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PubMed1979

Information content of the multibreath nitrogen washout.

The distribution of ventilation per unit volume (Va/Vol) in the lung is often studied using the multibreath N2 washout test. Most approaches have focused on the determination of a single Va/Vol distribution (consisting of from two compartments to a continuum) compatible with the data, but because the potential number of lung units greatly exceeds the number of breaths measured, many distributions are usually compatible with a given set of washout data. Interpretation of single distributions therefore requires evaluation of the variability among all such compatible distributions. The technique of linear programing is well suited to evaluation of these compatible distributions and its application to the N2 washout is explained. Twelve examples of washout data are analyzed in this way. The results indicate that using the first 20 or so breaths of the washout, narrow distributions of Va/Vol are well specified. Distributions with up to four distinct modes are also well specified, but for broad distributions the shape cannot be adequately defined. Good resolution in the region of high Va/Vol is found to be critically dependent on measuring the first few breaths of the washout.

Computers↗
PubMed1983

A simple model of VA/Q distribution for analysis of inert gas elimination data.

A general procedure for fitting compartments models of alveolar ventilation-perfusion ratio (VA/Q) distribution to inert gas elimination data is described. The method can be applied to any model consisting of a number of compartments ventilated and perfused in parallel, each compartment of the model having a fixed predetermined VA/Q ratio. The number of compartments and their VA/Q ratios required for adequately fitting real data have been examined. A 13-compartment model consisting of a shunt, a dead space, and 11 compartments equally spaced on a logarithmic scale from VA/Q of 0.01 to 100 was found to be suitable. The fitting procedure and the 13-compartment model form the basis of a method of analysis of inert gas elimination data. Essentially the method consists of calculating a sample of 30 distributions compatible with the data analyzed taking into account experimental errors in the inert gas measurements. From this sample, the averages and standard deviations of the flows to 13 zones on the VA/Q scale are estimated. The averages are estimates of the true flows to these zones, and the standard deviations give an indication of the range of flows compatible with the data. The method has some advantages over both the enforced-smoothing approach and the Monte Carlo linear programming scheme of Evans and Wagner (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42: 889-898, 1977).

Computers↗
PubMed1984

Sensitivity and specificity of the computational model for maximal expiratory flow.

The computational model for forced expiratory flow from human lungs of Lambert and associates (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 44-56, 1982) was used to investigate the sensitivity of maximal expiratory flow to lung properties. It was found that maximal flow is very sensitive to recoil pressure and airway areas but not very sensitive to lung volume, airway compliance, and airway length. Linear programming was used to show that a given air flow-pressure curves was compatible with a fairly wide range of airway properties. Additional data for maximal flow with a He-O2 mixture narrowed the range somewhat. It was shown that the flow-pressure curve contains more information about central than peripheral airways and that information about the latter is obtainable only from flows at recoils less than 2 cmH2O. Parameter ranges compatible with individual flow-pressure curves showed differences that demonstrated that such curves give some indication of individual central airway properties.

Airway Resistance↗
PubMed1990

Feed intake, weaning weight and net returns comparisons for four breeding systems.

Feed intake, weaning weight and direct and maternal contributions to weaning weight were estimated for four breeding systems using data collected between 1979 and 1986 from 773 cow-calf pairs at the Elora Beef Research Centre. Breeding systems included purebred Hereford (HE), small rotational dual purpose (SR) (a four-way rotational crossing system utilizing Tarentaise, Angus, Gelbvieh and Pinzgauer breeds), large rotational beef (LR) (composed of Maine-Anjou, Simmental and Charolais) and Angus-sired large rotational beef (AL) utilizing Angus as the sire breed and LR as the maternal breed. Large rotational dams had the highest feed intakes for both dry (8.9 kg DM/d) and lactation (11.5 kg DM/d) periods. Conversely, HE calves consumed the greatest amounts of creep feed (309 kg DM), followed by AL, SR and LR. The large rotational system had the highest weaning weights (265 kg) and direct (12.3 kg greater than average of observations) and maternal (9.6 kg greater than average of observations) contributions to weaning weight, followed by AL, SR and HE for all three traits. An equation was derived for net returns that included parameters for feed intake and direct and maternal weaning weight. A linear programming model was designed to incorporate this equation as the objective function and determine the breeding system(s) that maximized net returns under various production conditions. In general, LR produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size) included in the model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Influence of variations in biological and economical parameters on beef production net returns.

