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PubMed2001

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance.

The mechanisms leading to vasovagal syncope are still unclear. A simple discriminating test for the identification of syncope-prone subjects is not presently available. Fifty-two subjects had a stepwise orthostatic test with 60 degrees tilt and -20 and -40 mm Hg lower-body negative pressure before the appearance of impending syncope symptoms. Spectral and cross-spectral analyses of heart period and systolic pressure time series were performed to estimate the power of the high-frequency (approximately equals 0.25 Hz) and low-frequency (approximately equals 0.1 Hz) oscillations, the coherence between heart period and systolic pressure, and the mean low-frequency and high-frequency central frequency, phase shift, and transfer function at maximal coherence. According to time to presyncope, the 52 subjects were divided into two groups: 25 with normal orthostatic tolerance, and 27 with poor orthostatic tolerance. In the supine positions, the mean central low-frequency was significantly lower in poor-tolerance group than in normal-tolerance group, discriminating poor from normal orthostatic tolerance with 80% specificity and 83% sensitivity, and was significantly correlated to time to presyncope. In the 2 to 3 minutes preceding syncope, subjects with poor orthostatic tolerance had less tachycardia, lower low-frequency power of systolic pressure, higher respiratory frequency, and a less negative phase shift in high-frequency range. In presyncope, sympathetic activation is reduced in subjects with poor orthostatic tolerance. In addition, the higher breathing frequency and the smaller negativity of phase shift in high-frequency range, which may indicate an inadequate engagement of the baroreflex, suggest a causal role of respiration in the development of syncope. Supine central values of low frequency may be proposed as a valuable clinical index of orthostatic intolerance.

Adult↗
PubMed2002

31P-MR spectroscopy in children and adolescents with a familial risk of schizophrenia.

Based on a previous report [9] on alterations of membrane phosphorus metabolism in asymptomatic family members of schizophrenic patients, the aim of the present study was to extend and improve the evaluation and data processing of (31)P spectroscopic data obtained from a larger study population by including an analysis of the broad spectral component (BC) of membrane phospholipids (PL). Eighteen children and siblings of patients with schizophrenia and a gender- and age-matched control group of 18 healthy subjects without familial schizophrenia were investigated with phosphorus magnetic resonance spectroscopy ((31)P-MRS) by using image selected in vivo spectroscopy (ISIS) in the dorsolateral prefrontal regions (DLPFR) of the brain. Spectral analysis was performed by using both the full and truncated FID to estimate metabolic peak ratios of different (31)P metabolites and the intensity and linewidth of the broad component. A significantly higher PDE level (p<0.01) and increased linewidth of the PDE components were observed for the high-risk group compared with the control group (p=0.02). No significant differences were observed for PME as well as for other (31)P-metabolites. No differences were observed between the left and right hemispheres for different normalised (31)P-metabolic levels. Decreased intensities (p=0.03) and smaller linewidths (p=0.01) were obtained for the broad component in the high-risk group. Impairments of membrane metabolism that are typical for schizophrenic patients are partially observed in adolescent asymptomatic family members of schizophrenics, including increased levels of low molecular PDE compounds indicating increased membrane degradation processes, no changes for PME, and decreased intensities and linewidths of the BC indicating changes in the composition and fluidity of membrane phospholipids. Despite limitations to completely suppress fast-relaxing components by dismissing initial FID data points, the spectroscopic results indicate additional changes in the membrane metabolism of high-risk subjects beyond changes of synthesis and degradation.

Adolescent↗
PubMed1989

A view of the world through the bat's ear: the formation of acoustic images in echolocation.

