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Biomedical subjects

I Vardi

Publications and source records attributed to I Vardi.

6 recordsLinked to original sources
PubMed1995

Calcium channel blocker decreases pentagastrin-stimulated alkaline-tide: a role for extracellular calcium in gastric acid secretion.

We previously showed that repeated stimulation of the gastrin receptor may lead to down-regulation. We hypothesized that entry of extracellular Ca2+ may replenish cytosolic Ca2+ and enable continuation of the acid-secretion process. Pentagastrin-stimulated alkaline-tide study was performed in seven duodenal ulcer patients on 2 separate days--with and without pretreatment with verapamil (Ca2+ channel blocker). The alkaline-tide test may substitute the conventional gastric acid collection as previously described. A significant rise in base excess after pentagastrin injection was found on the first day of the study, from 0.400 +/- 1.233 to 2.230 +/- 1.330 (mean +/- SD, P = 0.02). On the second day the rise was not statistically significant, from -0.200 +/- 0.838 to 0.440 +/- 1.200 (mean +/- SD, P = 0.27). In 6 of the 7 patients the alkaline-tide decreased from 45.29 +/- 21.75 mEq/45 min on the first day to 21.56 +/- 17.48 mEq/45 min on the second day of the study (mean +/- SD, P = 0.029), a decrease of 63.6 +/- 36.2%. Our findings may support a dual source for Ca2+, the second messenger in gastrin-dependent gastric acid secretion. The first increase of intracellular Ca2+ comes from cellular stores, and the second from extracellular source by Ca2+ channels, which can be blocked by verapamil.

Acid-Base Equilibrium↗
PubMed1990

A vector-sum process produces curved aiming paths under rotated visual-motor mappings.

Under a 90 degrees rotation of motor space relative to visual space, human two-dimensional aiming movements frequently take the form of smooth arcs such as spirals and semi-circles. A time-independent differential equation explains this tendency in terms of a rotation-induced vector field made up, at each point in the two-dimensional space, of two input vectors. One vector represents a visual error signal and the other represents a motor error signal. A trajectory's instantaneous direction of movement at each point can be described as the resultant of the two vectors. This mathematical formulation incorporates plausible visual-motor mechanisms and, when expressed in polar coordinates, leads to a new method for analyzing the spatial properties of movements (i.e., movement paths). Plots of the angle between the resultant and the target vector (phi) against distance from the target (r, in the polar representation) summarize the arc-shaped movement paths as a simple relation that can be analyzed statistically with respect to properties such as monotonicity. The polar representation is a plausible representation of visually-guided movements, with the visual error vector functioning as an objective function relative to which behavior is optimized. We extend the model and the r, phi movement path analysis to non-90 degrees rotations, and we find that the model predicts an observed qualitative shift in behavior for rotations greater than 90 degrees. It also predicts qualitatively different path shapes observed under visual-motor reflections.

Cybernetics↗
PubMed1979

Detrusor hyperreflexia in multiple sclerosis. Alleviation by a combination of imipramine and propantheline, a clinico-laboratory study.

16 patients with multiple sclerosis, complaining of urgency, frequency and urge incontinence were studied urologically. They all suffered from detrusor hyperreflexia. We managed to improve this disturbance by lowering the parasympathetic tone and at the same time increasing the sympathetic tone of the urinary outlet, using a combination of imipramine and propantheline. The subjective clinical alleviation was also corroborated by cystomanometry and urethral pressure profile before and after treatment.

Adult↗