Av Values Research Articles

Asthma, Age, and Early Reversibility Testing

The aim of this study was to assess the effect of age on early reversibility testing (ERT) in patients with asthma. Forty-nine nonsmokers with asthma were investigated. In all cases, disease duration was less than 15 years; the absolute change (absolute variability, AV) in forced expiratory volume in 1 second (FEV1) on ERT was greater than 100 mL; and the increase in FEV1 on ERT was greater than 10%. Patients were categorized as group I (younger than 50 years; n = 24) and group II (50 years or older; n = 25). There were no significant differences between the groups regarding disease duration and severity. The mean patient ages in groups I and II were 40.3 ± 7.9 years and 59.2 ± 7.1 years, respectively, and the corresponding mean baseline FEV1 values were 62.2 ± 23.7% and 67.4 ± 21.1% of predicted value (p>0.05). Pulmonary function tests were performed at baseline, and then repeated for ERT 20 minutes after inhalation of 200 µg salbutamol. After ERT, the respective findings for groups I and II were as follows: AV 412 ± 184 mL and 247 ± 138 mL; percentage change (PC) in FEV1 21.5 ± 9.3% and 16.9 ± 7.5%; and percent of predicted change (PPC) in FEV113.6 ± 6.5% and 9.9 ± 4.9%. The AV, PC, and PPC values for group I all were higher than the corresponding findings for group II, and the differences in AV and PPC were statistically significant (p = 0.001, p<0.05). The study showed that elderly asthma patients exhibit significantly lower AV and PPC after ERT. To improve the accuracy of asthma diagnosis in elderly patients, limits of ERT should be redefined.

Separating changes in the intra- and extracellular water apparent diffusion coefficient following focal cerebral ischemia in the rat brain.

Selective intracellular (IC) and extracellular (EC) brain water apparent diffusion coefficient (ADC) values were measured in normal and ischemic rat brain. Selective T(1)-relaxation enhancement of the EC water, using intracerebroventricular (ICV) infusion of an NMR contrast reagent (CR), was used to separate the IC and EC signal contributions. In the CR-infused, normal brain (n = 4), T(1) = 235 +/- 10 ms and T(2) = 46 +/- 2 ms for IC water (85%) and T(1) = 48 +/- 8 ms and T(2) = 6 +/- 2 ms for EC water (15%). Volume-localized ADC(z) (z-gradient axis) values were 0.90 +/- 0.02 (EC+IC), 0.81 +/- 0.05 (IC), 0.51 +/- 0.02 (EC+IC), and 0.53 +/- 0.07 (IC), for normal, CR-infused, ischemic, and ischemic/CR-infused groups, respectively (ADC values are x10(-3) mm(2)/s; n = 5 for each group). Imaging ADC(z) values were 0.81 +/- 0.03 (EC+IC), 0.75 +/- 0.05 (IC), 0.51 +/- 0.04 (EC+IC), and 0.52 +/- 0.05 (IC), respectively, for the same groups. Imaging ADC(av) (average diffusivity) values for the same groups were 0.70 +/- 0.05 (EC+IC), 0.69 +/- 0.06 (IC), 0.45 +/- 0.06 (EC+IC), and 0.44 +/- 0.06 (IC), respectively. These results suggest that the IC water ADC determines the overall water ADC value in normal and ischemic rat brain.

A prospective, longitudinal diffusion tensor imaging study of brain injury in newborns.

To establish the magnitude and time course of the changes in water diffusion coefficient (D(av)) following newborn infant brain injury. Ten newborn infants at high risk for perinatal brain injury were recruited from the neonatal intensive care unit. Conventional and diffusion tensor MRI was performed on three occasions during the first week of life. Regions of injury were determined by evaluating conventional MR images (T1, T2, fluid-attenuated inversion recovery) at 1 week after injury. D(av) values were determined for these regions for all three scans. D(av) values were decreased in most infants 1 day after injury, but injury was not evident or underestimated in 4 of 10 infants despite the presence of injury on conventional imaging at 1 week. By the third day, D(av) values were decreased in injured areas in all infants, reaching a nadir of approximately 35% less than normal values. By the seventh day after injury, D(av) values were returning to normal (pseudonormalization). MR diffusion images (for which contrast is determined by changes in D(av)) obtained on the first day after injury do not necessarily show the full extent of ultimate injury in newborn infants. Images obtained between the second and fourth days of life reliably indicate the extent of injury. By the seventh day, diffusion MR is less sensitive to perinatal brain injury than conventional MR because of transient pseudonormalization of D(av). Overall, diffusion MR may not be suitable as a gold standard for detection of brain injury during the first day after injury in newborn infants.

