Standard Deviation Of RR Intervals Research Articles

Acute overconsumption of a high‐fat diet alters heart rate variability

Changes in heart rate variability (HRV) indicative of altered autonomic tone are seen chronic obesity, but changes in HRV due to acute overeating are less certain. This study determined if acute overeating of a high-fat diet (HFD) altered HRV during the day and/or night. Adult female New Zealand white rabbits (n=7) consumed a control diet (CONT) before switching to an ad-lib HFD. Using telemetry, 3-min ECG segments were recorded every 20 min for 3 d of CONT and the first 3 d of HFD. Data were analyzed during the day and night for heart rate (HR), RR interval standard deviation (RRISD), RMS of successive RR interval differences (RMSSD), low frequency (LF) and high frequency power (HF), and LF/HF. HFD and respective CONT periods were compared by paired t-test. (*p≤0.05) Table 1. HRV was altered by HFD more at night than during the day. At night, HR increased 37% and RRISD, RMSSD, and HF decreased 60%, 66%, and 86%, respectively. LF/HF increased 170%. HFD-induced daytime changes showed similar trends, but differences were not significant. Therefore, acute overeating of a HFD produced immediate nighttime HRV changes indicating parasympathetic withdrawal and a shift toward sympathetic dominance. Funded by NIH HL64913.

Circadian Variation in Heart‐Rate Variability in Localization‐related Epilepsy

Case-control studies of sudden unexpected death in epilepsy (SUDEP) have reported that SUDEP is more likely to occur during sleep and thus presumably during night hours. The circadian variation of heart-rate variability (HRV) might be of relevance to this risk. We examined night versus daytime HRV in patients with newly diagnosed and refractory localization-related epilepsy, assessing the effects of drug treatment and epilepsy surgery on the night/daytime HRV ratio. We used spectral analysis to assess HRV and calculated the night-time (00.00-05.00)/daytime (07.30-21.30) ratio of HRV in 14 patients with newly diagnosed localization-related epilepsy before and during carbamazepine (CBZ) treatment and in 21 patients with temporal lobe epilepsy before and after epilepsy surgery. Both groups were compared with age- and sex-matched controls. No significant differences were found from controls in the night/daytime ratios of HRV whether compared before or after initiation of treatment with CBZ in newly diagnosed epilepsy patients. When patients were used as their own controls, night/daytime ratios of standard deviation of RR intervals (p = 0.04) and total power (p = 0.04) were significantly lower during treatment than before. Compared with those of controls, the night/daytime ratios were lower in epilepsy surgery patients before surgery [low-frequency power (p = 0.04); high-frequency power (p = 0.04)]. Night/daytime ratios did not change significantly after surgery. The HRV of the patients was more affected during night-time when the risk of SUDEP seems to be highest in such patients.

SINGLE DOSE OF TIOTROPIUM DOES NOT EFFECT HEART RATE VARIABILITY

Aim: Anticholinergic drugs may alter cardiac autonomic modulation. The aim of this study was to investigate the effects of inhaled tiotropium on heart rate variability (HRV). Methods: A randomized, double-blind, crossover design study was conducted on 11 healthy volunteers. Tiotropium or placebo was administered in two different testing sessions. Time domain parameters; mean R-R interval (mean-RR), the standard deviation of R-R interval (SDNN) and the root mean square of successive R-R interval differences (RMSSD) and power spectral analysis of HRV were assessed in the supine position, during handgrip exercise and controlled breathing before and after drug administration. Results: There were no statistically significant difference in baseline HRV parameters obtained before each drug administration (p >0.05). HRV parameters obtained after each drug administration were found not to be different during supine position, controlled breathing and handgrip exercise. Conclusion: Administration of single dose tiotropium did not effect cardiac autonomic modulations in healthy volunteers.

Short‐term testing of heart rate variability in heart‐transplanted children: equal to 24‐h ECG recordings?

