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Biomedical subjects

C Johnson

Publications and source records attributed to C Johnson.

At least 397 records · Page 22Linked to original sources
PubMed1988

Orientation and specificity of fibrin protofibril binding to ADP-stimulated platelets.

We have investigated the molecular basis of platelet:fibrin binding by studying interactions between platelets and protofibrils, soluble two-stranded polymers of fibrin, which are intermediates on the fibrin assembly pathway. The specificity of these interactions was examined with transmission electron microscopy (TEM), which clearly showed thin fibers with lengths to 150 nm attached to the cell surface of normal, stimulated platelets. Immunogold electron microscopy using rabbit anti-human fibrinogen as the first stage antibody verified the identity of the surface-bound molecules, and the immunogold distribution paralleled that observed with the fibrin/fibrinogen molecules alone. Contacts between the ends of the fibers and the platelets were frequently observed, but lateral contacts were also evident. Given the diameter at the point of fibrin contact (18.2 +/- 1.3 nm), it is possible that several glycoprotein receptors were involved in binding each protofibril. Morphometric analyses demonstrated that normal platelets stimulated by ADP in the absence of exogenous fibrin(ogen) or in the presence of fibrin protofibrils and antibodies directed against the GPIIb/IIIa complex lacked this molecular layer on the surface. Neither protofibrils nor fibrin fibers adhered to the surface of Glanzmann's thrombasthenic platelets, as demonstrated by TEM and microfluorimetry. Synthetic peptides of sequence RGDS and HHLGGAKQAGDV effectively blocked the binding of protofibrils to the surface of normal, stimulated platelets while synthetic GHRP had no effect. These results provide direct evidence for multiple points of attachment between fibrin protofibrils and the glycoprotein IIb/IIIa complexes present in a functional conformation on the surface of normal, stimulated platelets.

Adenosine Diphosphate↗
PubMed1988

Contrast sensitivity after epikeratophakia.

Epikeratophakia is a rapidly evolving surgical procedure for the refractive correction of aphakia. Even when Snellen acuity after epikeratophakia is normal, patients often report a subjective degradation of the visual image through the surgically corrected eye. To further define visual performance in the patient with optically successful epikeratophakia, we examined contrast sensitivity in two patients surgically corrected for monocular aphakia. Contrast thresholds were measured over a range of spatial frequencies using both computer-generated sinusoidal gratings and a commercially available wall chart system. The eye with epikeratophakia in each case was compared with the opposite normal eye with comparable acuity. One patient was also tested prospectively in the same eye both before and after surgery. Data demonstrate a depression of the contrast sensitivity function in the middle and high spatial frequencies induced by the placement of an epikeratophakia lenticule when compared with the normal eye or contact lens-corrected, preoperative aphakic eye with comparable good acuity. These findings may explain the subjective experience of epikeratophakia patients.

Adult↗
PubMed1988

Sickle cell chronic lung disease: prior morbidity and the risk of pulmonary failure.

Sickle cell chronic lung disease (SCLD) is a prime contributor to mortality in young adult patients with sickle cell disease, especially those with sickle cell anemia (SS). Both perfusion and diffusion defects have been demonstrated, with generalized pulmonary fibrosis and disabling restrictive lung failure. We report 28 cases (25 SS, 1 S beta(0) thalassemia, 1 S beta(+) thalassemia and 1 SO-Arab) which began during the second decade of life and which ended in death by the fourth decade, after an ordered progression to pulmonary failure and cor pulmonale. Myocardial hypoxia with multifocal fibrosis and segmental infarction occurred in more than one-third of the cases and sudden death was a frequent final event. We define 4 stages of SCLD, based on pulmonary function tests, chest roentgenograms, blood gases, and noninvasive cardiac studies; each stage is 2 or 3 years in length, until death ensues in Stage 4. Case-control analysis showed that the significant risk factors associated with SCLD are 1) the total number of acute chest syndrome events in an individual before the onset of SCLD, (p = 0.0001), 2) sickle cell crisis marked by chest pain (p = 0.03) and 3) aseptic necrosis (p = 0.005). Temporal clustering of acute chest syndrome episodes frequently heralds the onset of SCLD. The pulmonary arterial bed, which has low oxygen tension and low pressure in a slow-flow system, is ideally suited to facilitate the polymerization of sickle hemoglobin, causing endothelial damage and culminating in an obstructive arteriolar vasculopathy. Identification of the significant risk factors predictive of SCLD can lead to early diagnosis of the disease; this is the only hope for effective intervention therapy.

