Spontaneous Heart Rate Variability Research Articles

Autonomic dysfunction in systemic sclerosis: time and frequency domain 24 hour heart rate variability analysis.

To evaluate the autonomic nervous control of the heart in patients with systemic sclerosis (SSc), spontaneous heart rate variability was investigated by means of time-domain and spectrum analysis of 24 h ECG ambulatory recordings in 30 SSc patients (four males, aged 45.2 +/- 9 yr, mean +/- S.D., range 27-60) and 30 age-matched healthy subjects. A significantly higher heart rate (P < 0.01) and lower circadian and spectral indices of heart rate variability (P < 0.01) were observed in SSc patients, compared with controls. A predictive value of age (P = 0.002), tachycardia (P = 0.002), circadian heart rate variability (P = 0.0025) and spectral power values (P = 0.005) for patient mortality was found. Moreover, the relative risk of death was higher (P = 0.05) in older subjects with circulating anti-Scl70. These abnormalities, detectable by a feasible, non-invasive diagnostic approach, indicate the presence of autonomic cardiac neuropathy in SSc patients.

Noninvasive assessment of cardiac autonomic function after passive tilt: the influence of ageing

Spontaneous heart rate variability (HRV), a frequency domain analysis, and induced heart rate peak (HRP) changes after passive head-up tilt, a time domain analysis, have been widely used for exploring the interactions between the autonomic nervous system and the heart [1] Decreases in both HRV and HRP have been demonstrated with increasing age as well as in autonomic failure. Autonomic reflex dysfunction is associated with an increased incidence of hypotension after induction of anaesthesia [2]. The combined analysis of both methods as well as their relations to ageing has never been reported. In order to assess the ageing effect on the autonomic modulation of heart rate (HR), the ECG recordings in 32 healthy volunteers (ages 24–71 years) were analysed. The HR was quantified in the time-domain measuring the three consecutive HRP (defined as P1, P2 and P3, see Fig. 4) induced by passive 70° head-up tilt. The HRV was quantified by means of the fast Fourier transform algorithm in both supine and upright positions, the frequency bands were ranged as medium (MF 0.04–0.15 Hz) and high (HF 0.15–0.4 Hz) frequencies. The population sample was split into two groups of 16: youngsters (<40 years, age: 32±1.4) and elderly (>40 years, age: 57±2.4). Unpaired t-test and cross-correlation were applied for statistical analysis.Fig. 4. (abstract 12).Significant differences were found between both groups (see Table 5). Significant positive cross-correlation were found between the HRP and the HRV and both parameters decreased with ageing. The amplitude of HRP showed a positive correlation with MF spectral bands of HRV, supine and upright (r=0.66 and 0.63, P<10−4 and 10−3 respectively, for n=32). These data suggest that changes in HRV as well as in HRP induced by passive tilt is at least partially controlled by a common physiological mechanism. The best variables to assess cardiovascular autonomic dysfunction in elderly patients were: 1. in the time domain analysis, the amplitude of the third peak; 2. In the frequency domain analysis, the MF band, considered as an index of cardiac sympathetic modulation.Table 5: abstract 12).The simultaneous analysis of HR on time- and frequency-domain is particularly useful in quantifying cardiovascular system ageing and could be considered as an alternative test in the assessment of autonomic failure.

Time and frequency domain analysis for the assessment of heart autonomic control in Parkinson's disease.

