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Biomedical subjects

R Iverson

Publications and source records attributed to R Iverson.

14 recordsLinked to original sources
PubMed2001

Observation of the Askaryan effect: coherent microwave Cherenkov emission from charge asymmetry in high-energy particle cascades.

We present the first direct experimental evidence for the charge excess in high-energy particle showers and corresponding radio emission predicted nearly 40 years ago by Askaryan. We directed picosecond pulses of GeV bremsstrahlung photons at the SLAC Final Focus Test Beam into a 3.5 ton silica sand target, producing electromagnetic showers several meters long. A series of antennas spanning 0.3 to 6 GHz detected strong, subnanosecond radio-frequency pulses produced by the showers. Measurements of the polarization, coherence, timing, field strength vs shower depth, and field strength vs frequency are completely consistent with predictions. These measurements thus provide strong support for experiments designed to detect high-energy cosmic rays such as neutrinos via coherent radio emission from their cascades.

Journal Article↗
PubMed1993

Rapidly progressive aphasic dementia and motor neuron disease.

Articulatory and language impairment heralded rapidly progressive motor neuron disease in 7 patients aged 54 to 77 years. One patient had a family history of a similar disorder. Severe nonfluent aphasia developed in all 7 patients and 4 were anarthric within a year. Other cognitive domains were impaired, yet 2 patients lived alone until 1 month before their deaths. Four died within 2 years. Abnormalities were found on electromyography, computed tomography, magnetic resonance imaging, single-photon emission computed tomography, and electroencephalography. Neuropathological examination in 3 patients showed bilateral hemispheric atrophy with neuronal loss and gliosis predominantly of superficial cortical layers. Pigmented and hypoglossal nuclei were relatively preserved. At all spinal levels there was degeneration of corticospinal tracts and loss of anterior horn cells with gliosis. Rapidly progressive aphasic dementia and motor neuron disease are a distinctive clinical entity whose nosology is poorly understood.

Aphasia↗
PubMed1991

Effects of alterations in pulmonary function and sleep variables on survival in patients with amyotrophic lateral sclerosis.

Breathing abnormalities and nocturnal hypoventilation occur in patients with amyotrophic lateral sclerosis (ALS). A prospective study was undertaken to determine the relationship of pulmonary function test abnormalities with quality of sleep and survival in 21 patients with ALS. Results of spirometry including determination of maximal respiratory pressures and arterial blood gases were compared with several formal polysomnographic variables and then also with 18-month survival. The patients had mild to moderate pulmonary function deficits, but the quality of sleep was best related to age (mean age, 58.5 years). The results of pulmonary function tests and arterial blood gas measurements did not correlate well with the presence of nocturnal breathing events or survival time, but the maximal inspiratory pressure was 86% sensitive for predicting the presence of a nocturnal oxygen saturation nadir of 80% or less and 100% sensitive for predicting 18-month survival. Although obstructive breathing events occurred, the primary explanation for the decline in nocturnal oxygen saturation was hypoventilation. We conclude that routine pulmonary function tests may be useful for screening for reductions in nocturnal oxygen saturation and also may have prognostic value. Further studies may determine whether treatment of nocturnal hypoventilation will have an effect on survival in patients with ALS who have breathing impairment.

Adult↗
PubMed1991

Late effects of paralytic poliomyelitis in Olmsted County, Minnesota.

We identified a cohort of 300 individuals who had paralytic polio between 1935 and 1955. All lived in Olmsted County, Minnesota. From the 247 survivors, we selected 50 subjects for detailed historical, functional, psychological, clinical, and electrophysiologic evaluation. Sixty-four percent of these 50 survivors complained of new symptoms of muscle pain, fatigue, and weakness after a period of prolonged stability. This led to changes in lifestyle or activity in only 18%. The likelihood of expressing new complaints was not related to present age or interval since polio, and electrophysiologic testing did not distinguish between those with or without new problems. The development of new difficulties in a limb was most strongly predicted by significant paralysis of that limb at the time of the acute illness. Patients with leg weakness were twice as likely to complain of new problems compared to those with arm weakness. Elevated creatine kinase levels were present only in those with new complaints.

Cohort Studies↗
PubMed1989

Effect of low frequency low energy pulsing electromagnetic field (PEMF) on X-ray-irradiated mice.

