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PubMed1994

Continuous monitoring of depth of sedation by EEG spectral analysis in patients requiring mechanical ventilation.

Twenty-three patients undergoing intensive therapy had continuous EEG recording in an attempt to assess depth of sedation using spectral analysis. Median power frequency (MPF) and spectral edge frequency (SEF) were calculated and correlated with the clinical sedation score and blood concentration of sedative drug. Fifteen patients received isoflurane and eight midazolam. There was no correlation between MPF or SEF and sedation score or blood concentration of drug. These results suggest that no simple measure of the EEG is likely to correlate with depth of sedation in critically ill patients.

Adolescent↗
PubMed1998

Spectral analysis of heart rate variability during tilt-table testing in patients with vasovagal syncope.

Spectral analysis of heart rate variability was used to assess changes in autonomic function in 44 patients with vasovagal syndrome and 20 normal controls before and during postural tilt and to attempt to relate such changes to specific types of haemodynamic response to tilt. Frequency domain measurements of the high (HF) and low (LF) frequency bands and the ratio LF/HF were derived from Holter recordings, computed by Fast Fourier Analysis for 4 min intervals immediately before tilt testing, immediately after tilting and just before the end of the test. In the syncopal patients the mean values of LF and HF decreased significantly in response to tilting, while the LF/HF ratio remained constant. All parameters showed a statistically significant increase just before the onset of syncope. In the control group there was an increase in the LF and LF/HF ratio and a decrease in the HF immediately after tilting. The three subgroups of patients had similar patterns of changes in autonomic activity. The results of this study show that syncopal patients have a different pattern of response to the tilting test. The pathological mechanism leading to vasovagal syncope appears to be independent of the specific type of haemodynamic response to tilt testing.

Autonomic Nervous System↗
PubMed1988

Spectral analysis of heart rate indicates reduced baroreceptor-related heart rate variability in elderly persons.

Spectral analysis of the cardiac interbeat interval was used to examine baroreceptor-related supine and standing heart rate variability (HRV) in young (less than 40 years of age) and elderly (greater than 60 years of age) healthy volunteers. Heart rates and blood pressures were examined also. When supine, average heart rate, systolic and diastolic blood pressure, and HRV for the young volunteers were 66.5 bpm, 113.0/64.3 mmHg, and 5.74 log units of relative power, respectively. The same values for the elderly group were 65.4 bpm, 126.3/74.0 mmHg, and 4.43 log units. Statistical analysis revealed that, compared to the young volunteers, supine elderly volunteers had similar heart rates, higher blood pressures, and lower baroreceptor HRV. There was little change in blood pressure in either group upon standing. However, upon standing, heart rate increased 17.7 bpm and baroreceptor HRV increased to 6.58 (+ 14.6%) in the younger volunteers. This was significantly different from the elderly volunteers, whose heart rate increased by only 10.9 bpm and their HRV to 4.72 (+ 6.5%). These results indicate that much of the reduction in HRV in old age results from decreases in baroreceptor modulation of heart rate. In addition, the difference between young and old persons is greatest in the standing position because elderly individuals exhibit less recruitment of baroreceptor activity with postural change.

Adult↗
PubMed1997

Power spectral analysis of heart rate variability in children and adolescents with IDDM.

OBJECTIVE: To investigate power spectral analysis (PSA) of heart rate variability (HRV) in children and adolescents with IDDM, its relationship with other measures of HRV and standard cardiovascular responses, and factors associated with reduced HVR. RESEARCH DESIGN AND METHODS: A total of 130 subjects with IDDM aged 12.8 +/- 3.2 years and 108 healthy control subjects were studied. Power spectra were analyzed from supine electrocardiograph (ECG) recordings by processing into consecutive R-R intervals and analysis using fast Fourier transformation. Standard cardiovascular responses to deep breathing and standing were performed. RESULTS: IDDM subjects had a reduction in total power including both low-frequency (0.05-0.14 Hz; P = 0.0001) and high-frequency (0.14-0.40 Hz; P = 0.0002) components. These changes were seen from diagnosis. Other measures of HRV, coefficient of variation (CV) and standard deviation (SD) of mean resting heart rate, were also significantly lower in IDDM. All 20 (15%) of the 130 IDDM subjects with total power less than the 5th percentile in control subjects also had reduced HRV when measured by CV of heart rate. There was an independent relationship between age and the high-frequency component in IDDM subjects and control subjects. Total power correlated with mean heart rate (r = -0.56; P < 0.0001), CV of heart rate (r = 0.90; P < 0.00001), SD of heart rate (r = 0.91; P < 0.00001), heart rate response to deep breathing (r = 0.45; P < 0.0001), and duration in IDDM subjects. There was no correlation with short-term or long-term metabolic control. Retesting of 27 subjects showed a variability in total power and its components comparable to other measures of HRV and standard heart rate responses. CONCLUSIONS: Changes in HRV are a sensitive and reproducible measure of early autonomic dysfunction in childhood. In this age-group, PSA appears no more sensitive a measure of reduced HRV than other closely correlated measures of HRV.

