Search PubMed⌕ Search

Biomedical subjects

S K Wolfson

Publications and source records attributed to S K Wolfson.

At least 37 records · Page 2Linked to original sources
PubMed1992

Lower extremity arterial disease and the aging process: a review.

Atherosclerotic disease is a major health problem in the elderly population in the U.S. To date, most research has focused on the coronary and cerebral manifestations of the disease. Lower extremity arterial disease (LEAD) has received less attention. However, the use of simple objective non-invasive diagnostic techniques in recent population-based studies has allowed identification of asymptomatic LEAD and shown that the prevalence of disease is several fold higher than previously estimated. The prevalence increases sharply with age, from 3% in those under 60 years to over 20% at 75+ years. Detection of LEAD in the elderly provides a rapid, easy assessment of the level of atherosclerosis in the body and identifies those at high risk for mortality and morbidity. LEAD is associated with a relative risk of 4 to 5 for all cause mortality. In about 25% of those with LEAD, the disease progresses over time, leading to loss of mobility, gangrene or amputation. This review summarizes current knowledge regarding the etiology and natural history of LEAD from an epidemiologic viewpoint, delineating areas in which additional research is needed.

Adult↗
PubMed1992

Distribution and correlates of sonographically detected carotid artery disease in the Cardiovascular Health Study. The CHS Collaborative Research Group.

BACKGROUND AND PURPOSE: This article describes the prevalence of extracranial carotid atherosclerosis assessed by ultrasonography, its association with risk factors, and its relation to symptomatic coronary disease and stroke in men and women aged > or = 65 years. METHODS: Maximum percent stenosis, maximum common carotid artery wall thickness, and maximum internal carotid artery wall thickness were assessed using duplex ultrasound in 5,201 men and women aged > or = 65 years in the Cardiovascular Health Study, a study of the risk factors and natural history of cardiovascular disease in the elderly. Existing coronary disease and stroke were assessed by physical examination and participant history. RESULTS: Detectable carotid stenosis was present in 75% of men and 62% of women, although the prevalence of > or = 50% stenosis was low, 7% in men and 5% in women. Maximum stenosis and maximum wall thickness measurements increased with age and were uniformly greater at all ages in men than in women (p < 0.00001). Established risk factors for atherosclerosis (hypertension, smoking, diabetes) and indications of vascular disease (left ventricular hypertrophy, major electrocardiographic abnormality, bruits, and history of heart disease or stroke) related to all three carotid artery measures in the elderly. Of the three ultrasound measures, the best correlate for a history of coronary disease was maximum internal carotid artery wall thickness. For stroke the best correlate was common carotid artery wall thickness. Multiple logistic regression models of prevalent coronary heart disease and stroke that included the ultrasound findings indicated, after adjustment for age and sex, that maximum internal wall thickness and maximum common carotid wall thickness were significant correlates of both. Maximum stenosis did not add significantly to the correlation. CONCLUSIONS: In the elderly the incidence of carotid atherosclerosis was high, although the frequency of severe disease was low. The prevalence and severity of carotid atherosclerosis continued to increase with age even in the late decades of life, and more disease was found in men than in women at all ages. Known risk factors for atherosclerosis continued to relate to carotid abnormalities in the later decades of life, both in symptomatic and asymptomatic subjects.

Aged↗
PubMed1992

Measurement variability in duplex scan assessment of carotid atherosclerosis.

BACKGROUND AND PURPOSE: The reproducibility of duplex scan measures of carotid atherosclerosis was evaluated as part of a study assessing the prevalence of carotid disease in elderly adults. METHODS: Doppler measures of blood flow velocity were used to evaluate disease severity, and extent of carotid plaque was scored from the B-mode image. A reader assigned a grade from 0 to 3 to each of seven segments in the carotid system, based on the number and size of lesions present. Reproducibility data were obtained from 30 study participants who underwent a repeat scan by a second sonographer. Each scan was then scored by two readers. RESULTS: Doppler measures of blood flow velocity were found to be highly reproducible, with intraclass correlation coefficients of 0.81 for the common carotid artery, 0.84 for the internal carotid artery, and 0.77 for the internal carotid artery velocity to common carotid artery velocity ratio. Reproducibility of plaque grade was evaluated using segment as the unit of analysis, and both sonographer and reader variation were analyzed. When readers differed perfect agreement was achieved in 84% of the segments (K = 0.67), and when sonographers differed perfect agreement was obtained in 78% of the segments (K = 0.56). When both sonographer and reader differed, perfect agreement was obtained in 77% of the segments (K = 0.53). The plaque index, created by summing plaque grades from selected segments, was highly reproducible, with an intraclass correlation coefficient of 0.86. CONCLUSIONS: The duplex scan protocol described here provides reliable measures of both extent and severity of carotid disease that are appropriate for use in cross-sectional studies.

