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Results for “Theoretical Effectiveness”

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At least 19 recordsLinked to original sources
PubMed1991

Temperature dependence of led and its theoretical effect on pulse oximetry.

Ambient temperature is known to affect the emission spectrum of a light-emitting diode (LED). This study has investigated the effect of changes in ambient temperature on the emission spectra of two LED with peak emission wavelengths similar to those used in pulse oximetry. There was a 5.5-nm increase in the peak wavelength for a 660-nm LED, and a 7.8-nm increase in the peak wavelength for a 950-nm LED as temperature increased from 0 to 50 degrees C. Using a simple theoretical model based on the Beer-Lambert law, the effect of these shifts in wavelength on pulse oximeter accuracy was examined and found to be negligible over the temperature range studied.

Electrodes↗
PubMed1990

Prediction of antibiotic dosing intervals from in vitro susceptibility, pharmacokinetics and post-antibiotic effect: theoretical considerations.

Because of the complexity of determining minimum inhibitory concentration (MIC) values on multiple drugs in routine laboratories, susceptibility testing has been designed to generate 2 or 3 broadly-predictive susceptibility categories: susceptible, (intermediate), and resistant. In contrast, recent dosing studies in vivo have shown that for some antibiotics optimum efficacy is best predicted by time above the known MIC and any postantibiotic effect (PAE). It is possible that the optimum dosing interval can be approximated by the sum of the time greater than MIC and the duration of PAE. PAE is known to be related to AUC of drug concentration and time of exposure. Formulae are presented that should make it possible to calculate the optimum dosing interval mathematically by knowing (i) the drug's pharmacological parameters and dose, (ii) the organism's MIC and (iii) the relationship between AUC and PAE for the drug-organism combination. Both (i) and (iii) are predetermined values obtained from studies. For some bacterial species, isolates in the susceptible range have very similar MICs (narrow range) and the MIC is therefore reasonably predictable. However, for other species, the precise MIC needs to be measured to perform the calculations. Examples of the application of these formulae are given.

Animals↗
PubMed1989

Theoretical effects of single and multiple transducer receptor coupling proteins on estimates of the relative potency of agonists.

A mathematical model is presented that simulates the steady state kinetics of agonists interacting with a promiscuous receptor. The model system consists of a single receptor that forms a ternary complex with either of two transducer proteins (G proteins). At a given agonist concentration, the concentrations of the two ternary complexes are determined by the relative quantities of the two G proteins and the ratio of the dissociation constants for the two ternary complexes. Accordingly, the potency of an agonist is dependent upon the relative quantities of the G proteins. If receptors are truly promiscuous and if the distribution of G proteins varies with tissue type, then the agonist potency ratio would be tissue dependent as well as receptor dependent. Experimental data from literature studies are reviewed in the context of the promiscuous receptor model, and implications of the model regarding pharmacologic classification of receptors are discussed.

GTP-Binding Proteins↗
PubMed1990

List-strength effect: II. Theoretical mechanisms.

Ratcliff, Clark, and Shiffrin (1990) examined the list-strength effect: the effect of strengthening (or weakening) some list items upon memory for other list items. The list-strength effect was missing or negative in recognition, missing or positive in cued recall, and large and positive in free recall. We show that a large number of current models fail to predict these findings. A variant of the SAM model of Gillund and Shiffrin (1984), involving a differentiation hypothesis, can handle the data. A variant of MINERVA 2 (Hintzman, 1986, 1988) comes close but has some problems. Successful variants of a variety of composite and network models were not found (e.g., Ackley, Hinton, & Sejnowski, 1985; Anderson, 1972, 1973; Metcalfe Eich, 1982; Murdock, 1982; Pike, 1984). The results suggest constraints on the future development of such models.

Cues↗
PubMed1975

Contrast sensitivity in humans with abnormal visual experience.

