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PubMed1997

Longitudinal sleep EEG power spectral analysis studies in adolescents with minor head injury.

Power spectral analysis (PSA) was used to evaluate the longitudinal overnight electroencephalographic (EEG) sleep recordings of eight subjects, between the ages of 15 and 19 years, who had sustained a minor head injury (MHI). Recordings occurred within 72 h, 6 weeks, and 12 weeks following MHI. A conditioning night preceded the first study night during which EEG electrodes were in place and subjects slept at least 7.5 h with a mean sleep efficiency of 91%. PSA was performed on four channels of EEG data recorded from fronto-temporal (F3-T3, F4-T4), and temporal (T3-T5, T4-T6) electrodes. The three waveforms associated with sleep, Delta, Theta, and Alpha-1 were all significantly elevated within 72 h post-MHI. Over time all wave forms decreased in mean log power. Theta in rapid eye movement (REM) sleep Cycle 1 decreased significantly within 6 weeks postinjury. The greatest number of significant changes, over the 12-week period were recorded during the non-REM (NREM) sleep. Changes included (1) significant decreases in mean log power of Theta and Alpha-1 in Cycle 1 from fronto-temporal leads; (2) significant decreases in Delta, Theta, and Alpha-1 in Cycle 2 from fronto-temporal leads, and (3) significant decreases in Delta and Theta for consistency during Cycle 2 from temporal leads. The intrusion of Theta into the first REM cycle within 6 weeks and its subsequent decrease within 6 weeks suggested the initiation of recovery toward baseline values. This was followed by decreased levels of Theta power during NREM Cycles 1 and 2, and Delta power in Cycle 2, both of which approached their lowest levels within 12 wks. The decrease in Alpha-1 power occurred last. Alpha-1 remained elevated through both Cycles 1 and 2 of the 6th week and then showed a precipitous decrease between the sixth and twelfth week. These findings suggested that following MHI, the brain has a specific sequence of recovery as illustrated by Delta, Theta, and Alpha-1 powers requiring different time frames to reach their lowest levels.

Adolescent↗
PubMed1993

Power spectral analysis of heart rate variability after spinal anaesthesia.

Power spectral analysis of heart rate (HR) variability is a useful tool with which to assess cardiac autonomic activity. The low frequency bands have been considered as both sympathetically and parasympathetically mediated components, while the high frequency bands have been assumed to be the parasympathetically mediated respiratory components. It has been anticipated that spinal anaesthesia to the thoracic level may modulate cardiac autonomic activity to reduce HR and arterial pressure by blocking cardiac sympathetic activity. In order to quantify the alterations in cardiac autonomic activity, we have analysed the power spectra of HR variability for 30 min after subarachnoid administration of hyperbaric amethocaine. Using 256-s R-R interval data obtained from continuously recorded ECG, low frequency (Lo: 0.04-0.15 Hz) and high frequency (Hi: 0.15-0.40 Hz) band widths were integrated and their serial alterations were computed by shifting subjected R-R intervals at 60-s intervals. After the subarachnoid injection, arterial pressure, HR and Lo decreased and Hi and the Hi:Lo ratio increased. These changes were observed within 15-20 min. Ventilatory frequency did not change throughout the study. These findings suggest that the decrease in HR and arterial pressure after subarachnoid administration of hyperbaric amethocaine reflect decreased sympathetic activity and increased parasympathetic activity in the cardiac autonomic nervous system.

Adult↗
PubMed1984

Power spectral analysis of visual evoked potentials in multiple sclerosis.

Power spectral analysis (PSA) was performed on the visual evoked potentials (VEPs) to counterphased checkerboard stimuli from 98 eyes in 49 patients with multiple sclerosis (MS) and 54 eyes of 27 normal volunteers. Attenuation of high frequency components of the transient visual evoked potential was found in 53% of MS patients and 4% of controls. Loss of high frequency components was poorly correlated with prolonged latency (r = 0.346). The consideration of both PSA and latency of the VEP increased the percentage of MS patients exhibiting visual pathway conduction abnormalities from 61% to 86%. The use of PSA in the diagnosis of MS is useful in increasing detection especially in cases where deformed waveforms preclude a reliable estimation of latency.

Adult↗
PubMed2004

EEG spectral analysis of relaxation techniques.

