to the total power mainly caused by changes of ULF and VLF components of HRV. The LF and HF spectral components were also decreased following EYT while their proportion in relation to the total variance of the power spectrum was increased. The proportional enhancement of the higher frequency and the decrease of the ULF and VLF components are probably an indicator of an improvement of autonomic regulation processes by more relaxed physical activity after the EYT training, thus supporting the plausibility of the improved QoL and better stress coping strategies.

Causes of autonomic dysfunction in idiopathic recurrent kidney stone formers

A higher prevalence of hypertension and adverse cardiovascular outcomes has been reported in kidney stone formers (KSF). We performed this study with the purpose of evaluating the autonomic nervous system (ANS) activity in KSF. We performed a 70° head-up tilt test in 30 idiopathic recurrent KSF aged 45.6 ± 12.1 years old (17 men: 13 women) and 30 healthy controls aged 42.0 ± 12.4 years old (17 women: 13 men). Thirteen KSF were hypertensive, and 17 were normotensive. Blood pressure (BP) and heart rate variability (HRV) were used for the non-invasive assessment of the efferent activity of the ANS. Discrete wavelet transform (DWT) was used to quantify the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.4 Hz) components during several periods of tilt. The results showed significantly higher HR and BP in KSF, in both supine and tilt positions. DWT revealed diminished HRV in the kidney stone patients during head-up tilt, with no increase in the LF and greater decrease in the HF components. The differences in the HF component of HRV were associated with obesity and hyperuricosuria, but the abnormalities of the LF component were independent of the explanatory variables. The LF component of systolic BP was significantly higher in KSF and was associated with hypertension. Several factors may contribute to the presence of autonomic dysfunction in patients with recurrent nephrolithiasis. This abnormality has significant implications in cardiovascular risk assessment and treatment planning.

Renal denervation in an animal model of diabetes and hypertension: Impact on the autonomic nervous system and nephropathy

BackgroundThe effects of renal denervation on cardiovascular reflexes and markers of nephropathy in diabetic-hypertensive rats have not yet been explored.MethodsAim: To evaluate the effects of renal denervation on nephropathy development mechanisms (blood pressure, cardiovascular autonomic changes, renal GLUT2) in diabetic-hypertensive rats. Forty-one male spontaneously hypertensive rats (SHR) ~250 g were injected with STZ or not; 30 days later, surgical renal denervation (RD) or sham procedure was performed; 15 days later, glycemia and albuminuria (ELISA) were evaluated. Catheters were implanted into the femoral artery to evaluate arterial pressure (AP) and heart rate variability (spectral analysis) one day later in conscious animals. Animals were killed, kidneys removed, and cortical renal GLUT2 quantified (Western blotting).ResultsHigher glycemia (p < 0.05) and lower mean AP were observed in diabetics vs. nondiabetics (p < 0.05). Heart rate was higher in renal-denervated hypertensive and lower in diabetic-hypertensive rats (384.8 ± 37, 431.3 ± 36, 316.2 ± 5, 363.8 ± 12 bpm in SHR, RD-SHR, STZ-SHR and RD-STZ-SHR, respectively). Heart rate variability was higher in renal-denervated diabetic-hypertensive rats (55.75 ± 25.21, 73.40 ± 53.30, 148.4 ± 93 in RD-SHR, STZ-SHR- and RD-STZ-SHR, respectively, p < 0.05), as well as the LF component of AP variability (1.62 ± 0.9, 2.12 ± 0.9, 7.38 ± 6.5 in RD-SHR, STZ-SHR and RD-STZ-SHR, respectively, p < 0.05). GLUT2 renal content was higher in all groups vs. SHR.ConclusionsRenal denervation in diabetic-hypertensive rats improved previously reduced heart rate variability. The GLUT2 equally overexpressed by diabetes and renal denervation may represent a maximal derangement effect of each condition.

