Search PubMed⌕ Search

Biomedical subjects

M Silverman

Publications and source records attributed to M Silverman.

At least 487 records · Page 27Linked to original sources
PubMed1965

A unified kinetic hypothesis of carrier mediated transport: its applications.

A model analysis of the process of carrier mediated membrane transport is presented, wherein the carrier is present in two forms of differing affinity for substrate. The two forms of carrier undergo interconversion by asymmetric metabolic reactions on each side of the membrane. From this model system expressions are derived for the steady-state distribution ratio for substrate, for the unidirectional fluxes of substrate and hence for the initial velocity of uptake of substrate, and for the effect of preloading cells upon the initial velocity of uptake of labeled substrate. These expressions are applied to published data for glycine transport in Ehrlich ascites tumor cells to obtain numerical values for the parameters of a concentrative membrane carrier system. Concentrative uptake is shown to be consequent to the differing affinities of the two forms of carrier. When the affinities of the two forms are equal, equilibrative uptake occurs. The model analysis is applied to the phenomena of metabolic and competitive inhibition.

Animals↗
PubMedDate not supplied

Central retinal vein occlusion complicating systemic lupus erythematosus.

Retinal lesions occur in 25 to 30% of patients with systemic lupus erythematosus (SLE). Visual loss, however, is rare. A patient who developed central retinal vein occlusion and blindness during the course of active SLE is described. The pertinent literature is reviewed with attention to possible pathophysiologic mechanisms.

Adolescent↗
PubMedDate not supplied

A comparison of acute reversible pre- and postsinusoidal portal hypertension on salt and water retention in the dog.

To define the relationship between portal hypertension and renal excretion of salt and water, two acute animal models of portal hypertension were investigated. In both models, it was necessary for systemic and renal hemodynamics to remain unchanged during the creation of portal hypertension so as to eliminate the effects of change in these parameters on renal excretion. In eight dogs, portal hypertension was induced by controlled tightening of a ligature around the superior hepatic vein and changes in hemodynamics were prevented by controlled i.v. titration with canine plasma. Rises in portal pressure 9.3 +/- 2.6 to 15.6 +/- 2.3 cm H2O were associated with significant decreases in urine volume 1.57 +/- 0.53 to 0.66 +/- 0.21 ml per min (p less than 0.05) and urinary sodium excretion [340 +/- 82 to 145 +/- 75 mEq per min (p less than 0.05)]. In contrast, similar experiments in five dogs in which the portal vein was partially ligated with increases in portal pressure from 8.3 +/- 0.6 to 18.6 +/- 0.5 cm H2O resulted in no change in urinary volume or sodium excretion. Acute reversible portal hypertension induced by hepatic vein constriction is associated with acute reversible retention of water and salt in the absence of changes in renal blood flow and creatinine clearance which only occur when the liver is involved and not with portal vein constriction.

Acute Disease↗
PubMedDate not supplied

The numerical analysis of pressure-flow curves in infancy.

Lung resistance (RL) and airway resistance (Raw) were measured in 33 healthy and sick infants. Using strict criteria for quality control, calibrated pressure-flow (P-V) curves were produced with the aid of a computer so that resistance could be analyzed at several points over the breathing cycle. In a subgroup of 11 infants from whom simultaneous measurements were obtained, values of RL and Raw were comparable, suggesting that the tissue component may make only a minimal contribution to lung resistance in infants. For both RL and Raw, the P-V relationship remained linear up to 50% maximum inspiratory flow in all infants. At other points of the respiratory cycle, there were marked changes in resistance, values calculated between points of mid-isovolume or peak pressure being significantly higher than those measured over the linear portion of inspiratory flow. While no single value can accurately reflect the changes in respiratory resistance that occur during the breathing cycle, the authors suggest that for purposes of comparison, RL or Raw should be measured as the slope of the inspiratory loop from the origin up to 50% of maximum inspiratory flow. From a calibrated tidal pressure flow curve values of resistance over other portions of the breathing cycle can easily be determined.

