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Biomedical subjects

R W Snyder

Publications and source records attributed to R W Snyder.

At least 55 records · Page 3Linked to original sources
PubMed1994

Acute cerebral blood flow response to dopamine-induced hypertension after subarachnoid hemorrhage.

The effects of dopamine-induced hypertension on local cerebral blood flow (CBF) were investigated in 13 patients suspected of suffering clinical vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The CBF was measured in multiple vascular territories using xenon-enhanced computerized tomography (CT) with and without dopamine-induced hypertension. A territorial local CBF of 25 ml/100 gm/min or less was used to define ischemia and was identified in nine of the 13 patients. Raising mean arterial blood pressure from 90 +/- 11 mm Hg to 111 +/- 13 mm Hg (p < 0.05) via dopamine administration increased territorial local CBF above the ischemic range in more than 90% of the uninfarcted territories identified on CT while decreasing local CBF in one-third of the nonischemic territories. Overall, the change in local CBF after dopamine-induced hypertension was correlated with resting local CBF at normotension and was unrelated to the change in blood pressure. Of the 13 patients initially suspected of suffering clinical vasospasm, only 54% had identifiable reversible ischemia. The authors conclude that dopamine-induced hypertension is associated with an increase in flow in patients with ischemia after SAH. However, flow changes associated with dopamine-induced hypertension may not be entirely dependent on changes in systemic blood pressure. The direct cerebrovascular effects of dopamine may have important, yet unpredictable, effects on CBF under clinical pathological conditions. Because there is a potential risk of dopamine-induced ischemia, treatment may be best guided by local CBF measurements.

Adult↗
PubMed1994

Localization of aquaporin CHIP in the human eye: implications in the pathogenesis of glaucoma and other disorders of ocular fluid balance.

PURPOSE: The existence of integral membrane proteins that serve as selective water channels has been postulated to explain the movement of water across plasma membranes. Aquaporin CHIP (channel-forming integral membrane protein of 28 kd) is the first such channel to be characterized and is abundant in human erythrocytes and a variety of secretory and absorptive epithelia of the rat. Because disturbances in the movement of water characterize several ocular diseases, the distribution of CHIP in the human eye was studied. METHODS: Affinity-purified antibodies against purified CHIP protein were used for the indirect immunofluorescence localization of CHIP in human eye structures. Labeling was confirmed by immunoblot analyses of membrane preparations from eye structures. RESULTS: CHIP immunolabeling was found in the corneal endothelium, the lens epithelium, the nonpigmented epithelium of the ciliary process, the iris epithelium, and the endothelium of the trabecular meshwork and the canal of Schlemm. CONCLUSIONS: The presence of CHIP water channels in the secretory and absorptive tissues of the human eye provides a mechanism for transcellular water movement and may be important for understanding diseases of the eye that involve excess or insufficient movement of ocular fluid such as glaucoma, cataracts, and Fuch's dystrophy. In addition, the existence of CHIP in the outflow pathways of the human eye provides a novel explanation for the movement of water out of the eye.

Adolescent↗
PubMed1994

Antibiotic therapy for ocular infection.

Infections of the eye can rapidly damage important functional structures and lead to permanent vision loss or blindness. Broad-spectrum antibiotics should be administered to the appropriate site of infection as soon as a diagnosis is made. Topical drops are preferred for corneal and conjunctival infections. Intravitreal antibiotics, and possibly subconjunctival and parenteral antibiotics, are preferred for endophthalmitis. Parenteral antibiotics are recommended for infection in deep adnexal structures. We review specific aspects of antibiotic therapy for ocular and periocular infection.

Anti-Bacterial Agents↗
PubMed1994

Resident phacoemulsification experience using the in situ nuclear fracture technique.

