Analysis Of RR Intervals Research Articles

Sympathetic and parasympathetic activities evaluated by heart-rate variability in head injury of various severities

Objective To investigate the autonomic function in patients with brain damage of various extents. The purposes were to correlate the parameters derived from spectral analysis of the heart-rate variability (HRV) with the classic Glasgow coma scale (GCS), and to evaluate the possible clinical application of HRV in the autonomic functions in patients with various severities of brain-stem injury. Methods A total of 90 patients was divided into 5 groups based on the GCS: I: 15, II: 9–14, III: 4–8, no pupil dilatation, IV: 4–8, pupil dilatation, and V: 3, brain death. Electrocardiogram was recorded for frequency-domain analysis of RR intervals. HRV were categorized into the low-frequency (LF, 0.04–0.15 Hz) and high-frequency power (HF, 0.15–0.40 Hz), LF to HF power ratio (LF/HF), normalized powers (LF and HF%). These HRV parameters were correlated with the severity of brain damage. Results The LF, HF, LF%, and LF/HF in Group I were essentially similar to those in the normal subjects. LF and HF decreased from Group I to IV. All parameters were nearly absent in Group V. Conclusions The increases in LF% and LF/HF with the decrease in HF indicate augmented sympathetic and attenuated parasympathetic drive. These changes were related to the severity of brain-stem damage. Both LF and HF were nearly abolished in brain death. Significance Our analysis indicates that HRV may be an useful tool for evaluating the autonomic functions in patients with brain damage of various degrees.

Nonlinear analysis of RR interval in euthymic bipolar disorder

Background The bipolar affective disorder is long been speculated to have an autonomic involvement. Nonlinear analysis of heart rate variability has recently been shown to be a reliable noninvasive test for quantitative assessment of the central sympathovagal interaction that modulates cardiovascular autonomic function. Methods We studied 32 euthymic bipolar patients and 24 controls. A high-resolution electrocardiogram was obtained during complete rest. Nonlinear analysis (Poincare plot, largest Lyaponuv exponent, minimal embedding dimension, symbolic dynamic) was used. Results There wasn't a statistically significant difference in the nonlinear analysis of the heart rate variability, between the euthymic bipolar patients and controls, in the rest situation. Conclusion The nonlinear analysis of heart rate variability didn't support the notation that there is a disturbance in the autonomic nerves system of bipolar patients in the euthymic state.

Real time electrocardiogram QRS detection using combined adaptive threshold.

BackgroundQRS and ventricular beat detection is a basic procedure for electrocardiogram (ECG) processing and analysis. Large variety of methods have been proposed and used, featuring high percentages of correct detection. Nevertheless, the problem remains open especially with respect to higher detection accuracy in noisy ECGsMethodsA real-time detection method is proposed, based on comparison between absolute values of summed differentiated electrocardiograms of one of more ECG leads and adaptive threshold. The threshold combines three parameters: an adaptive slew-rate value, a second value which rises when high-frequency noise occurs, and a third one intended to avoid missing of low amplitude beats.Two algorithms were developed: Algorithm 1 detects at the current beat and Algorithm 2 has an RR interval analysis component in addition.The algorithms are self-adjusting to the thresholds and weighting constants, regardless of resolution and sampling frequency used. They operate with any number L of ECG leads, self-synchronize to QRS or beat slopes and adapt to beat-to-beat intervals.ResultsThe algorithms were tested by an independent expert, thus excluding possible author's influence, using all 48 full-length ECG records of the MIT-BIH arrhythmia database. The results were: sensitivity Se = 99.69 % and specificity Sp = 99.65 % for Algorithm 1 and Se = 99.74 % and Sp = 99.65 % for Algorithm 2.ConclusionThe statistical indices are higher than, or comparable to those, cited in the scientific literature.

Altered profile of baroreflex and autonomic responses to lower body negative pressure in chronic orthostatic intolerance.