1. Grating contrast sensitivities have been determined over a range of spatial frequencies for a normal subject and for subjects who are visually biased in that they have a lower resolution capacity for targets of specific orientations. The bias si only found in astigmatic subjects and the grating orientation yielding poorest acuity coincides with the most defocused astigmatic meridian. However this resolution anisotropy remains when optical factors are accounted for. 2. For the normal subject, high and low frequency attenuation is found and a typical reduction in contrast sensitivity is exhibited for oblique target orientations. 3. The biased subjects, called meridional amblyopes because they have reduced acuity for a given grating orientation, show markedly abnormal contrast sensitivity functions. Their cut-off spatial frequencies are different for various target orientations and this difference applies also to contrast sensitivity over nearly the entire spatial frequency range tested (0-5-16 cycles/deg). The differences are of about the same magnitude for most frequencies and they are found in all types of meridional amblyopes. 4. Optical explanations of these differences are ruled out by laser-interference fringe tests and by varying effective pupil size. 5. Theoretical effects of defocus have been calculated to compare predicted visual deprivation with performance. Results indicate that reduced contrast sensitivity functions can be equivalent to a small defocus effect. 6. To examine the results in the spatial domain, inverse Fourier transforms of representative contrast sensitivity functions have been computed. The optical portion of the resulting spatial weighting functions has been parcelled out to obtain neural spatial weighting functions.

Amblyopia↗
PubMed1992

Is natriuresis on felodipine due to reversal of the renal effects of angiotensin II?

Felodipine induces natriuresis, possibly by renal hemodynamic and/or tubular effects. Theoretically, reversal of the sodium-retaining effect of angiotensin II (Ang II) could be involved. Therefore, we administered felodipine during Ang II infusion and during suppression of endogenous Ang II production in two double-blind studies in healthy volunteers. First, a gradually increasing dose of Ang II was infused during felodipine or solvent infusion. Before starting Ang II, felodipine had lowered renal vascular resistance (RVR) and filtration fraction (FF), and simultaneously increased CNa. The Ang II induced rise of mean arterial pressure (MAP) and renal vasoconstriction was partly antagonized and the falls in glomerular filtration rate (GFR) and CNa completely abolished by felodipine. The combination of felodipine and 3.0 ng/kg/min Ang II even enhanced natriuresis. Second, felodipine or solvent was infused after one week of pretreatment with placebo or the angiotensin converting enzyme (ACE) inhibitor ramipril, which reduced MAP and induced renal vasodilatation. Ramipril pretreatment did not influence significantly the blood pressure reduction, renal vasodilatation, and natriuresis caused by felodipine. In conclusion, it seems unlikely that the natriuretic effect of felodipine is due to interference with renal effects of endogenous Ang II. The fact that felodipine reverses sodium retention on exogenous Ang II may be explained by interference with systemic and renal hemodynamic effects of exogenous Ang II.

Adult↗
PubMed1978

Enhancement of air filtration using electric fields.

Although polarized electrostatic air filters are efficient air filtrating devices, their main disadvantages are difficulty in collecting conductive particles or in operating at relative humidities above 70%. We describe here a new filter design that eliminates these problems. A nonconductive media, normally a glass fiber mat, is placed between two insulated conductive screens. As the voltage across the screens is increased, the penetration of particles decreases exponentially. Increasing the electric field from 0 to 10 kV/cm will decrease the mass penetration from 60% to less than 10% of a polydispersed 0.8 micrometer ammd(sigma g = 2.0) sodium chloride aerosol. The experimental effects of face velocity, particle charge and size, packing density, fiber size, and screen insulation mirror the theoretical effects of these variables on particle penetration.

Air Conditioning↗
PubMed1991

Motivation to comply with infection control procedures.

