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PubMed1996

Spectral analysis of heart rate variability in the ICU: a measure of autonomic function.

Beat-to-beat heart rate variability (HRV) is a measure of autonomic nervous system activity, which can be quantified using frequency domain analysis. Despite its potential utility, routine serial analysis of HRV in an ICU setting has rarely been attempted. We have developed an automated system for real-time spectral analysis of HRV and have utilized this system to study the effect of alterations in HRV on mortality in a surgical ICU population. HRV measurements were performed every 6 hr on all patients in the ICU. Total spectral power in the variability signal (TP, a measure of overall autonomic activity) and the ratio of high frequency to low frequency components (HF/LF ratio, a measure of parasympathetic/sympathetic balance) were calculated. Over a 6-month period 7994 automated HRV measurements were made in 742 patients. Both low TP (low autonomic tone) and high HF/LF ratio (relative lack of sympathetic tone) were associated with increased mortality. A low HF/LF ratio (relatively high sympathetic tone) was associated with increased survival, especially in patients with low autonomic tone. We conclude that serial spectral analysis of HRV is practical in an ICU setting and that HRV parameters appear to be a clinically relevant indication of autonomic activity. Low sympathetic tone and vagal predominance are associated with increased mortality, while sympathetic predominance favors survival. Monitoring of HRV parameters has the potential to detect physiologic deterioration or response to therapy.

Adult↗

PubMed1987

Spectral analysis of fluctuations in heart rate: an objective evaluation of autonomic nervous control in chronic renal failure.

A quantitative, noninvasive method of assessing autonomic control, based on the spectral analysis of beat-to-beat fluctuations in heart rate (HR), was applied to patients with chronic renal failure (RF). Since the power spectrum of HR fluctuations measures the dynamic nervous control of HR, it can be used to quantitate a normal control system as opposed to a disturbed or depressed system. Indeed, in RF patients, a strong reduction in the HR power spectrum was observed in all frequency ranges, both sympathetically and parasympathetically mediated. A similar depression in autonomic control was demonstrated in patients on hemodialysis or peritoneal dialysis. RF patients not yet undergoing dialysis show a lesser degree of depression. Spectral analysis of HR fluctuations in RF patients makes it possible to quantitate autonomic dysfunction and to reliably measure its development as a function of time, and requires only a 10-min standard electrocardiogram recording.

Adult↗

PubMed2001

Screening of obstructive sleep apnoea: heart rate spectral analysis of nocturnal pulse oximetric recording.

Using heart rate spectral analysis of nocturnal pulse oximetry, we prospectively evaluated the utility of this methodology in patients clinically suspected of having obstructive sleep apnoea (OSA). A hundred and ninety-seven outpatients referred with symptoms compatible with the diagnosis of OSA were studied. All participants had nocturnal pulse oximetry performed simultaneously with conventional polysomnography. Power density of heart rate obtained by nocturnal pulse oximetry was analysed using fast Fourier transformation of a Hamming-windowed signal. Recording test results were classified as abnormal (suspicion of OSA) in the presence of a peak in the periodogram between period boundaries 30-70 sec. A normal test result was defined as the absence of the 30-70 sec peak in the periodogram. The total area of the periodogram (S(TOT)), the area enclosed in the periodogram between the period boundaries 30-70 sec (S(30-70)), the area enclosed in the period boundaries 30-70 sec with respect to the total area of the periodogram (S) and the peak amplitude 30-70 sec (PA) were measured. The presence of a peak in the periodogram has a sensitivity of 81.3%, a specificity of 91.5% a positive predictive value of 89.1% and a negative predictive value of 85.1% for OSA diagnosis. The OSA patients were found to have higher values of S(TOT), S(30-70), S and PA than the non OSA patients. Receiver operating characteristics (ROC) curve was constructed at different thresholds of S(TOT), S(30-70) S and PA. For a PA threshold of 10(%)2, heart rate spectra analysis sensitivity for OSA was 58% and specificity was 92%. Furthermore, the positive and negative predictive values for diagnosis of OSA were 87 and 72% respectively. Apnoea hypopnea index (AHI) correlated significantly with S(TOT) (r=0.44; P<0.001), S(30-70) (r=0.59: P<0.001), S (r=0.58; P<0.001) and PA (r=0.58; P<0.001). According to our results, heart rate spectral analys s obtained by nocturnal pulse oximetry and identification of peak in the periodogram between period boundaries 30-70 sec could be useful as a diagnostic technique for OSA patients.

