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PubMed1994

Can power spectral analysis of heart rate variability identify a high risk subgroup of congestive heart failure patients with excessive sympathetic activation? A pilot study before and after heart transplantation.

BACKGROUND AND OBJECTIVES: Autonomic dysfunction seems to be involved in the progression and prognosis of severe congestive heart failure. Parasympathetic activity can still be abnormal 4-8 weeks after haemodynamic improvement by heart transplantation. To identify patients in heart failure with a more pronounced neural derangement and to analyse the changes in sympathetic and parasympathetic activity soon after heart transplantation, spectral indices of heart rate variability were assessed in 30 patients in severe heart failure and in 13 patients after heart transplantation; a group of 15 age-matched subjects served as controls. METHODS AND RESULTS: Heart rate variability was assessed by standard electrocardiography (ECG) in patients in heart failure and by oesophageal ECG in patients after heart transplantation. Compared with controls, the mean RR interval and total power were reduced in heart failure. The 30 patients showed two different patterns of heart rate variability: in 14 no power was detected in the low frequency band (0.03-0.15 Hz) (LF) and total power was mainly concentrated in the high frequency band (0.15-0.45 Hz) (HF), whereas in the remaining 16 patients power in the LF band was increased and power in HF band was reduced compared with the controls. Patients with undetectable LF had a lower mean RR interval and total power (745(25) v 864(36) ms, p < 0.05; 118(16) v 902(202) ms2, p < 0.001), higher concentration of plasma noradrenaline (635(75) v 329(54) pg/ml, p < 0.05), and worse clinical status and prognosis (4 deaths v no deaths at 6 month follow up) than patients with a dominant LF band. In the post-transplant patients both the mean PP interval of the remnant atrium and total power resembled results in the patients with heart failure; in 7 of the 13 post-transplant patients no power was detectable in the LF band: when both HF and LF power were present the results resembled those in the 16 patients in heart failure. CONCLUSIONS: These data suggest that in more advanced stages of congestive heart failure, power spectral analysis of heart rate variability allows identification of a subgroup of patients with higher sympathetic activation and poorer clinical status who are at major risk of adverse events. In the short term after cardiac transplantation the spectral profile of the rhythm variability of the remnant atrium was not improved, suggesting that parasympathetic withdrawal and sympathetic hyperactivity persist, despite the restoration of ventricular function.

Echocardiography, Transesophageal↗
PubMed1997

A new method of assessing cardiac autonomic function and its comparison with spectral analysis and coefficient of variation of R-R interval.

A new non-linear method of assessing cardiac autonomic function was examined in a pharmacological experiment in ten healthy volunteers. The R-R interval data obtained under a control condition and in autonomic blockade by atropine and by propranolol were analyzed by each of the new methods employing Lorenz plot, spectral analysis and the coefficient of variation. With our method we derived two measures, the cardiac vagal index and the cardiac sympathetic index, which indicate vagal and sympathetic function separately. These two indices were found to be more reliable than those obtained by the other two methods. We anticipate that the non-invasive assessment of short-term cardiac autonomic function will come to be performed more reliably and conveniently by this method.

Adult↗
PubMed1999

Spectral analysis of arterial blood pressure and cerebral blood flow velocity during supine rest and orthostasis.

This study evaluates the effect of orthostasis on the low frequency (LF, 0.04 to 0.15 Hz) fluctuations in the blood flow velocity of the middle cerebral artery (MCAFV) in relation to its arterial blood pressure (ABP) equivalent to further define and quantify this relationship in cerebrovascular regulation. Spectral analysis was performed on 22 healthy subjects during supine rest and head-up tilt. The power in the LF range can be used to quantify the LF fluctuations, and four types of LF power data could be obtained for each individual: LF power of supine MCAFV, LF power of supine ABP, LF power of tilt MCAFV, and LF power of tilt ABP. By comparing LF power of MCAFV with LF power of ABP, two power ratios could be generated to describe the flow-pressure relationship during supine rest and head-up tilt, respectively, supine power ratio (LF power of supine MCAFV/ LF power of supine ABP) and tilt power ratio (LF power of tilt MCAFV/ LF power of tilt ABP). In addition, an index for dynamic autoregulation in response to orthostasis can be calculated from these two power ratios (tilt power ratio/supine power ratio). The authors found that this index was dependent on the extent of orthostatic MCAFV changes, and the dependency could be mathematically expressed (r = 0.61, P = .0001), suggesting its involvement in cerebrovascular regulation. Moreover, these data further support the previous observation that the LF fluctuations of MCAFV might result from modulation of its ABP equivalent, and the modulation effect could be quantified as the power ratio (LF power of MCAFV/ LF power of ABP). These observations could be an important step toward further insight into cerebrovascular regulation, which warrants more research in the future.