Fitting optical source counts with an infrared-defined model: insights into galaxy evolution

In order to improve the fit to the optical counts, the multi-wavelength source count model of Rowan-Robinson (2001) is improved in two ways. First, density evolution is incorporated to correspond to the mergers in hierarchical models of galaxy formation. Secondly, the evolution of dust opacity is taken into account. The luminosity and density evolution parameters and the characteristic opacity of the local universe are allowed to vary freely and the best overall fit to the B band is determined. This parameter set is then translated to other wavebands, showing significant improvement of goodness of fit in the optical, UV and near-IR bands, whilst retaining the goodness of fit in the far-IR and submillimetre bands of the original model. A significant fraction of the improvement of fit is shown to be due to the introduction of optical depth history. The mean value of Av in the local universe for the best-fitting model is 0.4. The goodness of fit to available star formation history data is not significantly altered and the form of the evolution of the luminosity function shown to be consistent with a semi-analytic, forward evolution model.

Evolutionarily Stable Leaf Area Production in Plant Populations

Using an analytical model, it was shown that for a given amount of nitrogen in the canopy of a stand ( N T ), there exists an evolutionarily stable leaf area index (ES-LAI), and therefore an evolutionarily stable average leaf nitrogen content ( n ES av ; n ES av = N T / ES− LAI), at which no individual plant in the stand can increase its photosynthesis by changing its leaf area. It was also shown that this ES-LAI is always greater than the optimal LAI that maximizes photosynthesis per unit N T of the stand. This illustrates that the canopy structure that maximizes photosynthesis of a population is not the same as the canopy structure that maximizes photosynthesis of individuals within a population. It was further derived that the ES-LAI at given N T increases with the ratio between the light-saturated photosynthesis and the N content per unit leaf area (leaf-PPNUE) and that it decreases with the canopy extinction coefficient for light ( K L ), the light availability and the apparent quantum yield ( Φ). These hypotheses were tested by comparing calculated ES-LAI and n ES av values to actual LAIs and leaf N contents measured for stands of a large variety of herbaceous plants. There was a close correspondence between the calculated and measured values. As predicted by the model, plants with high leaf-PPNUEs produced more leaf area per unit nitrogen than those with low leaf-PPNUEs while plants with horizontal leaves, forming stands with higher K L values, produced less leaf area than those with more vertically inclined leaves. These results suggest that maximization of individual plant photosynthesis per unit of nitrogen plays an important role in determining leaf area production of plants and the resulting canopy structure of stands of vegetation. They further suggest this optimization to be a mechanism by which leaf traits such as leaf-PPNUE and leaf inclination angle are causally related to structural characteristics of the population, i.e. the leaf area index of the stand.

Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars

Effective temperatures Teff, surface gravities log g and interstellar extinctions AV are found for 107 B stars. Distances d of the stars, which are based on the derived Teff, log g and AV values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the Teff and log g values with evolutionary computations, we infer masses, radii, luminosities, ages and relative ages of the stars. Empirical relations between the Teff and log g parameters, on the one hand, and the photometric indices Q, [c1] and β, on the other hand, are constructed; these relations give a fast method for the Teff and log g estimation of early and medium B stars. Inclusion of the infrared J, H and K colours into the Teff, log g and AV determination shows that (i) the Teff and log g parameters are altered only slightly; (ii) the AV value is rather sensitive to these colours, so an accuracy better than 0.05 mag in the JHK data is necessary for precise AV evaluation.

The influence of experimental conditions on the assessment of the toxicity of 2,4-dichlorophenol to anaerobic degradative bacteria

The toxicity of 2,4-dichlorophenol (2,4-DCP) to anaerobic bacteria in refuse cultures was investigated at two temperatures (30 and 37 degrees C) and after two different exposure periods to the toxicants. It was shown that at 0.52mM 2,4-DCP the time of exposure of microorganisms to 2,4-DCP affected the relative activity (Av) of the production of methane. Av values at the beginning of the steady-state phase were lower than those recorded two weeks later. The incubation temperature selected also critically affected the assessment of anaerobic toxicity; at 37 degrees C an imbalance of the activities of fermentative bacteria and acetogens with those of methanogens was observed.

