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Biomedical subjects

R E Sievers

Publications and source records attributed to R E Sievers.

At least 55 records · Page 3Linked to original sources
PubMed1987

Gas chromatographic measurement of carbon monoxide in hydrocarbon matrices with a redox chemiluminescence detector.

The rapid measurement of trace levels of carbon monoxide in ethylene by gas chromatography with redox chemiluminescence detection is described. Linear response for carbon monoxide over three decades and a detection limit in the sub-parts per million by volume (ppmv) concentration range were observed without methanation or preconcentration of the sample. Samples containing 0.2 ppmv of carbon monoxide in ethylene were readily quantitated.

Carbon Monoxide↗
PubMed1987

Verapamil and diet halt progression of atherosclerosis in cholesterol fed rabbits.

The present study was designed to evaluate the effects of oral verapamil and normal diet on regression of atherosclerotic plaque in cholesterol fed rabbits. Forty-three rabbits were separated into 6 groups and studied for 24 weeks. All groups had a cholesterol diet for the first 12 weeks. Group I was then sacrificed and had 38 +/- 23% (mean +/- standard deviation) aortic plaque. During weeks 13 to 24, group II (cholesterol diet) and group III (normal diet) had similar percentages of aortic plaque: 80 +/- 7% and 78 +/- 22%, respectively. Group IV (cholesterol diet), was treated with oral verapamil for 24 weeks and had significantly less plaque (54 +/- 10%) than group II, (80 +/- 7%). In group V (cholesterol diet), treatment with oral verapamil during weeks 13 to 24 did not significantly reduce plaque (70 +/- 23%), compared to group II, (80 +/- 7%). In group VI, normal diet and verapamil during weeks 13 to 24 significantly reduced aortic plaque (46 +/- 25) when compared to group II (80 +/- 7%). Group VI (46%) did not differ from group I (38%). It is concluded that verapamil combined with a normalized diet can halt the progression of aortic atherosclerosis after a 12 week atherogenic diet in rabbits. Verapamil or diet alone was ineffective in the second 12 weeks. Overall, verapamil was effective in preventing atherosclerosis but was ineffective in causing regression of atherosclerosis.

Animals↗
PubMed1987

Lactate accumulation in ischemic- and anoxic-isolated rat hearts assessed by H-1 spectroscopy.

Proton magnetic resonance (MR) spectroscopy with homonuclear editing was used to assess lactate accumulation in ischemic and anoxic hearts perfused according to the Langendorff method. An increase in the lactate signal was observed after 5 minutes of ischemia and after 10 to 20 minutes of anoxia. This study demonstrates that proton MR spectroscopy can be used to monitor the time course of MR-visible lactate levels in ischemic and anoxic isolated rat hearts.

Animals↗
PubMed1985

Selective retention of oxygen using chromatographic columns containing metal chelate polymers.

Porous polymers containing various metal chelates bonded to nitrogen functionalities on the surface of the polymer have been synthesized and found to bind oxygen reversibly. The stationary phases containing [5,5'-(1,2-ethanediyldinitrilo)-bis(2,2,7-trimethyl-3-octanonato)]cobalt(II) were found to be the most suitable of the phases investigated for separating oxygen for argon, nitrogen, and carbon monoxide. At ambient temperatures, near 25 degrees C, the reversible interaction of molecular oxygen with the transition-metal complex bonded to the stationary phase results in a marked increase in the retention time of oxygen, relative to species that have similar retention times in columns that do not contain the metal chelate. The stationary phase can be used alone to achieve the separation of low molecular weight gases or in series with another column. The metal chelate stationary phase is selective for oxygen and little change in the retention time of oxygen is observed after hundreds of injections over a several-month period, indicating that no appreciable degradation of the stationary phase had taken place under these conditions.

Argon↗
PubMed1984

Chromatographic analysis of organic compounds in the atmosphere.

Fused silica capillary columns with thick films of cross-linked coatings have been used to separate many of the organic compounds that are present in the volatile fraction of automobile exhaust and in ambient air. Techniques have been developed that allow reversible collection and pre-concentration of organic compounds in ambient air on polymeric sorbents with minimal artifacts. The exhaust samples, which are directly injected without pre-concentration on sorbents, contain many of the same organic compounds that are found in sorbent-collected samples of urban ambient air. Similar anthropogenic organic compounds are not, in general, detected (less than 0.02 ppbV) in air samples from remote, rural areas in Colorado.

Air↗
PubMed1984

Direct pharmacologic and osmolal effects of contrast media on the mechanics of heart muscle isolated from cats.

