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Biomedical subjects

D Richardson

Publications and source records attributed to D Richardson.

At least 145 records · Page 8Linked to original sources
PubMed1994

Auditory M100 component 1: relationship to Heschl's gyri.

This study was designed to localize the neuroanatomic generator of the 100 ms latency magnetic auditory evoked field (EF) component (M100) activated by an unattended tone pip. Magnetic EFs in response to 25 ms duration, 90 dB, 1 kHz tone pips were recorded from both hemispheres of nine normal adults, five males and four females, using a seven-channel second-order gradiometer. The source of the M100 was estimated, with confidence intervals, by a least squares based inverse solution algorithm. Magnetic resonance (MR) images of the brain were acquired with a 1.5 T system using a standard head coil. The superior temporal gyri (STG) were manually segmented from 1.7 mm thick coronal images, and the superior surfaces were then rendered from the 3-D volume data. Translation and rotation matrices were identified to locate the magnetoencephalography (MEG) determined sources within the reconstructed STGs. This population of 18 STGs in 9 individuals demonstrated two transverse gyri in 4 of 9 left hemispheres, and 5 of 9 right hemispheres. All 9 left hemisphere M100 sources were in or included Heschl's gyrus(i) in the confidence intervals. Seven of the 9 included Heschl's gyrus(i) on the right: the remaining two, both males, had sources slightly anterior to Heschl's gyrus(i). We conclude that all M100 source location estimates were compatible with an auditory koniocortex source in or adjacent to Heschl's gyri.

Adult↗
PubMed1994

A predictive model for fetal lung maturity employing gestational age and test results.

Most laboratory tests for fetal lung maturity (FLM) are optimized to exclude false-negative predictions of absence of respiratory distress syndrome (RDS), with a reciprocal low predictive value for maturity. The authors employed FLM Surfactant/Albumin Ratio (FLM S/A) test results to construct a predictive model for FLM that included the obstetric estimates of gestational age. The charts of 388 newborns were abstracted and reviewed. The clinical outcome was the gold standard of the multivariate logistic analysis. Both the obstetric estimates of gestational age and the test result were significant predictors of the clinical outcome (P values of < .0002 and .001, respectively). The prediction rule for RDS as a function of both of these variables allows for adjustment of the test cutoffs, so that there is a consistent probability of RDS at the cutoff FLM S/A result for different gestational ages. Fetal lung maturity probability reporting may facilitate clinical decision-making.

Albumins↗
PubMed1994

Prospective evaluation of extracranial carotid stenosis: MR angiography with maximum-intensity projections and multiplanar reformation compared with conventional angiography.