Adolescent↗
PubMed1979

Spectral analysis of urinary reactions: a preliminary study based on a novel concept.

The concept of spectral analysis of urinary reactions (a range of simple chemical tests combined with pattern analysis) is described. A preliminary study in which we used 10 nonspecific tested on untimed urine specimens from 20 controls and 20 diabetics, matched for age and sex, suggested that a combination of these tests could be used to separate diabetics from healthy subjects. This combination, however, did not prove satisfactory for a further group of 13 diabetics. Closer examination revealed that factors such as therapy and glycosuria affected the results of these tests. This approach, which should extend the usefulness of urinalysis, may prove viable when larger groups, and possibly a different set of tests, are used to establish a more robust combination of tests.

Adult↗
PubMed1986

The pharmacodynamic properties of lorazepam and methylphenidate drugs on event-related potentials and power spectral analysis in normal subjects.

The effect of lorazepam and methylphenidate on the ERPs and power spectral analysis was studied. Lorazepam caused prolonged latency and decreased amplitude of N200 and P300. This result suggests that lorazepam affects the neural processing of cognitive function. The drowsiness induced by lorazepam correlated inversely with alpha frequency power, but had no direct correlation with fast activity. On the contrary, when methylphenidate was given, there was no change in ERPs. There was an increase in percent alpha frequency correlated with the alertness of the subjects. An analysis of variance involving the factors of drug and time of rating showed that subjects showed a significant (p less than 0.0001) decrease in alertness over time while receiving lorazepam, and a significant (p less than 0.05) increase in alertness over time while receiving methylphenidate.

Adolescent↗
PubMed1996

Spectral analysis of heart rate variability before and during episodes of nocturnal ischaemia in patients with extensive coronary artery disease.

Spectral analysis of heart rate variability was used to assess autonomic nervous system activity associated with episodes of nocturnal myocardial ischaemia in 32 patients (20 men, age 58 +/- 9 years) with extensive coronary artery disease. Twenty-four hour Holter tape recordings were analysed and spectral indexes of heart rate variability were computed by fast Fourier analysis on 2 min segments covering the period from 10 min before to 10 min after each nocturnal ischaemic episode, defined as ST segment depression > or = 1 mm lasting at least 4 min. Spectral power was measured at low frequencies (LF: 0.06-0.10 Hz) and high frequencies (HF: 0.15-0.40 Hz) and the ratio LF/HF was calculated. RESULTS. A total of 30 episodes of nocturnal ischaemia were analysed. High frequency spectral power showed a clear decrease during the 10 min before the onset of ischaemia, remained steady until the end of the episode, and returned to normal by 6 min after. Low frequency spectral power fluctuated throughout the ischaemic episodes with no clear pattern of variation. The low/high frequency ratio reflected mainly the changes in high frequency. CONCLUSIONS. Sympathetic predominance due to para-sympathetic withdrawal is the principal change in autonomic nervous system activity associated with episodes of nocturnal ischaemia.

Aged↗
PubMed1999

Poststimulus EEG spectral analysis and P300: attention, task, and probability.

