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PubMedDate not supplied

Spectral analysis of spontaneous heart rate variation in diabetic patients.

In 28 diabetic patients and 62 control subjects spectral analysis of spontaneous beat-to-beat RR interval variations was performed. The spectral analysis focused on the dominant frequency of the mid-frequency band (0.04-0.12 Hz) or baro-oscillatory phenomenon (BOP). Compared with control subjects the dominant frequency of the BOP (BOP frequency) in the diabetic patients was lower (p less than 0.001), and the difference increased with age. The shift of the BOP frequency was positively correlated with the reduced variation in heart rate during deep breathing (r = 0.80, p less than 0.001) in the diabetic patients. These findings indicate that determination of the BOP frequency is a useful method for assessing cardiovascular autonomic function, supplementary to the known cardiovascular reflex tests. Measurement of the BOP frequency has the advantage that no active patient co-operation is required.

Adolescent↗
PubMed1994

Power spectral analysis of cardiovascular variability in patients at risk for sudden cardiac death.

The time series of successive heart periods present important variations around its mean value, determining the phenomenon of heart rate variability (HRV), assessed with both time and frequency domain approaches. A low standard deviation of the heart period (a time domain index of HRV) is a powerful prognostic indicator of sudden coronary death in patients recovering from acute myocardial infarction. Spectral analysis of HRV usually demonstrates two major components: indicated as LF (low frequency, approximately 0.1 Hz) and HF (high frequency, approximately 0.25 Hz). They are defined by center frequency and associated power, which is expressed in msec2 or normalized units. When assessed in normalized units, LF and HF provide quantitative indicators of neural control of the sinoatrial node. Numerous experimental and clinical studies have consistently indicated that the LF component is a marker of sympathetic modulation and HF a marker of vagal modulation; the LF/HF ratio is a synthetic index of sympathovagal balance. In the analysis of 24-hour Holter recordings of normal subjects, a circadian rhythmicity of spectral markers of sympathetic and vagal modulation is clearly present, with a sympathetic predominance during the day and a vagal predominance during the night. In patients recovering from an acute myocardial infarction, spectral analysis of HRV revealed an increased sympathetic and decreased vagal activity during early convalescence, and a return to their normal balance by 6 to 12 months. A clear increase of LF was also evident in patients studied within a few hours of the onset of symptoms related to an acute myocardial infarction, independent of its location. Similarly, LF increased during transient myocardial ischemia. An increase in markers of sympathetic activity has also been observed prior to episodes of malignant arrhythmias. Spectral analysis of HRV could help in the understanding of the role of abnormal neural mechanisms in sudden coronary death, thus contributing to its prevention.

Death, Sudden, Cardiac↗
PubMed2000

Critical value of baroreflex sensitivity determined by spectral analysis in risk stratification after myocardial infarction.

The risk of cardiac death in patients after MI is predicted by a decreased baroreflex sensitivity (BRS). The critical value of BRS based on phenylephrine administration is 3 ms/mmHg. The aim of this study was to determine the critical value of BRS assessed by spectral analysis of spontaneous fluctuations in pulse intervals and blood pressure. Digital blood pressure was recorded noninvasively (3 min, controlled breathing 0.33 Hz) in 112 patients, 8-18 days after MI. Nine patients died during the first year after MI. BRS was determined as the gain between the spectrum of the variability of systolic blood pressure and the cross-spectrum between the variability of pulse intervals and systolic blood pressure. The gain at the frequency of 0.1 Hz was taken as the measure of BRS. Sensitivity, specificity, and the positive predictive value were calculated in the range of 1-10 ms/mmHg in steps of 1 ms/mmHg. The value of BRS above which sensitivity no longer increases and specificity decreases was taken as the optimal value. The critical value of BRS determined by spectral analysis was 3 ms/mmHg (sensitivity 77%; specificity 71%). In conclusion, the spectral critical value of BRS determined by spectral analysis of spontaneous fluctuations in pulse intervals and blood pressure corresponds to the value determined by the phenylephrine method.

Baroreflex↗
PubMed1997

Abnormal passive head-up tilt test in subjects with symptoms of anxiety power spectral analysis study of heart rate and blood pressure.

