Relations between parameters of spectral power densities and deterministic chaos of heart-rate variability

To evaluate whether or not heart-rate variations (HRV) have both periodic and deterministic-chaotic properties in conscious and anaesthetized states, HRV of 9 rabbits were analysed by power spectral analysis and methods of deterministic chaos. In order to correlate these properties with the physiological structure of HRV, cholinergic and beta-adrenergic blockades and medullar transections were done. A predominant deterministic-chaotic structure of HRV with high fractal correlation dimension (CD) during conscious state changes to a more periodic structure and lower CD during general anaesthesia. The main periodic and deterministic-chaotic components of HRV are vagally mediated because of their strong reduction by cholinergic blockade, but not by beta-adrenergic blockade or medullar transection.

Deterministic--chaotic and periodic properties of heart rate and arterial pressure fluctuations and their mediation in piglets

OBJECTIVE

Only the simultaneous analysis of periodic and nonlinear properties of heart rate fluctuations (HRF) can describe completely this complex physiological process. Up to now there is, apart from a study of our own, no systematic and correlative investigation using both parameter groups, also not in early development. Thus, we tried to describe in this manner these properties of HRF, the corresponding mean arterial pressure fluctuations (MAPF) and respiratory movements (RM) and their mutual relations in neonatal pig.

METHODS

In 6 term newborn piglets, periodic properties of HRF, RM, and MAPF were analyzed by spectral and coherence analysis, and deterministic-chaotic properties by calculation of correlation dimension (CD), Lyapunov exponent (LE), and construction of phase space plots. The assumption of deterministic chaotic components was supported by Theiler's test for nonlinearity, by always positive leading LEs, and by the results of a nonlinear deterministic model. These analyses were done in sleep states, general anaesthesia, hypoxic hypoxia, in ventilated state, and during cholinergic and additional beta-adrenergic blockade.

RESULTS

In all experimental states, HRF and MAPF have periodic and nonlinear, very probably deterministic-chaotic properties, but in different relations. In anaesthetized piglets, periodic properties of HRF and MAPF dominate. In hypoxia the decreasing LE and CD of HRF and CD of MAPF were connected with increasing MAPF power density. Cholinergic blockade caused a decreased overall HRF and MAPF power and a decreasing LE and CD, but beta-adrenergic blockade decreased a small part of power density of both in 0.02-0.08 Hz only. The results of CD, LE, Theiler's test and the low dimensional deterministic model data suggested mainly deterministic-chaotic properties in the nonlinear part of HRF and MAPF.

CONCLUSIONS

Already in neonatal piglets, both periodic and nonlinear, very probably deterministic chaotic properties of HRF and MAPF exist which change both during hypoxia and cholinergic blockade. They are partly cholinergically and--to a small extent--also beta-adrenergically mediated. The decrease of nonlinear complexity of HRF and MAPF during hypoxia suggests characteristic pathological change even in early development.

Characterization of complex heart rate dynamics and their pharmacological disorders by non-linear prediction and special data transformations

OBJECTIVE

The aim of the presented method was the characterization of different complex heart rate dynamics in conscious rabbits as well as during general anaesthesia and vagal blockade. This was done by non-linear prediction of original measured and special surrogate data in the phase space.

METHOD

The development of the prediction error in dependence on the prediction time interval was investigated in the phase space. Two kinds of surrogate data were produced and tested with regard to non-linearities and orientation in the phase space. Typical characteristics of prediction error development were shown for simulated uncorrelated stochastic, correlated stochastic, regular deterministic, and deterministic chaotic signals. These characteristics were used to evaluate the measured heart rate data in connection with tests of surrogate data.

RESULTS

It could be shown that heart rate fluctuation cannot be described by one of these ideal models alone. Common consideration of all investigated prediction characteristics indicated chaos in the heart rate of conscious rabbits as well as during anaesthesia and vagal blockade, where non-linear correlated stochastic properties could not be excluded. The different amount of non-linearities and orientation was described quantitatively.

CONCLUSIONS

Detailed analysis of prediction error development in the phase space, connected with tests for non-linearities and orientation, enabled a specific quantitative characterization of complex heart rate dynamics and their pharmacological disorders.