The acute central nervous system effects of relaxation techniques (RT) have not been systematically studied. We conducted a controlled, randomized study of the central nervous system effects of RT using spectral analysis of EEG activity. Thirty-six subjects were randomized to either RT or a music comparison condition. After listening to an RT audiotape or music audiotapes daily for 6 weeks, the acute central nervous system effects of RT and music were measured using power spectral analysis of alpha and theta EEG activity in all cortical regions. RT produced significantly greater increases in theta activity in multiple cortical regions compared to the music condition. These findings are consistent with widespread reductions in cortical arousal during RT. They extend previous findings and suggest that theta, and not alpha, EEG may be the most reliable marker of the central nervous system effects of RT. These findings demonstrate that RT produce greater reductions in central nervous system activity than a credible comparison condition. The findings suggest that RT represent a hypoactive central nervous system state that may be similar to Stage 1 sleep and that RT may exert their therapeutic effects, in part, through cerebral energy conservation/restoration.

Adult↗
PubMed1997

Power spectral analysis of heart rate and diastolic blood pressure variability in migraine with and without aura.

Autonomic function in migraineurs during headache-free periods was studied by means of cardiovascular reflexes and power spectral analysis of heart rate and diastolic blood pressure variability. We examined 56 patients: 37 suffering from migraine without aura and 19 from migraine with aura. Cardiovascular responses to the tilt test and Valsalva manoeuvre showed a normal function of the overall baroreceptor reflex arc. Normal heart rate responses to Valsalva manoeuvre and deep breathing suggested an intact parasympathetic function. Power spectral analysis of both heart rate and diastolic blood pressure variability in basal conditions and during orthostatic test showed similar sympathovagal interactions modulating cardiovascular control in migraine patients and in controls.

Adult↗
PubMed1988

Heart-rate spectral analysis: a noninvasive probe of cardiovascular regulation in critically ill children with heart disease.

Children may die suddenly and unexpectedly following cardiac surgery, even while receiving intensive medical care, when current noninvasive and invasive monitoring techniques fail to warn us of an impending problem. This report examines the efficacy of heart-rate spectral analysis, a noninvasive method that quantitates the beat-to-beat fluctuations in heart rate, in characterizing and tracking cardiovascular regulatory status. A total of 45 heart-rate fluctuation studies, performed on selected patients, at the bedside, using heart-rate spectral analysis, were retrospectively correlated with clinical events. The spectral pattern of 18 patients who sustained a cardiac arrest differed significantly from the others in the study group (p less than 0.0001).

Adolescent↗
PubMed2002

Spectral analysis of heart rate and blood pressure variability in primary Sjögren's syndrome.

BACKGROUND: Autonomic dysfunction has been described in primary Sjögren's syndrome (SS). OBJECTIVE: To investigate the circulatory autonomic regulation in patients with primary SS by power spectral analysis of heart rate and blood pressure variability. METHODS: Forty three (42 female) patients with primary SS, mean age 52 years (range 23-80), with a mean disease duration of eight years (range 1-30) and 30 (15 female) healthy controls, mean age 43 years (range 21-68) were studied. In each patient blood pressure, heart rate, and respiration were measured continuously during supine rest and orthostatic challenge (60 degrees head-up tilt). Power spectral analysis was performed to determine possible differences in short term sympathetic and parasympathetic autonomic regulation between patients and controls. Furthermore, spectral parameters were studied in relation to illness severity and disease duration of the patients with primary SS. RESULTS: After controlling for differences in age, heart rate variability of the mid-frequency band and the variation coefficient of systolic blood pressure were significantly lower in patients with primary SS than in controls during supine rest. During 60 degrees tilt patients with primary SS showed a significantly higher mean heart rate, mean systolic blood pressure, and variation coefficient of diastolic blood pressure, and a significantly lower baroreflex index than controls. After controlling for age, no differences were found either in heart rate variability, blood pressure results, and baroreflex sensitivity during supine rest and tilt between the subgroups divided according to disease duration, Schirmer test results, or between the subgroups with different fatigue scores. No differences were found in spectral data between the groups with and without positive antinuclear antibody serology. CONCLUSION: For the group no differences in sympathetic and parasympathetic cardiac control were seen between patients with primary SS and controls, as assessed by spectral techniques, although some cardiovascular differences were found, particularly during orthostatic challenge.