OBJECTIVE: The purpose of this prospective study was to compare MR angiography of the carotid artery from the aortic arch through the circle of Willis using maximum-intensity projection (MIP) and multiplanar reformation (MPR) images with intraarterial angiography in the depiction of extracranial carotid atherosclerosis. SUBJECTS AND METHODS: The carotid arteries in 20 patients were studied with MR and intraarterial angiography. MR angiography included two-dimensional (2D) time-of-flight (TOF) sequences from the aortic arch through the skull base and three-dimensional (3D) TOF sequences centered at the carotid bifurcation and multiple overlapping thin slab acquisition (MOTSA) from the skull base to above the circle of Willis. Targeted MIP images of the 2D and 3D TOF MR angiograms through each carotid bifurcation were obtained. Last, MPR images of the 3D TOF MR angiograms at the obliquity that showed the greatest stenosis were obtained. All studies were reviewed in a double-blinded fashion by two neuroradiologists. Caliper measurements of MR angiograms and intraarterial angiograms were made by using North American Symptomatic Carotid Endarterectomy Trial criteria. Global MIPs of the aortic arch and common carotid arteries from the 2D TOF MR angiograms and targeted MIPs of the intracranial carotid arteries from the MOTSA MR angiograms were compared with the intraarterial angiogram and graded as normal, mild, moderate, severely stenotic, or occluded. RESULTS: MPR of the 3D TOF MR angiograms was highly correlated with intraarterial angiograms for both observers 1 and 2 (0.94/p < .001, 0.96/p < .001 [Pearson correlation/p value]). No statistically significant difference between 3D TOF MPR and intraarterial angiography was seen with a paired t-test. With an alpha = 0.05 (5% probability of type 1 error), the power to detect a difference as small as +/- 5% stenosis between 3D TOF MPR and intraarterial angiogram was 80% for observer 1 and 90% for observer 2. Although both MIPs of the 2D and 3D TOF MR angiograms showed high Pearson correlation coefficients (0.83, 0.90) with intraarterial angiography, the paired t-test revealed a statistically significant difference in the estimation of carotid stenosis. Both observers thought the global MIPs of the 2D TOF MR angiogram allowed good to excellent visualization of the common carotid arteries. The aortic arch was seen in 70% of patients; most of the missed cases occurred early in our experience, when the 2D axial images were not placed sufficiently inferior to include the arch. No stenosis of the great vessel origins was seen in this study. All four stenoses of the intracranial internal carotid artery identified with intraarterial angiography were seen with the MOTSA MR angiogram but with a tendency to overestimate stenosis. Only one carotid siphon was thought to show severe stenosis on the MR angiogram. Intraarterial angiography showed a 50% stenosis. CONCLUSION: It is possible to image the entire carotid artery from the aortic arch through the circle of Willis with MR angiography in a clinically acceptable time. MPR of the 3D TOF MR angiogram reliably shows the percentage of carotid stenosis with no statistically significant difference compared with intraarterial angiography. The role of MR angiography in showing lesions in the circle of Willis or the aortic arch is promising, but the limited number of tandem lesions in this study makes it difficult to draw any conclusions.

Aged↗
PubMed1994

A comparison of HIV risk between women and men who inject drugs.

Although there is growing evidence of differences between women and men who inject drugs (IDUs) in terms of level of risk for HIV infection, very little research has been conducted specifically addressing the risk practices of women IDUs. This study formed part of a national study of HIV infection risks in IDUs and the purpose of the present analysis was an exploration of gender differences in HIV risk practices, focusing on the HIV risk practices of IDU women. 1,245 IDUs from the inner city area of Sydney took part in this study. Of these, 908 were men and 331 were women. Notable results were that female respondents were more likely to report sharing needles, they injected heroin more times in a typical using month and were more likely to have shared with someone they later found out was HIV seropositive. Female respondents also reported more sexual partners than men, were more likely to engage in prostitution, and were more likely to have sexual partners who were themselves IDUs. The results provide support for the proposition that women who inject drugs may be at greater risk of HIV infection through both their drug taking and their sexual practices. Further research is needed to explore the reasons underlying the risk practices of women who inject drugs and an understanding of these factors needs to be incorporated into HIV risk-reduction and drug harm-reduction policies and programs.

Adolescent↗
PubMed1994

African-American physicians' views on health reform: results of a survey.

Little is known about African-American physicians' health system experience or their opinions on health reform. In an attempt to obtain socioculturally relevant data quantifying these experiences and opinions, the National Medical Association administered a 38-question, 80-item survey instrument in August 1993. The questionnaire was completed by 236 physicians. The results indicate that African-American physicians feel health care is a right and that the health system needs fundamental change. Although there was no consensus on the type of health reform needed, approximately 35% cited availability and access to care to be the greatest problem facing the system with high costs of care (18.2%) ranking second. Unique findings in the survey indicated respondents felt that the needs and concerns of most African Americans will not be fairly addressed in the reform of the health-care system, that African-African physicians are not included in the formation of health-care policies, and that African-American physicians are facing high levels of professional and healthcare system racial discrimination. More than 99% of African-American physicians reported some degree of racial discrimination in the practice of medicine including peer review, obtaining practice privileges at hospitals, hospital staff promotions, Medicaid and Medicare reimbursements, malpractice suits, private insurance oversight and reimbursements, and referral practices of white colleagues. These findings have profound health policy, health financing, and health service delivery implications and should be included in debates and deliberations on health reform.