Mayer‐wave related oscillations (MWROs) are present in the vagal outflow during chemosensitive challenge

The central coordination of respiratory and vasomotor functions is likely to be modulated by a diffuse neural network, providing a common rhythmical background, based on the interaction between respiratory and Mayer wave-related rhythms. While MWROs have been recently described in the brainstem respiratory network (Morris et al., 2010), evidence of the presence of this rhythm in vagal outflow is still lacking. In a decerebrate cat preparation, arterial blood pressure (BP), cervical sympathetic and vagal outflows were recorded at baseline (B) and during two stimuli: the injection of CO2-satured saline via vertebral artery (central chemoreceptor stimulation, CCS) and via carotid artery (peripheral chemoreceptor stimulation, PCS). BP and nerve activity signals were analyzed using a frequency domain approach, based on autoregressive spectral and cross-spectral analysis of heart rate (HR) variability. At baseline, low-frequency (LF, around 0.1 Hz, i.e., MWRO) and high-frequency (HF, synchronous with the respiratory rate) components were present in sympathetic and BP signals, while HR and vagal outflow showed only an HF component. Interestingly, a LF component was observed in vagal outflow during the PCS. These preliminary results support the hypothesis of a “common central oscillatory network” that promotes cardiorespiratory coupling. Supported by PRIN 2007 (NM) and NIH R37 NS019814 Grants.

II. Slow Oscillations in Vaginal Blood Flow: Regulation of Vaginal Blood Flow Patterns in Rat by Central and Autonomic Mechanisms

A new method for assessing female sexual arousal through changes in slow oscillatory patterns in vaginal blood flow was first described in the previous manuscript [1]. This method was translational and discriminated between normal healthy volunteers and women with female sexual arousal disorder. These studies addressed the influence of autonomic and central nervous systems on slow vaginal blood flow oscillations in rats. Vaginal blood flow oscillations were measured in urethane-anesthetized rodents using laser Doppler flowmetry. Acquired data were filtered for frequency analysis range of 0.013-2.5 Hz. Data were assessed for changes in a high frequency range (HF = 0.6-2.5 Hz), and low frequency range (LF = 0.013-0.6 Hz). The basal HF oscillatory component of vaginal blood flow was primarily vagally mediated, although could be modulated pharmacologically with p-chloroamphetamine in the absence of vagal innervation. The LF component could be modulated by antagonists of noradrenergic receptors but did not appear to be dependent upon tonic activation of sympathetic circuitry. The non-selective dopamine receptor agonist apomorphine induced changes in vaginal blood flow oscillations consistent with sexual arousal during metestrus in the presence of the peripheral antagonist domperidone but not in the presence of the centrally acting antagonist haloperidol. Electrical stimulation of the paraventricular nucleus (PVN) of the hypothalamus induced an anti-arousal response in vaginal blood flow oscillations. These data demonstrated that manipulation of the central nervous system alone (via centrally acting apomorphine or electrical stimulation of the PVN) could produce either a pro-arousal or an anti-arousal response in vaginal blood flow oscillations. Alterations in the LF/HF ratio measured from vaginal laser Doppler flowmetry were independently regulated from vasculature in the trunk, the tongue, and electrocardiogram-derived heart rate variability, and were independent of overall vasocongestion of the vagina as measured by mean blood flow. These data indicated that slow oscillations in vaginal blood flow from rodents may be utilized as an animal model of female sexual arousal. Changes in these oscillations are driven by the central nervous system and modulated by the autonomic nervous system.

