Showing papers on "Heart rate variability published in 1990"

Heart rate variability

Abstract: Reduced heart rate variability carries an adverse prognosis in patients who have survived an acute myocardial infarction This article reviews the physiology, technical problems of assessment, and clinical relevance of heart rate variability The sympathovagal influence and the clinical assessment of heart rate variability are discussed Methods measuring heart rate variability are classified into four groups, and the advantages and disadvantages of each group are described Concentration is on risk stratification of postmyocardial infarction patients The evidence suggests that heart rate variability is the single most important predictor of those patients who are at high risk of sudden death or serious ventricular arrhythmias

Heart rate and muscle sympathetic nerve variability during reflex changes of autonomic activity.

Abstract: Low-frequency (less than 0.15 Hz) fluctuations of heart rate are increased by maneuvers, such as standing or hemorrhage, that increase sympathetic outflow to the heart and vasculature. To test the hypothesis that low-frequency heart rate fluctuations provide an index of sympathetic efferent activity, we compared power spectral measures of heart rate variability with two measures of sympathetic outflow, peroneal nerve sympathetic activity and antecubital vein plasma norepinephrine concentrations. Autonomic outflow was varied with graded stepwise infusions of nitroprusside and phenylephrine, which lowered or raised average diastolic pressures by approximately 15 mmHg. Before vasoactive drug infusions, no spectral measure of heart rate variability correlated significantly with muscle sympathetic activity, plasma norepinephrine concentration, average heart rate, or arterial pressure. During increases of muscle sympathetic activity and probable reductions of cardiac vagal activity induced by nitroprusside, the fraction of heart rate spectral power at low frequencies, but not the absolute value, correlated significantly with muscle sympathetic activity and plasma norepinephrine. However, during reductions of muscle sympathetic activity and probable elevations of cardiac vagal activity induced by phenylephrine, no measure of heart rate variability correlated significantly with muscle sympathetic activity. These findings can be explained by a model of heart rate control in which low-frequency heart rate fluctuations result from changing levels of both the sympathetic and parasympathetic inputs to the sinoatrial node.

Short- and long-term effects of cigarette smoking on heart rate variability.

Abstract: The short- and long-term effects of cigarette smoking on autonomic cardiac regulation were investigated by power spectral analysis of heart rate variability under controlled respiration (15/min). The short-term effects were examined in 9 smokers without evidence of cardiopulmonary disorders after an overnight abstinence from smoking. The heart rate spectral component reflecting the respiratory sinus arrhythmia (0.25 Hz), a quantitative index of vagal cardiac control, decreased 3 minutes after smoking 1 cigarette (p = 0.0061) and the component reflecting Mayer wave sinus arrhythmia (0.04 to 0.15 Hz), which includes sympathetically mediated activity, increased after 10 to 17 minutes (p = 0.0124). The long-term effects were examined in 81 normal subjects comprising 25 nonsmokers, 31 moderate (1 to 24 cigarettes/day) smokers and 25 heavy (greater than 25 cigarettes/day) smokers after an overnight abstinence. Although the magnitude of the Mayer wave component was unaffected by the smoking status, the respiratory component in the supine position was smaller in the young (less than or equal to 30 years) heavy smokers than in the young nonsmokers or moderate smokers (p = 0.0078). Also, postural changes in the components, a decrease in the respiratory component and an increase in the Mayer wave component with standing, were observed in the nonsmokers but not in the heavy smokers. These results suggest that smoking causes an acute and transient decrease in vagal cardiac control, and that heavy smoking causes long-term reduction in vagal cardiac control in young people and blunted postural responses in autonomic cardiac regulation.