Echolocating bats perceive objects as acoustic images derived from echoes of the ultrasonic sounds they emit. They can detect, track, identify, and intercept flying insects using sonar. Many species, such as the big brown bat, Eptesicus fuscus, emit frequency-modulated sonar sounds and perceive the distance to targets, or target range, from the delay of echoes. For Eptesicus, a point-target's image has a sharpness along the range axis that is determined by the acuity of echo-delay perception, which is about 10 ns under favorable conditions. The image as a whole has a fine range structure that corresponds to the cross-correlation function between emissions and echoes. A complex target- which has reflecting points, called "glints", located at slightly different distances and reflects echoes containing overlapping components with slightly different delays--is perceived in terms of its range profile. The separation of the glints along the range dimension is encoded by the shape of the echo spectrum created by interference between overlapping echo components. However, Eptesicus transforms the echo spectrum back into an estimate of the original delay separation of echo components. The bat thus converts spectral cues into elements of an image expressed in terms of range. The absolute range of the nearest glint is encoded by the arrival time of the earliest echo component, and the spectrally encoded range separation of additional glints is referred to this time-encoded reference range for the image as a whole. Each individual glint is represented by a cross-correlation function for its own echo component, the nearest of which is computed directly from arrival-time measurements while further ones are computed by transformation of the echo spectrum. The bat then sums the cross-correlation functions for multiple glints to form the entire image of the complex target. Range and shape are two distinct features of targets that are separately encoded by the bat's auditory system, but the bat perceives unitary images that require fusion of these features to create a synthetic psychological dimension of range. The bat's use of cross-correlation-like images reveals neural computations that achieve fusion of stimulus features and offers an example of high-level operations involved in the formation of perceptual "wholes".

Animals↗
PubMed1996

Evaluation of an automated real-time spectral analysis technique.

An adaptive real-time Doppler peak-frequency tracing algorithm was evaluated in vitro and compared to manual peak-frequency traces. A computer-controlled pump was used to generate physiological flow waveforms in a vasculature-mimicking phantom. Spectral waveforms were obtained on an ATL HDI along with real-time estimates of diagnostic parameters, including maximum systolic, minimum diastolic, time-averaged peak frequencies and pulsatility and resistance indices. The effect of the signal-to-noise ratio on the measured parameters was investigated. The imprecision in the measured parameters was found to depend somewhat on the waveform shape; e.g., the imprecision in PI was 4.1% for a normal renal waveform and 8.5% for a waveform having reverse diastolic flow. The peak frequency envelopes of the same waveform data were traced manually by nine operators, and the resulting diagnostic parameters were compared to ones obtained from automated peak-frequency traces of the same waveform data. The agreement between parameters measured by the automated routine and those measured manually was found to depend somewhat on the waveform shape; e.g., the bias in the PI was 1.3% for a renal waveform lacking diastolic flow, and 12% for a waveform with reverse diastolic flow. The between-observer variations in the manual measurements ranged from 0.8% up to 9.4%. The overall variations associated with the automated traces were found to be smaller than or equal to those of the manual traces.

Algorithms↗
PubMed2001

In vivo 1H MR spectra analysis by means of second derivative method.

Short echo time (TE) in vivo PRESS 1H MR spectra (2 T, TE=35 ms) of normal brain were fitted in the frequency domain using the second derivative method. In this approach, local maxima and hidden peaks are found as local minima of spectrum second derivative. The Lorentzian robust minimisation procedure (referred to as maximum likelihood or m-estimate fitting) using Levenburg-Marquardt non-linear fitting engine was applied. Spectral lines were approximated under the assumption of the mixed Lorentzian/Gaussian lineshapes. The same procedure was applied to 18 proton spectra. The number of peaks found within the range of 0.74/4.2 parts per million (ppm) was 52+/-3 and their positions were almost the same. The fitted lines were assigned on the basis of the J-pattern recalculated for the field strength of 2 T and by comparing the chemical shifts with the shifts in the single compound spectra. The ratios of main metabolites, such as NAA/Cr, Cho/Cr, Cho/NAA and mI/Cr, are in accord with those obtained earlier using the software supplied with the MR imager and the absolute concentrations of N-acetylaspartate (NAA), choline containing compounds (Cho), myoInositol (mI), glucose (Glc) and glutamate (Glu) obtained from the fit agree with those reported in literature, which confirms the usefulness of the second derivative method in routine analyses of 1H MR brain spectra.

Adult↗
PubMed2006

Multiple and simultaneous fluorophore detection using fluorescence spectrometry and partial least-squares regression with sample-specific confidence intervals.

