Analysis Of RR Interval Variability Research Articles

Streamlining Analysis of RR Interval Variability in Elite Soccer Players: Preliminary Experience with a Composite Indicator of Cardiac Autonomic Regulation.

It is well recognized that regular physical activity may improve cardiac autonomic regulation preventing chronic non-communicable diseases. Accordingly, the assessment of cardiac autonomic regulation (CAR) with non-invasive techniques, such as RR interval Variability (V) might be of practical interest. We studied 56 soccer players (21.2 ± 4.2 years.) and 56 controls (22.2 ± 1.5 years.) and used a ranked Autonomic Nervous System Index (ANSI), resulting from the combination of multivariate statistical methodologies applied to spectral analysis derived indices from RRV. We hypothesized that ANSI would be higher in soccer players as compared to controls (p < 0.001) and that values would be greatest in defenders and midfielders, who are known to run longer distances during competitions. Conversely in the intrinsically stationary goalkeepers ANSI would be similar to controls. Our data show that it is possible to assess the overall level of autonomic performance in soccer players as compared to the general population, using a ranked composite autonomic proxy (ANSI). This approach suggests as well that CAR is better in those players who during competitions run for a greater distance. We conclude that it is possible to highlight the differences in autonomic profile due to distinct exercise routines, using ANSI, a simple ranked, composite autonomic proxy.

Effect of acute administration of vitamin C on muscle sympathetic activity, cardiac sympathovagal balance, and baroreflex sensitivity in hypertensive patients

Essential hypertension is characterized by both increased oxidative stress and sympathetic traffic. Experimental studies have shown that reactive oxygen species can modulate autonomic activity. The aim of this study was to determine whether acute administration of the antioxidant vitamin C modifies sympathetic nerve activity in essential hypertension. Thirty-two untreated patients with essential hypertension and 20 normotensive subjects received vitamin C (3 g intravenously in 5 min) or vehicle. Heart rate, noninvasive beat-to-beat blood pressure, and muscle sympathetic nerve activity (microneurography) were monitored at baseline and up to 20 min after the infusion. Spectral analysis of RR interval variability and spontaneous baroreflex sensitivity were also computed. Vitamin C infusion significantly lowered blood pressure in hypertensive patients but not in normotensive subjects (maximal changes in systolic blood pressure: -4.9 ± 10.1 compared with -0.7 ± 4.0 mm Hg, respectively; P < 0.05). Moreover, muscle sympathetic nerve activity was significantly reduced after vitamin C infusion in hypertensive patients (from 53.3 ± 12.2 to 47.4 ± 11.5 bursts/100 heart beats; P < 0.01) but not in healthy subjects (from 42.0 ± 10.1 to 42.7 ± 11.8 bursts/100 heart beats; NS). On the contrary, in 16 hypertensive patients, sodium nitroprusside in equidepressor doses induced a significant increase in muscle sympathetic nerve activity compared with vitamin C (+10.0 ± 6.9 bursts/100 heart beats). Sympathovagal balance and spontaneous baroreflex sensitivity were restored during vitamin C infusion in hypertensive subjects. These results indicate that acute administration of vitamin C is able to reduce cardiovascular adrenergic drive in hypertensive patients, which suggests that oxidative stress is involved in the regulation of sympathetic activity in essential hypertension.

Impaired gastric response to modified sham feeding in patients with postprandial distress syndrome

