Spectrum analysis of the variability of heart rate in athletes

OBJECTIVES: Characterize power spectrum pattern of the heart rate variability and assessment of the relative contributions of sympathetic and parasympathetic cardiac nervous system control in athletes. STUDY DESIGN: Prospective study of athletes and sedentary healthy control group sex and age matched. SUBJECT AND METHODS: 8 athletes, 3 female and 5 male, swimming (4), canoeing (2) and cycling (2), aged 17.4 +/- 3.6 years, and 8 sedentary healthy controls. ECG signals were recorded after a period of 15 minutes in supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive heart beats, we calculated the average, the standard deviation, the maximum and the minimum values and the rate between the longest and the shortest R-R interval (E/I). We also calculated, after computing the fast Fourier transform, the total spectrum power, the low frequency component (LF, from 0.01 to 0.15 Hz) and the high frequency component (HF, greater than 0.15 Hz) and its ratio (LF/HF). RESULTS: The average R-R interval was 921 +/- 154.2 msecs and 673.2 +/- 98 msecs, the standard deviation was 72.5 and 29.4 msecs and the ratio E/I 1.63 +/- 0.14 and 1.28 +/- 0.08, respectively for athletes and control group. Differences between groups were significant (p less than 0.01) for all parameters, with higher variability in the athletes. Both spectral bands (LF and HF) and higher power in athletes (LF = 0.54 +/- 0.23 and HF = 0.76 +/- 0.14) than in the control group (LF = 0.14 +/- 0.10 and HF = 0.18 +/- 0.15) (p less than 0.001). There were no significant differences for LF/HF ratio, or normalized LF (LF%) or normalized HF (HF%) between groups. CONCLUSIONS: The present results indicates higher power of both spectral bands (LF and HF) and higher amplitude of the respective peaks in athletes when compared with healthy sedentary, with a clear predominance of the HF band in the total spectral power density, which suggest that the higher heart rate variability observed in athletes reveals the predominance of parasympathetic activity, without reduction of the sympathetic tone.     

Spectrum analysis of heart rate. A method of studying the role of the autonomic nervous system in the regulation of blood circulation]

Spectral analysis of heart rate variability has recently been shown to be a reliable noninvasive test for quantitative assessment of cardiovascular automatic regulatory responses. In 12 ambulant normotensive healthy young males (mean age 23 +/- 1 years) after a period of 10 min. for stabilisation, a continuous ecg recording (lead CM-5) for 8 min. was obtained in the supine and standing position, with a controlled respiration rate 15/min. Power spectrum of 512 point time series (R-R intervals) in both positions was calculated using a fast Fourier transform-based window periodogram method. Based upon results from the literature the power spectrum analysis was performed on two components: low frequency LF (0.05-0.15 Hz) and high frequency HF (0.15-0.50 Hz). Mean R-R interval decreased on standing position from 0.79 +/- 0.10 s to 0.59 +/- 0.11 s (p less than 0.001). The ratio HF/LF in supine was 0.63 +/- 0.70 and on standing position 2.54 +/- 0.73 (p less than 0.001). The relative LF component of the total HR power spectrum increased from 22.8% +/- 12.1% to 42.9 +/- 14.4% (p less than 0.001) after changing the position from supine to standing, and the relative HF component decreased from 56.3 +/- 22.4% to 25.5 +/- 16.2 (p less than 0.001). The total power was significantly lower when standing in comparison to supine position (681 +/- 519 s2, 1188 +/- 963 s2 respectively, p less than 0.05). Our results suggest that heart rate fluctuations in supine position in normal men are mainly vagally determined (HF power spectrum component).(ABSTRACT TRUNCATED AT 250 WORDS)     

Paradoxical effects of pirenzepine on parasympathetic activity in chronic heart failure and control

We studied the effect of intravenous pirenzepine (3 mg) in normal subjects (n=15, 43+/-16 years old) and in patients with chronic heart failure (n=15, 61+/-12 years old) to assess the effect of low-dose pirenzepine on vagal activity. R-R intervals and the standard deviations, low-frequency power (LF: ln ms2, 0.04-0.15 Hz), high-frequency power (HF: ln ms2, 0.15-0.40 Hz) and the ratio of low- to high-frequency power (LF/HF ratio) were measured 10 min before and after pirenzepine using a Holter analysis system. Pirenzepine was found to cause a significant increase in the R-R interval from 903+/-112 to 956+/-129 ms in the control group (P<0.0001) and from 927+/-141 to 958+/-168 ms in patients with chronic heart failure (P<0.01). Pirenzepine also increased HF significantly from 4.29+/-0.32 to 5.16+/-0.38 ln ms2 in the control group (P<0.0001) and from 4.04+/-0.16 to 4.48+/-0.24 ln ms2 in the chronic heart failure group (P<0.05). Pirenzepine did not significantly alter the LF/HF ratio in either group. We emphasize that pirenzepine appears to have a vagoinimetic effect in patients with chronic heart failure and that it may be useful for augmenting vagal control of the heart in some patients with chronic heart failure.     