Aged↗
PubMed1991

Voltage polarity relay--optimal control of electrochemical urea oxidation.

Voltage polarity relay (VPR) is shown to optimize the urea oxidation rate and urea current utilization under constant current conditions in direct electrochemical urea oxidation. Direct electrochemical urea oxidation is characterized by reversible deactivation of the working electrode due to oxidation products remaining on the surface and the requirement that the working electrode potential remain below about 1.1 V relative to Ag/AgCl in order to prevent undesirable secondary electrochemical oxidations. The VPR method monitors the potential of the working electrode relative to a suitable reference and changes system polarity when the upper potential set limit is reached. Thus, what was the working electrode becomes the counter electrode and vice versa. Since urea oxidation products are desorbed from the counter electrode when its potential drops below about -0.6 V relative to Ag/AgCl, alternating electrode functions between working and counter provides cyclic electrode regeneration and continuous urea oxidation. VPR is believed to optimize constant current control for any electrochemical system that exhibits behavior similar to direct electrochemical urea oxidation.

Electrochemistry↗
PubMed1991

Use of sonography to evaluate carotid atherosclerosis in the elderly. The Cardiovascular Health Study. CHS Collaborative Research Group.

Carotid sonography is being performed on more than 5,000 participants in the Cardiovascular Health Study, a prospective, multicenter study of cardiovascular disease in men and women aged 65 years and older. The sonographic methods used to examine and measure the extracranial carotid arteries are described. Initial validation studies were performed on 61 subjects with a mean age of 68.6 years. Analysis of within- and between-sonographer differences and between-reader differences were performed for selected variables. In general, the mean absolute differences for within- and between-sonographer comparisons were small, with even less variability between readers. Variability was less for the common carotid artery than for the internal carotid artery. These data suggest that carotid sonography is a reliable and reproducible method for use in the study of carotid atherosclerosis in population studies.

Age Factors↗
PubMed1990

Autoregulation remains intact during stable xenon inhalation in the baboon.

To test the possible effect of 32% end-tidal Xe concentration upon autoregulation, 5 baboons, Papio anubis/cynocephalus, were anesthetized/paralyzed with propranolol 0.02, diazepam 0.1, morphine sulfate 0.1, and pancuronium 0.2 (mg/(h.kg)). The animals were subjected to a servocontrolled blood infusion-withdrawal program to control central aortic blood pressure (CAP). PaCO2 was held to 30 to 35 torr, with individual variation less than 3 torr by control of ventilation and by including CO2 in the Xe/O2 mixture. Three to six CBF measurements were made in each subject over the above range. In four animals the CAP was varied between 18 and 150 torr, with corresponding CBF measurements. The CAP range was extended to 196 torr in the 5th animal by IV administration of phenylephrine. Significant lowering of global blood flow did not occur above 40 torr mean CAP. While regulated flow persists to about 150 torr at the high end, there is a breakaway between 150 and 190 torr where flow increased 90%. A 4th order polynomial fit of the data has the characteristic appearance of the familiar autoregulation curve. We conclude that autoregulation is preserved even in the presence of FIXe of 32% in the breathing mixture.

Animals↗
PubMed1990

Xenon-enhanced computed tomography compared with [14C]iodoantipyrine for normal and low cerebral blood flow states in baboons.

