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Biomedical subjects

R J Peters

Publications and source records attributed to R J Peters.

66 records · Page 4Linked to original sources
PubMed1994

Effect of resisting tonometry on intraocular pressure.

BACKGROUND: Children and patients with developmental delay frequently resist the procedure of tonometry. Intraocular pressure (IOP) readings, if obtained under stressful circumstances, may have questionable reliability because IOP is influenced by numerous factors characteristic of the uncooperative patient. These factors include possible increases in arterial blood pressure, intraocular vascular engorgement, and pressure on the globe. A study of the effect upon IOP of these factors occurring simultaneously has not been reported previously. METHODS: We measured IOP using the Tono-Pen on 40 cooperative adults under normal conditions and again under conditions simulating the resistant patient. RESULTS: Paired t-test revealed a statistically significant difference between IOP readings under the two conditions (p < 0.001), with IOP under "resistant" conditions showing more variability and averaging 6mmHg higher than under normal conditions. CONCLUSIONS: We conclude that IOP readings in resistant patients should be viewed with caution. The possibility of obtaining false high readings in these patients could lead to unnecessary glaucoma evaluations if based only on elevated IOP readings.

Adult↗
PubMed1990

Frequency of myocardial indium-111 antimyosin uptake after uncomplicated coronary artery bypass grafting.

The reported incidence of myocardial damage after coronary artery bypass grafting (CABG) is highly related to the methods used. Since indium-111 monoclonal antimyosin antibody scintigraphy has been shown to be highly specific and sensitive for myocardial necrosis, even in small lesions, uptake of this radiotracer was evaluated after CABG. In 23 consecutive patients without previous myocardial infarction who underwent CABG for stable angina, 80 MBq indium-111 antimyosin was injected on the third postoperative day. Planar images were obtained 48 hours later and analyzed for myocardial uptake of indium-111 antimyosin. Scintigraphic results were related to creatine kinase MB levels, duration of both aortic cross-clamping and cardiopulmonary bypass, and electrocardiographic changes. In all patients surgical procedure and postoperative course was uncomplicated. Indium-111 antimyosin uptake was present in 19 of 23 patients (82%). It was diffused in 7 patients and localized in 12. No pathologic Q waves occurred postoperatively. Fourteen patients exhibited ST-segment changes. No good relation was found among indium-111 antimyosin uptake and creatine kinase MB levels, duration of cross-clamping or bypass, and ST-T changes. It is concluded that some degree of myocardial damage, though silent, is common after CABG.

Antibodies, Monoclonal↗
PubMed1988

Catecholamine release and potassium accumulation in the isolated globally ischemic rabbit heart.

The relation between the release of endogenous catecholamines and the rise in extracellular potassium concentration [( K+]0) was studied during global ischemia in the isolated perfused rabbit heart. An increase in release of catecholamines was observed only after ischemic periods longer than 10 min. In agreement with other studies, [K+]0 initially rose until a plateau phase was established after 8 min. During this phase [K+]0 actually decreased in several hearts. In these hearts, lactate release was larger (116.9 +/- 22.4 mumol/g dry wt, n = 5) than in hearts in which no decrease in [K+]0 was observed (83.3 +/- 16.0 mumol/g dry wt, n = 6). Blockade of the alpha- and beta-adrenoceptors by phentolamine (5 x 10(-6) M) and propranolol (10(-6) M), respectively, prevented the decrease in [K+]0. These findings show that the secondary decrease in [K+]0 is associated with increased glycolytic flux. Moreover, catecholamines are a prerequisite for this decrease and are frequently observed between 8 and 15 min of ischemia.

Animals↗
PubMed1985

Effects of unilateral stellate ganglion stimulation and ablation on electrophysiologic changes induced by acute myocardial ischemia in dogs.

We recorded direct-current extracellular electrograms simultaneously from 60 left ventricular epicardial sites in 38 alpha-chloralose-anesthetized dogs during repeated, 5 min coronary arterial occlusions. In each dog recordings made during control occlusions were compared with those made in occlusions after, or during, the following interventions on the sympathetic nervous system: left stellate ganglion stimulation, left stellectomy, right stellectomy, and clamping the abdominal aorta with intact sympathetic nerves to induce a rise of blood pressure equal to that present during left stellate stimulation. Heart rate was kept constant. Measurements included determination of TQ segment potentials and times of local activation. After 2 min of ischemia, the degree of TQ segment depression was increased by left stellate ganglion stimulation and was decreased by both left stellectomy and clamping the aorta. Also, the area showing negative TQ potentials, indicating decreased resting membrane potentials, was enlarged by both left stellate stimulation and right stellectomy and reduced by left stellectomy. No differences were found in the results of experiments in which the left anterior descending coronary artery was occluded and those in which the circumflex branch was occluded. Left stellate stimulation significantly improved conduction within the ischemic zone. No evidence was found to suggest that the arrhythmogenic effects of left stellate stimulation and of right stellectomy, confirmed in the present study, resulted from an increased likelihood for reentry in the subepicardium of the ischemic zone.