Axial rotation measurement of scoliotic vertebrae by means of computed tomography scans

STUDY DESIGN

This study evaluated the preconditions for exact axial rotation measurement and the possibility for other parameters to measure axial rotation and mechanical torsion.

OBJECTIVES

Quality criteria for axial rotation measurement in computed tomography scans are not established yet. Criteria should be found to improve axial rotation measurement.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, no systematic analysis of the errors of axial rotation measurement based on computed tomography scans has been performed.

METHODS

Axial rotation was measured in 259 computed tomography scans of 11 cadaveric vertebrae from scoliotic specimens. The sagittal axial rotation measurement angle of Aaro and Dahlborn and a new rotation parameter were measured with a pencil and ruler. Five landmarks were digitized and consequently five axial rotation parameters were computed. The influence of insufficient visualization of bony landmarks, mechanical torsion of the vertebra itself, and oblique position of the vertebra was evaluated.

RESULTS

Accuracy is considerably improved in central computed tomography scans (same distance to the top and bottom of the vertebral body) due to good visualization of landmarks and reduction of effects of mechanical torsion. The oblique vertebral position causes more errors. One mechanical torsion parameter with sufficient reliability is identified.

CONCLUSION

The sagittal axial rotation measurement method of Aaro and Dahlborn is superior to other techniques of measurement. It can be improved considerably if computed tomography scans fulfill certain quality criteria.

Vibroacoustic stimulation with a complex signal: effect on behavioral state in fetal sheep

An ideal vibroacoustic stimulus for testing fetal reactivity has yet to be developed. In the present study in fetal sheep we tested the effect on behavioral state of an amplitude and frequency-modulated signal produced at the abdominal surface of the ewe. The stimulus was presented during periods of fetal non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Evaluation of behavioral state was accomplished by visual observation of strip-chart recordings. Assessed in this manner, vibroacoustic stimulation during NREM sleep consistently resulted in a change to an indeterminate state. However, stimulation during REM sleep failed to have an effect. Additional evaluation applying spectral analysis to the fetal electrocorticogram during stimulation in NREM sleep revealed a marked decrease in delta band power from 100 to 27 +/- 5% and in theta band power from 100 to 40 +/- 4% resulting in a decrease in total power from 100 to 35 +/- 4% (p < 0.05). Stimulation during REM sleep revealed a significant increase in beta band power from 100 to 123 +/- 14%. Vibroacoustic stimulation in both NREM and REM sleep led to an increase in spectral edge frequency, implying central arousal.

Influence of severe hemodilution on brain function and brain oxidative metabolism in the cat

OBJECTIVE

It has been established that during constant pressure arterio-venous bypass perfusion, brain metabolism gradually deteriorates in parallel with the declining hematocrit. However, whether this is due to a disturbance of flow regulation or to the decline in the oxygen-carrying capacity of the blood has not been documented. Therefore, intact animals were submitted to severe hemodilution to determine the threshold for the beginning of functional and biochemical impairment of the brain.

METHODS

Six anesthetized and paralyzed adult mongrel cats were submitted to gradual isovolemic hemodilution by stepwise exchange of blood with Ringer lactate/dextran (1 : 1) solution. Exchange of 80 ml/kg body weight resulted in a final hematocrit level ranging from 6.1% to 11%.

RESULTS

Cerebral blood flow gradually increased during hemodilution, with a sharp rise to eight times the prehemodilution value when the hematocrit fell below 10%. The calculated oxygen delivery to the brain remained relatively unchanged. Hemodilution did not cause suppression of spontaneous ECoG or somatically evoked primary cortical potentials, even at the lowest hematocrit value of 6.1%. Brain tissue ATP and phosphocreatine content were largely maintained, although tissue lactate content was elevated (9.54 +/- 5.99 micromol/g).

CONCLUSIONS

The hemodynamically unimpaired healthy mammal is able to support a substantial degree of hemodilution without major functional or biochemical disturbance to the brain. The previously observed disturbances during prolonged bypass perfusion are, therefore, most probably due to the associated abnormalities of flow regulation.