Heart rate variability (HRV) is reduced in adults and children after cardiac transplantation. Testing of HRV has been used to assess re-innervation of the cardiac graft; its reliability in ruling out acute graft rejection is still under investigation. This study used a short-term test on HRV in 23 heart and heart-lung transplanted children and adolescents and compared the results with 24-h ECG recordings. Twenty-three subjects (16.3+/-4.2 yr; 10 females) underwent a 10-min HRV test at two occasions and one 24-h ECG. HRV was calculated according to the time domain method (RR interval, standard deviation of RR interval) and the frequency domain method (total power, LF and HF for assessment of sympathovagal modulation of heart rate). Correlation between the short-term tests and 24-h ECG was high with regard to the frequency domain analysis of HRV. Correlation was less pronounced in the time domain method. In heart and heart-lung-transplanted children and adolescents, due to reduced overall HRV short-term testing may give as reliable data as 24-h ECG. Therefore, especially when power spectral analysis has to be performed as a longitudinal assessment of re-innervation of the cardiac graft, short-term testing may offer an easily applicable and non-invasive diagnostic tool. Further studies are warranted to investigate whether HRV testing may contribute to rule out acute graft rejection.

Preprocessing RR interval time series for heart rate variability analysis and estimates of standard deviation of RR intervals

Heart rate variability is concerned with the analysis of the fluctuations in the interval between heart beats known as RR intervals. The long time RR time series obtained suffer from non-stationarity and the presence of ectopic beats, which prevents extraction of useful statistical information. The paper describes a wavelet-based technique for trend removal and a nonlinear filter to remove ectopic beats. This attempts to correct the limitations observed in a recent advanced heart rate toolkit [J. Niskanen, M.P. Tarvainen, P.O. Ranta-aho P.A. Karjalainen, Software for advanced HRV analysis, Comput. Meth. Prog. Biomed.,76 (2004) 73–81] when preprocessing. The results are encouraging. The preprocessed data are then used to obtain the standard deviation of RR interval time series (SDRR) of 15 healthy patients and 15 patients suffering from congestive heart failure. The results demonstrate the importance of preprocessing. The analysis show that the SDRR values of congestive heart failure patients are depressed compared to the healthy group.

Differences in heart rate variability between Asian and Caucasian children living in the same Canadian community

Heart rate variability (HRV) is an umbrella term for a variety of measures that assess autonomic influence on the heart. Reduced beat-to-beat variability is found in individuals with a variety of cardiac abnormalities. A reduced HRV positively correlates with obesity, poor aerobic fitness, and increasing age. Racial (black-white) differences are apparent in adults and adolescents. We aimed to evaluate (i) Asian-Caucasian differences in HRV and (ii) differences in HRV between girls and boys. Sixty-two children (30 male (15 Caucasian, 15 Asian) and 32 female (15 Caucasian, 17 Asians)) with a mean age of 10.3 +/- 0.6 y underwent 5 min resting HRV recording, fitness testing (Leger's 20 m shuttle), and self-assessed maturity. Outcome HRV measures were a ratio of low to high frequency power (LF:HF), standard deviation of R-R intervals (SDRR) and root mean square of successive R-R intervals (RMSSD). Data were compared between groups using analysis of covariance (ANCOVA). There were no race or sex differences for time domain variables, mean R-R, body mass index, or blood pressure. Compared with Caucasian children, Asian children displayed a higher adjusted (fitness, R-R interval) LF:HF ratio (72.9 +/- 59.4 vs. 120.6 +/- 85.3, p < 0.05). Girls demonstrated a higher adjusted LF:HF power than boys (117.2 +/- 85.1 vs. 76.6 +/- 62.4, p = < 0.05). In conclusion, Asian and Caucasian children display different frequency domain components of heart rate variability.

Reinnervation after heart transplantation in children: Results of short‐time heart rate variability testing

To detect impairment in short-term heart rate variability (HRV) in children after heart and heart-lung transplantation (TX) as reported in adults. To assess vagal and sympathetic influence on the donor heart rate using frequency domain analysis of HRV. Measurement of short-term HRV was performed in 17 patients (age 16.9+/-3.6, 6.1+/-3.7 yr after TX) and 12 healthy controls (age 14.8+/-3.0 yr). Testing consisted of a resting phase of 15 minutes followed by a tilt phase of 45 min. All HRV parameters were significantly impaired in transplanted patients: RR interval (RRI) 717.2+/-122.5 m/s (controls 827+/-139.7, p<0.05), standard deviation of RR interval (RRI-SD) 20.1+/-15.5 (89.9+/-38.4, p<0.001), RRI at tilt 607.9+/-79.7 (654.0+/-104.7, NS), RRI-SD at tilt 21.1+/-20.0 (60.4+/-31.4, p<0.001). Low-frequency (LF)/High-frequency (HF) ratio of HRV showed prominent sympathetic influence in TX-patients (3.38+/-5.60 vs. 1.18+/-0.86, NS) increasing during tilting (5.91+/-8.36 vs. 4.74+/-5.27, NS). In subgroup analysis, 4 yr after TX an increasing sympathetic control of heart rate was observed. Short-term HRV is severely impaired in children after TX. If changes are observed, they are time-related and show increasing sympathetic influence starting from 4 yr after TX.

