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Biomedical subjects

G Houston

Publications and source records attributed to G Houston.

At least 19 recordsLinked to original sources
PubMed1998

Manganese requirement and toxicity in patients on home parenteral nutrition.

Two patients who were receiving home parenteral nutrition complained of vague neurological symptoms of such severity that they underwent full clinical appraisal. The only positive finding was that plasma manganese concentrations were greater than twice the upper 95% confidence interval of normal (7-27|nmol/l). In the light of this result all nine patients receiving home parenteral nutrition underwent evaluation for possible manganese toxicity. One other patient had serum manganese concentrations exceeding twice the upper limit (127|nmol/l). The three patients with elevated serum Mn had evidence of manganese deposition in the brain on magnetic resonance imaging scanning. In contrast two patients with normal plasma results had negative scans. Patient susceptibility appears very variable. We suggest that current amounts of trace elements provided in nutrition solutions may be a potential source of nutrient activity. The fine tuning of supply and demand may be difficult on account of a limited range of commercially available trace element solutions.

Basal Ganglia↗
PubMed1996

Beta 3-adrenoceptors mediating relaxation of the oesophageal tunica muscularis mucosae and distal colon in the rat: comparative pharmacology and their desensitization by BRL 37344.

1. In the rat isolated distal colon and oesophagus, relaxant responses to (-)-isoprenaline were poorly antagonized by propranolol (0.1 microM), suggesting an involvement of beta 3-adrenoceptors. 2. In the presence of propranolol the rank order of potency for the agonist-induced relaxations was similar in the two tissues. 3. BRL 37344 was a partial agonist relative to isoprenaline in the colon but when a single maximal concentration of BRL 37344 (1 microM) was added, a full relaxation was observed. 4. BRL 37344 desensitized responses to isoprenaline in both the colon and oesophagus. 5. (+/-)-Cyanopindolol (1.0 microM) antagonized the relaxatory responses to both isoprenaline and BRL 37344 in the distal colon and oesophagus and reduced the desensitizing effect of BRL 37344. 6. The present study demonstrates that the beta-adrenoceptors mediating relaxation in both the rat isolated distal colon and oesophagus are of the beta 3-adrenoceptor subtype. Desensitization appears to result from the binding of BRL 37344 to the beta 3-adrenoceptor in a manner which is blockable by cyanopindolol.

Adrenergic beta-Agonists↗
PubMed1995

Preventing intimal hyperplasia with photodynamic therapy using an intravascular probe.

The purpose of this study was to determine the efficacy of intravascular photodynamic therapy (PDT) to prevent the development of intimal hyperplasia. Anesthetized New Zealand white rabbits underwent placement of Fogarty balloon catheters introduced via femoral artery cutdowns. Catheters were passed retrograde 10 cm into the lower abdominal aorta, inflated six times, and withdrawn toward the inguinal ligament. Rabbits were then randomly assigned to one of the following groups: group 1, drug with no light; group 2, no drug with 240 joules of light; group 3, drug plus 120 joules of light; or group 4, drug plus 240 joules of light. Uninjured carotid arteries served as negative control vessels (N) and injured but non-PDT-treated iliac artery segments served as positive controls (P). Porfimer sodium (photofrin) was administered in a dose of 5.0 mg/kg. Light was provided by a fiberoptic probe with a 1 cm cylindric diffuser attached to an argon pumped dye laser tuned to 630 nm to provide 1 W of laser light for 120 or 240 seconds. One month after PDT, rabbits were killed, perfusion fixed with glutaraldehyde, and vessels removed and examined microscopically. Intimal thickness (mean +/- SD) was calculated and expressed as ratios of the intima/media at four equal positions. Results for N, P, and groups 1, 2, 3, and 4 were 0.02 +/- 0.00, 1.18 +/- 0.71, 0.76 +/- 0.33, 0.96 +/- 0.43, 0.14 +/- 0.22, and 0.36 +/- 0.16, respectively. Intimal thickness was significantly reduced in groups 3 and 4 when compared with P, group 1, and group 2 (p < 0.001, ANOVA). These results showed that intravascular PDT was effective in reducing intimal hyperplasia following arterial injury. This may be a practical method of delivering light for PDT.

Animals↗
PubMed1995

Sinonasal hemangiopericytoma: case report and literature review.