Time and frequency analysis of beat-to-beat R-T interval variability in patients with ischaemic left ventricular dysfunction providing evidence for non-neural control of ventricular repolarisation

BACKGROUND: Determinants of temporal lability in ventricular repolarisation are not fully recognised. We aimed to analyse the sources of RT variability by comparing normal subjects and patients after myocardial infarction (MI) with either depressed or preserved left ventricular (LV) function. METHODS: One hundred and nine patients (27 women, 82 men, aged 51 +/- 9 years) were divided into three groups: 24 patients (pts) with an uncomplicated angiographically proven coronary heart disease (CHD-group), 59 post-MI pts with preserved LV function (LVEF > 40%, PMI-N-group) and 26 post-MI pts with depressed LV function (LVEF < 40%, PMI-L-group). An ECG signal of low-noise 512 heartbeats was recorded using a computer-assisted amplifier (16 bit, 2 kHz). The onset and offset of the R-wave and T-wave were determined automatically. The magnitude of R-R and R-T variability was measured as the standard deviation of all intervals (SD-RR and SD-RT, ms, respectively). Their relationship was quantified by the correlation coefficient r(RT/RR). Power spectral density of RR or RT variability was estimated with the FFT (Welch's averaged periodogram, Hanning window) and frequency relation was quantified using a squared coherence spectrum (SCS). For all spectral and cross-spectral measurements two frequency ranges were considered: high (0.15-0.50 Hz, HF) and low (0.04-0.15 Hz, LF). Spectral power and SCS of RR and RT variability for both ranges (HF(RR), LF(RR), HF(RT), LF(RT), SCS(HF), SCS(LF)), and the ratios LF/HF(RR) and LF/HF(RT) were drawn for comparisons. The central frequency of HF(RR) was considered as the frequency of respiration (f(resp), Hz). RESULTS: In the PMI-L group the SD-RT was significantly greater compared to the remaining groups and accounted for almost 10% of the SDRR. Also, the coefficient r(RT/RR) was weakest in this group. The spectral indices of RR variability were similar in all groups, while the greatest value of the HFRT was observed in the PMI-L group. The SCS(LF) was insignificant in this group, contrary to the CHD and PMI-N groups. Additionally, there were significant negative relationships between f(resp) and spectral indices of RT variability in PMI-patients with depressed LV function. CONCLUSION: A greater beat-to-beat variation in RT interval duration along with increased power of its HF component indicates an important role of respiration in ventricular repolarisation control, while reduced time- and frequency RT-RR relationships seem to relate to an impaired process of ventricular duration adaptation.     

Determination of baroreceptor-stroke volume reflex sensitivity by power spectral analysis: a quantitative probe of baroreceptor-cardiac reflex

Baroreceptor-cardiac reflex, which consists of baroreceptor-induced chronotropic and inotropic actions, is a very useful index of cardiac sympathovagal balance. Baroreceptor-heart rate reflex sensitivity, which reflects baroreceptor-induced chronotropic action, has been used as a marker of baroreceptor-cardiac reflex. However, it cannot be used in patients with chronotropic incompetence and/or implanted cardiac pacemaker. We hypothesized that baroreceptor-stroke volume (SV) reflex sensitivity, which reflects baroreceptor-induced inotropic action, may also be a useful method for measurement of baroreceptor-cardiac reflex, similar to the baroreceptor-heart rate reflex sensitivity. To test this hypothesis, we measured baroreceptor-SV reflex sensitivity expressed as ratio of low frequency (LF) power to total power of SV fluctuation (LF/TP(SV): %/mmHg) by spectral analysis of mean blood pressure and SV fluctuations, the gain in low-frequency band between two signals in supine and 60 degrees upright positions, and compared these values to baroreceptor-heart rate reflex sensitivity in 14 healthy subjects. Baroreceptor-SV reflex sensitivity correlated significantly with baroreceptor-heart rate reflex sensitivity (r = 0.73, p < 0.0001). In addition, baroreceptor-SV reflex sensitivity correlated significantly and positively with high frequency (HF) power (r = 0.57, p < 0.005) and negatively with LF/HF ratio (r = -0.57, p < 0.005) in power spectral analysis of R-R interval variability. Moreover, baroreceptor-SV reflex sensitivity in LF/TP(SV) correlated positively with the R-R interval (r = 0.70, p < 0.0001) and negatively with diastolic blood pressure (r = -0.50, p < 0.01). We conclude that baroreceptor-SV reflex sensitivity in LF/TP(SV) can be used as a quantitative probe of baroreceptor-cardiac reflex, similar to the baroreceptor-heart rate reflex sensitivity in healthy subjects, and it may enable us to estimate inotropic aspect in baroreceptor-cardiac reflex in patients with chronotropic incompetence and/or implanted pacemaker.     