The Effects of Glucose Consumption and 8 Hours of Submaximal Exercise on Heart Rate Variability in Trained Males

PURPOSE: The purpose of this study was to determine the effects of consuming a glucose beverage on heart rate variability (HRV) measures in trained males across 8 hours of submaximal exercise. METHODS: Subjects (n=8) completed two 8-hour bouts of exercise (Carbohydrate (CHO), placebo) alternating between 25-minute portions of cycling and treadmill walking with 5-minute rest periods. During each 25-minute interval, subjects exercised at varying moderate to hard workloads that were based on ventilatory threshold. For the CHO trial, 15 g of CHO in a 10% solution glucose beverage was provided every 15 minutes. Supine 4-minute HRV measurements were collected pre and post-exercise. Measurements included standard deviation of R-R interval (SDNN), low frequency (LF), and high frequency (HF). Data were collected with a Polar S-810i heart rate monitor and analyzed with Fourier Transform software. A 2-way, within subjects, repeated measures ANO VA was used for statistical analysis to assess effects of time and feeding strategy. RESULTS: Overall, SDNN was lower post-exercise (pre=69.94±32.32 versus post=47.39±23.09 ms, p < 0.05). No significant main effect changes occurred in LF or HF measurements. There was no treatment (CHO versus placebo) effect for any HRV measurement. CONCLUSIONS: These data demonstrate that 8 hours of exercise decreases SDNN, showing a decreased overall variability in heart rate, but this variability was not identified as specifically LF or HF. Consumption of a 12% solution glucose beverage throughout an 8-hour exercise regimen of cycling and treadmill walking does not affect any heart rate variability measurements.

Involvement of Voltage-Dependent Ca2+ Channel β3 Subunit in the Autonomic Control of Heart Rate Variability

Noradrenaline release from sympathetic nerve terminals is dependent on Ca²⁺ entry through neuronal voltage-gated N-type Ca²⁺ channels. The accessory β₃ subunits of Ca²⁺ channels (Ca_Vβ₃) are preferentially associated with the α_1B subunit to form N-type Ca²⁺ channels, and are therefore expected to play a functional role in the stimulation-evoked release of noradrenaline. In this study, we employed Ca_Vβ₃-null, Ca_Vβ₃-overexpressing (Ca_Vβ₃-Tg), and wild-type (WT) mice to investigate the possible roles of Ca_Vβ₃ in the sympathetic regulation of heart rate in vivo. Telemetry was used to monitor the ECG and both time and frequency domain analyses were carried out to evaluate heart rate variability. In the frequency domain analysis, power spectral density of the RR interval series was computed using the fast Fourier transform algorithm. The resting heart rate was increased in Ca_Vβ₃-Tg mice compared with both Ca_Vβ₃-null and WT mice. Mice overexpressing Ca_Vβ₃ displayed decreased heart rate variability, which was measured by the time domain analysis of the standard deviation of RR intervals. In the frequency domain analysis, Ca_Vβ₃-Tg mice showed decreased spectral powers compared with WT and Ca_Vβ₃-null mice. Pharmacological blockade of β-adrenergic receptors with metoprolol decreased the heart rate in all genotypes, but the extent of the decrease was most obvious in Ca_Vβ₃-Tg mice. On the other hand, the spectral powers were decreased in response to parasympathetic blockade (atropine) in WT and Ca_Vβ₃-Tg mice. These results indicate the functional roles of Ca_Vβ₃ in regulating sympathetic nerve signaling.

