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Biomedical subjects

A D Roberts

Publications and source records attributed to A D Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1990

A refractive and histopathologic study of excimer laser keratectomy in primates.

Using a 193-nm excimer laser, we produced wide-area, refractive keratectomies on 18 cynomolgus monkey corneas and followed them up for up to 18 months. All corneas developed some subepithelial haze by one month. Electron microscopy disclosed epithelial thickening, absence of Bowman's layer, and subepithelial activated fibroblasts surrounded by disorganized collagen. By six months, the haze faded to a variable degree, the epithelium regained normal thickness, and the collagen was more organized. Persistent corneal haze at 12 months in some corneas correlated with electronlucent spaces in the subepithelial zone. Corneas were 90 microns thinner centrally two weeks after myopic ablation, but returned to preoperative thickness by six months. Myopic flattening and hyperopic steepening of 6 diopters were targeted, and over 7 diopters of each were achieved initially. Regression of induced curvature stabilized over several months. At 18 months, 4.4 diopters of myopic flattening and 5.2 diopters of hyperopic steepening remained.

Animals↗
PubMed1990

Effect of rifabutin on disseminated Mycobacterium avium infections in thymectomized, CD4 T-cell-deficient mice.

Disseminated Mycobacterium avium infection is the major cause of bacteremia in patients with acquired immunodeficiency syndrome. We present here a new animal model of this disease, thymectomized C57BL/6 mice that were intravenously infused with monoclonal antibody to selectively deplete CD4+ T cells. The increased susceptibility of such animals to M. avium infection is comparable to that of C57BL/6 beige mice and thus may provide a viable alternative to the latter model. Further, using representative strains of acquired immunodeficiency syndrome-associated M. avium (serotypes 1, 4, and 8 and a rough isolate), we show that the course of such infections in thymectomized, CD4-deficient mice can be markedly restrained and in some cases the infections can be sterilized by treatment over a 120-day period with a regimen containing 40 mg of the new antimycobacterial agent rifabutin per kg (body weight).

Acquired Immunodeficiency Syndrome↗
PubMed1989

Human excimer laser lamellar keratectomy. A clinical study.

The first ten blind human eyes in the United States to receive excimer laser (ArFl 193 nm) lamellar keratectomy (reprofiling) are presented. Seven of these patients were followed 6 to 12 months after ablation. All eyes are grossly clear in the region of ablation. Results of slit-lamp examination of all flattened ablated areas show mild superficial haze at the epithelial/stromal interface. This haze might not interfere significantly with vision in patients 7 to 10. Serial pachymetry and keratometry measurements, refraction, and digital keratoscopy show a progressive filling in of the excavated area by approximately two thirds but a loss of initial diopteric correction of only one third. Histopathologic analysis was obtained for four eyes. Transmission electron microscopy of three eyes enucleated 3 to 12 days after ablation shows 40-microns ablation depths through Bowman's layer and superficial stroma with minimal adjacent tissue damage and no inflammatory cells. The epithelium is increased in thickness by 50%, and firmly attached to the underlying stroma. A 4-month postablation specimen shows keratocyte activation with increased protein synthesis (presumed collagen and ground substance).

Blindness↗
PubMed1989

Experimental corneal studies with the excimer laser.

The excimer laser is potentially capable of achieving wide area central corneal reprofiling because of its extreme precision and limited penetration into adjacent tissues. A beam modifying system designed for this application is described. Initial clinical studies in monkeys and in ten human patients with blind eyes were performed. Long-term clinical data and interim histologic analyses are available from these studies. The results indicate that following ablation with an ultraviolet laser in both humans and primates, the ablated tissue shows a normal healing reaction resulting in a mild to moderate stromal interface haze. The effects of this healing on best corrected vision must be elucidated through additional research. Some loss of refractive effect was seen early in the healing process with apparent stabilization.

Animals↗
PubMed1988

The variation in cervical hydroxyproline and cervical water with age.

The squamocolumnar junction is frequently not visible in the postmenopausal patient. This study attempts to identify some of the changes in the cervix that may account for this observation. Twenty-four cervical biopsy samples taken at the squamocolumnar junction were analysed for hydroxyproline (collagen) and water content. There was significantly more hydroxyproline (collagen) in the premenopausal woman than the postmenopausal woman. Similarly, there was higher percentage of water in the biopsies in the premenopausal woman than the postmenopausal woman. Further samples obtained deeper in the cervical stroma did not confirm these differences. It appears likely that differences in cervical water and cervical collagen near the surface of the cervix account, at least in part, for the lack of visibility of the squamocolumnar junction in the older woman.

Adult↗
PubMed1986

Long-term hormone implant therapy--hormonal and clinical effects.