心肌梗死后患者心率变异能谱分析及其昼夜规律

本文对５０例急性心肌梗死后１个月内连续病例及５１例正常人的心率变异性各能谱成份进行研究。结其睡眠段，白天段以及２４小时内每小时时间段进行比较，探讨变化的规律性。结果显示：１．睡眠段及清醒段总能谱，低能谱及高能谱组明显低于２组，两组差别有高度显著性。两个时间段极低能谱两组差别无显著性。     

Sympathetic rhythmicity in cardiac transplant recipients

BACKGROUND: Variability of R-R interval and muscle sympathetic nerve activity (MSNA) occurs predominantly at a low frequency (LF, +/-0.1 Hz) and a high frequency (HF, +/-0.25 Hz) in normal humans. Increased sympathetic drive in normal humans is associated with an increased LF component of the R-R interval and MSNA. Patients with severe heart failure have high sympathetic activity but decreased or absent LF power of both R-R and MSNA. We tested the hypothesis that this dysfunction in autonomic modulation in heart failure can be reversed by heart transplantation. METHODS AND RESULTS: We performed spectral analysis of resting MSNA, R-R interval, and respiration in 9 patients with heart transplants, 9 chronic heart failure patients, and 9 normal control subjects, all closely matched for age, sex, and body mass index. MSNA (bursts per minute) was higher in patients with heart transplants (74+/-3) than either patients with heart failure (56+/-6) or normal subjects (40+/-4) (P<0.001). LF variability in the R-R interval was reduced in both heart transplant recipients and heart failure patients compared with the control subjects (P<0.01). The LF variability in MSNA was also nearly absent in the heart failure patients (P<0.01). However, the LF and HF oscillations in MSNA in patients with heart transplants were comparable to those evident in the control subjects. CONCLUSIONS: Cardiac transplantation does not reduce MSNA. However, LF oscillations in sympathetic activity are restored after transplantation such that the MSNA oscillatory profile is similar to that observed in normal subjects.     

Effects of eicosapentaenoic acid on visceral fat and heart rate variability: assessment by power spectral analysis

OBJECTIVES: Effects of eicosapentaenoic acid (EPA)on visceral fat storage and the autonomic nervous system were evaluated by abdominal computed tomography (measurement of visceral fat area) and power spectral analysis of heart rate variability, respectively. METHODS: The parameters of visceral fat area and heart rate variability were compared between the control group (n=74; conventional therapy) and the EPA group (n=91; conventional therapy plus EPA 1800 mg/day) during a 6-month period. The power spectral analysis of heart rate variability [low frequency component (LF), high frequency component (HF)and LF/HF] was performed on 256 sec taken after a 30-minute rest. RESULTS: Systolic and diastolic blood pressures significantly decreased (p < 0.0001 and p = 0.0076, respectively)but heart rate remained unchanged in the EPA group during the 6 months. In the control group, these parameters showed no change. The values of visceral fat area did not alter in either group but body weight significantly decreased in the EPA group (p = 0.0003). A sex difference was noted in the parameter of visceral fat area; in female patients, the change in the parameter was insignificant, but in male patients this tended to decrease from 162 +/- 60 to 152 +/- 65 cm2 (p = 0.0586) during the 6 months. Serum triglyceride decreased significantly in the EPA group (p = 0.0339) but not in the control group. The ratio of LF/HF in heart rate variability significantly decreased in the EPA group (p = 0.0004) and the decrease was especially prominent in male patients. The LF/HF ratio remained unchanged in the control group. This parameter correlates well with visceral fat area, but not with systolic blood pressure. CONCLUSIONS: The oral intake of purified EPA significantly reduced blood pressure without altering heart rate during the 6-month treatment. EPA suppressed sympathetic nerve activity without inducing any parasympathetic nerve activity. The direct anti-sympathetic action of EPA was inferred and its action was found unrelated to blood pressure decrease. In male patients, diminished visceral fat area may be associated with depression of sympathetic nerve activity.     