In order to evaluate autonomic regulation in Parkinson's disease, the heart-rate responses to passive head-up tilt and the spectral analysis of spontaneous heart rate variability in supine position were studied in 18 young (30.8 +/- 1.38 years old) and 13 aged (61.9 +/- 1.61 years) healthy controls and 13 patients with Parkinson's disease (62.9 +/- 1.55 years). Patients were evaluated in the University Hospital of the Canary Islands by a neurologist and a specialist in rehabilitation. Finally, a computerized procedure developed in the Dept. of Physiology of La Laguna University was used to quantify the autonomic regulation of heart-rate (HR) variability. In relation to the younger group, elderly controls showed a reduction in the amplitude and no differences in the latency of the three successive peaks of HR response to tilt. In relation to the elderly matched controls, the Parkinson group showed a slight decrease for the second response amplitude and no differences for both the first or third response amplitude and the latency of the three responses. In the frequency domain analysis of the spontaneous HR oscillation in supine position recording, the elderly and Parkinson groups showed a decrease in the power spectrum for low frequency (<0.04Hz; thermoregulation related band), mid frequency (0.04-0.15Hz; related to sympathetic activity in response to baroreceptors stimulation) and high frequency (0.15-0.4Hz; related to sympathovagal tonus activated by respiratory movements). In relation to elderly controls, the Parkinson group showed lower power in the three spectral bands studied. Present data support the hypothesis that both sympathetic and parasympathetic control of heart activity are impaired in Parkinson's disease and that this dysfunction can be assessed by combining time-domain and frequency-domain analysis of HR changes.

Heart rate variability in left ventricular hypertrophy

BACKGROUND--Electrocardiographic left ventricular hypertrophy and strain are associated with increased cardiac morbidity and mortality. Impaired cardiac autonomic function, assessed non-invasively by spontaneous heart rate variability on Holter monitoring, is associated with an increased risk of sudden death after myocardial infarction. AIM--To study the effect of left ventricular hypertrophy on heart rate variability. PATIENTS--36 controls and 154 patients with left ventricular hypertrophy (94 with hypertension and 60 with aortic valve disease). SETTING--Tertiary referral centre. METHODS--Heart rate variability was measured on 24 h Holter recordings by non-spectral methods. Left ventricular mass index and fractional shortening were measured by echocardiography. RESULTS--Patients with left ventricular hypertrophy had a higher left ventricular mass index (P < 0.001) and reduced heart rate variability (P < 0.001) compared with those of the controls. A continuous inverse relation was apparent between heart rate variability and left ventricular mass index (r = -0.478, P < 0.001). Heart rate variability was not affected by age, the presence of coronary artery disease in patients with left ventricular hypertrophy, or beta blocker treatment for hypertension. Multivariate analysis showed that left ventricular mass index is the most important determinant of heart rate variability. CONCLUSION--Heart rate variability is significantly reduced in patients with left ventricular hypertrophy secondary to hypertension or aortic valve disease. A continuous inverse relation exists between heart rate variability and left ventricular mass index. Impaired cardiac autonomic function in left ventricular hypertrophy may contribute to the mechanism of sudden death.

Vascular resistance and arterial pressure low-frequency oscillations in the anesthetized dog

The spontaneous variability of heart rate and arterial blood pressure was investigated in chloralose-anesthetized dogs with the left iliac vascular bed mechanically uncoupled from the central circulation. Electrocardiogram, mean arterial pressure (ABP), iliac perfusion and venous pressures, and flow (FLOW) were recorded for 5 min in steady state. Autoregressive spectral and cross-spectral analyses and digital filtering were performed. The variation coefficient (VC%), calculated from the overall variance of each signal, was 5-7%, with the exception of perfusion pressure (VC% = 1%). The frequency-related percentage of total variance was distributed among three frequency bands: two were < 0.20 Hz [lower (F1) and higher (F2; low-frequency range = F1 + F2)], and one was > 0.20 Hz (respiratory, F3). F3 was not always present in RR, which, however, oscillated also in F1 and F2, although with limited amplitude; ABP showed large respiratory and low-frequency oscillations; the FLOW oscillations were in the low-frequency range. Cross-spectral analysis showed high squared coherence in the relevant frequency bands between variables in the three couples: RR-ABP, RR-FLOW, and ABP-FLOW. Changes in RR preceded changes in ABP and in FLOW by > or = 3 s, whereas FLOW was approximately in phase opposition to ABP. It was concluded that, in the chloralose-anesthetized dog, 1) arterial pressure and heart rate oscillate with frequencies corresponding to those described in conscious humans, 2) low-frequency arterial pressure oscillations are due to changes in peripheral vascular resistance, and 3) peripheral vascular resistance does not display respiratory oscillations. Furthermore it was suggested that oscillations of vasomotor tone are generated by a rhythm of central origin and that F1 and F2 oscillations may recognize a common mechanism.