Impaired vagal function has been reported to be important in some patients with functional dyspepsia (FD). However, the pathophysiologic mechanisms influencing the cephalic phase of vagal activity in FD are incompletely understood. The aim of this study was to investigate the gastric response to modified sham feeding (MSF) on ultrasound and cardiovascular autonomic function in FD patients. Nineteen patients with postprandial distress syndrome (PDS, 11 men and eight women; mean age: 48.2 years) and 26 healthy subjects (HS, 13 men and 13 women; mean age: 45.0 years) were studied prospectively. Firstly, cardiovascular autonomic function was assessed by spectral analysis of RR interval variability. Antral contraction was then evaluated by ultrasonography after MSF was performed to stimulate the cephalic phase of vagal activity. Spectral analysis of RR interval variability showed that the high-frequency component was significantly smaller in the patients than in the HS (P<0.01). The frequency of antral contraction in response to MSF over 15 min was also significantly lower in the PDS patients than in the HS. The 15-min integrated antral contractile response (area under the contraction vs time curve) was significantly smaller in the PDS patients than in the HS (P<0.01). Univariate analysis revealed a modest correlation between the high-frequency component of RR interval variability and the area under the contraction vs time curve (n=46, r=0.49, P<0.01). Autonomic abnormalities affecting the cephalic phase of vagal activity may be important in the pathogenesis of FD.

CORRELATION BETWEEN DIFFERENT MEASURES OF CARDIOVASCULAR AUTONOMIC REGULATION IN ESSENTIAL HYPERTENSION: PP.32.262

Objective: It is well established that essential hypertension is characterized by increased adrenergic tone in different districts. Aim of the study is to examine the correlation between different measures of cardiovascular autonomic regulation, muscle sympathetic nerve activity (MSNA) and spectral analysis of RR interval variability, and their possible relation with plasma markers of renin-angiotensin system and endothelin activity. Design and Methods: 35 untreated essential hypertensive patients (HT) and 14 normotensive subjects (NT), age-and gender-matched, were included. MSNA was recorded by microneurography of the peroneal nerve, together with beat-to-beat BP and ECG for heart rate (HR) evaluation. Fast Fourier Transform spectral analysis of RR interval variability was applied to obtain normalized high and low frequency (nHF and nLF respectively) power density, and their ratio. Plasma norepinephrine (NE), renin activity (PRA) and endothelin-1 (ET-1) were also measured. Log-transformation was applied for correlation of not normally distributed variables. Results: HT showed higher MSNA (51.5 vs 41.4 bursts/100 heart beats, p < 0.001), NE (342 vs 269 pg/ml, p = 0.03), and LF/HF (3.4 vs 1.9, p = 0.04) as compared to NT. MSNA and LF/HF showed a significant correlation in the HT group (r = 0.36,p = 0.04), but not in the NT group (r = 0.20,p = ns). MSNA was also inversely related to nHF (r = -0.48,p = 0.004) in HT. MSNA and LF/HF were not significantly related to HR or NE in both HT and NT groups. In HT patients, but not in NT, nLF was related to NE (r = 0.43,p = 0.03) and ET-1 (r = -0.69,p = 0.01), while LF/HF was related to ET-1 (r = -0.70,p = 0.02). MSNA was not related to any of these humoral parameters in HT and NT. Conclusions: MSNA increase and sympatho-vagal unbalance in HR modulation are associated in essential hypertension. Spectral components of RR interval variability, but not MSNA, seem to be influenced by endothelin system in HT.

Complementary medicine for the management of chronic stress: superiority of active versus passive techniques

Recent epidemiological data indicate that chronic stress is an important component of cardiovascular risk, implicitly suggesting that stress management might offer a useful complement to orthodox medical treatment and prevention of hypertension. In this context, information on mechanisms, such as subclinical increases in arterial pressure and sympathetic drive, is well documented. Conversely, evidence on methodologies and comparative efficacy needs to be improved. Accordingly, this study was planned to test the autonomic and subjective effects of two popular modalities of stress management. We studied 70 patients complaining of stress-related symptoms, avoiding any potential autonomic confounder, such as established hypertension or drug treatment. Patients were divided in three groups: group I (n = 30) followed a breathing-guided relaxation training (active); group II (n = 15) an oriental massage, shiatsu (passive); and group III (n = 25) followed a sham intervention. Subjective effects of stress were assessed by validated questionnaires and autonomic nervous system regulation by spectral analysis of RR interval variability. Factor analysis was used to extract information simultaneously embedded in subjective and functional data. Although the problem of a greater quantity of treatment procedure in the active group than in the passive group existed, results showed that active relaxation, further to slightly reducing arterial pressure, might be more effective in relieving symptoms of stress and inducing an improved profile of autonomic cardiovascular regulation, as compared with passive massage or sham intervention. This active technique seems capable of beneficially addressing simultaneously the individual psychological and physiopathological dimensions of stress in clinical settings, with potentially beneficial effects on cardiovascular risk profile.