Adult↗
PubMed1993

Facial nerve reconstruction following ablative parotid surgery.

Sacrifice of the facial nerve during surgery for parotid malignancy is rarely necessary, but the sequelae of facial nerve paralysis necessitates some form of facial re-animation. The technique which achieves the best results is that of immediate nerve grafting. This paper records our experience with 14 cases of extra temporal reconstruction of the facial nerve, utilizing the cutaneous branch of the radial nerve as an autograft.

Adolescent↗
PubMed1993

Uric acid and didanosine compliance in AIDS clinical trials: an analysis of AIDS Clinical Trials Group protocols 116A and 116B/117.

An analysis is presented that promotes the use of uric acid levels as an indicator of patients didanosine (ddI) use. Logistic regression techniques were used on data from two test groups that best represent patients entered on ACTG protocols 116A and 116B/117. Two classification functions resulted that are based on serial uric acid measurements and were used to classify patients to one of two groups: those treated with zidovudine (ZDV) and those treated with ddI. These functions correctly classified well over 70% of the patients in each of these two studies. Implications of these results with respect to the assessment of ddI compliance and limitations in the use of these classification functions are discussed.

Adult↗
PubMed1993

Dudley and Griswold: the development of fracture treatment in Kentucky.

The surgical record of the great state of Kentucky is impressive and one to be admired. Two Kentucky physicians helped pave the way to the modern treatment of fractures. Doctors Benjamin Dudley and R. Arnold Griswold contributed unique ideas and opinions to the practice of orthopaedic surgery. Their techniques and practices were ahead of their times, and today we see a little of each in our everyday treatment of fractures.

Fracture Fixation↗
PubMed1992

Two mechanisms of iron uptake from transferrin by melanoma cells. The effect of desferrioxamine and ferric ammonium citrate.

The effects of ferric ammonium citrate (FAC) and desferrioxamine (DFO) on iron (Fe), and transferrin (Tf) uptake have been investigated using SK-MEL-28 human melanoma cells, which express the Tf homologue, melanotransferrin, in high concentrations. Previously we demonstrated two separate Fe uptake mechanisms from Tf, viz. a specific process mediated by the transferrin receptor (TfR) and a nonspecific process (Richardson, D. R., and Baker, E. (1990) Biochim. Biophys. Acta 1053, 1-12). Cells exposed to DFO demonstrated up-regulation of the TfR with a concurrent increase in the rate of Fe uptake. Desferrioxamine also stimulated the nonspecific process of Fe uptake, resulting in a further increase in accumulation of Fe over Tf after saturation of the specific TfR. Ferric ammonium citrate had two effects. First, it resulted in down-regulation of the TfR. Second, and paradoxically, it markedly stimulated the rate of Fe uptake from Tf by the nonspecific process without increasing the rate of nonspecific Tf uptake. These data conclusively demonstrate that two entirely different mechanisms of iron uptake from Tf exist in melanoma cells and that ferric ammonium citrate may be a useful experimental tool to further characterize the specific and nonspecific mechanisms of Fe uptake from Tf.

Biological Transport↗
PubMed1992

Evaluation of the iron chelation potential of hydrazones of pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde using the hepatocyte in culture.

