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Biomedical subjects

G Vargas

Publications and source records attributed to G Vargas.

At least 19 recordsLinked to original sources
PubMed2006

Simple approach to prenatal diagnosis of transposition of the great arteries.

OBJECTIVE: To analyze the most relevant anomalies, seen in a sequential segmental transverse views approach to imaging the fetal heart, that provide clues to the diagnosis of complete transposition of the great arteries (TGA). METHODS: We reviewed retrospectively all the cases of isolated TGA diagnosed in our center or submitted for a second opinion through the spatio-temporal image correlation (STIC) telemedicine (TELE-STIC) program. Only transverse cardiac sweeps were obtained. Digital video clips and STIC volumes were reviewed. The abnormal features on four-chamber, five-chamber, three-vessel (3V) and three vessels and trachea (3VT) views were analyzed. RESULTS: The study population consisted of eight fetuses with TGA with normal extracardiac anatomy. The gestational age ranged from 13 to 32 (mean, 23) weeks. The maternal age ranged from 25 to 42 (mean, 32) years. A normal four-chamber view was seen in seven cases. Only one case demonstrated a significant ventricular septal defect. At the level of the five-chamber view a straight course arterial vessel arose from the left ventricle with lateral branches in all fetuses. In the 3V view, the ascending aorta was seen reaching more anteriorly than was the pulmonary artery in six cases. At the level of the 3VT view, two vessels (transverse aortic arch and superior vena cava) rather than three were seen in all cases. CONCLUSION: Our proposed sequential segmental approach to imaging the fetal heart apparently allows, in five-chamber and 3VT views, clear and confident signs to be detected that aid diagnosis of TGA.

Adult↗
PubMed2005

Distribution and enrichment evaluation of heavy metals in Mejillones Bay (23 degrees S), Northern Chile: geochemical and statistical approach.

A suite of 36 surface sediment samples, taken between 10 and 100 m water depth in Mejillones Bay (Northern Chile), were analyzed for mineralogy, grain size, total organic carbon, Al, and heavy metal content (Cd, Zn, Ni, Mn, V, Mo). Quartz and feldspars were the main lithogenic minerals and carbonate the predominant biogenic mineral. Sediments were fine sands in the shallow zone and organic silt in the deeper zone. Enrichment Factor and Factor Analysis approach showed that the presence of Mn in the marine sediment of Mejillones is due to a partial influence of continental input, while all other metals are not supported by lithogenic debris. Although all metals showed high concentrations in the marine sediment of Mejillones Bay, comparison between metal concentration in surface sediments and preindustrial levels in this bay, show that present values agree with natural levels.

Carbon↗
PubMed2005

Prenatal diagnosis of congenital heart disease using four-dimensional spatio-temporal image correlation (STIC) telemedicine via an Internet link: a pilot study.

OBJECTIVE: To assess whether the spatio-temporal image correlation (STIC) acquisition technique can be taught to a general obstetrician by e-mail; whether STIC volume datasets can be transmitted over the Internet; and whether STIC volume datasets analyzed offline at a remote setting can be used to confirm or exclude major cardiac defects (TELE-STIC). METHODS: This was a prospective study involving 50 pregnant women with gestational ages ranging between 20 and 36 weeks. These patients were selected by two general obstetricians (operators) working in geographically remote areas of Chile. Although both obstetricians were users of equipment capable of four-dimensional (4D) ultrasound with STIC, they lacked skill in the performance of fetal cardiac examination. A dedicated web disk was created to upload the acquired volume datasets using an Internet broadband connection. Offline analysis was performed by a single investigator experienced in fetal echocardiography (the administrator). RESULTS: A telemedicine link via the Internet was possible in all cases. Seventy-seven volume datasets were sent to the web server. A complete cardiac examination according to set criteria was achieved by the administrator in 86% of the cases scanned by one operator and 95% of the cases scanned by the other operator. Three patients had cardiac defects confirmed postnatally, two fetuses had extracardiac anomalies and one fetus had a suspected cardiac defect unconfirmed by second-opinion TELE-STIC. There were two isolated major congenital heart defects. Both patients were given advice by e-mail and teleconference using a web camera about the likely outcome and benefits of scheduling in utero transport to a tertiary care center. CONCLUSIONS: STIC volumes can be obtained by operators inexperienced in fetal echocardiography, transmitted via the Internet, and their analysis enables recognition of most of the structures and views necessary to assess fetal cardiac anatomy. The preliminary use of TELE-STIC allowed us to demonstrate that some intracardiac anomalies can be ruled out and others confirmed, allowing perinatal management to be tailored accordingly.