Fluorescent labeling is widely used in biological and chemical analysis, and the drive for increased throughput is stretching multiplexing capabilities to the limit. The limiting factor in multiplexed analyses is the ability to subsequently deconvolute the signals. Consequently, alternative approaches for interpreting complex data sets are required to allow individual components to be identified. Here we have investigated the application of a novel approach to multiplexed analysis that does not rely on multivariate curve resolution to achieve signal deconvolution. The approach calculates a sample-specific confidence interval for a multivariate (partial least-squares regression (PLSR)) prediction, thereby enabling the estimation of the presence or absence of each fluorophore based on the total spectral signal. This approach could potentially be applied to any multiplexed measurement system and has the advantage over the current algorithm-based methods that the requirement for resolution of spectral peaks is not central to the method. Here, PLSR was used to obtain the concentrations for up to eight dye-labeled oligonucleotides at levels of (0.6-5.3) x 10(-6) M. The sample-specific prediction intervals show good discrimination for the presence/absence of seven of the eight labeled oligonucleotides with efficiencies ranging from approximately 91 to 100%.

Confidence Intervals↗
PubMed2006

Arterial stiffness and baroreflex sensitivity following bouts of aerobic and resistance exercise.

We examined arterial stiffness, baroreflex sensitivity (BRS), and systolic arterial pressure (SAP) variability after an acute bout of aerobic exercise compared to resistance exercise. We hypothesized that arterial stiffness would be reduced after aerobic exercise, while it would be increased after resistance exercise, and these alterations would be associated with differential changes in BRS and SAP variability. Arterial stiffness, BRS, and SAP variability were assessed before and 20 min after a bout of aerobic exercise and resistance exercise in 13 male participants. Pulse wave velocity (PWV) was used to measure central (carotid-femoral) and peripheral (femoral-dorsalis pedis) arterial stiffness. BRS was derived via the sequence technique. Spectral decomposition of beat-to-beat SAP variability was used as an estimate of sympathetic vasomotor tone. A mode-by-time interaction (p < 0.001) was detected for central PWV, due to an increase in PWV (p < 0.05) following resistance exercise and a decrease in PWV following aerobic exercise (p < 0.05). A mode-by-time interaction was also detected for peripheral PWV (p < 0.05), due to a decrease in peripheral PWV following aerobic exercise (p < 0.05) with no change following resistance exercise. BRS was significantly lower following resistance compared with aerobic exercise (p < 0.004). SAP variability increased following resistance exercise (p < 0.05) but there was no interaction. In conclusion, aerobic exercise decreased both central and peripheral arterial stiffness, while resistance exercise significantly increased central arterial stiffness only. BRS was reduced after both bouts of exercise, but significantly greater reductions were seen following resistance exercise.

Adult↗
PubMed2006

Spectral correlations of fractional Brownian motion.

Fractional Brownian motion (fBm) is a ubiquitous nonstationary model for many physical processes with power-law time-averaged spectra. In this paper, we exploit the nonstationarity to derive the full spectral correlation structure of fBm. Starting from the time-varying correlation function, we derive two different time-frequency spectral correlation functions (the ambiguity function and the Kirkwood-Rihaczek spectrum), and one dual-frequency spectral correlation function. The dual-frequency spectral correlation has a surprisingly simple structure, with spectral support on three discrete lines. The theoretical predictions are verified by spectrum estimates of Monte Carlo simulations and of a time series of earthquakes with a magnitude of 7 and higher.

Journal Article↗
PubMed2005

The angular difference function and its application to image registration.

The estimation of large motions without prior knowledge is an important problem in image registration. In this paper, we present the angular difference function (ADF) and demonstrate its applicability to rotation estimation. The ADF of two functions is defined as the integral of their spectral difference along the radial direction. It is efficiently computed using the pseudopolar Fourier transform, which computes the discrete Fourier transform of an image on a near spherical grid. Unlike other Fourier-based registration schemes, the suggested approach does not require any interpolation. Thus, it is more accurate and significantly faster.

Algorithms↗
PubMed1981

The optics of human skin.