Previous reports that subjects with anxiety symptoms are at higher risk of sudden death may imply that anxiety induces stable sympathetic hyperactivity. To address this subject, in persons with and without anxiety symptoms, we evaluated autonomic nervous system activity by power spectral analysis of heart-rate and arterial-pressure variability at baseline (rest) and after sympathetic stress (tilt). The 117 subjects selected (56 men and 61 women, age range 23-87 years) were subdivided by questionnaire into three groups: 49 subjects (mean age 55.8+/-2.8 years) had no anxiety symptoms; 36 (mean age 56.8+/-3.6 years) had one anxiety symptom; and 32 (mean age 55.0+/-2.9 years) had two or more anxiety symptoms. Power spectral analysis recognizes three main components: high frequency (HF), chiefly reflecting vagal efferent activity; low frequency (LF), reflecting sympathetic activity; and very-low-frequency (VLF). The ratio of low- to high-frequency powers (LF:HF) of heart rate variability provides a measure of sympathovagal balance. Power spectral analysis showed that subjects with two or more anxiety symptoms had significantly lower resting values for all power spectral components of heart rate variability: total power (TP), VLF, LF, and HF than did symptomless controls (P<0.05). The highest anxiety-score groups also had a higher baseline LF:HF than the other two groups (P<0.05). Their resting LF:HF ratio correlated positively with anxiety symptom scores (r=0.72, P<0.0001). Tilt induced opposite results: the highest anxiety-score groups had a significantly lower LF:HF ratio; the ratio correlated inversely with their anxiety scores (r=-0.69; P<0.0001). Recordings of resting systolic arterial pressure variability showed that the group with two or more anxiety symptoms had significantly higher LF power (P<0.05) than symptomless controls. Our findings suggest that persons with high anxiety scores have baseline cardiac sympathetic hyperactivity. They also have low heart-rate variability, possibly explaining their susceptibility to sudden cardiac death.

Adult↗
PubMed2000

Assessment of autonomic cardiovascular changes associated with recovery from anaesthesia in children: a study using spectral analysis of blood pressure and heart rate variability.

Recovery from anaesthesia is associated with large changes in cardiovascular autonomic activity, which are poorly documented in children. This study was undertaken to investigate the cardiovascular autonomic activity in anaesthetized and recovering children, using a noninvasive approach based on spectral analysis of heart rate (HR) and blood pressure (BP) variability. Ten children (aged 5-13 years) undergoing major surgery were studied. Continuous HR and BP were recorded using a noninvasive device during deep anaesthesia and recovery. Spectral analysis was used to determine the main oscillatory components of HR and BP signals. For each power spectrum, the frequency components were identified as follows (i): the low frequency (LF) component (0.04-0.14 Hz) both parasympathetically and sympathetically mediated for HR and corresponding to vasomotor sympathetic modulation for BP; and (ii) the high frequency (HF) component (0.2-0.6 Hz) parasympathetically mediated for HR, and reflecting mechanical influence of ventilation on cardiac output for BP. In addition, the LF : HF ratio for HR, reflecting the cardiac sympathovagal balance, was calculated. Under deep anaesthesia, HR variability and BP variability were very low and mainly due to mechanical influence of intermittent positive pressure ventilation. Conversely, the recovery period was associated with a marked increase of HR and BP overall variability. Compared to anaesthesia, spectral analysis of HR and BP revealed that the LF component of BP and HR spectra increased 40-fold during recovery; the LF : HF ratio of HR was also increased during recovery (0.1 +/- 0.1 versus 1.3 +/- 1.2, P=0.008). The results of this study demonstrate that the recovery period is associated with an increase of cardiovascular sympathetic drive in children after major surgery.

Adolescent↗
PubMed1988

The use of EEG spectral analysis after thiopental bolus in the prognostic evaluation of comatose patients with brain injuries.

The value of EEG data and evoked potentials (EP), combined with the patient's clinical status, are important parameters used to document decerebration, but their reliability is at its best when the decerebration is nearly complete. Based on spectral analysis of the EEG we compiled criteria for the cerebral function with application of agents known to alter the normal EEG. We found very distinct and different pattern responses in spectral analysis of the EEG after the bolus injection of 100-500 mg Thiopental, correlating well with the patient's prognosis. In a study with 40 patients, those who showed a significant increase of power in all frequencies, especially a short lasting increase in beta (3-7 min) survived in 84%. On the other hand, all the patients who had a decrease of absolute power in all frequency band died, even when brainstem reflexes and various pain reactions were still present. Spectral analysis after Thiopental bolus injection also permits a very immediate assessment of slight improvements or deteriorations in the clinical course.