Chile↗
PubMed2002

Modulation by PKA of the hyperpolarization-activated current (Ih) in cultured rat olfactory receptor neurons.

The hyperpolarization-activated Ih channel is modulated by neurotransmitters acting through the cAMP messenger system. In rat olfactory receptor neurons (ORNs), dopamine, by inhibition of adenylyl cyclase, shifts the voltage of half-maximal activation (V1/2) of Ih to more negative potentials and decreases Ih maximal relative conductance. Whether these effects result from a phosphorylation-dependent mechanism is unclear. Therefore, we used whole-cell patch-clamp recording techniques to study cAMP-dependent phosphorylation via PKA on Ih in rat ORNs. General protein kinase inhibition (50 nM K252a) produced a hyperpolarizing shift in Ih V1/2 and decreased Ih maximal conductance. Specific inhibition of PKA with H-89 (500 nM) also shifted the V1/2 of Ih to more negative potentials, and, in some cells, decreased Ih maximal conductance. PKA-mediated phosphorylation (cBIMPS, 50 mM) shifted Ih V1/2 more positive, modulated the kinetics of Ih channel activation and increased Ih peak current amplitude. Internal perfusion of the catalytic subunit of PKA (84 nM) also shifted Ih V1/2 positive and this shift was blocked by co-perfusion with PKI (50 nM). These results show that in rat ORNs, the voltage dependence of Ih activation can be modulated by PKA-dependent phosphorylation. We also show that PKA and other protein kinases may be involved in the regulation of Ih maximal conductance. Our findings suggest that changes in the phosphorylation state of ORNs may affect resting properties as well as modulate odor sensitivity.

Animals↗
PubMed2001

Use of osmotically active agents to alter optical properties of tissue: effects on the detected fluorescence signal measured through skin.

BACKGROUND AND OBJECTIVE: Hyper-osmotic chemical agents were used to study the effects of transient tissue scattering on the remitted fluorescence emission intensity from a target placed under a tissue sample. STUDY DESIGN/MATERIALS AND METHODS: A fluorescent film was placed underneath in vitro and in vivo samples of hamster skin, and the remitted fluorescent signal traveling to the tissue surface was monitored over time as the tissue was treated with an osmotically active agent. RESULTS: The detected fluorescent signal increased as the scattering in tissue samples was substantially reduced. The increase was greater for dimethyl sulfoxide than glucose or glycerol. It was not statistically different between in vivo skin and in vitro skin. CONCLUSION: The study shows how chemical agents can be used to improve the detected signal for a specific optical application. It could be useful in a number of optical therapeutic and diagnostic applications that can benefit from an increase in the penetration depth of light.

Analysis of Variance↗
PubMed2001

Renal proximal tubular cell growth and differentiation are differentially modulated by renotropic growth factors and tyrosine kinase inhibitors.

BACKGROUND: The renotropic growth factors (GFs), hepatocyte GF (HGF), epidermal GF (EGF), and insulin-like GF-I (IGF-I) accelerate renal regeneration in animal models after toxic or ischemic injury. These GFs initiate their biological effects on renal tubular cells by interaction with specific transmembrane receptor tyrosine kinases. MATERIALS AND METHODS: In the proximal tubular cell line PT-1, the biological effects of HGF, EGF, and IGF-I and the growth-inhibitory effects of different tyrosine kinase inhibitors (TKIs) were investigated. Receptor binding and tyrosine kinase phosphorylation were determined by ligand binding studies and Western blot analysis. RESULTS: HGF, EGF, and IGF-I bound with nanomolar affinity to their specific cell membrane receptor tyrosine kinases. In contrast to EGF or IGF-I, HGF induced a variety of cell morphological changes, including cell scattering, formation of tubular structures, and expression of long microvilli on the apical cell membrane. HGF was a 10-fold more potent and more effective growth promoter than EGF or IGF-I. Among the TKIs tested, the mitogenic effect of HGF could be more specifically inhibited by emodin and tyrphostin, that of EGF by methyl-2,5-dihydroxycinnamate, lavendustin A, and genistein, and that of IGF-I by geldanamycin. CONCLUSIONS: In contrast to EGF and IGF-I, HGF stimulated both growth and differentiation of renal proximal tubular cells, demonstrating the amazing biological potency of this renotropic growth factor. Selective TKIs may be a promising approach to modulate diseases with abnormalities in protein kinase signalling pathways such as renal cell carcinoma.