Adult↗

PubMed1993

Evaluation of orthostatic hypotension using power spectral analysis.

To evaluate the pathogenesis of orthostatic hypotension, we studied the autonomic regulation system by measuring heart rate variability during 60 degrees passive head-up tilt using power spectral analysis in 21 patients with orthostatic hypotension (mean age 62 +/- 2 years, five with histories of cerebrovascular accidents, five with Parkinsonism, five with diabetes mellitus, three with pheochromocytoma, and three with unknown causes) and 15 normal healthy subjects as a control (mean age 63 +/- 2 years). We also assessed plasma epinephrine and norepinephrine response to tilt. During tilt, control subjects showed an increase in heart rate with no change in blood pressure. Spectral analysis of heart rate variability demonstrated increases in the low frequency band (LFB, mainly sympathetic) and low frequency band/high frequency band ratio (LFB/HFB, sympatho-vagal balance). All patients with orthostatic hypotension showed a significant reduction in blood pressure with an increase in heart rate. In patients with histories of cerebrovascular accidents and with Parkinsonism, LFB and the LFB/HFB ratio did not increase. However, in other patients with orthostatic hypotension, LFB and the LFB/HFB ratio increased during tilt. Norepinephrine increased in control subjects and in patients with diabetes mellitus, pheochromocytoma, and unknown causes. In contrast, patients with histories of cerebrovascular accidents and patients with Parkinsonism showed no increase in norepinephrine. Epinephrine responses paralleled those of norepinephrine, but the changes were not significant. Thus, neurological response to tilt is not uniform in patients with orthostatic hypotension. Patients with histories of cerebrovascular accidents and patients with Parkinsonism may have impaired function of central neural mechanisms controlling blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗

PubMed2003

Circulatory effects of angiotensin II during anaesthesia, evaluated by real-time spectral analysis.

BACKGROUND: General anaesthesia may stimulate the renin-angiotensin system. Exogenous administration of angiotensin II elevates blood pressure mainly via increased total peripheral resistance caused by direct vasoconstrictor actions. It is also well established that the hypertensive effect of angiotensin II involves a cerebrally mediated component. The hypertensive effect of an intravascular infusion of angiotensin II is substantially reduced by isoflurane anaesthesia. A likely mechanism is that isoflurane anaesthesia reduces the cerebral component of the angiotensin II effect on blood pressure, which involves influences on autonomic nervous activity. In an experimental study in sheep we used real-time spectral analysis of arterial blood pressure signals to obtain information on parasympathetic, respectively, sympathetic autonomic nervous activity in response to angiotensin II administration during isoflurane anaesthesia. METHODS: The study was performed on conscious and isoflurane-anaesthetized sheep that were subjected to an intracarotid infusion of angiotensin II (85 ng kg(-1) min(-1)) during 20 min followed by a recovery period of 30 min and thereafter an injection of the angiotensin II, AT1-receptor antagonist losartan (10 mg kg(-1)) i.v. Systemic and regional (renal and femoral) circulation was monitored in parallel to real-time spectral analysis of the arterial blood pressure signal. RESULTS: Isoflurane anaesthesia reduced both magnitude and duration of the hypertensive response to angiotensin II infusion. The power spectral density in the frequency band that represents sympathetic activation, correlated to the changes in mean arterial pressure in conscious animals, but not during isoflurane anaesthesia. CONCLUSION: We conclude that the cerebrally mediated component of the hypertensive effect of circulating angiotensin II is largely eliminated by isoflurane anaesthesia. Spectral power analysis of the blood pressure signal indicates that the cerebral angiotensin II effect involves activation of sympathetic nervous activity.

Anesthesia↗

PubMed1994

Restraining effects of captopril on sympathetic excitatory responses in dogs: a spectral analysis approach.