Chronic orthostatic intolerance (COI) is a common and disabling autonomic syndrome of unclear pathophysiology. We tested the hypothesis that baroreflex and autonomic responses to graded lower body suction (LBNP, up to -40 mmHg) could be altered in COI patients. Electrocardiogram (ECG), non-invasive arterial blood pressure and respiratory activity were measured during progressive LBNP (seven patients and seven volunteers). Lumped arterial baroreflex sensitivity (alpha index), and its arterial and cardiopulmonary components, were assessed by multivariate closed-loop analysis of RR interval and systolic arterial pressure (SAP) spontaneous variabilities and respiration. Monovariate spectral analysis of RR interval and SAP variability provided markers of autonomic regulation of the sinoatrial (SA) node and of vascular sympathetic modulation. Similar reductions in overall and cardiopulmonary baroreflex gain were observed in both groups in response to graded LBNP. In contrast, only controls demonstrated a selective increase in arterial baroreflex sensitivity, at low-grade LBNP. Clear increases in the low-frequency component of RR interval variability (LFRR) [and decreases in the high-frequency component of RR interval variability (HFRR), both in normalized units] were observed in controls with graded LBNP, while insignificant changes occurred in COI patients, who showed, conversely, exaggerated sympathetic vasomotor responses [as assessed by the low frequency component of SAP variability (LFSAP)]. Patients with chronic orthostatic intolerance show distinct signs of altered baroreflex and autonomic regulation of the SA node and of the vasculature in response to graded LBNP.

Selective reductions of cardiac autonomic responses to light bicycle exercise with aging in healthy humans

We examined on 56 (age 38±2 [range: 16–60] years) healthy subjects the effects of aging on cardiovascular autonomic responses to progressive supine bicycle exercise of light intensity. Autoregressive spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided measures of the exercise-induced changes in baroreflex gain (by index α) and in sympathetic and vagal modulation of the SA node (by the normalized low [LF] and high frequency [HF] component of RR interval variability, respectively), as well as of changes in sympathetic vasomotor control (LF SAP). For each hemodynamic and autonomic variable, the gain of the response was expressed both as individual step increments, and as the slope of the linear regression of the sequential data points from rest and during the three steps of exercise. Age resulted significantly correlated to changes in spectral derived markers of SA modulation (LF RR, HF RR and index α). Conversely, no significant relationships were found with changes in RR interval, in SAP and indices of vascular regulation (LF SAP). In addition, exercise-induced changes in indices of SA node regulation were more evident in the youngest tertile (age 25±1 years), compared to the oldest tertile (age 52±1 years). In conclusion, we have observed that aging progressively and selectively reduces the cardiac autonomic excitatory response to light exercise, while hemodynamic and vascular responsiveness are maintained.

Model-based assessment of autonomic control in obstructive sleep apnea syndrome.

To quantitatively assess autonomic cardiovascular control in patients with obstructive sleep apnea syndrome (OSAS) using a mathematical model that relates changes in R-R interval (RRI) to respiration and changes in systolic blood pressure (SBP), and to compare the results obtained with conventional techniques. Respiration, RRI, and arterial blood pressure were monitored noninvasively in awake subjects in the supine and standing postures. A mathematical model was used to partition the fluctuations in RRI into a component ("RSA") correlated with respiration and a component ("baroreflex") correlated with fluctuations in SBP. Sleep disorders laboratory in a hospital setting. 11 middle-aged male patients with untreated OSAS (apnea-hypopnea index = 75.9 +/- 11.1 (SE) events h-1) and 11 age-matched normal controls (10 males + 1 female). The subjects were monitored while breathing spontaneously in both supine and standing postures. Each subject also had to perform a battery of 5 standard autonomic stress tests (AST). Four of the 5 ASTs did not indicate any difference between controls and OSAS subjects. There were also no differences in the indices derived from power spectral analysis of RRI and blood pressure variability; however, these spectral indices were sensitive to postural changes (orthostatic stress). Both RSA and baroreflex gains estimated from the model were substantially depressed in OSAS (P < 0.02) Changes in posture affected RSA gain but not baroreflex gain. The time-courses of the dynamics of these model components were not significantly different between subject groups. OSAS leads to abnormal parasympathetic and sympathetic control of heart rate, as reflected in depressed RSA and baroreflex gains. Model-based assessment was more sensitive in detecting abnormal autonomic function, compared to standard autonomic testing and power spectral analysis. The model-based approach represents a relatively simple and nonintrusive means of quantifying the key aspects of autonomic control in spontaneously breathing OSAS patients during wakefulness.

