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PubMed1995

Effects of ketanserin on heart rate and blood pressure variability: implications for the effect on the baroreflex mechanisms.

Ketanserin is an antihypertensive drug with affinity to both serotonin S2- and alpha 1-adrenoceptors. The specific effects of ketanserin on the baroreflex are not fully understood. We, therefore, studied baroreflex regulation based on blood pressure (BP) and heart rate (HR) responses to several maneuvers before and after the administration of 2 x 5 mg of ketanserin i.v. both in supine and in standing posture. Seven young healthy volunteers were investigated. We measured spontaneous variability in HR and BP (Finapres), and performed deep inspiration, Valsalva, and lying-to-standing tests. We also used a modified Valsalva maneuver that consist of Deep Inspiration Breath-holding with closed glottis and EXpiration: DIBEX maneuver. From the BP recordings, peripheral resistance (TPR) and stroke volume (SV) were estimated by the Modelflow method. Thirty minutes after the administration of ketanserin, there was no significant change in mean HR, BP, spectral power of HR and BP variability, baroreflex sensitivity, or Valsalva ratio. Thus ketanserin did not affect the cardiac baroreflex mechanism. However, in standing position, SV increased and TPR decreased under the influence of ketanserin, and BP overshoot after the Valsalva and DIBEX maneuver was significantly decreased as well. There was also no reflex recovery of BP during the DIBEX maneuver in three volunteers, who felt faint. These observations indicate that there is a lack of vasoconstriction. We conclude that ketanserin is not a vasodilator but seems to inhibit vasoconstriction.

Adult↗

PubMed1993

Electromyographic power spectrum analysis of the paraspinal muscles. Long-term reliability.

As a prerequisite to the use of electromyographic power spectral analysis of the paraspinal muscles as a low-back pain treatment outcome measure, the long-term reliability of the technique was assessed. The myoelectric signals of the multifidus and iliocostalis lumborum muscles of healthy sedentary women were analyzed with regard to spectral parameters during a constant-force contraction, before and after a 3-month period. Results indicated that for both muscles, estimates of initial median frequency and amplitude had high test/retest reliability, but that the recovery and left-right difference parameters were not stable. Using a confidence interval method, test/retest variation for the fatigue parameter was found to be within the range of variability of potentially underlying metabolic processes.

Adult↗

PubMed2003

Time-dependent seafloor acoustic backscatter (10-100 kHz).

A time-dependent model of the acoustic intensity backscattered by the seafloor is described and compared with data from a calibrated, vertically oriented, echo-sounder operating at 33 and 93 kHz. The model incorporates the characteristics of the echo-sounder and transmitted pulse, and the water column spreading and absorption losses. Scattering from the water-sediment interface is predicted using Helmholtz-Kirchhoff theory, parametrized by the mean grain size, the coherent reflection coefficient, and the strength and exponent of a power-law roughness spectrum. The composite roughness approach of Jackson et al. [J. Acoust. Soc. Am. 79, 1410-1422 (1986)], modified for the finite duration of the transmitted signal, is used to predict backscatter from subbottom inhomogeneities. It depends on the sediment's volume scattering and attenuation coefficients, as well as the interface characteristics governing sound transmission into the sediment. Estimation of model parameters (mean grain size, roughness spectrum strength and exponent, volume scattering coefficient) reveals ambiguous ranges for the two spectral components. Analyses of model outputs and of physical measurements reported in the literature yield practical constraints on roughness spectrum parameter settings appropriate for echo-envelope-based sediment classification procedures.

Acoustics↗

PubMed1996

[Rest-activity cycle in man].