The correlation between the acute, invasive diffusible [14C]iodoantipyrine technique for cerebral blood flow and the noninvasive xenon-enhanced computed tomographic method has been assessed by simultaneous measurements in the baboon. Blood flows in small tissue volumes (about 0.125 cm3) were directly compared in normal and low flow states. These studies demonstrate a statistically significant association between the two methods (p less than 0.001). Similar correlations were obtained by both the Kendall (tau) and the Spearman (r) methods (r = 0.67 to 0.92, n greater than or equal to 19 for each study). The problems and limitations of such correlations are discussed.

Animals↗
PubMed1990

Factors associated with avoidance of severe complications after 25 yr of IDDM. Pittsburgh Epidemiology of Diabetes Complications Study I.

To identify characteristics associated with long-term avoidance of insulin-dependent diabetes mellitus (IDDM) complications, subjects taking part in an epidemiologic natural history study of childhood-onset IDDM, with a duration of disease greater than or equal to 25 yr, were studied. Nineteen percent of 175 subjects had avoided overt nephropathy, definite cardiovascular and peripheral vascular disease, clinical neuropathy, and proliferative retinopathy. Approximately half of the nonrenal complications occurred in the absence of renal disease. Subjects free of these advanced complications were characterized by a longer duration of disease (P less than 0.05), better lipid profile and blood pressure (P less than 0.01), and considerably lower glycosylated hemoglobin levels (P less than 0.001). Health-related behaviors, including recent medical contact, regular glucose monitoring, physical activity in youth, and avoidance of cigarette smoking, did not relate to complication status, although regular (at least weekly) alcohol consumption was more prevalent (P less than 0.05) in those without complications. We conclude that a lower mean glycosylated hemoglobin level is strongly related to the avoidance of all IDDM complications.

Adult↗
PubMed1990

Stable xenon-enhanced CT measurement of cerebral blood flow in reversible focal ischemia in baboons.

When the lateral striate arteries of the baboon are temporarily occluded for either 20 or 60 minutes, a near-cessation of blood flow is followed by a dramatic, transient local increase in blood flow values. These findings are evident from serial xenon (Xe)-computerized tomography (CT) measurement of cerebral blood flow (CBF). In this study, 20 minutes of vessel occlusion resulted in brief (less than 1 hour) hyperemia, with no subsequent CT alteration and minimal random neuronal injury. Sixty minutes of occlusion resulted in a more prolonged hyperemia, a low-density area on CT images within 3 hours of reperfusion, and infarction of all cellular elements within the anterior lentiform nucleus. The Xe-CT method provides a sensitive, noninvasive technique for examining sequential alterations of CBF in small regions deep within the brain. This method of recording CBF also permits correlative studies of cerebral infarction, both clinically and experimentally, and allows reasonable inference about the probabilities of neuronal tissue damage with or without reperfusion.

Animals↗
PubMed1989

Electrochemical glucose sensing at low potentials.

An electrochemical sensing method was studied, employing cyclic voltammetry at smooth Pt-electrodes in the low potential region. It has certain advantages over methods that employ higher potentials or constant voltage amperometry. There are also advantages over methods employing active enzymes or other unstable elements. In addition to a specific scanning potential we have studied voltage-delay-pulsing techniques for electrode rejuvenation and innovative methods of creating analyte-selective covering membrane. At potentials below -0.6 V vs Ag/AgCl, peaks of adsorbed glucose species have been observed in cyclic voltammograms. These peaks at about -0.7 V (oxidation peak) and -0.8 V (reduction peak) have yielded reproducible current-glucose concentration relationships, linear through the region of clinically important glucose concentrations (50-300 mg/dl) and stable over time. Since these potentials are not in the redox range of many potentially interfering substances, selectivity is enhanced.

Biosensing Techniques↗
PubMed1988

Stable xenon enhanced computed tomography in the study of clinical and pathologic correlates of focal ischemia in baboons.

When the lateral striate arteries of baboons are occluded, an immediate cessation of blood flow followed by a transient, minimal restitution of flow occurs in that vascular distribution. These findings are evident from serial xenon/computed tomography cerebral blood flow imaging. In our study, infarction consistently accompanied arterial occlusion for 6 hours or more. The xenon/computed tomography method provides a sensitive, noninvasive technique for examining sequential alterations of cerebral blood flow in small regions deep within the brain. This methodology for recording cerebral blood flow permits correlative studies of cerebral infarction, clinically and experimentally, and allows reasonable inferences about the probabilities of neural tissue damage.