Glossodynia and the function of the autonomic nervous system--frequency spectrum analysis of RR intervals recorded electrocardiographically

This study explored the relationship between the function of the autonomic nervous system (ANS) and glossodynia. The function of the ANS was examined in patients with glossodynia by frequency analysis of heart rate variability. The subjects were 50 women given the diagnosis of glossodynia and 24 healthy volunteers. The heart rate variability of these subjects was evaluated. Mean values of the high frequency power at rest were 1.323 +/- 1.484 ms2 in the group without functional disorders (NF group), 1.861 +/- 1.601 ms2 in the group with functional disorders (F group), and 3.229 +/- 2.044 ms2 in the standard group (H group). Mean values of HF/LF were 0.968 +/- 0.961 in the NF group, and 1.696 +/- 0.847 in the H group. Mean values of the high frequency power at rest were 1.032 +/- 977 ms2 in the group with CMIs in regions III and IV (III-IV group), 3.299 +/- 2.044 ms2 in the H group, and 2.314 +/- 1.883 ms2 in the group with CMIs in regions I and II (I-II group). Mean values of HF/LF were 0.965 +/- 0.744 in the III-IV group and 1.696 +/- 0.847 in the H group. The results of this study suggest that nervous tension, which was the cause of indefinite complaints in patients with glossodynia, had resulted from a pronounced reduction in activities of the parasympathetic nervous system, but not from an excessive increase in activities of the sympathetic nervous system. An assessment of the function of the ANS by means of heart rate variability seemed to be useful for comprehending the clinical conditions of glossodynia.

Tolérance orthostatique après vol spatial et simulation d’impesanteur par alitement prolongé

Cardiovascular modifications, specially orthostatic intolerance (OI) are well known after spaceflight or long duration head-down bed-rest (HDBR) There is no agreement about their mechanisms. The aim of the study was to compare OI after a 42 day HDBR (n = 7) and after a 90 to 198 day spaceflight (n = 10). The studies were made during a stand test of 10 minutes for HDBR following 10 min in supine position and 5 min in sitting position. In both groups the variables measured were blood pressure (BP by transcutaneous plethysmography, Finapres) and ECG for RR interval (RRi) determination which allowed us to calculate autonomic indexes by spectral analysis of RRi and to determine spontaneous baroreflex sensitivity. In the cosmonaut group, 1 subject experienced a vaso-vagal syncope and 2 asked to stop the test without a decrease in BP. In HDBR, 4 subjects out of 7 did not perform the whole stand test (1 vaso-vagal syncope, 1 tachycardia and 2 hypotensions). Cosmonauts or HDBR subjects had common profiles: tachycardia and a decrease in parasympathetic index and baroreflex sensitivity. Both groups have an OI (30% of the subjects). However the mechanisms are different even if they have a common postural orthostatic tachycardia syndrome (POTS). The spaceflight duration was not determinant and we have no indice to predict OI which was one of the aims of the study.

Evidence of parasympathetic impairment in some patients with cardiac syndrome X.

Cardiac syndrome X (SX) is a clinical condition characterised by angina, positive exercise stress test and negative coronary angiography; it has often been attributed to sympathetic hyperactivity. Here we tested the hypothesis that a parasympathetic, rather than a sympathetic, dysfunction could be the cause of the autonomic imbalance observed in SX. In 20 subjects with diagnosed SX and in 12 age-matched controls, we studied autonomic function by performing spectral analysis of RR interval and finger arterial pressure (SAP), in supine position and during head-up tilting. We also carried out a set of tests of parasympathetic function. The group of SX patients did not differ significantly from control subjects in any of the variables tested. In a subgroup of 13 SX, however, tilting increased the low-frequency power of SAP, but did not induce the expected increase in low-frequency and decrease in high-frequency power of RR. These patients, in supine position, had significantly lower sinus arrhythmia and a higher ratio of low to high frequency of RR, in comparison with control subjects. We interpreted these differences as signs of reduced parasympathetic, but essentially normal sympathetic, activity. The parasympathetic tests confirmed vagal impairment in the same SX subjects. On the other hand, all the tests indicated normal parasympathetic functions in the control subjects and in those SX patients who displayed the expected spectral changes in tilting. In about two thirds of the patients with SX, the pathophysiological mechanism causing the symptoms could be related to the reduced parasympathetic tone, rather than to an augmented sympathetic activity.

Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.

To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia. We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO2), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5,000 m, in a hypobaric chamber). We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during 'complete yogic breathing' (slow diaphragmatic + thoracic breathing, approximately 5 breaths/min) in yoga trainees, or simple slow breathing in controls. At baseline %SaO2, VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO2 decreased in all subjects (P< 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P< 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 +/- 45 to 770 +/- 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 +/- 0.5 to 3.2 +/- 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 +/- 0.31 to 3.07 +/- 0.24 In-mmHg2, P< 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing. No effect of altitude was seen on stimulation of carotid baroreceptors in both groups. Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia.

Smoothed pseudo Wigner–Ville distribution as an alternative to Fourier transform in rats

Techniques for examining signals in the time and frequency domains are well-established tools. These tools have their limitations; they tell us in a broad sense where the signal component exists in the frequency domain, but they do not tell us how its frequency characteristics change over time. The time-frequency has become a powerful alternative for the analysis of signals. Among various time-frequency distribution methods, one of the most studied is the Wigner–Ville distribution. The aim of this study was to evaluate in conscious rats smoothed pseudo Wigner–Ville distribution (SPWVD) as an alternative to the fast Fourier transform (FFT) in RR intervals and in systolic blood pressure (SBP), before and after adrenergic and cholinergic receptor blockade. Fourteen Wistar rats equipped with telemetry probe were evaluated: (1) under control conditions; (2) after injection of saline (100 μl kg −1 i.v.); (3) after atenolol (1 mg kg −1 i.v.); (4) after atropine methyl nitrate (0.5 mg kg −1 i.v.); and (5) after phentolamine (5 mg kg −1 i.v.). FFT and SPWVD were applied to RR intervals and SBP time series. Six-minute time series of RR intervals, systolic and diastolic pressures were analysed. The bias and distribution of differences between FFT and SPWVD methods in RR intervals under base conditions were 1.4±0.4% ( r 2=0.94; P<0.01) in LF/LF+HF; 1.5±0.5% ( r 2=0.92; P<0.01) in HF/LF+HF and 4.8±1.9% ( r 2=0.92; P<0.01) in LF/HF. In SBP the bias and distribution were 1.5±0.8% ( r 2=0.90; P<0.05) in LF/LF+HF and 1.7±0.6% ( r 2=0.92; P<0.01) in HF/LF+HF. In the frequency domain analysis of RR intervals and SBP there was no difference between FFT and SPWVD. The agreement between the methods demonstrates that in stationary signals both methods can be used interchangeably. SPWVD may be an interesting tool to analyse biomedical signals; it provides a good resolution at high frequency and a good frequency resolution at low frequencies independently if signals remain stationary.

Autonomic modulation of heart rate and blood pressure in normotensive offspring of hypertensive subjects

Predominant sympathetic cardiovascular modulation in the hyperkinetic phase of arterial hypertension has been well described. Less information is available on autonomic control in persons with a family history of arterial hypertension. To investigate this question, we selected 61 normotensive subjects (mean age 30.9 ± 1.8 years) whose mother or father or both had arterial hypertension and 30 normotensive patients (mean age 30.1 ± 1.4 years) whose parents had not had arterial hypertension (neither mother nor father) to undergo short-term power spectral analysis of RR interval and arterial pressure variabilities. The same recordings were used to determine baroreflex sensitivity or the alpha index by means of the transfer function. Normotensive offspring of hypertensive subjects had higher diastolic blood pressures (P <.05) and left ventricular mass index (P <.05) than did normotensive offspring of non-hypertensive subjects. They also had higher spectral densities of low frequency expressed in normalized units, both for R-R intervals (P <.05) and systolic pressure variabilities (P <.05); they also had a greater ratio of low-frequency to high-frequency powers of R-R interval variability (P <.05). No difference was observed between the two normotensive groups for baroreflex sensitivity. Our spectral data indicate that normotensive persons with a positive family history of arterial hypertension have lower parasympathetic modulation than those with a negative history. In normotensive persons with a family history of arterial hypertension, normal baroreflex sensitivity could be the mechanism that buffers the tendency for pressures to increase. The gradual loss of this regulatory mechanism may favor rising arterial pressures. (J Lab Clin Med 2000;135:145-52)