Adult↗
PubMed1998

Evaluation of compartmental and spectral analysis models of [18F]FDG kinetics for heart and brain studies with PET.

Various models have been proposed to quantitate from [18F]-Fluoro-Deoxy-Glucose ([18F]FDG) positron emission tomography (PET) data glucose regional metabolic rate. We evaluate here four models, a three-rate constants (3K) model, a four-rate constants (4K) model, an heterogeneous model (TH) and a spectral analysis (SA) model. The data base consists of [18F]FDG dynamic data obtained in the myocardium and brain gray and white matter. All models were identified by nonlinear weighted least squares with weights chosen optimally. We show that: 1) 3K and 4K models are indistinguishable in terms of parsimony criteria and choice should be made on parameter precision and physiological plausibility; in the gray matter a more complex model than the 3K one is resolvable; 2) the TH model is resolvable in the gray but not in the white matter; 3) the classic SA approach has some unnecessary hypotheses built in and can be in principle misleading; we propose here a new SA model which is more theoretically sound; 4) this new SA approach supports the use of a 3K model in the heart with a 60 min experimental period; it also indicates that heterogeneity in the brain is modest in the white matter; 5) [18F]FDG fractional uptake estimates of the four models are very close in the heart, but not in the brain; 6) a higher than 60 min experimental time is preferable for brain studies.

Brain↗
PubMed1990

[Spectral analysis of the ECG for detecting late potentials as risk factors of life-threatening cardiac arrhythmias].

Late potentials in the terminal phase of the QRS and early S-T segment are looked upon as a risk marker in patients prone to sustained ventricular tachycardia after myocardial infarction. Since the amplitude of late potentials at the body surface is very low (1-5 microV), most studies use signal averaging of the ECG to increase the signal-to-noise ratio. Two different approaches are generally used to analyze the signal-averaged ECG. In the time domain, the individual channels are combined into a vector magnitude and high-pass filtered in a bidirectional mode. Late potentials are suspected if the filtered QRS duration is greater than 120 ms and/or the amplitude in the terminal 40 ms of the QRS complex is less than or equal to 25 microV. The limitations of this method are that the definition of abnormality differs from one study group to another, highpass filters may introduce artificial signals, patients with bundle branch block in general have to be excluded, and the definitions depend upon the noise level. More recently, spectral analysis of the ECG with Fast Fourier Transform (FFT) has been performed. Late potentials are characterized by a higher frequency content in the otherwise low-frequent S-T wave. We analyzed 25 overlapping segments of the terminal QRS and early S-T wave time shifted in steps of 2 ms with FFT (spectro-temporal mapping). This method was shown to overcome some of the limitations of conventional time domain analysis: no highpass filters have to be applied, noise interference can be detected by a characteristic spectral pattern, and patients with bundle branch block need not be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗
PubMed1998

Investigating potential risk factors for seasonal variation: an example using graphical and spectral analysis methods based on the production of milk components in dairy cattle.

The objective of this study was to illustrate methods for investigating factors associated with seasonality, using milk-component production as an example. Milk-protein and fat percentages showed a seasonal pattern; percentages were lowest during June and July and highest in October and November. Graphical methods were used to compare herd calving patterns to seasonal production patterns and spectral analysis were used to compare seasonal production patterns between farm groups with different management practices. For the comparison of seasonality of production and herd calving patterns, data was obtained from archival records for all cows enrolled in Dairy Herd Improvement (DHI) milk recording in Ontario, Canada from 1990 to 1994. For comparisons of seasonality and management practices, monthly protein and fat percentages were obtained from the Dairy Farmers of Ontario from March 1985 to July 1994. Management information was obtained from responses to questionnaires completed by 364 dairy producers in Ontario. Graphical analyses provided a visualization of the relationship between herd calving patterns and seasonality of production-however, graphical methods alone did not allow statistical inferences to be made. Spectral analyses provided a formal statistical test of the null hypothesis of no association between an independent variable (farm management type) and seasonal production pattern in the data over time, provided that the outcome followed the same seasonal pattern regardless of covariate levels under the null hypothesis.