Long-term effects of hormone implants (estradiol or estradiol plus testosterone) were examined in 75 menopausal women. Both therapies relieved vasomotor symptoms with a return of significant flushing after six months, thus reimplantation was performed every six months. Estradiol levels had not returned to baseline by six months, and significant accumulation of estradiol occurred by three years. The patients given testosterone experienced a similar accumulation of testosterone. There was no significant change in mean weight, blood pressure, or liver function tests during three years. Both therapies reversed the bone biochemical changes of menopause, and in both groups there was no significant loss in bone density. Supplementation of estradiol with testosterone in implant therapy was not observed to provide additional benefit in terms of the parameters studied.

Adult↗
PubMed1984

Danazol and prolactin status in patients with endometriosis.

A group of 55 women with endometriosis was studied before and during danazol therapy. An unexpectedly high proportion (36%) had a raised serum prolactin level before treatment which was reduced after 50 days of danazol (before treatment 783 +/- 333 mU/l; on danazol 243 +/- 113 mU/l, P less than 0.001). In contrast patients with normal serum prolactin levels showed no significant drop on danazol therapy. In all patients serum oestradiol was significantly reduced during treatment (before treatment 449 +/- 188 pmol/l; on danazol 207 +/- 117 pmol/l, P less than 0.001). In one patient with hyperprolactinaemia danazol reduced both basal and stimulated prolactin levels, whereas in 5 women with normal prolactin levels we could detect no gross alteration in metoclopramide or TRH stimulated prolactin levels associated with danazol therapy. The possibility that normalisation of raised prolactin levels may be secondary to reduced oestrogens and that patients with endometriosis have an increased sensitivity to oestrogen-induced prolactin secretion is discussed.

Danazol↗
PubMed1983

Polyglycolic acid and catgut sutures, with and without oral proteolytic enzymes, in the healing of episiotomies.

Polyglycolic acid (PGA) sutures and traditional catgut were compared in 190 patients undergoing episiotomy. Each group was also randomly allocated to a double blind comparison of therapy with oral proteolytic enzymes (Chymoral) and placebo. The combination of Chymoral and polyglycolic acid sutures was shown to reduce the level of pain, assessed subjectively, and there was a significant reduction in analgesic requirements in the Chymoral/PGA group.

Anti-Inflammatory Agents↗
PubMed1982

Anaerobic muscle enzyme changes after interval training.

In contrast to endurance training, little evidence is available concerning the effects of sprint-type training programs on the anaerobic metabolism of skeletal muscle. Four male subjects completed a mean of 16 training sessions consisting of eight 200-m runs at 90% of maximal speed, which were separated by 2-min rest periods. Before and after the 5-week training period, muscle biopsies were taken out of the lateral head of m. gastrocnemius and analyzed for the activities of phosphorylase, phosphofructokinase (PFK), glyceraldehyde phosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH). Following training there was a significant increase in the subjects' performance time in a treadmill test at a speed of 16 km/h speed and 15% grade. Significant increases were observed in the activities of phosphorylase, PFK, GAPDH, LDH, and MDH, whereas the 17.5% increase in SDH was not statistically significant. It is concluded that interval training with high intensity and a 1:4 work-rest ratio leads to increased activities of key enzymes involved in glycogenolysis and anaerobic glycolysis of skeletal muscle.

Adult↗
PubMed1980

A biomechanical evaluation of the role of fatigue in middle-distance running.

Eight college level runners were filmed using high speed photography at the 500 m, 1,300 m, 2,100 m and 2,900 m stages of a 3,000 m time trial. Kinematic and spatio-temporal data were obtained through an interfaced digitiser computer system. Mean horizontal velocities of 5.18 m/s, 5.17 m/s, 5.18 m/s and 5.16 m/s indicated that minimal variations occurred from the four stages of the trial. No significant changes in biomechanical data were apparent between the first three stages of the trial; however, changes were evident when Stage 4, the 2,900 m mark, was compared to the earlier sections of the trial. With the development of fatigue stride length decreased while stride rate increased to maintain the constant velocity. There was also a small shift to increase the period of support and correspondingly decrease the period of non-support. The leg was more angled at foot strike, the thigh was less extended at the end of the support phase, and the trunk was carried further forward during the running cycle. Success in middle-distance running requires the athlete to maintain an efficient co-ordinated movement pattern over the entire race. The coach who can identify the changes in movement patterns over a race increases the likelihood of success for his athletes.

Biomechanical Phenomena↗
PubMed1978

Total and alactic oxygen debts after supramaximal work.

The total and alactic oxygen debts were measured in eight subjects following supramaximal treadmill running (14.5--16.1 km/h, 20% grade) to exhaustion, on two duplicate tests separated by 48 h. Mean total oxygen debts on the two trials were 5.28 +/- 0.42 1 and 4.57 +/- 0.46 1, (r = 0.34). Mean alactic oxygen debts were 2.81 +/- 0.21 1 and 2.74 +/- 0.121 (r = 0.89). Values for maximal total and alactic oxygen debts in this study were in close agreement to those found in the literature. The inability of the subjects to adequately reproduce an exhausting supramaximal effort was the major factor preventing reliable measurement of total oxygen debt. It is concluded that the method developed for the measurement of oxygen debt is both reliable and valid for the alactic portion of the debt.

Adult↗