Evidence for an intrinsic mechanism regulating heart rate variability in the transplanted and the intact heart during submaximal dynamic exercise

Abstract: Study objective – The aim was to assess the changes in sympatho-vagal balance which occur with exercise. Design – The power spectnun of RR interval fluctuations (low frequency [LF] and high frequency components [HF]) was determined before, during, and after graded work load exercise on a cycle ergometer. The power spectrum of the respiratory signal, oxygen consumption, and respiratory volumes were also evaluated. In all subjects HF was considered to be an index of respiratory sinus arrhythmia. In normal subjects HF and LF were considered to be indices of relative vagal and sympathetic activity, respectively, whereas in heart transplant subjects HF was considered as a respiratory modulation of the intrinsic heart rate, and not dependent on autonomic tone. Heart rate variability was evaluated as RR interval variance. Subjects – 15 normal subjects (six trained cyclists and nine healthy sedentary subjects) and six orthotopic heart transplant recipients took part in the study. Measurements and main results – During the fust part of exercise, heart rate increased, RR interval variance decreased, HF decreased, and the relative amount of LF increased both in sedentary and athletic subjects, suggesting a relative increase in sympathetic tone. However, when approaching peak exercise, while heart rate further increased and the variance slightly decreased, the relative proportion of LF decreased and HF proportionally increased. At peak exercise HF accounted for 99.9% of heart rate variability in athletic subjects and for 88.9% in sedentary subjects (p<0.001 v baseline and v LF in both groups). In heart transplant subjects both the variance and the HF increased from the beginning of exercise (p<0.05), and showed a direct correlation with ventilatory variables and an inverse correlation with heart rate (r=0.794, p<0.001, multiple regression analysis). No measurable LF components could be obtained in these subjects. During recovery, while the heart rate decreased and the RR interval variance increased, there was a relative increase in LF and a relative decrease in HF in normal subjects (either sedentary or athletic). Similariy, in heart transplant subjects, there was a decrease in HF during recovery. Thus the increase in HF at peak exercise in normal subjects contrasts with all the other data which suggest a prevalence in sympathetic tone during the entire exercise and the early recovery period, but appears similar to the increase in HF observed in heart transplant subjects due to the effect of increased ventilation during exercise. Conclusions – These findings suggest that at peak exercise a non-autonomic mechanism, possibly intrinsic to the heart muscle, may determine heart rate fluctuations in synchrony with ventilation in the intact as well as in the denervated human heart.

Heart-rate variability and cardiac autonomic function in diabetes.

Abstract: Cardiac autonomic function was measured in 25 subjects with insulin-dependent diabetes mellitus and 11 control subjects. Autonomic integrity was assessed with standard tests of autonomic function and a new technique of measuring heart-rate variability (HRV) for 24 h. All of the diabetic subjects were selected on the basis of peripheral or autonomic neuropathy or long-term poorly controlled diabetes. They were divided into groups according to presence or absence of vagal neuropathy based on the results of standard tests of autonomic function. Thirteen diabetic subjects had normal autonomic function tests (group 1), and vagal neuropathy was detected in 12 diabetic subjects (group 2). All subjects were monitored by ambulatory electrocardiograph, and the recordings were played back through an analyzer that identified and timed successive pulse (R-R) intervals. HRV was measured from the standard deviation of the successive differences between R-R intervals. HRV was significantly reduced in group 1 (mean +/- SE 73 +/- 9 ms) and group 2 (65 +/- 12 ms) diabetic subjects compared with the control group (138 +/- 10 ms). The standard tests of autonomic function did not distinguish the vagal dysfunction noted with HRV monitoring in group 1 diabetic subjects compared with control subjects. Measurement of 24-h HRV can detect small changes in cardiac autonomic function compared with currently available tests.

Reproducibility and circadian rhythm of heart rate variability in healthy subjects.

Abstract: Low heart rate (HR) variability, expressed as the standard deviation of cardiac cycle lengths, has been shown to be associated with increased mortality in patients with coronary artery disease.1,2 HR variability can be easily measured from 24-hour electrocardiographic recordings using recently developed software.1,2 However, reference values for HR variability and their reproducibility in normal persons are not well studied. We estimated the reproducibility and circadian rhythm of HR variability, measured from repeated 24-hour electrocardiographic recordings, in young healthy adults to establish normal values and determine patterns of reproducibility.