Animal Husbandry↗
PubMed1990

Spectral analysis of airflow sounds in patent versus occluded tracheostomy tubes: a pilot study in tracheostomized adult patients.

Cannula occlusion is a life-threatening postoperative complication of tracheostomy. Current management largely relies on nursing care for prevention of fatalities because no proven mechanical, machine-based support monitoring exists. The objective of this paper was to address the problem of monitoring the state of cannula patency, based on analysis of airflow acoustic spectral patterns in tracheostomized adult patients in the patent and partially occluded cannula. Tracheal airflow sounds were picked up via a condenser microphone air-coupled to the skin just below the tracheal stoma. Signal output from Mic was amplified, high-pass filtered, digital tape-recorded, and analyzed on a mainframe computer. Although airflow frequencies for patient cannulae were predominantly low-pitched (0.1 to 0.3 kHz), occluded tubes had discrete high-pitched spectral peaks (1.3 to 1.6 kHz). These results suggest that frequency analysis of airflow sounds can identify a change in the status of cannula patency.

Adult↗
PubMed1994

[Differential effects of isoflurane, sevoflurane and halothane on autonomic function determined by spectral analysis of heart rate variability].

The effects of isoflurane, sevoflurane and halothane on heart rate variability were studied in 18 patients scheduled for minor otolaryngeal surgery. After the surgery, R-R intervals were determined at minimum alveolar concentrations of 2.0, 1.5, 1.0 and 0.5 under mechanical ventilation. The data were plotted on a one-dimensional map and analyzed further by autoregressive spectral analysis. All three anesthetics suppressed both the low frequency component (Mayer wave related sinus arrhythmia; MWSA) and the high frequency component (respiratory sinus arrhythmia; RSA). The MWSA reflecting sympathetic activity was less affected by sevoflurane while the RSA reflecting parasympathetic function was less influenced by halothane. The one-dimensional map was useful to visualize the depth of anesthesia.

Adolescent↗
PubMed1996

Effects of pentobarbital and etomidate on plasma catecholamine levels and spectral analysis of blood pressure and heart rate in dogs.

The present paper investigates the effects of two anaesthetic drugs (pentobarbital and etomidate) on both short-term variabilities of systolic blood pressure (SBP) and heart rate (HR) using fast Fourier transformation and catecholamine plasma levels. HR and BP were continuously recorded through an arterial catheter and blood samples were taken from the jugular vein. Spectral analysis was performed first in the conscious state and six minutes after induction of anaesthesia on a series of 256 consecutive BP and HR values (delta t: 2 Hz). The area under the curve (AUC) was determined in the low-frequency component of the SBP (LF: 40-150 mHz), in the high-frequency band of HR (HF: respiratory frequency +/- 50 mHz) and in the total frequency spectra. Results were normalized by calculation of the ratio between AUC of LF and HF and the total AUC of the corresponding spectrum (TS). Etomidate (2 mg/kg i.v.) induced a significant increase in TS and LF without changing the LF/TS ratio or the HR variability when compared with the awake period. Catecholamine plasma levels did not change. In contrast, pentobarbital (30 mg/kg i.v.) decreased the values of LF, HF, LF/TS and HF/TS and catecholamine plasma levels. These results suggest that pentobarbital decreases the activity of the two components of the autonomic nervous system whereas etomidate induces only minimal changes.

Adjuvants, Anesthesia↗
PubMed1981

A new method in differential diagnosis of the liver: identification of liver pulsating activities by spectral analysis of radio-isotope counts during liver scan. Comparative studies by ultrasonography.

Liver scanning with 99mCi 99Tc sulphur-colloid was practiced in 50 patients: 30 suffering from malignant tumors, 10 from hepatic cirrhosis and 10 from pyrexia of unknown origin. Liver radioactivity was recorded by a gamma-camera connected to a computer, 1 frame each 10 seconds for 15 minutes. The spectral analysis of the radioactivity counts taken in different region of interest, showed evidence of a periodic fluctuation, with a period value around 1 minute. Comparative ultrasonographic dynamic study showed evidence of the same phenomena in 16 examined patients. The period of pulsation was found different in each of the following groups: normal liver, cirrhotic, metastatic and infectious diseases.

Diagnosis, Differential↗
PubMed1991

Autonomic control of cardiac chronotropic function in man as a function of age: assessment by power spectral analysis of heart rate variability.