Polarimetric Investigations of Stellar Associations

The degree of polarization of light from stars in 44 O B associations as a function of interstellar absorption is investigated. It is shown that the character of the dependence of P on AV for stars in associations and stars not in associations depends on the value of AV: for AV ≤ 2m.5 it has a linear character and is the same for both groups of stars. For AV > 2m.5 the dependence of P on AV for stars in and not in associations departs from linearity and for AV = 4m.5 it reaches Pass = 1.8% and Pnonass = 1%, respectively. Such a difference is explained by the additional depolarization in stellar associations. Such strong depolarization in associations may be due to the overall magnetic field of the Galaxy and to physical peculiarities in the association itself.

Ag, Ge and Sn reference samples for elastic peak electron spectroscopy (EPES), used for experimental determination of the inelastic mean free path and the surface excitation parameter

Reference samples are needed for experimental determination of the inelastic mean free path (IMFP) of electrons by elastic peak electron spectroscopy (EPES). High-quality (microcrystalline mirror) Ni reference samples were used for IMFP measurements. For surface excitation parameter experiments, new types of reference samples are needed. They should exhibit pronounced surface-loss spectra, such as amorphous Ge (aGe), Sn and Ag. A new procedure is presented for their preparation. Microcrystalline Ag and Sn reference samples were deposited on highly polished (by Buehler alumina alpha micropolish 1C) brass (60% Cu, 40% Zn) substrates. Electrolytic deposition was used for Ag and for Sn and resulted in excellent surface quality. The average surface roughness γ av was checked by scanning tunnelling microscopy or atomic force microscopy before and after Ar + ion bombardment cleaning. Typical γ av values were 4-6 nm for Ag, 3-4 nm for Sn and 2-4 nm for brass substrate. The aGe sample was deposited by magnetron sputtering or by evaporation in a high vacuum on an Si substrate. Its γ av was 4-5 nm. The samples were studied by EPES/reflection electron energy-loss spectroscopy, covering the 0.2-5 keV energy range, with the ESA 31 HSA electron spectrometer. The IMFP of Sn was determined by EPES. The surface excitation parameters for the Si, Ge and Sn samples were determined from their inelastic scattering cross-section spectra. For Ag the surface excitation parameter was estimated by using the above reference samples.

Far-infrared dust opacity and visible extinction

We present an extinction map of the Polaris molecular cirrus cloud derived from star counts and compare it with the Schlegel et al. [13] extinction map derived from the far-infrared dust opacity. We find that, within the Polaris cloud, the Schlegel et al. [13] AV values are, on average, a factor 2 higher than the star count values. We propose that this discrepancy results from a difference in τFIR/AV between the diffuse atomic medium and the Polaris cloud. We use the difference in spectral energy distribution, warm for the diffuse atomic medium, cold for the Polaris cloud, to separate their respective contribution to the line of sight integrated infrared emission and find that the τFIR/AV of cold dust in Polaris is on average 4 times higher than the Schlegel et al. [13] value for dust in atomic cirrus. This change in dust property could be interpreted by a growth of fluffy particles within low opacity molecular cirrus clouds such as Polaris. Our work suggests that variations in dust emissivity must be taken into account to estimate AV from dust emission wherever cold infrared emission is present (i.e. molecular clouds).