An integrated review of the transfer of optical radiation into human skin is presented, aimed at developing useful models for photomedicine. The component chromophores of epidermis and stratum corneum in general determine the attenuation of radiation in these layers, moreso than does optical scattering. Epidermal thickness and melanization are important factors for UV wavelengths less than 300 nm, whereas the attenuation of UVA (320-400 nm) and visible radiation is primarily via melanin. The selective penetration of all optical wavelengths into psoriatic skin can be maximized by application of clear lipophilic liquids, which decrease regular reflectance by a refractive-index matching mechanism. Sensitivity to wavelengths less than 320 nm can be enhanced by prolonged aqueous bathing, which extracts urocanic acid and other diffusible epidermal chromophores. Optical properties of the dermis are modelled using the Kubelka-Munk approach, and calculations of scattering and absorption coefficients are presented. This simple approach allows estimates of the penetration of radiation in vivo using noninvasive measurements of cutaneous spectral remittance (diffuse reflectance). Although the blood chromophores Hb, HbO2, and bilirubin determine dermal absorption of wavelengths longer than 320 nm, scattering by collagen fibers largely determines the depths to which these wavelengths penetrate the dermis, and profoundly modifies skin colors. An optical "window" exists between 600 and 1300 nm, which offers the possibility of treating large tissue volumes with certain long-wavelength photosensitizers. Moreover, whenever photosensitized action spectra extend across the near UV and/or visible spectrum, judicious choice of wavelengths allows some selection of the tissue layers directly affected.

Epidermis↗
PubMedDate not supplied

Energy distributions from a racetrack microtron measured with a magnetic spectrometer.

Energy spectra of accelerated electron beams from a racetrack microtron were measured using a magnetic spectrometer. The spectrometer utilized a 90 degrees dipole magnet. A ray-tracing program was developed to determine the slit positions of the spectrometer based on a detailed map of the magnetic field measured at field strengths corresponding to about 20 and 50 MeV. The total a priori uncertainty (previously often called systematic or class B uncertainty) of the measured most probable energy Ep is 0.22% (one approximate standard deviation) and the a posteriori uncertainty (previously often called random or class A uncertainty) is 0.04% (1 sigma). The estimated energy resolution (delta E/E) of the spectrometer is 4 x 10(-4). Spectral energy distributions of the electron beam were measured at a Ep = 21.1 and 51.6 MeV, and the obtained full width at half-maximum of the energy distributions were 53 and 34 keV, respectively. All the measurements were performed in vacuum to minimize the influence of electron energy loss and scatter.

Electrons↗
PubMed2006

Measuring the critical band for speech.

The current experiments were designed to measure the frequency resolution employed by listeners during the perception of everyday sentences. Speech bands having nearly vertical filter slopes and narrow bandwidths were sharply partitioned into various numbers of equal log- or ERBN-width subbands. The temporal envelope from each partition was used to amplitude modulate a corresponding band of low-noise noise, and the modulated carriers were combined and presented to normal-hearing listeners. Intelligibility increased and reached asymptote as the number of partitions increased. In the mid- and high-frequency regions of the speech spectrum, the partition bandwidth corresponding to asymptotic performance matched current estimates of psychophysical tuning across a number of conditions. These results indicate that, in these regions, the critical band for speech matches the critical band measured using traditional psychoacoustic methods and nonspeech stimuli. However, in the low-frequency region, partition bandwidths at asymptote were somewhat narrower than would be predicted based upon psychophysical tuning. It is concluded that, overall, current estimates of psychophysical tuning represent reasonably well the ability of listeners to extract spectral detail from running speech.

Adolescent↗
PubMed2001

Respiratory modulation of human autonomic rhythms.