Linear and Fractal Heart Rate Dynamics during Sleep at High Altitude

To investigate the effects of hypoxia during sleep on linear and self-similar components of heart rate variability (HRV) in eight healthy subjects at high altitude on Mount Everest. ECG was monitored by using an innovative textile-based device, the MagIC system. For each subject three night recordings were performed at sea level (SL), at 3500 m and 5400 m above SL. RR Interval (RRI) was derived on a beat-by-beat basis from the ECG and the VLF, LF and HF spectral components and the LF/HF ratio were estimated. Short- (α₁) and long-term (α₂) scale exponents as well as the recently proposed spectrum of self-similarity coefficients, α(n) were estimated by detrended fluctuation analysis (DFA). With respect to SL, all HRV parameters but one (α₂) were significantly modified at 3500 m. However, at 5400 m they tended to return to the SL values and this was in contrast with the increase in the hypobaric hypoxia and in the number of central sleep apneas occurring at higher altitude. The only HRV index that displayed changes at 5400 m was the DFA α(n) spectrum, with α(n) values significantly lower than at SL for 20 < n <50 and higher for 200 < n <400, being n the box size. While the biological interpretation of these results is still in progress, our data indicates that the cardiac response to high altitude hypoxia during sleep can hardly be fully explored by traditional HRV estimators only, and requires the additional support of more sophisticated indexes exploring also nonlinear and fractal features of cardiac variability.

Detection of low-frequency oscillations in renal blood flow

Detection of the low-frequency (LF; approximately 0.01 Hz) component of renal blood flow, which is theorized to reflect the action of a third renal autoregulatory mechanism, has been difficult due to its slow dynamics. In this work, we used three different experimental approaches to detect the presence of the LF component of renal autoregulation using normotensive and spontaneously hypertensive rats (SHR), both anesthetized and unanesthetized. The first experimental approach utilized a blood pressure forcing in the form of a chirp, an oscillating perturbation with linearly increasing frequency, to elicit responses from the LF autoregulatory component in anesthetized normotensive rats. The second experimental approach involved collection and analysis of spontaneous blood flow fluctuation data from anesthetized normotensive rats and SHR to search for evidence of the LF component in the form of either amplitude or frequency modulation of the myogenic and tubuloglomerular feedback mechanisms. The third experiment used telemetric recordings of arterial pressure and renal blood flow from normotensive rats and SHR for the same purpose. Our transfer function analysis of chirp signal data yielded a resonant peak centered at 0.01 Hz that is greater than 0 dB, with the transfer function gain attenuated to lower than 0 dB at lower frequencies, which is a hallmark of autoregulation. Analysis of the data from the second experiments detected the presence of approximately 0.01-Hz oscillations only with isoflurane, albeit at a weaker strength compared with telemetric recordings. With the third experimental approach, the strength of the LF component was significantly weaker in the SHR than in the normotensive rats. In summary, our detection via the amplitude modulation approach of interactions between the LF component and both tubuloglomerular feedback and the myogenic mechanism, with the LF component having an identical frequency to that of the resonant gain peak, provides evidence that 0.01-Hz oscillations may represent the third autoregulatory mechanism.

Electroacupuncture Improves Imbalance of Autonomic Function under Restraint Stress in Conscious Rats

Acupuncture may modulate the imbalance of the autonomic nervous system. It is well known that restraint stress delays gastric emptying via inhibiting parasympathetic activity and/or stimulating sympathetic activity in rats. We have previously shown that electroacupuncture (EA) improves delayed gastric emptying induced by restraint stress in rats. To investigate whether the beneficial effect of EA on delayed gastric emptying is associated with its modulatory effects on autonomic nervous activity, we utilized spectral analysis of heart rate variability (HRV). In rats, the power in the low frequency (LF; 0.04-1.0 Hz) and high frequency (HF; 1.0-3 Hz) band of HRV represent sympathetic and parasympathetic activities, respectively. Electrocardiography (ECG)-electrodes were implanted on the subcutaneous tissues of the back. One week after the surgery, ECG was recorded before, during and after the restraint stress loading in a conscious state. EA (10 Hz) was applied at bilateral acupuncture points [ST-36 (lower leg) or BL-21 (back)] during restraint stress loading. In response to restraint stress, heart rate and LF component were increased, suggesting the increased activity of sympathetic tone. EA at ST-36 significantly reduced the elevated heart rate and LF, compared to that of control group. EA at ST-36 also significantly increased HF component after finishing the stress loading. In contrast, EA at BL-21 had no significant effect on the heart rate, LF and HF. It is suggested that EA at ST-36 stimulates parasympathetic activity and inhibits sympathetic activity under the restraint stress in rats.