Theoretical Models of Polarized Dust Emission from Protostellar Cores

We model the polarized thermal dust emission from protostellar cores that are assembled by supersonic turbulent flows in molecular clouds. Self-gravitating cores are selected from a three-dimensional simulation of supersonic and super-Alfvenic magnetohydrodynamic (MHD) turbulence. The polarization is computed in two ways. In model A it is assumed that dust properties and grain alignment efficiency are uniform; in model B it is assumed that grains are not aligned at visual extinction larger than AV,0 = 3 mag, consistent with theoretical expectations for grain alignment mechanisms. Instead of using a specific set of grain properties, we adopt a maximum degree of polarization Pmax = 15%. Results are therefore sensitive mainly to the topology of the magnetic field (model A) and to the gas distribution that determines the distribution of AV (model B). Furthermore, the radiative transfer in the MHD model is solved with a non-LTE Monte Carlo method, to compute spectral maps of the J = 1-0 transition of CS. The CS spectral maps are used to estimate the turbulent velocity, as in the observations. The main results of this work are the following: (1) Values of P between 1% and 10% (up to almost Pmax) are typical, despite the super-Alfvenic nature of the turbulence. (2) A steep decrease of P with increasing values of the submillimeter dust continuum intensity I is always found in self-gravitating cores selected from the MHD simulations if grains are not aligned above a certain value of visual extinction AV,0 (model B). (3) The same behavior is hard to reproduce if grains are aligned independently of AV (model A). (4) The Chandrasekhar-Fermi formula, corrected by a factor f ≈ 0.4, provides an approximate estimate of the average magnetic field strength in the cores. Submillimeter dust continuum polarization maps of quiescent protostellar cores and Bok globules have recently been obtained. They always show a decrease in P with increasing value of I consistent with the predictions of our model B. We therefore conclude that submillimeter polarization maps of quiescent cores do not map the magnetic field inside the cores at visual extinction larger than AV,0 ≈ 3 mag. The use of such maps to constrain models of protostellar core formation and evolution is questionable. This conclusion suggests that there is no inconsistency between the results from optical and near-IR polarized absorption of background stars and the observed polarization of submillimeter dust continuum from quiescent cores. In both cases, grains at large visual extinction appear to be virtually unaligned.

Far-infrared dust opacity and visible extinction in the Polaris Flare

We present an extinction map of the Polaris molecular cirrus cloud derived from star counts and compare it with the Schlegel et al. (1998) extinction map derived from the far--infrared dust opacity. We find that, within the Polaris cloud, the Schlegel et al. Av values are a factor 2 to 3 higher than the star count values. We propose that this discrepancy results from a difference in $\tau_{FIR}/ A_V$ between the diffuse atomic medium and the Polaris cloud. We use the difference in spectral energy distribution, warm for the diffuse atomic medium, cold for the Polaris cloud, to separate their respective contribution to the line of sight integrated infrared emission and find that the $\tau_{FIR}/ A_V$ of cold dust in Polaris is on average 4 times higher than the Schlegel et al. value for dust in atomic cirrus. This change in dust property could be interpreted by a growth of fluffy particles within low opacity molecular cirrus clouds such as Polaris. Our work suggests that variations in dust emissivity must be taken into account to estimate Av from dust emission wherever cold infrared emission is present (i.e. molecular clouds).

Pb and Cu Speciation and Bioavailability in Port Wine

Information about the speciation of Pb and Cu in different types of Port wines (white, single-year and blended aged red, and young red wines) was gathered to estimate their respective bioavailabilities to man. For this purpose, wines were subjected to in vitro simulated gastrointestinal digestion, and the following properties were studied in the wines and its gastric and intestinal digests: (1) average conditional stability constant (K(av)) of the Cu complexes (by potentiometry), of the strongest Pb complexes (those inert to cathodic voltammetry, K'(av)), and of the respective ligand concentrations (CC or CC(inert)); (2) the distribution of the metal among the different groups of compounds of different molecular weights and/or polarities in the different bands separated by reverse phase high-performance liquid chromatography; (3) the total metal concentration present in the wines and the respective fractions present in the soluble and in the dialyzable fractions of the digest (an estimation of the assimilable fraction). The study showed that the complexing affinity for Pb (expressed by either CC(inert) or K'(av)) of white and very aged red Port wines was lower than for the remainder of the wines. For Cu, the strength of the ligands in the white wines was lower (<log K(av) values) than in the other wines, but their concentrations (CC) were higher. For Pb, CC(inert) was much higher after the digestion than for the untreated wines, whereas the log K'(av) values were approximately 1 order of magnitude lower. These parameters could not be determined for Cu in the gastrointestinal digests. For all of the studied wines the dialyzable fraction of Pb during the intestinal digestion was low (10-22% of the total Pb) and the dialyzable fractions of Cu were close to 50% of the total Cu.

Infrared Observations of Three Extremely Red Objects

Deep infrared and optical surveys have recently revealed a large number of very red (R-K > 6) galaxies, labeled extremely red objects (EROs). Many have been identified with broadband photometry, but very few have been observed spectroscopically. From the limited spectra available, it appears that they may form a heterogeneous population. There are EROs at high redshifts with dusty, active star formation (studied by Dey and coworkers) as well as EROs with old stellar populations and little dust (studied by Soifer and coworkers). In order to further the study of these galaxies, we have taken near-infrared spectra with the Keck Telescope of three EROs found in the fields of high-redshift active galactic nuclei. The continuum is well detected in each, but no emission lines or spectral breaks are detected. We have found probable redshifts, extinctions, ages, and star formation histories for each of these EROs based on fitting their spectral energy distributions. For every age and star formation model, the fits are constrained in redshift and reddening to small regions. Due to the unknown nature of these objects, we cannot rule out values of Av as high as 15 at low redshifts. None of the EROs have spectra consistent with the redshifts of their nearby high-redshift objects.

