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Biomedical subjects

B Segal

Publications and source records attributed to B Segal.

At least 19 recordsLinked to original sources
PubMed1991

Conductivity response of porous electrodes supported on perfluorosulfonic acid membranes to acidic gas mixtures.

Gold or platinum films deposited on a Nafion membrane were used to measure surface conductance of the membrane. Acidic gases such as HCI or SO2, introduced as mixtures with an inert gas, were found to affect the conductance of the membrane surface facing this mixture while the other side of the membrane was constantly supplied with a moist inert gas. The relative conductance (G/Go) is most affected within the 0-0.5 and 3-4.5 vol % ranges both for HCI and SO2. The effect is higher for the Pt-deposited than it is for the gold-deposited membrane: for an HCI concentration of 1.5 vol %, G/Go is 5 for Pt deposited on Nafion while it is only 1.3 for gold deposited on Nafion. This is attributed to different geometries and porosity of the Pt and Au electrodes. No conductance response was observed for CO2 which yields with water a much weaker acid than those formed by HCI and SO2.

Electric Conductivity↗
PubMed1991

Adaptive plasticity in the gaze stabilizing synergy of slow and saccadic eye movements.

When a normal human subject is briefly turned in total darkness while trying to "look" at a spatially fixed target, the vestibulo-ocular reflex (VOR) produces slow-phase compensatory eye movements tending to hold the eyes on target. However, slow-phase compensation per se is generally inadequate in these circumstances. Nevertheless it has recently been found, that even in the dark, this inadequacy tends to be corrected by supplementary saccades usually acting in the compensatory direction. The present study further investigates this phenomenon by measuring the respective contributions of saccadic, slow-phase and overall net compensation in 9 subjects tested before and after 30% adaptive attenuation of VOR slow-phase gain. In each test series, subjects attempted to stabilize their gaze on a previously seen target during each of 40 brief (approximately 0.5 s) whole body rotations (40 degrees/s, 20 degrees amp) conducted in complete darkness. The adaptive experience comprised 2 h of full-field visual suppression of the VOR during sinusoidal rotation of subject and surround at 1/6 Hz and 40 degrees/s velocity amplitude. Before adaptation, the cumulative slow-phase and cumulative saccadic components produced on average 78% and 14% respectively of the ideal (100%) compensation, thus yielding an overall net compensation which was 92% of the desired value. After adaptation, the corresponding values in the same population were 53%, 18% and 71% respectively. Thus after adaptation, the combined saccadic-slow-phase response brought the final gaze position to a point in space that was systematically shifted in the direction of head rotation (i.e. undercompensation). Subjects re-exposed to 30 min of normal visual-vestibular interaction displayed a variety of recovery patterns using different combinations of slow and saccadic eye movements. However, there was a consistent "synergistic" tendency for saccadic eye movements to improve slow-phase performance, regardless of the subject's adaptive state. In one subject, compensatory saccadic eye movements corrected a consistent directional asymmetry in the slow-phase response. It is suggested that a conscious vestibular percept of self-rotation might underlie the combined saccadic-slow-phase response, and that the net under performance after adaptation might reflect attenuation of this percept relative to the actual rotational stimulus.

Acclimatization↗
PubMed1991

Adaptive modification of vestibularly perceived rotation.

Results from Bloomberg et al. (1991) led to the hypothesis that saccades which accompany the dark-tested vestibulo-ocular reflex (VOR) tend to move the eyes towards a vestibularly derived percept of an intended oculomotor goal: also that this is so even when that percept has been adaptively modified by suitably prolonged visual-vestibular conflict. The present experiments investigate these implications by comparing the combined VOR + saccade performance with a presumed "motor readout" of the normal and adaptively modified vestibular percept. The methods employed were similar to those of an earlier study Bloomberg et al. (1988) in which it was found that after cessation of a brief passive whole body rotation in the dark, a previously seen earth-fixed target can be accurately located by saccadic eye movements based on a vestibular memory of the preceding head rotation; the so-called "Vestibular Memory-Contingent Saccade" (VMCS) paradigm. The results showed that the vestibular perceptual response, as measured after rotation by means of the VMCS paradigm, was on average indistinguishable from the combined VOR + saccade response measured during rotation. Furthermore, this was so in both the normal and adapted states. We conclude that these findings substantiate the above hypothesis. The results incidentally reaffirm the adaptive modifiability of vestibular perception, emphasing the need for active maintenance of its proper calibration according to behavioural context.