Heart Rate Variability and Central Angiotensin II Receptors in Heart Failure: Role of Exercise Training

Nebraska Medical Center, Omaha, Nebraska, 68198-5850 Exercise training (EX) has become an important modality enhancing survival of patients with chronic heart failure (CHF). Heart rate variability (HRV) is a non-invasive method assessing sympathovagal balance and predicting mortality in CHF. Enhanced HRV occurs in CHF following EX. We showed a down-regulation of brain angiotensin II receptors (AT1), a reduction in plasma Ang II and normalization of baseline renal sympathetic nerve activity (SNA) and an enhanced HRV for total power and standard deviation of R-R interval (SDRR) with EX in a rapid pacing model of CHF in New Zealand white rabbits. We hypothesized that prevention of Ang II normalization in CHF-EX rabbits would prevent the beneficial effects of EX on AT1 expression, SNA and HRV. The table shows HRV parameters, baseline SNA and AT1 expression using Western-blot and RT-PCR in the rostral portion of the ventrolateral medulla. When plasma Ang II levels were “clamped” and prevented from normalization with EX, down-regulation of AT1 expression was abolished and the total power was depressed through a reduction in the low frequency (LF) component of the total power (TP). The enhanced SDRR with EX was preserved despite Ang II infusion with EX. These data suggest that the reduction in plasma Ang II and/or AT1 expression may be responsible for lowering SNA and that Ang II influences on HRV are reflected by the LF component of the TP and this influence does not affect SDRR, perhaps due to maintenance of vagal tone following EX in CHF. NIH grant PO-I HL-62222

Heart Rate Variability during Night Sleep and after Awakening in Overtrained Athletes

This study was conducted to test the hypothesis of autonomic imbalance in overtrained athletes during sleep and after awakening with analyses of heart rate variability (HRV) and nocturnal urine stress hormones. We examined 12 athletes diagnosed to be severely overtrained (OA, 6 men and 6 women, mean age (+/-SD) 25 +/- 7 yr) and 12 control athletes (CA, 6 men and 6 women, mean age 24 +/- 5 yr). Overtraining diagnosis was further supported by higher perceived stress in OA than in CA (24.8 +/- 10.8 vs 15.3 +/- 5.5, P < 0.05). HRV was analyzed with time and frequency domain methods from RR intervals (RRI) recorded during sleep and after awakening. Nocturnal urine stress hormones were analyzed by liquid chromatography. No differences were found in HRV or stress hormones during night sleep. After awakening, the standard deviation of RRI (84 +/- 31 vs 116 +/- 41 ms, P < 0.05) and low-frequency power of RRI (2153 +/- 2232 vs 4286 +/- 2904 ms, P < 0.05) were lower in OA than in CA. From sleep to after awakening, the coefficient of variation of RRI decreased more in OA than in CA (from 11.8 +/- 3.3 to 7.7 +/- 2.5%, P < 0.001 vs from 11.9 +/- 1.8 to 10.0 +/- 2.5%, P < 0.01, respectively, interaction P < 0.05). The present findings suggest that in OA, cardiac autonomic modulation is at the level of control athletes during sleep, but the parasympathetic cardiac modulation is slightly diminished after awakening. Further investigations should concentrate on autonomic responses to different challenges, such as awakening in the present study.

Heart and respiration rate changes in the neonate during electroencephalographic seizure

An investigation of changes in the neonatal electrocardiogram (ECG) and respiration signals from labelled seizure data for five neonatal patient records is reported. A decrease during seizure of 5.70% in the mean RR-interval was found. The mean respiration rate per epoch was found to decrease by a mean 18.44% during seizure. No significant change in the RR-interval standard deviation or in the mean respiration amplitude during seizure was observed. These results raise the possibility of using ECG and respiration based methods instead of existing electrcoenceplogram (EEG) based methods, or in concert with EEG-based neonatal seizure detection methods to improve on previously reported seizure detection methods.

Acute Effects of Aldosterone on the Autonomic Nervous System and the Baroreflex Function in Healthy Humans