Effects of spinal section and of positive-feedback excitatory reflex on sympathetic and heart rate variability

The sympathetic outflow appears to be capable of displaying a rhythmicity synchronous with cardiovascular Mayer's waves even after spinal section. To test the hypothesis that spinal sympathetic low frequency (LF) oscillation can be enhanced during sympathetic excitation, we recorded cardiac sympathetic nerve activity (SNA), R-R interval, arterial pressure, and ventilation in 9 unanesthetized decerebrate-vagotomized cats before and after C1 spinal section. LF and high frequency (HF) components were detected in the variability of SNA, R-R interval, and systolic arterial pressure both before and after spinal section. In this latter condition, a significant coherence between LF(SNA) and LF(R-R) was present in 5 animals, whereas HF(SNA) and HF(R-R) were correlated in 4 animals. During an excitatory sympathetic spinal reflex elicited by aortic constriction, the efferent sympathetic firing was markedly enhanced (from 7+/-2 to 33+/-7 spikes/s); concomitantly, the powers of both LF(SNA) and HF(SNA) were also increased. Coherence between LF(SNA) and LF(R-R) became significant in all cases, whereas HF(SNA) and HF(R-R) became correlated in 6 animals. In 3 animals, the reflex sympathetic excitation was no longer elicitable after interrupting a vast contingent of sympathetic afferents by means of thoracic dorsal root section. We report for the first time that LF and HF oscillations are detectable in SNA, R-R interval, and systolic arterial pressure variabilities of decerebrate-vagotomized spinal cats and that an excitatory spinal reflex is capable of increasing the power of both SNA spectral components.     

Autonomic modulation of heart rate during obstructive versus central apneas in patients with sleep-disordered breathing

Sleep-disordered breathing is associated with an altered sympathovagal balance determined by the nocturnal cyclic alternating of apneas and hyperventilation. The aim of this study was to determine whether the autonomic modulation of heart rate during obstructive apneas (OA) and central apneas (CA) in patients with sleep-disordered breathing is different. Therefore, by using the time-varying Wigner-Ville transform spectral analysis we described, in 17 patients, the time course of the low-frequency (LF) and the high-frequency (HF) components of the interbeat interval (R-R interval) reflecting, at large, respectively, the sympathetic and the parasympathetic modulation, during OA (n = 185) and CA (n = 51) and during the postapneic hyperventilation. In both types of apneas we found cyclic lengthening/shortening in R-R interval, during apneas/postapneic hyperventilation, respectively, with more marked bradycardia during OA (R-R: 1,011 +/- 23 versus 893 +/- 30 ms2, p < 0.01). In OA the HF oscillations decreased from the apnea to the postapneic hyperventilation (from 1,964 +/- 244 to 387 +/- 98 ms2, p < 0.0001), whereas the LF oscillations increased (from 2,649 +/- 230 to 9,820 +/- 716 ms2, p < 0.0001). Conversely, in CA the HF oscillations increased from the apnea to the postapneic hyperventilation (from 452 +/- 177 to 1,485 +/- 406 ms2, p < 0.0001), whereas the LF component remained unchanged. These results show markedly different autonomic alterations during and after OA versus CA, suggesting a surge in sympathetic modulation after the obstructive episodes.     

Studies on cardiac sympathovagal balance and large artery distensibility in patients with untreated essential hypertension.