Animals↗
PubMed1986

Cerebral blood flow measured by xenon-enhanced computed tomography as a guide to management of patients with cerebrovascular disease.

CT scanning performed before and sequentially during the inhalation of stable xenon (32%), coupled with end-tidal xenon measurements, has made possible the routine construction of regional cerebral blood flow (rCBF) maps with resolution that approximates that of the CT scanner. The capability of obtaining quantitative flow maps with direct anatomic correlation is now available with a commercial package of hardware and software adapted to the General Electric 9800 scanner. The ability to distinguish between normal and reduced rCBF in specific vascular territories has proved useful in the management of cerebrovascular disease. Specific clinical dilemmas that have been addressed with rCBF information from xenon-enhanced CT scanning include the following: In the patient with asymptomatic occlusive disease, is normal rCBF preserved? Is there adequate collateral flow? Are cerebrovascular symptoms a result of emboli or chronic regional low flow? In the patient with complex multivessel occlusive disease, which revascularization procedure is indicated first? Did operation improve rCBF? Should a further procedure be added? May a diffusely diseased but patent artery, which is the source of emboli, be sacrificed safely without compromising rCBF? On the basis of experience with 155 patients, the management and understanding of cerebrovascular disease has been aided substantially by the incorporation of rCBF mapping by xenon-enhanced CT scan in the evaluation of these patients.

Aged↗
PubMed1985

Neurogenic hypertension: etiology and surgical treatment. I. Observations in 53 patients.

Although an extensive literature exists concerning essential arterial hypertension, the primary etiology has been unclear. Arterial compression of the left lateral medulla oblongata by looping arteries of the base of the brain was seen incidently in 51 of 53 hypertensive patients who underwent left retromastoid craniectomy and microvascular decompression for unrelated cranial nerve dysfunctions. Such compression was not noted in normotensive patients. Treatment by vascular decompression of the medulla was performed in 42 of the 53 patients. Relief in the hypertension was seen in 32 of the patients and improvement in four. Arteriosclerosis and arterial ectasia contribute to arterial elongation and looping. If pulsatile compression of the left lateral medulla occurs, hypertension may develop as a consequence of an imbalance in the neural control systems that normally regulate blood pressure. The hypertension may further contribute to arterial elongation, providing a vicious circle of pathophysiologic changes.

Adult↗
PubMed1985

Neurogenic hypertension: etiology and surgical treatment. II. Observations in an experimental nonhuman primate model.

In a companion paper (Ann Surg 1985; 201(3):391-398), clinical data which suggest that neurogenic hypertension may be caused by arterial compression of the left medulla oblongata was presented. A chronic pathophysiologic animal model of neurogenic hypertension using a substitute for arterial pulsation, the neurovascular compression simulator (NCS), was developed. This paper presents data that demonstrate how development of hypertension in a nonhuman primate baboon (5 subject animals, 5 control animals) can be caused by the NCS, and the blood pressure can subsequently return to normal following cessation of NCS activity. These experiments show that pulsatile compression of the left ventrolateral medulla oblongata results in cardiovascular changes consistent with the sequence found in human neurogenic hypertension. Arteriosclerosis and arterial ectasia in the human contribute to arterial elongation and looping at the base of the brain. An arterial loop, by causing pulsatile compression of neural structures, elicits an increase in blood pressure initiated by an increase in cardiac output. This may be due to interference with the autonomic control of the heart and/or by alteration of the relative capacitance of the vascular system.

Animals↗
PubMed1985

Simultaneous measurements of cerebral blood flow by the xenon/CT method and the microsphere method. A comparison.

Simultaneous measurements of cerebral blood flow have been performed in baboons to assess the correlation between the acute and invasive nondiffusible microsphere technique and the noninvasive xenon-enhanced CT method. Blood flows in small tissue volumes (approximately 1 cm3) were directly compared. The results of these studies demonstrate a statistically significant association between the two methods (P less than .001). Similar correlations were obtained by both the Kendall tau (tau) and the Spearman (r) methods. The problems and limitations of such correlations are discussed.

Animals↗