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Biomedical subjects

J Escalona

Publications and source records attributed to J Escalona.

14 recordsLinked to original sources
PubMed2006

Regulating noise-induced spiking using feedback.

We report successful manipulation of the noise provoked spiking behavior using delayed feedback control. Experiments were performed in a three electrode electrochemical cell under potentiostatic conditions. The uncontrolled system exhibited noise invoked oscillations whose regularity was quantified using normalized variance (NV). Superimposing delayed feedback, for appropriate values of delay (t), an enhancement in the regularity of the spike sequence was attained. Numerical simulations corroborated experimental observations.

Journal Article↗
PubMed2004

Parameter space reduction criteria to search for synchronization domains in coupled discrete systems.

Based on analytical considerations, we introduce criteria that enable us to encapsulate the parameter domains for which chaotic synchronization in linearly coupled map systems may be attained. Our aim is to provide means to readily determine parameter regions which preclude synchronization. This results in a significant reduction of parameter space that one needs to explore. Our findings hold for both identical and quasi-identical (small parameter mismatch) maps subjected to unidirectional and bidirectional coupling. As a testing ground we present numerical calculations for the logistic and cubic maps which validate the predictive capability of our approach. Our main contribution relies on the applicability of one of our criteria to experimental situations. Since in real life it is almost impossible to construct two truly identical systems, the results for quasi-identical maps are of particular relevance.

Journal Article↗
PubMed2004

Noise-aided synchronization of coupled chaotic electrochemical oscillators.

We report experimental and numerical results on noise-enhanced synchronization of two coupled chaotic oscillators. Enhanced synchronization is achieved through superimposing small-amplitude Gaussian noise on a common system parameter of the two chaotic oscillators. A resonancelike behavior is found: at an optimum level of noise, maximum synchronization is attained. The simulations show that the resonance behavior occurs with both identical and nonidentical oscillators. Noncommon (asymmetric and independent) noise does not enhance synchronization; common noise seems to enhance synchronization.

Journal Article↗
PubMed2000

Numerical studies on the dynamics of the globally coupled maps with sequential updating

A system of globally coupled logistic maps with sequential updating is analyzed numerically. It is found that deterministic asynchronous updating schemes may have dramatical influences on the dynamical behaviors of globally coupled systems. Transitions from spatiotemporal chaos to spatially organized states are observed as the coupling parameter varies. It is shown that the model system may exhibit a variety of collective properties such as clustering, traveling wave patterns, and spatial bifurcation cascades.

Journal Article↗
PubMed2000

Noise-aided control of chaotic dynamics in a logistic map

Controlling chaos involves employing small perturbations to a control parameter, resulting in the stabilization of the system (naturally chaotic) on one of the infinite unstable periodic orbits embedded in the chaotic attractor. In this Brief Report we study the constructive role of external noise in increasing the efficiency of controlling chaos. Using a logistic map as an example, control of chaotic dynamics is achieved using a linear delayed-feedback strategy. Working in the subthreshold regime of control (where the value of control constant is less than the minimum value required to stabilize the period-1 target state), system dynamics in the presence of superimposed noise (system plus control plus noise) exhibit a resonance effect. Furthermore it is observed that the time required to reach the target state decreases appreciably in the presence of an optimum level of noise.

Journal Article↗
PubMed1999

[Achondroplasia and Down syndrome in the same patient. Report of a case].

Achondroplasia and trisomy 21 are, within their respective categories, conditions the most frequent genetic diseases found in newborns. The simultaneous presence of both conditions in the same patient, has been however, reported only once in the world literature. In this paper we present a patient affected by both entities (Achondroplasia and Trisomy 21). The clinical findings and the reasons for the rare reported frequency of these cases are discussed.

Achondroplasia↗
PubMed1997

Two male siblings with cavum septum pellucidum, cavum vergae, macrocephaly, seizures and mental retardation. A new hereditary syndrome?

We report two brothers from non-consanguineous parents who share a particular constellation of clinical and radiographic findings, including macrocephaly, mental retardation and seizures as well as megalencephaly, cavum septum pellucidum and persistence of cavum vergae. The similar characteristics of these two brothers suggest a hereditary syndrome.

Abnormalities, Multiple↗
PubMed1994

Spinal cord compression by amyloid deposits.

STUDY DESIGN: Dorsal spinal cord compression caused by amyloid tissue deposits in the posterior vertebral arch and epidural space of the T6-T7 region in a 29-year-old woman is reported. RESULTS: Studies did not show any primary cause of amyloidosis. CONCLUSIONS: This case can be classified as primary localized tissue because other causes and amyloid deposits were not discovered. This patient was the youngest person reported to have dorsal spinal cord compression caused by amyloid tissue deposits, and the spinal cord compression was localized in the thoracic region, which occurred in six of the seven cases reported.

Adult↗
PubMed1994

[Complicated placental chorioangioma: infrequent cause of premature labor].

