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Biomedical subjects

J T Brown

Publications and source records attributed to J T Brown.

At least 55 records · Page 3Linked to original sources
PubMed1987

Need for insulin therapy in type II diabetes mellitus. A randomized trial.

To identify patients with type II diabetes mellitus for whom insulin therapy is most beneficial, we conducted a randomized controlled trial in the general medicine clinic of a university hospital. Asymptomatic, obese, insulin-treated patients were given diet and diabetes education and, in half of these patients, insulin therapy was withdrawn. Over six months, patients developing hyperglycemic symptoms or acetonemia were counted as study failures. Failure criteria developed in 13 of 25 insulin-withdrawal patients, at a median of four weeks after withdrawal, compared with two of 24 control subjects. Elevated stimulated glucose levels predicted the need for insulin therapy. Hyperglycemia worsened in insulin-withdrawal patients who did not meet study failure criteria, but it improved in control patients. Study patients were insulin deficient as shown by low baseline C peptide values (0.43 +/- 0.05 nmol/L). The prompt metabolic decompensation precipitated by insulin withdrawal suggests that insulin-deficient patients may benefit from insulin therapy and may need it to prevent symptomatic hyperglycemia.

Adult↗
PubMed1986

Light dosimetry in brain tissue: an in vivo model applicable to photodynamic therapy.

The intensity of blue-green (488 nm) and red (633 nm) light as a function of increasing distance from an implanted laser fiberoptic source in the brains of anesthetized rats was measured. There was significant (90%) attenuation of the light intensity for both 488 nm and 633 nm at a distance of 2.5 mm from the intracerebral laser light-emitting source. At greater distances from the light-emitting source that corresponded to areas in the cerebral cortex, there was greater attenuation of light intensity for increasing distance with 488 nm than with 633 nm because of the increased vascularity of the cortical mantle and absorption of 488 nm by hemoglobin. When hematoporphyrin derivative was given intravascularly, there was increased attenuation of 633 nm through the cerebral cortex that was similar to that seen for 488 nm in normals. Direct assessment of light intensity in living tissue, which we have shown is possible in this report, will aid in our understanding and interpretation of the histological changes that occur following photodynamic therapy.

Animals↗
PubMed1986

Aneurysm formation after low power carbon dioxide laser-assisted vascular anastomosis.

A series of 125 adult rats was operated upon to perform end-to-end anastomosis of the femoral artery using either a carbon dioxide laser or conventional suture technique. Vessels were inspected at varying time intervals grossly and microscopically. Overall, the rate of aneurysm formation for the laser group was 18.6% (21/113). Late aneurysm formation (1 week or longer after operation) was seen in 29.8% (20/67) of the laser group. No aneurysms were noted in the suture group either early or late. Histological examination of the laser-joined vessels revealed widespread necrosis and loss of elastic elements in the media. In time, abnormal spindle-shaped cells appeared in this damaged layer. Histologically, the aneurysms were indistinguishable from those reported in human cerebral aneurysm cases. This technique provides an experimental aneurysm model and lends support to the acquired/degenerative theory of human cerebral aneurysm formation.

Aneurysm↗
PubMed1985

Thermal effects of the Nd:YAG and carbon dioxide lasers on the central nervous system.

The use of laser is becoming commonplace in neurological surgery because of the potential for surgical precision with minimal surrounding trauma, improved hemostasis, freedom from electrical interference of evoked potentials recordings, and a variety of other benefits. Despite this enthusiasm, there are little significant data regarding various laser-neural tissue interactions. Thermal transformation was studied using both carbon dioxide and Nd: YAG lasers on rat cerebral cortex. The Nd: YAG laser produced a significant quantity of heat which spread far beyond the boundaries of the histologically identified lesion. The thermal profile of the carbon dioxide laser on brain indicated minimal thermal spread change, even immediately adjacent to the physical edge of the lesion. Mechanisms and ramifications are discussed.

Animals↗
PubMed1985

Microvascular anastomosis using the milliwatt CO2 laser.

The milliwatt CO2 laser was used to anastomose small vessels in a rat femoral artery model. The technique requires multiple brief applications of 60-70 mW after placement of three equidistant 10-0 nylon stay sutures. The vessel histology is described immediately and 1, 3, 7, and 21 days after the procedure. The laser effects tissue bonding through changes in the collagen of the adventitia and media. Subsequent healing consists of new collagen deposition in the adventitia and reendothelialization of the intima associated with neointimal proliferation at 3 weeks.

Animals↗
PubMed1985

Fibrinolytic activity following laser-assisted vascular anastomosis.

New technology has allowed tissue bonding to be feasible using carbon dioxide laser energy. Laser-assisted vascular anastomosis (LAVA) has shown comparable patency results with standard suture anastomosis, but LAVA procedures produce thermally induced transmural structural alterations. To assess functional intimal recovery in LAVA versus sutured vessels, a fibrinolytic slide technique was utilized in 21 rats which had LAVA performed in one femoral artery while the opposite limb underwent a conventional microsuture anastomosis. Conventional anastomosis had persistent fibrinolytic activity while LAVA had return of fibrinolytic activity by 48 hours. Intimal fibrinolysis inhibition following LAVA is reversible and this technique does not lead to an increased incidence of thrombosis.