Time-varying spectral analysis of heart rate and left ventricular pressure variability during balloon coronary occlusion in humans: A sympathoexcitatory response to myocardial ischemia

OBJECTIVESWe assessed time-varying spectral components of heart rate and left ventricular (LV) pressure variability during coronary angioplasty to elucidate dynamic autonomic responses to transient myocardial ischemia.BACKGROUNDSympathoexcitatory reflexes elicited by acute coronary occlusion are rarely addressed in the clinical settings because of a lack of technique to monitor transient changes in sympathetic activation.METHODSRR interval and LV pressure and volume were serially recorded in 14 patients with effort angina during balloon coronary angioplasty. Wavelet analysis was applied for determination of nonstationary spectral components of RR interval and LV peak pressure variability.RESULTSThe wavelet analysis revealed that coronary occlusion provoked low-frequency (LF) fluctuations of RR interval (seven patients) and LV peak pressure (six patients) at 0.06 ± 0.01 Hz, but not in the remaining patients. Following the balloon inflation, the LF component of RR interval began to increase after the onset of myocardial ischemia, peaked at about 80 s, and then declined in the late phase of inflation. Consequently, the ratio of low to high frequency component rose to be significantly greater in the LF augmentation group than in the no LF augmentation group in the middle phase of coronary occlusion. The patients with no LF augmentation had little evidence of myocardial ischemia as reflected by changes in ST segment and LV systolic function during coronary occlusion.CONCLUSIONSThe wavelet analysis of RR interval and LV pressure variability clearly showed a dynamic profile of spectral components in response to transient coronary artery occlusion. The resultant regional myocardial ischemia elicited a profound sympathoexcitatory response followed by a gradual suppression. This method provides a useful tool to gain a new insight into the nonstationary autonomic influence on the cardiovascular system.

Power spectral analysis of short-term RR interval and arterial blood pressure oscillations in the lizard, Gallotia galloti: effects of sympathetic blockade.

The role of the sympathetic limb of the autonomic nervous system (ANS) in the mediation of oscillations in consecutive beat-to-beat RR interval (RRI) and systolic blood pressure (SBP) values of lizards, Gallotia galloti, was investigated using spectral analysis and measuring effects of autonomic blockers. alpha-Adrenergic blockade decreased the power spectral density (PSD) of both RRI and SBP very low frequency (VLF: 0.007-0.055 Hz) and low frequency (LF: 0.055-0.150 Hz) bands, whereas beta-adrenergic blockade increased the PSD of both RRI- and SBP-VLF and RRI- and SBP-LF bands. These findings suggest that in lizards 1) the VLF and LF peaks of RRI and SBP power spectra are alpha-adrenergic mediated, and that 2) the beta-adrenergic activity of the sympathetic system may act buffering all RRI and SBP oscillations below 0.150 Hz. These results, when analyzed jointly with the ones obtained from a previous study (De Vera and González. 1997. Comp Biochem Physiol 85A:389-394) on the effects of parasympathetic blockade on lizards' RRI and SBP oscillations, demonstrate that these reptiles, like mammals, exhibit spontaneous short-term oscillations in their HR and SBP which are mediated by the ANS. However, unlike mammals, the RRI and ABP low-frequency oscillations in Gallotia seem to be similarly affected by the ANS and appear to be powered by alpha-adrenergic and parasympathetic activities and buffered by beta-adrenergic activity.

