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PubMed2000

Stability of the noninvasive baroreflex sensitivity assessment using cross-spectral analysis of heart rate and arterial blood pressure variabilities.

BACKGROUND: Depressed baroreflex sensitivity (BRS), usually estimated using the invasive phenylephrine method or the nitroprusside test, is significantly and independently associated with an increased risk of malignant ventricular arrhythmias and sudden cardiac death in patients surviving acute myocardial infarction. Several investigators have compared the standard phenylephrine test and different noninvasive methods. HYPOTHESIS: This study evaluated the influence of different body positions with different breathing regimes on cross-spectral baroreflex indices (coherence between the spectral densities of blood pressure and cardiac cycle variabilities) in both low- and high-frequency bands. METHODS: The data were obtained in 103 patients (73 males, aged 53 +/- 12 years) with coronary artery disease and/or hypertension. Simultaneous electrocardiographic and noninvasive blood pressure recordings were obtained in each subject in both supine and sitting positions during both spontaneous and slow and fast controlled respiration (0.1 and 0.33 Hz). RESULTS: The results show a significant bias and disagreement between noninvasive baroreflex sensitivity (BRS) indices. The mean values of the baroreflex in low frequency ranged from 5.0 +/- 5.3 to 10.1 +/- 7.9 ms/mmHg, while in high frequency, the mean values ranged from 6.6 +/- 6.1 to 10.1 +/- 7.9 ms/mmHg. The limits of agreement ranged from +/-1.7 to +/-4.1 ms/mmHg with bias from -1.0 to +0.7 ms/mmHg. CONCLUSION: A comprehensive comparison of different methods shows that BRS estimated in low-frequency band in sitting position during spontaneous respiration is the most representative part of the global baroreflex gain.

Adult↗

PubMed2003

Conditional data processing for single-shot spectral analysis by use of laser-induced breakdown spectroscopy.

Schemes of conditional data processing are evaluated based on either the peak-to-base ratio or the signal-to-noise ratio as a metric for analyte detection in single-shot laser-induced breakdown spectra. The analyte signal investigated is the 288.1-nm Si I emission line provided by an aerosol stream of monodisperse 2.5-microm-sized silica microspheres. Both the Si emission line and a spectral region corresponding to continuum emission are used to evaluate the statistical distribution of spectral noise. The probability of false hits is determined by evaluating various conditional processing thresholds. As the detection threshold increases, the rate of detected silica particle hits decreases along with the expected fraction of false-particle hits (i.e., spectral noise). For all threshold values the signal-to-noise ratio is found to provide a more robust metric for single-shot analyte detection compared with the peak-to-base ratio.

Journal Article↗

PubMed2004

Classification of arterial plaque by spectral analysis in remodelled human atherosclerotic coronary arteries.

We aimed to characterise and to identify the predominant plaque type in vivo using unprocessed radiofrequency (RF) intravascular ultrasound (US) backscatter, in remodelled segments of human atherosclerotic coronary arteries. A total of 16 remodelled segments were identified using a 30-MHz intravascular ultrasound (IVUS) scanner in vivo. Of these, 9 segments were classified as positively remodelled (>1.05 of the total vessel area in comparison with the proximal and distal reference segments) and 7 as negatively remodelled (<0.95 of reference segment area). Spectral parameters (maximum power, mean power, minimum power and power at 30 MHz) were determined and plaque type was defined as mixed fibrous, calcified or lipid-rich. Positively remodelled segments had a larger total vessel area (16.5 +/- 1.1 mm2 vs. 8.7 +/- 0.9 mm2, p<0.01) and plaque area (7.3 +/- 1.1 mm2 vs. 4.4 +/- 0.8 mm2, p=0.05) than negatively remodelled segments. Both positively and negatively remodelled segments had a greater percentage of fibrous plaque (p<0.01) than calcified or lipid-rich plaque. Comparing positively and negatively remodelled segments, there was no significant difference between the proportion of fibrous, calcified or lipid-rich plaque. We have been able to characterise and to identify plaque composition in vivo in human atherosclerotic coronary arteries. Our data suggest that remodelled segments are predominantly composed of fibrous plaque, as identified by RF analysis, although plaque composition is similar, irrespective of the remodelling type.

Adaptation, Physiological↗

PubMed1991

Spectral analysis of sleep electroencephalography in rotating three-shift work.