Differences in heart rate variability during haemodialysis and haemofiltration

The aim of our study was to evaluate whether convective (haemofiltration, Hf) and diffusive (haemodialysis, Hd) dialysis techniques induce different patterns of long- and short-term autonomic adjustments in haemodynamically stable dialysis patients. Ten haemodynamically stable Hd patients were studied. Each patient underwent a block of six Hd sessions, then was switched to six Hf. During the last session of each dialytic treatment, continuous beat to beat measurements of systolic arterial pressure (SAP) and heart rate (HR) were performed. Spectral analysis of heart rate variability (HRV) was made before and during the treatment to evaluate the modification of autonomic nervous system activity. Baseline values of plasma sodium, body weight, HR and SAP were not different for the two considered methods of dialysis, while the baseline values of normalized LF were significantly higher in Hf as compared to Hd and the opposite was observed for HF powers (P < 0.001). Sodium balance and body weight loss per hour did not differ between Hd and Hf while body temperature was kept constant in all sessions. Throughout the dialytic procedures, with both techniques, SAP was constant, while HR diminished from the first hour till the end of the procedure (P < 0.05). An increase in LF (and decrease in HF) was noticed only in the case of Hd, considering normalized units (P < 0.05). These selective changes were maintained also during the recovery after the procedure. The spectral analysis of RR interval variability during Hd and Hf suggests a potential autonomic advantage with Hf, to be added to the well-recognized intrinsic greater haemodynamic stability.

Is reduced baroreflex gain a component of the metabolic syndrome? Insights from the LINOSA study

To assess the relationship between insulin resistance and baroreflex gain (BRS) in the context of the metabolic syndrome. Observational population study. We studied the healthy population of a small Mediterranean island (Linosa, about 0.5 square miles, 450 inhabitants) where genetic, psychosocial and behavioral bias is likely to be minimal for historical and social reasons. Baroreflex gain (BRS, by the frequency domain alpha index) and indices of autonomic regulation of the sino-atrial (SA) node derived from spectral analysis of RR interval variability were obtained, together with metabolic and behavioral indicators in the 144 participating subjects (age range 20-82 years). Carotid artery thickness (CCA) was also obtained with computer-aided ultrasound techniques. Insulin resistance was estimated by the homeostasis model assessment (HOMA), and subjects divided in tertiles accordingly. BRS appeared to be reduced progressively with increasing levels of HOMA (respectively, 21.0 +/- 2.6, 17.7 +/- 1.7, 15.7 +/- 1.9 ms/mmHg, P < 0.03), while spectral indices of autonomic SA regulation appeared to be only insignificantly affected. Conversely, CCA was significantly increased with increasing HOMA (P < 0.024). Furthermore, BRS appeared to be significantly correlated with various elements of the metabolic syndrome, with CCA and abdominal obesity showing the strongest link. In an otherwise healthy population, BRS, but not spectrally derived indices of SA node autonomic regulation, are progressively reduced with increasing severity of insulin resistance, possibly as a consequence of attendant carotid artery thickening.