Event-related potentials (ERPs) were elicited with auditory stimuli, and spectral analysis was performed on the poststimulus electroencephalographic (EEG) activity to assess how variables that influence the P300 affect spectral parameters of the resultant ERP. In Experiment 1, a no-stimulus condition was compared with a single repeated tone that was either ignored or counted. In Experiment 2, an auditory oddball paradigm was used in which the subject ignored all stimuli, counted only the target, or counted both the target and the standard stimuli in different conditions. In Experiment 3, stimulus probability was manipulated in separate conditions (.20, .50, .80), with the subject required to count the target stimulus. Delta and theta band spectral power increased whenever P300 amplitude increased. However, as the attentional requirements increased across tasks, alpha-1 and alpha-2 power and mean frequency increased. The findings indicate that auditory stimulus processing modulates the EEG more than just by adding ERP components to the epoch.

Adult↗
PubMed1989

Spectral analysis of antepartum heart rate variability.

The present paper illustrates the basic methodological aspects of the power spectral analysis applied to fetal ECG starting from a gestational age around the 25th week of gestation until term. An abdominal ECG signal is recorded and fetal and maternal QRSs are recognised through selective digital filtering and averaging techniques. Power Spectral Density (PSD) of the discrete R-R series is then calculated through an autoregressive (AR) technique. In analogy with what happens in adult human subjects, fetuses manifest variability in correspondence to particular bands in the spectrum which are sensitive to the sympatho-vagal balance which controls many cardiovascular functions and respiration in different physiological conditions. Such a method is easily implemented on a personal computer and may be used to asses the development of the autonomic nervous system in fetuses as well as to show the physiopathological reasons which perturbate the relevant control mechanisms.

Cardiotocography↗
PubMed2002

Impairment in cardiac autonomic regulation preceding arterial hypertension in humans: insights from spectral analysis of beat-by-beat cardiovascular variability.

BACKGROUND: Subjects in the upper-normal range of arterial pressure have an excess cardiovascular risk, which suggests that other factors, such as impaired autonomic regulation, might be implicated. This study was designed to assess whether noninvasive markers of cardiac and vascular autonomic regulation might already be altered in subjects with high-normal arterial pressure levels. METHODS AND RESULTS: We performed an observational study on a population comprising 300 subjects of both sexes with arterial pressure ranging from 90/60 to 210/120 mm Hg, who were divided into 3 groups (each n=100) with average systolic pressures of 103, 133, and 163 mm Hg. Autonomic regulation was inferred from spectral analysis of RR interval and systolic arterial pressure variability, considering rest and stand-induced changes, to account for sympathetic excitatory components. Significant alterations in markers of sinoatrial regulation (increased low-frequency normalized units, reduced high-frequency normalized units, and alpha-index) were already apparent in subjects in the second tertile, ie, those with arterial pressure within normal limits. Markers of vascular regulation instead showed significant alterations in the third (hypertensive) tertile. In response to standing, changes in markers of sinoatrial modulations were gradually reduced, whereas those of vascular regulation were increased. A tight link between progression of arterial pressure and the continuum of changes in autonomic markers as shown by simple correlation analysis appeared strongly affected by age and was spread across many spectral analysis-derived variables. Hypertensive autonomic dysregulation was particularly apparent in the youngest group. CONCLUSIONS: RR-variability parameters might prove useful to assess, with longitudinal studies, the mechanistic role of autonomic impairment in the increased risk of prehypertensive conditions.

Adolescent↗
PubMed1989

Spectral analysis of pendular waveforms in congenital nystagmus.

We analyzed quantitatively electronystagmographic recordings of pendular waveforms via spectral analysis methods. We found (1) symmetrical pendular oscillations in orbital positions spanning a range as wide as 40 degrees, with frequencies between 2 and 8 Hz; (2) stable and small pendular oscillations in patients without a null zone and unstable and large pendular oscillations in patients with a neutral zone; (3) a non-decreasing relationship between the amplitude and the frequency of the eye oscillations, and (4) pendular components in orbital positions at the two sides of a neutral zone. It is argued that pendular nystagmus can be generated independently of normal (jerk) nystagmus in the same orbital position.

Adolescent↗
PubMedDate not supplied

Real time sound spectral analysis for early detection of thrombosed Björk-Shiley standard disc valves.

