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Biomedical subjects

K A Allen

Publications and source records attributed to K A Allen.

33 records · Page 2Linked to original sources
PubMed1990

Topography of ganglion cells in human retina.

We quantified the spatial distribution of presumed ganglion cells and displaced amacrine cells in unstained whole mounts of six young normal human retinas whose photoreceptor distributions had previously been characterized. Cells with large somata compared to their nuclei were considered ganglion cells; cells with small somata relative to their nuclei were considered displaced amacrine cells. Within the central area, ganglion cell densities reach 32,000-38,000 cells/mm2 in a horizontally oriented elliptical ring 0.4-2.0 mm from the foveal center. In peripheral retina, densities in nasal retina exceed those at corresponding eccentricities in temporal retina by more than 300%; superior exceeds inferior by 60%. Displaced amacrine cells represented 3% of the total cells in central retina and nearly 80% in the far periphery. A twofold range in the total number of ganglion cells (0.7 to 1.5 million) was largely explained by a similar range in ganglion cell density in different eyes. Cone and ganglion cell number were not correlated, and the overall cone:ganglion cell ratio ranged from 2.9 to 7.5 in different eyes. Peripheral cones and ganglion cells have different topographies, thus suggesting meridianal differences in convergence onto individual ganglion cells. Low convergence of foveal cones onto individual ganglion cells is an important mechanism for preserving high resolution at later stages of neural processing. Our improved estimates for the density of central ganglion cells allowed us to ask whether there are enough ganglion cells for each cone at the foveal center to have a direct line to the brain. Our calculations indicate that 1) there are so many ganglion cells relative to cones that a ratio of only one ganglion cell per foveal cone would require fibers of Henle radiating toward rather than away from the foveal center; and 2) like the macaque, the human retina may have enough ganglion cells to transmit the information afforded by closely spaced foveal cones to both ON- and OFF-channels. Comparison of ganglion cell topography with the visual field representation in V1 reveals similarities consistent with the idea that cortical magnification is proportional to ganglion cell density throughout the visual field.

Adult↗
PubMed1981

The use of beta-thromboglobulin to detect platelet damage by therapeutic ultrasound in vivo.

Three sequential blood samples were drawn from arms of adult human volunteers by means of a cannula technique, and the plasma levels of beta-thromboglobulin (beta-TG an index of platelet damage) were measured. Ultrasound (0.75 MHz, continuous wave; spatially averaged intensity 0.34 to 0.5 W/cm-2) was applied to the blood vessels while the second sample of each series was being taken. No elevation of beta-TG was detected, indicating that under these conditions ultrasonic irradiation had not damaged an appreciable number of platelets. There was, however, an indication of decreased platelet sensitivity following insonation; and it is postulated that this may be the result of either increased production or secretion of the potent endothelial platelet inhibitor, prostacyclin, or both.

Adult↗
PubMed1978

Release of beta-thromboglobulin from human platelets by therapeutic intensities of ultrasound.

The effects of therapeutic intensities of ultrasound on human platelets in whole blood were investigated by monitoring the release of the platelet specific protein beta-thromboglobulin (beta-TG). More beta-TG was released as the intensity of the ultrasound was increased and also as the driving frequency was decreased from 3.0 to 0.75 MHz. Some beta-TG was released at spatially-averaged intensities as low as 0.6 W/cm2 at 0.75 MHz, a value significantly lower than that observed for the onset of aggregation of platelet rich plasma (obtained from the same volunteer) in the same exposure system. Liberation of beta-TG by ultrasound was diminished but not abolished in the presence of inhibitors which rendered the platelets functionally inert. Our data suggests that beta-TG is liberated in two ways, firstly as a result of platelet disruption by cavitation, and subsequently by potent aggregating agents, liberated in parallel with beta-TG, inducing the physiological release reaction in adjacent platelets. The low therapeutic intensities and short exposure times (30 s or less) necessary to liberate beta-TG from normal human platelets in vitro, suggests that patients with abnormally sensitive platelets and/or 'hypercoagulable state' could be at risk if subjected to high therapeutic intensities of ultrasound.

Beta-Globulins↗
PubMedDate not supplied

Social support lowers cardiovascular reactivity to an acute stressor.

