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Biomedical subjects

M Pavel

Publications and source records attributed to M Pavel.

At least 19 recordsLinked to original sources
PubMed2003

[Radio-frequency-ablation (RFA) with wet electrodes in the treatment of primary and secondary liver tumours].

INTRODUCTION: The majority of patients with primary and secondary tumours of the liver cannot be treated curatively by surgery. The treatment of these patients with radio-frequency thermoablation using perfused needle applicators (wet electrodes) was evaluated in a feasibility study. METHOD: Patients with primary and secondary tumours of the liver and contraindications against surgery or LTX were included into the feasibility study. RFA was performed percutaneously under ultrasound guidance. The patients were followed up sonographically and by computed tomography. RESULTS: 20 patients (9 male, 11 female) with 35 lesions were treated with RFA. 12 patients (22 tumour locations) suffered from HCC and 8 patients (13 tumour masses) had liver metastases (colorectal, breast, pancreas, carcinoid). The median age was 65.6 years (36 to 83 years). The median tumour size was 33.5 mm. 59 RFTA applications (1.7 applications per tumour mass) were performed. The mean duration of RFTA per patient was 16.2 minutes. During the procedure isotonic saline was injected at a mean flow rate of 6.63 ml/min. All patients received local anaesthesia. In 33 sessions an additional analgosedation was necessary (average dose 63.8 mg Pethidine and 1.4 mg Midazolam). In 2 cases a reduction of the haemoglobin level, occurred, necessitating a blood transfusion. 3/4 of the treated metastases could be eradicated completely. Within a median follow-up of 145 days no intrahepatic local recurrence but 4 distant metastases occurred. 2/3 of the treated HCC could initially be brought into complete remission (CR). After a median follow-up of 329 days 5 of the 8 initially successfully treated patients with HCC were still in complete remission. In 3 cases an intrahepatic local recurrence developed. CONCLUSION: RFA with wet electrodes is a safe, effective and inexpensive treatment for primary and secondary tumours of the liver, measuring less than 4 cm in diameter.

Adult↗
PubMed2002

Multiple endocrine neoplasia 2A syndrome: Surgical management.

BACKGROUND/PURPOSE: Currently, molecular genetic diagnostics allow familial types of medullary thyroid carcinoma to be detected at an asymptomatic stage and surgery thus to be performed at a time when prognosis is good. The current report aims to determine the appropriate age for safe prophylactic thyroidectomy in children with multiple endocrine neoplasia (MEN) 2A and mutations at codon 609 according to genotype-phenotype correlations and will discuss surgical procedures. METHODS: The authors describe the case of a family with hereditary MEN 2A syndrome. A DNA analysis of 7 family members confirmed the diagnosis by a mutation at codon 609 of the RET proto-oncogene. RESULTS: A phaeochromocytoma developed in 2 family members. Four had medullary thyroid carcinoma. A grandson underwent a prophylactic thyroidectomy at the age of 5 on account of genetic evidence. Despite the negative preoperative and intraoperative findings he already had an invasive medullary thyroid carcinoma. CONCLUSIONS: Few genotype-phenotype correlations have been established for MEN 2A disease. According to the natural history of the disease, families with the genotype RET cys609gly should have a more benign disease than high-risk families (mutations at codon 634, 618). From this report the authors conclude that prophylactic thyroidectomy in "609" families should be performed earlier than actually recommended, favorably at the age of 2 to 4 years. Further multicenter studies are needed to provide more clinical and prognostic data for less frequent (codon 609, 630, 791, and 891) RET genotypes.

Adult↗
PubMed2001

Eye movements during visual search: the costs of choosing the optimal path.