Adolescent↗
PubMed1995

Arterial spontaneous rhythmic contractile activity in humans and rats: spectral analysis and regulatory mechanisms.

OBJECTIVE: Many experimental observations have demonstrated the presence of spontaneous cyclic vasomotor activity (CVA) in large and small arteries. This study aimed to evaluate the characteristics of spontaneous CVA in rat and human resistance arteries, and to investigate its possible interference with the evaluation of sympathetic activity by means of spectral analysis of blood pressure in vivo. DESIGN AND RESULTS: In study 1 we examined small mesenteric arteries of spontaneously hypertensive rats and Wistar-Kyoto rats, as well as small omental arteries of normotensive subjects and hypertensive patients (Mulvany and Halpern technique). CVA was enhanced by the agonists of nitric oxide release, and was abolished by the inhibitors of nitric oxide or cyclic GMP synthesis. A potassium channel, which is barium- and zinc-sensitive and tetraethylammonium-insensitive, seems to play a crucial role in the genesis of CVA. In rats and in humans the frequency of CVA fell exactly in the frequency band ('low frequencies') of power spectral analysis of blood pressure usually considered to be an 'index of sympathetic activity'. In study 2, a power spectral analysis of blood pressure variability before and after intra-arterial infusion of noradrenaline or acetylcholine was performed in 18 patients with mild-to-moderate hypertension. The absolute and normalized spectral power of the low-frequency systolic blood pressure peak increased remarkably after noradrenaline and acetylcholine infusion, while its central frequency shifted from 0.10 Hz to approximately 0.06 Hz, exactly the frequency of CVA observed in vitro. CONCLUSIONS: A potassium channel appears to be involved in the genesis of CVA. Also, CVA might contribute to the blood pressure variability independently of the autonomic nervous system activity, and thus probably plays a role in the genesis of the low-frequency peak in the rat and in humans.

Acetylcholine↗
PubMed1996

Spectral analysis of ventricular fibrillation and closed-chest cardiopulmonary resuscitation.

This study was designed to assess the interference by closed-chest cardiopulmonary resuscitation (CPR) on the ventricular fibrillation (VF) ECG signal in a porcine model of cardiac arrest and to elucidate which variable of VF spectral analysis reflects best myocardial blood flow and resuscitation success during CPR. Fourteen domestic pigs were allocated to receive either 0.4 U/kg vasopressin (n = 7) or 10 ml saline (n = 7) after 4 min of VF and 3 min of CPR. Using radiolabeled microspheres, myocardial blood flow was determined during CPR before, and 90 s and 5 min after, drug administration. Using spectral analysis of VF, the median frequency, dominant frequency, edge frequency and amplitude of VF were determined simultaneously and before the first defibrillation attempt. Using filters in order to specify frequency ranges, stepwise elimination of mechanical artifacts resulting from CPR revealed that at a frequency bandpass of 4.3-35 Hz, median fibrillation frequency has a sensitivity, specificity, positive and negative predictive value of 100% to differentiate between resuscitated and non-resuscitated animals. The best correlation between myocardial blood flow and fibrillation frequency was found at a median frequency range of 4.3-35 Hz. We conclude that spectral analysis of VF can provide reliable information relating to successful resuscitation. In this model after elimination of oscillations due to mechanical CPR, median fibrillation frequency best reflects the probability of resuscitation success.

Analysis of Variance↗
PubMed1997

Cross spectral analysis in assessment of baroreflex gain in patients with coronary artery disease.