An actigraph (ZAK company) is a small device that can be worn on the wrist like a watch. We carried out a study to compare sleep efficiency and total sleep time as determined by actigraphy and polysomnography. The number of body movements per minute is a density function. The integrated function shows a virtually constant gradient in the wake state and a different constant gradient during sleep. The body movement density function per hour provides a useful threshold for correctly differentiating between wake and sleep states. This threshold is defined as the minimum between the two maxima of the bimodal logarithmic body movement density distribution. In the second step we computed a rank scale of the different gradients and approximated the integrated function for every scale element using linear graphs. The points of intersection of the straight lines define the time points for sleep onset and end of sleep. Sleep efficiency is given by SE = 100 (TST-sleep interruption time)/TST. Total sleep time is the interval between sleep onset and end of sleep. Actigraphy is a suitable semi-objective method for estimating sleep efficiency and total sleep time, and--for cost reasons--should be used for screening before approaching a sleep laboratory. Actigraphy carried out over several days shows only small differences in comparison with polysomnography. The estimation of parameters is more accurate the longer the patient wears the actigraph, and a minimum of five days is recommended. Spectral analysis of the intregrated body movement density provides important information for detecting subclinical sleep disorders.

Circadian Rhythm↗

PubMed1976

[Study of mouse liver cell phosphorescence at deep cooling].

The spectrum and decay curves of phosphorescence of mouse liver cells at --180 degrees C was studied using the phosphorescence microscope. The phosphorescence studied was shown to involve two components with different life spans. Part of either component in the total spectrum is estimated. A conclusion is made that at least two different centers (or groups of centers) exist in cells with the same spectral region of phosphorescence with highly diverging life times of triplet states.

Animals↗

PubMed1977

Manganese cytochrome c. Structure and properties.

Oxidized and reduced manganese cytochromes c, Mn Cyt c+ and Mn Cyt c, have been synthesized. Mn Cyt c+ and Fe Cyt c+ have identical electrophoretic and ion exchange mobilities. Mn Cyt c+ does not bind F-, CN-, or N3- ions; Mn Cyt c does not bind CO or O2. Mn Cyt c is very rapidly autooxidized by O2 even at -50 degrees. The manganese ion is readily dissociated from Mn Cyt c at acidic pH values. Both Mn Cyt c and Mn Cyt c+ are high spin complexes with 3d5 S = 5/2 and 3d4 S = 2 electronic configurations, respectively. The epr spectrum of Mn Cyt c is rhombic with (formula: see text). Both oxidized and reduced Mn Cyt c react with NO; the former reaction is reversible and the product has the following epr spectral parameters: (formula: see text). There is no superhyperfine interaction observable with the NO ligand, and the unpaired electron density is estimated to be mostly in the metal ion d xy orbital. The structure is best formulated as Mn Cyt c (NO)+. The half-reduction potential of Mn Cyt c is + 60 +/- 40 mV. It is neither oxidized by cytochrome oxidase nor reduced by NADH, NADPH, or succinate cytochrome reductase. These physical, chemical, and enzymic properties of manganese cytochromes c suggest a five-coordinate metalloporphyrin prosthetic group with the manganese ion situated significantly out-of-plane toward the side of His-18.

Cytochrome c Group↗

PubMed1989

Conformational properties of streptokinase.

The conformational properties of streptokinase (SK) have been assessed by the techniques of differential scanning calorimetry, circular dichroism (CD), and through a combinational approach employing several algorithms which are predictive of secondary structural characteristics. In low ionic strength buffers, SK undergoes a reversible two-state thermal transition with a temperature of maximum heat capacity (Tm) of 46.1 +/- 0.9, a delta Hcal of 98 +/- 11 kcal/mol and a delta Hcal/delta HvH of approximately 1. In high ionic strength buffers, similar calorimetric properties were obtained with the exception that the delta Hcal/delta HvH values were considerably less than 1, indicating the existence of an additional irreversible thermally induced alteration in the molecule, most likely resulting in its aggregation. The effect of pH on the thermal unfolding properties of SK was determined. The results demonstrated that single two-state thermal transitions were obtained, with progressively decreasing Tm values, as the pH was reduced from 6.4 to 3.4, indicating a destabilization of the entire molecule at reduced pH. In the alkaline region, between pH 8.4 and 9.4, stabilization of a separate region of the molecule was obtained, as evidenced by an increase in the delta Hcal/delta HvH to values approximating 2. CD analysis was performed in order to estimate secondary structural characteristics of SK. The best fit of secondary structural parameters to the experimental CD spectrum provided estimates of 17% helices, 28% beta-sheet, 21% beta-turns, and 34% disordered structures. Both the intensity of the spectral band at 208 nm and the level of antiparallel beta-sheet strongly suggest that SK is an alpha + beta protein.

