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Biomedical subjects

A R Martin

Publications and source records attributed to A R Martin.

123 records · Page 7Linked to original sources
PubMed1967

An analysis of facilitation of transmitter release at the neuromuscular junction of the frog.

1. Experiments were done on Mg-blocked neuromuscular junctions of the frog to study in detail the magnitude and time course of facilitation of the end-plate potential (e.p.p.).2. When two shocks were applied to the motor nerve with an interval of 5 msec or less between them, the amplitude of the second e.p.p. was facilitated by approximately 100%. This facilitation decreased as the interval was lengthened.3. The facilitation could be separated into two components on the basis of the time course of its decay as the interval between the two shocks was increased. The first component decayed exponentially after the conditioning shock with a time constant of about 35 msec. The second became apparent 60-80 msec after the conditioning shock, rose to a maximum of approximately 15% at about 120 msec and decayed thereafter with a time constant of the order of 250 msec.4. The growth of e.p.p. amplitude during short trains of repetitive stimulation at frequencies up to 100/sec and its subsequent decay could be predicted by assuming that the magnitude and time course of both components of facilitation were the same for every shock in the train and that these individual facilitatory effects summed linearly.

Journal Article↗
PubMedDate not supplied

Low bone mineral density and risk of fracture in white female nursing home residents.

CONTEXT: Low bone mineral density (BMD) is a strong risk factor for fracture in community-dwelling white women, but the relationship in white female nursing home residents, for whom fracture rates are highest, is less clear. OBJECTIVE: To assess the relative contribution of low BMD to fracture risk in nursing home residents. DESIGN: Prospective cohort study with baseline data collected April 1995 to June 1997, with 18 months of follow-up. SETTING: Forty-seven randomly selected nursing homes in Maryland. PATIENTS: A total of 1427 white female nursing home residents aged 65 years or older. MAIN OUTCOME MEASURE: Documented osteoporotic fracture occurring during follow-up as a function of baseline BMD measurements higher vs lower than the median, and after controlling for demographic, functional, cognitive, psychosocial, and medical factors. RESULTS: A total of 223 osteoporotic fractures occurred among 180 women. Low BMD and transfer independence were significant independent risk factors for fracture in this nursing home sample (P<.001) and the 2 factors acted synergistically (P =.06) to further increase fracture risk. Compared with women whose BMD was higher than the median (0. 296 g/cm(2)), those whose BMD was lower than the median had an unadjusted hazard ratio for risk of fracture of 2.1 (95% confidence interval [CI], 1.5-2.8); women who were independent in transfer had a hazard ratio of 1.6 (95% CI, 1.2-2.2) compared with women dependent in transfer. Among residents independent in transfer, those with BMD below the median had a more than 3-fold increase in fracture risk compared with those with higher BMD (unadjusted hazard ratio, 3.1; 95% CI, 2.2-4.4). Among residents dependent in transfer, those with BMD below the median had a 60% increase in fracture risk (unadjusted hazard ratio, 1.6; 95% CI, 1.1-2.3). Adjustment for covariates did not alter the BMD-fracture relationship. CONCLUSIONS: Our data indicate that low BMD and independence in transfer are significant predictors of osteoporotic fracture in white female nursing home residents. JAMA. 2000;284:972-977

Aged↗
PubMedDate not supplied

Stress in residency: a challenge to personal growth.

Postgraduate residency training requires young physicians to make the difficult transition from student to doctor. Recent evidence suggests that this period is associated with significant depression, anger, cynicism and emotional withdrawal, and there are concerns about its effect on the attitudes and future functioning of physicians. The perceived stresses are not unique to physicians and represent, in part, a need for personal growth that is common in the human service professions. Training programs can be more helpful to residents as they move through this transition. More attention must be paid to needs for sleep and time away from the hospital. Residents require more support and guidance in the personal aspects of becoming a physician, and programs can do much better at helping residents develop the communication skills needed to be an effective physician. The benefit of these efforts may be the development of physicians less likely to become impaired and more likely to give competent humane care to their patients.

Attitude of Health Personnel↗
PubMedDate not supplied

gamma-Aminobutyric acid and glycine activate Cl- channels having different characteristics in CNS neurones.

We have studied the properties of Cl- channels in Müller cells of the lamprey brain, which are activated by two putative neurotransmitters, glycine and gamma-aminobutyric acid (GABA). Previous studies have shown that in these cells the two ligands act through different receptors, and it was of interest to determine whether or not the two receptors, in turn, activate separate channels having different properties. We have shown previously that the channels activated by glycine have large conductances which decrease rapidly as the intracellular Cl- concentration [Cl-]i is increased above normal. We show here that GABA-activated channels have much smaller conductances which are independent of [Cl-]i over the experimental range and also that the response to a saturating application of glycine is not occluded by simultaneous GABA application. These observations indicate that the glycine and GABA receptors are coupled to separate Cl- channels having different characteristics.

Animals↗