Airway Resistance↗
PubMedDate not supplied

Pressure-flow curves in infancy.

Calibrated pressure-flow (P-V) curves were plotted by computer using data from both the plethysmographic method for measuring airway resistance and the esophageal balloon technique for measuring lung resistance. P-V curves from 100 sick, healthy, and convalescent infants (age range 2 days to 19 months, weight range 0.9-10.4 kg) were classified into five distinctive types according to shape and direction of looping. Two of these patterns, one with a virtually closed, the other with a narrow figure-of-eight loop, reflected the normal physiologic changes in airway caliber that may occur during tidal breathing. The remaining three patterns, with far more marked changes in resistance, were associated with particular pathophysiologic mechanisms of airway obstruction. A wide figure-of-eight configuration, in which the expiratory loop rotated clockwise with marked flow limitation toward end expiration, was found for infants with chronic lung disease. By contrast, a rise in initial expiratory resistance due to dynamic glottic narrowing, with an anticlockwise rotated expiratory P-V loop, occurred in infants with reduced or unstable lung volumes. A clockwise inspiratory loop was observed only for infants intubated during the neonatal period, many of whom had clinical evidence of extrathoracic airway obstruction. Inspection and analysis of P-V curves provides more information about the state of the airways than does a single numerical expression of resistance. However, since normal patterns of P-V curves are not restricted to infants with healthy airways, a combined qualitative and quantitative approach to these measurements is recommended.

Airway Resistance↗
PubMedDate not supplied

Anatomical effects of sudden middle ear pressure changes.

Acute middle ear (ME) and inner ear changes following brief unilateral phasic ME pressure changes (up to +/- 6000/mm H2O) were studied in the guinea pig. Middle ear findings included perforation of the tympanic membrane, serous and serosanguinous exudate and hemorrhage of tympanic membrane and periosteal vessels. Changes were related to magnitude of applied pressure. Perforation and hemorrhage were more commonly seen with negative rather than positive pressure. Air bubbles behind the round window were seen with positive pressures. Occasional distortion, but never perforation of the round window, was noted. Hemorrhage of the scala tympani was observed with both positive and negative pressures; scala vestibuli hemorrhage was found with negative ME pressure. In some instances pressure direction and magnitude related changes were seen in the contralateral ear.

Animals↗
PubMedDate not supplied

Role of visual attention in cognitive control of oculomotor readiness in students with reading disabilities.

This study investigated eye movement and comprehension therapy in Grade 6 children with reading disabilities (RD). Both order of therapy and type of therapy were examined. Furthermore, the implications of visual attention in ameliorating reading disability are discussed. Thirty-one students with RD were identified using standardized reading comprehension tests. Eye movements were analyzed objectively using an infra-red recording device. Reading scores of participating children were 0.5 to 1 SD below the national mean. Testing took place before the start of therapy (T1) and was repeated after 12 weeks (T2) and 24 weeks (T3) of therapy. One group of students had eye movement therapy first, followed by comprehension therapy; in the other group, the order was reversed. Data were evaluated using a repeated measures MANOVA and post hoc tests. At T1, mean reading grade was 2 years below grade level, and eye movement scores were at about Grade 2 level. Mean growth in reading comprehension for the total sample was 2.6 years (p < .01) at T3; equally significant improvement was measured in eye movements (p < .01). Learning rate in reading comprehension improved from 60% (T1) to 400% (T3). Although within-group differences were statistically significant, between-group differences were not significant for comprehension or eye movements. Order of therapy (comprehension first or eye movements first) was not significant. Improvements in within-group scores for comprehension and eye movements were consistently significant at T2 and T3. Eye movement therapy improved eye movements and also resulted in significant gains in reading comprehension. Comprehension therapy likewise produced improvement both in eye movement efficiency and in reading comprehension. The results support the notion of a cognitive link among visual attention, oculomotor readiness, and reading comprehension.