C3H/Km flora-defined mice were used to investigate the effect of exposure to pulsing electromagnetic field (PEMF) after total body x-ray irradiation. Prolonged exposure to PEMF had no effect on normal nonirradiated mice. When mice irradiated with different doses of x-ray (8.5 Gy, 6.8 Gy, and 6.3 Gy) were exposed to PEMF 24 h a day, we observed a more rapid decline in white blood cells (WBC) in the peripheral blood of mice exposed to PEMF at all the x-ray dosages used. No effect of exposure to PEMF was observed on the survival of the mice irradiated with 6.3 Gy and 8.5 Gy; in mice irradiated with 6.8 Gy, 2 out of 12 survived when exposed to PEMF as compared to 10 out of 12 control mice that were irradiated only. At day 4 after irradiation autoradiographic studies performed on bone marrow and spleen of 8.5-Gy-irradiated mice showed no difference between controls and mice exposed to PEMF, whereas on 6.8-Gy mice the bone marrow labeling index was lower in mice exposed to PEMF. In mice irradiated to 6.3 Gy we observed that the recovery of WBC in the peripheral blood was slowed in mice exposed to PEMF and their body weight was significantly lower than in control mice that were irradiated only. The spleen and bone marrow of the mice irradiated to 6.3 Gy and sacrificed at days 4, 14, 20, and 25 after irradiation were analyzed by autoradiography to evaluate the labeling index. Half of the spleens from mice sacrificed at day 25 after irradiation were used to evaluate the RNA content. Autoradiography showed that in the spleen and bone marrow of control mice, there were more cells labeled with [3H]thymidine at days 4 and 14 and less at days 20 and 25 after irradiation in comparison with mice irradiated and exposed to PEMF. The Northern blot analysis of histone H3 and p53 protein RNAs extracted from the spleens at day 25 after irradiation showed a slight increase in cycling cells among spleens of mice exposed to PEMF. We suggest that the exposure to PEMF immediately after x-ray irradiation results in increased damage.

Animals↗
PubMed1979

Estradiol 17 beta-dehydrogenase and estradiol binding in human mammary tumors.

The metabolism of estradiol was studied in 31 human breast carcinoma in vitro. All 16 estrogen-receptor-poor tumors transformed estradiol to estrone with percent conversions ranging from 11.4 to 95 except for one poorly differentiated tumor where 0.5% conversion to estrone was observed. On the contrary, only 3 out of 15 estrogen-receptor-rich tumors showed higher than 10% conversion of estradiol to estrone (p = 0.001). There is indication that the enzymatic activity in receptor-poor tumors steadily decreases in premenopausal patients as they approach menopausal age, whereas, the activity steadily increases in post-menopausal patients as the duration of menopause lengthens.

17-Hydroxysteroid Dehydrogenases↗
PubMed1979

Aromatization of androgens by human breast cancer.

The metabolism of dehydroepiandrosterone and testosterone by human mammary tumor was investigated. Estrogen synthesis from dehydroepiandrosterone was observed in 9 of 10 estrogen-receptor-negative tumors and only in 2 of 8 receptor-positive tumors (p less than 0.025). Conversion of testosterone to estrogens was observed in 7 of 8 receptor-negative and 2 of 7 receptor-positive tumors. Tumors which are capable of transforming dehydroepiandrosterone to estrogens were also able to aromatize testosterone suggesting that the presence of the aromatase enzyme is inherent to certain tumor cells. No estrogen formation was detected by the mitochondrial-microsomal fraction of normal breast cells while fractions from both fat cell and tumor cell showed estrogen synthesis. Estrogen formation by tumor cell fraction ranged from 5 to 190 times that observed for fat cells. The physiological significance of these results in the neoplastic tissue and its relationship to hormone dependence are discussed.

Adenocarcinoma↗
PubMed1979

Metabolism of pregnenolone by human breast cancer. Evidence for 17 alpha-hydroxylase and 17,20-lyase.

The metabolism of 7-(3)H-pregnenolone was studied in vitro using 16 human breast carcinomas. All mammary tumors transformed pregnenolone to progesterone. All estrogen receptor poor tumors and 4 out of 8 estrogen receptor rich tumors converted pregnenolone to 17-hydroxypregnenolone. Five estrogen receptor poor tumors showed the presence of 17,20-lyase as evidenced by formation of dehydroepiandrosterone and androstenedione. In two estrogen receptor poor tumors, conversions of pregnenolone to progesterone, 17-hydroxy pregnenolone, dehydroepiandrosterone, androstenedione and finally to estradiol was documented, providing a hypothetical pathway for steroid metabolism in human breast cancer. The conversion of pregnenolone to 17-hydroxypregnenolone was significantly less in receptor rich tumors and was totally absent in 4 receptor rich tumors with estrogen receptors of over 45 fmol/mg protein.

17-alpha-Hydroxypregnenolone↗
PubMedDate not supplied

Development and qualification of a novel virus removal filter for cell culture applications.

Commercial bioreactors employing mammalian cell cultures to express biological or pharmaceutical products can become contaminated with adventitious viruses. The high expense of such a contamination can be reduced by passing all gases and fluids feeding the bioreactor through virus inactivation or removal steps, which act as viral barriers around the bioreactor. A novel virus barrier filter has been developed for removing viruses from serum-free cell culture media. This filter removes the 20 nm minute virus of mice by >3 log reduction value (LRV), the 28 nm bacteriophage PhiX174 by >4.5 LRV, the mycoplasma Acholeplasma laidlawii by > or =8.8 LRV, and the bacteria Brevundimonas diminuta by > or =9.2 LRV. Robust removal occurs primarily by size exclusion as demonstrated over a wide range of feedstocks and operating conditions. The filtered media are indistinguishable from unfiltered media in growth of cells to high densities, maintenance of cell viability, and productivity in expressing protein product. Insulin and transferrin show high passage through the filter. The virus barrier filter can be autoclaved. The relatively high membrane permeability enables the use of a moderate filtration area.

Acholeplasma laidlawii↗