We report a case of a 32 week pregnant patient who was admitted to our ward in preterm labor. After delivery, the examination of the placental tissue showed a large pedunculated tumor, complicated with torsion. Histology of the tumor revealed a placental chorioangioma. We propose that the complication of the tumor is the etiologic factor that brought about preterm labor in this patient.

Adult↗
PubMed1992

Pharmacological characterization of adenosine A1 and A2 receptors in the bladder: evidence for a modulatory adenosine tone regulating non-adrenergic non-cholinergic neurotransmission.

1. The nerve-evoked contractions elicited by transmural electrical stimulation of mouse urinary bladders superfused in modified Krebs Ringer buffer containing 1 microM atropine plus 3.4 microM guanethidine were inhibited by adenosine (ADO) and related nucleoside analogues with the following rank order of potency: R-phenylisopropyladenosine (R-PIA) greater than cyclohexyladenosine (CHA) greater than 5'N-ethylcarboxamido adenosine (NECA) greater than ADO greater than S-phenylisopropyladenosine (S-PIA). Tissue preincubation with 8-phenyltheophylline (8-PT) displaced to the right, in a parallel fashion, the NECA concentration-response curve. 2. The contractions elicited by application of exogenous adenosine 5'-triphosphate (ATP) were also inhibited by ADO and related structural analogues. The rank order of potency to reduce the motor response to ATP was: NECA greater than 2-chloroadenosine (CADO) greater than R-PIA greater than ADO greater than CHA greater than S-PIA. 3. The ADO-induced ATP antagonism was of a non-competitive nature and was not specific. Tissue incubation with 10 microM NECA not only reduced the motor responses elicited by ATP, but also 5-hydroxytryptamine, acetylcholine and prostaglandin F2 alpha. The action of NECA was antagonized following tissue preincubation with 8-PT. The inhibitory action of NECA was not mimicked by 10 microM CHA. 4. The maximal bladder ATP contractile response was significantly increased by tissue preincubation with 5-30 microM 8-PT. 5. The 0.15 Hz evoked muscular twitch was significantly increased by 8-PT while dipyridamole consistently reduced the magnitude of the twitch response. These results are consonant with the hypothesis that an endogenous ADO tone modulates the bladder neurotransmission. 6. A working model is proposed suggesting the presence of ADO-Al and A2 receptors in the mouse urinary bladder. The A1 receptor subpopulation is probably of presynaptic origin whereas the smooth muscle membranes contain a population of the A2 receptor subtype.

Adenosine↗
PubMed1990

Dermal and subdermal tissue filling with fetal connective tissue and cartilage, collagen, and silicone: experimental study in the pig compared with clinical results. A new technique of dermis mini-autograft injections.

The early reaction to the injection of silicone, collagen, and lyophilized heterologous fetal connective and cartilage tissues into the limiting zone deep dermis-superficial subcutaneous tissue was histologically examined in the pig and compared with clinical results. The inflammatory reaction to lyophilized heterologous fetal tissue is considerably more intense than that to collagen and silicone and lasts for several weeks. Therefore, it is not recommended for soft tissue filling in the face. Admitting an inferior antigenicity of fetal tissues, the authors suggest that enzymatically denaturalized collagen should be manufactured from heterologous fetal connective tissue, to be then further tested. The reaction of tissue to silicone and collagen is minimal. Silicone is preferred for dermal injections since in clinical experience it remains in the site of injection much longer. For subdermal injections, however, collagen is preferred. Based on experience with over 600 patients since 1958, the first author continues using liquid silicone. The lack of complications is probably a result of the fact that only small amounts (milliliters) of silicone were used in wrinkles or small depressions in the dermal layer and that from the beginning injection into the subcutaneous tissue was avoided. Since 1988 a new technique for the treatment of wrinkles and skin depressions with injections of dermal miniautografts has been used with satisfactory results.

Animals↗
PubMed1990

Morphological studies of cytotoxic lesions in reversible endotoxic shock.

Reversible endotoxic shock was induced in adult rats by intravenous injection of E. coli 0111:B4 lipopolysaccharide (LPS) and the progression of metabolic and morphological alterations was evaluated. Serum samples and biopsies from adrenal gland, liver and lung were studied at different times after LPS injection. Histological changes in these tissues were observed after endotoxin administration, coinciding with both the acute-phase and the recovery-phase of shock (24-72h after LPS injection). Signs of tissue regeneration can be correlated with the regression of some serum parameters to their normal values. All these results indicate that in this experimental model of endotoxic shock, a reversible status was established, which will allow further studies of the endotoxic pathophysiological mechanisms in vivo, avoiding the complexity of the non-reversible process.

Adrenal Glands↗
PubMedDate not supplied

[Sarcoma of the larynx].

The soft-tissue sarcomas are rarely encountered in the larynx. A case the undifferentiated soft-tissue sarcoma of the larynx is presented, analyzing, the clinical features, the diagnosis and incidence into the laryngeal carcinoma. The prognosis and therapeutic measures are also discussed.

Adolescent↗