Non-invasive assessment of human baroreflex during different body positions

Two techniques for evaluating human baroreflex sensitivity (BRS), i.e. the sequence technique and the cross-spectral technique, were compared during the following four different body positions; 6° head-down tilt (HDT), supine (Sup), 60° head-up tilt (HUT) and upright (Upr). The sequence technique is based on the slope of linear regression between beat-to-beat RR intervals and systolic blood pressures. The cross-spectral technique is based on the cross-spectral analysis of RR interval and systolic blood pressure variabilities, and the estimates of BRS were computed separately for the low-frequency region (0.04–0.15 Hz) and the high-frequency region (0.15–0.5 Hz). The BRS obtained by the sequence technique had a significant correlation to that obtained by the cross-spectral technique for the low-frequency region in HDT, Sup and HUT, but not in Upr. There was a significant correlation between the BRS obtained by the sequence technique and that obtained by the cross-spectral technique for the high-frequency region in every body position. It became clear that the sequence technique is mutually related to the cross-spectral technique for the high-frequency region, but not necessarily identical to the cross-spectral technique for the low-frequency region. Moreover, a comparison was also made between the baroreceptor activating sequence and the deactivating sequence in the sequence technique during the four different body positions. Although the estimates of BRS of the activating sequence and the deactivating sequence were similar in every body position, the numbers of their sequences were progressively separated in the order of HDT, Sup, HUT and Upr. The numbers of the activating sequence and the deactivating sequence in the sequence technique were found to be separated in a sympathetically dominant condition.

Hyperinsulinemia produces cardiac vagal withdrawal and nonuniform sympathetic activation in normal subjects.

The exact mechanisms for the decrease in R-R interval (RRI) during acute physiological hyperinsulinemia with euglycemia are unknown. Power spectral analysis of RRI and microneurographic recordings of muscle sympathetic nerve activity (MSNA) in 16 normal subjects provided markers of autonomic control during 90-min hyperinsulinemic/euglycemic clamps. By infusing propranolol and insulin (n = 6 subjects), we also explored the contribution of heightened cardiac sympathetic activity to the insulin-induced decrease in RRI. Slight decreases in RRI (P < 0.001) induced by sevenfold increases in plasma insulin could not be suppressed by propranolol. Insulin increased MSNA by more than twofold (P < 0.001), decreased the high-frequency variability of RRI (P < 0.01), but did not affect the absolute low-frequency variability of RRI. These results suggest that reductions in cardiac vagal tone and modulation contribute at least in part to the reduction in RRI during hyperinsulinemia. Moreover, more than twofold increases in MSNA occurring concurrently with a slight and not purely sympathetically mediated tachycardia suggest regionally nonuniform increases in sympathetic activity during hyperinsulinemia in humans.

Chronic orthostatic intolerance: a disorder with discordant cardiac and vascular sympathetic control.

Chronic orthostatic intolerance (COI) is a debilitating autonomic condition in young adults. Its neurohumoral and hemodynamic profiles suggest possible alterations of postural sympathetic function and of baroreflex control of heart rate (HR). In 16 COI patients and 16 healthy volunteers, intra-arterial blood pressure (BP), ECG, central venous pressure (CVP), and muscle sympathetic nerve activity (MSNA) were recorded at rest and during 75 degrees tilt. Spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided indices of sympathovagal modulation of the sinoatrial node (ratio of low-frequency to high-frequency components, LF/HF) and of sympathetic vasomotor control (LFSAP). Baroreflex mechanisms were assessed (1) by the slope of the regression line obtained from changes of RR interval and MSNA evoked by pharmacologically induced alterations in BP and (2) by the index alpha, obtained from cross-spectral analysis of RR and SAP variabilities. At rest, HR, MSNA, LF/HF, and LFSAP were higher in COI patients, whereas BP and CVP were similar in the two groups. During tilt, BP did not change and CVP fell by the same extent in the 2 groups; the increase of HR and LF/HF was more pronounced in COI patients. Conversely, the increase of MSNA was lower in COI than in control subjects. Baroreflex sensitivity was similar in COI and control subjects at rest; tilt reduced alpha similarly in both groups. COI is characterized by an overall enhancement of noradrenergic tone at rest and by a blunted postganglionic sympathetic response to standing, with a compensatory cardiac sympathetic overactivity. Baroreflex mechanisms maintain their functional responsiveness. These data suggest that in COI, the functional distribution of central sympathetic tone to the heart and vasculature is abnormal.