This study examined whether social support can reduce cardiovascular reactivity to an acute stressor. College students gave a speech in one of three social conditions: alone, in the presence of a supportive confederate, or in the presence of a nonsupportive confederate. Systolic and diastolic blood pressure were measured at rest, before the speech, and during the speech. While anticipating and delivering their speech, supported and alone subjects exhibited significantly smaller increases in systolic and diastolic blood pressures than did nonsupported subjects. Supported subjects also exhibited significantly smaller increases in systolic blood pressure than did alone subjects before and during the speech. Men had higher stress-related increases in blood pressures than did women; but gender did not moderate the effects of social support on cardiovascular reactivity. These results provide experimental evidence of potential health benefits of social support during acute stressors.

Adaptation, Psychological↗
PubMedDate not supplied

Competency assessment and proficiency testing.

Competency assessment is an ongoing, continuous process of monitoring individuals' abilities to perform their specific job functions. A variety of methods are useful in monitoring cytology competency, including rescreening studies, descriptive monitors (abnormality rates), discrepancy rates, workload patterns, competency-based educational programs and programs using unknown slide challenges. The goal of proficiency testing (PT) is to ascertain and assess the ability of individuals beyond the particular items or challenges presented. However, cytology PT faces many challenges for implementation as it cannot duplicate normal working conditions, and there is often no gold standard to define the truth. PT is just one measure of performance and should be considered in conjunction with other quality assessment monitors. There is no consensus on the value or validity of a large-scale regulatory PT program. Any regulatory PT program should be field tested prior to implementation, and the grading system should be scientifically defensible. Scoring of performance on PT should occur in a timely fashion, and there should be an opportunity for educational feedback. The ultimate aim of both competency assessment and PT is to positively affect laboratory procedures and improve the cervical cancer screening process.

Cell Biology↗
PubMedDate not supplied

Bronchoalveolar lavage in liver transplant patients.

Because immunosuppression is required to control rejection, liver allograft recipients are susceptible to a variety of opportunistic pathogens. A total of 191 bronchoalveolar lavage (BAL) specimens from 89 patients (53 adults and 36 children) who underwent orthotopic liver transplantation was reviewed. One case each of cytomegalovirus (CMV), staphylococcal and Enterobacter pneumonia was diagnosed with the aid of pretransplant BAL. The pretransplant BAL in 62 patients showed rare yeasts in 24.2%; these probably represent oropharyngeal contaminants since the patients involved had no symptoms of Candida pneumonia. Among 54 patients who developed respiratory symptoms and underwent posttransplant BAL, 23 (42.6%) were infected with opportunistic pathogens, including Pneumocystis carinii (22.2%), CMV (22.2%) and herpes simplex virus (HSV) (7.4%). Frequently, infection with multiple organisms was present. Adults constituted 100% of the HSV-infected group, 69.2% of the CMV-infected group and 16.6% of the group infected with P carinii. The diagnosis of these infections was aided by a combination of cytology, microbial culture and in situ hybridization techniques. Although BAL permitted the diagnosis and treatment of opportunistic infections, high mortality (62.5%) occurred with CMV and HSV pneumonia. Further studies into methods that permit earlier diagnoses of these infections are necessary.

Adult↗
PubMedDate not supplied

Bronchoalveolar lavage in the diagnosis of disseminated lung tumors.

We report our experience with bronchoalveolar lavage (BAL) and its value in the diagnosis of malignant lung infiltrates. A total of 162 patients with biopsy- or autopsy-proven cancer had an analysis of BAL fluid performed. Cytologic examination showed malignant cells in 123 (76%) patients. The diagnostic accuracy varied depending on the neoplastic nature and growth pattern of the disease. BAL disclosed cancer cells in 93% of 44 bronchioloalveolar carcinomas. Carcinomatous lymphangitis due to metastatic cancer was diagnosed in 83% of 69 cases. Hematogenous metastases (with sharply circumscribed nodules on chest radiography) were diagnosed in 45% of 22 such cases. We recognized 67% of 15 non-Hodgkin's lymphomas and 3 of 9 cases of Hodgkin's disease with pulmonary involvement. Immunocytochemistry using monoclonal and/or polyclonal antibodies was of value in the identification and classification of cells in non-Hodgkin's lymphoma.

Adenocarcinoma, Bronchiolo-Alveolar↗