Adolescent↗
PubMed1988

Vitamin-mineral supplement use: association with dietary intake and iron status of adults.

Although vitamin-mineral supplement use is increasing in the United States, few researchers have examined whether supplement users have better nutritional status than do nonusers. Data from 10,515 persons examined in the second National Health and Nutrition Examination Survey (NHANES II) were used to compare mean dietary intakes of several nutrients and food groups, hemoglobin, mean corpuscular volume, transferrin saturation, erythrocyte protoporphyrin, and serum ferritin between regular supplement users and nonusers aged 16 to 74 years. Prevalences of impaired iron status also were compared between user groups. Users consumed more vitamin C and ate fruits and vegetables more frequently than did nonusers in all age/sex groups. No significant differences in mean iron status indicators were observed except in the 65 to 74 year age/sex groups: transferrin saturation among men and mean corpuscular volume, erythrocyte protoporphyrin, and serum ferritin among women. In each case, users had higher values than nonusers in this age group. Prevalences of impaired iron status did not differ between users and nonusers in any age/sex group. In general, iron status was not associated with supplement use.

Adolescent↗
PubMed1987

Severe hypophosphatemia associated with diabetes mellitus in six dogs and one cat.

Severe hypophosphatemia was found in 6 diabetic dogs and in one diabetic cat. The cat suffered from hemolysis, and one dog had seizures, both apparently as a result of the severe hypophosphatemia. Clinical signs were not determined solely by the serum concentration of phosphorus, as seen in 5 other patients that did not have signs of disease despite similar serum phosphorus concentrations.

Animals↗
PubMed1987

Inhibition of lymphocyte proliferation by fluid-phase C3b as influenced by macrophages.

The effect of fluid-phase C3b on mitogen-induced lymphocyte proliferation in the presence and absence of macrophages was studied. In general, C3b inhibited the proliferation of lymphocytes when monocytes (macrophages) were present. The degree of inhibition by C3b was different for B and T lymphocytes and varied for different subpopulations of lymphocyte classes. In the absence of monocytes (macrophages), there was insignificant inhibition by C3b of lymphocyte proliferation, and thus the observed inhibition appeared to be due to the effect of C3b on the monocytes/macrophages present in the mixed lymphocyte preparations.

Cell Division↗
PubMed1987

Increased monomeric immunoglobulin A levels in tears from multiple sclerosis patients.

Mucosal immunity and the secretory antibody are known to be important defense mechanisms against many common viruses. Tears were selected as a representative mucosal fluid, and immunoglobulin A (IgA) was examined by enzyme-linked immunosorbent assay and immunoblot. Tears from 38 normal controls and patients with systemic or ocular diseases contained almost exclusively polymeric IgA. In contrast, almost 75% of 23 patients with multiple sclerosis had detectable monomeric IgA in addition to polymeric IgA. The functional importance of this alteration in the molecular form of secretory IgA remains to be determined.

Adolescent↗
PubMed1987

Unexpected reading precocity in a normal preschooler: implications for hyperlexia.

This is a case study of a left-handed, preschool boy of superior intelligence who read very early and at a level well beyond what his IQ would predict. He is developmentally normal with no signs of autism or related disorders. His reading age was 9.3 at age 2-11 and 11.2 at 4-2; these levels are considerably beyond what would be predicted by his IQ or language age. He was able to read nonwords and both regular and irregular words equally well, indicating his mechanisms of lexical access in reading are similar to those of normal readers. Unlike classical hyperlexics, his reading comprehension for both single words and sentences was well above age level. When his precocious reading first appeared, he was also advanced in reading-related linguistic skills, such as phoneme awareness, auditory verbal short-term memory, and word retrieval, but not in visuospatial skills. These results imply that neither pathological language and/or social development, nor pathological variation in the normal mechanisms of lexical access in reading are necessary causes for reading precocity in early childhood. A model for integrating subtypes of precocious readers with subtypes of normal and dyslexic readers is proposed.