Hemangiopericytoma (HPC) is a rare vascular tumor that can arise in any organ system, but occurs most frequently in skeletal muscle. We present a case of a primary sphenoid sinus HPC unusual for its spontaneous remission after biopsy. There have been approximately 55 cases of sinonasal HPC reported in the literature, representing less than 5% of all lesions. In general, HPC behaves aggressively, demonstrating greater than 50% local recurrence and 10% metastatic disease. Although extended surgical resection is traditionally considered the most effective therapy for all HPC, critical literature review does not support this method of treatment for HPC occurring in the paranasal sinuses and skull base. Long-term follow-up indicates that the majority of sinonasal HPC have a benign clinical course regardless of treatment. As a result, we do not recommend extended resection as the initial therapy for sinonasal HPC. Instead, a period of observation coupled with serial MRI or CT scans should be used to detect tumor progression. These indolent tumors should undergo extended resection only after progression has been confirmed. In addition to the case report, a synopsis of the reviewed literature and a summary of treatment recommendations are also presented.

Case Reports↗
PubMed1994

A statistical analysis of Modified Clinical Technique vision screening of preschoolers by optometry students.

Fourth year optometry students screened 745 preschoolers using a slightly altered Modified Clinical Technique (MCT) under the supervision of a faculty doctor. Children who failed the MCT were randomly selected and then matched by age, sex, and ethnic origin to children who had passed the screening battery. The 61 screening failures and 45 matched controls were later given full eye examinations with cycloplegia by University of Alabama at Birmingham faculty doctors who were unaware of the screening results. The positive predictive value (PPV) (0.52) and negative predictive value (NPV) (0.78) of the MCT were calculated directly from the 2 x 2 contingency table crossing screening results and a standard diagnosis. Sensitivity [0.50, k(1,0) = 0.29], specificity [0.79, k(0,0) = 0.30], efficiency [0.70, k(0.5,0) = 0.29] of the MCT, and the prevalence (0.30) of children failing the standard diagnosis were estimated using statistics appropriate to the prospective sampling design. The reproducibility of the diagnosis, estimated by analyzing multiple, independent diagnosis of each study child by seven doctors was moderate (kappa D 0.58). Statistics summarizing the agreement between the MCT and the diagnosis by the individual study doctor are similar to those obtained with comparison to the standard diagnosis. The characteristics of the MCT may be generalized only to similar populations that are screened by clinicians with similar experience, using the same tests.

Child↗
PubMed1993

Experimental mandibular regrowth by distraction osteogenesis. Long-term results.

The use of gradual distraction to grow bone (distraction osteogenesis) has gained widespread orthopedic acceptance, but has only recently been applied to craniofacial skeletal defects. The use of bifocal distraction osteogenesis to fill experimental segmental mandibular defects with regenerate bone was recently reported. Though all canines in that study demonstrated normal oromandibular function, they were observed for only 4 weeks following defect closure. The study that is now reported describes the long-term (12-month) functional, morphologic, and biomechanical results when bifocal distraction osteogenesis was applied to the same model. In this long-term study, three canines had 2.5-cm unilateral segmental mandibular body defects filled with structurally stable bone using bifocal distraction osteogenesis. These dogs exhibited normal oromandibular function for 1 year following segment regrowth and external fixator removal. Macroscopic and histologic evaluation of the regrown segments revealed a re-formation of the cortical and medullary architecture. Stress testing demonstrated the average ultimate strength of the regrown segment at 53 MPa, which corresponded to 77% +/- 5.7% of normal mandibular bone. The data suggest that clinical trials applying this technique to segmental mandibular reconstruction are warranted.

Animals↗
PubMed1992

Experimental tracheal replacement using a revascularized jejunal autograft with an implantable Dacron mesh tube.

Defects comprising more than 50% of the trachea cannot be reliably reconstructed by any current technique or prosthesis. A composite tracheal replacement implant consisting of a Dacron-urethane mesh tube and revascularized jejunal autograft was applied to this problem. This composite implant was used to replace 7 to 10 cm of trachea in eight dogs. The implant was sewn to the outside (serosal surface) of the jejunum to provide permanent structural support to the autograft, and an intraluminal silicone tube was placed inside the jejunal segment and left for 4 weeks following reconstruction. Six of eight animals survived the predetermined time periods and were killed painlessly in groups of two animals at 1, 2, and 6 months after removal of the intraluminal silicone tube. Postoperative intubation, ventilation, or tracheostomy was not necessary. Excessive secretions were not seen in any of the animals, and a fair to good performance status was maintained until death in all but one animal. Histologic examination revealed slight thinning of the jejunal mucosa, with no change in the jejunal muscularis. These data suggest that with further refinement this composite implant may be a viable reconstructive option in humans.

Animals↗
PubMed1991

Does lithium reduce the mortality of recurrent mood disorders?

