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Biomedical subjects

M A Chuman

Publications and source records attributed to M A Chuman.

7 recordsLinked to original sources
PubMed1987

Selective blockade of components of potassium activation in Myxicola axons.

The K+ conductance in Myxicola giant axons activates in two phases which are pharmacologically separable. The fast phase of K+ activation is specifically inhibited by 4-aminopyridine and by the substitution of D2O for H2O. We suggest Myxicola giant axons, like the amphibian node of Ranvier, may possess more than one variety of K+ channel.

4-Aminopyridine↗
PubMed1986

Color vision tests to identify elevated digoxin levels.

The purpose of this study was to determine the usefulness of color vision screening in identifying patients with elevated digoxin levels (greater than or equal to 2.0 ng/ml). Test-retest color vision measurements were obtained on 56 subjects with elevated digoxin levels and 93 non-digoxin subjects. Two tests, the Ishihara and Sahlgren's Saturation Test (SST), identified digoxin levels of 2.9 ng/ml or more. These tests also yielded a high percentage of improved retest scores among subjects with elevated digoxin levels (greater than or equal to 2.7 ng/ml) of more than 4-days duration and a low percentage of improved retest scores among the non-digoxin group. The Ishihara, SST, and other bedside color vision tests may prove useful in the routine monitoring of patients on digoxin therapy, especially those with a high risk for toxicity.

Adult↗
PubMed1986

Potassium channels in Myxicola giant axons.

This article describes an initial step in the study of potassium ion (K+) channel properties and their role in the control of patterns of action potential frequency. The purpose of the study was to determine the effect of the K+ channel blocker 4-aminopyridine on the conductance of the K+ channels in Myxicola. If this pharmacologic agent modifies one or more of the multiple kinetic components of the K+ channel conductance, it may be expected to alter the physiological properties of normal and pathological nerve fibers. Experiments were performed on 19 internally perfused voltage-clamped Myxicola infundibulum giant axons. After accounting for the time-dependent accumulation of K+ in the surrounding periaxonal spaces, the K+ conductance activates biphasically. The external application of 4-aminopyridine (20 mmol/L) specifically blocks the fast component of activation of the K+ conductance.

4-Aminopyridine↗
PubMed1985

Color vision deficiencies in two cases of digoxin toxicity.

Color vision deficiencies are a common sign of digoxin intoxication and color vision testing can be used to diagnose digoxin toxicity. We tested two patients, a 79-year-old man and a 61-year-old man, with digoxin toxicity by means of the Farnsworth-Munsell 100-hue test, AOH-R-R plates, and Ishihara plates. Initial testing disclosed both red-green and blue-yellow color vision deficiencies. These improved when digoxin levels diminished. The deficiencies were superimposed on preexisting acquired and congenital deficits. As serum digoxin levels decreased, the color vision deficiencies lessened on all three tests. The Farnsworth-Munsell 100-hue test gave the best quantifiable measure of color vision deficiencies, but proved difficult to use for routine bedside testing.

Aged↗
PubMed1985

Risk factors associated with ulnar nerve compression in bedridden patients.

This study was undertaken to determine the incidence of ulnar nerve compression in patients on bedrest and to determine which historical risk factors and assessment measures were most predictive of ulnar nerve compression. Thirty subjects were chosen from the orthopedic, neurological/neurosurgical, and rehabilitation units of two teaching hospitals. The incidence of ulnar nerve compression in this population was 23 percent (seven cases). The overall incidence of compression was then compared with the incidence of subjects having certain risk factors. A combination of two risk factors in subjects carried a greater relative risk of ulnar nerve compression than the presence of single risk factors alone. Using multiple regression analysis, the best multivariate model consisted of four variables which explained 72.8 percent of the variance in ulnar nerve compression. The findings suggest the use of an elbow flexion test and simple questioning as a method for screening patients at higher risk of ulnar nerve compression.

Adult↗