Net returns were defined as a function of the monetary returns (revenue) generated by the outputs less the monetary costs generated by the variable inputs. Outputs included total weaning weights of steers and heifers, weight of cull cows and weight of open heifers. Inputs included both feed and nonfeed costs. The net returns equation was incorporated as the objective function in a linear programming model. By maximizing the objective function, the breeding system that generated the highest net returns could be identified considering certain resource constraints. Breeding systems included purebred Herefords; small rotational dual purpose (SR), utilizing the breeds Angus, Pinzgauer, Gelbvieh and Tarentaise; large rotational (LR), a three-way rotational cross with the breeds Charolais, Simmental and Maine-Anjou; and Angus-sired terminal (AL) utilizing Angus as the sire breed and LR heifers as the maternal breed. Large rotational generally produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size), calving rates, management systems, environment, beef to feed price ratios and purchased or farm-produced (inexpensive) feed utilized. Only under the conditions of a herd size constraint and farm-produced feed did AL exceed SR in net returns. Hereford had larger net returns than LR only when the two breeding systems were evaluated in an environment assumed to be reproductively stressful to LR. Ranking of breeding systems were dependent on specific conditions and indicated that one must consider each resource constraint and environment in which cattle are expected to produce before making breeding system recommendations.

Animal Feed↗
PubMed1991

A Markovian decision model for beef cattle replacement that considers spring and fall calving.

In certain production environments, beef cows are mated during a breeding season that starts in early summer. Cows found not to be pregnant at the end of the breeding season could either be culled or retained and remated the following summer. Alternatively, nonpregnant cows could be mated in the winter. This option would result in having both a spring and a fall calving herd. The purpose of our study was to determine the optimal replacement policy (maximizing long-run average net returns) for a specific production environment by determining for each age of cow, reproductive status (nonpregnant or pregnant), and season of pregnancy checking (spring or fall) whether the cow should be retained to the next breeding season (summer or winter) or be replaced by a pregnant heifer. The problem was formulated as a Markovian decision process and the optimal policy was found by linear programming. The optimal policy was one in which nonpregnant cows were always culled and replaced by heifers in the summer breeding herd, resulting in spring calving only.

Animals↗
PubMed1975

Rumen modeling: rumen input-output balance models.

Two models of rumen fermentative relationships expressed as systems of simultaneous linear equations and based on requirements for maintenance of balances of elementary imput and output and metabolic pathways are presented in matrix format consistent with solution by linear programs. Matrix entries defining the two models were verified carefully based upon a survey of the literature, and conceptual bases of the models were validated by comparisons of model outputs with experimental data not used in model construction. The models then were used to evaluate interactions among feed composition, volatile fatty acid yields and patterns, microbial growth yields and efficiencies, and microbial metabolic pathways.

Amino Acids↗
PubMed1983

Selecting groups of sires by computer to maximize herd breeding goals.

A computerized linear program, MAXBULL, selects sires for dairymen to obtain maximum Predicted Difference milk while maintaining other goals. Goals are minimum average Predicted Differences fat percent and type, six individual type traits, and maximum average semen price. Individuals traits for bulls are coded +1, 0, -1 according to evaluations from breed associations. Dairymen restrict bulls offered to the program by specifying unacceptable repeatability, Predicted Differences, and price. They further control breed, stud organizations, minimum bull numbers, use of sires with low repeatability (less than 50%) and without type proofs, and maximum use of specific bulls and sons of sires. Goals for individual type are specified as the percentage of cows in the herd needing improvement in each trait. The solution contains at least that percentage of semen from sires coded +1 in each trait. The dairyman receives a count of bulls surviving each of his edits, a reiteration of his goals, a list of recommended units and all information for each sire, averages for all traits weighted by the units recommended, and the expected increase in Predicted Difference milk from relaxing each goal one unit. MAXBULL has led to individualized breeding programs characterized by reasonable goals, balance in emphasis among traits, and stability in goals over time.

Animals↗
PubMed1990

Formulation, nutritive value and sensory evaluation of a new weaning food based on sweet corn (Nutrimaiz) dehydrated pulp.

