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Biomedical subjects

H Gomes

Publications and source records attributed to H Gomes.

At least 19 recordsLinked to original sources
PubMed2005

Removal of organic contaminants from soils by an electrokinetic process: the case of atrazine. Experimental and modeling.

The atrazine behaviour in soils when submitted to an electric field was studied and the applicability of the electrokinetic process in atrazine soil remediation was evaluated. Two polluted soils were used, respectively with and without atrazine residues, being the last one spiked. Four electrokinetic experiments were carried out at a laboratory scale. Determination of atrazine residues were performed by enzyme-linked immunosorbent assay (ELISA). The results show that the electrokinetic process is able to remove efficiently atrazine in soil solution, mainly towards the anode compartment: Estimations show that 30-50% of its initial amount is removed from the soil within the first 24h. A one-dimensional model is developed for simulating the electrokinetic treatment of a saturated soil containing atrazine. The movement of atrazine is modelized taking into account the diffusion transport resulting from atrazine concentration gradients and the reversed electro-osmotic flow at acidic soil pH.

Atrazine↗
PubMed2005

Fetal hemangiopericytoma with an associated cerebral anomaly.

We report the first case of infantile hemangiopericytoma explored prenatally by fetal ultrasonography and magnetic resonance imaging (MRI). It was associated with a developmental cerebral anomaly identified on MRI. The largest lesions of the multifocal hemangiopericytoma were located in the soft tissue adjacent to the left temporal bone, and smaller lesions were found in the lumbar area and in the retroperitoneum. MRI showed no connection between the tumor and the fetal brain but there was anomalous cerebral gyration in the region and the Sylvian fissure beneath the tumor was enlarged. The pregnancy was terminated because of the severe brain anomalies and postmortem examination confirmed the prenatal findings. Microscopic analysis of the tumor tissue showed branching vessels which are typical of hemangiopericytoma. The lesions in our case occurred in association with macrosomia with visceromegaly detected at autopsy, suggesting a possible role of tumor suppressor genes.

Abnormalities, Multiple↗
PubMed2005

Acute ischemic hepatitis in aortocaval fistula.

OBJECTIVES: To characterise liver dysfunction in patients with aortocaval fistula. DESIGN: Retrospective study. MATERIALS: All four patients operated on for aortocaval fistula between 1999 and 2003. Three were males with ruptured abdominal aortic aneurysm (AAA). One was a female who underwent lumbar disk surgery. Four patients operated on for ruptured AAA were used as controls. METHODS: Measurement of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and creatinine from the preoperative period until full recovery. RESULTS: The median delay between the presumed formation of the fistula and surgery was 2 days (range 1-3 days). High levels of AST, ALT and LDH were observed in all patients, starting from the preoperative period, reaching the maximum on the first two postoperative days and normalising thereafter. Median peak values were: AST=4256 IU/l (range 816-7779), ALT=2487 IU/l (range 960-5645) and LDH=15165 IU/l (range 3122-32361). Serum creatinine also sustained alterations with a similar time course. Median peak values were: 256 micromol/l (range 230-468). All the patients survived. CONCLUSIONS: Acute ischemic hepatitis appears to be a consistent or, at least, a common complication of aortocaval fistula. Although a concern during the perioperative period, its course is benign and fully resolves upon successful surgery.

Acute Disease↗
PubMed2002

[Pitfalls of hematopoietic growth factors on MR images].

We report the effects of hematopoietic growth factors on MR signal intensity of bone marrow in 2 children undergoing chemotherapy for musculoskeletal malignancies. The two patients with initially fatty marrow had signal intensity changes: diffuse decreased signal of the distal femoral metaphysis and patchy areas in the diaphysis of both tibia and fibula, simulating metastases. These changes coincided with dramatic increase in neutrophil counts. Technetium 99 skeletal scintigraphy was normal. After a three year follow-up the patients are in good health.

Adolescent↗
PubMed2001

Spatiotemporal maturation of the central and lateral N1 components to tones.