Child, Gifted↗
PubMed1987

Rewarming in accidental hypothermia: radio wave versus inhalation therapy.

Anesthetized random-source dogs were cooled by refrigeration (3 C) to a stable core temperature of 25 C, and subsequently were rewarmed with warm, humidified inhalation (43 C, 450 mL of minute ventilation per kilogram) or radio frequency induction hyperthermia (4 to 6 watts/kg). The mean time required for core rewarming to 30 C was 231 +/- 3 minutes for warm, humidified ventilation and 106 +/- 32 minutes for radio wave therapy (P less than .01). These data suggest that radio wave heating is a more rapid noninvasive therapy for core rewarming of accidental hypothermia.

Animals↗
PubMed1987

Evaporation versus iced gastric lavage treatment of heatstroke: comparative efficacy in a canine model.

We compared the speed of cooling and treatment efficacy for evaporative cooling vs. iced gastric lavage in a canine heatstroke model. Nine random-source, mongrel dogs were anesthetized, shaved, and internally heated until the core temperature reached 43.0 degrees C. The animals were then randomly assigned to be cooled to 37 degrees C either by iced (1 degree C) tap water gastric lavage (n = 5200 ml/min) through a large (32-Fr) orogastric tube, or by spraying with tap water (n = 4, 15 degrees C, 12 L/min) before a large fan blowing room temperature air (23 degrees C) across the dog at 0.5 m/sec from a height of 50 cm. Temperatures were monitored by thermocouples in both tympanic membranes and the pulmonary artery. BP, pulse, and cardiac output were measured every 5 min. Evaporative cooling was twice as fast as iced gastric lavage (0.16 +/- .05 degree vs. 0.08 +/- .01 degree C/min X m2, p less than .01). Animals in the evaporatively cooled group also experienced a quicker and more complete return to baseline cardiac indices than the lavage-treated group. Moreover, all animals treated with evaporation survived and were neurologically intact 48 h later, while only one lavage-treated dog was neurologically intact over the same period. The others in the lavage group died one hour after cooling (n = 1), were grossly ataxic (n = 1), or were persistently comatose (n = 2). A simple evaporative cooling technique, readily available in the emergency department, appears to be the most rapid and effective means for cooling and treating heatstroke in the dog.

Animals↗
PubMed1987

Hydroa vacciniforme with inflammatory keratitis and secondary anterior uveitis.

A 6-year-old boy had numerous episodes of hydroa vacciniforme. Several of these episodes were accompanied by an anterior uveitis with corneal clouding and stellate keratic precipitates. Wearing sunglasses prevented new eye lesions from developing despite recurrences of skin lesions. Phototesting on facial skin revealed reproduction of skin lesions with ultraviolet B but not ultraviolet A. One should be aware of eye involvement in hydroa vacciniforme, and children who experience this form of photodermatitis should have a careful eye examination and be advised to wear protective sunglasses.

Child↗
PubMed1987

Early acquisition of cytomegalovirus infection.

Two hundred and fifty three infants were screened for cytomegalovirus (CMV) in the urine at birth and were followed up at regular intervals for one year. Twelve per cent (of 249) were excreting virus at 3 months, and 20% (of 234) at 12 months. In all cases infection was subclinical. The major factors determining risk of acquiring infection were the mother's serological state and whether the infant was breast fed. There was no association with social class, mother's age, or whether the child had been in a special care baby unit or a postnatal ward. By one year 33% (of 123) of infants of seropositive mothers had acquired CMV infection compared with 4% (of 123) born to seronegative mothers. Twenty per cent (17) of seropositive women who breast fed had virus isolated from their breast milk on at least one occasion, and 76% (13) of their infants became infected. In four mother-infant pairs comparison of CMV isolates from the mother's milk and the child's urine was made by restriction endonuclease digestion; in each pair infection had apparently occurred with the same strain of virus. All 13 infected infants followed up for three years were still shedding virus. Infection with CMV is common in infancy, and virus shedding persists for years. Congenital infection cannot be distinguished from acquired infection unless the presence of CMV in the urine is identified within three or four weeks after birth, even when clinical problems suggestive of congenital infection are present.

Actuarial Analysis↗