The objective of the present work was to develop a formulation for complementary infant and child feeding employing linear programing as a mathematical model for optimization. High lysine/high tryptophan sweet corn pulp in the dehydrated form was used as the main ingredient. The restrictions imposed on the model were nutrient requirements, adequate protein/energy ratio and minimum cost. The formula derived by the computer (FC) matched the amino acid requirements, the protein/energy ratio (NDPCal%) and was rated high in laboratory tests in terms of sensory qualities. The cost determined for this formula was competitive in relation to commercial products used for the same purpose. Formula A, which contained 5% more sweet corn pulp and 10% less whole powdered milk, did not differ in nutritional, sensorial and functional properties from the formula FC and was chosen for the field acceptability trial because of its lower cost. Formula A had protein efficiency ratio and Biological Value similar to casein for the rat but protein digestibility and net protein utilization were statistically lower (p less than 0.05) for formula A than for casein. Acceptability tested on children who were 8-18 months of age ranged from 80-90%, average value 87%.

Amino Acids↗
PubMed1989

Indirect calorimetry evaluation of dietary protein and animal fat effects on energy utilization of laying hens.

A multichamber indirect calorimeter was constructed and used to measure energy utilization of laying hens. Four basic diets were formulated by a least cost linear program for use in this study. The first diet was formulated to meet the 1984 National Research Council (NRC) recommendations and contained by analysis 14.5% protein, .58% TSAA, and .68% lysine (designated NRC). The second diet (NRCAA) was formulated to the same amino acid specifications without a protein restriction and contained 12.9% protein, .57% TSAA, and .69% lysine. Another pair of diets was formulated with higher protein (HP) and amino acid restrictions. The HP diet contained 16% protein, .67% TSAA, and .85% lysine; whereas the HPAA diet had 14% protein, .68% TSAA, and .86% lysine. Four additional diets were formulated with the inclusion of 3% animal fat, using the same protein and amino acid restrictions as were used to formulate the first four diets. Animal fat supplementation significantly (P less than .05) improved energy balance (retention) of birds fed all formulations compared with the diets without added fat. Formulation of a diet based on amino acid restrictions significantly increased net energetic efficiency of birds fed amino acid levels higher than those recommended by the NRC (79.2 for HPAA vs. 62.1% for HP), but did not significantly affect net efficiency of birds fed the lower amino acid levels (NRC and NRCAA).

Animal Feed↗
PubMed1976

Adrenodoxin reductase-adrenodexin complex.

Adrenodoxin reductase and adrenodoxin have been shown (Chu, J.-W., and Kimura, T. (1973) J. Biol. Chem. 248, 5183-5187) to form a low dissociation constant, 1:1 complex when both proteins are in the oxidized form. We have found that when adrenodoxin: adrenodoxin reductase ratios are varied by increasing the adrenodoxin concentration, with adrenodoxin reductase held constant, an increasing rate of cytochrome c reduction, with NADPH as reductant, is seen up to a ratio of 1:1, indicating that cytochrome c reduction occurs via the protein-protein complex. Spectra observed during titration of this protein-protein complex with NADH were resolved into components by the linear programming method, using a computer program written in Fortran IV. Analysis of the data has shown that the flavoprotein is reduced prior to the iron sulfur protein, and that the midpoint oxidation-reduction potentials (pH 7.5) of the two proteins are -295 and -331 mV, respectively, when both are present in the complex. Complex formation does not alter the potential of adrenodoxin reductase, but changes that of adrenodoxin by -40 mV. Equilibrium constants derived from potential measurements show that the strength of the protein-protein interaction in the complex is unaltered by reduction of adrenodoxin reductase, but is decreased by about 1 kcal due to reduction of adrenodoxin. The low dissociation constants for both oxidized reduced forms of the adrenodoxin reductase-adrenodoxin complex indicate that the complex must remain associated throughout its catalytic cycle. Titration of the adrenodoxin reductase-adrenodoxin complex with the physiologic reductant, NADPH, was followed by EPR and visible spectra, and yielded an order of reduction of the components identical with that seen when NADH was used as reductant. Reduction of the protein-protein complex with NADPH yielded a ternary complex between NADP+, flavoprotein, and iron sulfur protein, with the two electrons located in a "charge transfer" complex between flavoprotein and pyridine nucleotide.

Adrenal Cortex↗
PubMed1990

[The optimization of the dosimetric plan in the intracavity radiotherapy of patients with cancer of the corpus uteri].

The potentialities of mathematical optimization were investigated with respect to dosimetric design of radiation therapy of endometrial cancer patients using AGAT-V and AGAT-VU [correction of Agat-B and Agat-Y] apparatus. The effectiveness of linear programming for creating in a pathological focus and in normal tissues of a dose distribution, meeting clinical requirements to the maximum, was shown.