Aldosterone has been reported to impair the baroreflex response in animal models. The present study aimed to investigate the acute effects of aldosterone on the autonomic nervous system and the baroreflex control of muscle sympathetic nerve activity (MSNA) and heart rate in healthy humans. Nine healthy subjects were examined in a double-blind, placebo-controlled, cross-over study design, receiving either i.v. aldosterone (100 microg) or placebo on the experimental day. Heart rate variability (HRV) was measured at rest, whereas blood pressure, heart rate and MSNA (assessed by microneurography from the peroneal nerve) were monitored both at rest and during baroreflex tests. Baroreceptor stimulation and deactivation was induced by i.v. infusion of incremental doses of phenylephrine and sodium nitroprusside. HRV indices at rest were specifically changed by aldosterone with a significant increase in standard deviation of RR intervals and total power, and a trend towards increased time domain parameters indicating parasympathetic predominance in heart rate regulation. Basal MSNA, blood pressure and heart rate remained unaffected by aldosterone administration. Sodium nitroprusside decreased diastolic blood pressure and increased MSNA as well as heart rate in both the aldosterone and placebo experiments. However, the tachycardic response to arterial baroreceptor deactivation was more pronounced in the aldosterone experiments. By contrast, baroreflex control of MSNA and heart rate during phenylephrine infusion was not affected by aldosterone. Thus, our study demonstrates that, in healthy humans, aldosterone tends to increase cardiac vagal activity and enhances the heart rate response to nitroprusside whereas MSNA remains unaffected.

Relations of inflammatory markers to lipid levels and autonomic tone in patients with moderate and severe chronic kidney disease and in patients under maintenance hemodialysis

Chronic kidney disease is associated with enhanced inflammatory response and autonomic dysfunction. Evidence exists of a potential interaction of inflammation and nervous system. We sought to investigate determinants of heart rate variability (HRV) and relations between the inflammatory markers C-reactive protein (CRP) and interleukin-6 (IL-6) and autonomic tone in patients with moderate and severe chronic kidney disease and in maintenance hemodialysis patients, and relations of CRP and IL-6 with clinical characteristics and lipid levels. This was a cross-sectional study of 51 hemodialysis and 53 moderate and severe chronic kidney disease patients. Autonomic tone was assessed using 24-hour HRV analysis in time and frequency domain. All patients underwent measurements of high sensitivity CRP, IL-6 and lipid levels. CRP and IL-6 were elevated in the non-dialysis group at levels similar to hemodialysis patients. Hemodialysis patients had lower total cholesterol, LDL cholesterol and apolipoprotein B levels (p < 0.05), and in this group of patients lipids were related to CRP and IL-6 (p < 0.05). The inflammatory marker IL-6 was associated to HRV in the moderate and severe chronic kidney disease group (R = -0.4, p < 0.01 for standard deviation of RR intervals and very low frequency power, R = -0.5, p < 0.01 for standard deviation of all five-minute RR intervals, R = 0.35, p < 0.05, for total power and low frequency power). Adequacy of dialysis, but not the inflammatory markers, was associated to HRV in the hemodialysis group (R = 0.6, p < 0.01 for high frequency power). Enhanced inflammatory response occurs already in stages 3 and 4 chronic kidney disease. IL-6 is related to HRV in these patients, but not in the hemodialysis group, suggesting that IL-6 may interact with autonomic tone in that stage of disease.

Heart Rate Variability: Does it Change After RF Ablation of Reentrant Supraventricular Tachycardia?

Following RF ablation of reentrant supraventricular tachycardia, inappropriate sinus tachycardia may occur. Local parasympathetic denervation is a possible mechanism for these rhythm disturbances. The purpose of this study was to determine the incidence of sinus tachycardia and to determine the relation between endocardial lesions at different ablation sites and alterations in autonomic tone in several different groups of patients with supraventricular tachycardia, using techniques of heart rate variability analysis. The subjects of this study were 75 patients (48 women, 27 men) with a mean age of 39.99 (SD = 13.39). They underwent RF ablation of AV nodal slow pathways (40 cases), posteroseptal APs (23 cases), left lateral and right free wall APs (12 cases) because of symptomatic tachycardias. The mean sinus rate and time domain (standard deviation of RR intervals and root mean square of differences of adjacent RR intervals) and frequency domain (low frequency, high frequency and low frequency/high frequency ratio) analyses of heart rate variability were obtained by use of 24 hour Holter monitoring before and 1 month after ablation compared with pre-ablation values. Analysis of 24 hour ambulatory Holter-monitors, performed 1 month after RF ablation, showed no significant changes in time and frequency domain parameters of heart rate variability in different groups. A significant increase in mean heart rate was noted after RF ablation at AV nodal slow pathway group and left freewall/right free wall accessory pathways group. Patients undergoing RF ablation of right or left posteroseptal accessory pathways had no significant increase in the mean heart rate. In summary, an increase in sinus tachycardia may be initiated by RF ablation of atrioventricular reentrant tachycardia (AVNRT) and right free wall or left free wall accessory pathways. This finding shows that the modifications of heart rate are not directly related to the posteroseptal region or to the accessory pathways.

