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Biomedical subjects

W L Smith

Publications and source records attributed to W L Smith.

At least 307 records · Page 17Linked to original sources
PubMed1983

Ultrasound screening of premature infants: longitudinal follow-up of intracranial hemorrhage.

Ninety-four infants weighing less than 2 kg were screened for intracranial abnormalities on the third and seventh days after birth using high-resolution real-time ultrasound. An overall abnormality rate of 37% was documented, with intracranial hemorrhage making up 83% of the abnormalities. Infants with abnormalities were then followed up for one to 12 months. Reversion to a normal ultrasound appearance was unlikely on follow-up in patients with lateral ventricular dilatation on the day-seven scan, whether or not dilatation was accompanied by intracranial hemorrhage. The ultrasound appearance became normal in 93% of the infants with intracranial hemorrhage but without dilated ventricles on their day-seven scan. The authors conclude that ultrasound is an efficient screening method for intracranial abnormalities in low birth weight infants.

Cerebral Hemorrhage↗
PubMed1983

Reduced platelet thromboxane formation in uremia. Evidence for a functional cyclooxygenase defect.

A qualitative platelet abnormality and a bleeding tendency are frequently associated with renal failure and uremia. We demonstrated previously that uremic patients display an abnormal platelet aggregation to arachidonic acid and reduced malondialdehyde production in response to thrombin and arachidonic acid. The objectives of this investigation were: (a) to compare platelet prostaglandin (PG) and thromboxane (TX) production in whole blood and in platelet-rich plasma (PRP) of 21 uremic patients and 22 healthy subjects; (b) to evaluate the concentration and activity of platelet PG- and TX-forming enzymes; (c) to assess the functional responsiveness of the platelet TXA(2)/PGH(2) receptor; (d) to explore the hemostatic consequences of partially reduced TXA(2) production.Platelet immunoreactive TXB(2) production during whole blood clotting was significantly reduced, by approximately 60%, in uremic patients as compared to age- and sex-matched controls. Exogenous thrombin (5-30 IU/ml) failed to restore normal TXB(2) production in uremic platelets. Uremic PRP produced comparable or slightly higher amounts of TXB(2) than normal PRP at arachidonate concentrations 0.25-1 mM. However, when exposed to substrate concentrations >2 mM, uremic PRP produced significantly less TXB(2) than normal PRP. To discriminate between reduced arachidonic acid oxygenation and altered endoperoxide metabolism, the time course of immunoreactive TXB(2) and PGE(2) production was measured during whole blood clotting. The synthesis and release of both cyclooxygenase-derived products was slower and significantly reduced, at all time intervals considered. Furthermore, PGI(2) production in whole blood, as reflected by serum immunoreactive 6-keto-PGF(1alpha) concentrations, was significantly reduced in uremic patients as compared with healthy subjects. PGH synthase levels, as determined by an immunoradiometric assay, were not significantly different in platelets from uremic patients as compared to control platelets. A single 40-mg dose of aspirin given to five healthy volunteers reduced their serum TXB(2) to levels found in uremic patients. This was associated with a significant increase of threshold aggregating concentrations of ADP and arachidonic acid and prolongation of bleeding time. Substantially similar threshold concentrations of U46619, a TXA(2) agonist, induced aggregation of normal and uremic platelets. Prostacyclin induced a significant elevation of uremic platelet cyclic AMP, which was suppressed by U46619, further suggesting normal responsiveness of the TXA(2)/PGH(2) receptor. WE CONCLUDE THAT: (a) an abnormality of platelet arachidonic acid metabolism exists in uremia, leading to a reduced TXA(2) production; (b) the characteristics of this abnormality are consistent with a functional cyclooxygenase defect; (c) reduced TXA(2) production may partially explain the previously described abnormality of platelet function in uremia.

Adult↗
PubMed1983

Concentrations of prostaglandin endoperoxide synthase and prostaglandin I2 synthase in the endothelium and smooth muscle of bovine aorta.