Animals↗
PubMed2001

The effect of repeated controlled ovarian stimulation in donors.

BACKGROUND: The effect of repeated controlled ovarian stimulation in young, healthy women who consented to donate their oocytes was assessed through a retrospective study. METHODS AND RESULTS: Between March 1994 and February 2000, 284 donors consented to at least two controlled ovarian stimulation cycles, with four donors undergoing up to nine cycles. Through an intra-group analysis we studied the oocyte retrieval rate, controlled by the duration and doses of stimulation, as well as the interval between cycles, finding that the number of retrieved oocytes was maintained during repeated controlled ovarian stimulation cycles. The oocyte quality, assessed as fertilization, implantation and pregnancy rates, was similar through five repeated controlled ovarian stimulation cycles. The same result was obtained when the interval in days was analysed as a continuous variable or categorized in <90 and > or =90 days. CONCLUSIONS: The analysis of the data suggests that successive stimulation cycles do not impair ovarian response in terms of quantity and quality of the oocytes obtained in this group of women. Furthermore, the interval between cycles does not influence the result of the stimulations.

Adolescent↗
PubMed2001

An alternative to sutures.

Cyanoacrylate tissue adhesives are used in numerous settings to close wounds without the use of sutures. The product and its use for closing chest tube wounds is discussed.

Cyanoacrylates↗
PubMed2000

Pulsed laser-induced thermal damage in whole blood.

An investigation of the effects of laser irradiation with a wavelength of 532 nm and pulse duration of 10 ms on whole blood was performed in vitro. Threshold radiant exposures for coagulation were quantified and transient radiometric temperatures were measured. The progression of effects with increasing radiant exposure--from evaporation to coagulation-induced light scattering to aggregated coagulum formation to ablation--is described. Results indicate that coagulation and ablation occur at temperatures significantly in excess of those assumed in previous theoretical studies. An Arrhenius rate process analysis based on hemoglobin data indicates good agreement with experimental results.

Biomedical Engineering↗
PubMed2000

An alternative to sutures.

Cyanoacrylate tissue adhesives are used in numerous settings to close wounds without the use of sutures. The product and its use for closing chest tube wounds is discussed.

Chest Tubes↗
PubMed1999

Common components of patch-clamp internal recording solutions can significantly affect protein kinase A activity.

Common components of whole-cell internal recording solutions were tested both in vitro and in patch-clamp experiments for their effects on the activity of cAMP-dependent protein kinase. Potassium fluoride (KF), 440 mM trimethylamine chloride and exclusion of bovine serum albumin (BSA) decreased the activity of the enzyme, while ethylene glycol-bis (beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) and the potassium salts of aspartate, gluconate, methylsulfate and monobasic phosphate increased its activity. Addition of KF to the internal solution produced a hyperpolarizing shift in the V1/2 of Ih channel activation, consistent with the KF-induced reduction of protein kinase A activity. Therefore, consideration of the composition of internal solutions is warranted when studying channel physiology by patch-clamp techniques.

Animals↗
PubMed1999

Use of an agent to reduce scattering in skin.

BACKGROUND AND OBJECTIVE: A method to increase light transport deeply into target areas of tissue would enhance both therapeutic and diagnostic laser applications. The effects of a hyperosmotic agent on the scattering properties of rat and hamster skin were investigated. STUDY DESIGN/MATERIALS AND METHODS: A hyperosmotic agent, glycerol, was applied in vitro and in vivo to rat and hamster skin to assess the changes in tissue optical properties. Changes in the reduced scattering coefficient after application of the agent in vitro to rat skin and after the skin has been rehydrated were assessed to evaluate the effect of the agent on tissue. RESULTS: Experimental results showed a transient change in the optical properties of in vitro rat skin. A 50% increase in transmittance and decrease in diffuse reflectance occurred within 5-10 min after the introduction of anhydrous glycerol. In addition, reduction of light scattering with this technique increased depth of visibility with optical coherence tomography. Injection of glycerol under the skin allowed in vivo visualization of blood vessels. CONCLUSIONS: The application of the agent reduces the amount of refractive mismatch found in the tissue and markedly reduces random scattering, thereby making the skin less turbid for visible wavelengths for a controlled period of time.