BACKGROUND: Interest in determination of baroreflex sensitivity in clinical practice is growing because of its prognostic information in patients with heart disease. The purpose of the present study was to assess the feasibility of cross spectral analysis in the determination of baroreflex gain from spontaneous RR interval and systolic pressure fluctuations, and to compare the results to the traditional pharmacological method in patients with coronary artery disease. Methods. We measured the gain and time lag between RR interval and systolic pressure variabilities in the frequency domain, and compared baroreflex indexes obtained by this technique with standard phenylephrine tests in 32 patients with coronary artery disease. Results. Cross spectral analysis by fast Fourier transform techniques yielded acceptable (> 0.5) coherence between systolic pressure and RR interval in the mid- (0.07-0.15 Hz) and in the respiratory-frequency (0.15-0.40 Hz) band fluctuations in 30 patients (94%), with mean coherences of 0.69 and 0.74. The mean phase difference in the mid-frequency hand was greater than in the respiratory-frequency band (-83 vs -23 degrees, P < 0.001), suggesting that the mid-frequency fluctuations of RR intervals followed nearly 2 seconds after pressure changes, while respiratory-frequency fluctuations of RR intervals occurred nearly concomitantly with systolic pressure. The mean baroreflex slope derived from the bolus phenylephrine technique was 6.2 ms/mmHg (range 1.6-16.0), 5 patients had an abnormally low (<3 ms/mmHg) baroreflex sensitivity. Baroreflex gain determined by cross spectral analysis from the mid-frequency band correlated significantly (r = 0.60, P < 0.001, n = 27) with the baroreflex gain determined by the phenylephrine test, while the correlation in the respiratory-frequency band was not significant (r = 0.35, P = 0.09, n = 26). Conclusions. Baroreflex slopes derived from cross spectral techniques provide reliable (but not perfect) information regarding baroreflex gain derived from the clasic phenylephrine technique, even in patients with depressed baroreflex responses. Cross correlation calculation of spontaneous baroreflex slopes should be limited to data in the mid-frequency range, where the slopes are likely to reflect simple baroreflex physiology.

Adult↗
PubMed2001

Limitations of the use of spectral analysis of heart rate variability for the estimation of cardiac sympathetic activity in heart failure.

Spectral analysis of heart rate variability has gained popularity as a simple, non-invasive tool for assessing autonomic function in both normal subjects and in patients in a variety of clinical settings. However, the use of this method as a means of estimating the magnitude of cardiac sympathetic activation in individual patients with heart failure has proved disappointing, with a lack of concordance with more direct measures of sympathetic outflow. This review will describe the rationale involved in using sympathetic indices obtained from spectral analysis of heart rate variability to assess cardiac sympathetic outflow in normal subjects and patients with heart failure. The specific limitations and technological concerns that dictate how it may most effectively be used in this patient population will be discussed.

Animals↗
PubMed1999

Comparison between spectral analysis and the phenylephrine method for the assessment of baroreflex sensitivity in chronic heart failure.

Baroreflex sensitivity assessed by means of the phenylephrine test plays a prognostic role in patients with previous myocardial infarction, but the need for drug injection limits the use of this technique. Recently, several non-invasive methods based on spectral analysis of systolic arterial pressure and heart period have been proposed, but their agreement with the phenylephrine test has not been investigated in patients with heart failure. The two methods (phenylephrine test and spectral analysis) were compared in a group of 49 patients with chronic congestive heart failure both at rest and during controlled breathing. The linear correlation and the limits of agreement between the phenylephrine test slope and the alpha-index [alpha(c); corrected by the coherence function between the interbeat interval (RR interval) and systolic arterial pressure] were evaluated. Only 16 patients had a measurable alpha-index at rest in both the low-frequency (LF) and high-frequency (HF) bands; the alpha(c)-index allowed measurements in all patients. It correlated moderately with the phenylephrine test slope at rest (r=0. 71 and P<0.001 in LF; r=0.57 and P<0.001 in HF) and during controlled breathing (r=0.51 and P<0.001 in LF; r=0.63 and P<0.001 in HF). Multivariate regression analysis showed that only alpha(c)LF during rest and alpha(c)HF during controlled breathing contributed significantly to baroreflex gain estimation. However, the agreement between methods was weak; the normalized limits of agreement and bias were -162 to 243% (0.46 ms/mmHg) for alpha(c)LF and -185 to 151% (-0.99 ms/mmHg) for alpha(c)HF. Thus the comparison between baroreflex sensitivity measurements obtained by the phenylephrine test and spectral analysis showed a moderate correlation between the two methods; however, despite the linear association, a consistent lack of agreement between the two techniques was found. Because both systematic and random factors contribute to the difference, these two techniques cannot be considered as alternatives for the assessment of heart failure.