Clinical usefulness of sound spectral analysis (SSA) in early detection of thrombosed Bjork-Shiley standard tilting disc prostheses (B-SP) was evaluated. Among a total of 365 B-SP, nine valves developed thrombosis. These included seven MVR and two AVR, and replacement of the affected valves was performed in all cases. Thrombus formation was localized at the minor strut in two cases in which the SSA demonstrated preoperative abnormalities of only opening clicks. In four cases, thrombus formation was noted at both minor and major struts, and the SSA showed abnormalities both on opening and closing clicks. In two cases with pannus formation, no abnormalities were found by SSA. As the thrombi were seen on the minor strut during surgery in all cases with thrombosed valves, the minor strut is considered as the preferred, and probably initial area of thrombus formation, and the diagnosis therefore could be made by abnormal findings on opening clicks. In conclusion, the SSA was found to be a useful diagnostic tool for early detection of thrombosis of B-SP, because the opening clicks of the tilting disc valves were often too low in amplitude for abnormalities to be detected by auscultation.

Adult↗
PubMed1993

[Spectral analysis of long-term blood pressure measurements in patients with sleep-related respiratory disorders].

Spectral analysis of long-term recordings of blood pressure is a convenient method to recognise and reveal the amplitude and periodicity of changes in blood pressure during sleep. The increased variability of nocturnal blood pressure in patients with sleep apnoea is mainly determined by two types of oscillating variations in blood pressure: 1. Oscillations in a low frequency range of 0.0-0.06 Hz associated with breathing disorders and consecutive arousals. 2. Oscillations in a higher frequency range of 0.2-0.5 Hz associated with three different patterns of breathing. Normal undisturbed breathing, regular snoring and ineffective breathing efforts during obstruction of the upper airways. Furthermore, the interaction between breathing or breathing disorder and arterial blood pressure is determined by the influence of the sleep stages.

Adult↗
PubMed1998

[Temporal and spectral analysis of heart rate variability in primary dilate cardiomyopathy: evaluation by case control study].

Temporal and spectral analysis of heart rate variability over 24 hours (HRV) was undertaken in 89 patients with primary dilated cardiomyopathy (DCM) confirmed by left ventriculography with normal coronary angiography and compared with 60 control subjects. The left ventricular ejection fraction was 35 +/- 12% in the DCM patients (71 men and 18 women: age 51 +/- 11 years). Clinical signs of cardiac failure were observed in 66% of patients, requiring medication in 62% of patients (diuretics: 47%, digitalis: 45% and ACE inhibitors: 33%). The HRV was significantly lower in the DCM patients than in the control group, even in the absence of clinical signs of cardiac failure. The global HRV was correlated to left ventricular fractional shortening (r = 0.5, p < 0.001) and peak oxygen consumption on exercise (r = 0.56, p < 0.01), but was independent of the degree of left ventricular dilatation, pulmonary capillary pressure and cardiac index. It was not significantly different in cases of sustained or non-sustained ventricular tachycardia on Holter ECG or in cases with late ventricular potentials on signal averaging of the surface ECG. During follow-up of 51 +/- 35 months, patients with decreased HRV on the global indices and those reflecting sympathetic activity had a much higher risk of cardiovascular death and of cardiac transplantation (p < 0.01). The authors conclude that HRV is decreased in DCM. This is mainly related to the degree of left ventricular dysfunction and is independent of the ventricular arrhythmogenic substrate. The HRV may also identify subgroups of patients with DCM at high risk of cardiovascular death or of haemodynamic decompensation requiring cardiac transplantation.

Adult↗
PubMed1996

Application of time series spectral analysis theory: analysis of cardiovascular variability signals.

The paper focuses on the most important application problems commonly encountered in spectral analysis of short-term (less than 10 min) recordings of cardiovascular variability signals (CVSs), critically analysing the different approaches to these problems presented in the literature and suggesting practical solutions based on sound theoretical and empirical considerations. The Blackman-Tukey (BT) and Burg methods have been selected as the most representative of classical and AR spectral estimators, respectively. For realistic simulations, 'synthetic' CVSs are generated as AR processes whose parameters are estimated on corresponding time series of normal, post-myocardial infarction and congestive heart failure subjects. The problem of resolution of spectral estimates is addressed, and an empirical method is proposed for model order selection in AR estimation. The issue of the understandability and interpretability of spectral shapes is discussed. The problem of non-stationarity and removing trends is dealt with. The important issue of identification and estimation of spectral components is discussed, and the main advantages and drawbacks of spectral decomposition algorithms are critically evaluated.