Platelets adhere to the subendothelial layer of newly deendothelialized arteries. Attachment can be reduced with exogenous prostacyclin (PGI2). Thus, the subendothelium may be unable to produce sufficient PGI2 to prevent platelet adherence and subsequent platelet-platelet interaction. Consistent with this explanation are data from an earlier report (1977. Moncada S., A. G. Herman, E. A. Higgs, and J. R. Vane. Thromb. Res. 11:323-344) indicating that the smooth muscle layer of aorta has only 10-15% of the capacity of endothelial cells to synthesize PGI2. We have measured the concentrations of PGI2 synthase and prostaglandin endoperoxide (PGH) synthase in bovine aorta and obtained results quite different from those described in this earlier report. Tandem immunoradiometric assays for PGI2 synthase and PGH synthase antigens were used to quantitate these proteins in detergent-solubilized homogenates of endothelial cells and smooth muscle tissue prepared from 10 different bovine aorta. The concentrations of PGI2 synthase in endothelial cells and smooth muscle were found to be the same. However, the concentration of PGH synthase in endothelial cells averaged greater than 20 times that of smooth muscle. Results similar to those determined by immunoradiometric assay were also obtained when PGH synthase and PGI2 synthase catalytic activities were measured in preparations of endothelial and smooth muscle cells. Furthermore, when bovine aorta and renal arteries were subjected to immunocytofluorescence staining using monoclonal antibodies to PGI2 synthase, fluorescence staining of equivalent intensity was detected in both the endothelial cells and the smooth muscle. Moreover, the intensity of fluorescence was similar throughout cross-sections of vascular smooth muscle, indicating that there is no gradient in PGI2 synthase concentrations between the endothelium and adventitia. Our results indicate that the propensity of platelets to adhere to the subendothelium of deendothelialized arteries and form aggregates cannot be attributed simply to an inability of the denuded vasculature to produce PGI2 from PGH2, but may be a consequence of the low PGH synthase activity of smooth muscle. Consistent with this concept are the results of Eldor et al. (1981. J. Clin. Invest. 67:735-741) who reported that increases in PGH synthase activity are associated with formation of a nonthrombogenic neointima.

Animals↗
PubMed1983

The visiting lectureship in radiology: an evaluation.

This study was designed to assess the effectiveness of didactic lectures in radiology by visiting faculty. Residents attending a lecture given by a visiting professor of radiology were subjected to a pre- and postlecture test on the contents of the lecture. Results indicated substantial gain in base knowledge of the subject material. Other studies indicate that increasing medical knowledge through lectures is of debatable effectiveness. This study indicates significant information transfer when short-term retention was tested. The level of retention was independent of the two sites of training and independent of level of training.

Analysis of Variance↗
PubMed1983

Interrupting visual feedback in writing.

To test the effects of interrupting visual feedback on writing, two groups of subjects--9 experienced and 9 inexperienced writers--were prevented from re-reading as they produced written texts. Their texts were then analyzed for error, syntax, over-all quality, and sentence connectedness. While both groups of writers were able to produce relatively well-formed sentences when they could not re-read, both were nonetheless hindered at the level of discourse production. Each group, however, reacted to that hinderance with different linguistic strategies.

Adult↗
PubMed1982

Respiratory distress following elective repeat cesarean section.

The clinical course and chest radiographs of 47 infants with respiratory distress after elective cesarean section were reviewed. The mean difference between the gestational age determined prenatally and that postnatally was 2.6 +/- 1.6 weeks. However, 14 of the infants were delivered at term. All 47 infants required more than 40% oxygen, and 18 infants required a respirator. Fifteen infants developed a pneumothorax; one, a pneumopericardium; one, bronchopulmonary dysplasia; and one infant died. Chest radiographs and the clinical course were consistent with hyaline membrane disease in 17 patients; respiratory distress syndrome type II in 24; and in three the radiographic findings were normal. These data suggest that some of the respiratory morbidity subsequent to elective repeat cesarean section is not secondary to iatrogenic delivery of a premature infant, and that much of it is not due to hyaline membrane disease. These data emphasize that respiratory distress in an infant delivered by elective cesarean section does not necessarily suggest poor prenatal care in regard to the timing of delivery.

Cesarean Section↗
PubMed1982

Adrenergic receptors in the nucleus tractus solitarii of the rat.