Impact of Chronic Psychosocial Stress on Autonomic Cardiovascular Regulation in Otherwise Healthy Subjects

Elevated psychosocial stress might favor the occurrence of cardiovascular disease; however, mechanisms are incompletely understood. We hypothesized that patients (n=126; 44+/-1 years of age) referred to an internal medicine clinic because of symptoms related to chronic psychosocial stress would demonstrate signs of autonomic dysregulation compared with controls (n=132; 42+/-1 years of age). We used autoregressive spectral analysis of RR interval variability to obtain indirect markers of sympathetic and of vagal (respectively, low-frequency and high-frequency components, both expressed in normalized units) oscillatory modulation of sinoatrial node, as well as of sympathetic vasomotor regulation (low-frequency component of systolic arterial pressure variability) and of cardiac baroreflex sensitivity (alpha-index). Higher values of systolic and diastolic arterial pressure (respectively, 124+/-1 versus 117+/-1 mm Hg and 80+/-1 versus 75+/-1 mm Hg; both P<0.001), altered markers of autonomic regulation (increased normalized low-frequency and reduced high-frequency component of RR variability, P<0.005; increased-low frequency component of systolic arterial pressure variability, P<0.002), and reduced baroreflex sensitivity (19.3+/-1.4 versus 23.0+/-2.0 ms/mm Hg; P<0.05) were observed in patients compared with controls. Autonomic responses to active standing were also blunted in stressed patients. Autonomic markers were significantly correlated to stress perception score and were capable of discriminating between controls and patients with a high degree of accuracy. Chronic real-life stress in humans appears associated to increased arterial pressure and to impaired autonomic regulation of cardiovascular functions. The combination of sympathetic predominance, vagal withdrawal, and blunted baroreflex sensitivity might represent a treatable mechanistic link between psychosocial factors and future incidence of hypertension.

A direct analytical demonstration of the essential equivalence of detrended fluctuation analysis and spectral analysis of RR interval variability

Detrended fluctuation analysis (DFA) of heart rate variability appears to yield improved prognostic power in cardiovascular disease, through calculation of the fractal scaling exponent α. We have recently used Taylor series approximations to propose that DFA is closely related to standard spectral analysis measures. We now present a direct analytical approach using integration and explicit expressions for the steps involved in DFA. This demonstrates clearly how DFA corresponds to standard spectral analysis.

Cardiac sympathetic denervationmodulates the sympathoexcitatoryresponse to acute myocardial ischemia

ObjectivesThis study was designed to elucidate the influence of cardiac sympathetic denervation on the sympathoexcitatory response to acute myocardial ischemia during balloon coronary occlusion (BCO) in humans. BackgroundAlterations of cardiac sympathetic nerve function could modulate sympathetic reflexes originating from the ischemic area. MethodsIn 23 patients with angina pectoris, we quantified the baseline cardiac sympathetic denervation of the ischemia-related area by iodine-123 metaiodobenzylguanidine (123I-MIBG), and transient changes in sympathetic activity during BCO by wavelet analysis of RR interval variability. ResultsBalloon coronary occlusion resulted in a transient augmentation of low-frequency (LF: 0.04 to 0.14 Hz) spectral components of RR interval variability in 4 of 12 patients with cardiac denervation and in 8 of 11 patients without denervation (p < 0.01 by the chi-square test). Consequently, the increase in LF components was significantly less during BCO in patients with cardiac denervation (34%) than in those without denervation (273%) (interaction: p < 0.05). In seven patients with severe ischemia provoked by a fall of ≥10% in the left ventricular ejection fraction, LF components increased by 506% during BCO, regardless of the condition of cardiac denervation. In contrast, in patients with mild ischemia provoked by a fall of <10% in the ejection fraction, changes of LF components during BCO were significantly less in patients with denervation than in those without denervation (84 vs. 344%, p < 0.05). ConclusionsThese findings suggest that if the provoked ischemia is not severe, cardiac sympathetic denervation could prevent ischemia-induced sympathoexcitation.

Hemodynamic and autonomic adjustments to real life stress conditions in humans.