Adult↗
PubMed2003

Spectral analysis of heart rate variation following simultaneous pancreas and kidney transplantation.

Only marginally improved results have been observed in standard autonomic function tests (AFT) in follow-up studies after simultaneous pancreas and kidney transplantation (SPK). We therefore used power spectral analysis (PSA) of heart rate variability (HRV) to assess the effect of SPK on autonomic neuropathy in patients with type I diabetes mellitus (DM I). We evaluated 82 patients with DM I who were insulin and dialysis free following SPK. Both pre- and posttransplant (at [mean +/- SD], 25 +/- 15 months post-SPK) examinations were performed in 29 patients. Posttransplant evolution was examined in another 60 patients with two serial examinations at 20 +/- 20 and 43 +/- 27 months after SPK. Comparisons included 32 age-matched healthy controls and 13 patients with kidney transplant alone (KTA) matched for age and duration of DM I at a comparable time point posttransplant. Short-term time (modified Ewing battery) and frequency domain (PSA of HRV: LF-low, HF-high frequency, and TP-total spectral power) analysis was performed with a telemetric, on-line, computer-aided system. Significantly worse results in all standard AFT and PSA indexes were obtained for SPK patients compared with controls at all time points. No significant improvement was seen in SPK patients in the posttransplant period and no differences were found compared with KTA patients. Thus the results of a power spectral analysis of HRV failed to show improvement following SPK. This examination adds little positive information to that obtained from standard autonomic function tests.

Adult↗
PubMed1995

Time-frequency spectral analysis of electric field plethysmography signals.

Cardiac activity contaminates respiratory electric field plethysmography (EFPG) signals, and vice versa, and is usually treated as an artefact. On the other hand, simultaneous information on respiration and cardiac activity is often required in clinical practice. Hence, we use time-frequency spectral analysis (TFSA) by means of the spectrogram (SG) to investigate the instantaneous cardio-respiratory information contained in EFPG-signals and show that it is a practical means of extracting this information out of a single EFPG-signal. Comparisons with a Wigner distribution reveal sufficient time-frequency resolution of the SG for detection of physiological events in EFPG-signals. SG-analysis indicates spectral peaks related to respiration and cardiac activity (depending on the electrode configuration, up to the third and fifth harmonic, respectively) and the possibility to detect respiratory sinus arrhythmia by means of EFPG-measurements. Intermodulation products cause overlaps of respiratory and cardiac spectra pointing out nonlinear relationships. Additionally, SG-analysis supplies essential information for the separation of EFPG-signals into respiratory and cardiac components, by means of filter techniques.

Adolescent↗
PubMed2005

Assessment of heart rate variability during alterations in stress: complex demodulation vs. spectral analysis.

Complex demodulation (CDM) has been proposed as a method for the analysis of high- and low-frequency variabilities of heart rate and blood pressure under non-stationary conditions. In contrast to power spectral analysis, CDM provides time-dependent changes in signal amplitude and frequency on a continuous basis and may yield insights into short-term alterations in autonomic regulation. In particular, CDM may be uniquely suited for quantifying changes in respiratory sinus arrhythmia (RSA) at the onset of acute physical or mental stress conditions. In a simulation analysis we generated R-R interval time series within a normal physiological range that represented different typical sources of non-stationarity present during varying stress. Sources of non-stationarity included abrupt changes in a) mean level (from 1000 to 500 ms within 60 sec), b) oscillatory amplitude (from 50 to 10 ms), c) oscillatory frequency (from 0.2 to 0.4 Hz), and d) a combination of the above. In general, CDM-estimated amplitude and frequency accurately reproduced characteristics of the simulation data under all conditions, even after substantial noise and a 0.09 Hz oscillation were added. However, during some transitions CDM estimates fluctuated around the true values for up to 15 sec before they stabilized. Compared to CDM, power spectral analysis results were less informative since they did not allow the disentangling of unique contributions of distinct amplitudes and frequencies at different time points. Our analyses indicate that CDM provides a powerful means of continuously assessing time-dependent changes in RSA during varying physical or mental stress. CDM may also hold promise for a range of physiological and environmental non-steady state conditions where rapid dynamic alterations in autonomic control are likely to occur.

