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Biomedical subjects

H W Thompson

Publications and source records attributed to H W Thompson.

68 records · Page 4Linked to original sources
PubMed1989

Tobramycin iontophoresis into corneas infected with drug-resistant Pseudomonas aeruginosa.

Iontophoretic application of tobramycin was used to deliver drug to the cornea of rabbit eyes infected with a tobramycin-resistant strain of Pseudomonas aeruginosa (MIC = 31.25 micrograms/ml). Corneas infected with P. aeruginosa 27853/pMG6 were treated 22 hours after infection with tobramycin delivered by either iontophoresis, mock iontophoresis (eye cup without current), or application of fortified topical drops. Corneal iontophoresis of tobramycin at 25 mg/ml caused more than a three log reduction in bacteria; yielding a significantly lower number of bacteria compared to untreated controls and all other treatments (P less than or equal to 0.0001). Corneal iontophoresis of tobramycin at 10 mg/ml showed a one log reduction in the number of bacteria per cornea, yielding a significantly lower number of bacteria compared to untreated controls (P less than or equal to 0.0001), corneas treated with nine topical applications of 1.36% tobramycin drops (P less than or equal to 0.0001), and corneas treated with mock iontophoresis (P less than or equal to 0.02). These results suggest that iontophoresis is a powerful ocular delivery system for tobramycin and may be suitable for use with other chemotherapeutic agents.

Administration, Topical↗
PubMed1988

Accuracy and precision of the Tono-Pen in measuring intraocular pressure after keratoplasty and epikeratophakia and in scarred corneas.

Intraocular pressure measurements with the Goldmann and Schiotz tonometers are unreliable when the cornea is irregular due to disease or surgery. The Tono-Pen (Oculab, Glendale, Calif) is an electronic applanation tonometer based on the same principle as the MacKay-Marg tonometer. We measured intraocular pressure in 37 eyes with irregular corneas, in 50 eyes that had recently undergone penetrating keratoplasty, in 16 eyes that had undergone epikeratophakia, and in 12 eyes with normal corneas with both the MacKay-Marg and Tono-Pen tonometers. The same two instruments were used, and the sequence of measurement was randomized. Analysis of variance demonstrated no significant difference between measurements obtained with the two tonometers in any of the groups. The data suggest that the Tono-Pen is as accurate as the MacKay-Marg tonometer in those situations where the Goldmann tonometer is inaccurate.

Cicatrix↗
PubMed1988

Collagen shield drug delivery: therapeutic concentrations of tobramycin in the rabbit cornea and aqueous humor.

Collagen shields made of porcine collagen were placed in a solution containing tobramycin sulfate (40 or 200 mg/ml) for five minutes, then applied to rabbit eyes. One, four, or eight hours after application, the corneas, aqueous humor samples, and shields were assayed for antibiotic. At all intervals, the concentration of antibiotic in the corneas and aqueous humor samples exceeded the mean inhibitory concentration for tobramycin, as determined for most strains of Pseudomonas. Shields immersed in 200 mg/ml tobramycin produced significantly higher concentrations of antibiotic in the cornea at one hour than subconjunctival injections of tobramycin (20 mg) (P = .0001). Shields immersed in 40 mg/ml tobramycin produced higher, although not significantly higher, concentrations of antibiotic in the cornea at one hour than subconjunctival injections of tobramycin (20 mg) (P = .318). Shields immersed in commercially available tobramycin drops or injectable tobramycin solution (40 mg/ml) caused no epithelial damage visible by slitlamp examination. Collagen shields containing antibiotics can serve as a vehicle for drug delivery and may prove superior to current methods for preoperative and postoperative antibiotic prophylaxis and the initial treatment of bacterial keratitis.

Animals↗
PubMed1988

Neural activity from the acutely infected HSV-1 rabbit cornea.

Herpes simplex virus type 1 (HSV-1) infections of the human cornea are often accompanied by abnormal sensations. In this study, a combination of physiological and structural methods was used to examine the innervation of the corneas of rabbits with HSV-1 lesions of varying severity. Degeneration of the plexiform neural layer adjacent to dendritic lesions and surrounding normal neurology provided a basis for the limited physiological changes. Extensive degeneration of the corneal innervation at all levels occurred within the anesthetic area of the geographic lesion. Abnormal physiological activity characterized by hyperexcitability and loss of stimulus specificity were included in the physiological profile. Collateral sprouts seen in the geographic lesion were suggested as an anatomical substrate for the abnormal neural activity. Thus, the neural changes could be associated with the severity of HSV-1 lesions.

Action Potentials↗
PubMed1983

Thrombotic thrombocytopenic purpura. Potential benefit of splenectomy after plasma exchange.

Two patients with thrombotic thrombocytopenic purpura (TTP) were treated with a combination of antiplatelet drugs, corticosteroids, and plasma exchange. There was immediate clinical and laboratory improvement in both patients. However, the improvement did not persist following plasma exchange, even with infusions of fresh frozen plasma. Splenectomy was performed on both patients with subsequent sustained remission of the disease. Platelet counts returned to normal within eight days (case 1) and five days (case 2). Follow-up at eight months in one patient and at four months in the other disclosed normal laboratory values with no evidence of recurrent TTP. These cases suggest that in addition to other therapies, splenectomy may be beneficial in some patients.