Numerous follow-up studies have shown that patients with mood disorders who do not receive prophylactic medication are at increased risk of death, particularly from suicide. After 11 years follow-up we compared the mortality of 103 patients attending a lithium clinic with that expected on the basis of age/sex/year-specific rates for England and Wales. Only 10 patients died during the study, although the expected number of deaths was 18.31 (P = 0.052, two-tailed) and no deaths from suicide were observed. After correcting for the prevalence of mood disorder in the general population, the relative risk was 0.60 (95% CI 0.29-1.12) which suggests that lithium reverses the excess mortality associated with recurrent mood disorders, including that from suicide.

Bipolar Disorder↗
PubMed1990

Cryogenically preserved adult and juvenile goat mandibular condylar transplantation.

Loss of a functional temporomandibular joint (TMJ) has long been a clinical challenge in both children and adults. Although reconstruction to date has been performed with various prosthetic devices or autogenous costochondral grafts, these procedures have a potential for complications and morbidity. Our studies were performed to determine the feasibility of healing, growth, and long-term function of TMJ reconstruction techniques with cryogenically preserved mandibular allografts in the goat model. This species was chosen because the surgical anatomy and biomechanics of the goat TMJ are very similar to those of the human TMJ. The positive results of the studies and their relevance will be described.

Animals↗
PubMed1990

The effect of size on paired 'C/D' estimations.

This article describes a comparative study of the accuracy of proportional ratio estimations on stylized optic nerve head targets by experienced optometrists, student clinicians and beginning optometry students. Within limits, these estimations approximate the perceptual and cognitive tasks involved in the clinical estimation of cup-to-disc (C/D) ratios. There was no significant difference (alpha = 0.05) in the accuracy of estimations relative to clinical experience. The overall frequency of exactly correct paired estimations (i.e., both horizontal and vertical correct) for the 16 stylized targets was 18.6%. In a subanalysis of the data, less than half (45.4%) of the estimations were within +/- .05 of the true "C/D" ratios. Statistically, observers were more accurate for the smallest targets and less accurate for the medium and larger targets. Potential clinical implications of these findings, relative to C/D ratio documentation in glaucoma diagnosis and management, are presented and discussed.

Analysis of Variance↗
PubMed1989

Reliability of assessing the cup/disc ratio using a 90 D lens photograph.

The reliability of estimating the cup to disc (C/D) ratio using a retinal camera photograph was compared to the same task using a photograph taken with the slit-lamp and +90 D lens. Twenty observers (10 optometry students, 10 faculty members) were asked to judge the C/D ratio of four eyes by the two photographic methods. When comparing the two clinically accepted photographic methods, statistically significant differences were noted for the vertical dimension estimate in two of four eyes. However, these differences were not clinically significant. C/D ratio estimates with the retinal camera photograph were typically larger than those of the slitlamp and +90 D lens photograph. Neither photographic method provided an advantage or disadvantage to clinicians with different levels of experience.

Fundus Oculi↗
PubMed1989

Evaluation of a new criterion of binocularity.

The purpose of this study was to assess a new criterion for binocular comfort analogous to the classical Sheard's criterion. Instead of equating the fusional demand with the monocular phoria as is done when Sheard's criterion is applied, the new criterion uses a calculated binocular fusional demand. The binocular demand was derived using a clinical measurement of the convergence accommodation per convergence (CA/C) ratio. Sheard's criterion was also evaluated. Other commonly used indicators of binocularity (heterophoria, vergences, accommodative amplitude, facility and response, fixation disparity, and the associated phoria) were measured. One hundred subjects (52 males, 48 females; mean age 26 years) were classified as either symptomatic or asymptomatic by an interviewing clinician. The examining clinician was intentionally masked as to the classification of the subjects. We hypothesized that the new criterion would best discriminate between the two groups of patients inasmuch as it is based on currently accepted dual-interaction models of accommodation and vergence. Our analysis confirmed that the CA/C ratio corresponded closely to those published previously (mean = 0.06 D/delta). Significant differences (p less than 0.05) were determined between the symptomatic and asymptomatic groups for gender, near phoria through a +2.00 D add, accommodative amplitude, positive vergences at near, and both the classical Sheard's and the new criterion. The new criterion was the best discriminator between the groups, identifying 72% correctly, an improvement of 6% over the classical Sheard's. However, various stepwise discriminant analysis procedures consistently failed to demonstrate that the calculated binocular fusional demand or the new criterion was superior to the near phoria or the classical Sheard's value. These results suggest potential clinical utility for new procedures based on recently described models of accommodation and vergence, but further development appears necessary.

Accommodation, Ocular↗