This paper examines maturational changes in the spatiotemporal features of central and lateral N1 components of the auditory evoked potentials (AEPs) to tone stimuli presented with a long stimulus onset asyncrony (SOA; 4200 ms) using the scalp current density (SCD) technique. A group of typically developing children ranging from 6 to 12 years of age and a group of adults were studied. Recently studies have begun to explore the topography of these components in children. These studies, however, often used rapidly presented stimuli and did not elicit observable central N1s in the younger children. Our stimuli elicited both central and lateral N1s. Peak latencies of both components decreased with age. Peak amplitude also decreased with age for the lateral N1 but not for the central N1. Consequently, the difference between the lateral N1 and the central N1 amplitudes (or the ratio of lateral N1 amplitude to central N1 amplitude) also decreased with age, dramatically altering the morphology of the elicited AEP waveforms. Topography of the lateral N1 did not change with age. The location of maximal activation for the central N1 appeared to move more medially with age but this 'apparent' movement is probably due to the decreasing impact of the partially overlapping lateral N1 component whose amplitude is significantly smaller in adults than in children.

Acoustic Stimulation↗
PubMed2001

The detection of constancy amidst change in children: a dissociation of preattentive and intentional processing.

This study examined whether 7-9-year-old children preattentively build memories of constancy for individual stimulus features, and if these representations are affected by variability of other stimulus features. This was achieved by looking at the mismatch negativity (MMN) event-related potential to a duration deviant occurring in a stimulus environment in which one or two other features constantly changed. Performance data were also collected, to look at the correspondence between the effects of this manipulation on preattentive and intentional deviance detection. MMN data indicated that the children built a preattentive feature-based memory of constancy that was not affected by the number of varying features. In contrast, intentional deviance detection was considerably impaired by the introduction of feature variability. This dissociation is at variance with previous studies that usually report close association between MMN and behavior.

Acoustic Stimulation↗
PubMed2000

Effect of frequency separation and stimulus rate on the mismatch negativity: an examination of the issue of refractoriness in humans.

Refractoriness of the generators of the mismatch negativity (MMN) was examined in two experiments in which two deviant tones occurred in a row. In Experiment 1, the size of the MMN elicited by the first deviant was manipulated by using deviants that were close to or far from the standard in frequency. In Experiment 2, the time between two identical deviants was varied. It was found that neither the size of the MMN elicited by the first deviant, nor the time between two deviants, affected the amplitude of the MMN elicited by the second deviant. It was concluded that refractoriness played no role in the amplitude of the MMN for the parameters used.

Adult↗
PubMed2000

The development of auditory attention in children.

In this paper we review the development of four components of auditory attention: arousal, orienting, selective attention and sustained attention. We focus especially on the processes responsible for the selection of specific stimuli for further processing because these are essential for learning and development. Although much work still needs to be done, there is evidence of developmental change in some of the components of attention, especially early in infancy. Later developmental improvements seem to be primarily attributable to higher cognitive processes, such as motivation, strategy development and implementation, and voluntary direction and regulation of attention.

Arousal↗
PubMed2000

Sinus pericranii: advantages of MR imaging.

Sinus pericranii is a rare vascular anomaly involving an abnormal communication between the extracranial and intracranial circulations. A 3-year-old girl presented with a 2 x 2-cm, midline soft-tissue mass at the vertex. Plain skull films and CT using bone windows showed erosion of the parietal bones. MRI confirmed the clinical diagnosis by identifying communication of the vascular mass with the intracranial dural venous sinus. The advantages of MRI are discussed.

Child, Preschool↗
PubMed2000

Mismatch negativity in children and adults, and effects of an attended task.

Attention has been shown to modulate the amplitude of the mismatch negativity (MMN) elicited by a small deviation in auditory stimuli in adults. The present study examined the effects of attention and deviant size on MMN amplitude in children. Children and adults were presented with sequences of tones containing standards (1000 Hz) and three deviants varying in degree of deviance from the standard (1050, 1200, and 1500 Hz). Tones were presented in three conditions: (1) while participants ignored them; (2) while participants listened to them and responded to all three deviants; and (3) while participants again ignored them. We found that the MMNs elicited by the hard deviant (1050 Hz) were larger when the children were actively discriminating the stimuli than when they were ignoring them. However, the MMNs elicited by the easy and medium deviants (1500 and 1200 Hz, respectively) in the children and by all three deviants in the adults were not affected by attention.

Adult↗
PubMed1999

Electrophysiological evidence of developmental changes in the duration of auditory sensory memory.