Adult↗
PubMed1999

[The Ewing test for autonomic neuropathy and spectral analysis of heartrate variability aid in the diagnosis of Charcot's osteoarthropathy].

UNLABELLED: The objective of the work was to evaluate the contribution of examining autonomic neuropathy in diabetic patients to early diagnosis of Charcot's osteoarthropathy by classical Ewing's tests, as well as the more recent method--spectral analysis of heart rate variability. The authors examined 18 diabetic patients in the early stage of Charcot's osteoarthropathy and the results were compared with a group of 30 subjects matched for age and sex. The results of examination by Ewing's test (heart rate variability during deep breathing, in orthostasis and during Valsalva's manoeuvre and blood pressure changes during orthostasis) revealed autonomic neuropathy in all examined patients, in one subject incipient neuropathy and in 17 of 18 patients manifest or severe neuropathy. The patients differed from controls highly significantly in all parameters of Ewing's tests with the exception of parameter 30:15 in orthostasis. The greatest sensitivity was recorded in the examination of the I-E difference during deep respiration. RRmax/RRmin and the brake index in orthostasis and Valsalva's ratio. The lowest sensitivity was recorded in the examination of the orthostatic fall of blood pressure. On spectral analysis the patients differed highly significantly from controls in all investigated parameters, the highest discriminating value was found in parameters of the total spectral power in the standing position (2) and the power in the low-frequency area in position 2, the first parameter alone was correctly discriminated in 94%. SUMMARY: Examination of autonomic neuropathy significantly improves the diagnosis of Charcot's osteoarthropathy. In addition to the classical Ewing tests spectral analysis of heart rate variability proved also a suitable method for its evaluation.

Arthropathy, Neurogenic↗
PubMedDate not supplied

Spectral analysis during fatigue. Surface and fine wire electrode comparison.

Fine wire (FW) intramuscular electrodes and spectral analysis have not previously been used to quantify metabolic muscle fatigue in deep muscles not accessible with surface electrodes. This study compares initial median frequency (IMF) and decline in median frequency with fatigue (SLOPE) using surface and FW electrodes. Eighteen men performed isometric biceps contractions for 100 s. Electromyographic signals were collected using FW and surface electrodes. The recordings of SLOPE was greater with FW (-0.44 v -0.23 %IMF/s) and IMF was higher (195 v 69 Hz). Intrasession reliability for slope was better with FW electrode (intraclass correlation coefficient (ICC) = 0.74; P<0.0001) than with the surface electrode (ICC = 0.43; P = 0.006), but intersession reliability was best with the surface electrode (ICC = 0.50; P = 0.03). Spectral analysis using FW electrodes provides earlier detection of muscle fatigue and can be used in deep muscles, but the reliability must be improved before clinical application.

Adult↗
PubMed1997

Blunted parasympathetic modulation in salt-sensitive patients with essential hypertension: evaluation by power-spectral analysis of heart-rate variability.

OBJECTIVE: To evaluate autonomic nervous function by power-spectral analysis of heart-rate variability in salt-sensitive and non-salt-sensitive patients with essential hypertension under the conditions of low and high salt intakes. DESIGN AND METHODS: The blood pressures, heart rates, and electrocardiogram R-R intervals of 20 hypertensive patients were measured at intervals of 30 min during a 24 h period using a portable recorder (TM-2425) on the last day of the high- (250 mmol NaCl/day) and low-salt (25 mmol NaCl/day) diet periods. The patients whose 24 h average mean blood pressures were increased by more than 10% by the high salt intake were defined as salt-sensitive (n = 10); the other patients were considered non-salt-sensitive (n = 10). Power-spectral analysis of R-R intervals was performed to obtain the low-frequency component (0.05-0.15 Hz) and the high-frequency component (0.15-0.40 Hz). RESULTS: The average 24 h blood pressure in the salt-sensitive patients was increased by the high salt intake [by 19.1 +/- 2.0/9.1 +/- 0.8 mmHg (mean +/- SEM)], whereas the heart rate did not change. In contrast, the increase in 24 h blood pressure in the non-salt-sensitive patients caused by the high salt intake was not significant and the heart rate was decreased significantly by the high salt intake (by 5.9 +/- 1.4 beats/min). The high-salt diet increased significantly the high-frequency component and decreased the low-frequency:high-frequency component ratio both during the daytime and during the night-time for the non-salt-sensitive patients. In contrast, the high-frequency component and the night-time low-frequency: high-frequency component ratio of the salt-sensitive patients did not respond to dietary salt manoeuvres. CONCLUSIONS: Responses of the parasympathetic and sympathetic nervous systems to dietary salt manoeuvres were blunted in salt-sensitive patients. These altered modulations of the autonomic nervous system may contribute to the salt sensitivity of the blood pressure in patients with essential hypertension.

