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Biomedical subjects

O Albert

Publications and source records attributed to O Albert.

18 recordsLinked to original sources
PubMed2006

Nonlinear mirror based on cross-polarized wave generation.

We present a new type of nonlinear mirror based on the generation of a cross-polarized wave through a nonresonant electronic third-order process. It is characterized by a reflection coefficient that depends on the input intensity. Its behavior results from the interference between the nonlinearly generated cross-polarized wave and a pi/2 phase-retarded wave. This setup has a lot of advantages: it does not require any phase matching, it is achromatic and suitable for femtosecond pulses, linear losses are easily adjustable, and the overall behavior is predictable. The device has been experimentally tested using BaF2 and YVO4 crystals.

Journal Article↗
PubMed2006

Comment on "Generation of 10(11) contrast 50 TW laser pulses".

We argue for a different physical interpretation of the results given in the recent Letter by Chvykov et al. [Opt. Lett.31, 1456 (2006)] in which a double nonlinear crystal scheme for cross-polarized wave generation is analyzed. We discuss the most important factors that explain the origin of the two-crystal scheme's increased efficiency, namely, the Kerr lensing effect and a Gouy phase shift. The position and orientation of the second crystal relative to the first one are unambiguously defined; related effects are illustrated by already published works on the subject.

Comment↗
PubMed2006

Adaptive correction of a tightly focused, high-intensity laser beam by use of a third-harmonic signal generated at an interface.

By using the third-harmonic signal generated at an air-dielectric interface, we demonstrate a novel way of correcting wavefront aberrations induced by high-numerical-aperture optics. The third harmonic is used as the input physical parameter of a genetic algorithm working in closed loop with a 37-actuator deformable mirror. This method is simple and reliable and can be used to correct aberrations of tightly focused beams, a regime where other methods have limitations. Improvement of the third-harmonic signal generated with an f/1.2 parabolic mirror by 1 order of magnitude is demonstrated.

Journal Article↗
PubMed2004

[Femtosecond laser: a micromachining system for corneal surgery].

INTRODUCTION: The authors present the diode-pumped, all-solid state, neodymium:glass femtosecond laser from the Laboratory of Ocular Biotechnology, Hotel-Dieu Hospital. MATERIALS AND METHODS: We worked with a 1,065-nm wavelength infrared laser. This laser is composed of an oscillator and amplification glass matrix mixed with neodymium. Its stretching and compression system is capable of producing pulses lasting a few hundred femtoseconds. The repetition rate is adjustable, ranging from 1 to 10 kHz, and can reach energies up to 60 microJ. The delivery system was set up on an optical table, with human corneal samples fixed to an anterior chamber system, which can be moved over the X-Y-Z axis by a computer-guided translation motor with micrometric precision. We analyzed the biological effects of laser impacts in human corneal tissue, obtained from the French Eye Bank. RESULTS: The femtosecond laser provides automated corneal cutting with a high level of precision, which can be verified on the corneal surface regularity by scanning electron microscopy analysis. Silicon samples can also be cut and can be used for calibration testing of the laser. CONCLUSION: The set-up composed of the femtosecond laser and the described delivery system enable precise corneal cutting and offer the opportunity to study its characteristics.

Calibration↗
PubMed2002

Adaptive correction of depth-induced aberrations in multiphoton scanning microscopy using a deformable mirror.

We demonstrate adaptive aberration correction for depth-induced spherical aberration in a multiphoton scanning microscope with a micromachined deformable mirror. Correction was made using a genetic learning algorithm with two-photon fluorescence intensity feedback to determine the desired shape for an adaptive mirror. For a 40x/0.6 NA long working distance objective, the axial scanning range was increased from 150 mm to 600 mm.

Microscopy, Confocal↗
PubMed1999

Serotonin, bradykinin and endothelin signalling in a sheep choroid plexus cell line.

The secretion of cerebrospinal fluid by the epithelial cells of choroid plexus is regulated by membrane receptors coupled to adenylyl cyclases or to phospholipase C. These intracellular signalling pathways as their interactions were investigated in a sheep choroid plexus cell line. Endothelin-1, bradykinin and serotonin induced a transient dose-dependent increase in intracellular calcium. EC 50 were 10(-8) M for endothelin-1, 10(-8) M for bradykinin and 10(-6) M for serotonin. Maximal increase in intracellular calcium was comparable for bradykinin and serotonin, but was 3 to 5 fold larger for endothelin-1. Successive stimulations with endothelin-1, serotonin or bradykinin elicited calcium increases similar to single stimulations reflecting absence of heterologous desensitization between these receptors. Forskolin-induced cAMP accumulation was potentiated by bradykinin, but not by serotonin and endothelin-1. This potentiation resulted from an increase in cAMP production rather than to an inhibition of cAMP hydrolysis. These data suggest that serotonin, endothelin-1 and bradykinin each use specific signalling pathways in the sheep choroid plexus cells.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Effects of 4-deoxypyridoxine on the isovolumic perfused rat heart: influence of oxygenation and glucose availability.