Circadian rhythm of heart rate variability after acute myocardial infarction and its influence on the prognostic value of heart rate variability

Abstract: This study examined heart rate (HR) variability in patients surviving acute myocardial infarction (AMI) to find the optimum time and duration of recording of the ambulatory electrocardiogram for the prediction of the risk of sudden cardiac death, or serious arrhythmic events, or both. Twenty patients (group I) who initially survived an AMI but later experienced serious events (death or symptomatic sustained ventricular tachycardia) during a 6-month follow-up were compared with 20 patients (group II) who remained free of complications for greater than 6 months after discharge. Groups I and II were matched with regard to age, gender, infarct site, ejection fraction, and beta-blocker treatment. HR variability was assessed in the 24-hour electrocardiograms recorded during the first 2 weeks after an AMI and in various portions of the complete 24-hour recording, with both the beginning and the length of the analyzed portion varied by 20 minutes (a total of 5,113 possibilities). The maximum reduction of HR variability in group I patients was systematically found when assessing HR variability in recordings starting approximately at 6 A.M. and lasting for approximately 8 hours. In the low-risk patient, the diurnal rhythm of HR variability is more marked than in the high-risk patient and the long-term components of HR variability due to the diurnal variation must be included in the measurement of HR variability when using it as a long-term predictor of risk from arrhythmic events after an AMI.

Progression of diabetic autonomic neuropathy over a decade in insulin-dependent diabetics.

Abstract: The prognosis for diabetics with autonomic neuropathy is little known. We therefore studied the progress of young insulin-dependent diabetics, first identified as having abnormal autonomic function 10-15 years ago. We have shown that the mortality of diabetics with symptomatic autonomic neuropathy is increased, but is less than previously reported. Mortality in asymptomatic diabetics with an isolated abnormality in autonomic function tests is not increased. The heart rate variability declines at 1.02 +/- 0.47 (SD) per annum in diabetics with an initially normal heart rate variability. While symptoms of autonomic neuropathy do not usually remit even over a decade, they do not commonly progress. Three groups of young insulin-dependent diabetics had heart rate variability tested between 1972 and 1977 and have been reviewed 10-15 years later. Group A (n = 49) had symptomatic autonomic neuropathy and an abnormal heart rate variability (less than 12), Group B (n = 24) were asymptomatic yet had an abnormal heart rate variability and Group C (n = 38) were asymptomatic and had a normal heart rate variability (16-26). The 10-year survival in Group A (73.4 per cent) was less (P less than 0.05) than in Groups B (91.7 per cent) or C (89.5 per cent) which did not differ from each other. The 18 Group A deaths were due predominantly to renal failure (n = 4), myocardial infarction in patients with nephropathy (n = 3) and sudden unexpected death (n = 3). The chief symptoms of autonomic neuropathy--diarrhoea, postural hypotension and gustatory sweating, were very persistent but did not necessarily deteriorate or become disabling in the majority of patients. The development of autonomic symptoms in asymptomatic patients with abnormal heart rate variability was uncommon over a decade.

Diurnal variations in vagal and sympathetic cardiac control.

Abstract: To investigate the diurnal variation in autonomic cardiac control, the magnitudes of the power spectral components of supine and standing heart rate variability were measured during controlled resp...

Circadian variation of heart rate variability

Abstract: Study objective – The aim of the study was to examine the circadian variation in heart rate variability and to test the hypothesis that the variation is due to vagal influence. Design – Human subjects, some with vagal neuropathy, underwent ambulatory 24 h electrocardiographic monitoring, the recordings being played back through an analyser which identified and timed successive pulse (R-R) intervals. Heart rate variability was measured for each 30 min period over 24 h as the standard deviation of the successive differences between R-R intervals, which filtered out low frequency components of heart rate variability that were not autonomic in origin. Modelled curves of heart rate variability were compared using analysis of variance. Subjects – The subjects were aged between 33 and 65 years and were matched in three groups for age and sex. There were 11 healthy controls, 12 insulin dependent diabetics and seven alcoholics with vagal neuropathy. Results – A significant circadian variation in heart rate variability was present, characterised by a rise during sleep. Mean heart rate variation was significantly reduced in groups with vagal neuropathy, although the amplitude of the cycle and time of peak variability was not significantly different. The circadian variation was sustained regardless of the degree of vagal neuropathy. Conclusions – The cycle of heart rate variability is not dependent on vagal interaction. It may be due to fluctuations in sympathetic activity affecting beat to beat variability.