The nucleus tractus solitarii (NTS) is an area of the medulla in which baroreceptor afferent fibers mediating an inhibition of vasoconstriction terminate. The NTS also appears to be a site at which alpha-adrenergic receptors may be involved in blood pressure control. alpha- and beta-adrenergic agonists and antagonists were injected into the NTS via stainless steel cannulae and the effects on blood pressure determined. Norepinephrine (NE) and isoproterenol (ISO) caused dose-related decreases in mean arterial blood pressure (MABP). Phentolamine (PH) and propranolol (PR) caused dose-related increases in MABP. PH pretreatment in the NTS blocked the effects of ISO, but not NE. The effect of increased baroreceptor impulses to the NTS, produced by altering perfusion of the carotid sinus was blocked by propranolol. These results indicate the presence of beta- as well as alpha-receptors in the NTS, and also suggest the existence of presynaptic beta-receptors which facilitate neurotransmission.

Adrenergic beta-Antagonists↗
PubMed1982

Interrelationships among prostaglandins, vasopressin and cAMP in renal papillary collecting tubule cells in culture.

To determine the influence of prostaglandins on cAMP metabolism in renal papillary collecting tubule (RPCT) cells, intracellular cAMP levels were measured after incubating cells with prostaglandins (PGs) alone or in combination with arginine vasopressin (AVP). PGE1, PGE2 and PGI2, but not PGD2 or PGF2 alpha, increased intracellular cAMP concentrations. At maximal concentrations (10(-5) M) the effects of PGE2 plus PGI2 (or PGE1), but not of PGI2 plus PGE1, were additive suggesting that at least two different PG receptors may be present in RPCT cell populations. Bradykinin treatment of RPCT cells caused an accumulation of intracellular cAMP which was blocked by aspirin and was quantitatively similar to that observed with 10(-5) M PGE2. PGs, when tested at concentrations (e.g. 10(-9) M) which had no independent effect on intracellular cAMP levels, did not inhibit the AVP-induced accumulation of intracellular cAMP in RPCT cells. These results indicate that PGs do not block AVP-induced accumulation of intracellular cAMP in RPCT cells at concentrations of PGs which have been shown to inhibit the hydroosmotic effect of AVP on perfused collecting tubule segments. However, at higher concentrations of PGs (e.g. 10(-5) M), the effects of AVP plus PGE1, PGE2, PGI2 or bradykinin on intracellular cAMP levels were not additive. Thus, under certain conditions, there is an interaction between PGs and AVP at the level of cAMP metabolism in RPCT cells.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Normal sagittal diameter and variation in the pediatric cervical spine.

The sagittal diameter of the cervical spinal canal is traditionally evaluated when an expansile intraspinal lesion is suspected. Some workers have concluded that the normal sagittal diameter gradually decreases from C1 to C7 in some people, while in others it decreases from C1 to C3 and remains nearly constant from C4 to C7. The authors' study of 158 young individuals with no evidence of cervical cord lesions showed that gradual widening of the lower canal and even ballooning of the mid-canal are frequently seen in normal children 10 years old or younger, and occasionally in persons up to 18 years of age. The mechanism by which the canal attains a funnel-shaped appearance in adults is discussed.

Adolescent↗
PubMed1982

Femoral artery spasm in children: catheter size is the principal cause.

The incidence of femoral artery spasm and subsequent thrombosis complicating angiography is greater in children than adults. This study was designed to assess femoral artery spasm and to determine its causes in children. In 100 unselected, consecutive infants and children undergoing left heart angiocardiography by the Seldinger technique, angiography of the femoral artery was performed to include the puncture site after completion of angiocardiography. Arterial spasm was quantified and, with mathematical analysis, related to various clinical and angiographic factors. Some degree of arterial spasm was noted in 62% of all cases; it was more frequent and severe in neonates. Although it was more intense in the infant with a small femoral artery, analysis of the data indicates that patient age, weight, length of catheterization, size of femoral artery, and catheter size have only minimal relative importance in the occurrence and severity of arterial spasm. The most important factor in spasm is the relative size of catheter to artery.

Adolescent↗