Attention↗
PubMedDate not supplied

A randomized control trial of an Ultra-Short zidovudine regimen in the prevention of perinatal HIV transmission in rural Zimbabwe.

OBJECTIVE: To assess the practicality and effectiveness of an Ultra-Short zidovudine regimen for prevention of perinatal HIV transmission in rural Zimbabwe. DESIGN: Double-blinded placebo-controlled randomized clinical trial. SETTING: The Salvation Army Howard Hospital, a district hospital in rural Zimbabwe. SUBJECTS: 222 HIV positive pregnant women presenting for antenatal care prior to 36 weeks were randomized. Twenty nine women were lost to follow up. INTERVENTION: In the Thai regimen, mothers received zidovudine (300 mg po bid) from 36 weeks gestation until labour, and zidovudine (300 mg po q3h) during labour, and the neonates received a placebo. In the Ultra-Short regimen, the mothers received a placebo from 36 weeks to labour, then zidovudine (300 mg po q3h) in labour. The neonates received zidovudine (2 mg/kg po qid) for the first three days of life. MAIN OUTCOME MEASURE: Infant HIV RNA status at six weeks of life. RESULTS: Results were available for 90 infants from the Thai group and 89 infants from the Ultra-Short group. Infant HIV seroconversion rates at six weeks of life were 18.9% (95%CI 10.8 to 27.0) with the Thai regimen, and 15.7% [95% Confidence Interval (CI) 8.1 to 23.4] with the Ultra-Short regimen. The upper bound of seroconversion in the Ultra-Short group was lower than the 25% seroconversion boundary that was specified to show equivalence. CONCLUSIONS: Although the Ultra-Short regimen has equivalent efficacy to the Thai regimen, it also has many practical advantages. Ultra-Short is thus a preferable protocol.

Adult↗
PubMedDate not supplied

Partial expiratory flow-volume curves in infancy: technical aspects.

We have constructed a simple pressure-jacket with which to produce passive forced expiration in sleeping, supine infants by thoraco-abdominal compression. During expiration, flow and volume were measured at the airway opening with a face-mask and pneumotachograph. From partial expiratory flow-volume (PEFV) curves, peak expiratory flow rate (PEFR) and maximum expiratory flow at a lung volume equal to the functional residual capacity (VmaxFRC) were obtained. Using the jacket in groups of normal and wheezy infants, we have assessed the effects on PEFR and VmaxFRC of variable inflation pressure, rate and duration of jacket inflation, timing of chest compression in relation to the breathing cycle and subject interaction with the compression manoeuvre. The within-subject reproducibility of PEFR and VmaxFRC was measured. Consistent values were produced by inflating the jacket within 100 ms at end inspiration to a pressure of 3-4 kPa and maintaining the inflation (in wheezy infants) for at least 1 s. The median within-subject coefficients of variation of PEFR and VmaxFRC for both normal infants and wheezy infants were 9 and 12% respectively. The technique is clearly reproducible and can provide information about intrathoracic airway function in infancy.

Forced Expiratory Flow Rates↗
PubMedDate not supplied

The total compliance of the respiratory system during the first year of life.

Respiratory system compliance (Crs) was measured in 34 spontaneously breathing infants during the first year of life. An occlusion technique was used whereby several expiratory occlusions were performed at different lung volumes within the tidal range. The airway opening pressure generated during a plateau after occlusion was related to the volume included above the end-tidal level by a regression equation. The slope of this equation represented the compliance of the infant's respiratory system; the intercept was significantly different for preterm (-0.5 ml) and post-term (-5.5 ml) infants and may represent the difference between end-expiratory lung volume during tidal breathing and the relaxed functional residual capacity. The values for respiratory system compliance were similar to those previously reported for infants during muscle relaxation. As a function of body length, Crs = 1.58 X length3.13 X 10(-4) ml . kPa-1. The technique described is simple to apply and is independent of oesophageal pressure measurements.

Body Height↗