BACKGROUND: Power spectral analysis of heart rate variability and arterial distensibility are non-invasive measures of cardiac autonomic modulation and mechanical vessel wall properties, respectively. The aim of the present study was to assess cardiac sympathovagal balance, carotid and brachial artery distensibility and a possible relation between these parameters in mildly hypertensive patients as compared to normotensive controls. METHODS: Total power (TP, 0.01 to 0.5 Hz) and spectral components (low frequency 0.04-0.15 Hz, mainly sympathetic cardiac modulation; high frequency 0.15-0.4 Hz, mainly vagal cardiac modulation) and cardiac sympathovagal balance (LF/LH ratio) of short term heart rate variability (ECG-recording) were calculated in 15 untreated essential hypertensive patients (HYP) and 15 age- and sex-matched healthy controls (CON). Brachial and carotid artery distensibility coefficient (DC) was measured with a multigate doppler system (echo-tracking). RESULTS: TP (ms2 x 10(-3)) (11.2 +/- 0.8 vs 13.6 +/- 0.9, P < 0.03), LF/HF ratio (1.07 +/- 0.08 vs 0.75 +/- 0.07, P < 0.01) and HF (ms2 x 10(-3)/%) (0.7 +/- 0.1/49 +/- 2 vs 1.3 +/- 0.2/58 +/- 2, P < 0.01/P < 0.01) were significantly reduced in HYP compared to CON subjects. LF (ms2 x 10(-3)/%) was 0.7 +/- 0.1/50 +/- 2 vs 0.9 +/- 0.1/41 +/- 2, P = 0.16/P < 0.01. Carotid artery DC (15 +/- 2 vs 26 +/- 2, P < 0.001) and brachial artery DC (4.7 +/- 0.6 vs 9 +/- 1.0, P < 0.001) were significantly reduced in HYP. There was a significant correlation between carotid DC and LF/HF (rho = -0.41, P < 0.03). CONCLUSION: The data shows reduced heart rate variability and altered cardiac sympathovagal balance as well as impaired arterial distensibility in untreated mildly hypertensive patients. The relative increase in sympathetic modulation and decreased carotid distensibility appear to be related.     

Alterations of autonomic nervous activity in recurrence of variant angina

OBJECTIVE: To investigate whether autonomic nervous activity is involved in the recurrence of spontaneous coronary spasm in variant angina. DESIGN: Retrospective analysis. SETTING: Cardiology department of a university hospital. PATIENTS: 18 patients with variant angina were divided into single attack group (SA; nine patients) and multiple attack group (MA; nine patients) according to the frequency of ischaemic episodes with ST segment elevation during 24 hour Holter monitoring. METHODS: Heart rate variability indices were calculated using MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non-linear least squares method for fitting analysis, at 30 second intervals for 30 second periods, from 40 minutes before the attack to 30 minutes after the attack. High frequency (HF; 0.04-0.15 Hz) was defined as a marker of parasympathetic activity, and the ratio of low frequency (LF; 0.15-0.40 Hz) to high frequency (LF/HF) as an indicator of sympathetic activity. The averaged value during the 40 to 30 minute period before an attack was defined as the baseline. RESULTS: Compared with baseline, the HF component decreased in both groups at two minutes before the attack (p < 0.01), and the LF/HF ratio decreased at three minutes before the attack (p < 0.01). The baseline LF/HF was lower in the MA group than in the SA group (p < 0. 01). CONCLUSIONS: A reduction of sympathetic activity may play a key role in determining the recurrence of transient ischaemic events caused by spontaneous coronary spasm in patients with variant angina.     

Association of hyperglycemia with reduced heart rate variability (The Framingham Heart Study)

This study was designed to examine the association of heart rate variability (HRV) with blood glucose levels in a large community-based population. Previous reports have shown HRV to be reduced in diabetics, suggesting the presence of abnormalities in neural regulatory mechanisms. There is scant information about HRV across the spectrum of blood glucose levels in a population-based cohort. One thousand nine hundred nineteen men and women from the Framingham Offspring Study, who underwent ambulatory electrocardiographic recordings at a routine examination, were eligible. HRV variables included the SD of normal RR intervals (SDNN), high-frequency (HF, 0.15 to 0.40 Hz) and low-frequency (LF, 0.04 to 0.15 Hz) power, and LF/HF ratio. Fasting plasma glucose levels were used to classify subjects as normal (<110 mg/dl; n = 1, 779), as having impaired fasting glucose levels (110 to 125 mg/dl; n = 56), and as having diabetes mellitus (DM >/=126 mg/dl or receiving therapy; n = 84). SDNN, LF and HF power, and LF/HF ratio were inversely related to plasma glucose levels (p <0.0001). SDNN and LF and HF powers were reduced in DM subjects (4.28 +/- 0.03, 6.03 +/- 0. 08, and 4.95 +/- 0.09) and in subjects with impaired fasting glucose levels (4.37 +/- 0.04, 6.26 +/- 0.10, and 5.06 +/- 0.11) compared with those with normal fasting glucose (4.51 +/- 0.01, 6.77 +/- 0.02, and 5.55 +/- 0.02, all p <0.005), respectively. After adjusting for covariates (age, sex, heart rate, body mass index, antihypertensive and cardiac medications, systolic and diastolic blood pressures, smoking, and alcohol and coffee consumption), LF power and LF/HF ratio were lower in DM subjects than in those with normal fasting glucose (p <0.005). HRV is inversely associated with plasma glucose levels and is reduced in diabetics as well as in subjects with impaired fasting glucose levels. Additional research is needed to determine if low HRV contributes to the increased cardiovascular morbidity and mortality described in subjects with hyperglycemia.     