Fourteen male rotating three-shift workers were subjected to 24-h ambulatory polysomnographic recording in connection with morning, afternoon, and night shift work (at home and at work). Total sleep time, stage 2, rapid-eye-movement sleep, and slow-wave sleep (stages 3 + 4) were significantly reduced during sleep in connection with the night and morning shifts. Other visually scored sleep parameters and slow-wave energy (spectral power density integrated across sleep) were not affected. The content of the sleep cycles did not differ between shifts. The sleep before the morning shift was characterized by subjectively increased difficulties of sleep initiation and sleep termination, as well as by insufficient recuperation. The night shift was characterized by increased subjective difficulties of maintaining sleep, but also by increased ease of sleep initiation. It was concluded that both morning and evening shifts interfered with sleep, although no effects of sleep deprivation were found.

Adult↗

PubMed2001

Optimized thiol derivatizing reagent for the mass spectral analysis of disubstituted epoxy fatty acids.

A novel procedure is described for the derivatization of fatty acid epoxides in the presence of their corresponding diols. The acidic character of 2,3,5,6-tetrafluorobenzenethiol promotes favorable mass fragmentation of linoleate and arachidonate derived epoxide derivatives and reduces alkene isomerization to a manageable side reaction, eliminated through the addition of a thiol scavenger. After silylation, regioisomeric mixtures of epoxy- and dihydroxylipids are simultaneously detected and discriminated using gas chromatography with electron impact mass spectral detection. Silylated hydroxysulfanyloctadecanoids yielded instrumental detection limits of 5 pg/microl, sufficient sensitivity for the quantification of endogenous epoxylipids.

Epoxy Compounds↗

PubMed1993

Time-resolved infrared spectral analysis of the KL-to-L conversion in the photocycle of bacteriorhodopsin.

Time-resolved infrared spectra of the hydrated film of light-adapted bacteriorhodopsin were recorded from earlier than 200 ns to 450 microseconds after light excitation in the 1800-900-cm-1 region on a newly designed dispersive-type infrared spectrometer [Iwata & Hamaguchi (1989) Appl. Spectrosc. 44, 1431-1437]. Both the KL-to-L and L-to-M conversions were detected in this time range. The spectral shape of KL is similar to K measured at 77 K except for the intense hydrogen out-of-plane vibrational band at 984 cm-1. The kinetics of this band are different from those of the other KL-specific bands at 1510, 1296, and 956 cm-1. Since the hydrogen out-of-plane vibrational bands are intensified by twists of the polyene chain, a change in the twist of the chromophore is suggested within the lifetime of KL. During the decaying process of L, the KL-specific vibrational bands are observed in parallel with L, indicating that KL and L are in equilibrium.

Bacteriorhodopsins↗

PubMed1984

Spectral analysis of sung vowels. I. Variation due to differences between vowels, singers, and modes of singing.

Average 1/3-oct filter spectra of vowels, sung by seven professional male and seven professional female singers , were measured. The material consisted of nine different vowels, sung at six fundamental frequencies (F0, ranging from 98 up to 880 Hz). For each vowel the singers were requested to sing in the following nine modes: neutral, light, dark, pressed, free, loud, soft, straight, and extra vibrato . To study origins of spectral variation, the quantity of spectral variance, based on band filter sound levels, was used. For each fundamental frequency and separately for males and females, portions of total spectral variance associated with the main effects and the interactions of the factors "vowels," " singers ," and "modes of singing," were computed. A considerable decrease in total spectral variance was found when F0 rose from 98 to 880 Hz, mostly due to the reduced spectral variance between vowels. Above about F0 = 660 Hz spectral variation was dominated by differences related to singers and modes of singing. Additional analyses revealed that for all F0 values vowel spectra of the tenor and the soprano singers varied more than those of the bass and the alto singers , there was only a slight dependence of spectral differences between vowels on the mode of singing, and the amount of spectral variation in a vowel, sung by different singers with different modes of singing, was vowel dependent.

Female↗

PubMed1999

Fetal magnetoencephalogram recordings and Fourier spectral analysis.

This study investigates the fetal brain activity in normal and pre-eclamptic pregnancies. Measurements were performed by means of a Superconducting Quantum Interference Device (SQUID) in an electrically shielded room of low magnetic noise. The study was prospective. Eleven pregnant women with pre-eclampsia and 21 normal pregnancies were included. All were at 37-40 weeks of pregnancy. Biomagnetic signals (waveforms), recorded from the fetal brains in the frequency range of 2-7 Hz, were expressed in terms of magnetic power spectral amplitudes. These were low (mean, 376.67; SD, 28.66) in almost all normal pregnancies, and high (mean, 554.91; SD, 149.56) in most pregnancies complicated with preeclampsia. These findings were of statistical significance (Student's t -test, P < 0.005). Biomagnetic measurements of fetal brain activity is a promising screening procedure for assessing the cerebral function, especially in high risk pregnancies.