The analysis of age-related features of the autonomic heart rate control during various periods of postnatal human ontogenesis is presented. The study was performed in 354 apparently healthy individuals of either sex, ranging in age from 3 months to 89 years. The method of spectral analysis of heart rate variability was used. We demonstrated different ratios between the sympathetic and the parasympathetic influences upon heart rate control in relation to age. In infancy and after 50 years, there is a prevalence of the sympathetic activity against a background of weak parasympathetic activity. In early years, the prevalence of the parasympathetic activity is observed at a sufficiently high sympathetic activity level.

Adolescent↗
PubMed1995

Spectral analysis of blood pressure variability in heart transplant patients.

The cardiac transplant patient provides a unique model for the study of blood pressure variability in the absence of heart rate variability. We examined the harmonic and fractal components of blood pressure variability in 14 heart transplant patients (12 men, 2 women; 21 to 62 years of age) and in age-and sex-matched control subjects during seated rest, supine rest, and supine rest with fixed-pace breathing (12 respirations per minute). Heart rate was faster in transplant patients than in control subjects, with much less heart rate variability (P < .0001). Spectral analysis of blood pressure variability revealed no difference in total power for either systolic or diastolic pressure, but transplant patients had less low-frequency (0 to 0.15 Hz) harmonic spectral power in both systolic (P < .01) and diastolic (P < .03) pressure and more high-frequency power (0.15 to 0.5 Hz) in diastolic pressure than control subjects. The ratio of high-frequency power in diastolic relative to systolic pressure was consistently higher (P < .0001) in the transplant patients (0.29 to 0.51) than in control subjects (0.11 to 0.13). The slope of the fractal component of systolic pressure was approximately 1.8 in both transplant patients and control subjects. This was greater than the slope for heart rate variability (approximately 1.1 in control subjects). These data provide clear evidence of independence of the fractal component of heart rate and blood pressure variabilities in both transplant patients and control subjects. The heart rate component of the arterial baroreflex minimized high-frequency diastolic pressure changes while contributing to low-frequency variations in both systolic and diastolic pressures.

Adult↗
PubMed1996

Power spectral analysis of RR interval and blood pressure short-term variability at rest and during dynamic exercise: comparison between cyclists and controls.

To determine the adaptations of the autonomic nervous system in the control of heart rate and blood pressure induced by endurance training, 10 competitive cyclists aged 27 +/- 7 years and 10 age-, weight- and height-matched sedentary controls were subjected to Power Spectral Analysis of the RR interval and of blood pressure at supine rest and during submaximal cycloergometric exercise test in the supine position at 20% and 40% of maximal workload. At rest, the high-frequency (HF) power of the RR interval was higher in cyclists (p < 0.05) compared to controls, whereas the power spectrum of both systolic and diastolic blood pressure did not differ between cyclists and controls. During exercise the variance, the low-frequency (LF) and the HF power of the RR interval decreased significantly (p < 0.005) and similarly in cyclists and controls. The LF/HF ratio of the RR interval increased (p < 0.001) and the alfa index of baroreflex sensitivity decreased (p < 0.05) without differences between cyclists and controls. The variance of both systolic and diastolic blood pressure increased (p < 0.001 and p < 0.005, respectively) as well as the HF power of systolic blood pressure (p < 0.001) similarly in cyclists and in controls. In conclusion, the data of the present study suggest that competitive cycling causes an enhanced vagal drive to the sinus node, whereas the neural control of blood pressure is not affected. During exercise a vagal withdrawal and a sympathetic activation in the neural control of heart rate, together with a reduction of baroreflex sensitivity are operative. These changes are similar in cyclists and controls.

Adaptation, Physiological↗
PubMed1976

Spectral analysis of spontaneous contractions of the isolated portal vein of rats.

The spontaneous contractions of segments of rat portal veins have been examined in vitro under isotonic and isometric conditions. The power density spectra of recorded time series lasting 10-60 min were calculated. The spectra usually consist of harmonic frequency components. Only during shorter periods of analysis (10 min time series) we sometimes found additional non-harmonic components. All frequency components are proportionally shifted by changes of the bath temperature according to an average Q10 of 2.0. Increase of the load decreases the frequency of the contractons. The results of the spectral analysi, indicating a preponderance of a single source of periodicity, were supported by direct evidence of a pacemaker region. By recording contractions after systematic dissections of the portal vein segment, we found that spontaneous activity is generated at the central end of the segment.

Animals↗
PubMed2004

Linear-dichroic infrared spectral analysis of Cu(I)-homocysteine complex.