Buffers↗

PubMed1971

Micellar properties of sodium fusidate, a steroid antibiotic structurally resembling the bile salts.

The properties of sodium fusidate micelles were determined by a spectral shift technique, surface tension measurements, and ultracentrifugal analysis. The critical micellar concentrations, mean molecular areas, and apparent aggregation numbers were estimated as a function of the concentration of counterion (0.001-1.0 m Na(+)) at 20 degrees C. The critical micellar concentrations were studied over a temperature range of 10 degrees C to 40 degrees C at one counterion concentration (0.001 m Na(+)), and from these data the standard thermo-dynamic functions of micellization were calculated. The ability of sodium fusidate solutions to solubilize the insoluble swelling amphiphiles, lecithin and monoolein, was investigated, and the results were compared with the solubilizing properties of sodium taurocholate. The critical micellar concentrations of sodium fusidate approximated those of sodium taurocholate. The values fell in the range of 1.44-4.56 mm, varying with the technique used, counterion concentration, and temperature. The percentage of counterions bound to fusidate micelles in water, calculated from the log critical micellar concentration-log Na(+) curve, was estimated to be negligible, which compares with sodium taurocholate micelles. The critical micellar concentration of sodium fusidate exhibited a minimum at 20 degrees C, a phenomenon observed with other ionic detergents and with bile salts. Micelle formation in sodium fusidate solutions was shown to be primarily entropy-driven at 10 degrees and 20 degrees C, whereas at 30 degrees and 40 degrees C the enthalpy factor predominated. From the surface tension measurements the molecular areas of sodium fusidate and sodium taurocholate were calculated. The mean molecular area of fusidate was 101 A(2), whereas sodium taurocholate possessed a molecular area of 88 A(2). It was demonstrated that the sodium fusidate molecule, like a bile salt molecule, lies with its longitudinal axis horizontal at an air-water interface. The apparent aggregation number of sodium fusidate micelles increased from 5 to 16 as the concentration of counterion increased from 0.01 to 0.60 m Na(+). These values are slightly larger than the corresponding aggregation numbers of sodium taurocholate micelles.

Bile↗

PubMed1977

[Distribution of mineral salts in structures of the compact substance of human bone].

Mineral distribution has been studied in osteoni and intermediate spaces of the compact substance in fibular and occipital human bones. The material has been taken from 34 corpses. Total mineral content was estimated by the contact microroentgenography technique. Calcium, phosphorus and magnium content and distribution were studied by means of X-ray spectral microanalysis. The results obtained characterized bone morphological structure depending on the degree of their miniralization. Peculiarities in calcium and phosphorus distribution along radius osteoni were studied. Quantitative data were obtained on their content in the bone morphological structures. In spite of uneven distribution of some elements in the bone samples, constant molar Ca/P ratio was noted.

Adult↗

PubMedDate not supplied

Noninvasive evaluation of systolic pressures of pulmonary artery and right ventricle using contrast-enhanced doppler echocardiography: comparative study using sonicated albumin or glucose solution.