Psychological stress represents a risk factor for hypertension, but mechanisms are not known in detail. In this investigation we tested the hypothesis that real-life stress conditions produce changes in autonomic cardiac and vascular regulation that might differ in magnitude. University students, a well-established model of mild real-life stress, were examined shortly before a university examination, and a second time 3 months afterward, during holiday. Autonomic cardiovascular regulation was assessed by a noninvasive approach, based on autoregressive analysis of RR interval variability (V) and of systolic arterial pressure (SAP) V. The overall level of stress in the two sessions was gauged from the elevated salivary cortisol (5.6+/-0.5 versus 2.4+/-0.2 ng/mL, P<0.05) and altered cytokine profile (P<0.05). During the stress day, the RR interval was reduced and arterial pressure increased significantly; simultaneously, the normalized low frequency component of RRV (a marker of sympathetic modulation of the sinoatrial node) was increased and the index alpha (a measure of baroreflex gain) reduced. Concomitantly, the autonomic response to the sympathetic excitation produced by standing was altered: cardiac response was impaired and vascular responsiveness increased. Markers of autonomic regulation of the sinoatrial node correlated significantly with cortisol levels, both at rest and also considering standing induced changes, suggesting a gradual range of effects. The data support the concept that mild real-life stress increases arterial pressure and impairs cardiovascular homeostasis. These changes, assessable with spectral analysis of cardiovascular variability, might contribute, in susceptible individuals, to the link between psychological stress and increased cardiovascular risk of hypertension.

めまいを主訴とした体位性頻脈症候群症例

Postural tachycardia syndrome (POTS) has recently been recognized as a syndrome in which patients have an increased heart rate without orthostatic hypotension. Patients with POTS may complain of presyncope, vertigo, dizziness, light-headedness, general fatigue or unsteadiness. However, the etiology of POTS is unclear. We report a typical case of POTS; a 24 year-old woman who had suffered from dizzy sensations during postural changes for six months. No abnormalities had been observed in ECG, echocardiography, clinical chemistry, blood test and brain MRI. On the first visit, no abnormal responses were noted on neuro-otological examinations or for the CMI and SRQ; D psychological questionnaires. However, the patient's heart rate increased by 34 beats/min from supine to standing position, and in addition, she complained of a headache and fatigue without hypotension during Schellong test. Power spectral analysis of RR interval variability during Schellong test revealed that the normalized powers of low frequency (LFnp) and ratio of LF and high frequency powers (LF/HF) increased when standing upright from supine position. We diagnosed her with POTS and administered atenolol (β1 blocker, 50mg every morning) in formula, which markedly reduced her subjective symptoms.

Effects of Desipramine on Autonomic Input to the Heart

To examine the impact of age on the effects of desipramine (DMI) on autonomic input to the heart. Twenty-four-hour electrocardiograms were obtained from 42 subjects, aged 7 to 66 years, while off and on DMI. To obtain measures of autonomic input to the heart, heart rate variability was assessed via spectral analysis of RR interval variability. DMI treatment was associated with a significant increase in 24-hour mean heart rate and significant decreases in RR interval variability in all spectral bands, including in the high-frequency band, which provides a measure of parasympathetic input to the heart. RR interval variability was greater in younger individuals both off and on DMI. DMI treatment was associated with a marked decline in RR interval variability, indicating that DMI affects autonomic input to the heart. Specifically, DMI reduced parasympathetic input, which, in theory, may increase vulnerability to arrhythmias. However, the magnitude of DMI's impact on RR interval variability did not vary with age.