Journal Article↗

PubMed1988

Spectral analysis of impedance respirogram in newborn infants.

Respiratory rate (RR), transthoracic electric impedance (TEZ) and transcutaneous PO2 and PCO2 were monitored during the 5 first postnatal days in 54 neonates on three separate occasions. There was no difference in the overall RR between the term and healthy preterm babies on different days of recordings but RR of the babies with RDS (who were all ventilated) was lower on day 1 (p less than 0.01). When the power spectrum of the TEZ respirogram was computed and the spectral density was divided into low-frequency (LF, less than 0.20 Hz) and high-frequency (HF, greater than 0.20 Hz) areas, the LF/HF ratio of healthy preterm babies was greater than that of term babies on day 1 (p less than 0.01). The preterm babies with RDS did not differ from the term babies in this respect. The LF/HF ratio was negatively correlated with gestational age and it had a positive correlation to PtcO2 (p less than 0.05) and PtcCO2 (p less than 0.01) (R2 = 0.07). The result evidences that the control of respiration changes in relation to maturity and the LF/HF ratio is a quantitative indicator of respiratory variability reflecting this development.

Blood Gas Monitoring, Transcutaneous↗

PubMed2001

Fibrillation power, an alternative method of ECG spectral analysis for prediction of countershock success in a porcine model of ventricular fibrillation.

BACKGROUND: Noninvasive prediction of defibrillation success after cardiac arrest and cardiopulmonary resuscitation (CPR) may help in determining the optimal time for a countershock, and thus increase the chance for survival. METHODS: In a porcine model (n=25) of prolonged cardiac arrest, advanced cardiac life support was provided by administration of two or three doses of either vasopressin or epinephrine after 3 or 8 min of basic life support. After 4 min of ventricular fibrillation and 18 min of life support, defibrillation was attempted. The denoised power spectral density of 10 s intervals of the ventricular fibrillation electrocardiogram (ECG) was estimated from averaged and smoothed Fourier transforms. We have eliminated the spectral contribution of artifacts from manual chest compressions and provide a definition for the contribution of ventricular fibrillation to the power spectral density. This contribution is quantified and termed "fibrillation power". RESULTS: We tested fibrillation power and two established methods in their discrimination of survivors (n=16) vs. non-survivors (n=9) in the last minute before the countershock. A fibrillation power > or =79 dB predicted successful defibrillation with sensitivity, specificity, positive predictive value and negative predictive value of 98%, 98%, 99% and 97% while a mean fibrillation frequency > or =7.7 Hz was predictive with 85%, 83%, 90% and 77% and a mean amplitude > or =0.49 mV was predictive with 95%, 90%, 94% and 91%. CONCLUSIONS: We suggest that fibrillation power is an alternative source of information on the status of a fibrillating heart and that it may match the established mean frequency and amplitude analysis of ECG in predicting successful countershock during CPR.

Animals↗

PubMed2001

Autonomic nervous function in patients with peptic ulcer studied by spectral analysis of heart rate variability.

This study is intended to clarify the relationship between occurrence of peptic ulcer disease and dysfunction of the autonomic nervous system. We studied heart rate variability and assessed the circadian rhythm of autonomic nervous function in 20 patients with peptic ulcer (PU group) and 20 age-matched healthy controls (N group) using 24-hour Holter monitoring. Moreover, the relationship between gastric juice secretion and autonomic activity was examined under intravenous injection of insulin or butylscopolamine in adult mongrel dogs. High frequency spectral (HF) power, an indicator of parasympathetic tone, was increased markedly at night in the PU group. Low frequency spectral (LF) power, an indicator of sympathetic tone modified by vagal tone, was higher during the day than at night in the N group, whereas this normal circadian rhythm of LF power disappeared in 11 cases (55%) in the PU group. In addition, the LF power was increased significantly at night (p<0.01) in the PU group. HF power and gastric juice secretion was increased by the administration of insulin. High sympatho-vagal tone at night may result in spasm of gastric arteries and excess secretion of gastric acid in the PU group. These results suggest that the nocturnal acceleration of LF, HF, and LF/HF is related to peptic ulcer diseases.