The interaction between homocysteine (HCysSH) and Cu(II) leads to the formation of a yellow complex [Cu(I)(HCysS-SCysH)2]Cl (1) after redox processes in the Cu(II)-homocysteine system resulting in dimerization of the ligand and formation of a mononuclear Cu(I) complex with two dimers. The structure of (1) was obtained by IR-LD spectral analysis of a solid amorphous sample oriented in nematic liquid crystal medium. The original technique for orientation developed here and the polarized IR spectra thus obtained, permit the determination of the complexation sites and coordination mode of diamagnetic complexes. In the complex (1), Cu(I) is coordinated through the two O atoms of one COO- group of each of the ligands and the metal ion coordination sphere represents a distorted tetrahedron.

Circular Dichroism↗
PubMed1994

Stress wave velocity measured in intact pig lungs with cross-spectral analysis.

In anesthetized pigs (25-40 kg), we generated stress waves in the lung by rapid deflation of an esophageal balloon. The source distortion was measured by an accelerometer (1 g wt) bonded to the balloon. Stress waves were detected by three accelerometers bonded to intercostal muscle and to the skin near midchest. The distance between the source and chest receivers were measured radiographically. Cross-spectral analysis was used to calculate transit times. We measured stress wave velocities at airway pressures of 0 (functional residual capacity) and 25 cmH2O. Transpulmonary pressure (Ptp) was measured by an esophageal balloon. In vivo, stress wave velocities increased from 291 +/- 117 (SD) cm/s at 3.0 +/- 0.9 cmH2O Ptp to 573 +/- 73 cm/s at 13.8 +/- 3.5 cmH2O Ptp (n = 6). These velocities agreed with longitudinal wave velocities measured in isolated sheep lungs and predictions based on the elastic moduli of lung parenchyma. Post-mortem edema was induced by intratracheal instillation of 200 ml of saline, resulting in a wet-to-dry weight ratio of 7.7 +/- 1.4 (n = 5). At 15 cmH2O Ptp, stress wave velocities decreased from 565 +/- 155 cm/s before edema to 445 +/- 130 cm/s after edema. This decrease correlated well with predictions based on the increased lung density, as dictated by elasticity theory.

Animals↗
PubMed2002

Brain death assessment using instant spectral analysis of heart rate variability.

OBJECTIVE: Confirmation of brain death requires an urgent diagnosis to allow rapid vital organ removal for transplantation. Evaluation of forebrain functions is commonly performed through electroencephalogram. Nevertheless, there are, for the moment, no methods that allow for an instantaneous evaluation of brainstem functions. During acute brain injury, heart rate variability is an independent neurologic prognosis indicator resulting from a close relationship between brain stem and cardiac autonomic nervous system. This study aims to evaluate a new heart rate variability spectral analysis method, on a beat-to-beat basis, continuously over the time, during brain death. DESIGN: Prospective, nonrandomized, observational study. SETTING: Intensive care unit. SUBJECTS: Ten patients (age range 25-64 yrs, mean age 41 yrs) with acute brain injury leading to brain death. INTERVENTION: No intervention beyond standard of care MEASUREMENTS AND MAIN RESULTS: Heart rate, arterial blood pressure, heart rate variability in time and frequency domains method, which included calculation of the instant center frequency of spectrum. Brain death was associated with tachycardia (R-R interval 703 +/- 69 vs. 551 +/- 34 msec, p <.05), dramatic reduction of the global spectral power (44.919 +/- 31.511 vs. 3.204 +/- 1.469 msec(2), p <.05), and an abrupt shift of instant center frequency to a higher frequency range (0.17 +/- 0.01 vs. 0.26 +/- 0.03 Hz, p <.05). CONCLUSIONS: Such a method allows an instant, noninvasive determination of brainstem death based on a time and frequency domain analysis of heart rate variability.

Adult↗
PubMed2003

Effects of tenotomy surgery on congenital nystagmus waveforms in adult patients. Part I. Wavelet spectral analysis.

Congenital nystagmus (CN) is an aperiodic oscillatory eye movement disorder. Horizontal rectus tenotomy with simple re-attachment has been proposed as a therapy for CN. This therapy might affect vision and/or eye movements. Another paper deals with improvements in visual acuity. This and the companion paper examine changes in eye movements. In this study, we examined the effect of tenotomy on nystagmus waveforms using wavelet spectral analysis. No common effect was found across the patients on the wavelet spectra of the CN beat, suggesting that tenotomy surgery has no effect, or only a quite small effect, on the waveform structure of CN.

Adult↗