Dynamic changes in cardiac vagal tone as measured by time-series analysis.

Abstract: A time-series analysis of heart rate variability was evaluated as a marker of cardiac vagal tone using well-characterized autonomic interventions. Heart period (R-R interval) was recorded in 14 mongrel dogs from which the amplitude of the respiratory sinus arrhythmia (0.24-1.04 Hz) was determined. Exercise elicited significant (P less than 0.01) reductions in the index of vagal tone (control 6.3 +/- 0.3 ln ms2 vs. exercise 2.4 +/- 0.4 ln ms2) that were accompanied by significant (P less than 0.01) increases in heart rate (control 123.1 +/- 5 vs. exercise 201.0 +/- 7.7 beats/min). The vagal tone index remained greater than 0 throughout exercise. After propranolol HCl pretreatment, the vagal tone index rapidly decreased toward zero (control 6.2 +/- 0.5; exercise 0.7 +/- 0.3 ln ms2), despite significantly lower increases in heart rate (control 109.3 +/- 4.2; exercise 178.0 +/- 7.6 beats/min). Atropine given during exercise evoked significantly greater increases in heart rate in the control (+48.7 +/- 7.9 beats/min) vs. propranolol (+14.2 +/- 6.7 beats/min) conditions. These data suggest that 1) high levels of cardiac vagal tone remain during exercise; 2) vagal withdrawal is largely responsible for the heart rate increase after beta-adrenergic receptor blockade; and 3) time-series analysis of the R-R interval can provide a dynamic and noninvasive index of cardiac vagal tone.

Effects of transdermal scopolamine on heart rate variability in normal subjects

Abstract: A decrease in cardiac parasympathetic tone is a recognized finding in patients with ischemic heart disease, sudden cardiac death and heart failure, correlating closely with disease severity and overall survival. To study the clinical potential of vagomimetic intervention, the effect of transdermal scopolamine on fluctuations in heart rate was studied in 32 healthy adult subjects using both time-domain (mean RR interval, standard deviation of the mean RR interval, mean of the differences between consecutive RR intervals) and frequency-domain measures (spectrum analysis of 128 consecutive RR intervals) of heart rate variability. After an exposure of 24 hours, transdermal scopolamine resulted in a significant increase in all indexes tested. The increase was most pronounced in the 0.25-Hz respiratory peak of the RR interval power spectrum, compatible with a strong vagomimetic mode of action of transdermal scopolamine. Results indicate that transdermal scopolamine may have potential merit as a selective vagotonic agent in certain patients with myocardial infarction, heart failure or ventricular arrhythmias.

Spectral analysis of heart rate variability signal and respiration in diabetic subjects

Abstract: The paper deals with methods of processing ECG and respiration signals which aim at detecting parameters whose values may be correlated to normal and diabetic subjects with or without cardiovascular autonomic neuropathy (CAN). Beatto-beat R-R duration values of the ECG and discrete series of respiration are obtained from original signals using a recognition algorithm. Power spectrum analysis (autospectra, cross-spectra and coherence via autoregressive modelling) is carried out on segments of about 200 consecutive cardiac cycles. Spectral parameters of the R-R variability signal are obtained as follows: total power, power of low-frequency (LF) and high-frequency (HF) components, power of the signal which is (or is not) coherent with respiration, in absolute or in percentage values. The experimental protocol considers 40 diabetic patients (21 of whom have diabetic neuropathy) and 14 normals in three different conditions: resting, standing and controlled respiration. The developed spectral parameters seem sensitive enough to differentiate between normal and pathological subjects. These parameters may constitute a quantitative means to be edded to the classical diabetic tests for the diagnosis of cardiovascular autonomic neuropathy.