Heart Diseases↗
PubMed1995

Spectral analysis of fetal heart rate in flat recordings.

Flat heart rate recordings may be observed in different fetal states such as chronic distress and sleep. Their visual analysis do not allow the distinction between these two states. We used spectral analysis to study the heart rate patterns in 25 fetuses. Two significant (P < 5 x 10(-5)) groups were apparent from the determination of the position of the maximum energy peak (PMEP) in the high-frequency band (0.20-0.50 Hz): a PMEP at about 0.20 Hz (group 1), and another around 0.30 Hz (group 2). The two groups did not differ in spectral density (SD). The outcome of neonates showed that group 1 fetuses made good progress and produced healthy neonates; whereas group 2 comprised cases of chronic fetal distress, or even death in utero, and neonatal distress. The significance of this difference in PMEP between fetal heart rate patterns in chronic distress and sleep is unclear. Studies combining the assessment of fetal movements and the determination of PMEP are planned.

Female↗
PubMed1994

Effects of lorazepam on cardiac vagal tone during rest and mental stress: assessment by means of spectral analysis.

Dose-dependent effects of intravenously administered lorazepam on haemodynamic fluctuations were studied by means of spectral analysis, in order to elucidate sympathetic and parasympathetic components in cardiovascular control during situations of rest and mental stress after benzodiazepine administration. In a double-blind randomized cross-over study, nine male volunteers participated in two sessions: a placebo and lorazepam session. During these sessions, the subjects repeatedly performed a 10-min version of the Stroop Color Word Test (CWT), with 10 min of rest between the CWTs. Lorazepam was administered before each rest period in increasing doses of 0.0, 0.06, 0.13, 0.25 and 0.5 mg (total cumulative dose: 0.94 mg). During the placebo session the subjects received five placebo injections. For five of the nine subjects the lorazepam session was their first session. Heat rate (HR), blood pressure (BP) and respiration were recorded continuously. Power spectra were calculated per 2.5-min periods for HR, systolic (SBP) and diastolic BP (DBP). Spectral density was assessed for three frequency bands: low (LFB: 0.02-0.06 Hz), mid (MFB: 0.07-0.14 Hz) and high (HFB: 0.15-0.40 Hz). During the consecutive periods of rest, lorazepam induced a dose-dependent decrease in HR, and a dose-dependent increase in LFB, MFB and HFB power of HR, but lorazepam had no effect on BP. The effects were significant after 0.44 mg lorazepam for HR and HFB power, and after 0.94 mg lorazepam for the HR fluctuations in the LFB and MFB. Lorazepam did not influence the cardiovascular responses to the CWT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Ultrasound Doppler spectral analysis in the diagnosis of occlusive lesions of the carotid arteries.

To evaluate the accuracy of Ultrasound Doppler Spectral Analysis (USDA), 432 carotid arteries were examined [group I consisted of 145 cases of normal ICA (internal carotid artery), group II--187 cases of ICA stenosis and group III--100 cases of ICA occlusion]. The maximal systolic peak (Smax), maximal diastolic peak (Dmax), the spectral broadening index (SB) and the pulsativity index (PI) were calculated and related to the degree of stenosis as determined by contrast arteriography. Our results indicate that the change of the value of Smax is the main diagnostic criterion: for carotid arteries' stenoses, it increases to over 3.2 kHz. A Smax over 6.0 kHz is a veritable index of ICA stenosis above 50%: in such cases as the stenosis increases by 10%, this corresponds to an approximately 1 kHz increase of Smax. In ICA occlusion, the main criterion was the absence of blood flow in the distal ICA segment. The UDSA sensitivity in hemodynamically insignificant stenosis is 73.9% which is far higher than in the periorbital Doppler examination; in hemodynamically significant stenosis and ICA occlusions, the sensitivity is 98.6 and 99%, respectively.

Arterial Occlusive Diseases↗