Saccadic eye movements are usually assumed to be directed to locations containing important or useful information, but such assumptions fail to take into account that planning saccades to such locations might be too costly in terms of effort or attention required. To investigate costs of saccadic planning, subjects searched for a target letter that was contained in either one of two clusters located on either side of a central fixation target. A target was present on each trial and was more likely (probability=0.8) to appear in one cluster than the other. Probabilities were disclosed by differences in cluster intensities. The distance between each cluster and central fixation varied (60'-300'). The presentation time was limited (500 ms) to ensure that a successful search would require a wisely chosen saccadic plan. The best chance of finding the target would be to direct the first saccade to the high-probability location, but only one of the six subjects tested followed this strategy consistently. The rest (to varying degrees) preferred to aim the first saccade to the closer location, often followed by an attempted search of the remaining location. Two-location searches were unsuccessful; performance at both locations was poor due to insufficient time. Preferences for such ineffective strategies were surprising. They suggest that saccadic plans were influenced by attempts to minimize the cognitive and attentional load attached to planning and to maximize the number of new foveal views that can be acquired in a limited period of time. These strategies, though disastrous in our task, may be crucial in natural scanning, when many cognitive operations are performed at once, and the risk attached to a few errant glances at unimportant places is small.

Attention↗
PubMed2000

The psychophysics of visual search.

Most theories of visual search emphasize issues of limited versus unlimited capacity and serial versus parallel processing. In the present article, we suggest a broader framework based on two principles, one empirical and one theoretical. The empirical principle is to focus on conditions at the intersection of visual search and the simple detection and discrimination paradigms of spatial vision. Such simple search conditions avoid artifacts and phenomena specific to more complex stimuli and tasks. The theoretical principle is to focus on the distinction between high and low threshold theory. While high threshold theory is largely discredited for simple detection and discrimination, it persists in the search literature. Furthermore, a low threshold theory such as signal detection theory can account for some of the phenomena attributed to limited capacity or serial processing. In the body of this article, we compare the predictions of high threshold theory and three versions of signal detection theory to the observed effects of manipulating set size, discriminability, number of targets, response bias, external noise, and distractor heterogeneity. For almost all cases, the results are inconsistent with high threshold theory and are consistent with all three versions of signal detection theory. In the Discussion, these simple theories are generalized to a larger domain that includes search asymmetry, multidimensional judgements including conjunction search, response time, search with multiple eye fixations and more general stimulus conditions. We conclude that low threshold theories can account for simple visual search without invoking mechanisms such as limited capacity or serial processing.

Discrimination, Psychological↗
PubMed1999

[Monosymptomatic hyperthyroidism and TSH-producing adenoma: successful therapy with octreotide].

HISTORY AND FINDINGS: Magnetic resonance imaging (MRI) of the central nervous system was performed on a 72-year-old woman who was hyperthyroid without suppression of the thyroid-stimulating hormone (TSH) and had complained of a recent onset of headaches. MRI demonstrated a space-occupying lesion, 1 cm in diameter, in the anterior pituitary. The clinical symptoms were marked by a long-standing monosymptomatic illness of rapidly changing mood swings with depressive and manic phases. INVESTIGATIONS: Endocrinological-biochemical tests showed hyperthyroidism (fT3 10.55 pmol/l and fT4 39 pmol/l) but no TSH suppression (TSH: 2.9 microU/ml). Octreotide scintigraphy documented an activity-rich area in the anterior pituitary and the upper anterior mediastinum. Mediastinal MRI revealed a 5 cm space-occupying mass lying on the right atrium. 131I scintigraphy identified the mass as a retrosternal goitre. TREATMENT AND COURSE: As an operation on the anterior pituitary would have carried a high risk for the patient who was in a poor general condition and she had refused to be operated, treatment with octreotide, a long-acting somatostatin analogue, was initiated. This achieved a euthyroid state with partly suppressed TSH, and the patient's emotional swings ceased. CONCLUSION: If hyperthyroidism coexists with non-suppressed TSH levels, a TSH-producing hypophyseal adenoma should be considered in the differential diagnosis despite its rarity. Octreotide administration is an effective and safe treatment and is the method of choice, especially when there are contraindications to surgical resection of the anterior pituitary.

Adenoma↗
PubMed1999

Syllable intelligibility for temporally filtered LPC cepstral trajectories.