Animals↗
PubMedDate not supplied

Characterization of plaque components with intracoronary ultrasound imaging: an in vitro quantitative study with videodensitometry.

We investigated whether videodensitometry provides a possibility of objective plaque characterization by intracoronary ultrasound imaging. Histologically matched 30 MHz ultrasound images of characteristic atherosclerotic lesions in saline solution and blood-perfused human coronary arteries in vitro were digitized, and regions of interest were analyzed by calibrated videodensitometry. Pixel gray-level distributions were represented as frequency histograms, and mean pixel gray level, skewness, and kurtosis were calculated. Similarly, images of flowing blood in vitro (n = 9; hematocrit 40%) were analyzed. Mean pixel gray levels differed between the three lesion types (lipid rich [n = 6], 71 to 92 [mean 80]; fibromuscular plaque [n = 14], 94 to 162 [mean 124]; and calcified plaques [n = 8]; 161 to 196 [mean 178]) (all comparisons p < 0.001). Ranges of mean pixel gray levels for flowing blood in vitro were within the range of those for fibromuscular plaque (86 to 103; mean 98). During blood perfusion in nine specimens, pixel gray levels were 85% +/- 7% of those during saline perfusion but with similar differences between plaque types. We conclude that homogeneous plaque types can be distinguished in vitro by videodensitometry on intracoronary ultrasound images.

Aged↗
PubMedDate not supplied

Histopathologic validation of intracoronary ultrasound imaging.

The purpose of this study was to validate intracoronary ultrasound imaging by correlation with histologic examination. In this in-vitro study of pressure-perfused human coronary arteries, 104 matching intracoronary ultrasound imaging images and histologic cross-sections from 12 hearts were compared to determine the diagnostic accuracy of 30 MHz commercially available intracoronary ultrasound imaging. For lipid deposits, sensitivity was 46% and specificity 97%. The smallest lipid deposit that was visualized measured 0.25 mm in axial diameter on histologic study. For calcific deposits, sensitivity was 77% and specificity 100%. The smallest calcific deposit that was visualized measured 0.25 mm in axial diameter on histologic examination. Atherosclerotic intimal thickening could not be distinguished qualitatively or quantitatively from nonatherosclerotic intimal thickening unless there were localized deposits of lipids or calcium. Intracoronary ultrasound imaging is accurate in detecting lipid and calcium deposits. Intimal thickening in intracoronary ultrasound imaging images does not prove the presence of atherosclerosis.

Adult↗
PubMedDate not supplied

Determinants of echodensity at the intima-media interface with intracoronary ultrasound imaging.

A thin, echodense layer (EL) is sometimes observed at the intima-media interface on intravascular ultrasonographic images. We reviewed a series of 119 histologically matched, 30 MHz, in vitro ultrasound cross sections of human coronary arteries for factors determining the occurrence of an EL. ELs were observed in 19 (27%) of 71 images with optimal gain settings, in two (17%) of 12 with high gain settings, and in none of 26 with low gain settings. In 17 (94%) of 18 cross sections with eccentric catheter positions, an EL was visible only in parts of the vessel wall that were perpendicular to the ultrasound beam. ELs were seen behind fibrous, lipid-rich, and mixed lesions but not behind calcified lesions because of acoustic shadowing. The presence or morphologic elements of the internal elastic lamina did not influence the occurrence of an EL. We conclude that the occurrence of an EL at the intima-media interface depends on acoustic factors and gain settings, and it provides no anatomic information per se.

Cardiac Catheterization↗
PubMedDate not supplied

The relationship between future orientation and street substance use among Texas alternative school students.

Self-reported substance use data were collected from 963 alternative school students in grades 7-12 who were surveyed through the Safer Choices 2 study in Houston, Texas. Data were collected between October 2000 and March 2001. Logistic regression analyses indicated that lower levels of future orientation was significantly associated (OR = 0.88, 95% CI = 0.81-0.97) with thirty-day substance use after controlling for age and gender. In addition, lower levels of future orientation was found to have a significant association with students' lifetime substance use (OR = 0.93, 95% CI = 0.87-.99) after controlling for age, race, and gender. While the relationships tested in this study are exploratory, they provide evidence for an important connection between future orientation and substance use among adolescents attending alternative schools.

Adolescent↗
PubMedDate not supplied

The role of hearing protectors in leisure noise.

Ear muffs and ear plugs are widely used in the workplace to provide hearing protection for employees exposed to high levels of noise. Through an examination of the use of ear protectors in the workplace this paper explores the extent to which these devices can play a similar role in protecting members of the public from hearing damage arising from exposure to high levels of noise from leisure activities. It is concluded that the major limitation to the effective use of ear protectors for leisure use is likely to be the lack of easily accessible information, advice and guidance on the nature of the hearing protection risk from noisy leisure activities, and on the availability, selection and use of protectors, and of the need for regular hearing checks.

Audiometry↗