Acclimatization↗
PubMed1991

Adolescent initiation into drug-taking behavior: comparisons over a 5-year interval.

Acquisition curves for six substances were compared for adolescents in two samples separated by a 5-year interval. Individual variations in initiation ages were found for different substances, but the general pattern of exposures to drugs was essentially stable over the time interval. The findings suggest that there appears to be a range of first experience with drugs that extends from 13 to 16 years. Special emphasis was given to the implications which the findings have for education and intervention programs, and for further research.

Adolescent↗
PubMed1991

Haptoglobin levels among alcoholics in Alaska.

The levels of haptoglobin, plasma proteins and amino acids were studied in a non-fasting population of alcoholics. In 25 subjects, only small differences were seen between the means when Native subjects were compared to non-Native. There did not appear to be any acute phase response differences between these two groups. This study did not substantiate other reports on the correlation of the severity of alcoholism with glycoprotein synthesis.

Alaska↗
PubMed1990

AIDS cardiomyopathy: first rule out other myocardial risk factors.

Consecutive autopsies of 59 male AIDS patients revealed that 21 had other myocardial risk factors: 17 were alcohol abusers and 6 had hypertension or coronary artery disease. AIDS patients with these myocardial risk factors were older (mean age 45 versus 35 years, P less than 0.01), and were more likely to have cardiomegaly (mean heart weight 397 grams versus 350 grams, P = 0.06) than patients with AIDS alone. When evaluating patients for AIDS cardiomyopathy, other myocardial risk factors must be considered.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Effects of methylphenidate on adolescents with aggressive conduct disorder and ADDH: a preliminary report.

The effect of methylphenidate on aggression in adolescents diagnosed with both aggressive conduct disorder and attention deficit disorder with hyperactivity was assessed in nine male adolescents. After three open trials, a placebo controlled double-blind design was used. During methylphenidate treatment of the six double-blind subjects, there was a significant reduction of aggressivity (p's less than 0.05), as measured by the Adolescent Antisocial Behavior Checklist. Conners Teacher Rating Scale Hyperactivity and Aggression scores were in the predicted directions, but the differences were not statistically significant.

Adolescent↗
PubMed1989

Tricuspid valve endocarditis.

TVE is mainly a disease of intravenous drug abusers. Although the infecting organisms are often highly virulent, they frequently respond to medical treatment. The prognosis for patients with TVE is fairly good. About 25% of TVE patients require surgical intervention. Persistent sepsis and intractable congestive heart failure are indications for surgery. Tricuspid valvulectomy without prosthetic replacement is the surgical intervention of choice. Right-sided heart failure is the principal complication after valvulectomy without a prosthesis. A significant percentage of patients require insertion of prosthetic valves at a future date.

Adult↗
PubMed1986

Age and first experience with psychoactive drugs.

By utilizing the Gutman Scaling technique and by plotting acquisition curves, a number of different patterns of involvement with different psychoactive drugs were discerned. A stable, sequential, and cumulative hierarchy of experience with drugs was found to be established at age 15, but different peak years exist for trying different drugs. It was also found that drug use may be cumulative for some drugs and not for others. Special emphasis has been given to discussing the research implications that have arisen from the present study.

Adolescent↗
PubMed1985

Symptomatic renal artery stenosis superimposed on chronic glomerulonephritis.

We present two patients with proved chronic glomerulonephritis who had severe refractory hypertension and chronic renal failure. In both patients normal-sized kidneys were demonstrated in addition to vascular bruits and Grade III hypertensive retinopathy. These findings raised the suspicion of an etiological condition other than chronic glomerulonephritis underlying the hypertension and renal failure. Renal angiography revealed bilateral severe renal artery stenosis. In both cases renal revascularization was followed by a drop in blood pressure to normal or near normal levels. In selected cases with severe hypertension and chronic renal failure, renal artery stenosis should be considered, despite the coexistence of chronic glomerulonephritis.

Antihypertensive Agents↗
PubMed1979

Chronic pyoderma in splenectomized patient.

This is a report of a case with a chronic peculiar intractable pyoderma. The process started a year after splenectomy because of trauma. In the absence of an apparent other reason, we assume that a relationship exists between the operation and the skin disease.

Adolescent↗