倾斜试验中晕厥患者自主神经功能的变化

目的　运用频谱法研究直立倾斜试验中血管性晕厥的发生机制。方法　对 2 7例不明原因晕厥患者行直立倾斜试验 ,运用频谱法计算低频 (LF)、高频 (HF)及LF/HF的变化。结果　 15例发生晕厥或先兆晕厥 (阳性组 ) ,12例未出现症状 (阴性组 ) ,倾斜前两组LF、HF和LF/HF差异无显著性 ;阴性组倾斜后即刻HF明显下降 ,LF/HF显著升高 ,平卧后恢复到倾斜前水平 ,阳性组晕厥或先兆晕厥发作时 ,HF突然升高 (10 4 7± 4 0 4→ 32 95± 10 4 8) ,明显高于倾斜前 (2 3 4 4± 4 2 0→32 95± 10 4 8,P <0 0 5 ) ,LF/HF显著下降 (3 2 8± 0 39→ 1 0 7± 0 31,P <0 0 1) ,试验终止平卧后 ,HF和LF/HF恢复 ,两组LF在倾斜前后不同阶段均无明显变化。结论　在平卧、静息状态下 ,阳性患者和阴性患者的自主神经功能差异无显著性 ,倾斜后阳性患者迷走神经兴奋性在抑制过程中突然过度增强 ,导致晕厥或先兆晕厥发生。     

Effects of sleep stage and age on short-term heart rate variability during sleep in healthy infants and children

STUDY DESIGN: Power spectrum analysis of heart rate variability (HRV) is a noninvasive technique that provides a quantitative assessment of cardiovascular neural control. Using this technique, we studied the autonomic nervous system changes induced by sleep in 14 healthy subjects: 7 infants (mean age, 9.40 +/- 2.32 months) and 7 children (mean age, 8.93 +/- 0.65 years) during a standard all-night polysomnographic recording. Our primary aim was to assess the effect of sleep stage and age on short-term HRV during sleep in healthy infants and children. Power spectral density was estimated by autoregressive modeling over 250 consecutive R-R intervals. In this study, we mainly considered two spectral components: the high-frequency (HF) component (0.15 to 0.40 Hz), which reflects parasympathetic cardiovascular modulation; and the low-frequency (LF) component (0.04 to 0.15 Hz), generally considered due to both parasympathetic and sympathetic modulation. RESULTS: Heart rate was higher (p < 0.01 in all sleep stages) and total power lower (p < 0. 02) in infants than in children. HF power was higher in children than in infants (p < 0.05). In infants and children, the ratio between LF and HF powers changed with the various sleep stages (p < 0.02 in infants; p < 0.01 in children): it decreased during deep sleep and increased during rapid eye movement sleep. However, it was invariably lower in children than in infants. CONCLUSION: These findings show that the sleep stage and age both significantly influence short-term HRV during sleep in healthy infants and children. Hence, to provide unbiased results, HRV studies investigating the effects of age on autonomic nervous system activity should segment sleep into the five stages. In addition, despite a relatively small study sample, our data confirm greater parasympathetic control during sleep in children than in infants.     

Beneficial effect of candesartan treatment on cardiac autonomic nervous activity in patients with chronic heart failure: simultaneous recording of ambulatory electrocardiogram and posture