Effect of inhibitors on the coordination geometries of cadmium at the metal sites in angiotensin-I-converting enzyme

Perturbed angular correlation of gamma-rays (PAC) spectroscopy has been used to investigate the angiotensin-I-converting enzyme (ACE) of rabbit lung. By substituting the zinc ions in ACE with excited 111mCd2+ ions, analysis of PAC spectra gave directly the percentage of cadmium ions bound to ACE. The result of the analysis was a dissociation constant of about 1 microM for the cadmium-ACE complex, and a stoichiometry of two moles cadmium/mole enzyme. Cadmium binding is thus about two orders of magnitude weaker than zinc binding to ACE but two orders of magnitude stronger than cobalt binding. PAC spectra monitor the nuclear quadrupole interaction (NQI) for 111mCd. The NQI for ACE exhibits very low frequencies in the PAC spectra with a rather large spectral broadening. In the presence of the inhibitor ramiprilat, the frequencies increase but the spectral broadening is about the same as for ACE without inhibitor. When the inhibitor captopril is added, very high frequencies are obtained consistent with sulfur binding, but now with a narrower distribution of NQI's. A simple molecular orbital analysis of the obtained NQI's has been performed, using a coordination sphere of two His, one Glu residue and a solvent ligand, equivalent to the zinc ligands in thermolysin and carboxypeptidase. The calculated spectral parameters could be modelled with the measured parameters if the solvent ligand is H2O in free ACE, carboxylate from ramiprilat in the ACE-ramiprilat complex and a mercapto group in the ACE-captopril complex. The coordination geometry for cadmium carboxypeptidase obtained by X-ray diffraction gives a calculated set of NQI parameters consistent with the measured parameters for cadmium in the captopril-ACE complex using a mercapto group as the solvent ligand. However, for ACE and its complex with ramiprilat, a significant distortion of the cadmium geometry for carboxypeptidase A had to be adopted in order to calculate NQI's close to the experimental values.

Structure of metal site in Cd-substituted His117Gly mutant of azurin with and without addition of imidazole derivatives

The present work uses 111mCd-perturbed angular correlations of gamma-rays (PAC) to investigate the structure of the metal site of the His117Gly mutant of Pseudomonas aeruginosa azurin in aqueous solution and the effect on the structure upon addition of the following exogenous ligands: imidazole, 4-methyl imidazole, 1-methyl imidazole, 2-methyl imidazole and histidine. The nuclear quadrupole interaction of cadmium bound to the mutant without addition of exogenous ligands shows a strong pH dependence with three different nuclear quadrupole interactions consistent with two pKa values at about 7.2 and 8.6 at 2 degrees C. Addition of the imidazole derivatives resulted in a significant change in the PAC spectrum showing that they coordinate. This is in accordance with observations by EPR for the same mutant with copper at the metal site [den Blaauwen, T. & Canters, G. W. (1993) J. Am. Chem. Soc. 115, 1121-1129]. However, whereas EPR and ultraviolet/visual absorption show that the characteristics of the wild-type copper protein are regained by addition of the imidazole derivatives with the exception of the possible bidentates (histidine and histamine), the comparison of the PAC results to model calculations shows that the cadmium ion must be fourfold coordinated in most cases, probably binding an additional water or hydroxide ligand. A fourfold coordination is in contrast to cadmium-substituted wild-type azurin where PAC data inferred a threefold coordination by a Cys and two His residues [Danielsen, E. Bauer, R., Hemmingsen, L., Andersen. M., Bjerrum, M. J., Butz, T., Tröger, W., Canters, G. W., Hoitink, C. W. G., Karlsson, G., Hansson, O. & Messerschmidt, A. (1995) J. Biol. Chem. 270, 573-580]

EBRA: a method to measure migration of acetabular components

In orthopedics there is a demand for determining migration of hip sockets by evaluation of standard radiographs. In this case problems are caused mainly by changing pelvis positions on the X-ray table at successive exposures. A method (EBRA) is described that evaluates standard AP radiographs without requiring additional means at exposure (e.g. ball markers). Simulating the spatial situation it computes parameters of longitudinal and transverse migration of prosthetic cup and femoral head. A comparability algorithm using a grid of transverse and longitudinal tangents of the pelvis contour divides serial radiographs into sets of comparable ones. Comparability of serial radiographs takes place if the distances of corresponding grid lines do not transcend a given limit L. Migration is measured only between comparable radiographs. Different studies are described concerning the interdependence of pelvis rotations and changes of the grid lines, the degree of pelvis rotations appearing in practice, the choice of the limit L, the properties of the comparability algorithm and the accuracy of EBRA. The 95% confidence limits for EBRA results are 1.0 mm for longitudinal and 0.8 mm for transverse migration.