This study was planned to clarify the effects of captopril administration on the autonomic control of the circulation in conscious dogs and in dynamic conditions using spectral analysis of R-R interval and systolic arterial pressure (SAP) variabilities. Changes in sympathovagal balance modulating the sinoatrial (SA) node were inferred, respectively, from the low (LFR-R)- and high-frequency (HFR-R) components of R-R variability; LFSAP furnished a marker of sympathetic vasomotor control. Increases in sympathetic activity were induced by three different experimental maneuvers [bilateral carotid occlusion (BCO), coronary artery occlusion (CAO), and dynamic exercise] capable of increasing sympathetic outflow to the SA node and to the vessels. Studies were performed both before and after intravenous captopril administration. During BCO, only LFSAP increased from 4.3 +/- 1.5 to 19.7 +/- 4.1 mmHg2; during CAO, both LFR-R and LFSAP increased, respectively, from 3 +/- 1 to 21 +/- 2 normalized units (nu) and from 4.1 +/- 1.3 to 7.2 +/- 1.5 mmHg2. Dynamic exercise at 2 and 4 km/h progressively raised LFR-R from 8 +/- 2 to 58 +/- 7 and 75 +/- 5 nu, respectively; LFSAP showed a parallel trend increasing from 2.5 +/- 0.7 to 8.04 +/- 1.9 and 12.7 +/- 2.2 mmHg2. In all experimental conditions, captopril significantly (P < 0.05) blunted the increase of LFSAP. A restraining effect on LFR-R was apparent only with CAO. Spectral analysis of cardiovascular variabilities indicates that, in the conscious dog, acute captopril administration has an important inhibitory effect on cardiac sympathetic excitatory mechanisms as well as on sympathetic vasomotor control.

Animals↗

PubMedDate not supplied

Spectral analysis of /s/ sound with changing angulation of the maxillary central incisors.

PURPOSE: The aim of the study was to measure the influence of the maxillary central incisors free from adaptation phenomena using spectral analysis. MATERIALS AND METHODS: The maxillary dentures of 18 subjects were duplicated. The central incisors were fixed in a pivoting appliance so that their position could be changed from labial to palatal direction. A mechanical push/pull cable enabled the incisor section to be handled extraorally. Connected to the control was a sound generator producing a sinus wave whose frequency was related to the central incisor angulation. This acoustic signal was recorded on one channel of a digital tape recorder. After calibration of the unit, the denture duplicate was inserted into the subject's mouth, and the signal of the /s/ sounds subsequently produced by the subject was recorded on the second channel during alteration of the inclination angle simultaneously with the generator signal. Spectral analysis was performed using a Kay Speech-Lab 4300B. RESULTS: Labial displacement in particular produced significant changes in spectral characteristics, with the lower boundary frequency of the /s/ sound being raised and the upper boundary frequency being reduced. CONCLUSION: Maxillary incisor position influences /s/ sound production. Displacement of the maxillary incisors must be considered a cause of immediate changes in /s/ sound distortion. Therefore, denture teeth should be placed in the original tooth position as accurately as possible. Our results also indicate that neuromuscular reactions are more important for initial speech sound distortions than are aerodynamic changes in the anterior speech sound-producing areas.

Acoustics↗

PubMed1995

Power spectral analysis of electroencephalographic desynchronization induced by cocaine in rats: correlation with evaluation of noradrenergic neurotransmission at the medial prefrontal cortex.