We retrospectively reviewed all of the 176 phacoemulsification procedures attempted by two third-year residents from July 1, 1991 to June 30, 1992. The in situ nuclear fracture technique was performed in 131 eyes; a nonfracture technique in 45. Overall, the rate of vitreous loss was 4.5% (8 of 176). The rate of vitreous loss associated with the in situ nuclear fracture technique was 3.1% (4 of 135); with the nonfracture technique, 8.9%. We conclude that phacoemulsification can be learned and performed by residents with vitreous loss rates comparable to those reported for extracapsular cataract extraction.

Cataract Extraction↗
PubMed1994

Transscleral repair of recalcitrant, inadvertent, postoperative cyclodialysis cleft.

We present a patient with a cyclodialysis cleft in whom, after established medical, laser, and initial surgical interventions had failed to close the cleft, we successfully used ab externo suture placement to appose and close it. Although we present only one case, we believe this procedure, which may be useful in pseudophakic and aphakic eyes, is easier to perform than previously described techniques.

Cataract Extraction↗
PubMed1993

Corticosteroid treatment and trabecular meshwork proteases in cell and organ culture supernatants.

Steroid-induced glaucoma is believed to result from increased aqueous outflow resistance and evidence suggests that this is the result of an excess accumulation of extracellular matrix components. This accumulation could result from an imbalance in the natural turnover of these components. We have investigated the effect of corticosteroid treatment of trabecular meshwork (TM) organ and cell cultures on the extracellular activities of the matrix metalloproteinases and plasminogen activators. We find that corticosteroid treatment results in decreased extracellular activity of stromelysin and tissue plasminogen activator in trabecular meshwork cell culture, and decreased 92 kDa collagenase IV, stromelysin, and tissue plasminogen activator in trabecular meshwork organ culture. These data suggest that decreased levels of proteolytic activities could account, in part, for the accumulation of some extracellular matrix components and be a contributing mechanism in steroid-induced glaucoma.

Cells, Cultured↗
PubMed1993

Fluorescein angiographic appearance of Dalen-Fuchs nodules in sympathetic ophthalmia.

A case of sympathetic ophthalmia is presented in which a single lesion located posteriorly at the level of the retinal pigment epithelium caused a serous macular detachment. We believe that this lesion represented an atypical Dalen-Fuchs nodule. Most reports of the fluorescein angiographic appearance of Dalen-Fuchs nodules describe multiple sites of choroidal leakage during the early phases, which may coalesce during the late phases of the angiogram. The lesion we detected was hypofluorescent in early phases of the fluorescein angiogram and showed late staining. The early hypofluorescence seen in the lesion may be explained by an intact retinal pigment epithelium over the presumed Dalen-Fuchs nodule, blockage of choroidal fluorescence by the nodule, and areas of granulomatous inflammation in the inner choroid and choriocapillaris. The staining in the late phases of the fluorescein angiogram may be explained by accumulation of fluorescein into the presumed Dalen-Fuchs nodule.

Adult↗
PubMed1992

Hemodynamic effects of intranasal cocaine in humans.

Intranasal cocaine, 2 to 3 mg/kg body weight, is a commonly used local anesthetic for rhinolaryngologic procedures, and many persons who abuse it ingest a similar amount. Previous studies in humans showed that this dose of cocaine causes coronary vasoconstriction, and studies in animals showed that larger amounts given intravenously diminish myocardial performance. This study assessed the hemodynamic effects of intranasal cocaine, 2 mg/kg, in humans. In 15 patients (8 men and 7 women, aged 30 to 70 years) referred for cardiac catheterization, heart rate, systemic arterial pressure, cardiac index, pulmonary capillary wedge and pulmonary artery pressures and left ventricular pressure and its first derivative (dP/dt) were measured before and 15, 30 and 45 min after intranasal administration of saline solution (n = 5) or cocaine, 2 mg/kg (n = 10). No variable changed with saline solution. In those given cocaine, there was an increase in heart rate (17 +/- 16%, mean +/- SD), mean systemic arterial pressure (8 +/- 7%), cardiac index (18 +/- 18%) and positive and negative dP/dt (18 +/- 20% and 15 +/- 22%, respectively) (p less than 0.05 for all). Thus, intranasal cocaine in a dose similar to that used medicinally or "recreationally" does not exert a deleterious influence on intracardiac pressures and left ventricular performance.