BACKGROUND: Reclining in the right lateral decubitus position in chronic heart failure (CHF) is a self-protective mechanism for normalizing impaired cardiac autonomic nervous activity (CANA). HYPOTHESIS: Candesartan, an angiotensin II receptor blocker, exerts beneficial effects on CANA and postural preferences in patients with CHF. METHODS: We studied 15 patients with CHF due to coronary artery disease. Cardiac autonomic nervous activity was assessed using spectral heart rate variability (HRV) analysis based on 24-h ambulatory electrocardiogram monitoring before and after an 8-week treatment with candesartan. The patients' posture was simultaneously recorded using a specially devised detector, as the right (R) or left (L) lateral decubitus or supine (S) positions, to evaluate postural modulations of CANA. Normalized high-frequency (0.15 to 0.40 Hz) power (nHF) and the low-frequency (0.04 to 0.15 Hz)/high-frequency power ratio (LF/HF) were used as indices of vagal activity and sympathovagal balance, respectively. RESULTS: When HRV was analyzed in each position, CANA was changed in L and S, but not in R, from sympathetic to parasympathetic prevalence by the treatment (R, nHF, 50 +/- 20 vs. 52 +/- 19 nu, p = 0.87; LF/HF, 1.39 +/- 1.11 vs. 1.32 +/- 1.32, p =0.93; L, nHF, 28 +/- 13 vs. 47 +/- 19 nu, p = 0.019; LF/HF, 3.34 +/- 2.48 vs. 1.56 +/- 1.39, p = 0.029; S, nHF, 38 +/- 17 vs. 53 +/- 16 nu, p = 0.0023; LF/HF, 2.43 +/- 2.21 vs. 1.03 +/- 0.59, p = 0.025). The fractions of the time in R and L were decreased and increased, respectively, by the treatment (R, 40 +/- 30 vs. 18 +/- 24%, p = 0.0018; L, 11 +/- 20 vs. 27 +/- 26%, p = 0.025). CONCLUSIONS: In patients with CHF, candesartan treatment improves cardiac autonomic balance, and the preference for the right lateral decubitus position disappears after the treatment.     

Sympatho-vagal control of heart rate variability in patients treated with suppressive doses of L-thyroxine for thyroid cancer

OBJECTIVE: This study aimed to analyze the autonomic control of heart rate variability (HRV) in subjects receiving chronic l-thyroxine (l-T4) treatment after total thyroidectomy and (131)I therapy for differentiated thyroid carcinoma. METHODS: Blood pressure (BP) and sympatho-vagal activity (evaluated by power spectral analysis (PSA) of time-domain parameters of HRV) were studied in clinostatism and after orthostatism in 24 healthy controls, and in 12 patients taking l-T4 (125-200 mug/day) to maintain serum TSH levels at <0.01 muIU/ml. The study of HRV by PSA is a non-invasive method of analyzing sympatho-vagal control of HRV by quantifying high-frequency (HF) (0.15-0.4 Hz) and low-frequency (LF) (0.04-0.15 Hz) powers. RESULTS: Patients on L-T4 treatment had undetectable TSH levels, serum free T4 (fT4) above the normal range or at the upper limit in one case, and normal free tri-iodothyronine (fT3) levels. Heart rate and R-R intervals were not different in the two groups, both in clinostatism and in ortostatism. Systolic and mean BP were higher in patients than in controls and were inversely correlated with actual serum fT4 levels. During clinostatism, thyroid patients showed significantly lower LF power (P = 0.035), LF/(LF + HF) (P = 0.008) and LF/HF (P = 0.01) than controls. When patients moved from lying to standing, there was a significantly different decrease in orthostatic LF power (P = 0.001), LF/(LF + HF) (P = 0.044) and LF/HF (P = 0.047) versus controls. CONCLUSIONS: Changes in autonomic control of HRV, characterized by decreased sympathetic activity and impaired sympatho-vagal balance with preserved vagal tone, are detectable in patients with hyperthyroxinemia due to suppressive l-T4 therapy and increased systolic and mean, but not diastolic, BP.     

Patients with uncomplicated coronary artery disease have reduced heart rate variability mainly affecting vagal tone

AIM: To investigate whether uncomplicated chronic coronary artery disease causes changes in heart rate variability and if so, whether the heart rate variability pattern is different from that described in patients with acute myocardial infarction. METHODS: Heart rate variability was studied in 65 patients with angina who had no previous myocardial infarcts, no other diseases, and were on no drug that could influence the sinus node. Results were compared with 33 age matched healthy subjects. The diagnosis of coronary artery disease in angina patients was established by coronary angiography in 58, by thallium scintigraphy in six, and by exercise test only in one. Patients and controls were Holter monitored 24 hours outside hospital, and heart rate variability was calculated in the frequency domain as global power (GP: 0.01-1.00 Hz), low frequency peak (LF: 0. 04-0.15 Hz), high frequency peak (HF: 0.15-0.40 Hz), LF/HF in ms(2), and in the time domain as SDNN (SD of normal RR intervals), SDANN (SD of all five minute mean normal RR intervals), SD (mean of all five minute SDs of mean RR intervals), rMSSD (root mean square of differences of successive normal RR intervals) (all in ms), and pNN50 (proportion of adjacent normal RR intervals differing more than 50 ms from the preceding RR interval) as per cent. RESULTS: The mean age in patients and controls was 60.4 (range 32-81) and 59.1 (32-77) years, respectively (NS), the male/female ratio, 57/65 and 24/33 (NS), and the mean time of Holter monitoring, 23.0 (18-24) and 22.8 (18-24) hours (NS). Mortality in angina patients was 0% (0/65) at one year, 0% (0/56) at two years, and 3% (1/33) at three years. Compared with healthy subjects angina patients showed a reduction in GP (p = 0.007), HF (p = 0.02), LF (p = 0.02), SD (p = 0.02), rMSSD (p = 0.01), and pNN50 (p = 0.01). No significant difference was found in RR, LF/HF, SDNN, or SDANN. CONCLUSIONS: Uncomplicated coronary artery disease without previous acute myocardial infarction was associated with reduced high and low frequency heart rate variability, including vagal tone. SDANN and SDNN, expressing ultra low and very low frequencies which are known to reflect prognosis after acute myocardial infarction, were less affected. This is in agreement with the good prognosis in uncomplicated angina in this study.     