We applied continuous, on-line and real-time spectral analysis of electroencephalographic (EEG) signals and microdialysis to evaluate the possible participation of noradrenergic neurotransmission at the medial prefrontal cortex (mPFC) in EEG desynchronization induced by cocaine. Male Sprague-Dawley rats that were under chloral hydrate anesthesia were used. Intravenous administration of cocaine (1.5 or 3.0 mg/kg) dose-dependently induced EEG desynchronization, as represented by a decrease in root mean square (RMS) and an increase in mean power frequency (MPF) value of the EEG signals. Power spectral analysis further revealed that whereas both doses of cocaine promoted a reduction in the alpha (8-13 Hz), theta (4-8 Hz), and delta (1-4 Hz) components, the lower dose of cocaine decreased, and the higher dose increased the beta band (13-32 Hz). Microdialysis data indicated an elevation in extracellular concentration of norepinephrine at the mPFC that paralleled temporally and correlated positively with the maximal effect of cocaine on EEG activity. Bilateral microinjection of the selective noradrenergic neurotoxin, DSP4 (50 micrograms), or equimolar concentration (500 pmol) of the alpha 1-adrenoceptor antagonist, prazosin, or alpha 2-adrenoceptor antagonist, yohimbine, into the mPFC significantly blunted the decrease in delta component (prazosin) or both delta and theta components (DSP4 or yohimbine) of EEG activity by the lower dose of cocaine. On the other hand, the same pretreatments appreciably antagonized the increase in beta band by cocaine at 3.0 mg/kg. The potency of the antagonism by yohimbine, however, was higher than prazosin. These results suggest that cocaine may elicit EEG desynchronization via noradrenergic neurotransmission, and that alpha 2-adrenoceptors, and to a lesser extent, alpha 1-adrenoceptors, at the mPFC may be involved in the subtle dose-dependent changes in individual EEG spectral components.

Adrenergic Agents↗

PubMed2002

Wavelength interval selection in multicomponent spectral analysis by moving window partial least-squares regression with applications to mid-infrared and near-infrared spectroscopic data.

A new wavelength interval selection procedure, moving window partial least-squares regression (MWPLSR), is proposed for multicomponent spectral analysis. This procedure builds a series of PLS models in a window that moves over the whole spectral region and then locates useful spectral intervals in terms of the least complexity of PLS models reaching a desired error level. Based on a proposed theory demonstrating the necessity of wavelength selection, it is shown that MWPLSR provides a viable approach to eliminate the extra variability generated by non-composition-related factors such as the perturbations in experimental conditions and physical properties of samples. A salient advantage of MWPLSR is that the calibration model is very stable against the interference from non-composition-related factors. Moreover, the selection of spectral intervals in terms of the least model complexity enables the reduction of the size of a calibration sample set in calibration modeling. Two strategies are suggested for coupling the MWPLSR procedure with PLS for multicomponent spectral analysis: One is the inclusion of all selected intervals to develop a PLS calibration model, and the other is the combination of the PLS models built separately in each interval. The combination of multiple PLS models offers a novel potential tool for improving the performance of individual models. The proposed procedures are evaluated using two open-path Fourier transform infrared data sets and one near-infrared data set, each having different noise characteristics. The results reveal that the proposed procedures are very promising for vibrational spectroscopy-based multicomponent analyses and give much better prediction than the full-spectrum PLS modeling.

Journal Article↗

PubMed1981

Power spectral analysis of EEG characteristics during sleep in epileptics.

Power spectral analysis of spontaneous EEG activity recorded during non-rapid eye movement (REM) sleep was employed in an effort to identify characteristic EEG substrate abnormalities in epileptics. All-night polygraphic recordings were obtained from 10 poorly controlled subjects with mixed and generalized seizures. Similar data were obtained from 10 matched nonepileptic subjects. Continuous 10 min samples of non-REM sleep were identified at the beginning and end of these all-night recordings. EEG activity recorded during these periods from left sensorimotor and parieto-occipital bipolar leads was digitized, subjected to the fast Fourier transform, and then sorted into successive 4 Hz frequency bands between 0 and 23 Hz. Mean spectral density was determined for each frequency band from both samples in both groups. Comparison of these values disclosed both similarities and differences between the two groups. All subjects showed a significant "time-of-night effect," with power at 0-3, 4-7, and 8-11 Hz greater at the beginning of the night. This finding was related to a similar observation in developing infants and attributed to a circadian influence on neuronal generators. In group comparisons, epileptics showed selective differences in common when compared with nonepileptics. These differences were reduced when data from a small group of unmedicated epileptic subjects were partialled out. Medicated epileptics showed differences restricted to the early morning non-REM sleep sample, which included significantly greater power at 4-7 Hz and significantly lower power at 12-15 Hz. Unmedicated subjects showed these differences in both samples and also showed significantly greater power in the 0-3 Hz band. It was suggested that anticonvulsant medications may exert a general normalizing influence on EEG characteristics during sleep, particularly at the beginning of the night in proximity to their administration. The documentation of significant EEG deviations restricted to two basic rhythmic patterns during sleep suggests a disturbance of underlying thalamocortical mechanisms.

