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Biomedical subjects

K W Small

Publications and source records attributed to K W Small.

54 records · Page 3Linked to original sources
PubMed1991

Pigmented paravenous retinochoroidal atrophy. Discordant expression in monozygotic twins.

We studied a 43-year-old woman affected with pigmented paravenous retinochoroidal atrophy and her unaffected monozygotic twin. The affected twin had stable visual acuity (20/25), typical fundus findings, markedly constricted visual fields, abnormal color vision, and an abnormal electroretinogram, all consistent with pigmented paravenous retinochoroidal atrophy. Results of examinations and studies in her twin were entirely normal. Fingerprinting for DNA performed on the twins strongly supported monozygosity. Our findings suggest that either our patient did not inherit pigmented paravenous retinochoroidal atrophy or that an unusual (nonmendelian) genetic mechanism occurred.

Adult↗
PubMed1991

North Carolina macular dystrophy: exclusion map using RFLPs and microsatellites.

The autosomal dominant macular dystrophies are a confusing group of poorly understood diseases. Linkage studies will greatly aid our classification of these disorders and hopefully provide insight into central retinal function and dysfunction such as occurs in age-related macular degeneration. North Carolina macular dystrophy is one such disease that has been amenable to linkage analysis because of the large pedigree size. Seventy-six polymorphic markers have been tested for linkage and exclusion data are presented.

Chromosome Mapping↗
PubMed1991

Non-ferromagnetic retinal tacks are a tolerable risk in magnetic resonance imaging.

Should patients with cobalt alloy (ASTM F563) retinal tacks (Grieshaber cat. #611.95) in their eyes be subjected to the magnetic fields used in magnetic resonance imaging? Although the tacks are not ferromagnetic, they will experience a retarding torque when they are moved at the high angular velocities of human eye motion. Because retinal tacks are small (2.85 mm x 0.9 mm), the torque is difficult to measure. Rather, we measured the torque on a model 25.4 times larger and used a scaling law derived from Maxwell's equations to calculate the force on the tack. The scaling law states that the torque varies with the cube of the object's length. To mimic the motion, models of retinal tacks were attached to Plexiglas rods and the assemblies were swung as pendulums. The pendulums were oriented in the magnetic field of a 1.5 T imager to experience the greatest retardation. Retarding torques were estimated from the rate of decrease of the pendulum amplitude, both inside and outside the magnet. Even if the retinal tacks were as conductive as 6061T6 aluminum alloy (25 MS/m) and the velocity of the surface of the eye were 24 cm/s (angular vel. of 1130 deg/s), the retarding torque would be only 1.6 times the weight of the tack acting with a lever arm as long as the distance from its tip to its center of gravity. The maximum retarding torque on an implanted retinal tack in a 1.5 T magnet is similar to the torque produced by gravity alone acting on the tack and is a tolerable risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Alloys↗
PubMed1991

North Carolina's dominant progressive foveal dystrophy: how progressive is it?

We studied 34 family members at risk of having dominant progressive foveal dystrophy of Lefler, Wadsworth, and Sidbury (also called North Carolina macular dystrophy) and found 17 to be affected. Fifteen of these affected subjects were observed over at least a 10-year period for evidence of progressive macular degeneration. Only one subject showed objective evidence of progressive deterioration in only one eye. Our findings further substantiate that this dystrophy generally has a stable course, contrary to its original description.

Adolescent↗
PubMed1990

Ocular findings in primary hyperoxaluria.

Primary hyperoxaluria (primary oxalosis) is a rare autosomal recessive inborn error of glyoxylate metabolism that causes widespread calcium oxalate crystal deposition in diverse tissues. Because others have reported only occasional ocular involvement, we reviewed the ophthalmologic findings in our 24 patients with primary hyperoxaluria to document its funduscopic variability and to determine its visual prognosis and its possible systemic significance. Eight (30%) of our 24 patients with primary hyperoxaluria exhibited a bilaterally symmetrical retinopathy. The abnormalities were predominantly confined to the posterior pole and ranged from many small (100- to 200-microns) subretinal black ringlets to single large (2- to 3-disc diameter) geographic lesions. In 3 of the 8 patients with oxalate retinopathy, diffuse optic disc pallor was evident. Five patients with both normal-appearing optic discs and oxalate retinopathy had relatively good visual acuities. The maculopathy of primary hyperoxaluria caused mild visual impairment while optic nerve dysfunction associated with this disease appeared to be much visually debilitating. Also, the presence of oxalate maculopathy was associated with a more severe systemic course for the disease.

Acute Kidney Injury↗
PubMed1990

Confirmation of linkage in von Hippel-Lindau disease.