Spontaneous arrhythmias and heart rate variability in models of cardiac hypertrophy in rat: a Holter monitoring study

1From the Departments of Physiology, Paris, France *Cardiology, Pontcbaillou Hospital, 35000 Rennes, Paris, France †INSERM U127 and the Department of Cardiology, Lariboisière Hospital, 75010 Paris, France

Physiological correlates of sleep development in premature and full-term neonates

Differentiation of motor and automatic function control during different sleep states appears early in human ontogeny. Time of first appearance, magnitude of between-state differences and modifications with age depend on which particular parameters are considered. For some parameters, significant between-state differences appear at 31 weeks conceptional age (wk CA). For nearly all parameters, this difference is clear from 35 wk CA onwards. The analysis presented herein is based on studies of body movements, spontaneous skin potential responses, respiratory characteristics, heart rate and heart rate variability, and correlations between different functions. It examines clinically and neurologically normal premature and full-term neonates of 28-41 wk CA.

EFFECTS OF CLONIDINE ON BLOOD PRESSURE AND HEART RATE RESPONSES TO AN EMOTIONAL STRESS IN THE RAT: A SPECTRAL STUDY

1. The fluctuations that underlie the spontaneous variability of blood pressure (BP) and heart rate (HR) were investigated in conscious normotensive rats using power spectral analysis. 2. Air jet stimulation determined a significant BP rise associated with a tachycardia. This environmental mild stressor amplified the 195-605 mHz oscillations of HR which are under autonomic control. No habituation to this stressor was observed since a second stimulation determined similar responses. 3. Clonidine (10 micrograms/kg, i.v.) prevented the BP rise normally associated with air jet stimulation. In addition, clonidine dramatically reduced the amplitude of BP and HR oscillations in the frequency region of 195-605 mHz. 4. It is concluded that a mild emotional stressor elicits in normotensive rats a rise in BP and HR associated with modified spectral profiles reflecting sympathetic hyperactivity. Clonidine minored the effects of stress on BP and HR variability and also prevented BP elevation.

Clonidine Reduces Blood Pressure and Heart Rate Oscillations in the Conscious Rat

We investigated the effects of clonidine on the fluctuations that underlie the spontaneous variability of blood pressure (BP) and heart rate (HR) in conscious rats. Analog-to-digital conversion of the intrafemoral BP was used to determine systolic, diastolic, and mean BP and HR every 200 ms. The equidistant sampling allowed a direct spectral analysis using a fast Fourier transform algorithm. An i.v. dose of 10 micrograms/kg of clonidine markedly reduced the variability of BP and HR after 20 min as indicated by a reduction in the variances by approximately one-half of the control value for BP and to one-third of the control value for HR. At this time, clonidine had not significantly altered BP or HR. Spectral profiles of systolic BP and HR illustrated the alterations in the spontaneous oscillations underlying these variance changes. Clonidine dramatically reduced the amplitude of BP and HR oscillations in the frequency region of 195-605 mHZ, which depends on the activity of the autonomic nervous system. We suggest that an increased sensitivity of the baroreflex is responsible for the apparent better control of BP and HR with clonidine.

Spectral analysis of blood pressure and heart rate in conscious rats: effects of autonomic blockers