Recombinant interferon alpha treatment decreases heart rate variability indices and impairs exercise tolerance in patients with chronic hepatitis

Complications of interferon (IFN) therapy include cardiac arrhythmias, impaired cardiac function and myocardial ischemia. Decreased heart rate variability (HRV) indices, impaired exercise tolerance and decreased left ventricular (LV) function are related to unfavorable outcome of heart disease. To investigate the effect of IFN therapy on HRV, exercise tolerance and cardiac function, 24-h ambulatory electrocardiographic monitoring (AECG), two-dimensional echocardiography, and exercise treadmill testing (ETT) was performed in 9 patients (age 56 ± 9 years-old) with chronic hepatitis and without underlying heart disease before and after treatment with IFN (recombinant alpha 2b; 10 × 10 6 U/day for 4 weeks). HRV parameters consisted of standard deviation of RR interval (sdNN, ms), SDANN (ms), S.D. index (ms), rMSSD (ms), pNN50 (%) and frequency analysis of heart rate spectrum resulted in low (ms, 0.04–0.15 Hz), high (ms, 0.15–0.40 Hz) and total (ms, 0.01–1.00 Hz) frequency components. Ischemia was not detected by AECG or ETT, and LV function was normal after INF treatment in all patients. However, INF treatment resulted in a decrease in exercise tolerance time (449 ± 94 s vs. 329 ± 67 s, P < 0.05) and a decrease in several HRV parameters (S.D. index, 42 ± 5 ms vs. 37 ± 9 ms; rMSSD, 22 ± 5 ms vs. 19 ± 4 ms; pNN50, 4 ± 3% vs. 2 ± 1%; P < 0.05). Further, patients treated with INF tended to have a lower sdNN and total frequency spectra, although this difference did not reach the level of statistical significance. These data suggest that the arrhythmogenic effect of INF may be mediated by decreases in HRV and impairment of exercise tolerance even in patients without overt heart diseases. Further, INF therapy may be contraindicated in patients with predisposing severe cardiac disorders, including arrhythmias, ischemia and decreased LV function.

Heart rate variability (HRV) of patients with traumatic brain injury (TBI) during the post-insult sub-acute period

Objective: To evaluate heart rate variability (HRV) of patients with traumatic brain injury (TBI).Methods: By a prospective study, the HRV was assessed in 20 patients with TBI during the sub-acute period post-injury (the first test was performed at a mean time post-insult of 38 days) and a matched control. The patients were examined twice, 1 month apart. The assessment included HRV (both in time and frequency domains), GCS, length of coma, brain CT, FIM and FAM.Results: A significant difference was found between patients and controls concerning HRV total power, i.e. frequencies between 0.01–0.6 Hz (high frequency p = 0.003, low frequency p = 0.013, total power p = 0.034) and for standard deviation of RR interval p = 0.011. HRV changes were related more to the timing of the evaluation than to the severity of the brain damage.Conclusion: HRV differed of patients with TBI and in the control group. Tendency to HRV normalization changes was detected during the first 3 months after the injury, which suggests recovery of the autonomic nervous system.

Heart Rate Variability after Isocaloric Exercise Bouts of Different Intensities

To examine cardiac autonomic modulation, via heart rate variability (HRV), after exercise bouts at 50% (LO) and 80% (HI) of VO2 reserve (VO2R). Thirteen male volunteers (age: 25.7+/-3 yr) exercised on a treadmill at either LO or HI (randomly assigned) on separate days, expending 300 kcal during each bout. During each visit, electrocardiogram (ECG) recordings were obtained during a supine 5-min period before exercise (PRE) and during 30 min of postexercise supine recovery (POST). The last 25 min of POST was divided into five 5-min segments to closely examine postexercise HRV. ECG segments were analyzed for the standard deviation of RR intervals (SDNN), whereas total- (lnTP), low- (lnLF), and high-frequency (lnHF) power were obtained via spectral analysis. LF and HF were further normalized (LFNU and HFNU) to better quantify autonomic balance. There were main effects of time and intensity on SDNN such that it was lower than PRE until 15 min POST, and lower after HI. There were significant intensity x time interactions on lnTP, lnLF, lnHF, LFNU, HFNU, and lnLF/lnHF. Post hoc analysis revealed that lnTP and lnLF were lower than PRE up to 20 min POST after HI. lnHF was lower than PRE for 25 min POST for HI, and for 10 min POST for LO. LFNU and lnLF/lnHF were greater, whereas HFNU was lower, compared with PRE up to 15 min POST, and from 20-25 min POST for HI only. Exercise at 50% VO2R caused less of a shift in the cardiac autonomic balance, with a quicker restoration of vagal modulation than exercise at 80% VO2R.