Cloning and characterization of a second AP-2 transcription factor: AP-2 beta

AP-2 has been characterized previously as a unique 52 × 10(3) M(r) transcription activator encoded by a single gene that is expressed in a restricted pattern during embryonic morphogenesis of the peripheral nervous system, face, skin and nephric tissues. Here we report the isolation of genomic and cDNA clones encoding for a second AP-2 related transcription factor, designated AP-2 beta. AP-2 beta binds specifically to a series of well-characterized AP-2 binding sites, consensus to the sequence G/CCCN3GGC, and transactivates transcription from a reporter plasmid under the control of an AP-2-dependent promoter. A C-terminal domain known to mediate homodimerization of the previously cloned AP-2 alpha transcription activator is highly conserved and sufficient to mediate interaction between the two proteins. Northern blot and in situ hybridizations revealed that the two genes are expressed in murine embryos between days 9.5 and 19.5 p.c. Coexpression of both mRNAs was detected in many tissues at day 13.5 and 15.5 of embryogenesis but some regions of the developing brain and face including the primordium of midbrain and the facial mesenchyme differed in their expression pattern of AP-2 genes. AP-2 alpha and AP-2 beta signals in the central and peripheral nervous system overlapped with regions of developing sensory neurons. In adult tissues AP-2 alpha expression was found mainly in the skin, eye and prostate and AP-2 beta expression in the kidney. In summary, our analyses of embryonic and adult mice demonstrate that two different AP-2 transcription factors are specifically expressed during differentiation of many neural, epidermal and urogenital tissues.

Inhibition of endotoxin-induced cytokine release and neutrophil activation in humans by use of recombinant bactericidal/permeability-increasing protein

To investigate the effects of a recombinant endotoxin-binding protein, bactericidal/permeability-increasing protein (rBPI23), on cytokine release and neutrophil activation in endotoxemia in humans, 8 volunteers were challenged twice with endotoxin and concurrently received either rBPI23 or placebo in a randomized, placebo controlled, double-blind crossover study, rBPI23 treatment significantly lowered circulating endotoxin levels (P = .02) and resulted in a significant reduction in the release of tumor necrosis factor (TNF), soluble TNF receptors p55 and p75, interleukin (IL)-6, IL-8 (P < .01 for each), and IL-10 levels (P = .02) but did not prevent the endotoxin-induced rise in body temperature. The early endotoxin-induced leukopenia was blunted (P = .08), and neutrophil degranulation, as measured by circulating levels of elastase/alpha 1-antitrypsin complexes (P = .03) and lactoferrin (P < .01), was largely prevented by rBPI23. The results of this study indicate that rBPI23 is capable of neutralizing many of the biologic effects of endotoxin in humans.

Biological and pharmacological activities and further constituents of Hyptis verticillata

Several extracts of Hyptis verticillata and isolated compounds were evaluated for their anti-inflammatory, antibacterial, antisecretory, and cytotoxic properties. The aerial parts yielded (R)-5-hydroxypyrrolidin-2-one and essential oil with the main components alpha-pinene, beta-pinene, and thymol. Spectroscopic methods (UV, IR, 1H-NMR, 13C-NMR, mass, CD) fully characterized (R)-5-hydroxypyrrolidin-2-one, as it was isolated by a bioassay guided fractionation. The essential oil, (R)-5-hydroxypyrrolidin-2-one, as well as the previously isolated rosmarinic acid and dehydropodophyllotoxine contributed to the antibacterial effects of H. verticillata. Furthermore, rosmarinic acid showed significant capillary stabilizing effects. Sideritoflavone inhibited prostaglandin synthase to a significant extent and had antisecretory effects comparable to those of NPPB. The cytotoxicity of the aqueous extract, as demonstrated using KB and HT 29 cell lines, may be of toxicological relevance in cases of internal application.