The intelligibility of syllables whose cepstral trajectories were temporally filtered was measured. The speech signals were transformed to their LPC cepstral coefficients, and these coefficients were passed through different filters. These filtered trajectories were recombined with the residuals and the speech signal reconstructed. The intelligibility of the reconstructed speech segments was then measured in two perceptual experiments for Japanese syllables. The effect of various low-pass, high-pass, and bandpass filtering is reported, and the results summarized using a theoretical approach based on the independence of the contributions in different modulation bands. The overall results suggest that speech intelligibility is not severely impaired as long as the filtered spectral components have a rate of change between 1 and 16 Hz.

Adult↗
PubMed1997

[Adrenal gland incidentaloma is not a "time bomb"--arguments for follow-up control].

Adrenal masses are nowadays more and more diagnosed incidentally. In the vast majority of cases these "incidentalomas" are benign adrenocortical adenomas which do not compel operative therapy. In about 12% of patients an endocrine activity is detected. With Increasing tumor size the risk of malignancy increases. This article summarizes recommendations, only to allow patients with endocrine activity or an increased risk of malignancy to be selected for surgery. A small uncertainty will always remain, but may be minimized by an individually tailored follow-up.

Adrenal Gland Neoplasms↗
PubMed1994

[Calcitriol administration during pregnancy in a partial DiGeorge anomaly].

A 23-year-old pregnant woman was known since birth to have partial DiGeorge syndrome with idiopathic hypoparathyroidism and clinically suspected thymus hypoplasia. The hypocalcaemia had until recently been treated with 1000 IU vitamin D3 daily. During the 9th week of pregnancy the serum calcium level was 1.9 mmol/l, the phosphate one 1.58 mmol/l and parathormone 5.6 pg/ml. To ensure better control, calcitriol was given (1.25-[OH]2-vitamin D3, initially 1 microgram daily and then, from the 22nd week of pregnancy onward, 1.5 micrograms daily), as well as calcium gluconate and lactate (initially 300 mg daily, then 900 mg daily). The serum calcium level at that time was between 2.0 and 2.5 mmol/l. Because of toxaemia of pregnancy the patient was hospitalized and confined to bed during the 37th week, whereupon the serum calcium level rose from 2.2 to 2.7 mmol/l, but a decrease in calcitriol dosage resulted in a decrease to within normal limits within one day. A girl was delivered by section in the 39th week: she had normal serum calcium and phosphate levels and appeared healthy.

Adult↗
PubMed1992

Extrapolation of linear motion.

We investigated observers' ability to extrapolate a linear trajectory of a moving point, in order to determine how effectively the visual system can combine orientation and position information for moving stimuli. Observers saw a probe dot moving along a straight line toward a stationary target dot. The probe dot extinguished before reaching the target, and the observers' task was to judge whether an extrapolation of the trajectory of the probe would pass to the left or right of the target. Performance was measured as a function of probe velocity, length of the visible trajectory, and location of the target. The empirical results indicated that over a range of conditions, performance on this task is qualitatively similar to, but somewhat less accurate than, that on an analogous task with static stimuli. A four-component model is presented to account for the results. The model specifies an accurate extraction of probe motion parameters, extrapolation of the motion by an ideal observer, and limitations on the input to these processes in the form of visual field spatial inhomogeneity and temporal decay of position information.

Depth Perception↗
PubMed1991

Percepts of rigid motion within and across apertures.

Humans consistently err in their percepts of rotational motion viewed through an aperture. Such errors provide insight into the constraints observers use to interpret retinal images. In the 1st of 2 experiments, Ss consistently perceived the fixed center of rotation for an unmarked line viewed through an aperture as located on the line, regardless of its actual location. Accuracy greatly improved with visible line endings. This finding was extended to explain why a square appears nonrigid when it rotates behind a partial occluder. This illusion may result from observers misperceiving the center of rotation of the unmarked square sides. In this situation, Ss seemed unable to apply an object rigidity constraint across apertures. These findings support a conceptualization of the visual system in which consistent local information must be clearly present before prior knowledge can be used to interpret retinal stimulation.

Attention↗
PubMed1990

The visible persistence of stimuli in stroboscopic motion.