Significance of the Accuracy of RR Interval Detection for the Analysis of New Dynamic Measures of Heart Rate Variability

Background: Interest in the analysis of RR interval variability by new dynamic methods is growing, because these methods give different, complementary information on heart rate behavior compared to the traditional measures of HRV. Several new methods have been recently introduced for studying complex heart rate dynamics, but the validity of these methods in analyzing RR interval behavior from Holter recordings is not well established.Methods: A real‐time microprocessor QRS detector system using a 1‐ms timing accuracy and a conventional 24‐hour ECG recording system with a sampling frequency of 128 Hz were compared in the measurement of new dynamic components of HRV in a sample of ten healthy subjects and ten patients with acute Ml.Results: Significant errors were observed in the analysis of approximate entropy (ApEn; mean difference 11 %) and in the short‐term scaling exponent value a1 (mean difference 3%) in detrended fluctuation analysis (DFA). In the Poincaré analysis, notable differences were also observed in short‐term instantaneous RR‐interval variability (SD1; mean difference 5%). In spectral analysis, low‐to‐high frequency ratio was also influenced by the sampling frequency (mean difference 14%). The magnitude of all these differences grew proportionately when the overall heart HRV diminished.Conclusions: The data suggest that conventional Holter recordings should be used with caution in the analysis of new dynamic HRV parameters, especially approximate entropy and the ratio between low and high frequency spectral components, particularly in patient populations with low total HRV.

Assessment of Heart Rate Variability Changes During Dipyridamole Infusion and Dipyridamole-Induced Myocardial Ischemia: A Time Variant Spectral Approach

Objectives. We sought to evaluate changes in RR interval variability during dipyridamole infusion and dipyridamole-induced myocardial ischemia.Background. Myocardial ischemia and the autonomic nervous system can be mutually interdependent. Spectral analysis of RR interval variability is a useful tool in assessing autonomic tone.Methods. We used a time variant autoregressive spectral estimation algorithm that could extract spectral variables even in the presence of nonstationary signals. Two groups were considered: group A (patients with ischemia, n = 15) with effort or mixed angina, angiographically assessed coronary artery disease and positive exercise and dipyridamole echocardiographic test results, and group B (control subjects, n = 10) with normal exercise and dipyridamole echocardiographic test results. We investigated the following variables: RR interval mean and variance, low frequency (LF) and high frequency (HF) power in normalized units, LF ratio (LF/LFbasal power), HF ratio (HF/HFbasal power) and LF/HF ratio. For each test epoch, we calculated for group A and group B the mean value ± SE of all indexes considered. Differences due to an effect either of group (ischemic vs. control) or of time (including both drug and ischemia effects) were analyzed by using analysis of variance for repeated measurements.Results. Dipyridamole injection was characterized by a reduction of all spectral components in negative test. The LF ratio was the only variable able to discriminate patients with ischemia from control subjects (p < 0.05), whereas a time effect was evident for both mean RR interval and high frequency power in normalized units (p < 0.05). The LF ratio decreased in group B from 1 ± 0.00 (basal) to 0.31 ± 0.22 (peak), and increased in group A from 1 ± 0.00 to 15.41 ± 6.59, respectively. Results of an unpaired t test comparing the peak values of the two groups were also statistically significant (p < 0.01).Conclusions. Our data show that time variant analysis of heart rate variability evidences an increase in the low frequency ratio that allows differentiation of positive from negative test results, suggesting that the electrocardiogram may contain ischemia information unrelated to ST-T variations, even if their enhancement requires a more complex data processing procedure.

Effects of aging and of chronic obstructive pulmonary disease on RR interval variability

Clinical and experimental investigations suggest that spectral analysis of RR interval variability might be employed to assess changes in autonomic regulation of the SA node occurring in various chronic, cardiac or respiratory conditions. We studied three groups of subjects: young healthy, older healthy, and old patients with chronic obstructive pulmonary disease (COPD), considering RR interval and breathing, i.e. tidal volume, variability in the frequency domain (AR algorithms), in order to obtain markers of the sympathetic and vagal modulation of the SA node [by way, respectively, of the low (LF) and high frequency (HF) spectral components]. The gain of the relationship between tidal volume and heart period variation (index β) was also examined. COPD patients demonstrated a reduced resting RR variance with maintained spectral power distribution; upon tilting they did not manifest the usual increase of LF (and attendant decrease of HF) component. Additionally, we observed that the index β at rest was significantly reduced in older as opposed to younger subjects. This index was also reduced by tilt, in both groups. In patients the index β was reduced as compared to the group of similar age and younger subjects, and did not diminish further with tilt. This study indicates that in patients with COPD, sympathetic excitatory modulation of the SA node is depressed. Furthermore, the index β, which provides an assessment of the gain of respiratory modulation of RR interval variability is significantly reduced in patients, as compared to healthy subjects of similar age. These abnormalities of autonomic control, may represent a functional correlation of the hyperinflated state present in this clinical condition which can be assessed non-invasively with spectral analysis of RR interval and respiration.