Von Hippel-Lindau (VHL) disease was initially reported to be linked to the RAF1 oncogene (3p25). We have ascertained and sampled two large multigenerational VHL families for linkage studies, in order to confirm the localization of the VHL gene as a prelude to fine mapping studies. The probes used in the analysis were p627 (RAF1) and pHeA12 (thyroid hormone receptor B) (3p24.1-3p22). VHL was analyzed as an autosomal dominant trait with age-dependent penetrance. The maximum lod score combining both families was z(theta) = 2.16 at theta = 0.0 for RAF1 and z(theta) = 2.20 at theta = 0.05 for thyroid hormone receptor B. Multipoint analysis using the RAF1 and thyroid hormone receptor B loci resulted in a peak lod score of 3.1 confirming linkage of VHL to this region of chromosome 3. However, the position of VHL relative to the two loci could not be established with certainty.

Angiomatosis↗
PubMed1990

Presumed choroidal metastasis of Merkel cell carcinoma.

Merkel cell carcinoma is a rare skin tumor of neural crest origin and is part of the amine precursor uptake and decarboxylase system. It typically occurs on the face of elderly people. Distant metastasis is almost uniformly fatal. Choroidal metastasis, to our knowledge, has not been described. We report a patient with Merkel cell carcinoma who had a synchronous solid choroidal tumor and a biopsy-proven brain metastasis. Our 56-year-old patient presented with a rapidly growing, violaceous preauricular skin tumor. Computed tomography of the head disclosed incidental brain and choroidal tumors. Light and electron microscopy of biopsy specimens of both the skin and the brain lesions showed Merkel cell carcinoma. Ophthalmoscopy, fluorescein angiography, and A and B echography revealed a solid choroidal mass. The brain and skin tumors responded well to irradiation. A radioactive episcleral plaque was applied subsequently to the choroidal tumor. All tumors regressed, and the patient was doing well 28 months later. To our knowledge this is the first case of presumed choroidal metastasis of Merkel cell carcinoma.

Biopsy↗
PubMed1989

Surgical management of retinal traction caused by toxocariasis.

We reviewed the results of vitreous surgery in 12 eyes of 12 patients with tractional macular detachment from Toxocara canis. We performed a vitrectomy and membrane peeling in all eyes, with additional scleral buckling in four eyes. After a minimum of six months' follow-up, ten of the 12 eyes (83%) had complete retinal reattachment. Visual acuity improved in seven eyes, two had no change, and three eyes had decreased visual acuity. Good postoperative vision correlated best with good preoperative vision. Preoperative traction retinal folds through the macula were associated with a poor visual outcome.

Adolescent↗
PubMed1989

North Carolina macular dystrophy, revisited.

Progression of the maculopathy in North Carolina macular dystrophy (NCMD) was not well documented. Thus, the author recently examined 22 affected members of the original kindred. Evidence of progression of the macular disease was sought through comparison of the recent fundus findings with old fundus photographs and from subjective complaints of worsening visual acuity. Only 1 of the 22 affected subjects had evidence of such change. Additionally, two new findings of NCMD were observed: (1) severe macular lesions which were staphylomatous or excavated in appearance, not flat, and atrophic as previously described; and (2) peripheral retinal drusen variably present in affected subjects, in contrast to the "normal peripheral retina" originally described. These new findings, along with the generally stable course of the disease would seem to alter our understanding of the relationship of NCMD to other dominant macular dystrophies.

Adolescent↗
PubMed1987

On-line detection of reversible myocardial ischemic injury by measurement of myocardial electrical impedance.

The metabolic and physiological alterations associated with changes in myocardial tissue electrical resistivity during ischemia were characterized to assess the feasibility of using such resistivity as an on-line indicator of the onset of ischemic injury. Twelve anesthetized dogs underwent rapid cardiac extirpation; 5 served as untreated controls, and 7 were pretreated with metoprolol tartrate. Beta blockade was used to alter the time course of ischemic injury as demonstrated previously in studies using this experimental model. In vitro measurement of myocardial resistivity, the detection of ischemic contracture, and serial measurements of tissue adenosine triphosphate (ATP) and lactate were obtained from totally ischemic left ventricles at 37 degrees C. Myocardial resistivity began to increase significantly before onset of ischemic contracture in the untreated control group (resistivity at 42.3 +/- 3.1 minutes, contracture at 53.8 +/- 3.7 minutes; p less than 0.025) as well as the metoprolol group (resistivity at 50.7 +/- 1.5 minutes, contracture at 70.0 +/- 3.5 minutes; p less than 0.005). As expected, ischemic contracture was delayed in the beta-blocked group compared with controls (p less than 0.01). Similarly, the onset of myocardial resistivity increase was delayed in the beta-blocked group (p less than 0.025). ATP and lactate levels at the onset of myocardial resistivity increase were consistent with severe but reversible injury. Resistivity changes during ischemia correlated linearly with simultaneous ATP depletion and lactate accumulation (r = 0.88 to 0.98; p less than 0.05). Furthermore, during global ischemia studied in 3 anesthetized dogs in vivo, the onset of myocardial resistivity increase occurred after 20 minutes. Finally, 6 anesthetized dogs underwent 60 minutes of in vivo regional ischemia by coronary artery occlusion, followed by 60 minutes of reperfusion. Myocardial resistivity in the ischemic region increased immediately and steadily after coronary occlusion, followed by a rapid decrease during subsequent reperfusion. These data show that myocardial resistivity may be useful for identifying severe but still reversible ischemic injury in on-line fashion during regional and global myocardial ischemia.