This paper addresses the critical issue of motivating hospital staff to comply with standard infection control procedures. Previous psychological assessment of infection control knowledge, attitudes and behaviour has indicated that the reasons for non-compliance are very basic and reflect inter alia a low perception of the importance of the measures and a lack of motivation. It is argued that, although staff have a theoretical awareness of the value of complying with such procedures, in practice these seem to have a low priority. Compliance levels, therefore, are variable and generally of a low order. If recent advances in the fields of social psychology, behavioural psychology and clinical psychology could be imported to hospital medicine, they could have a dramatic impact in infection control. The Elaboration Likelihood Model, an effective theoretical approach to message-based persuasion, and the energizing effects of intrinsic and extrinsic motivational processes are defined. Finally, the implications of these concepts for persuasive intra-hospital communication in infection control are highlighted. They can provide a framework for developing effective infection prevention programmes.

Health Knowledge, Attitudes, Practice↗
PubMed1992

Effect of age on ibuprofen pharmacokinetics and antipyretic response.

The effect of age on ibuprofen pharmacokinetics and antipyretic effect was studied in 49 infants and children aged 3 months to 10.4 years. The relationship of plasma concentration to antipyretic effect was examined in 38 of the children by using an iterative least squares technique that allows estimation of drug concentration with time in a theoretical effect compartment and rate constant for elimination of drug from the effect compartment. There was a delay of 1 to 3 hours between peak ibuprofen plasma concentration and peak temperature decrement. The mean elimination rate constant from the effect compartment was 0.6 hour-1, corresponding to a half-life of drug in the effect compartment of 1.1 hours. The mean slope of the effect compartment concentration versus temperature regression line was -0.242 degrees C/mg per liter. Age did not significantly influence the rate of absorption of ibuprofen, its plasma concentration, its rate of elimination, or the time course of ibuprofen concentration in the effect compartment. However, in younger children the onset of antipyresis was earlier, maximum antipyretic effect was greater, and the area under the curve of the percentage of change in temperature from baseline versus time was greater than in older children. We conclude that the greater relative body surface area in younger children may allow more efficient dissipation of heat in response to antipyretic-induced lowering of the temperature "set point" in the hypothalamus.

Acute Disease↗
PubMed1991

The doctrine of double effect: reflections on theoretical and practical issues.

The Doctrine of Double Effect and the Principle of Do No Harm raise important theoretical and practical issues, some of which are discussed by Boyle, Donagan, and Quinn. I argue that neither principle is correct, and some revisionist, and probably nonabsolutist, analysis of constraints on action and omission is necessary. In making these points, I examine several approaches to deflection of threat cases, discuss an argument for the permissibility of voluntary euthanasia, and present arguments relevant to medical contexts which justify intentionally harming some to aid others, with and without the consent of those harmed.

Bioethical Issues↗
PubMedDate not supplied

The effect of digital unsharp-mask filtering on the signal-to-noise ratio in computed radiography.

The effect of image processing in computed radiography (CR) has been analyzed in many ROC studies. The results have not shown great diagnostic improvements, except in some special occasions. The theoretical effect of image enhancement on the signal-to-noise ratio in CR images has so far not been assessed. Concerning the previous results, the changes induced in the signal-to-noise ratio by digital image processing are certainly of interest. We calculated the signal-to-noise ratio in various conditions according to the principles of the Rose model, using the computerized image data of storage phosphor radiography. Seventy-seven computed radiographs processed by Gaussian unsharp-mask filtering using different kernel widths were analyzed. The signal-to-noise ratio was reduced in all images by more than 40% when the smallest kernels were used, and increased slowly towards the original value with greater kernel sizes. In no conditions did the ratio exceed the original one. The results show that although edges and signal contrast can be enhanced by unsharp-mask filtering, this happens at the cost of increased noise. This might at least in part explain why image processing does not significantly improve the diagnostic information content of a computed radiograph.

Filtration↗
PubMed1989

[A method for evaluating the hepatitis B vaccination program].

Two mathematical models have been created in order to estimate the effectiveness (number and proportion of infections saved) and the cost/effectiveness ratio (cost per infection saved) of a hepatitis B vaccination strategy among hospital personnel. The aim of the models is to analyse the mathematical relationship between the measurement of strategy impact and some variables: theoretical effectiveness of vaccine, proportion of assent to the programme, epidemiological characteristics. Applying models to Piedmont situation it has been possible to identify factors which have negatively influenced the effectiveness and efficiency of strategy.