We studied 56 right ventricular papillary muscles isolated from cats to determine whether the direct mechanical effects of contrast media are due to their pharmacologic action or to the hyperosmolality caused by them. A 10% solution of Renografin-76 abruptly decreased force 22% below control, then slowly increased it to 22% above control. To elucidate these changes we also studied: (1) Renografin-60 (lower concentration of diatrizoate); (2) meglumine and diatrizoate; (3) meglumine alone; (4) diatrizoate sodium; (5) ethylene diamine tetra-acetic acid (EDTA) (same concentration as in Renografin-76); (6) sucrose to increase osmolality; and (7) Amipaque (metrizamide), a contrast medium without meglumine or diatrizoate. All solutions containing meglumine, and EDTA alone decreased force. Diatrizoate sodium also decreased force initially, presumably due to the high sodium concentration. Meglumine alone decreased force abruptly and substantially. In contrast, metrizamide and 100 mmol sucrose only increased force. Thus, the abrupt decrease in force was caused by the pharmacologic action of meglumine, EDTA, or high sodium in the contrast media, whereas the slow increase in force was caused by hyperosmolality.

Animals↗
PubMed1984

Ventricular diastolic pressure-volume shifts during acute ischemic left ventricular failure in dogs.

Ischemic left ventricular failure was produced in eight acutely instrumented, anesthetized dogs to study the contribution of changing myocardial compliance and pericardial pressure to shifts in right and left ventricular diastolic pressure-volume relations. Right and left ventricular and pericardial volumes were measured by ungated computed tomography. Cardiac volumes were manipulated by infusion of saline solution, hemorrhage, phenylephrine infusion and, during failure only, nitroglycerin administration. During both control and failure periods, these interventions shifted the left and right ventricular pressure-volume relations by changing pericardial pressure only; that is, these interventions caused no change in the ventricular transmural pressure-volume relation. The induction of failure as such increased pericardial pressure only minimally and did not change the left ventricular or right ventricular transmural pressure-volume relations significantly. Volume loading during the control period caused an apparent pericardial creep which attenuated the pericardial effect on ventricular pressure-volume relations. During failure, volume loading caused an increase of right ventricular volume, but tended to decrease left ventricular volume; this was associated with a leftward displacement of the interventricular septum. In conclusion, in the presence of ischemic left ventricular failure as well as normally, changes in preload, afterload and circulating blood volume shift ventricular diastolic pressure-volume relations by stretching or relaxing the pericardium, thus changing pericardial pressure. In these circumstances, there were no consistent changes in myocardial compliance.

Animals↗
PubMed1983

Influence of atrial systole on the Frank-Starling relation and the end-diastolic pressure-diameter relation of the left ventricle.

The influence of atrial systole on the left ventricular function curve (stroke volume vs end-diastolic pressure or end-diastolic diameter) and on the left ventricular end-diastolic pressure diameter relation was studied in nine anesthetized, open-chest dogs whose atrioventricular (AV) node had been completely blocked. Measurements were made during volume loading with the pericardium closed and opened and during alternate AV sequential pacing (to permit atrial contribution to ventricular filling) and AV simultaneous pacing (to prevent atrial contribution). When the pericardium was closed, withdrawal of the atrial contribution shifted the stroke-volume end-diastolic pressure relation downward, but did not shift the stroke volume-end-diastolic diameter relation, i.e., it reduced stroke volume for a given end-diastolic pressure according to a reduction in end-diastolic volume. The downward shift of the stroke volume-end-diastolic pressure relation was caused by an upward shift of the end-diastolic pressure-diameter relation, which, for a given end-diastolic pressure, resulted in a smaller end-diastolic diameter and, thus, in a smaller stroke volume. The reason for the upward shift in the end-diastolic pressure-diameter relation was that the atrium remained full and thus increased pericardial pressure by increasing pericardial volume. Opening the pericardium shifted the end-diastolic pressure-diameter relation downward and to the right, shifted the stroke volume-end-diastolic diameter relation upward and abolished the effect of withdrawal of the atrial contribution on these curves. We conclude that in the presence of an intact pericardium, atrial systole shifts the stroke volume-end-diastolic pressure relation because it shifts the end-diastolic pressure-diameter relation and it improves left ventricular performance by increasing preload.

Animals↗
PubMed1982

Measurement of coronary sinus blood flow by fiber-optic laser Doppler anemometry.