Heart Rate Variability and the Exercise Pressor Reflex during Dynamic Handgrip Exercise and Postexercise Arterial Occlusion

The exercise pressor reflex is thought to be an important cardiovascular control mechanism that may be compromised in disease states such as congestive heart failure and other metabolic syndromes. The purpose was to describe the exercise pressor reflex by observing heart rate variability and blood pressure responses to handgrip-exercise and postexercise arterial occlusion. Continuous electrocardiography, arterial blood pressure, and pneumotachogram data were collected on 38 participants (age, 20 +/- 1 year) during spontaneous breathing, venous-occluded exercise (60% maximal voluntary contraction, 0.5 Hz) and immediate postexercise arterial occlusion. Data were analyzed for mean R-R interval, standard deviation of R-R intervals (SDNN), normalized low (0-0.15 Hz) frequency power (LFnu), mean arterial pressure (MAP), and respiratory rate. During exercise, increases in respiratory rate (+4.55 +/- 6.48 breaths/min), LFnu (+9.39 +/- 16.83%), and MAP (+25.40 +/- 17.55 mm Hg) were observed. Mean R-R interval (-230.73 +/- 125.79 msec) and SDNN (-38.54 +/- 36.02 msec) decreased (P < 0.05). Respiratory rate (+0.12 +/- 4.61 breaths/min), SDNN (-17.89 +/- 64.41 msec), and LFnu (9.89 +/- 21.01%) recovered during forearm arterial occlusion (P < 0.05). However, Mean R-R interval and MAP remained elevated above spontaneous breathing (P < 0.05). The sustained elevation in MAP during postexercise arterial occlusion suggests metaboreceptor-mediated heightened sympathetic activity. The increase in LFnu during exercise and its subsequent recovery during postexercise occlusion is consistent with dynamic exercise-induced parasympathetic withdrawal but a strong vagal activation upon cessation of dynamic activity despite persistent sympathetic activity originating from afferent input from the occluded forearm.

Autonomic modulation and clinical outcome in patients with chronic heart failure

Objective Several studies documented the relevance of autonomic activity in the pathophysiology of heart failure. In our study we evaluated the adjustment of this activity under different stimuli, by means of heart rate variability (HRV), and correlated these findings with long-term mortality and sustained VT occurrence. Patients and method Fifty-three patients (mean age 54±9 years) with heart failure were submitted to time and frequency domain HRV analysis. This latter analysis was performed at rest, during paced breathing and during passive tilt. Results Lower standard deviation of RR intervals (76.76±24 versus 107.70±43, p=0.02), mean of the 5-min standard deviations of RR intervals (35.14±15 versus 62.39, p<0.01), standard deviation of the 5-min average RR intervals (69.42±19 versus 91.79±30, p=0.02), and baseline Low-Frequency (LF) power (15.15±12 versus 40.39±24 nu, p=0.001) characterized patients who died. Paced breathing induced a significant reduction of LF (40.39±24 to 20.12±18 nu, p<0.0001) and increase of High Frequency power (HF) (47.31±23 to 70.63±16 nu, p<0.0001) in survivors, while tilting induced a reduction of HF (47.31±23 to 29.80±16 nu, p<0.0001). Patients who died did not show significant variation of HRV neither during paced breathing nor during tilt. Reduced time domain indexes were significantly correlated to sustained VT occurrence. Conclusions Patients with heart failure with a better prognosis are characterized by a responsiveness of autonomic modulation. Simple maneuvers, such as tilting and paced breathing, seem to provide more useful information, than the baseline evaluation of autonomic status, in identifying patients with a higher mortality. Time domain analysis was more helpful to estimate arrhythmic risk.