Effects of Bilateral Stellate Ganglion Block on Autonomic Cardiovascular Regulation

Stellate ganglion block (SGB) is performed for the diagnosis and treatment of sympathetic dependent pain in the head, neck and upper limbs. However, the effects of bilateral SGB on cardiovascular and autonomic regulation remain unknown. The aim of this study was to assess the effects of bilateral SGB on cardiovascular and autonomic function by measuring heart rate variability (HRV), systolic blood pressure variability (SBPV) and spontaneous baroreflex sensitivity (SBRS). Twenty healthy volunteers were randomly allocated to receive right or left SGB with 8 ml 1% lidocaine solution; after 20 min, the contralateral side SGB was performed. Changes in the RR interval (RRI), systolic blood pressure (SBP), HRV, SBPV and SBRS were assessed before and after bilateral SGB. The low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.15-0.4 Hz) components of HRV and SBRS decreased significantly; however, no significant changes were found in RRI, SBP and the LF and HF components of SBPV after bilateral SGB. In subjects with symptoms of vagal blockade, HRV, SBP and SBRS were significantly affected by bilateral SGB. Bilateral SGB should be performed cautiously because it can reduce cardiac vagal modulation and BRS, especially for those with symptoms of vagal blockade after bilateral SGB.

Benefits of exercise training in diabetic rats persist after three weeks of detraining

Regarding all benefits of exercise training, a question remains: how long are these benefits kept? This study evaluated the effect of 3-week detraining after 10 weeks of training in STZ-diabetic rats. Male Wistar rats were assigned into: sedentary controls, trained controls, trained–detrained controls, sedentary diabetic, trained diabetic and trained–detrained diabetic. Arterial pressure (AP) and heart rate (HR) were recorded by a data acquisition system. Baroreflex sensitivity (BRS) was evaluated by HR responses to AP changes induced by infusion of vasoactive drugs. Intrinsic heart rate (IHR), sympathetic tonus (ST) and vagal tonus (VT) were evaluated by pharmacological blockade with atenolol and atropine. Spectral analysis of systolic AP and HR variabilities (HRV) was performed to estimate autonomic modulation to the heart and vessels. Diabetes cardiovascular and autonomic dysfunctions were reversed by exercise training and partially maintained in the 3-week detraining period. In controls, training decreased AP and HR and improved BRS, changes that returned to baseline values after detraining. IHR and VT were improved in trained diabetic rats and remained in detrained diabetic ones. LF component of HRV decreased in trained control group. In diabetics, exercise training improved variance, and absolute LF and HF components of HRV. Only HF was maintained in detrained diabetic group. Moreover, there was an inverse relationship between plasma glucose and the absolute HF component of HRV. These changes probably determined the different survival rate of 80% in diabetic detrained and 51% in diabetic sedentary rats.

Abstract 2403: Inspiratory Muscle Training Decreases Central and Peripheral Sympathetic Activity Improves Reflex Vasodilatory Blood Flow in Patients with Chronic Heart Failure