Administration, Intranasal↗
PubMed1992

Efficacy of laser punctal occlusion.

Dry eye is a common problem and in its more severe form may be treated with punctal occlusion. Photothermal coagulation of the puncta with the argon laser has recently been advocated to occlude the lacrimal puncta. Its long-term efficacy has not been investigated. The authors examined 22 puncta that had been occluded with the argon laser an average of 16 months before this study. Of the 22 puncta, 19 (86%) were patent. The results of our retrospective studies suggest that argon laser punctal occlusion is not an efficacious method for producing long-term punctal closure. The authors also used an animal model to investigate the effect on tissue of thermal cauterization and argon laser photothermal coagulation and found that thermal cauterization resulted in more widespread coagulative necrosis.

Adult↗
PubMed1992

Disruption of the cytoskeleton-extracellular matrix linkage promotes the accumulation of plasminogen activators in F9 derived parietal endoderm.

When F9 teratocarcinoma cells are treated with retinoic acid plus cyclic AMP (RACF9) they differentiate into parietal endoderm. Differentiation is accompanied by the acquisition of substrate adhesion sites and a change in the pattern of gene expression, including the synthesis of tissue-type plasminogen activator (tPA). We demonstrate here that dihydrocytochalasin B (DHCB) treatment of differentiating F9 cells prevents the assembly of a structured actin cytoskeleton and generates a more rounded and stellate cell morphology. This morphological change is accompanied by the accumulation of the usually visceral endoderm-specific marker urokinase-type plasminogen activator (uPA) and an increase in tPA levels in comparison to untreated RACF9 controls. The increase in tPA accumulation is preceded by an increase in tPA mRNA levels. These effects are reversible, with a lag, when DHCB is removed, and PA accumulation can be stimulated within 24 h when differentiated cells are exposed to DHCB. Exposure to the microtubule disrupting agent colchicine has no effect on uPA or tPA accumulation. In addition, antibody directed against the beta 1 integrin subunit can also specifically elicit increased PA production. Thus disturbing the cytoskeleton and cytoskeleton associated substrate adhesions promotes PA accumulation.

Actins↗
PubMed1992

Pulmonary toxicity following exposure to methylene chloride and its combustion product, phosgene.

Chemical paint removers containing methylene chloride are widely used in domestic and industrial settings where exposure to a heat source with conversion to phosgene is possible. We describe a case of noncardiogenic pulmonary edema and subsequent hyperreactive airways following such an exposure. In addition, the various problems that have been associated with exposure to methylene chloride and phosgene are reviewed.

Adult↗
PubMed1992

Treating dry eye.

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Dry Eye Syndromes↗
PubMed1991

Quantitation of scleral tobramycin levels.

We have devised a new method to solubilize sclera in order to permit quantitative determination of tobramycin by commercially available and widely utilized means. The sclera, containing tobramycin, was digested with Alcalase (Subtilisn A, NOVO Enzymes) and the tobramycin level was quantitated by TDX autoflourophotometry. This technique is accurate and sensitive. The tissue digestion and antibiotic assay are relatively simple to perform and should be applicable to a variety of antibiotics and possibly other therapeutic agents.

Animals↗
PubMed1991

Microbial keratitis associated with plano tinted contact lenses.

The use of plano contact lenses for cosmetic purposes is a recent phenomenon. We report five cases of severe microbial keratitis associated with the use of these lenses. This subpopulation of patients who possess no refractive error are at risk of developing severe complications from contact lens wear. We have identified several issues which should be addressed by eye care professionals and regulatory agencies.

Acanthamoeba Keratitis↗
PubMed1990

Skunk lung.

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Adult↗