Adolescent↗

PubMed2004

Power spectral analysis of the heart rate variability of goat fetuses during extrauterine incubation.

Our aim is to determine the relationship between heart rate and behavioral states of a fetal goat using power spectral analysis. Electrocardiograms, electrocortical activity, and fetal breathing movements are recorded from 7 goat fetuses during extrauterine incubation. The heart rate power spectrum is classified into very low, low, and high frequency bands, and behavioral states are classified into low-voltage electrocortical activity with fetal breathing movements (LVB), low-voltage electrocortical activity without fetal breathing movements (LVN), and high-voltage electrocortical activity (HVN). There is a significant difference in total power spectral density in the high frequency band between LVN and HVN, and LVN and LVB. The relationship between each fetal behavioral state is assessed by power spectral analysis.

Animals↗

PubMed2006

Power spectral analysis of finger plethysmographic waveform in patients with coronary artery disease and after coronary artery bypass graft surgery.

BACKGROUND: The aim of the present study was to assess the clinical significance of spectral analysis of plethysmographic waveform in patients with coronary artery disease (CAD) and after coronary artery bypass graft (CABG) surgery. METHODS AND RESULTS: The study group comprised 26 healthy subjects, 15 CAD patients, and 24 CAD patients after CABG. Finger plethysmographic waveforms from both right and left index fingers were recorded and analyzed using power spectral analysis. The total power of the right pulse was found to be higher than that of left pulse in the 3 groups of subjects. In CABG patients, the total power of both pulses was increased, the right-to-left ratio of bilateral total power was decreased, and the power of the harmonics of the right pulse shifted from high-frequency to low-frequency. The normalized power of the 4th harmonic of the left pulse and of the 3rd and 4th harmonics of right pulse decreased, whereas that of the 1st harmonic of right pulse increased in CABG patients. Several harmonics correlated significantly to some heart rate variability measures in both controls and CAD patients, but not in CABG patients. CONCLUSIONS: The increase in the total power of both pulses, the shift of the normalized power of harmonics of the right pulse from high- to low-frequency, and the decrease in the right-to-left ratio of the total power of both pulses are the 3 significant changes in the power spectra of the pulses in CAD patients after CABG. The plethysmographic waveform of normal controls and CAD patients may be modulated by the autonomic nervous system, and in CAD patients the CABG surgery may have diminished the effect of autonomic nervous modulation on the pulse waveforms.

Aged↗

PubMed1986

Bio-electrical brain relations of pain and acupuncture effects on EEG spectral analysis in healthy volunteers.

Pain description and objective evaluation is difficult. In the last few years, a number of neuro-physiological methods have been used in the study of pain and acupuncture analgesia. EEG spectral analysis allows the description and objective quantification of brain bio-electrical activity changes. The present study aims at evaluating ischemic experimental pain, electroacupuncture (EA) and ischemic pain following EA on EEG spectral analysis in healthy volunteers.

Acupuncture Therapy↗

PubMedDate not supplied

The effect of verapamil calcium antagonist on autonomic imbalance in migraine: evaluation by spectral analysis of beat-to-beat heart rate fluctuations.

Abnormalities in autonomic control have been documented in migraine even during the headache-free interval. It has long been recognized that spectral analysis of heart rate (HR) fluctuations can reflect the autonomic function, especially the sympathetic to parasympathetic balance. This technique is the basis for a quantitative approach to the investigation of migraine applied in the present study. A 24-hour Holter ECG recording was performed for each subject in a group of five migraine patients during the interheadache period. In addition, shorter 5-minute-long recordings of blood flow (BF) and blood pressure (BP) were made in these patients in both supine and standing positions. Short, 256-second subtraces were taken every 30 minutes along the 24-hour ECG signal and were submitted, as well as the BF and BP traces, to A/D conversion and computation of the power spectrum of fluctuations in HR, BF, and BP. Spectral analysis of fluctuations in these hemodynamic parameters was performed in the migraine patients before and during the treatment with verapamil and compared to that of a healthy control group. This procedure enabled us to assess the autonomic function, the sympathetic vs parasympathetic balance, and their response to a change in position, before and during calcium blockade. A characteristic autonomic abnormality is revealed in the group of untreated migraine patients in supine position: enhanced low frequency (LF) fluctuations reflecting increased sympathetic sensitivity during the inter-headache phase. An exaggerated sympathetic response is measured in the migraine patients during the transition from supine to standing position with a concomitant nonsignificant decrease in parasympathetic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2006

Dynamic spectral analysis findings in first episode and chronic schizophrenia.