We studied the influence of three types of breathing [spontaneous, frequency controlled (0.25 Hz), and hyperventilation with 100% oxygen] and apnea on R-R interval, photoplethysmographic arterial pressure, and muscle sympathetic rhythms in nine healthy young adults. We integrated fast Fourier transform power spectra over low (0.05-0.15 Hz) and respiratory (0.15-0.3 Hz) frequencies; estimated vagal baroreceptor-cardiac reflex gain at low frequencies with cross-spectral techniques; and used partial coherence analysis to remove the influence of breathing from the R-R interval, systolic pressure, and muscle sympathetic nerve spectra. Coherence among signals varied as functions of both frequency and time. Partialization abolished the coherence among these signals at respiratory but not at low frequencies. The mode of breathing did not influence low-frequency oscillations, and they persisted during apnea. Our study documents the independence of low-frequency rhythms from respiratory activity and suggests that the close correlations that may exist among arterial pressures, R-R intervals, and muscle sympathetic nerve activity at respiratory frequencies result from the influence of respiration on these measures rather than from arterial baroreflex physiology. Most importantly, our results indicate that correlations among autonomic and hemodynamic rhythms vary over time and frequency, and, thus, are facultative rather than fixed.

Adult↗
PubMed2002

Autonomic neural control of dynamic cerebral autoregulation in humans.

BACKGROUND: The purpose of the present study was to determine the role of autonomic neural control of dynamic cerebral autoregulation in humans. METHODS AND RESULTS: We measured arterial pressure and cerebral blood flow (CBF) velocity in 12 healthy subjects (aged 29+/-6 years) before and after ganglion blockade with trimethaphan. CBF velocity was measured in the middle cerebral artery using transcranial Doppler. The magnitude of spontaneous changes in mean blood pressure and CBF velocity were quantified by spectral analysis. The transfer function gain, phase, and coherence between these variables were estimated to quantify dynamic cerebral autoregulation. After ganglion blockade, systolic and pulse pressure decreased significantly by 13% and 26%, respectively. CBF velocity decreased by 6% (P<0.05). In the very low frequency range (0.02 to 0.07 Hz), mean blood pressure variability decreased significantly (by 82%), while CBF velocity variability persisted. Thus, transfer function gain increased by 81%. In addition, the phase lead of CBF velocity to arterial pressure diminished. These changes in transfer function gain and phase persisted despite restoration of arterial pressure by infusion of phenylephrine and normalization of mean blood pressure variability by oscillatory lower body negative pressure. CONCLUSIONS: These data suggest that dynamic cerebral autoregulation is altered by ganglion blockade. We speculate that autonomic neural control of the cerebral circulation is tonically active and likely plays a significant role in the regulation of beat-to-beat CBF in humans.

Adult↗
PubMed2006

Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus.

Autonomic control of heart rate variability and the central location of vagal preganglionic neurones (VPN) were examined in the rattlesnake (Crotalus durissus terrificus), in order to determine whether respiratory sinus arrhythmia (RSA) occurred in a similar manner to that described for mammals. Resting ECG signals were recorded in undisturbed snakes using miniature datalogging devices, and the presence of oscillations in heart rate (fh) was assessed by power spectral analysis (PSA). This mathematical technique provides a graphical output that enables the estimation of cardiac autonomic control by measuring periodic changes in the heart beat interval. At fh above 19 min(-1) spectra were mainly characterised by low frequency components, reflecting mainly adrenergic tonus on the heart. By contrast, at fh below 19 min(-1) spectra typically contained high frequency components, demonstrated to be cholinergic in origin. Snakes with a fh >19 min(-1) may therefore have insufficient cholinergic tonus and/or too high an adrenergic tonus acting upon the heart for respiratory sinus arrhythmia (RSA) to develop. A parallel study monitored fh simultaneously with the intraperitoneal pressures associated with lung inflation. Snakes with a fh<19 min(-1) exhibited a high frequency (HF) peak in the power spectrum, which correlated with ventilation rate (fv). Adrenergic blockade by propranolol infusion increased the variability of the ventilation cycle, and the oscillatory component of the fh spectrum broadened accordingly. Infusion of atropine to effect cholinergic blockade abolished this HF component, confirming a role for vagal control of the heart in matching fh and fv in the rattlesnake. A neuroanatomical study of the brainstem revealed two locations for vagal preganglionic neurones (VPN). This is consistent with the suggestion that generation of ventilatory components in the heart rate variability (HRV) signal are dependent on spatially distinct loci for cardiac VPN. Therefore, this study has demonstrated the presence of RSA in the HRV signal and a dual location for VPN in the rattlesnake. We suggest there to be a causal relationship between these two observations.