From various kinds of heart rate variability to chronocardiology

Abstract: We wish to show that cardiologic variability can be examined with benefit by the concepts and computer methods of chronobiology, the science (logos) of life's (bios) time (chronos) structure. From heart rate data in a recent article, 1 dynamic end points are obtained to quantify health. 2 On a group basis, when conventional end points applied to 2 sets of electrocardiographic records fail to separate for sudden adult death, chronobiologic end points already do so. 2 Novel information not obtained by conventional location or dispersion indexes 3 can be provided by the computation of the circadian and other amplitudes. 4 Beyond sudden death after myocardial infarction, the importance of these amplitudes has been demonstrated in several additional cases of cardiologie interest 2 : (1) the amplitudes of several rhythmic components of systolic or diastolic blood pressure separate groups of human newborns with a positive versus negative family history of high blood pressure or cardiovascular diseases, or both, when the mean based on the same data does not do so; (2) in children ≥9 years old, the circadian amplitude and acrophase of blood pressure, but not the mean, separate groups at low or high risk of developing high blood pressure later in life; (3) at 15 years of age, the circadian amplitude of diastolic blood pressure, but not the mean, correlates with the thickness of the interventricular septum of the heart.

Sympathetic--parasympathetic interaction and sudden death.

Abstract: The effects of the autonomic nervous system on malignant arrhythmias, particularly in the setting of ischemic heart disease, have been widely investigated and described. Specifically, it has been shown that while sympathetic hyperactivity is arrhythmogenic, an increased vagai activity often exerts a beneficial effect. New insights on the relationship between autonomie activity and sudden cardiac death have been obtained in conscious dogs in which a healed myocardial infarction, acute myocardial ischemia, and exercise are combined. In this chronic animal model it was shown that myocardial infarction reduces baroreflex sensitivity and heart rate variability (markers of vagai reflex and tonic activity to the heart) and that a depressed baroreflex sensitivity or a reduced heart rate variability after myocardial infarction indicate an increased risk for ventricular fibrillation. The validity of these experimental observations was confirmed in clinical studies in patients with a myocardial infarction. The protective effect of vagai activity was further confirmed in two experimental studies in which muscarinic stimulation, both electrically and pharmacologically induced, was able to prevent ventricular fibrillation during acute myocardial ischemia. These observations have led to new research directions. At the experimental level, the effect of Gi proteins activity blockade by pertussis toxin on the cardiac response to vagai activation is currently evaluated in conscious dogs. At the clinical level, the prognostic value after myocardial infarction of baroreflex sensitivity and of heart rate variability will be tested in a large, multicenter, prospective study.

QT Prolongation on the Electrocardiogram in Diabetic Autonomic Neuropathy

Abstract: Patients with Type 1 diabetes and autonomic neuropathy have an increased risk of sudden death for which the mechanism remains obscure. Prolongation of the QT interval on the electrocardiogram may occur with sympathetic dysfunction and is also associated with ventricular arrhythmia and sudden death. We have therefore measured the QT interval in patients with Type 1 diabetes with normal, borderline, and definitely abnormal autonomic function tests and in non-diabetic control subjects. The maximum QT interval was measured on 12-lead electrocardiograms recorded at rest and then plotted against the RR interval. The QT interval was above the upper 95% limit for the non-diabetic control subjects in 5 diabetic patients with abnormal autonomic function tests (33%), but in no cases with normal or borderline tests. Multivariate analysis confirmed that autonomic score contributed significantly (p less than 0.025) to the variance in QT interval. The raw Valsalva ratio alone also contributed significantly to the variance in QT interval (p = 0.025). Heart rate variability, heart rate response to standing, age, sex, and the presence of symptoms of autonomic neuropathy did not contribute significantly.