Algorithms↗
PubMed2004

[Spectral analysis of heart rate variability in diagnosis of vegetative autonomic dysfunction in patients with attacks of atrial fibrillation.].

AIM: Elucidation of possible role of suprasegmental and segmental autonomic vegetative disturbances in pathogenesis of paroxysmal atrial fibrillation. MATERIAL: Untreated patients (n=22) with nonrheumatic paroxysmal atrial fibrillation and 10 healthy subjects. METHODS: Clinical cardiological and neurological examination, assessment of the state of vegetative nervous system, emotional sphere, patterns of sleep, and spectral analysis of heart rate variability. RESULTS: According to data of spectral analysis of heart rate variability patients with paroxysmal atrial fibrillation were characterized by marked vegetative dysfunction which was more pronounced in women, patients older than 52 years, with higher level of anxiety, with duration of symptoms longer than 6 years, and with predominantly nocturnal attacks. CONCLUSION: The data obtained should be considered in selection of therapy aimed at prevention of attacks of atrial fibrillation.

Atrial Fibrillation↗
PubMed1996

Power spectral analysis of heart rate in hyperthyroidism.

The aim of the present study was to evaluate the impact of hyperthyroidism on the cardiovascular system by separately analyzing the sympathetic and parasympathetic influences on heart rate. Heart rate variability was evaluated by autoregressive power spectral analysis. This method allows a reliable quantification of the low frequency (LF) and high frequency (HF) components of the heart rate power spectral density; these are considered to be under mainly sympathetic and pure parasympathetic control, respectively. In 10 newly diagnosed untreated hyperthyroid patients with Graves' disease, we analyzed power spectral density of heart rate cyclic variations at rest, while lying, and while standing. In addition, heart rate variations during deep breathing, lying and standing, and Valsalva's maneuver were analyzed. The results were compared to those obtained from 10 age-, sex-, and body mass index-matched control subjects. In 8 hyperthyroid patients, the same evaluation was repeated after the induction of stable euthyroidism by methimazole. Heart rate power spectral analysis showed a sharp reduction of HF components in hyperthyroid subjects compared to controls [lying, 13.3 +/- 4.1 vs. 32.0 +/- 5.6 normalized units (NU; P < 0.01); standing, 6.0 +/- 2.7 vs. 15.0 +/- 4.0 NU (P < 0.01); mean +/- SEM]. On the other hand components were comparable in the 2 groups (lying, 64.0 +/- 6.9 vs. 62.0 +/- 6.5 NU; standing, 77.0 +/- 6.5 vs. 78.0 +/- 5.4 NU). Hence, the LF/HF ratio, which is considered an index of sympathovagal balance, was increased in hyperthyroid subjects while both lying (11.3 +/- 4.5 vs. 3.5 +/- 1.1; P < 0.05) and standing (54.0 +/- 12.6 vs. 9.8 +/- 2.6; P < 0.02). This parameter was positively correlated with both T3 (r = 0.61; P < 0.05) and free T4 (r = 0.63; P < 0.05) serum levels. Among traditional cardiovascular autonomic tests, the reflex response of heart rate during lying to standing was significantly lower in hyperthyroid patients than in controls (1.12 +/- 0.03 vs. 1.31 +/- 0.04; P < 0.002). No statistically significant difference in reflex responses between the two groups was found in deep breathing or Valsalva's maneuver. In the 8 patients reexamined after methimazole treatment, we observed complete normalization of altered cardiovascular parameters, with slight predominance of the vagal component compared with controls. These results suggest that thyroid hormone excess may determine reduced parasympathetic activity and, thus, a relative hypersympathetic tone.

Adolescent↗
PubMed1998

Usefulness of Doppler spectral analysis and power Doppler sonography in the differentiation of cervical lymphadenopathies.