Animals↗
PubMed2003

Passive standoff detection of Bacillus subtilis aerosol by Fourier-transform infrared radiometry.

An analysis is presented on the passive standoff detection and identification of Bacillus subtilis (BG) clouds with the Compact ATmospheric Sounding Interferometer (CATSI) sensor. This research is based on recent spectral measurements obtained during the Technology Readiness Evaluation trial held July 2002 at Dugway Proving Ground, Utah. Results obtained from three trial BG cloud episodes are used to explain and demonstrate the detection capability of the CATSI sensor. The BG clouds were measured at a distance of 3 km from the sensor in a near-horizontal path scenario. It was found that the low thermal contrast of approximately 0.2 K between the BG cloud and the background yielded weak but observable spectral signatures. The processing of the spectral signatures with the GASeous Emission Monitoring (GASEM) algorithm has provided a rough estimate of BG cloud column densities. The results of a series of simulations with the FASCOD3 transmission model have shown that the detection sensitivity for BG can be greatly improved for both slant path uplooking and downlooking scenarios.

Aerosols↗
PubMed2005

Excited-state absorption and anisotropy properties of two-photon absorbing fluorene derivatives.

The electronic structure of fluorene derivatives N-(7-benzothiazol-2-yl-9,9-bis-decyl-9H-fluoren-2-yl)-acetamide (1); 9,9-didecyl-2,7-bis-(N,N-benzothiazoyl)fluorene (2); 4,4'-{[9,9-bis(ethyl)-9H-fluorene-2,7-diyl]di-2,1-ethenediyl}bis(N,N-diphenyl)benzeneamine (3); and 4,4',4"{[9,9-bis(ethyl)-9H-fluorene-2,4,7-triyl]tri-2,1-ethenediyl}tris(N,N-diphenyl)benzeneamine (4) were investigated by a steady-state spectral technique, quantum-chemical calculations, and a picosecond pump-probe method. These derivatives are of interest for their relatively high two-photon absorption. The steady-state excitation anisotropy spectra reveal the nature of the ground-state absorption bands. Semiempirical quantum-chemical calculations of the fluorene derivatives (AM1, ZINDO/S) show good agreement with experimental data. The spectral positions and alignment of various electronic transitions of derivatives 1-4 were estimated from their excited-state absorption and anisotropy spectra.

Absorption↗
PubMed1996

Prevalence of pulmonary hypertension in limited and diffuse scleroderma.

STUDY OBJECTIVES: To characterize the prevalence of undiagnosed pulmonary hypertension in patients with limited and diffuse scleroderma. DESIGN: Prospective cross-sectional study. SETTING: University-based outpatient clinic. PATIENTS: Thirty-four consecutive patients with limited (n = 29) or diffuse (n = 5) scleroderma but without the clinical diagnosis of pulmonary hypertension. MEASUREMENTS AND RESULTS: All patients had 12-lead ECGs and two-dimensional and Doppler echocardiograms. The pulmonary artery systolic pressure (PAs) was calculated as the sum of the Doppler transtricuspid pressure gradient and the right atrial pressure as estimated by the caval respiratory index. Thirty-three patients (97%) had adequate spectral signals of tricuspid regurgitation. The velocity of tricuspid regurgitation ranged from 1.6 to 4.5 m/s. The calculated PAs ranged from 15 to 95 (mean +/- SD = 30 +/- 14 mm Hg). Twelve patients (35% of the total cohort) had pulmonary hypertension defined as PAs of 30 mm Hg or greater. CONCLUSIONS: Undiagnosed elevation of PAs is common in patients with scleroderma. Noninvasive assessment of PAs can be performed accurately in most patients independent of clinical signs of pulmonary hypertension. If successful treatment strategies are identified, it may be possible to identify patients early in the development of pulmonary hypertension and intervene before significant end-organ damage occurs.

Adult↗