Adult↗

PubMedDate not supplied

Spectral analysis of sudden bradycardia during intrathecal meperidine anesthesia.

BACKGROUND AND OBJECTIVES: Severe bradycardia occurring suddenly during spinal anesthesia, although rare, is potentially fatal. Bradycardias are more common after intrathecal meperidine. We report two such episodes occurring in elderly male patients undergoing transurethral surgery. METHODS: Subarachnoid block was provided using 50 mg meperidine. Autonomic function was assessed by measuring heart rate (HR) variability using R-R intervals from standard electrocardiographic recordings. Frequency-domain spectra were constructed from 512 heartbeats, and an autoregressive method was used to calculate spectral power. RESULTS: In both patients, bradycardia (HR <50 beats/min) occurred after about 10 minutes and was associated with severe hypotension and a 10- to 100-fold increase in spectral density in both the low (0.04-0.15 Hz), mainly sympathetic, and the high (0.15-0.40 Hz), mainly parasympathetic, frequency bands. These spectral increases were subsequently attenuated by intravenous atropine. Heart rate slowing was noted to be periodic, or oscillatory, in one patient. CONCLUSION: Sudden increases in vagal, or parasympathetic, activity probably accounted for bradycardia.

Adjuvants, Anesthesia↗

PubMed1983

An accurate recording system and its use in breath sounds spectral analysis.

An accurate recording system was set up and used for analyzing normal and asthmatic breath-sound features. Breath sounds are recorded at the trachea simultaneously with the airflow signal at 0.5- and 1-1/s levels. The study was carried out in the frequency domain using a fast-fourier transform (FFT). FFTs are taken on 1,024-sample blocks (one block = 200 ms) over a duration of about 20 s. Different characteristics of the spectra are calculated in the range 60-1,260 Hz for 11 normal and 10 asthmatic subjects. This allows the computation of an index that discriminates (P less than 0.0005) asthma cases from normal cases. Spectral features strongly depend on the flow rate both for normal and asthmatic subjects. Increasing the flow rate raises the high-frequency components of the spectra.

Adult↗

PubMed1989

Long-term spectral analysis of heart rate variability--an algorithm based on segmental frequency distributions of beat-to-beat intervals.

Reduced heart rate variability has been reported as a predictor of long-term mortality in recent myocardial infarction patients. However, it has not been systematically investigated whether the reduction in heart rate variability in those post myocardial infarction patients who later suffer death or severe arrhythmias is caused by a reduction of short-term variability of heart rate (such as respiratory arrhythmia) or whether the differences in long term variability (such as diurnal rhythm) are involved. In order to perform such an evaluation, a new algorithm has been developed which permits different wavelength components (including the long-term components due to diurnal rhythm) of heart rate variability to be approximated. In general, the method uses segmental frequency distributions of durations of intervals between successive normal cardiac beats. To assess the spectral components of heart rate variability, a scale of wavelength limits is used and for each limit of this scale, the algorithm excludes the rate changes of wavelength longer than the given bound. The method was applied to the analysis of electrocardiograms recorded in 14 post myocardial infarction patients who later suffered death or ventricular tachycardia, and in 14 other randomly selected patients with an uncomplicated course following acute myocardial infarction. The rate variability spectra obtained for both groups of patients were compared statistically and the results showed that the groups of positive and negative cases were most significantly distinguished when including both short- and long-term components of heart rate variability. Separate evaluation of different wavelength components showed that the very long-term components of heart rate variability were more powerful in distinguishing between positive and negative cases than the short term components.

Algorithms↗

PubMed1984

Synthesis, spectral analysis, and mutagenicity of 1-, 3-, and 6-nitrobenzo[a]pyrene.