Central Vagotonic Effects of Atropine Modulate Spectral Oscillations of Sympathetic Nerve Activity

Low-dose atropine causes bradycardia either by acting on the sinoatrial node or by its effects on central muscarinic receptors increasing vagal activity. Any central muscarinic effects of high-dose atropine on RR interval are masked by peripheral muscarinic blockade at the sinoatrial node, which causes tachycardia. Effects of central parasympathetic activation on sympathetic activity are not known. Using power spectral analysis of RR interval, intra-arterial blood pressure, respiration, and muscle sympathetic nerve activity (MSNA), we examined the effects of both low (2 microgram/kg IV) and high (15 microgram/kg IV) doses of atropine. After low-dose atropine, RR increased by 9+/-1% (P<0.0001), the low-frequency (LF) component (in normalized units, NU) of RR variability decreased by -32+/-8%, and the high-frequency (HF)NU component increased (+74+/-19%); hence, LF/HF of RR variability fell by 52+/-10% (all P<0.01). Although overall MSNA did not change, LFNU of MSNA decreased (-15+/-5%), HFNU of MSNA increased (+31+/-3%), and LF/HF of MSNA fell (-41+/-8%) (all P<0.01). After high-dose atropine, LFNU of MSNA decreased (-17+/-12%), HFNU of MSNA increased (+22+/-3%), and LF/HF of MSNA fell (-51+/-21%) (all P<0.02). Increasing central parasympathetic activity with low-dose atropine is associated with an increase in the HF and a decrease in the LF oscillations of both RR interval and MSNA variability. High-dose atropine similarly induces an increase in the HF and a decrease in the LF components of MSNA variability. Thus, central parasympathetic activation is able to modulate the oscillatory characteristics of sympathetic nerve traffic to peripheral blood vessels.

Cardiac autonomic modulation and incidence of late potentials in essential hypertension: role of age, sex, ventricular mass and remodeling

The influence of age, sex, left ventricular hypertrophy (LVH) and geometry on the autonomic activity to the heart was investigated in 96 hypertensive out-patients (53 men, mean age 53 +/- 9 years) and 39 healthy subjects (19 men, mean age 43 +/- 1 years). Using 24-h Holter recordings, time [the standard deviation of all RR intervals (SDNN) and the square root of the mean of the squared differences between adjacent normal RR intervals (RMSSD)] and power spectral analysis of RR intervals [Fast Fourier algorithm, low/high frequency (LF/HF) ratio] were calculated over 24 h, daytime (D) and nighttime (N) periods in all subjects. Signal averaged electrocardiogram was recorded in 50 patients to detect late potentials. Stepwise multiple linear regression analysis showed that the 24-h LF/HF ratio was influenced by age and sex, D-LF/HF by age and N-LF/HF by sex, a higher LF/HF ratio being found in younger patients and in men. These data suggest a more prominent sympathetic modulation of cardiac activity in these groups. No differences in RR period variations were observed between patients with or without LVH. Late potentials were observed in 10 patients, and did not correlate with any of the measured parameters.

Power spectral analysis of short-term RR interval and arterial blood pressure oscillations in lizard ( Gallotia galloti): Effects of parasympathetic blockade

Spontaneous short-term oscillations in consecutive beat-to-beat RR interval (RRI) and systolic blood pressure (SBP) values of lizards ( Gallotia galloti) in basal conditions and under parasympathetic blockade with atropine at 23°C body temperature were investigated using spectral analysis. In control conditions, both RRI and SBP spectra exhibited two major oscillations in very low (VLF 0.008–0.030 Hz) and low (LF 0.030–0.100 Hz) frequencies. Most lizards presented a high frequency (HF) respiratory peak in the SBP spectra whenever the lizard's ventilatory pattern was rhythmic. Parasympathetic blockade decreased all RRI oscillations and LF and HF oscillationsof SBP. VLF and LF oscillations of RRI and SBP were still clearly present after blockade, which shows that other neural or humoral systems different from parasympathetic could mediate also low frequency RRI and SBP variability. SBP-RRI cross-spectral analysis showed in control conditions a linear relationship between SBP and RRI variations in the VLF, LF and HF bands, with SBP variations leading RRI; the parasympathetic limb of the baroreflex seems to be involved in maintaining the SBP-RRI coherence in the LF and perhaps in the HF band.