Effect of grain size and domain state on thermal demagnetization tails

Thermal demagnetization of viscous remanence (VRM) and partial thermoremanence (pTRM) of 20‐ and 135‐µm natural magnetites reveals a broad spectrum f(TUB) of unblocking temperatures TUB, both &gt; and &lt; TB, the blocking temperature. In contrast, 0.04‐µm single‐domain (SD) grains demagnetize sharply at TUB ≈ TB. High‐ and low‐TUB tails of f(TUB) were wider for 135‐µm multidomain (MD) grains than for 20‐µm PSD grains. 10‐mT alternating‐field demagnetization rendered the VRM of the 20‐µm magnetite more SD‐like in subsequent thermal cleaning, selectively erasing both low‐ and high‐TUB tails of f(TUB). Primary and secondary remanences are then cleanly separated, and non‐linear Thellier paleointensity determination becomes linear. Our results agree well with (TB, TUB) data for 105‐year thermoviscous overprints in the Milton Monzonite over the range of log(time) common to the two studies. Because (TUB)av ≈ TB for PSD and MD as well as SD grains, the Pullaiah et al. paleothermometry method will work if (TUB)av values are used instead of (TUB)max values.

Near–Infrared Line Imaging of the Circumnuclear Starburst Ring in NGC 7771

We present high spatial resolution near-infrared broadband JHK images and, for the first time, Brγ 2.1661 μm and H2 1-0 S(1) 2.122 μm emission-line images of the circumnuclear star-forming ring (major axis diameter 7'' = 2 kpc) in the starburst galaxy NGC 7771. These data are used to investigate the morphology and extinction of the starburst ring and to study its star-forming properties and history by comparing the observed quantities with an evolutionary population synthesis model. The clumpy morphology of NGC 7771 varies strongly with wavelength, as a result of the combination of extinction (for which we derive an average value of AV = 2.8), emission from hot dust and red supergiants, and several stellar generations in the ring. Also, the ellipticity and the position angle of the ring depend on the wavelength. The starburst ring in NGC 7771 exhibits small Brγ equivalent widths. Assuming a constant star formation model with Mu = 100 M☉ results in very long lifetimes of the star-forming regions (up to 1 Gyr), in disagreement with the clumpy near-infrared morphology and the observed radio spectral index of NGC 7771. This situation is only slightly remedied by assuming a reduced upper mass cutoff (Mu = 30 M☉), resulting in ages between 8 and 180 Myr. We prefer an instantaneous star formation model with Mu = 100 M☉, which can explain the derived Brγ equivalent widths if a single starburst occurred 6-7 Myr ago. The main excitation mechanism of the molecular gas, based on the observed S(1)/Brγ ratio, appears to be excitation by UV radiation from hot young stars. We derive M 1900 M☉ for the mass of the excited H2.

Interaction of skeletal muscle cells with collagen type IV is mediated by perlecan associated with the cell surface.

We have previously shown that the expression of perlecan, a heparan sulfate proteoglycan localized on the myoblast surface, is down-regulated during terminal differentiation of skeletal muscle myoblasts (Larraín et al. [1997] Exp. Cell Res. 234:405-412). In this study, we have evaluated the biochemical characteristics of perlecan, its association with the myoblast surface, and its involvement in C(2)C(12) myoblast adhesion to different substrates. Perlecan associated with myoblasts was solubilized by Triton X-100, whereas heparin, high salt, and RGD peptides were unable to solubilize perlecan. Pre-incubation of myoblasts with [(35)S]-Na(2)SO(4), followed by solubilization with Triton X-100 and immunoprecipitation with antibodies against murine perlecan, demonstrated that this proteoglycan present on the cell surface has a heterogeneous size profile with a K(av) value of 0.45, determined by Sepharose CL-4B chromatography. Myoblasts were found to adhere with decreasing affinities to collagen type IV, type I, laminin, fibronectin, perlecan, and matrigel. We found that cell adhesion to collagen type IV was inhibited by blocking this substrate with exogenous perlecan prior to cell plating, whereas no effect was observed for laminin. Furthermore, adhesion of myoblasts to collagen type IV was inhibited by the perlecan core protein obtained by treatment of perlecan with heparitinase, as well as by pre-incubation of the cells with antibodies against murine perlecan. These data support the idea that skeletal muscle cells interact with collagen type IV through the perlecan core protein present on the surface of undifferentiated myoblasts.