Cd-substituted horse liver alcohol dehydrogenase: catalytic site metal coordination geometry and protein conformation

The coordination geometry of the catalytic site in Cd-substituted horse liver alcohol dehydrogenase (LADH) has been investigated as a function of pH using the method of perturbed angular correlation of gamma-rays (PAC). LADH in solution fully loaded with cadmium, including radioactive 111mCd in the catalytic site [Cd2(111mCd)Cd2LADH], was studied over the pH range 7.9-11.5. Analysis of the PAC spectra showed the ionization of a group with pKa of 11. This pKa value is about 2 pH units higher than that of native zinc-containing LADH. A pKa of 9.6 was found for the binary complex of Cd2(111mCd)Cd2LADH with NAD+. This value is also about 2 pH units higher than that of the binary complex of native zinc-containing enzyme and NAD+. No pH dependency was detected for the binary complex of Cd2(111mCd)Cd2LADH with NADH within the pH range measured (pH 8.3-11.5). Assuming that metal-coordinated water is the ionizing group [Kvassman, J., & Pettersson, G. (1979) Eur. J. Biochem. 100, 115-123], we conclude that the larger ionic radius of Cd(II) relative to Zn(II) in the catalytic site causes the elevated pKa values of metal-bound water. Interpretation of nuclear quadrupole interaction (NQI) parameters derived from PAC spectra is based on the use of the angular overlap model, using the coordinates for the catalytic zinc site from the 1.8 A resolution crystal structure of the ternary complex between LADH, NADH, and dimethyl sulfoxide as a model.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain peroxidative and glutathione status after moderate hypoxia in normal weight and intra-uterine growth-restricted newborn piglets

In order to investigate the pathogenetic factors causing the relatively frequent occurrence of brain injury in intrauterine growth-restricted newborns, lipid peroxidation products (TBAR), glutathione (GSH, GSSG) and in vitro production of reactive oxygen species (chemiluminescence, stimulated lipid peroxidation, H2O2 formation) were studied in the brain of normal weight (NW) and intra-uterine growth-restricted newborn piglets (IUGR) after 1 hour of hypoxia (FiO2 11%) and 90 min reoxygenation. Cardiocirculatory parameters and catecholamine release into the blood were also measured. In the cerebellum, higher GSH content, but also higher in vitro production of lucigenin amplified chemiluminescence were found in comparison to other brain regions, independent of growth restriction and hypoxia. Moderate hypoxia without acidosis and hypercapnia resulted in GSH depletion especially in the brain of IUGR, but no changes in GSSG concentrations were measured. Though TBAR decreased after hypoxia/reoxygenation, in some brain areas of IUGR higher TBAR values were found in comparison to NW. H2O2 formation, stimulated lipid peroxidation and lucigenin and luminol amplified chemiluminescence in the 9000 x/g supernatant of brain tissue did not reveal special response of IUGR to hypoxia/reoxygenation. Hypoxia-induced circulatory centralisation due to increased release of catecholamines into the plasma prevented oxygen deficiency also in the brain of IUGR. The role of brain monoamine metabolism in the production of reactive oxygen species, followed by greater GSH depletion and higher in vivo formation of lipid peroxides in IUGR is discussed.

Heart rate fluctuations of lower frequencies than the respiratoryrhythm but caused by it

In conscious adult rabbits, "classical" respiratory sinus arrhythmia does not occur because the respiratory frequency (RF) always exceeds half the heart rate (HR). However, slow HR fluctuations, not synchronous with the respiratory rhythm but affected by it, occur systematically. We have shown that these can be calculated by using aliasing rules. During general anaesthesia, when the RF decreases so that respiratory frequency is less than half the heart rate, classical respiratory sinus arrhythmia occurs and can be greatly reduced by vagal blockade. The slow HR fluctuations which are not synchronous with the respiratory rhythms, but are affected by it are mainly vagally mediated, because vagal blockade virtually eliminates them.