Blood Pressure↗
PubMed2005

[Spectral analysis of heart period variability in anorexia nervosa].

The aim of this study was to investigate the response of autonomic cardiac control to postural change using spectral analysis, in patients with anorexia nervosa. Spectral components of total variability as well as of low and high frequencies were analyzed for 17 anorexic patients with mean body mass index (14.9 +/- 1.9) kg/m2 and for 9 healthy age-matched women with body mass index (20.3 +/- 1.7) kg/m2 , in supine and standing postures. During standing posture, increased heart rate in all subjects was accompanied by the decrease in total variability and high frequency spectral powers. In supine posture, anorexic patients demonstrated the reduced low frequency spectral power. Compared to control women, during standing posture anorexic patients showed higher heart rate, reduced total variability and high frequency spectral powers. Statistically significant correlation was noticed between body mass index and spectral power of low frequency in both supine and standing posture. Alterations in autonomic cardiac control induced by anorexia nervosa could be estimated by spectral analysis of heart period variability.

Adult↗
PubMed1998

Estimation of component and parameter distributions in spectral analysis.

A method is presented for estimating the distributions of the components and parameters determined with spectral analysis when it is applied to a single data set. The method uses bootstrap resampling to simulate the effect of noise on the computed spectrum and to correct for possible bias in the estimates. A number of bootstrap procedures are reviewed, and one is selected for application to the kinetic analysis of positron emission tomography dynamic studies. The technique is shown to require minimal assumptions about noise in the measurements, and its small sample properties are established through Monte-Carlo simulations. The advantages and limitations of spectral analysis with bootstrap resampling for deriving inferences for tracer kinetic modeling are illustrated through sample analyses of time-activity curves for [18F]fluorodeoxyglucose and [15O]-labeled water.

Algorithms↗
PubMedDate not supplied

[A spectral analysis of the cardiac rhythm in children with cardiovascular diseases living in areas under radiation control].

Spectral analysis of cardiac rhythm has determined characteristics of humoral, sympathetic and parasympathetic regulation in children with cardiac abnormalities and thyroid hyperplasia. The examinees demonstrated low activity of humoral immunity, high sympathetic influences, slight variability of frequency-amplitude characteristics. Sanatorium treatment improved regulation of cardiac activity. Spectral analysis of cardiac rhythm proved efficient for optimization of physiotherapy.

Adolescent↗
PubMed1996

Auto- and cross-spectral analysis of cardiovascular fluctuations during pentobarbital anesthesia in the rat.

We applied auto- and cross-spectral analysis of systemic arterial pressure (SAP) and heart rate (HR) signals to quantify the effects of pentobarbital sodium on short-term cardiovascular fluctuations in adult, male Sprague-Dawley rats. Intravenous administration of pentobarbital, delivered as a bolus injection (5, 10, or 20 mg/kg) or continuous infusion (10, 20, or 40 mg.kg-1.h-1), elicited only mild hypotension and tachycardia. This was accompanied by a dose-related depression of the very low (0-0.25 Hz) and low (0.25-0.8 Hz)-frequency components of both SAP and HR signals and high (0.8-2.4 Hz)-frequency component of HR signals. Cross-spectral analysis of SAP and HR signals during intravenous infusion of pentobarbital revealed a maintained coherence in the high-frequency range, together with a gradual and dose-related decrease in magnitude of transfer function and baro-receptor reflex sensitivity. Stable plasma concentration and all hemodynamic parameters were observed during 120 min of infusion at 20 mg.kg-1.h-1. Under this dosing condition, autonomic blockade by phentolamine, propranolol, or atropine still evoked discernible but differential reductions in the SAP and HR spectral components. Our data suggest that continuous intravenous administration of pentobarbital at 20 mg.kg-1.h-1 offers maintained anesthesia while preserving the capacity of cardiovascular regulation.

Anesthesia↗