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Biomedical subjects

C Macdonald

Publications and source records attributed to C Macdonald.

27 records · Page 2Linked to original sources
PubMed1984

Evidence that von Willebrand factor is not required for the clotting of plasma in the presence of platelets and kaolin (Hardisty-Hutton test).

Antihemophilic factor (AHF) essentially free of von Willebrand factor (vWF) was used to determine whether vWF affected the coagulant activity of AHF in a kaolin-activated system using platelet-rich plasma. The AHF was prepared by sequential chromatography on solid-phase polyelectrolyte (PE E-5), and on Sepharose CL-4B in the presence of a high concentration of CaCl2. Residual traces of vWF antigen were removed by affinity chromatography with immobilized anti-vWF IgG. The essentially vWF-free AHF corrected the clotting defect of plasma from three patients with severe von Willebrand's disease (vWD) as measured by the kaolin-activated clotting time in the presence of normal or vWD platelets ( Hardisty - Hutton test). Addition of hemophilic plasma as a source of vWF did not cause additional improvement, nor did a potent antibody to vWF raised in rabbits inhibit the ability of AHF to shorten the clotting time of vWD plasma. Thus we found no evidence that vWF is necessary for AHF to function in the coagulation of recalcified kaolin-activated vWF-deficient platelet-rich plasma.

Blood Coagulation↗
PubMed1984

Comparing tiltmeters for crustal deformation measurement--a preliminary report.

A collection of high-precision tiltmeters is being operated at Pinon Flat Observatory, southern California, both to compare instruments and to measure tectonic deformation. We report on 1.2 years of data from four of these: two Michelson-Gale long fluid tiltmeters, one long center-pressure tiltmeter, and a shallow borehole tiltmeter. The three long-base instruments are all located on the same baseline, with a precise leveling line running between their end-monuments. At nontidal frequencies, only the two Michelson-Gale instruments show some coherence (gamma 2 = .3 for periods of 2 to 4 days), while the center-pressure instrument is correlated with air temperature at periods from a few days to a few weeks. The most stable tilt record shows a secular rate of 0.28 mu rad/a, which may be real. Over much longer times, leveling to specially stabilized bench-marks should confirm this. Comparing instruments has identified more and less successful measurement techniques; it appears that low-noise data will most probably be produced only by relatively complex and expensive instruments, though even for these, the operating costs over any reasonable lifetime will exceed the capital cost. Even the best existing sensors must be improved to measure continuous tectonic motions.

Disasters↗
PubMed1978

Are curves detected by 'curvature detectors'?

Five experiments which attempted to evaluate the relationship between orientation and curvature selectivity in human vision are described. In the first two experiments, threshold elevation for curved gratings was measured after exposure to similar gratings, with the use of either an adaptation (experiment 1) or a masking (experiment 2) paradigm. In both experiments threshold elevation occurred which was selective for both the degree and the direction of curvature of the adapting pattern. Experiment 3 compared the effects of adapting to tilted rectilinear or vertical curved gratings upon threshold for a vertical rectilinear grating. Threshold elevation declined systematically as the adapting gratings were either tilted or made more curved. Experiment 4 measured curvature selectivity as a function of the orientation of a curved adapting grating. Threshold elevation declined as the adapting grating was tilted more, but curvature selectivity remained. Experiment 5 measured the orientation tuning for curved gratings directly. Threshold elevation declined to 50% of its maximum value at an adpating orientation of about 28 degrees. This was constant for all values of curvature used. The resulsts are discussed with reference to the question of whether the human visual system contains 'curvature detectors' or linear-contour detectors which respond to the tangents of curves.

Adaptation, Physiological↗
PubMed1978

Lymphocyte transformation in extrinsic bronchial asthma.

Lymphocytes from sixteen patients with extrinsic bronchial asthma and sixteen normals were investigated for their in vitro reactivity to stimulation with phytohaemagglutinin (PHA) and concanavalin A (Con A). No significant differences in maximum lymphocyte responses to PHA or Con A, either in the presence of foetal calf serum or autologous plasma, were found. The significance of these results in relation to T suppressor cell control of IgE formation is discussed.

Adolescent↗
PubMed1977

Subtotal neonatal calvariectomy for severe craniosynostosis.

This report sets forth an example of a new mode of management of severe craniosynostosis in the neonate: subtotal calvariectomy. An infant with synostosis of sagittal, coronal, and lambdoidal sutures who had signs of increased intracranial pressure with impending neurologic complications was operated on at 13 days of age. Wide excision of the bony calvarium from the underlying dura was accomplished from the supraorbital ridge to near the foramen magnum; the entire area of the coronal sutures was included. Regeneration of the calvarium occurred over two to 12 weeks and was accompanied by the presence of "sutures" in a usual location. These procedures have allowed for normal brain growth without reoperation up to the current age of two years. Neurologic and intellectual performance has been satisfactory, and cosmetic results appear to be preferable to those obtained by more limited surgery. The observations suggest that this approach may permit better craniofacila growth by minimizing secondary deformities in growth of the cranial base.

Child, Preschool↗
PubMed1966

A double-blind comparison of two analgesics with placebo control.

The value of adding a sedative to commonly used analgesic agents to promote further the relief of pain was studied by a double-blind procedure in 90 post-surgical patients during 188 pain episodes. In moderate pain episodes, no statistically significant difference between the analgesic-sedative combination (Fiorinal-C(1/4)) and the analgesic (APC-C) was observed, although both compounds were superior to placebo (p <0.001). In severe pain episodes, the analgesic-sedative combination was superior to the analgesic alone; the analgesic, in turn, was superior to placebo (p <0.001).It is concluded that analgesia is more effective if associated apprehension is relieved by sedation.

Adolescent↗