Search PubMed⌕ Search

Biomedical subjects

R Navarro

Publications and source records attributed to R Navarro.

At least 109 records · Page 6Linked to original sources
PubMed1989

Development of compliance chamber diaphragms with reduced permeability.

The implantable ventricular assist systems currently undergoing clinical readiness testing shuttle the displaced gas between the non-blood side of the pumping diaphragm and an elastic chamber generally called a "compliance chamber" or variable volume device. The movement of the stored gas allows the pump to fill and empty without compression or expansion of the gas behind the pump diaphragm. The material used for the construction of compliance chambers should be fatigue resistant to withstand the 63 million flexes per year of the blood pump. The material should also be biocompatible and highly impervious to gases. Significant diffusion of gases from the compliance system necessitates external make-up gases to somehow be added to the internal system. Material selection is complicated by the fact that most fatigue-resistant elastomers also have high gas permeability. In order to solve this problem, bilayer compliance chambers have been developed using biocompatible and fatigue-resistant polyolefin rubber comolded with relatively impervious butyl rubber.

Assisted Circulation↗
PubMed1988

Effects of neonatal treatment with estrogens on the development of the thymus in rats.

In order to study the effects of sex hormones administered during the neonatal period on the thymic development we have injected 5 days old female rats with a single dose (0.1mg) of estradiol benzoate. The evolution of the thymus gland after treatment was morphometrically analyzed. The thymus of the estrogen-injected animals diminished in size between the 7th and the 15th day, increasing afterwards. The cortex was the most sensitive compartment in the thymus to estrogenic treatment. Both thymic involution and enlargement were associated to changes in the frequency of large lymphoid cells in the subcapsular region and variations in the thymic cortex weights. The observed effects are tentatively attributed to alterations in the thymocyte differentiation probably due to modifications in the secretion of thymic hormones.

Animals↗
PubMed1986

Optical quality of the eye lens surfaces from roughness and diffusion measurements.

The Purkinje-Sanson images and the image of the anterior lens surface, formed by coherent light, are studied in this paper. The roughness and the diffusing behavior of the anterior lens surface are studied by two complementary methods: measurement of the scattering halo in the third Purkinje image and speckle-contrast measurements in the image of the anterior surface (lens epithelium). The scattering properties of the anterior lens surface are represented by an equivalent Gaussian diffusing surface defined by the standard deviation of the surface height, sigma h = 0.143 micron, and the correlation length, r0 = 7 microns. The relative contribution of this surface to the intraocular scattering has been evaluated, and it depends strongly on the age of the subjects.

Adult↗
PubMed1985

Accommodation-dependent model of the human eye with aspherics.

We consider a schematic human eye with four centered aspheric surfaces. We show that by introducing recent experimental average measurements of cornea and lens into the Gullstrand-Le Grand model, the average spherical aberration of the actual eye is predicted without any shape fitting. The chromatic dispersions are adjusted to fit the experimentally observed chromatic aberration of the eye. The polychromatic point-spread function and modulation transfer function are calculated for several pupil diameters and show good agreement with previous experimental results. Finally, from this schematic eye an accommodation-dependent model is proposed that reproduces the increment of refractive power of the eye during accommodation. The variation of asphericity with accommodation is also introduced in the model and the resulting optical performance studied.

Accommodation, Ocular↗
PubMed1985

Incorporation of intraocular scattering in schematic eye models.

Beckmann's theory of scattering from rough surfaces is applied to obtain, from the experimental veiling glare functions, a diffuser that when placed at the pupil plane would produce the same scattering halo as the ocular media. This equivalent diffuser is introduced in a schematic eye model, and its influence on the point-spread function and the modulation-transfer function of the eye is analyzed.

Humans↗
PubMed1985

A mathematical model to predict the optimal control mode for a pusher-plate total artificial heart (TAH).