A controlled study of the autonomic changes produced by habitual cigarette smoking in healthy subjects

An increased sympathetic drive, in view of its proarrhythmic, proatherosclerotic, and prothrombotic actions, could contribute to the elevated cardiovascular risk of habitual smokers. However, the underlying mechanisms are still debated. In this study we address the hypothesis that spectral analysis of RR interval and systolic arterial pressure short-term variabilities may be used to assess the complex autonomic changes produced by habitual cigarette smoking.A cross-sectional design compared heavy (> 20 cigarettes/day) habitual smokers (n = 20; 40 +/- 3 years), with similar age controls. Spectral analysis of RR interval variability provided markers of the sympatho-vagal balance modulating the SA node, by way of the normalised low frequency (LF approximately equal to 0.10 Hz) and high frequency (HF approximately equal to 0.25 Hz) components. The LF component of systolic arterial pressure (SAP) variability assessed the sympathetic vasomotor modulation. The frequency domain index (alpha) measured the baroreflex gain of the SA node. Subjects were studied at rest, and during the sympathetic excitation produced by active standing.In smokers LFRR was, at rest, greater than in controls (70.6 +/- 3.8 vs 46.0 +/- 2.5 normalised units, nu); concurrently HFRR was reduced (22.1 +/- 3.2 vs 42.0 +/- 2.8 nu). Baroreflex gain and RR variance were also smaller in smokers. LFSAP was, instead, similar in the smokers and control groups. The standing induced increase in LFRR was blunted (P < 0.001) in smokers.Spectral analysis of RR interval and systolic arterial pressure variability indicates that habitual cigarette smoking induces selective alterations in neural control of the SA node. An increase at rest in markers of sympathetic modulation is accompanied by signs of reduced vagal drive and depressed baroreflex gain; while sympathetic vasomotor modulation appears similar in controls and smokers. Data are consistent with the hypothesis that autonomic alterations may contribute to the increased cardiovascular risk present in smokers.

A controlled study of the autonomic changes produced by habitual cigarette smoking in healthy subjects

An increased sympathetic drive, in view of its proarrhythmic, proatherosclerotic, and prothrombotic actions, could contribute to the elevated cardiovascular risk of habitual smokers. However, the underlying mechanisms are still debated. In this study we address the hypothesis that spectral analysis of RR interval and systolic arterial pressure short-term variabilities may be used to assess the complex autonomic changes produced by habitual cigarette smoking. A cross-sectional design compared heavy (> 20 cigarettes/day) habitual smokers (n = 20; 40 +/- 3 years), with similar age controls. Spectral analysis of RR interval variability provided markers of the sympatho-vagal balance modulating the SA node, by way of the normalised low frequency (LF approximately equal to 0.10 Hz) and high frequency (HF approximately equal to 0.25 Hz) components. The LF component of systolic arterial pressure (SAP) variability assessed the sympathetic vasomotor modulation. The frequency domain index (alpha) measured the baroreflex gain of the SA node. Subjects were studied at rest, and during the sympathetic excitation produced by active standing. In smokers LFRR was, at rest, greater than in controls (70.6 +/- 3.8 vs 46.0 +/- 2.5 normalised units, nu); concurrently HFRR was reduced (22.1 +/- 3.2 vs 42.0 +/- 2.8 nu). Baroreflex gain and RR variance were also smaller in smokers. LFSAP was, instead, similar in the smokers and control groups. The standing induced increase in LFRR was blunted (P < 0.001) in smokers. Spectral analysis of RR interval and systolic arterial pressure variability indicates that habitual cigarette smoking induces selective alterations in neural control of the SA node. An increase at rest in markers of sympathetic modulation is accompanied by signs of reduced vagal drive and depressed baroreflex gain; while sympathetic vasomotor modulation appears similar in controls and smokers. Data are consistent with the hypothesis that autonomic alterations may contribute to the increased cardiovascular risk present in smokers.

