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Biomedical subjects

R Low

Publications and source records attributed to R Low.

32 records · Page 2Linked to original sources
PubMed1983

Circadian rhythm of hourly ventricular arrhythmia frequency in man.

Three twenty-four hour electrocardiographic recordings from 164 untreated patients were analyzed. A clear, statistically significant, diurnal pattern in hourly ventricular arrhythmia frequency was found. It was consistent across days and between seven diagnostic groups. A high frequency Noon to 4:00 PM peak contrasted with a low frequency 1:00 AM to 5:00 AM trough with zero hourly frequencies not uncommonly present. These findings appear applicable to large ambulatory populations and may well influence the design of future investigations of modalities which alter ventricular arrhythmia frequency.

Aged↗
PubMed1982

Auditory evoked potentials compared to performance measures and EEG in assessing excessive daytime sleepiness in narcolepsy-cataplexy.

The AEP to the repetitive stimuli of the Wilkinson auditory vigilance task was compared between untreated patients with narcolepsy-cataplexy and matched controls for periods during which the tones were preceded by 13 sec or more of wakefulness (defined by EEG-polygraphic criteria). During these periods it had been found previously that narcoleptics did not perform worse than did controls. The AEP, nevertheless, showed significant differences for narcoleptics. These were similar to changes described for drowsiness in normals. The AEP, therefore, showed changes related to excessive day time drowsines in narcolepsy-cataplexy when a sensitive performane measure and visual analysis of EEG-polygraphic recordings did not.

Adult↗
PubMed1982

Thermodynamics of mixing of dipalmitoyl phosphatidylcholine and egg phosphatidylcholine in hydrated bilayers.

Dipalmitoyl phosphatidylcholine (DPPC) and egg phosphatidylcholine (egg PC) are not completely miscible at all temperatures. Their phase diagram was determined by differential scanning calorimetry (DSC) of aqueous mixtures of the two. From the integrated DSX curves we obtained the enthalpy of solution of DPPC in egg PC delta hs, as a function of the mole fraction of DPPC, X, and using the empirical relationship between delta hs and X, the solubility Xsat as a function of temperature, T. The latter could be described by the semiempirical relationship: R1nXsat = a + blnT - c/T, where a = 6.57 X 10(-2) kcal.mol-1. degree -1 and c = 20.5 kcal. mol-1 (1 cal = 4.1868 J); the coefficient b was very small and could be ignored. The quantity delta hs can be given as XdeltahDPPC + deltah mix, where deltah DPPC is the gel - liquid crystalline transition enthalpy of DPPC (8.74 kcal.mol-1) and deltah mix is the enthalpy of mixing the two liquid crystalline lipids. Deltahmix depends on X in approximately a parabolic fashion, having a maximal value of 4.8 kcal.mol-1 at X = 0.6. It was shown that both the solubility and mixing enthalpy data can be described by the theory of regular solutions (RST). In RST, the activity coefficient of the solute (component 2) of a binary solution is given by RTIngamma 2 = (1 - Theta2)2deltaU, while the mixing enthalpy is given by delta hmix = Theta1 Theta2 delta U/v2, where Theta1 and Theta2 are the volume fractions of solvent and solute (egg PC and DPPC, respectively), v2 is the partial molar volume of DPPC, and deltaU is the energy change per mole on interchanging a DPPC and an egg PC molecule between their respective liquid crystalline phases. The thermodynamic data are accurately described by RST, the molar volume of DPPC being found to be about half that of egg PC solution and the interchange energy deltaU having a value of 10-11 kcal.mol-1. There was some evidence that deltaU may be an increasing function of temperature. The large value of the deltaU accounts for the pronounced temperature dependence of the solubility Xsat, which decreases from 0.35 at 35 degrees C to 0.02 at 10 degrees C. The presence of cholesterol in the mixtures decreases both the transition enthalpy of DPPC and the mixing enthalpy in a linear fashion, so that deltahs is zero at Xcholesterol greater than or equal to 0.2. The results are consistent with recent data including the formation of a PC-cholesterol complex oc stoichiometry approximately 4:1.

Animals↗
PubMed1981

Efficacy of percutaneous transluminal coronary recanalization utilizing streptokinase thrombolysis in patients with acute myocardial infarction.

Since coronary thrombosis is a principal factor in the evolving necrotic process in the majority of patients with acute myocardial infarction (AMI), a prospective study was conducted in 25 AMI patients who underwent expeditious coronary arteriography. Of these patients, 22 with totally occluding thrombus also received early streptokinase (STK) administration. STK was given by intracoronary (20 patients) or systemic (two patients) infusion, 2000 to 50,000 IU/min, to a total dose of 125,000 to 500,000 IU within 10 hours of AMI symptom onset. Eighteen patients had angiographically visualized successful coronary thrombolysis; the shorter the interval between onset of symptoms to treatment, the more rapid was the clot dissolution. Successful thrombolysis occurred concomitantly with readily managed reperfusion ventricular tachyarrhythmias in nearly all patients. In addition, STK recanalization resulted in relief of ongoing chest pain in 10 of 12 patients, 10 of 16 evidenced immediate normalization of hyperacute ST segment abnormalities, and 8 of 14 demonstrated subsequent improvement of angiographically visualized left ventricular (LV) ejection fraction. In the percutaneous transluminal coronary recanalization (PTCR) procedure, the step of using a soft-tipped guide wire itself was transiently useful in only one of seven patients in whom this was attempted; reocclusion took place without added STK therapy. Nitroglycerin (NTG) alone produced only slight distal patency in but 1 of 19 patients with coronary occlusion given the nitrate. Importantly, in 14 control AMI patients receiving conventional treatment without STK, 10 showed angiographically complete occlusion of the coronary artery supplying the infarct region 1 month after infarction, thereby excluding spontaneous clot lysis mimicking STK-PTCR-induced reperfusion. These data support the concept that coronary occlusion by thrombosis is inherently involved with AMI and that rapid PTCR application of intracoronary STK provides potent thrombolysis, superior to that provided by NTG and guide wire passage in reestablishing coronary flow with attendant salvage of jeopardized myocardium and with subsequently improved LV function.

