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Biomedical subjects

R A Sanchez

Publications and source records attributed to R A Sanchez.

12 recordsLinked to original sources
PubMed1992

Comparison of the physical properties of two types of polydimethyl siloxane for fabrication of facial prostheses.

The in vitro physical properties of two types of polydimethyl siloxane, MDX 4-4210 and a new material A-2186, were compared. The properties that were investigated in this study were tensile strength, elongation, tear strength, and surface hardness. The properties tested were selected because of their clinical significance for fabricating a facial prosthesis. According to the results obtained in this investigation, the new material, A-2186, had greater tear resistance, tensile strength, and a larger percentage of elongation. A-2186 material, also proved to be softer at the surface than the MDX 4-4210. This combination of physical properties makes this material, A-2186, a better choice than the traditional MDX 4-4210 for the fabrication of facial prostheses.

Biocompatible Materials↗
PubMed1992

Simulated implant surgery in rabbit long bones: a descriptive study.

The objectives of this study were: (a) to observe and describe the variability of bone healing in implant receptor sites which were prepared in rabbit femurs by use of different surgical methods; and (b) to determine if the animal model which was used was suitable for the detection of differences in healing reactions in implant receptor sites which were prepared by different surgical methods. Three 3-mm-wide implant receptor sites were prepared in the right and left femurs of four large New Zealand white rabbits. The surgical parameters used in preparation of the different sites included: low speed with no irrigation (LSO); low speed with internal irrigation only (LSI); low speed with external irrigation only (LSE); high speed with no irrigation (HSO); or high speed with external irrigation only (HSE). The sites were randomized so that each animal had one of each type of site in either the right or left femur. A non-treated control site was located in each animal for comparison with experimental sites. The animals were killed at 7, 14, 21, and 28 days post-operatively. The resultant samples were fixed, embedded, sectioned, and stained with basic fuchsin and toluidine blue. The results indicated that this was probably not a suitable animal model, since no discernible differences were detected in the various healed sites.

Animals↗
PubMed1991

Superoxide anion and hydrogen peroxide metabolism in soybean embryonic axes during germination.

The total rate of mitochondrial O2- production in the presence of NADH as substrate increased from 200 to 1340 pmol/min per axis between 2 and 30 h of imbibition. The activities of the enzymes involved in hydroperoxide metabolism, e.g., superoxide dismutase, catalase, peroxidase and glutathione and ascorbate peroxidases, markedly changed during the germination of soybean embryonic axes. Superoxide dismutase was the enzymatic activity affected the most during the initial stages of germination. Intracellular O2- steady-state concentration, calculated from the rate of O2- production and superoxide dismutase activity, showed a 2-fold increase from 2 x 10(-8) M to 4 x 10(-8) M in germination phase I, declined in phase II to 2 x 10(-8) M and remained constant over the rest of the incubation period. The reaction of H2O2 and luminol catalyzed by Co2+ was utilized to measure H2O2 diffused out of the soybean axes after 5 to 10 min of incubation. The catalase-sensitive luminol emission of diffusates prepared from axes previously imbibed from 2 to 30 h corresponded to a H2O2 intracellular steady-state concentration in the range of 0.3 to 0.9 microM. The activity of metal-containing antioxidant enzymes was determined in the extracellular fluid. Cell wall peroxidase activity increased from 10 to 300 mumol/min per mg protein and appears as a potentially important pathway for H2O2 utilization. Hydrogen peroxide metabolism in soybean embryonic axes during early inhibition appears to have the following main features: (a) mitochondrial membranes are the most important source of cytosolic O2- and H2O2; (b) H2O2 is regulated at a steady-state concentration of 0.3-0.9 microM; (c) catalase is the main enzyme in terms of H2O2 utilization; (d) H2O2 exo-diffusion is quantitatively important destiny of intracellular H2O2; and (e) extracellular peroxidase located at the cell wall affords an enzymatic system able to use diffused H2O2.

Catalase↗
PubMed1991

Positional accuracy of four die tray systems.

This study evaluated the positional accuracy of dies with four die tray systems. The die trays were: (1) Accu*trac Precision die system, (2) Model-Tray system, (3) Sterdo Split model tray, and (4) Tricodent One*Cast die tray system. Positional change of the dies was measured by using an Olympus binocular scanning tunneling microscope (STM). Positional change of the dies was the difference between preremoval and postremoval die position. Results show that all four die tray systems are not significantly different in most measurement categories, although the Model-Tray system was significantly different from the other die tray systems in one measurement category.

Analysis of Variance↗
PubMed1991

Recovery of erythrocyte Na(+)-K(+)-Cl- cotransport activity by enalapril.