The study was performed with isolated perfused isovolumic rat hearts. After a 40 min stabilization period, the effect of 4-deoxypyridoxine (DOP) 10(-5) M was studied with 3 Glc concentrations: 0, 3.3 and 11 mM. DOP was perfused during a 20 min normoxic or anoxic period followed by 40 min of normal perfusion. During normoxia with 11 mM Glc, DOP decreased the contracture observed in the control group. With 0 mM Glc, DOP improved developed pressure and dP/dt+ without a decrease in glycogen stores. During anoxia followed by reoxygenation, a partial protection towards CK release was observed with DOP (3.3 mM Glc). Intracellular PLP levels were higher in the 11 mM Glc group than in the other groups with and without DOP, and DOP with 11 mM Glc increased PLP levels (DOP N2 vs. DOP O2). Glycogen stores increased with 11 mM Glc without DOP (O2 vs. N2), whereas they decreased with DOP without Glc (DOP N2 vs. N2). DOP could improve the yield in glycogenolysis in normoxia and might activate mitochondrial anaerobic metabolism during anoxia.

Animals↗
PubMed1981

The effect of intravenous diazepam on rise of intraocular pressure following succinylcholine.

Because succinylcholine raised intraocular pressure, its use to facilitate tracheal intubation for ocular surgery, especially in emergency open-eye cases, has been a controversial topic among anaesthetists for more than two decades. In recent years, intravenous diazepam pretreatment before succinylcholine has been reported to reduce the untoward side effects of myalgia, and elevation of serum potassium and creatine phosphokinase. This study was designed to assess the effect of pretreatment with intravenous diazepam 0.1 mg kg-1 on control (base-line) intraocular pressure and to determine if such pretreatment diminished the rise in intraocular pressure following the standard anaesthesia induction sequence of thiopentone 3 - 5 mg kg-1., followed by tracheal intubation. Such diazepam pretreatment was shown to reduce the intraocular pressure from control levels and to diminish the rise of intraocular pressure following succinylcholine and tracheal intubation. Because succinylcholine produces rapid onset of neuromuscular block for tracheal intubation and since only minor intraocular pressure elevation occurs following thiopentone and succinylcholine in patients pretreated with diazepam, its use in ocular surgery, including emergency open-eye cases, can be rationally advocated. The addition of 0.6 mg kg-1 d-tubocurarine to the diazepam pretreatment did not produce a further reduction of the increase of intraocular pressure following succinylcholine.

Adult↗
PubMed1978

Cerebral metabolic, hemodynamic and antihypoxic properties of l-eburnamonine.

l-Eburnamonine--16-oxoeburnane--assumes experimental cerebral 'oxygenator' and antihypoxic properties which appear more pronounced than those of vincamine. In anesthetized dogs, l-eburnamonine increases the cerebral oxygen supply and the cerebral oxygen consumption, without cerebral vasodilation; l-eburnamonine improves the cerebral capillary circulation, as observed on the rheoencephalogram. l-Eburnamonine inhibits the effects of hypobaric hypoxia in mice (increase of survival time) and in rats (inhibition of amnesic effects of hypoxia). l-Eburnamonine decreases the electroencephalographic consequences of the acute and iterative asphyxic anoxia in curarized rats and, by means of the protection of the cerebral cortex, inhibits the postischemic increase of thalamic somesthetic evoked potentials in curarized cats. Further studies are necessary to precise the mechanisms involved in these 'cerebral protective' properties of l-eburnamonine.

Acute Disease↗
PubMedDate not supplied

The effects of 5-fluorouracil on contractility and oxygen uptake of the isolated perfused rat heart.

Clinical cardiotoxicity related to 5-fluorouracil (5-FU) simulates either myocardial ischemia or left ventricular dysfunction. In order to characterize the changes occurring in the heart following 5-FU administration, the isovolumic perfused rat heart model according to Langendorff has been used. Particular emphasis was laid on contractility and oxygen uptake. Perfusion of isolated hearts with 1 mg/L 5-FU for 80 minutes failed to show any differences in contractility and oxygen consumption in comparison with the control group. On the contrary, 5-FU pretreatment of Wistar rats (50 mg/kg I.P. for 5 consecutive days) led to a decrease in inotropism without any change in maximum relaxation rate. The most significant finding was the consistent increase in oxygen consumption throughout the 80 minutes of perfusion (p less than 0.05) associated with a decrease in the fractional extraction of oxygen. Mean coronary flow was consistently increased in the 5-FU-pretreated group. Lactate release and CK Leakage did not differ in the two groups. In the 5-FU-pretreated group the ratio of oxygen consumption to rate-pressure product remained significantly elevated throughout 80 minutes of perfusion in comparison with the control group (p less than 0.05). Inappropriately high oxygen uptake could be a reflection of cellular metabolic disturbances responsible for post-ischemic dysfunction.

Animals↗
PubMedDate not supplied

Comparative study of isoproterenol and 4-deoxypyridoxine effects on the isovolumic rat heart model.

Isovolumic rat hearts were perfused for 20 min (T20) or 40 min (T40) with 10(-6) M isoproterenol (ISO), 10(-5) M 4-Deoxypiridoxine (DOP) or with both drugs (ISO-DOP). ISO increased developed pressure 51% and 31%, coronary flow (C.F.) 37% and 52%, heart rate 50% and 60%, lactate production 160% and 76%, and CK activity in the effluent perfusate 182% and 173% at T20 and T40 respectively, whereas glycogen stores decreased by 47% and 77%. DOP needed at least 40 min to increase heart rate 32%, C.F. 40% and to decrease glycogen reserves by 33% and pyridoxal-5-phosphate 13%. In the ISO-DOP group, the ISO inotropic effect was lowered by 23% (T20) and 25% (T40) and DOP reduced ISO induced glycogenolysis.

Animals↗