Alterations of sympathovagal balance in patients with hypertrophic and dilated cardiomyopathies assessed by spectral analysis of RR interval variability.

Spectral analysis of RR interval variability was performed in 35 ambulatory patients with early hypertrophic cardiomyopathy (HCMa, NYHA class I), 21 hospitalized patients with advanced hypertrophic cardiomyopathy (HCMh, NYHA class II or III), and 18 hospitalized patients with dilated cardiomyopathy (DCMh, NYHA class I, II or III). Twenty-nine ambulatory subjects (COTa) and 20 hospitalized volunteers (COTh) served as normal controls. The RR interval standard deviation (SD), the high-frequency power (HF: 0.15-0.40 Hz) corrected by the mean RR interval (CCVHF) and the normalized unit of the HF power (NUHF) served as markers of vagal modulation. Low-frequency power (LF: 0.04-0.15 Hz) corrected by the mean RR interval (CCVLF) and the normalized unit of LF power (NULF) were markers of sympathetic modulation. The LF/HF ratio was an index of sympathovagal balance. There was no significant difference in the SD, CCVHF, NUHF, CCVLF, NULF or the LF/HF ratio between the HCMa and COTa groups. At night, the SD was lower in the HCMh group relative to the COTh group (P < 0.01). The HCMh group demonstrated lower CCVHF and NUHF values (P < 0.01), higher NULF values (P < 0.01) and higher LF/HF ratios (P < 0.05) at night relative to the COTh group. Two patients who later died suddenly in the HCMh group had markedly reduced CCVHF values (0.2-0.8%) relative to the survivors in the group (mean +/- SD in the morning, afternoon and night, 1.07 +/- 0.43%).(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of Cardiac Autonomic Control in Humans by Angiotensin II

Angiotensin II (Ang II) exerts an inhibitory action on vagal activity in animals and may also facilitate sympathetic activity. The object of this study was to compare autonomic activity resulting from equivalent steady-state baroreflex activation during intravenous Ang II infusion with that resulting from a control infusion of phenylephrine. Eight healthy subjects aged 22 to 34 years were studied in a single-blind, randomized, prospective crossover study. Autonomic activity was determined by computer analysis of RR interval variability in the time and frequency domains. Despite equal experimental hypertension with Ang II and phenylephrine infusion, at peak infusion rates the mean RR interval was significantly shorter with Ang II (983 +/- 179 milliseconds; mean +/- SD) than with phenylephrine (1265 +/- 187 milliseconds, P < .01). The variability of RR intervals was not significantly different, but the variability (median interquartile difference) of RR interval successive differences was significantly lower with Ang II (66 milliseconds) than with phenylephrine (104 milliseconds, P < .02). Power spectral analysis revealed the power of the 0.25-Hz component in normalized units to be significantly smaller during Ang II infusion (20.5 +/- 12.7 U) than during phenylephrine (38.2 +/- 14.7 U, P < .05), whereas the power of the 0.1-Hz component was significantly greater during Ang II infusion (67.8 +/- 17.1 U) than phenylephrine (38.8 +/- 20.3 U, P < .05). Measures of vagal modulation of heart rate were significantly attenuated, and sympathetic modulation appeared to be increased during Ang II infusion compared with control phenylephrine infusions. These observations may underlie reports of increased vagal activity during angiotensin-converting enzyme inhibitor therapy.