Adenosine Triphosphate↗
PubMed1987

Retinal blood flow in normal and diabetic dogs.

We have found retinal blood flow to be decreased in diabetic dogs 5 months after the onset of diabetes, which is long before they can be expected to develop morphological changes of diabetic retinopathy. Retinal blood flow was determined using radionuclide labelled microspheres. In eight alloxan diabetic dogs without retinopathy, the retinal blood flow was 0.53 +/- 0.08 (mean +/- SE) ml/min/gm dry tissue weight. This compares with 0.91 +/- 0.17 (mean +/- SE) ml/min/gm dry tissue weight in seven normal dogs. The decreased blood flow in diabetic retinas is statistically significant (P = 0.05). Blood glucose levels did not significantly affect retinal blood flow. This data suggest that changes in retinal blood flow and oxidative metabolism may precede the morphological signs of diabetic retinopathy.

Animals↗
PubMed1987

Left ventricular dysfunction and dilatation resulting from chronic supraventricular tachycardia.

It has been suggested that patients with chronic supraventricular tachycardia may have impaired ventricular function, which returns to normal after surgical procedures that eliminate the tachycardia. The purpose of this study was to determine the functional consequences of prolonged supraventricular tachycardia in 12 awake dogs in which permanent asynchronous atrial pacemakers were implanted and programmed to a rate of 190 +/- 5 beats/min. Serial radionuclide angiograms were obtained immediately after pacemaker activation and at regular intervals over a 3 month period. Chronic tachycardia resulted in a significantly depressed ejection fraction (49% +/- 1% to 29% +/- 3%; p less than 0.0005) compensated for by a dramatic increase in left ventricular end-diastolic volume (69 +/- 4 to 105 +/- 9 ml, p less than 0.005). Stroke volume and cardiac output were not significantly changed. Five dogs were allowed to recover, and serial radionuclide angiograms were obtained for 12 weeks. Although ejection fraction returned to control values (50% versus 47%, p = no significant difference), end-diastolic volume remained persistently elevated after a 12 week recovery period in all animals (67 +/- 5 versus 91 +/- 6 ml, p less than 0.05). Thus prolonged tachycardia resulted in significant functional changes associated with cardiac enlargement, which were not immediately reversible.

Animals↗
PubMed1986

The effect of chemical ablation of the endocardium on ventricular fibrillation threshold.

The purpose of this study was to examine the effects of ablation of the superficial endocardium and Purkinje network on left ventricular fibrillation threshold. Lugol's solution was applied through small ventriculotomies to the left and right ventricular endocardium of 10 dogs on cardiopulmonary bypass. Two control groups of five animals each underwent either endocardial application of saline or epicardial application of Lugol's solution. Ventricular fibrillation threshold was measured before and after each intervention by the single-stimulus technique. Application of Lugol's solution to the endocardium resulted in a 102 +/- 15% increase in ventricular fibrillation threshold from a control value of 26 +/- 2 to 53 +/- 6 mA (p less than .005). In two animals, ventricular fibrillation could not be initiated postoperatively. In the control groups, there were no significant changes in ventricular fibrillation threshold. Histologic examination revealed that Lugol's solution obliterated less than 0.5 mm of superficial endocardium while sparing the adjacent myocardium. Electrophysiologic and rheologic data confirmed the discrete nature of the chemical injury. Thus ablation of the superficial ventricular endocardium with Lugol's solution results in a profound increase in the ventricular fibrillation threshold with only minimal tissue destruction.

Animals↗
PubMedDate not supplied

Coronary blood flow in chronic insulin-dependent diabetic dogs.

Diabetic patients appear to be at an increased risk for perioperative morbidity and mortality following coronary artery bypass grafting. Many have suggested that microangiopathy is a primary cause. Using radionuclide labelled microspheres, we measured the perfusion of the subendocardium, midmyocardium, subepicardium, and the subendocardium/subepicardium ratio in alloxan-induced diabetic and normal dogs. We found no statistical difference in the myocardial perfusion of dogs made diabetic for five months when compared to normal dogs. By using repeated measures two-factor analysis of variance-regression model, changing blood glucose levels had no effect on coronary blood flow in either the diabetic or normal dogs.

Analysis of Variance↗