We investigated the fluctuations which underly the spontaneous variability of blood pressure and heart rate in conscious rats. Intrafemoral blood pressure was computed to generate evenly spaced signals (systolic, diastolic, mean blood pressure, heart rate) at 200 ms intervals. This equidistant sampling allowed a direct spectral analysis using a Fast Fourier Transform algorithm. Systolic blood pressure and heart rate exhibited low-frequency oscillations (Mayer waves, 20–605 mHz) and a high- frequency oscillation related to respiration (1855 mHz). The respiratory fluctuations in heart rate were almost abolished by vagal blockade (atropine). Heart rate fluctuations in the low-frequency regime were diminished by vagal blockade or cardiac sympathetic blockade (atenolol). The respiratory frequency fluctuations in systolic blood pressure were markedly increased by α-sympathetic blockade (prazosin). In contrast, the low-frequency oscillations in systolic blood pressure were reduced by α-sympathetic blockade. These data indicate that in conscious rats: (1) the heart rate oscillation with respiration is vagally mediated; (2) the heart rate fluctuation in the low-frequency range is jointly mediated by β-sympathetic and parasympathetic activities; (3) the respiratory oscillation in systolic blood pressure depends on fluctuations in cardiac output and is normally counteracted by the sympathetic tone; (4) the low-frequency oscillations in systolic blood pressure reflect the sympathetic activity to the resistance vessels.

Decreased spontaneous heart rate variability in congestive heart failure

Heart rate (HR) variability is a noninvasive index of the neural activity of the heart. Although also dependent on the sympathetic activity of the heart, HR variability is mainly determined by the vagal outflow of the heart. Several HR abnormalities have been described in patients with congestive heart failure (CHF); however, there are no data on HR variability in CHF patients. In the present study HR variability was assessed in 20 CHF patients and 20 control subjects from 24-hour Holter tapes. HR variability was evaluated by calculating the mean hourly HR standard deviation and by analyzing the 24-hour RR histogram. Mean hourly HR standard deviation was markedly and significantly reduced in CHF patients both over the 24-hour period (97.5 ± 41 vs 233.2 ± 26 ms, p < 0.001) as well as during most of the individual hours examined. The 24-hour RR histogram of CHF patients had a different shape and had a decreased variation compared to control subjects (total variability 356 ± 102 vs 757 ± 156 ms, p < 0.001). Thus, CHF patients with depressed ejection fraction (<30%) have a low HR variability compared to normal individuals. This result can be interpreted as adjunctive evidence for decreased parasympathetic activity to the heart during CHF.

Heart rate variability and ventricular ectopic activity in hypertensive patients.

In order to investigate whether the severity of ventricular ectopic beats in hypertensive patients is influenced by the autonomic drive to the heart, we evaluated the relationship between the degree of dysrhythmias and 24-h spontaneous heart rate variability, an index of sympatho-vagal balance at cardiac level. Ambulatory 24-h ECG monitoring was used to examine 42 untreated essential hypertensives, previously scored for the presence and the extent of hypertensive target organ damage. No significant difference was found in the prevalence of complex ventricular ectopic beats in patients with a heart rate variability that was lower and higher than the arbitrary cut off points selected to divide subjects into groups. Neither heart rate variability nor the degree of arrhythmias was correlated with blood pressure levels, whereas the degree of ectopy was influenced by the presence of target organ damage and left ventricular hypertrophy (by ECG). Our results seem to exclude an association between dysrhythmias in hypertensives and autonomic outflow to the heart as detected by the analysis of heart rate variability.

Impact of thermal vasomotor control on the heart rate variability of newborn infants

The reactivity of the periodic heart rate variability (HRV) to the thermal vasomotor control was studied during quiet sleep in a total of 20 neonates which were classified in 5 groups according to their maturity. Thermal stimulation on the peripheral skin was applied by an air blower at the rates of 5, 2.5 and 1.5 cycles/min. The oscillation of successive R-R intervals of the ECG was determined by a hybrid computer technique during thermal stimulations and compared to spontaneous HRV activity. The indices of the HRV and the total power of the periodic HRV remained unchanged during thermal stimulations. The response of the periodic HRV was selective at the spectral band corresponding to the frequency of stimulation. It was maximal at 5 cycles/min. The relative response was highly significant (P less than 0.001) and it increased with increasing maturity. The state of SGA (small for gestational age) seemed to decrease the vasomotor response of the HRV. The results suggested that the thermal vasomotor control was functional already in small preterm infants and it tended to increase with increasing maturity as does the autonomic cardiac control in general.

Patterns of sympathetic neuron activity associated with Mayer waves.

Patterns of sympathetic neuron activity associated with Mayer waves.