A range of new analogues of the promising iron chelator pyridoxal isonicotinoyl hydrazone was prepared and assessed for activity in reducing hepatocyte iron, mechanism of action and potential in iron-chelation therapy. A total of 45 compounds were synthesized by condensation of aromatic aldehydes (pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde) with various acid hydrazides prepared by systematic substitutions on the benzene ring or by the replacement of the ring with an acetyl, pyridyl, furoyl or thiophene moiety. The effects of these compounds on 59Fe uptake and intracellular distribution in hepatocytes in culture and on 59Fe mobilization from prelabeled hepatocytes were assessed. Toxicity, lipophilicity and the ability to chelate plasma transferrin-bound 59Fe were also evaluated. Several compounds were much more active than pyridoxal isonicotinoyl hydrazone and may have clinical potential. These included pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone, pyridoxal m-fluorobenzoyl hydrazone and pyridoxal 2-pyridyl hydrazone. All were more effective at reducing iron uptake than mobilizing hepatocyte iron; they also may act primarily on the transit iron pool rather than on storage iron. Other compounds (e.g., salicylaldehyde p-t-butyl-benzoyl hydrazone) redistributed ferritin-59Fe to different intracellular sites but had little net effect on hepatocyte iron levels.

Animals↗
PubMed1992

In vivo MR evaluation of Gd-DTPA conjugated to dextran in normal rabbits.

A dextran-Gd-DTPA compound has been recently synthesized utilizing 70,800 Da molecular weight dextran. This polymeric contrast agent for magnetic resonance imaging has been found chemically to be very stable and to demonstrate in vitro improved relaxivities of 1.5 to 2.3 times that of monomeric Gd-DTPA at 100 MHz. This MR experiment examines the in vivo distribution and relaxivity of the 70,800 Da molecular weight dextran-Gd-DTPA compound in a rabbit model by measuring the change in signal-to-noise ratio of a variety of organs (renal cortex, renal medulla, liver, brain, and torcula herophile) compared to the preinjection state. Results demonstrate prolonged (beyond 60 min) enhancement of the renal cortex, renal medulla, liver and torcula, and no enhancement of brain parenchyma.

Animals↗
PubMed1992

Attenuation of the cutaneous vasoconstrictor response to cold in elderly men.

This study tested the hypothesis that the cutaneous vasoconstrictor response to cold is reduced in elderly individuals. We measured laser Doppler flux (LDF) in the fingertip and blood cell velocity (CBV), via videodensitometry, in individual capillaries of the finger nailfold both before and during submersion of the contralateral arm in a 15 degrees C water bath. Subjects were 10 young (M = 25 years) and 10 old (M = 71 years) male adults. During the first minute of cooling, both the young (Y) and old (O) groups experienced a significant (p < .004) decrease in LDF. Over the subsequent 4 minutes of cold stress, LDF remained significantly depressed in the Y group, whereas LDF returned to values not significantly different from pre-cooling control in the O subjects. During the cold stress, CBV significantly decreased in the Y (p < .03) subjects; however, the degree of change was much less than that of LDF (49% decrease in LDF versus 14% decrease for CBV). In contrast to the Y subjects, the O group showed no significant change in CBV during cooling (p > .28). These results indicate that indirect cooling elicits a reflex decrease in cutaneous bloodflow, which is more pronounced in the deep vessels than in the superficial capillaries, and that these effects are attenuated with advancing age.

Adult↗
PubMed1992

On the pharmacological and physiological role of glibenclamide-sensitive potassium channels in colonic smooth muscle.

Actions of activators of glibenclamide sensitive K+ channels on canine colonic circular muscle were investigated. Cromakalim as well as its (-) enantiomer lemakalim caused inhibition of spontaneous phasic contractile activity (EC50's 4.4 +/- 0.1 x 10(-7) M and 2.3 +/- 0.4 x 10(-7) M, respectively) and of carbachol induced activity (EC50's: 9.4 +/- 5.1 x 10(-7) M and 4.3 +/- 1.4 x 10(-7) M, respectively). Cromakalim and lemakalim effects were completely inhibited by glibenclamide. Additive effects between K+ channel activators and other drugs relaxing colonic muscle (the L-type calcium channel blocker D600 and forskolin) were seen. A physiological role for specific glibenclamide sensitive K+ channels, if existing, remains unresolved. The present study indicates that the non-adrenergic inhibitory nerves do not act through these channels, neither does stimulation of muscarinic or beta-adrenergic receptors.

Animals↗