The quantified analysis of the electroencephalogram (qEEG) has enabled the extraction of additional psychophysiological information from the raw EEG, but in turn has introduced a number of distortions. This study compared Dynamic Spectral Analysis (DSA), a novel and mathematically stringent technique for the evaluation of qEEG activity with conventional power spectral analysis in subjects with both first episode and chronic schizophrenia and matched controls. Advantages of the technique in the automated processing of data, rejection of artefact, avoidance of artefact introduced by the mathematical trans-formation of the data and the identification of irregular low frequency artefactual activity "pi" are discussed in detail. Using this method, the study has confirmed past observations of increased slow wave activity in schizophrenia, and identified a decrease in peak frequency in the alpha band in the subjects with chronic schizophrenia. The two clinical groups differed in mean peak frequency in the delta band with the first episode schizophrenia subjects having a raised mean peak frequency and the subjects with chronic schizophrenia having a lowered mean peak frequency. The results suggest continued change in the EEG with illness chronicity in schizophrenia. These changes were most evident in the frequency domain emphasizing the importance of routine measurement of mean band frequencies in qEEG studies.

Adolescent↗

PubMed1991

Power spectral analysis of occlusal sounds of natural dentition subjects.

Fifteen subjects with complete natural dentitions were selected for investigation of their occlusal sounds on the left and right sides by means of power spectral analysis. It was found that the occlusal sounds consisted of various frequency components. Their mean power frequencies (MPF) and frequencies at 10, 20, 50, 80 and 90% of cumulative power (F10, F20, F50, F80, F90) on the left and right sides were almost identical (P greater than 0.05). The correlation coefficients between MPF and F50, MPF and F50 with the others were high. The results indicate that F20, MPF or F50 and F80 may be used as indices to describe the power spectral shape, and that power spectral analysis of occlusal sounds may be used as a contribution to diagnosis of occlusal conditions.

Adult↗

PubMed1992

Colour-coded echographic flow imaging and spectral analysis of cerebrospinal fluid (CSF). Part III. In-vitro study of low flow velocity detection related to decreasing particle concentration (hematocrit) and tube lumen.

An in-vitro steady flow system was designed to determine the lowest flow velocities that can be detected by echographic colour flow imaging and spectral analysis. The flow detection level was determined hydrostatically by reducing the fluid level to below the point at which a flow signal was visible, then increasing the height until the colour flow reappeared. This was confirmed in all instances by spectral analysis. The height (angle-corrected velocity) of the spectral envelope was also determined. Mean volume flow was then obtained by using a graduated cylinder and a stop watch. The lowest hematocrit detectable was identified using a stepwise dilution of packed human red blood cells with 0.9% sodium chloride. Three different PVC-tubes with inner diameters of 2.1 mm, 1.1 mm and 0.51 mm were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Air↗

PubMed1995

Power spectral analysis of the foetal magnetocardiogram.

The results of power spectral analysis of foetal magnetocardiographic (FMCG) data, acquired using a DC-SQUID-based system, are reported. Similar analyses have been previously reported using foetal electrocardiographic data, but it is believed that our work represents one of the first attempts to analyse, in the frequency domain, the magnetic fields produced by foetal cardiac activity. Analysis of the data in this way may enable the integrity of the foetal nervous system, and thus the status of the foetus as a whole, to be monitored and evaluated during a significant part of the antenatal period. The results obtained are discussed with reference to the probable underlying physiological mechanisms. This preliminary study highlights some of the advantages of FMCG as a novel, non-invasive technique for obtaining clinically useful information. Fourier analysis of the FMCG data is likely to yield new information, not only about cardiac function but also about the foetal central nervous system.

Algorithms↗