The Doppler shift of a laser has been used to measure the velocity of blood in the coronary sinus of the dog. The laser was delivered along a fine fiber-optic probe, which was also used to receive the reflected light. The Doppler shift was measured from the output of a digital spectrum analyzer. This measurement, proportional to the velocity of blood, was correlated with the blood flow measured by an electromagnetic flowmeter. Studies were performed on 112 successful maneuvers in eight consecutive anesthetized dogs. In the minimally damped electromagnetic flow traces, the correlation between coronary sinus blood flow velocity and coronary sinus blood flow was high (r greater than 0.95). This measurement will give absolute flow values only if the exact dimensions of the coronary sinus are known. The linear relationship of coronary sinus velocity and flow supports the postulate that coronary sinus dimension remains similar during normal and high flows. This technique, fiber-optic laser Doppler anemometry, is an accurate measure of relative coronary sinus blood flow. It is suitable for use in human coronary sinuses, especially to monitor the effect of interventions.

Animals↗
PubMed1982

Verapamil preserves myocardial contractility in the hereditary cardiomyopathy of the Syrian hamster.

We attempted to alter the inherited myocardial damage and loss of contractility of the cardiomyopathic Syrian hamster (strain U-MX7-1) by giving cardiac drugs that altered intracellular calcium and myocardial workload. Thirty-seven 21-day-old cardiomyopathic and thirty-seven 21-day-old normal hamsters were divided into five groups each: verapamil-, propranolol-, digoxin-, hydralazine-, and saline-injected. On their 90th day of life, the hamsters were killed. Of the five cardiomyopathic groups, only verapamil reduced myocardial damage. When both "control" and cardiomyopathic hamsters were treated with saline, digoxin, or propranolol, the cardiomyopathic hamsters had significantly less contractile force, maximal rate of force development, and maximum velocity of unloaded shortening. When both groups were treated with verapamil or hydralazine, there were no significant group differences in the indices of contractility. However, when saline-treated cardiomyopathic hamsters were compared with drug-treated cardiomyopathic hamsters, only verapamil preserved myocardial contractility. There was also a weak correlation between the Vmax and the actin-activated ATPase activity of the cardiomyopathic hamsters (r = 0.63, P less than 0.001). We conclude that verapamil helped protect the myocardium of genetically cardiomyopathic hamsters against structural damage, and helped preserve myocardial contractility.

Actins↗
PubMed1977

Environmental trace analysis of organics in water by glass capillary column chromatography and ancillary techniques. Products of ozonolysis.

A method employing a polymeric sorbent has been used for analysis of volatile organic components in water. Trace level organics are sparged from water with nitrogen gas and are concentrated on Tenax GC prior to analysis with either flame ionization gas chromatography or gas chromatography-mass spectrometry. Glass capillary columns were used to obtain maximum resolution of chromatographic peaks. Specifically, the method has been applied to a qualitative and quantitative study of the products which result from ozonization of secondary treated domestic wastewater. The principal volatile products of ozonolysis are n-hexanal, n-heptanal, n-octanal and n-nonanal. Representative samples contained 0.7 ppb** of n-heptanal and less than 1 ppb of any of the volatile compounds.

Chromatography, Gas↗
PubMed1976

Microdetermination of nitrates and nitrites in saliva, blood, water, and suspended particulates in air by gas chromatography.

A generally applicable method for the analysis of nitrates and nitrites has been used for a wide variety of samples, including human saliva, blood, drinking water, and airborne particulates. Aqueous nitrate ion is first converted to nitrobenzene by reaction with benzene (or another aromatic reactant) in the presence of a catalyst. The nitrobenzene is then quantitated by electron capture gas chromatography (GC-ECD). Nitrite ion and gaseous oxides of nitrogen can be determined also if such samples are treated appropriately prior to CG-ECD analysis. Other reactants such as 1,3,5-trimethoxybenzene can also be used in the place of benzene. The high sensitivity of ECD allows the quantitation of as little as 0.1 ppm (w/w) nitrate in a single drop of saliva or blood.

Adsorption↗
PubMed1975

Analysis for aqueous nitrates and nitrites and gaseous oxides of nitrogen by electron capture gas chromatography.

A highly sensitive gas chromatographic method is presented for the determination of aqueous nitrates. By suitable chemical pretreatment, this method is also applicable to the analysis of aqueous nitrites and gaseous oxides of nitrogen. The method has been applied to the analysis of drinking water, urine, and nitric acid. The technique involves the conversion of the nitrate ion to nitrobenzene with subsequent analysis by electron capture gas chromatography. The detection limit for nitrobenzene is ca. 10(-12) g, making possible the analysis of environmentally significant concentrations of aqueous nitrates and nitrites and gaseous oxides of nitrogen.

Chromatography, Gas↗