Evaluation of pulmonary arterial pressure is essential for the diagnosis and management of patients with congenital heart disease; it is usually done by cardiac catheterization. An alternative, noninvasive method may be clinically more useful. The purpose of this study was to assess the usefulness of the noninvasive determination of systolic pressure of the pulmonary artery and right ventricle by contrast-enhanced Doppler echocardiography. We selected 30 pediatric patients (28 with trivial or nonsignificant tricuspid regurgitant Doppler signals and 2 with significant tricuspid regurgitant Doppler signals) aged 2 months to 21 years. The flow velocity of tricuspid regurgitation was measured with continuous-wave Doppler of the right ventricular inflow view or left parasternal or apical four-chamber view before and after injection of two types of contrast medium (hand-agitated 5% glucose or sonicated albumin). The systolic pressure of the pulmonary artery was assessed as the estimated right ventricular systolic pressure (albumin method) minus the peak pressure gradient across the pulmonary valve (nonenhanced Doppler method). After injection of hand-agitated 5% glucose and sonicated albumin, trivial tricuspid regurgitation signals were enhanced in 25 of 28 patients (89%). In two patients, spectral envelopes were well defined enough to obtain the peak systolic velocity of the tricuspid regurgitation jet without contrast medium injection. Peak velocity was not altered by injection of contrast medium in these patients. There was significant correlation between the estimation by contrast-enhanced Doppler using hand-agitated 5% glucose and the cardiac catheterization measurement of the transtricuspid pressure gradient (r = 0.88). The transtricuspid pressure gradients obtained by continuous-wave Doppler during sonicated albumin enhancement corresponded closely to those measured by cardiac catheterization (r = 0.95). Pulmonary arterial and right ventricular systolic pressures measured by Doppler using sonicated albumin and those obtained by cardiac catheterization were highly correlated (right ventricle, r = 0.96; pulmonary artery, r = 0.95). In conclusion, this technique may be a valuable noninvasive method for determining accurate right ventricular and pulmonary arterial systolic pressures.

Adolescent↗

PubMed2006

Quantification in simultaneous (99m)Tc/(123)I brain SPECT using generalized spectral factor analysis: a Monte Carlo study.

In SPECT, simultaneous (99m)Tc/(123)I acquisitions allow comparison of the distribution of two radiotracers in the same physiological state, without any image misregistration, but images can be severely distorted due to cross-talk between the two isotopes. We propose a generalized spectral factor analysis (GSFA) method for solving the cross-talk issue in simultaneous (99m)Tc/(123)I SPECT. In GSFA, the energy spectrum of the photons in any pixel is expressed as a linear combination of five common spectra: (99m)Tc and (123)I photopeaks and three scatter spectra. These basis spectra are estimated from a factor analysis of all spectra using physical priors (e.g. Klein-Nishina distributions). GSFA was evaluated on (99m)Tc/(123)I Monte Carlo simulated data and compared to images obtained using recommended spectral windows (WIN) and to the gold standard (GS) images (scatter-free, cross-talk-free and noise-free). Using GSFA, activity concentration differed by less than 9% compared to GS values against differences from -23% to 110% with WIN in the (123)I and (99m)Tc images respectively. Using GSFA, simultaneous (99m)Tc/(123)I imaging can yield images of similar quantitative accuracy as when using sequential and scatter-free (99m)Tc/(123)I imaging in brain SPECT.

Algorithms↗

PubMed1994

On-line beat-to-beat monitoring of spectral parameters of heart rate variability signal using a pole-tracking algorithm.

Spectral parameters extracted from the heart rate variability (HRV) signal are obtained on a beat-to-beat basis, following a procedure which uses two recursive algorithms. In the first step of the procedure the set of the AR model coefficients is updated each time a new RR value is available. Then from the estimated AR model parameters, the new position of the poles of the model transfer function in the complex z-plane is evaluated and, finally, through a residual calculation, it is possible to calculate the spectral parameters which quantify the control of the autonomic nervous system in assessing the cardiac frequency (i.e., power and frequency of LF and HF components). The whole procedure has first been tested on a simulated time series, in order to evaluate its performance in tracking the dynamic changes during different conditions; next the algorithms were employed in the study of the HRV signal for continuous monitoring of non-stationary conditions.

Algorithms↗

PubMed1996

Decision rules of listeners in spectral-shape discrimination with or without signal-frequency uncertainty.