Adult↗
PubMedDate not supplied

Use of blood components containing red cells by donors of allogeneic bone marrow.

Bone marrow transplantation is performed for an increasing number of disorders. Although much has been written about blood transfusion in bone marrow recipients, there is little information dealing with blood transfusion in bone marrow donors. We examined the records of 129 consecutive allogeneic bone marrow transplants to determine blood use by bone marrow donors. We attempted to correlate blood transfusion requirements with a number of variables in both donors and recipients of bone marrow. The volume of marrow harvested correlated closely with the number of units of blood transfused (r = 0.82). When these two variables were expressed as a percent of estimated blood volume, the correlation improved slightly (r = 0.85). Although the volume of marrow correlated highly with the total number of mononuclear cells harvested (r = 0.92), the correlation between total cells harvested and number of units of blood transfused was not as high (r = 0.75). By knowing the number of marrow cells the recipient requires for transplantation, the volume of donor marrow required and donor blood transfusion requirements can be estimated. In most instances, autologous blood could be used exclusively, thus eliminating the risks associated with homologous blood transfusion.

Adolescent↗
PubMedDate not supplied

Evaluation of a volumetric intravenous fluid infusion pump for transfusion of blood components containing red cells.

A method was devised to evaluate the suitability of an infusion pump for transfusing components containing red cells. With simulated transfusions of units of whole blood tested before or after the expiration date there was no increase in the plasma hemoglobin level in pumped blood compared with blood that was put through a standard blood transfusion set. With outdated units of red cells there was an increased level of plasma hemoglobin after pumping. The increases were greatest at maximum pump rates, but were not statistically or clinically significant. The authors' evaluation indicates that this pump causes minimal damage to the red cells, although care should be exercised when rapidly transfusing red cells with high hematocrit values.

Blood Transfusion↗
PubMedDate not supplied

Comparison of corneal epithelial wound healing after photorefractive and lamellar keratectomy.

BACKGROUND: The rate of corneal epithelial wound healing may be determined, in part, by the characteristics of the stromal surface. The excimer laser has the ability to produce a highly uniform ablated surface, which may facilitate reepithelialization after photorefractive keratectomy (PRK). METHODS: The rate of corneal epithelial wound healing after excimer laser PRK was compared with the rate of reepithelialization after manual lamellar keratectomy. Ten rabbits received a 4-mm diameter ablation in one eye (fluence = 160 mJ/cm2) and a shallow, 5-mm diameter, manual lamellar keratectomy in the contralateral eye. At 0, 4, 8, 12, 24, 36, 48, 60, and 72 hours after wounding, sodium fluorescein was instilled, and photographs were taken, converted to video images, and digitized. Wound area was calculated for each time point and converted to wound radius; the slopes of the wound radius, plotted over time, were compared to determine rates of healing. Scanning electron microscopy was performed immediately after wounding to examine surface regularity. RESULTS: By 24 hours after wounding, corneas that had undergone PRK demonstrated a significantly faster rate of epithelial wound healing compared with eyes that underwent lamellar keratectomy (33.4 +/- 1.9 microns/hr vs 27.8 +/- 1.4 microns/hr, respectively, for 12 to 72 hours) (p < 0.0001). Scanning electron microscopy showed greater stromal surface irregularity in the corneas that had undergone lamellar keratectomy, compared with the laser-ablated corneas. CONCLUSIONS: This study demonstrates that the rate of epithelial wound healing is significantly faster after excimer laser PRK than after lamellar keratectomy in the rabbit. Variations in surface regularity and wound edge profile may contribute to differences in wound healing.

Animals↗
PubMedDate not supplied

Diclofenac sodium attenuates neural activity after photorefractive keratectomy in rabbits.

BACKGROUND: Photorefractive keratectomy for treating myopia has been associated with severe postoperative pain. The purpose of the present study was to investigate, in a rabbit model, the early effects of laser ablation on the physiology of the sensory nerves of the cornea. METHODS: Neurophysiologic monitoring of the corneal nerves was carried out 4 to 6 hours after 5-mm diameter, circular PRK ablations with a central depth of 85 microns. The effect of topical 0.1%, 0.25%, and 0.5% diclofenac sodium on the physiologic response to chemical and mechanical stimulation was evaluated. Corneas were prepared for anatomic studies of corneal innervation. RESULTS: Heightened neural activity was observed in the corneal nerves after ablation, and exaggerated responses to sensory stimulation with hypertonic sodium chloride solutions were recorded. Diclofenac sodium at 0.1% decreased the response to 0.5 M NaCl and 0.7 M NaCl to 67 +/- 9% and 68 +/- 7% (mean +/- standard error) of the control response. Mechanically sensitive nerves were more resistant to diclofenac; 0.1% diclofenac had no effect, but 0.25% diclofenac reduced the response significantly (P < 0.05). Anatomic observations showed that the ablation extended through the neural plexus. By 72 hours, long neurites tipped with growth cones had advanced into the injured region, indicating the initiation of neural regeneration. CONCLUSIONS: Diclofenac sodium was effective in attenuating neural activity in the cornea after excimer laser ablation. The action of this agent was shown to be different from that of a topical anesthetic, which rapidly and totally inhibited the response to all forms of stimulation.

Animals↗