OBJECTIVE: Our purpose was to depict the characteristics of the global vasculature of cervical lymphadenopathies and to clarify the efficiency of Doppler spectral analysis and power Doppler sonography in the differential diagnosis. SUBJECTS AND METHODS: Prospectively, 289 lymph node lesions underwent Doppler flow studies and were grouped as metastasis, lymphoma, tuberculosis, and benign lymphadenopathies. Sonographic assessments included vascular pattern and vascular density (presented as vascularity index) as revealed by power Doppler sonography. Vascular resistive index and pulsatility index were assessed by at least three flow samplings. Values of both the highest and the lowest resistance were analyzed. Vascularity index, resistive index, pulsatility index, nodal size, and age were correlated. RESULTS: Most benign lymphadenopathies (87%), tuberculous lymphadenopathies (72%), and lymphomas (71%) revealed an avascular or hilar vascular pattern. Vascular patterns of most metastatic lymphadenopathies (90%) were of spotted (26%), peripheral (11%), or mixed (53%) type. The vascularity indexes of metastatic lymphadenopathy (mean, 0.176) and lymphoma (mean, 0.122) were significantly higher than those of tuberculous and benign lymphadenopathy (mean, 0.054 and 0.042, respectively). In vascular resistance studies, the highest pulsatility index and resistive index in metastatic lymphadenopathy statistically exceeded those of benign lymphadenopathy, whereas no difference was found in the lowest values. Negative correlation was found between the vascularity index of metastatic lesions and their lowest vascular resistance, and positive correlation was found between vascularity index and nodal size in benign lymphadenopathies. CONCLUSION: In addition to vascular resistance assessed traditionally with Doppler spectral analysis, vascular pattern and vascular density assessed with power Doppler sonography can better differentiate the nature of lymphadenopathies.

Adolescent↗
PubMed1993

Electrochemical and spectral analysis of the long-range interactions between the Qo and Qi sites and the heme prosthetic groups in ubiquinol-cytochrome c oxidoreductase.

The results are presented of an electrochemical and high-resolution spectral analysis of the heme prosthetic groups in the bc1 complex from mouse cells. To study the long-range interactions between the Qo and Qi quinone redox sites and the b heme groups, we analyzed the effects on the proximal and distal b heme groups, and the c1 heme, of inhibitors that tightly and specifically bind to the Qi or Qo redox site. A number of results emerged from these studies. (1) There is inhomogeneous broadening of the b heme alpha band absorption spectra. Furthermore, contrary to the conclusion from low-resolution spectral analysis, the higher energy transition in the split-alpha band spectrum of the bL heme is more intense than the lower energy transition. (2) Inhibitors that bind at the Qi site have significant effects upon the electronic environment of the distal bL heme. Conversely, Qo site inhibitors induced changes in the electronic environment of the distal bH heme. (3) In contrast, inhibitor binding at either site has little effect upon the midpoint potential of the distal heme. (4) Experiments in which both a Qi and a Qo inhibitor are bound at the redox sites indicate that the long-range effects of one inhibitor are not blocked by the second inhibitor; enhanced effects are often observed. (5) In the double-inhibitor titrations involving the Qo inhibitor myxothiazol, there is evidence for two electrochemically and spectrally distinct species of the bL heme group, a phenomenon not observed previously. (6) The high-resolution deconvolutions of alpha band absorption spectra allow an interpretation of these inhibitor-induced changes in terms of homogeneous broadening, inhomogeneous broadening, and changes in x-y degeneracy. The general conclusion from these experiments is that when an inhibitor binds to a quinone redox site of the cytochrome b protein, it produces local conformational changes that, in turn, are transmitted to distal regions of the protein. The ligation of the bH and bL hemes between two parallel transmembrane helices provides a mechanism by which long-distance interactions can be propagated. The lack of long-range effects upon the midpoint potentials of the heme groups suggests, however, that protein conformational changes are unlikely to be a major control mechanism for the transmembrane electron- and proton-transfer steps of the Q cycle.

Animals↗
PubMed1992

Propranolol in the prophylaxis of migraine--evaluation by spectral analysis of beat-to-beat heart rate fluctuations.