A correlation technique was used to assess the decision rules of three listeners in two cases of spectral-shape discrimination tasks. In one case the signal frequency was fixed, and in the other it was randomly varied within each block of trials. In order to estimate the decision rule of the listeners, the experimenter superimposed random level perturbations on each frequency component upon each stimulus presentation. Over many trials, correlation coefficients were computed between the random perturbations and the binary responses of the listeners, and were expressed as a function of signal level. For both the fixed- and random-signal cases, the measured correlation functions were in reasonably good agreement with those predicted based on the likelihood-ratio decision rules. Thus the listeners appeared to use information nearly optimally in discriminating spectral shapes. This investigation demonstrated that the correlation technique can be used to reveal the decision rules for cases where the decision statistics are nonlinear functions of the observations.

Auditory Perception↗

PubMed2001

Sympathetic restraint of respiratory sinus arrhythmia: implications for vagal-cardiac tone assessment in humans.

Clinicians and experimentalists routinely estimate vagal-cardiac nerve traffic from respiratory sinus arrhythmia. However, evidence suggests that sympathetic mechanisms may also modulate respiratory sinus arrhythmia. Our study examined modulation of respiratory sinus arrhythmia by sympathetic outflow. We measured R-R interval spectral power in 10 volunteers that breathed sequentially at 13 frequencies, from 15 to 3 breaths/min, before and after beta-adrenergic blockade. We fitted changes of respiratory frequency R-R interval spectral power with a damped oscillator model: frequency-dependent oscillations with a resonant frequency, generated by driving forces and modified by damping influences. beta-Adrenergic blockade enhanced respiratory sinus arrhythmia at all frequencies (at some, fourfold). The damped oscillator model fit experimental data well (39 of 40 ramps; r = 0.86 +/- 0.02). beta-Adrenergic blockade increased respiratory sinus arrhythmia by amplifying respiration-related driving forces (P < 0.05), without altering resonant frequency or damping influences. Both spectral power data and the damped oscillator model indicate that cardiac sympathetic outflow markedly reduces heart period oscillations at all frequencies. This challenges the notion that respiratory sinus arrhythmia is mediated simply by vagal-cardiac nerve activity. These results have important implications for clinical and experimental estimation of human vagal cardiac tone.

Adrenergic beta-Antagonists↗

PubMed2005

Simulation analysis of the performance of a novel high sensitive spectral index for quantifying M-wave changes during fatigue.

A high sensitive fatigue index is desired to improve stimulation strategy and to prevent muscle damage in functional electrical simulations. The great number of indexes used shows that there is no index that satisfies all investigators. A way to develop a high sensitive index for quantifying M-wave changes during fatigue and to estimate its performance was analyzed. The changes in M-wave and its frequency distribution due to variations of intracellular action potential (IAP) and muscle fibre propagation velocity (MFPV) with fatigue were simulated. It was found that the ratio between the spectral moments of order -1 and 2 was considerably more sensitive to peripheral muscle fatigue than the mean (the ratio between the spectral moments of order 1 and 0) and median frequency traditionally used. The sensitivity of the new index depended on the electrode arrangement and position in respect to the active fibres. The belly-tendon detection promised the highest index sensitivity. The length of the active fibres also affected the index sensitivity. The shorter the fibres the lower was the index sensitivity. The sensitivity of the new index could be relatively high even in the case of traditionally used high-pass cut-off frequencies that could distort the M-wave shape.

Action Potentials↗

PubMed1995

Continuous positive airway pressure increases heart rate variability in congestive heart failure.