Background: Inspiratory muscle training (IMT) improves functional capacity of patients with CHF but the mechanisms of this effect are unknown. Objective: We tested the hypothesis that IMT could decrease sympathetic activity and improve the reflex muscle vasodilatory response during exercise in patients (CHF) and inspiratory muscle weakness. Methods: Six patients with CHF and inspiratory muscle weakness (maximal inspiratory pressure &lt;70% of predicted) NYHA Class II–III, EF &lt;35%, peak VO(2) &lt; 20 ml/kg/min, were submitted to a IMT during 12 weeks (30 minute breathing with an inspiratory resistance of 30% of maximal inspiratory pressure). Muscle sympathetic nerve activity (MSNA) was recorded by microneurography, LF (sympathetic) and HF (parasympathetic) components of the heart rate variability and LF/HF ratio were assessed by the use of power spectral analysis of RR interval. Forearm blood flow (FBF) was measured by venous occlusion plethysmography at baseline and during hand grip (HG) manouver. Paired student t-test was used to analyze the impact of IMT in this population. Results: Compared to baseline, IMT significantly (p &lt; 0,05) caused: an increase in inspiratory muscle force by 130%; a 15% reduction in MSNA (40 ± 1 vs 33 ± 1 bursts/min); an increase in forearm blood flow (0.8+/−0.1 mL/min/100 g) during HG manouver; a decrease in LF% (59 ± 5 vs 39 ± 3 U); an increase in HF% (40 ± 5 vs 61 ± 3 U); a decrease in LF/HF ratio (1,74 vs 0,66). Conclusions: Twelve weeks of Inspiratory muscle training in patients with CHF and inspiratory muscle weakness promoted a significant improvement in cardiovascular parameters, such as increase in limb blood flow, cardiac autonomic balance and baroreflex sensitivity, associated with a decrease in peripheral sympathetic activity.

Heart rate and arterial pressure variability in the experimental renovascular hypertension model in rats

This study was conducted in one kidney, one clip (1K1C) Goldblatt hypertensive rats to evaluate vascular and cardiac autonomic control using different approaches: 1) evaluation of the autonomic modulation of heart rate (HR) and systolic arterial pressure (SAP) by means of autoregressive power spectral analysis 2) assessment of the cardiac baroreflex sensitivity; and 3) double blockade with methylatropine and propranolol.The 1K1C group developed hypertension and tachycardia. The 1K1C group also presented reduction in variance as well as in LF (0.23±0.1 vs. 1.32±0.2 ms2) and HF (6.6±0.49 vs. 15.1±0.61 ms2) oscillations of pulse interval. Autoregressive spectral analysis of SAP showed that 1K1C rats had an increase in variance and LF band (13.3±2.7 vs. 7.4±1.01 mmHg2) in comparison with the sham group. The baroreflex gain was attenuated in the hypertensive 1K1C (−1.83±0.05 bpm/mmHg) rats in comparison with normotensive sham (−3.23±0.06 bpm/mmHg) rats. The autonomic blockade caused an increase in the intrinsic HR and sympathetic predominance on the basal HR of 1K1C rats. Overall, these data indicate that the tachycardia observed in the 1K1C group may be attributed to intrinsic cardiac mechanisms (increased intrinsic heart rate) and to a shift in the sympathovagal balance towards cardiac sympathetic over-activity and vagal suppression associated to depressed baroreflex sensitivity. Finally, the increase in the LF components of SAP also suggests an increase in sympathetic activity to peripheral vessels.

On arousal from sleep: time-frequency analysis

Time-frequency analysis of the heart rate variability during arousal from sleep, with and without EMG activation, coming from five obese healthy subjects was performed. Additionally, a comparative analysis of three time-frequency distributions, smooth pseudo Wigner-Ville (SPWVD), Choi-Williams (CWD) and Born-Jordan distribution (BJD) is presented in this study. SPWVD showed higher capacity for eliminating the cross terms independently of the signal. After applying Hilbert transformation to real signals BJD and CWD lost some important mathematic properties as marginals, on the contrary PSWVD remains unchanged. BJD showed results comparable with CWD. During arousal episodes, analogous energy distribution and spectral indexes were obtained by the three time-frequency representations. Arousals with chin activity presented stronger changes in RR intervals and LF (related to sympathetic activity) component, being statistically different with respect to arousal without chin activity, only around the period of maximum change in beta activity on the EEG. These results suggest a more evident stress for the heart when an arousal is related to external muscular activity.