Administration, Topical↗
PubMed1999

Dopamine modulates inwardly rectifying hyperpolarization-activated current (Ih) in cultured rat olfactory receptor neurons.

The presence of dopamine receptors in olfactory receptor neurons (ORNs) suggests that odor sensitivity may be modulated by neurotransmitters at the level of primary sensory neurons. Using standard patch-clamp techniques on rat ORNs, we found that 1 microM dopamine, 500 microM SQ 22536 (SQ, an adenylyl cyclase inhibitor), 20 and 50 microM quinpirole (a selective dopamine D2 receptor agonist), and 1 mM adenosine 3', 5'-cyclic monophosphate (cAMP) modulate the hyperpolarization-activated current Ih. On hyperpolarizing from a holding potential of -58 mV, a small Cs+-sensitive inwardly rectifying current (Ih) was observed. Increases in extracellular K+ increased Ih amplitude without shifting its voltage dependence of activation, whereas increases in temperature produced an increase in Ih amplitude and a hyperpolarizing shift in the activation curve. Application of 1 microM dopamine reversibly shifted Ih activation to more negative potentials and decreased Ih current amplitudes. These effects were blocked by concomitant application of dopamine with sulpiride, a selective dopamine D2 receptor antagonist. The effects of dopamine were mimicked by quinpirole. Quinpirole (20 microM) decreased Ih current amplitude, but was without effect on Ih voltage dependence of activation. However, 50 microM quinpirole produced both a reduction of Ih peak currents and a hyperpolarizing shift in the activation curve for Ih. External application of the adenylyl cyclase inhibitor SQ 22536 produced a reversible decrease in peak currents but had no effect on Ih voltage dependence of activation, whereas internal application of cAMP shifted Ih activation to more depolarized potentials. Because Ih modulates cell excitability and spike frequency adaptation, our findings support a role for dopamine in modulating the sensitivity and output of rat ORNs to odorants.

Adenine↗
PubMed1999

Laser fluence for permanent damage of cutaneous blood vessels.

Treatment of vascular disorders may be improved by a more thorough understanding of laser-blood vessel interaction. In this study, the probability of permanent damage to a given type and size of blood vessel was determined as a function of fluence at the top (superficial edge) of the vessel lumen. A 532 nm wavelength, 10 ms pulse duration, 3 mm spot size laser was used to perform approximately 250 irradiations of subdermal blood vessels in the hamster dorsal skin flap preparation. The radiant exposure required for a 50% probability of permanent damage was calculated using a probit analysis of experimental results. Threshold radiant exposure increased with larger blood vessel diameters and was greater for arterioles than venules. Monte Carlo modeling of a typical blood vessel geometry revealed that fluence at the top of the blood vessel lumen was amplified by a factor of approximately 2.4 over tissue surface radiant exposure, due to light scattering in the tissue and internal reflection at the skin-air interfaces.

Animals↗
PubMed1998

Capillary electrophoresis separation of the new anti-AIDS agents 9-(2-phosphonylmethoxyethyl)adenine and 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine in mixtures with some monoribonucleotides or the most common deoxynucleotides.

The present work describes an electrophoretic method for the separation and determination of the new antivirals, 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and 9-(2-phosphonylmethoxyethyl)-2,9-diaminopurine (PMEDAP) in model mixtures with some monoribonucleotide isomers (3'-AMP, 2'-CMP, 3'-CMP, 3'-GMP, 2'-GMP, 3'-UMP, 5'-GMP, and 5'-UMP) or with the most common deoxynucleotides (dCMP, dCDP, dCTP, dTMP, dTDP, dTTP, dGMP, dGDP, dGTP, dAMP, dADP, dATP). A fused-silica capillary tube, 75 microm ID, 67.8 cm total length (60.3 cm length to the detector), with detection at 210 nm was employed. A hydrodynamic injection for 10 s (1.5 psi vacuum) was utilized to introduce the sample, and 30 kV voltage was applied for the separation. The complete separation of PMEA and PMEDAP from the mononucleotide isomers and deoxynucleotide mixtures is possible in less that 10 min and 25 min, respectively, using 20 mM borate buffer, pH 9.9, with the addition of 10 mM beta-cyclodextrin. Efficiencies of more than 120 000 and resolution higher than 1.9 were reached for each of the compounds studied. This capillary electrophoretic procedure opens the possibility for future determination of PMEA and PMEDAP in cell pool samples.

Adenine↗