OBJECTIVES: Our objective was to determine whether continuous positive airway pressure augments the low heart rate variability of congestive heart failure, a marker of poor prognosis. BACKGROUND: Nasal continuous positive airway pressure improves ventricular function in selected patients with heart failure. METHODS: In 21 sessions in 16 men (mean [+/- SE] age 56 +/- 2 years) with New York Heart Association functional class II to IV heart failure, we assessed the effects of 45 min with (n = 14) and without (as a time control, n = 7) nasal continuous positive airway pressure (10 cm of water) on heart rate variability and end-expiratory lung volume. Coarse-graining spectral analysis was used to derive total spectral power (PT), its nonharmonic component (fractal power [PF]) and the low (0.0 to 0.15 Hz [PL]) and high (0.15 to 0.50 Hz [PH]) frequency components of harmonic power. Standard deviation of the RR interval, high frequency power and the PH/PT ratio were used to estimate parasympathetic activity in the time and frequency domains, and the PL/PH ratio was used to estimate cardiac sympathetic activity in the frequency domain. RESULTS: Use of continuous positive airway pressure increased end-expiratory lung volume by 445 +/- 82 ml (p < 0.01) and both time (p < 0.006) and frequency domain indexes of heart rate variability: Total spectral power (p < 0.01), nonharmonic power (p < 0.023) and low (p < 0.04) and high (p < 0.05) frequency components of harmonic power all increased. Time alone had no effect on these variables. By comparison, the PH/PT ratio increased during nasal continuous positive airway pressure (p < 0.004), whereas the PL/PH ratio was unchanged. Breathing rate remained constant in both groups. CONCLUSIONS: Short-term application of nasal continuous positive airway pressure increases heart rate variability and time and frequency domain indexes of parasympathetic activity without influencing cardiac sympathetic activity. This increase may occur reflexively, through stimulation of pulmonary mechanoreceptor afferents.

Adult↗

PubMed1981

Detection of tones in band-reject noise.

Three experiments were conducted to investigate the detectability of tonal signals simultaneously presented with computer-generated, long duration (.5 sec), band-reject maskers. In Experiment 1, detectability of a tone of 500, 1000, or 2000 Hz presented at 50 dB SPL was measured as a function of the width of a spectral "notch" symmetrically placed around the tone. A narrow notch resulted in decreased detectability relative to the wide band (zero-notch width) control condition. Further increases in notch width resulted in increased detectability until subjects approached errorless performance. In Experiment 2, psychometric functions were obtained for a 1000-Hz tone presented in four notch-noise conditions. The slopes of the psychometric functions were consistently steeper in the band-reject conditions relative to the zero notch-width condition. These slope differences result in relationships between threshold and notch width that depend upon the region of the psychometric function from which the threshold estimates are obtained. In Experiment 3, the decrease in performance associated with the notch was found to increase in proportion to notch depth. The data suggest that spectral edges placed in the immediate vicinity of a tone reduce the detectability of the tonal signal. This "edge effect" is discussed in relation to two-tone inhibition that has been observed in the auditory nerve.

Acoustic Stimulation↗

PubMed1994

Comparison of transducer placement sites for Doppler echocardiography in dogs with subaortic stenosis.

Effects of transducer placement site and various operators on Doppler echocardiographic measures were evaluated in 12 dogs with subaortic stenosis. Dogs sedated by IV administration of acepromazine and buprenorphine were examined by 2 observers. Maximal aortic velocity and aortic velocity time integral were determined from Doppler aortic velocity spectra recorded, using a 1.9-MHz continuous wave nonimaging transducer placed at 3 echocardiographic sites: left ventricular apex (LA), suprasternal notch (SSN), and subcostal (SC). Doppler-estimated left ventricular-to-aortic pressure gradients were calculated from the traced velocity spectra by application of the modified Bernoulli equation. Each observer recorded high-quality Doppler spectral signals in all dogs from the SC and LA transducer sites and in 83% of dogs from the SSN window. Mean values for maximal aortic velocity and velocity time integral differed among sites (P < 0.05), but not between observers. Maximal velocity and velocity time integral measured from the SC transducer site were higher than those measured from the SSN or LA positions. Presumably, SC transducer placement provided the highest aortic velocities because of optimal alignment with aortic outflow. The maximal pressure gradient estimated from SC velocities exceeded SSN values by 27 mm of Hg and LA measurements by 38 mm of Hg. In this study, the optimal site for the Doppler echocardiographic detection of subaortic stenosis and assessment of this lesion's hemodynamic importance in most affected dogs was the SC position.

Analysis of Variance↗