Spectral characteristics of heart rate variability before and during postural tilt. Relation to aging and risk of syncope

Abstract: Fourier analysis of heart rate (HR) may be used to characterize overall HR variability as well as low- and high-frequency components attributable to sympathetic and vagal influences, respectively. We analyzed HR spectral characteristics of 12 healthy young (18-35 years) and 10 healthy old (71-94 years) subjects before and during 60 degrees head-up tilt. Total spectral power in the 0.01-0.40-Hz frequency range and low-frequency (0.06-0.10 Hz) and high-frequency (0.15-0.40 Hz) components of the HR power spectrum were significantly lower in old than in young subjects in supine and upright positions. To characterize and compare overall HR variability in young and old subjects, we computed the regression lines relating the log amplitude to the log frequency of the supine HR spectra (l/fx plots). The regression lines for old subjects were lower and steeper (mean slope, -0.78 [5%, 95% confidence limits (CL), -0.73, -0.83]) than in young (mean slope, -0.67 [CL, -0.62, -0.72]), indicating not only reduced overall spectral amplitude but also relatively greater attenuation of high-frequency HR components in the old subjects. This finding illustrates a novel way to quantify the loss of autonomic influences on HR regulation as a function of age. During postural tilt, HR variability was unchanged in the old subjects. For the entire group of young subjects, total HR variability increased during tilt. Six young subjects developed vasovagal syncope during tilt, enabling us to examine differences in the HR spectra of these subjects while they were asymptomatic before syncope.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of long term components of heart rate variability for the further prognosis after acute myocardial infarction

Abstract: Study objective – The study examined heart rate variability to find out whether shorter ECG records can predict long term mortality following acute myocardial infarction as efficiently as 24 h recordings. Design – Heart rate variability was assessed in 24 h electrocardiograms recorded during the first 2 weeks following acute myocardial infarction and in separate l h portions of the complete recording. The spectral analysis of complete 24 h records was performed and different short and long term components of heart rate variability were used to distinguish between patients with and without later complications. Subjects – 20 patients who initially survived acute myocardial infarction but later experienced serious events (death or symptomatic sustained ventricular tachycardia) during a 6 month follow up (group I) were compared with 20 patients (group II) who remained free of complications for more than 6 months after discharge and who were matched with group I for age, gender, infarct site, ejection fraction, and β blocker treatment. Measurements and main results – The distinction based on components limited to changes of heart rate within periods ≤1 h was as significant (p<0.00l, paired t test) as when using the components limited to changes of periods ≤10 h. However, heart rate variability of separate 1 h portions of the complete 24 h records differed between the groups significantly only for certain 1 h intervals of the day (the p values varied from 0.2 to 0.0005). Conclusions – Whilst the maximum value of short term heart rate variability is sufficient for stratifica- tion of the high risk post-myocardial infarction patients, an arbitrarily selected short term ECG recording is unlikely to register the maximum heart rate variability. It is concluded that the heart rate variability assessed from arbitrary 1 h electrocardiographic records is not as prognostically important as the variability estimated from 24 h recordings.

Noninvasive methods to study autonomic nervous control of circulation.

Abstract: The major findings and conclusions of this study are the following: 1. Indirect evidence suggested that nervous afferentation from the cutaneous thermoreceptors and nervous efferentation to the skin blood vessels mediated the 0.01-0.10 Hz thermally entrained response of the oscillations of the forearm skin blood flow in supine and upright subjects. 2. Postural stimulation decreased skin blood flow and oscillations of skin blood flow. The 0.10 Hz thermal stimulation interacted with the postural stimulation by increasing the oscillations of skin blood flow from sitting to standing position on the contrary to the expected postural effect. 3. The thermal entrainment of periodic heart rate variability was not constant. Both 0.01-0.10 Hz thermal and postural and sensory stimulations affected the periodic heart rate variability selectively at the frequency of the periodic stimulus or the less than 0.12 Hz frequencies. 4. The periodic thermal stimulation had a frequency-selective effect on the oscillations of the neonatal heart rate. The thermally stimulated reactivity increased with an increased maturity of a neonate. 5. Intermittent tilting had a frequency-selective influence on the oscillations of heart rate. Continuous deep breathing entrained the periodic heart rate variability. The estimation of the power spectral density function of heart rate quantified the chronotropic respiratory effects more accurately than the statistical indices of heart rate variability. 6. Response of periodic heart rate variability to intermittent tilting and deep breathing stimulation suggested normal vagal control of heart rate in children with juvenile diabetes and juvenile rheumatoid arthritis. 7. Normal vagal bradycardic response was found during the phase IV of the Valsalva manoeuvre in functionally abnormal nervous control of circulation. The simulated diving test was not found clinically useful. 8. The ratio of electrical to electromechanical systole of the heart was greater than 1.00 both at rest and during the orthostatic, Valsalva and diving reflex tests. This finding suggested constantly exaggerated sympathetic cardiac inotropic control during vagal and sympathetic stimulation of heart rate. 9. The decreased thermally stimulated heart rate variability was interpreted as an indication of inhibited vagal modulation of the sinoatrial node of the heart in subjects with dystonic symptoms and orthostatic intolerance. The exaggerated sympathetic reactivity of these subjects explained the abnormally high gain of periodic heart rate variability to 0.01-0.03 Hz periodic thermal stimulation.