The mutagenic environmental pollutants 1-, 3-, and 6-nitrobenzo[a]pyrene were synthesized. Nitration of 7,8,9,10-tetrahydrobenzo[a]pyrene with sodium nitrate in trifluoroacetic acid and acetic anhydride at ambient temperature gave a mixture of 1-, 3-, and 6-nitro-7,8,9,10-tetrahydrobenzo[a]pyrene, which was separated by chromatography. Dehydrogenation of the isolated nitrotetrahydrobenzo[a]pyrenes with 2,3-dichloro-4,5-dicyano-1,6-benzoquinone produced 1-, 3-, and 6-nitrobenzo[a]pyrene in high yield. Comparison of the spectral data of these compounds with those obtained from direct nitration of benzo[a]pyrene confirmed that 1- and 3-nitrobenzo[a]pyrenes are indeed the minor products of the latter reaction. This confirmation also verifies that 1- and 3-nitrobenzo[a]pyrene were the minor nitrated products of benzo[a]pyrene formed in model air atmospheres. The 1-, 3-, and 6-nitrobenzo[a]pyrene were mutagenic in Salmonella typhimurium tester strains TA98 and TA100 in the presence of a mammalian microsomal (S9) activating system. Both 1- and 3-nitrobenzo[a]pyrene, but not 6-nitrobenzo[a]pyrene, were also direct-acting mutagens in these strains. However, only 6-nitrobenzo[a]pyrene exhibited weak mutagenic activity when tested in Chinese hamster ovary cells, while only 3-nitrobenzo[a]pyrene produced a concentration-dependent decrease in cellular survival.

Benzopyrenes↗

PubMed2005

Fractal spectral analysis of pre-epileptic seizures in terms of criticality.

The analysis of pre-epileptic seizure through EEG (electroencephalography) is an important issue for epilepsy diagnosis. Currently, there exist some methods derived from the dynamics to analyse the pre-epileptic EEG data. It is still necessary to create a novel method to better fit and explain the EEG data for making sense of the seizures' predictability. In this paper, a fractal wavelet-based spectral method is proposed and applied to analyse EEG recordings from rat experiments. Three types of patterns are found from the 12 experiments; moreover three typical cases corresponding to the three types of seizures are sorted out and analysed in detail by using the new method. The results indicate that this method can reveal the characteristic signs of an approaching seizure, which includes the emergence of long-range correlation, the decrease of anti-persistence behaviour with time and the decrease of the fractal dimension. The pre-seizure features and their implications are further discussed in the framework of the theory of criticality. We suggest that an epileptic seizure could be considered as a generalized kind of "critical phenomenon", culminating in a large event that is analogous to a kind of "critical point". We also emphasize that epileptic event emergence is a non-repetitive process, so the critical interpretation meets a certain number of cases.

Algorithms↗

PubMedDate not supplied

Use of power spectral analysis of respiratory sinus arrhythmia to detect graft rejection.

Some evidence has suggested that graft rejection in heart transplant recipients is accompanied by sinus node dysfunction. To test this hypothesis the electrocardiograms of 21 orthotopic heart transplant recipients receiving cyclosporine were recorded at regularly scheduled biopsies. This resulted in 105 good quality recordings of at least 10 minutes each. All exhibited normal sinus rhythm. These recordings were then processed through patented digital routines that calculated the power spectrum of the RR intervals. All recordings exhibited Mayer wave and respiratory sinus arrhythmia (RSA) periodicities. Peak spectral power of RSA (PSP-RSA) demonstrated good repeatability at 2 weeks (r = 0.81). A paired t test comparing the baseline PSP-RSA in eight subjects who experienced rejection episodes with their individual average PSP-RSA during periods of rejection revealed a significant decrease (p = 0.039). As a global measure, PSP-RSA greater than 1 (natural logarithmic scales) demonstrated a sensitivity of 1.0, specificity of 0.42, positive predictive value of 0.22, and negative predictive value of 1.0. These tentative results demonstrate that PSP-RSA may be a sensitive, noninvasive marker for graft rejection of heart transplant patients receiving cyclosporine for immunosuppression. A larger, more extensive study needs to be conducted to confirm these results.

Adult↗

PubMed2000

Spectral analysis of heart rate variability in premature infants with feeding bradycardia.

An elevated level of baseline parasympathetic activity was noted in a group of premature infants suffering from bradycardia during feeding. At approximately 34 wk post-conceptional age, the heart rates of 12 infants with feeding bradycardia (birth weight = 1539 +/- 279 g; gestational age = 31.0 +/- 1.6 wk) and 10 controls (birth weight = 1710 +/- 304 g; gestational age = 32.0 +/- 1.4 wk) were recorded 1 h before and 1 h after feeding. EKG data were digitized and 3.2-min segments of data were analyzed to determine the spectral power at very low (VLF = 0.003-0.03 Hz), low (LF = 0.03-0.39 Hz), and high (HF = 0.40-1.00 Hz) frequencies. In preterm infants with feeding bradycardia, an elevation in baseline parasympathetic activity was evident before feeding, as indicated by significantly higher HF power and a lower LF/HF ratio. This elevation in baseline parasympathetic activity may contribute to the observed bradycardia during feeding.

Apgar Score↗