Migraine patients seem to suffer from a continuous autonomic imbalance. Sympathetic instability, expressed by enhanced low frequency fluctuations, which exists during the headache free intervals, was observed in our previous study by spectral analysis of heart rate (HR) fluctuations. Propranolol--a beta adrenoceptor antagonist, is widely used in migraine prophylaxis. In order to specify and quantitate propranolol efficacy in migraine, spectral analysis of heart rate fluctuations was performed on 10 migraine patients before and during the treatment with propranolol. They were compared to 10 healthy control patients and 6 migraine patients who were treated for several months with propranolol and then discontinued the medication. The analysis was carried out on a 24h Holter ECG recording, which was performed for each subject during a headache free interval. Short 256 sec subtraces, taken every 30 min from the 24h ECG signal, were submitted to A/D conversion, R wave detection and computation of heart rate power spectrum. Propranolol achieved a marked effect, when comparing the power spectra of HR fluctuations in treated versus untreated migraine patients. A strong reduction (to normal level) in the low frequency HR fluctuations in the range below 0.1 Hz., was apparent in patients treated with propranolol. Subjects who had received propranolol in the past and discontinued the drug, displayed a carry-over effect of reduced fluctuations even 2-3 months after its discontinuation. It seems that the propranolol efficacy in migraine is associated with the mechanism of stabilizing the fluctuations within the frequency band related to sympathetic activity, hereby moderating the vascular instability in migraine.

Adult↗
PubMed1997

The acute effects of inhaled salbutamol on the beat-to-beat variability of heart rate and blood pressure assessed by spectral analysis.

AIMS: We wanted to study the effects of a 600 micrograms inhaled salbutamol dose on the cardiovascular and respiratory autonomic nervous regulation in eight children suffering from bronchial asthma. METHODS: In this randomized, double-blind, placebo-controlled, crossover study we continuously measured electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry at baseline as well as 20 min and 2 h after the drug inhalation. The R-R interval (the time between successive heart beats) and SAP variabilities were assessed by using spectral analysis. Baroreflex sensitivity was assessed by using cross-spectral analysis. RESULTS: Salbutamol significantly decreased the total and low frequency (LF) variability of R-R intervals as well as the high frequency (HF) variability of R-R intervals and of SAP. Salbutamol significantly increased the LF/HF ratio of R-R intervals and of SAP, minute ventilation, heart rate and forced pulmonary function in comparison with placebo. The weight of the subjects significantly correlated positively with baroreflex sensitivity and negatively with heart rate after the salbutamol inhalation. CONCLUSIONS: We conclude that the acute salbutamol inhalation decreases cardiovagal nervous responsiveness, increases sympathetic dominance in the cardiovascular autonomic balance, and has a tendency to decrease baroreflex sensitivity in addition to improved pulmonary function.

Administration, Inhalation↗
PubMed1992

Effects of fentanyl-diazepam-pancuronium anesthesia on heart rate variability: a spectral analysis.

The effects of induction of anesthesia with fentanyl, 62.1 +/- 7.9 micrograms/kg, diazepam, 0.21 +/- 0.08 mg/kg, and pancuronium on beat-to-beat heart rate variations were studied in seven patients undergoing cardiac surgery. Spectral analysis was used to determine the intensity of the variations in each of the two main frequency bands in which variations are known to occur: (1) high-frequency band, mediated by the parasympathetic nervous system, at the frequency band of respiration, and (2) the low-frequency band, mediated by both sympathetic and parasympathetic nervous systems, at 0.04-0.12 Hz. Both the mean low- and high-frequency band areas were significantly decreased after induction of anesthesia. The ratio of high-to-low frequency band areas increased significantly after induction of anesthesia, from 45% to 62% (P less than 0.05). These results suggest that fentanyl-diazepam-pancuronium anesthesia decreases total autonomic nervous system activity and alters the balance between parasympathetic and sympathetic activities. Thus, spectral analysis of heart rate variations during anesthesia may provide a quantitative measure of assessing the activity of the autonomic nervous system.

Adult↗
PubMed1995

Detection of mechanical changes to prosthetic heart valves by spectral analysis of valve closing sounds.

This study investigates the possibility of using spectral analysis of the closing sounds of a prosthetic heart valve to indicate minor changes to its mechanical state. Sounds are recorded in vitro in a large effectively anechoic tank of water, and the elastically mounted valve is actuated pneumatically within the water. This provides a noise-free environment for recordings. Analysis of the valve sounds is by spectral averaging and digital filtering, with each individual valve used to create its own filter. Results show that it is possible using this technique to detect reliably changes in the mechanical state of a valve, such as the addition of a small mass to the structure of the valve.

Acoustics↗