Effect of posture on spontaneous and thermally stimulated cardiovascular oscillations.

Abstract: Study objective – The aim of the study was to investigate the effect of posture on thermally stimulated cardiovascular oscillations. Design – The effect of increased gravitational stress (rising from sitting to standing position) on the thermally stimulated cardiovascular oscillations was measured in young male volunteers. Extensive cardiovascular function data were obtained using a cardiovascular investigation protocol. Subjects – The volunteers were five fit young men, aged 20-21 years. Experiments and main results – Cardiovascular changes from sitting to standing indicated increased sympathetic and decreased parasympathetic influence on heart and skin blood vessels; mean heart rate increased, beat to beat heart rate variability diminished, high frequency periodic heart rate variability decreased, low frequency heart rate oscillations and ratio of low frequency to high frequency heart rate variability increased, mean skin blood flow and oscillations of skin blood flow decreased (all p<0.05). Thermal skin stimulation at 0.01-0.10 Hz frequency increased both sitting and standing 0.10 Hz periodic heart rate variability (p<0.05), and 0.10 Hz thermal stimulation entrained the heart rate oscillations in sitting and standing subjects (p<0.05). In contrast, skin blood flow oscillations in sitting subjects decreased, while in standing subjects it increased during 0.10 Hz thermal stimulation compared to the corresponding prestimulus values (p<0.04). Conclusions – On the basis of previous physiological experiments, these results suggest coupling between thermoregulatory and 0.10 Hz reflex activities.

Spectral analysis of short-term heart rate variability in diabetic patients.

Abstract: Spectral analysis of short term R-R variability estimated by autoregressive modelling is a recently developed method for the evaluation of cardiovascular autonomic function. This new test also allows to study the interaction on heart rate variability of parasympathetic and sympathetic system. The sensitivity of the method for detection of cardiovascular autonomic neuropathy has been evaluated in a group of diabetic patients in comparison with the sensitivity of a battery of the most commonly used cardiovascular autonomic tests (deep-breathing, lying-to-standing, Valsalva Manoeuvre, postural hypotension and hand grip). Spectral analysis of heart rate variability resulted in a very sensitive method for early detection of diabetic autonomic neuropathy, about one-fourth of diabetic patients with normal traditional cardiovascular autonomic tests had abnormal results at spectral analysis. Both sympathetic and vagal control of heart rate resulted alterated in diabetic autonomic neuropathy.

EEG burst-suppression pattern correlates with the instantaneous heart rate under isoflurane anaesthesia.

Abstract: The correlation between electroencephalogram (EEG) and instantaneous heart rate was studied in deep isoflurane anaesthesia when the EEG showed a burst-suppression pattern in 15 patients aged 19-39 years. At the onset of EEG burst, the heart rate started to accelerate, and at the onset of suppression it started to decelerate. These changes in heart rate are similar to those we have previously described with enflurane, despite several differences in the effects of these two anaesthetics on EEG and on the cardiovascular system. We hypothesise that the heart-rate changes are due to central inhibition mediated by the vagus nerve during EEG suppression.