The effect of glucose-insulin-potassium solution on ventricular late potentials and heart rate variability in acute myocardial infarction.

BACKGROUND: Blunted heart rate variability (HRV) and presence of ventricular late potentials (VLPs) are known to correlate with an increased risk of ventricular tachycardia and sudden cardiac death in acute myocardial infarction (AMI). In the present study, we investigated the effect of glucose-insulin-potassium (GIK) solution on the VLPs and HRV in AMI. METHODS: Seventy-two consecutive patients with first Q wave AMI were randomized to GIK solution and placebo. HRV analysis and ambulatory electrocardiographic recordings were taken in all patients between 24 and 48 h. Sub-maximal exercise testing and echocardiography were performed and signal-averaged electrocardiography (SAECG) was recorded before discharge. RESULTS: Total filtered QRS duration (FQRS: 102 +/- 7 versus 108 +/- 11 ms; P < 0.05), low-amplitude signal (LAS: 25 +/- 8 versus 32 +/- 11 ms; P < 0.01) and frequency of VLPs (21 versus 45%; P < 0.05) were found to be significantly lower while root-mean-square voltage of the terminal 40 ms of QRS (RMS-40: 45 +/- 18 versus 36 +/- 20 microV; P < 0.05), and left ventricular ejection fraction (EF: 55 +/- 6 versus 48 +/- 7; P < 0.05) were significantly higher in the GIK group when compared to placebo. During the hospital period, the presence and frequency of post-myocardial infarction angina were significantly lower in the GIK group (15 versus 29%, P < 0.05), whereas an insignificant decrease in frequency of ventricular arrhythmias was observed in these patients. On HRV analysis, there was no significant difference between two groups in either time domain (SD, SDNN, RMS-SD) or frequency domain (HF, LF, LF/HF ratio) parameters. CONCLUSION: GIK solution may be beneficial to VLPs, ischaemic events, and left ventricular systolic performance in the early period of AMI. This therapy has no significant effect on HRV in AMI patients.     

Suppression of cardiac sympathetic nervous system during dental surgery in hypertensive patients.

We determined the changes in blood pressure, pulse rate, and heart rate variability during dental surgery in hypertensive patients. The study included 18 essential hypertensives and 18 age and sex matched normotensive controls who underwent tooth extraction at our hospital. Holter electrocardiographic monitoring was used to determine the power spectrum of R-R variability before and during dental surgery. The low frequency (LF: 0.041 to 0.140 Hz), high frequency (HF: 0.140 to 0.500 Hz), and total spectral powers (TF: 0.000 to 4.000 Hz) were calculated, and the ratio of LF to HF and the percentage of HF relative to TF (%HF: HF/TF x 100) were used as indexes of sympathetic and parasympathetic activities, respectively. The baseline blood pressure for hypertensive patients (149 +/- 4/85 +/- 2 mmHg) was significantly higher than that for normotensive patients (119 +/- 3/71 +/- 2 mmHg). The baseline pulse rates were similar between the two groups. Blood pressure increased during tooth extraction in both groups; however, changes in blood pressure did not differ between them. Administration of local anesthetic significantly decreased the %HF in normotensive patients (before vs. after anesthesia; 22.3 +/- 2.4 vs. 13.8 +/- 2.7%, p < 0.05). In contrast, the LF/HF significantly decreased during the local anesthesia and tooth extraction in hypertensive patients. These results suggest that pressor response induced by tooth extraction did not differ between normotensive and hypertensive patients, and that suppression of the cardiac sympathetic nervous system during dental surgery might attenuate the pressor response in patients with hypertension.