Sympathetic overactivity and plasma leptin levels in Rett syndrome

Rett syndrome (RTT) is a severe developmental–neurological disorder, characterized by profound and progressive loss of intellectual functioning, occurring after a period (of at least 6 months) of normal development with classic stereotype hand movements, gait ataxia, jerky truncal ataxia, deceleration of brain and body organ growth and cardiac dysautonomia. Pathogenesis of sympathetic overactivity in RTT is unknown, but a previous study observed increased plasma leptin levels in Rett girls and it is well known the role of leptin in the regulation of sympathetic nervous system activity. Aim of our study is to evaluate a relationship between plasma leptin levels and sympathetic activity in RTT. Thirty-two female patients (12.1 ± 6.3 years), affected by RTT were enrolled in the study. In all the subjects, we analyzed heart rate variability, QT corrected interval and plasma leptin levels. A significant correlation was found between plasma leptin levels and LF/HF (expression of sympatho-vagal balance) (Spearman r = 0.44, p = 0.001). There is also a significant negative correlation between HF component (expression of vagal activity) and plasma leptin levels (Spearman r = −0.037, p = 0.03) and a positive correlation between LF component and plasma leptin levels (Spearman r = 0.047, p = 0.01). These results show that in RTT higher plasma leptin levels appear to be associated with sympathetic overactivity, suggesting a role for leptin in cardiac dysautonomia.

Spectral and spectral-temporal heart rate analysis in newborns

Spectral (in 3-min segments) and spectral-temporal (in 36-s windows with a 9-s step) analyses were carried out on the basis of cardiointerval recordings of newborns (full-term and preterm) during 24 h. It was found that each of the 3-min intervals of the 24-h cardiointerval recordings in the newborns had a unique spectrum; the spectra could be combined into several types. During 24 h, a spectrum with a marked LF component prevailed in the newborns. A spectrum with a peak in the HF region recorded in the newborns in the range from 0.4 to ∼1 Hz was an indicator of the rhythmic pattern of the variation of cardiointervals related to respiratory waves. Owing to the diversity of patterns of the spectral behavior of cardiointervals in a newborn during 24 h, no single short segment of the cardiointerval recording could serve as an unambiguous characteristic of the newborn’s physiological state. The actual heart rate variability pattern could be seen by means of the spectraltemporal analysis, visualizing the dynamics of conversion of one spectral type to another, i.e., the change of the dominant system of regulation.

Autonomic regulation during orthostatic stress in highlanders: comparison with sea‐level residents

This report is a comparison of orthostatic tolerance and autonomic function in three groups of high-altitude dwellers: Andeans with and without chronic mountain sickness (CMS) and healthy Ethiopians. Results are compared with those from healthy sea-level residents. The aim was to determine whether different high-altitude populations adapted differently to the prevailing hypobaric hypoxia. Orthostatic tolerance was assessed using a test involving head-up tilt (HUT) and graded lower body suction. This was performed at the subjects' resident altitude. Blood pressure (Portapres) and R-R interval (ECG) were recorded during the test, and spectral and cross-spectral analyses of heart period and systolic blood pressure time series were performed using data obtained both while supine and during HUT. The transfer function gain in the low-frequency range (LF, approximately 0.1 Hz) at the point of maximal coherence was used as a measure of cardiac baroreflex sensitivity (BRS). As previously reported, Peruvians displayed an unusually good orthostatic tolerance, while Ethiopians showed an orthostatic tolerance comparable to that of healthy sea-level residents. There were no significant differences between groups in the supine values of the spectral analysis results. Head-up tilt induced the expected changes in Ethiopians (an increase in the LF components and a decrease in the respiratory components) but not in Andeans. Cross-spectral analysis showed abnormal results from all groups of high-altitude dwellers. These results indicate that Ethiopians, but not Peruvians, behave similarly to sea-level residents in terms of orthostatic tolerance and autonomic responses to orthostatic stress, as assessed from spectral analyses, and this indicates good adaptation to their environment. However, in all the high-altitude groups the results of cross-spectral analysis were atypical, suggesting some degree of impairment in baroreflex function.