Table I lists the physiological criteria for ranking each control mode (hemodynamic conditions assumed are listed in Figure 4). For each criteria, each mode was given a ranking of 0 to 3, with 3 the best. At the bottom of the table is the total of all criteria grades. The ranking from best to worst mode is in order: IND, LMA/LMS, Low FR/High FR, RMA/RMS. A discussion of Table I follows: FR is a reliable control mode and has been used extensively clinically, including the recent TAH human implants. The advantage of this mode is its simplicity: if the venous return is below pump capacity, then all incoming blood can be pumped out without any sophisticated controller. However, when the flow demand exceeds the pump capacity, HR must be increased. The ideal situation would be to set FR at one HR and %S, and leave these settings over the life of the recipient. However, a high HR like this would result in relatively high atrial pressures and low flow rates with respect to IND (as shown theoretically, in vitro, and in vivo). Although the patient would have a high maximum COR, the daily COR would be low, resulting in a relatively high AVO2 difference. Finally, FR lacks afterload sensitivity. RMA and RMS received the lowest grade of all modes. Because of the L-L shunt, the stroke length of these modes are smallest, and thus the CO curves and FPS are poorer than any other mode.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMedDate not supplied

Vibrational study of a nucleoside analogue with antiviral activity, 5-chloro-2'-deoxyuridine, CDU.

The experimental FTIR and FT-Raman spectra of 5-chloro-2'-deoxyuridine have been assigned on the basis of normal coordinate analyses, in the light of observed and calculated wavenumbers and isotopic shifts. The results indicate that virtually all normal modes of IDU involve some degree of vibrational coupling between the chlorouracil base and the deoxyribose moiety.

Antiviral Agents↗
PubMedDate not supplied

Consequences of polymorphism of 5'-GMP.Na2 in the vibrational spectra of metal complexes and isotopic derivatives.

The commercial mononucleotides are frequently used to obtain metal complexes and isotopic derivatives. Normally, the spectra of these new compounds are compared with the spectra of the commercial mononucleotides. Nevertheless, important variations in the vibrational spectra of the disodium 5'-guanosine monophosphate, 5'-GMP, have been observed in this work produced by submitting the commercial salt to the same general laboratory process that the obtained compounds, i.e., solving the commercial salt in water and subsequent recrystallization. These changes have been analyzed and interpreted. The variations are not significant in disodium 5'-cytosine monophosphate, 5'-CMP. It is important to take this information into account before carrying out vibrational studies with this type of molecules, since some bands attributed to isotopic substitutions or to the metal attack may be a result of manipulation of the nucleotide (solving and recrystallization) instead of the studied effect. Thus, before any work in which the nucleotide salt is manipulated (deuteration, synthesis of other isotopic derivatives or metal-nucleotide complexes), it should be noted that the process to which the sample is submitted on its own is enough to modify the vibrational spectrum. Then, attention should be paid to the changes observed in the vibrational spectra of recrystallized mononucleotides, since recrystallization may lead to a considerable phase change, and this can notably alter the vibrational spectra.

Crystallization↗
PubMedDate not supplied

In vitro and in vivo performance evaluation of a totally implantable electrohydraulic left ventricular assist system.

The biolized electrohydraulic left ventricle assist devices were tested in 14 calves with an average survival time of 162 days and as long as 250 days without the use of anticoagulants. In vitro, the system pumped 4.1 L/min at a low 4.8 mmHg fill pressure with a mean afterload of 100 mmHg and rate of 46 bpm. A flow rate of 13.5 L/min was observed at 155 bpm and 110 mmHg afterload. Motor frequency and current increased with increasing flow rate (162 Hz, 0.67 amp at 2.5 L/min; 484 Hz, 2.43 amp at 13.5 L/min). Flow rate did not change significantly with afterload pressure. The complete system was implanted in a 100 kg calf. Synchronization of the blood pump with the natural heart was demonstrated at heart rates of 85 to 167 bpm. The synchronized flow rate varied from 6 to 10.5 L/min despite the considerable heart rate changes and stroke variations. The system hemodynamic performances were acceptable and met NIH requirements.

Animals↗