Cost-Benefit Analysis↗
PubMed1992

How to evaluate class III antiarrhythmic drug efficacy clinically: the benefits and shortcomings of the noninvasive approach.

Holter monitoring is the most commonly used noninvasive method for assessing antiarrhythmic drug therapy. It can easily be performed and we know the exact criteria for the definition of drug efficacy and the proarrhythmic effect. However, the value of Holter monitoring to predict clinical outcome in patients with malignant ventricular arrhythmias is controversial. Several authors claim that Holter monitoring is useless to evaluate antiarrhythmic drug effects. Theoretical considerations will explain that it is not the technique by itself that is useless; it is the way it is applied. Merely by changing the efficacy criteria, the value of Holter monitoring to assess antiarrhythmic effects can be improved significantly. Nevertheless, Holter monitoring is far from being the ideal method. It focuses only on arrhythmia density, denying that other risk factors such as heart rate variability, ischemia, and QT changes may be of additional prognostic value. Further studies with Holter monitoring should concentrate on the role of these parameters.

Anti-Arrhythmia Agents↗
PubMed1992

Bronchodilatory activity and pharmacokinetics of new xanthines in guinea-pigs.

1. The in vitro biological activities and the effect of protein binding on the relaxant effects in vivo of N-3-alkylxanthine and N-3-alkyl-N-1-methylxanthine derivative were investigated in guinea-pigs. 2. A significantly positive correlation was observed among the in vitro muscle relaxant activity, the cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) inhibitory activity and the protein-binding potency of xanthine derivatives. However, there was a weak relationship between these activities and affinity for adenosine receptors. 3. When theophylline, enprofylline and 1-methyl-3-propylxanthine (MPX) were injected intravenously in guinea-pigs, their ED50 values were 6.1, 3.3 and 1.0 mg/kg, respectively. Plasma concentrations of these drugs obtained following the intravenous injection of the ED50 approximated the theoretically effective concentration (EC50) predicted from both the relaxant effects in vitro and the protein binding parameters. A good linear correlation was observed between bodyweight in four species (rats, guinea-pigs, rabbits and humans) and certain pharmacokinetic parameters of enprofylline and theophylline. 4. The present study indicates that differences in the relaxant effects of these drugs in vitro and in vivo can be explained in part by protein binding, and that the protein binding of these xanthine bronchodilators is an important determinant for their pharmacological activity. Guinea-pigs provide a useful model for studying pharmacodynamic-pharmacokinetic relationships of new bronchodilators.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMedDate not supplied

Selecting the optimum method of contraception for each patient.

The factors relating to the choice of the optimal method of contraception are discussed, indicating the wide range of variables which must be evaluated. Religious, cultural, educational and social factors are considered, as well as age and family size. Facts elicited through discussion of general medical, family, obstetric and menstrual histories help to indicate the advantages and disadvantages of available methods. The influences of the doctor, relatives, friends, and publicity are shown to affect the patient's choice and indicate that the theoretical effectiveness of a particular method forms only one part of a complex situation.

Contraception↗
PubMed1990

Effect of carbon dioxide flow-rate on the separation of triacylglycerols by capillary supercritical fluid chromatography.

Triacylglycerols (TAGs) were separated using capillary supercritical fluid chromatography at various carbon dioxide densities and flow-rates at 150 degrees C. The flow-rate was controlled with integral restrictors made directly at the end of the column. With a 50 microns I.D., df 0.20 micron, DB-5 [(95%)dimethyl(5%) diphenylpolysiloxane] column, separation numbers (Tz) of up to one per one triacylglycerol carbon number difference per metre were achieved at a practical optimum carrier flow-rate at 0.3-0.4 cm/s. Height equivalent to an effective theoretical plate-average linear carrier velocity-triacylglycerol carbon number three-dimensional plots at different pressures are presented.

Carbon Dioxide↗