A New Derivation of the Extinct ion-to-CO Column Density Ratio in the Chamaeleon I Dark Cloud

We have analyzed new datasets of 13CO (J = 1−0) and C18O (J = 1−0) emission obtained with NANTEN and visual extinction, AV, derived from DENIS J-band observations in the Chamaeleon I dark cloud. The column densities of both molecular isotopes, N(13CO) and N(C18O, have been derived assuming LTE. Both N(13CO) and N(C18O are linearly correlated with AV in the range AV≲ 10 mag. We established the relationships N(13CO) (cm-2)=(1.2± 0.1)× 1015AV(mag)+(0.7± 0.3)× 1015 and N(C18O) (cm-2)=(3.5± 0.3)× 1014AV(mag)-(5.7± 1.3)× 1014. In a region of clustered T Tauri stars, however, both the AV-N(13CO) and AV-N(C18O) relationships are by a factor of ∼ 2 steeper than the above. This may be mainly due to underestimates of the AV values, and the J-band star count might deserve a more careful examination for possible underestimates of associated young stars. Compared with the relationships for the other clouds, the slope of the AV-N(13CO) relationship is relatively shallower and that of the AV-N(C18O) relationship in a non-cluster forming region is slightly steeper. These facts suggest that cloud-to-cloud variation is significant in the AV-N(CO) relationships.

SIZE EXCLUSION CHROMATOGRAPHY OF HUMIC SUBSTANCES: LIMITS, PERSPECTIVES AND PROSPECTIVES

The fractionation range of chromatographic media used in size exclusion chromatography (SEC) depends strongly on the kind of substances eluted. Although the fractionation range reported by the manufacturer for globular proteins on Sephadex G-200 is 5000 to 250,000 daltons and that for dextrans 1000 to 150,000 daltons, phenolcarboxylic acids (pH = 8, 0.1 mmol/L NaOH) are eluted much earlier than would be predicted based on their molecular weight (MW). The actual MWs for this group of compounds ranges from 200 to 500 daltons, whereas their MWs determined by SEC calibrated with proteins is much higher (7200-180,000 daltons). Ion exclusion, which is the basis for this behavior, originates from residual ionized groups and limits the possibility of applying SEC to the study of conformational changes of humic substances (HS). A correct selection of experimental conditions enables the use of SEC for various applications such as the study of metal-binding equilibria and fractionation according to molecular size. To determine the MW distribution of HS, columns should be calibrated with standard humic and fulvic acids with known MWs determined by colligative properties such as vapor pressure osmometry. It should be noted, however, that SEC studies on fractions of HS originating from various soils, result in a series of significantly differing calibration curves. The linearity of the relationship between the distribution coefficient (K av ) values and the logarithm of the MWs implies the constancy of partial specific volumes. It also suggests that HS extracted from the same soil constitute a homologous series in which the structure of the larger components is formed by the repetition of structurally similar units and is, therefore, more regular than previously believed. The experimental results obtained by SEC also suggest that in regard to the sensitivity of the technique, charge density differences are small within a certain series compared with size differences.

Brain water diffusion in normal and creatine-supplemented rats during transient global ischemia.

Brain water diffusion in response to transient global ischemia (12 min), reperfusion (60 min), and cardiac arrest was monitored by localized proton magnetic resonance spectroscopy. The trace of the apparent diffusion coefficient tensor (ADC(Av)) was determined at high temporal resolution (10 sec) to assess the putative neuroprotective potential of oral creatine (Cr) in rats that received 2.2 g Cr-monohydrate per kg body weight per day for 10 days (n = 8) relative to controls (n = 9). Cr-fed rats revealed a statistically significant increase of the cerebral concentration ratio of Cr to choline-containing compounds (20%). The decrease of the ADC(Av) value during acute ischemia showed a three-phasic behavior in line with energy depletion, cytotoxic edema, and brain cooling. In Cr-fed rats, slightly less severe and mildly delayed diffusion changes during ischemia and similar beneficial trends during early reperfusion did not reach statistical significance. Magn Reson Med 42:798-802, 1999.