We studied total exchangeable sodium, ion transport activity at maximal rate, and erythrocyte Na+ content in response to angiotensin converting enzyme inhibition in mild-to-moderate essential hypertensive patients with normal renal function. Twenty-five patients (mean age 56 years, range 40-62 years) who had abnormal red blood cell Na(+)-K(+)-Cl- cotransport or red blood cell Li(+)-Na+ countertransport were treated with either enalapril (20 mg daily) or hydrochlorothiazide (50 mg daily) during a 30-day period. During the period of enalapril treatment, Na(+)-K+ pump and Na(+)-K(+)-Cl- cotransport increased significantly from 4,282 +/- 255 to 5,236 +/- 325 mumol/l red blood cell/hr (p less than 0.01) and 166 +/- 21 to 220 +/- 24 mumol/l red blood cell/hr (p less than 0.05), respectively. Mean intracellular Na+ content in erythrocytes decreased from 11.4 +/- 0.40 to 10.0 +/- 0.33 mmol/l (p less than 0.01) and exchangeable Na+ from 39.8 +/- 0.6 mmol/kg to 35.6 +/- 0.6 mmol/kg (p less than 0.001). Sodium reduction correlated with the recovery of Na(+)-K(+)-Cl- cotransport activity (r = -0.65, p less than 0.01). During treatment, systolic and diastolic blood pressures were reduced significantly (p less than 0.01). In 12 patients treated with hydrochlorothiazide, Na(+)-K(+)-Cl- cotransport, Na(+)-K+ pump, Na(+)-Li+ countertransport, and Na+ permeability did not change significantly while Na+ content decreased from 11.7 +/- 0.3 to 10.3 +/- 0.2 mmol/l (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Effect of stress conditions on Escherichia coli outer and inner membranes, separated by Sephacryl S-500 chromatography.

A chromatographic method for the separation of outer and inner membranes of Escherichia coli is described. This method is much faster than the generally used equilibrium centrifugation and has a greater versatility in the volumes that can be treated. Both techniques are used to examine the effects of different stress conditions on the E. coli membrane. The obtained results illustrate the equivalence of both methods.

Acrylic Resins↗
PubMed1989

Renal sodium handling abnormalities in hypertensive and normotensive patients with a family history of hypertension.

We measured the effective renal plasma flow, the glomerular filtration rate and the fractional excretion of sodium under low and high sodium intakes in the normotensive offspring of hypertensives and in essential hypertensive patients. During the high sodium intake, 57% of the offspring and 42% of the hypertensive patients showed an increase in effective renal plasma flow and fractional excretion of sodium. In the remaining hypertensives, enalapril improved the renal haemodynamic and sodium-handling responses. Enalapril also reduced the blood pressure in all hypertensives, whether they showed a normal or an abnormal response to a high sodium intake. In the hypertensive patients with an abnormal response to a high sodium intake, the intra-erythrocyte sodium content was higher than in the normal responders. Thus, abnormal renal haemodynamic and sodium-handling responses to a high sodium intake were observed in 50% of the hypertensive patients and the offspring. The high intra-erythrocyte sodium content observed in the hypertensive patients suggests that extrarenal alterations in sodium handling were present.

Adult↗
PubMed1987

Role of cardiopulmonary mechanoreceptors in the postural regulation of renin.

To change the stretch on cardiopulmonary mechanoreceptors, large shifts of blood in the capacity space were elicited by tilting and by exerting positive lower body pressure in the tilted position. Twelve volunteers underwent invasive hemodynamic studies and in 10 other subjects cardiac size was determined by radionuclide cardiography. In all 22 subjects tilting caused the expected increase of renin, which was abolished by lower body compression. Decompression caused renin to increase again. Right atrial pressure in invasive studies and end-systolic and end-diastolic counts in noninvasive studies showed a significant and strong negative correlation with renin and norepinephrine levels. Thus, the degree of stretch of the cardiopulmonary mechanoreceptors is a major determinant of reflex regulation of renin release in humans.

Adolescent↗
PubMedDate not supplied

Verifying the reliability of interchanging casts with semiadjustable articulators.

Interchangeability of a semiadjustable articulator could be of significant convenience and economic benefit to the restorative dentist. The manufacturer of the Whip-Mix Model 2240 articulator claims such interchangeability. This study evaluated the accuracy of the cross-mounting capability of eight such articulators, then compared the measured results with those obtained from eight semiadjustable instruments for which the manufacturer makes no such promise of interchangeability. It was determined that the Model 2240 articular did possess accuracy when a measuring device was transferred between the eight materials tested.

Analysis of Variance↗