In behavioral studies, children's memory for tonal frequency has been found to persist for less time than adults' (T. A. Keller & N. Cowan, 1994). The present study was done to evaluate the argument that this effect is due to changes in auditory sensory memory and not to attentional mechanisms. This question was investigated using mismatch negativity (MMN), an auditory event-related potential considered to be insensitive to attention. Participants were 6-7-, 8-10-, and 11-12-year-old children and adults. They were presented with trains of stimuli, beginning with either a standard (1000 Hz) or a deviant (1200 Hz) tone with trains separated by either 1 s or 8 s. All 4 groups exhibited MMNs after delays of 1 s, but only the adults and oldest children exhibited MMNs after 8 s, indicating that there are maturational changes in the duration of auditory sensory memory.

Acoustic Stimulation↗
PubMed1998

Feature conjunctions and auditory sensory memory.

This study sought to obtain additional evidence that transient auditory memory stores information about conjunctions of features on an automatic basis. The mismatch negativity of event-related potentials was employed because its operations are based on information that is stored in transient auditory memory. The mismatch negativity was found to be elicited by a tone that differed from standard tones in a combination of its perceived location and frequency. The result lends further support to the hypothesis that the system upon which the mismatch negativity relies processes stimuli in an holistic manner.

Acoustic Stimulation↗
PubMed1998

Neonatal hip: from anatomy to cost-effective sonography.

Therapeutic success in treating congenital dysplasia of the hip is associated with early diagnosis, but the specific neonatal anatomy makes screening difficult. The purpose of this study was to determine whether this specific neonatal anatomy is taken into account by current ultrasound (US) techniques. Anatomic studies were performed on 22 hips, US examinations on 7750 neonatal hips; 2370 untreated hips were reexamined at 1 month by US and at 3 months by X-ray. The transformation of the neonatal cartilaginous acetabulum into an osseous cavity is dependent on harmonious metaphyseal growth and a properly seated femoral head. Defects in the acetabular roof, together with displacement of the femoral head, cause an abnormal anatomical relationship which leads to further deformities. The described sonographic techniques give only partial information on these specific abnormalities. The sonographic monoplanar methods as used in Graf's technique, which relies largely on acetabular development, lead to difficulties in assessing posterior coverage of the femoral head and difficulties in assessing alignment of the metaphyseal weight-bearing surface with the femoral head. Combining Graf's morphological analysis with Novick's dynamic technique enables one to more accurately define the relationship of the femoral head and the acetabulum and increases the reliability and predictive value of the examination, while reducing the number of doubtful cases. This makes screening cost effective.

Cost-Benefit Analysis↗
PubMed1998

Reactivation of a dormant representation of an auditory stimulus feature.

Research with the mismatch negativity component of event-related potentials has uncovered a system that detects change in the acoustic environment on an automatic basis. The system is considered to compare incoming stimuli to representations of the past and to emit an MMN if change is detected. Previous investigations have shown that the relevant memory of the past can become dormant and then be reactivated by a reminder stimulus. It is unclear, however, whether what is reactivated is an holistic representation of stimuli or separate representations of features of stimuli. The present study provides data that supports the latter possibility but leaves open the former one.

Acoustic Stimulation↗
PubMed1998

[Kidney transplantation in patients with type I and type II diabetes mellitus].

A total of 618 patients with end-stage renal disease received kidney transplants between 1980 and September 1996. Twenty eight of them were diabetics. Better results were achieved for type 1 diabetic patients than for type 2 (mortality: 5.9% vs 27.3%; functioning graft: 88.2% vs 72.7%). The morbility was also higher in those patients (infections: 81.8% vs 29.4%; vascular complications: 45.5% vs 17.6%). Actuarial patient and graft survival were lower for type 2 than for non diabetic patients. For type 1 diabetics the results are similar to those for non diabetics. Better results can probably be achieved by restricting the selection criteria. The decision to transplant or maintain on dialysis should be made on a case by case basis.

Adult↗
PubMed1997

Anatomic study of the pre- and neonatal hip. Physiopathologic considerations on dysplasia and congenital dislocation of the hip.

Therapeutic success in dysplasia and congenital dislocation of the hip depends on an early diagnosis. The physiopathology remains very debatable and several concepts are propounded. For a better physiopathologic understanding, the authors have carried out a study of the morphology and development of 22 pre- and neonatal hips. At first, the acetabulum is cartilaginous and distorted by the moving femoral head; this acetabulum is histologically affected by the femoral pressure. The pathologic hip is characterized by defective posterior bony coverage of the femoral head by the acetabulum. The acetabulum ossifies during the 3 months following birth, forming a cup-like cavity under the pressure of the femoral head. Therefore, neonatal screening tests such as sonography must take place in the first weeks of life.

Acetabulum↗