Resting and Postexercise Cardiac Autonomic Control in Trained Masters Athletes

This study used measures of heart rate variability during recovery from high-intensity exercise in trained Master athletes to examine postexercise cardiac autonomic regulation. Seven males (mean age 52.1 +/- 3.3 yr; mass 85.1 +/- 18.0 kg) and 6 females (mean age 50.5 +/- 2.9 yr; mass 63.1 +/- 6.0 kg) performed incremental exercise to an intensity that induced a >4.5 mmol capillary blood lactate concentration, followed by incremental exercise to volitional exhaustion (VO2(max)). A 6 min ECG recording before (Pre) and after (Post) exercise was analyzed in the time (mean rr interval, sd rr) and frequency domains (total power, very low frequency [VLF: 0-0.04 Hz], low frequency [LF: 0.04-0.15 Hz], high frequency [HF: 0.15-0.4 Hz]). VO2(max) for males and females was 49.4 +/- 7.1 ml kg(-1) min(-1) and 45.1 +/- 10.1 ml kg(-1) min(-1), respectively. Lower mean rr interval (Pre: 1,048 +/- 128 ms; Post: 730 +/- 78 ms; P < 0.001) and lower sd rr (Pre: 77 +/- 30 ms; Post: 43 +/- 17 ms; P < 0.001) were recorded following exercise, with no differences based on gender. Total power decreased following exercise (Pre: 6,331 +/- 6,119 ms; Post: 1,921 +/- 1,552 ms). When normalized for changes in total power, a decreased HF component (Pre: 34.52 +/- 14.79 n.u.; Post: 18.49 +/- 13.64 n.u.; P < 0.05) with no change in LF component (Pre: 61.00 +/- 18.66 n.u.; Post: 69.63 +/- 23.97 n.u.; P = 0.34) was recorded. No gender differences in HRV in the frequency domain were recorded. Decreased heart rate variability in both time and frequency domains suggested an increased parasympathetic withdrawal during the autonomic control of postexercise tachycardia in trained Master athletes.

Circadian Rhythms in Autonomic Cardiac Function in Mice

Circadian rhythms in cardiovascular function are critical in health maintenance. The purpose was to determine time-specific patterns in blood pressure (BP), pulse interval (PI) and autonomic balance in C57Bl mice (n = 5, light/dark; 0500/1700h). 24 hr radiotelemetric BP recordings were made. Recordings were divided into 8 periods (4 light/4 dark) and analysis performed on 30-min segments. BP (mmHg) and PI (ms2) oscillations were characterized in time and frequency domains (low and high) using autoregressive spectral analysis. As expected, there was a light/dark rhythm in BP and PI, higher levels in the dark phase (p < 0.02). For PI variance and its LF component, there was a rhythm (ANOVA, p < 0.05 and < 0.01, variance and LF, respectively). There was no day/night rhythm in systolic BP variance. There was a marked decrease in PI variance (~ 2 fold) and PI-LF (~ 3 fold), with onset of the dark phase. PI variance was 75 ± 10 vs. 40 ± 5 ms2 and PI-LF was 36 ± 5 vs. 11 ± 1 (light vs dark). There was no change in HF for either PI or SBP. There was a day/night rhythm in baroreflex. Results demonstrate differences in the circadian autonomic rhythm for PI and BP. For the cardiac axis, there was a clear day/night rhythm which was not seen for the vasculature. The changes in variance and its LF component suggest that there are rhythmic alterations in sympathetic/parasympathetic balance. This study provides important information on the nature of normal autonomic rhythms in mice.