Animals↗
PubMed1985

Comparison of bursting strength between suture- and laser-anastomosed vessels.

The bursting strength of suture- and laser-assisted vascular anastomosis (LAVA) was assessed using a standard rat femoral artery model. Vessels were studied from 1 hour to 3 weeks. LAVA arteries consistently demonstrated lower bursting strengths than those of suture controls, with significant differences at 1 day, 3 days (P less than 0.001), and 1 weeks (P less than 0.01). Return of strength occurred in a pattern reminiscent of wound-healing models. Relatively low bursting strengths at 1 and 3 days in the LAVA cohort may explain the high aneurysm rate reported to complicate this procedure.

Animals↗
PubMed1985

Photodynamic therapy of prostate cancer: an in vitro study.

The photo-induced toxicity of hematoporphyrin derivative on Dunning R3327 rat prostate cancer cells was studied. Dunning R3327 cells in culture were incubated for two hours in hematoporphyrin derivative and then exposed to red light at 630 nanometers wavelength from an argon pumped dye laser. Cell survival was measured for varying laser power densities, variable concentrations of hematoporphyrin derivative and variable light exposure times. AT1 cells not incubated with hematoporphyrin derivative were directly killed by laser light exposure at power densities greater than 500 mw./cm.2, probably due to hyperthermia. Cells that retained hematoporphyrin derivative were effectively killed using non-thermal levels of red light exposure due to a photochemical effect. Decreasing cell survival of cells that retained hematoporphyrin was related to increasing time of exposure to red light. This form of therapy may be applicable to the treatment of locally invasive prostatic carcinoma in man.

Animals↗
PubMed1984

Laser workshops in neurological surgery.

With the recent increased popularity of laser use in neurosurgery, there arises the question of the value and necessity of a "hands-on" laser workshop in preparing the surgeon for clinical use of the instrument. To find an answer, a questionnaire was recently circulated to those who had participated in such a workshop. Participants were asked whether they were actually using the laser clinically since attending the workshop and, if so, the type of laser they were using. Whether the course was influential in their decision to use a laser and whether they felt they could have used the instrument without such a course was also asked. In addition, the surgeons were asked how long it took them to become comfortable using the laser. The types of procedures, the percentage of operative cases and the mode (freehand or microlinked) in which the laser was used was also investigated. Finally, absolute indications for laser use in neurosurgery and methods to improve laser education were sought. The answers were varied and interesting, but it is our conclusion that a "hands-on" workshop is both a valuable and necessary means of preparing a neurosurgeon for clinical use of a laser, and participation in such a course should be encouraged.

Clinical Competence↗
PubMed1984

In vivo response time of transcutaneous oxygen measurement to changes in inspired oxygen in normal adults.

We examined the in vivo response time of transcutaneous oxygen measurement (PtcO2) to a step increase (100 per cent oxygen) or decrease (air) of inspired oxygen in five normal adults (age 27 +/- SD 4.5 years). The PtcO2 electrode was placed on the upper chest (sensor temperature 44 degrees C). The mean +/- SEM 63 and 95 per cent response times of PtcO2 to a step increase in inspired oxygen were 2.9 +/- 0.2 and 6.8 +/- 0.2 and to a step decrease were 2.4 +/- 0.2 and 5.1 +/- 0.3 minutes. The 63 and 95 per cent response times for the pulmonary washin of oxygen were 1.0 and 2.6 minutes and washout were 0.8 and 2.3 minutes. We conclude that the in vivo response time of the PtcO2 is reproducible but substantially longer than that of the pulmonary washin and washout times and inadequate to monitor rapid changes in arterial oxygenation during anaesthesia, perioperative period or sleep in adults.

Adult↗
PubMed1984

Postoperative pulmonary function in children. Comparison of scoliosis with peripheral surgery.

We measured lung volumes, forced expirograms, and arterial blood gases in 2 groups of elective pediatric surgical patients (mean age, 11.4 +/- SD 2.8; n = 11, 12 operations) the day prior to surgery (control) and between the first and eighth postoperative days. The patients were Group I: peripheral surgery (n = 6) and Group II: reconstructive surgery for scoliosis (n = 5). The preoperative lung volumes and forced expiratory volume in one second were within the predicted normal range in both groups, except for a reduction in total lung capacity (TLC) and vital capacity (VC) in Group II. The postoperative lung volumes in Group I were not significantly different from the preoperative volumes. In group II, on postoperative Days 2 and 3, the lung volumes as a percent of preoperative volumes (mean +/- SEM) were VC, 44 +/- 11; functional residual capacity (FRC), 81 +/- 6; residual volume, 124 +/- 10; TLC, 61 +/- 10. Although the mean FRC returned to the preoperative volume by postoperative Days 5 and 6, the VC and its components remained reduced on postoperative Days 5, 6, and 8. We conclude that postoperative lung volume abnormalities are related to the site and magnitude of surgery and associated phenomena, such as pain, and preoperative respiratory function abnormalities.

Adolescent↗