Adult↗
PubMed1981

Intra-aortic balloon counterpulsation: rationale, application and results.

Intra-aortic balloon counterpulsation is an effective means of reducing myocardial ischemia and supporting the failing circulation. Its therapeutic benefits are the direct result of distolic augmentation and systolic unloading, the former increasing myocardial perfusion and the latter enhancing cardiac performance. Indirect effect include diminution of ischemia by decrease in the determinants of myocardial oxygen demand and improved ventricular function secondary to the decreased ischemia. Intra-aortic balloon counterpulsation is indicated in clinical syndromes related to intractable cardiac ischemia, including myocardial infarction shock and severe left ventricular failure, refractory ischemic pains, and ventricular arrhythmias unresponsive to medical management. It is also of importance in other situations associated with low cardiac output. This therapeutic modality has recently been considered for early use in extensive myocardial infarction to limit cardiac damage and avert complications. Recent technical advances have facilitated the ease and safety of application of intra-aorta balloon counterpulsation. Complication are of low frequency but can be serious and employment of the method is predicated upon consideration of both potential benefits and risks.

Acute Disease↗
PubMed1980

Effects of oral pentaerythritol tetranitrate in cardiac failure and angina pectoris. Assessment by hemodynamic measurement and exercise capacity.

Oral pentaerythritol tetranitrate produces sustained beneficial hemodynamic effects in patients with cardiac failure of varied etiology. The principle action is a reduction of elevated left ventricular filling pressure. In a small group of angina patients, the oral nitrate in high dosage resulted in considerable increase in angina-limited exercise capacity compared to placebo for four hours following drug administration. No side effects were associated with ingestion of pentaerythritol tetranitrate in these investigations.

Administration, Oral↗
PubMed1980

Heterogeneous catalysis by phospholipase A2: mechanism of hydrolysis of gel phase phosphatidylcholine.

Hydrolysis of gel phase dipalmitoylphosphatidylcholine (DPPC) at 37 degrees C catalysed by Crotalus atrox phospholipase A2 (PLA) is described extremely well by the "path 1" kinetic mechanism of Tinker and Wei (1979) (Can. J. Biochem. 57, 97-106), if reversible adsorption is allowed as a side reaction. Progress curves show an initial rapid phase, the initial velocity being a Michaelis-Menten function dependent on the catalytic properties of the enzyme (kcat approximately equal to 9200 min-1, Km approximately equal to 0.12 mM), then level off to a slower rate determined by the desorption equilibrium constant (KD approximately equal to 0.01 mM) and desorption rate constant (kD approximately equal to 0.15 min-1). The relaxation time, tau, for the transition to the desorption-limited reaction is approximately 0.5 min; this large value of tau probably arises from a slow conversion of active, dimeric enzyme to an inactive protein species adsorbed to the lipid surface. At later times in the reaction there is an increase in the rate of hydrolysis, attributed to a stimulation of desorption by the products. The desorption equilibrium constant KD is a quadratic function of the surface concentration of products and increases 20- to 30-fold when all accessible substrate is hydrolysed. Both lysophosphatidylcholine (lyso-PC) and fatty acid were found to stimulate the desorption, but lyso-PC was also found to be a competitive inhibitor of the catalysis. Adsorption of PLA to DPPC and egg PC vesicles was directly measured using a gel partition technique. Strong binding to egg PC was observed, which was not dependent on the presence of calcium ion (essential for catalysis); PLA inhibited by acylation of up to four lysine residues per mole of monomeric enzyme with ethoxyformic anhydride was equally strongly adsorbed, indicating that lipid binding is not dependent on catalytic activity. Reaction products greatly weakened the binding of PLA to the lipid surface as expected. Cholesterol had two effects on the hydrolytic reaction: there was a striking decrease in the rate of the slower, desorption-limited phase, the rate of which decrease to almost zero at 15 mol% cholesterol, but there was also evidence for the formation of a complex with stoichiometry 1 cholesterol: 2 DPPC in which DPPC is no longer a substrate for the enzyme. Implications of the proposed mechanism for specificity and control of surface catalysis by PLA are discussed.

Crotalid Venoms↗
PubMed1979

Giant adrenal myelolipoma and testicular interstitial cell tumor in a man with congenital 21-hydroxylase deficiency.

The occurrence of a giant myelolipoma of the adrenal gland reported in a patient with congenital adrenal hyperplasia (21-hydroxylase deficiency). Associated significant findings include a massive proliferation of adrenocortical cells as an integral part of the myelolipoma and coincidental tumor of the interstitial cells of the testis. The clinical, radiologic, endocrinologic, and pathologic features of this case are correlated with a review of the literature. The additional myelolipomas are also reported here for the first time. Similar lesions have been induced experimentally in rats and provide further evidence suggesting a hyperplastic rather than a neoplastic nature for this complex lesion, at least in its earlier stages.

17-Ketosteroids↗
PubMedDate not supplied

CT findings in acute renal cortical necrosis.

Acute renal cortical necrosis has three characteristic findings on contrast enhanced CT: (a) lack of enhancement of the renal cortex, (b) enhancement of the renal medulla, and (c) absent renal excretion.

Adult↗