This paper reports an improved paradigm to measure visible persistence. The stimulus is a pair of lines stroboscopically displayed in successive positions moving in opposite directions. The subjects' judgement of simultaneous appearance of all the presented lines is used to estimate visible persistence. This paradigm permitted independent manipulation of spatial and temporal stimulus separations in linear motion. The resulting estimates of visible persistence increase with spatial separation up to 0.24 deg of visual angle and approaches a maximum value at larger spatial separations. The results are consistent with the existence of a hypothetical visual gain mechanism that operates over small retinal distances to effectively decrease persistence duration with decreasing spatial separation.

Afterimage↗
PubMed1987

Limits of visual communication: the effect of signal-to-noise ratio on the intelligibility of American Sign Language.

To determine the limits of human observers' ability to identify visually presented American Sign Language (ASL), the contrast s and the amount of additive noise n in dynamic ASL images were varied independently. Contrast was tested over a 4:1 range; the rms signal-to-noise ratios (s/n) investigated were s/n = 1/4, 1/2, 1, and infinity (which is used to designate the original, uncontaminated images). Fourteen deaf subjects were tested with an intelligibility test composed of 85 isolated ASL signs, each 2-3 sec in length. For these ASL signs (64 x 96 pixels, 30 frames/sec), subjects' performance asymptotes between s/n = 0.5 and 1.0; further increases in s/n do not improve intelligibility. Intelligibility was found to depend only on s/n and not on contrast. A formulation in terms of logistic functions was proposed to derive intelligibility of ASL signs from s/n, sign familiarity, and sign difficulty. Familiarity (ignorance) is represented by additive signal-correlated noise; it represents the likelihood of a subject's knowing a particular ASL sign, and it adds to s/n. Difficulty is represented by a multiplicative difficulty coefficient; it represents the perceptual vulnerability of an ASL sign to noise and it adds to log(s/n).

Adult↗
PubMed1984

The effect of expectations on slow oculomotor control--IV. Anticipatory smooth eye movements depend on prior target motions.

Prior work had shown that smooth eye movements depend both on the motion of the target on the retina and on the subject's expectations about future target motion (Kowler and Steinman, 1979a,b). Effects of expectation cannot be eliminated by making target motions unpredictable (Kowler and Steinman, 1981). The experiment reported here shows that effects of expectations on smooth eye movement depend in a lawful way on the history of prior target motions. Anticipatory smooth eye movements (involuntary drifts in the direction of future target motion) were measured while subjects fixated a stationary target that was expected to step in an unpredictable direction (right or left). Anticipatory smooth eye movement velocity depended on the sequence of steps in prior trials, e.g. velocity was faster to the right when the prior steps were to the right. The influence of prior steps diminished the further back into the past the step occurred. Sequential dependencies were also observed for the saccades used to track the target steps. Anticipatory smooth eye movement velocity was predicted by a two-state Markov model developed by Falmagne et al. (1975) for similar sequential dependencies observed in a manual reaction-time task (button-pressing). The model uses the prior sequence of target motions to predict the subject's expectation, and assumes that the expectation determines anticipatory smooth eye movement velocity. The fit of the model to the data was good which shows that taking expectations into account is both necessary and feasible. Taking expectations into account, quantitatively, allows accurate predictions about smooth eye movement velocity when target motions are unpredictable.

Eye Movements↗
PubMed1981

Invariant characteristics of partial masking: implications for mathematical models.

The loudness of a tone in a noisy background increases very rapidly above its threshold with increasing intensity of the tone. The particular curve describing loudness growth as measured by a loudness matching paradigm depends on the level of the background noise. We introduce the hypothesis that an increment in masking noise induces a shift of the loudness matching curve in a diagonal direction (the matching curve being plotted in conventional log--log coordinates). This shift invariance is shown here to hold empirically for individual subjects within a monaural loudness matching task, based on a 2IFC paradigm using 1000-Hz tones and a wide band Gaussian noise. Shift invariance places considerable restrictions on models feasible for such data. In conjunction with a very general class of models involving the notion of gain control, the shift invariance property determines all parametric forms possible for the loudness matching functions. The fit of such parametric expressions to the data reported here yields very satisfying results. The resulting model is also found to be consistent with relevant results in the literature.

Humans↗