Brachytherapy↗
PubMed1988

Quantitative management techniques in dietetics: improving practice through technology transfer.

A content analysis of articles appearing chronologically in the Journal of The American Dietetic Association since its inception in 1925 reveals the breadth and depth of management practice in the dietetic profession. This historical review highlights the introduction, demonstration, and adoption of management tools and techniques in the profession, with particular emphasis on quantitative management science techniques. Seven classifications of management science techniques were used for the content analysis. Although applications of forecasting, simulation, linear programming, and queuing models have been reported in the Journal, a gap is evident between the demonstration of management science techniques and operational use of these techniques in dietetic practice. Dietetic researchers, practitioners, and educators have vital roles in facilitating the transfer of quantitative management science technology into operational dietetic practice. Assessment of the state-of-the-art of dietetic management practice relative to proven quantitative management science techniques reveals the need for improved technology transfer to enhance professional ability in both tactical and strategic decision making.

Dietetics↗
PubMed1986

Are larger dental practices more efficient? An analysis of dental services production.

Whether cost-efficiency in dental services production increases with firm size is investigated through application of an activity analysis production function methodology to data from a national survey of dental practices. Under this approach, service delivery in a dental practice is modeled as a linear programming problem that acknowledges distinct input-output relationships for each service. These service-specific relationships are then combined to yield projections of overall dental practice productivity, subject to technical and organizational constraints. The activity analysis reported here represents arguably the most detailed evaluation yet of the relationship between dental practice size and cost-efficiency, controlling for such confounding factors as fee and service-mix differences across firms. We conclude that cost-efficiency does increase with practice size, over the range from solo to four-dentist practices. Largely because of data limitations, we were unable to test satisfactorily for scale economies in practices with five or more dentists. Within their limits, our findings are generally consistent with results from the neoclassical production function literature. From the standpoint of consumer welfare, the critical question raised (but not resolved) here is whether these apparent production efficiencies of group practice are ultimately translated by the market into lower fees, shorter queues, or other nonprice benefits.

Cost-Benefit Analysis↗
PubMed1986

A model to assess the quality-cost tradeoff in nursing homes.

We develop a model for assessing quality-cost tradeoffs as they arise in nurse staffing and task assignment decisions commonly faced by nursing home administrators and industry regulators. As prospective reimbursement schemes and resource utilization groups (RUGs) are implemented, we expect that tradeoffs such as these will become even more critical than they are now. The model permits the inclusion of quality-related considerations, such as restricting tasks to personnel at specified skill levels, requiring minimum staff levels at each skill level, and selective raising of wage rates. The model is also sensitive to changes in patient needs, labor availability, and technological innovations, permitting its use for general staffing purposes. Because it utilizes linear programming techniques, standard computer software can be used to find solutions very quickly, even on a small personal computer. We describe the application of this model to a nursing home in upstate New York, but the procedure is widely applicable to other health care facilities.

Aged↗
PubMed1985

[Results of radiotherapy of lung cancer in women].

Radiation therapy was provided to 38 (11.5%) of 331 lung cancer female patients at the N. N. Petrov Research Institute of Oncology, USSR Ministry of Health. The combination of radiation- and chemotherapy was used in 9 patients. The Rokus, Rad gamma-therapeutic units or a linear accelerator were used for radiation therapy. Daily single focal doses were 1.2-2.0 Gy, the summary dose was 40-60 Gy. Two-five irradiation fields with the choice of optimum conditions on a computer using the linear programming method were used. The lymph outflow tracts were irradiated from isolated fields and in central lung cancer the tumor and mediastinal region (the root, bifurcation and paratracheal lymph nodes on the affected side) were incorporated in the irradiated zone. Five women received split course irradiation. An analysis of the long-term results of conservative therapy of lung cancer in women has shown that radiation therapy or its combination with chemotherapy is the most effective. These results were slightly better than those in men.

Adenocarcinoma↗
PubMed1984

A patient mix model for hospital financial planning.

A linear programming model was formulated to examine the impact on hospital finances and resource use of changes in patient mix under current and proposed government reimbursement regulations. The model specifically incorporated the costs, revenues, and resource consumption patterns associated with patients drawn from different intensity level and payer class combinations. The necessary data were obtained from financial reports and other records, and the model was used in policy analysis at a major university teaching hospital.

Costs and Cost Analysis↗
PubMedDate not supplied

[Calculation of the minimal substrate expenditures for energy metabolism in microorganisms].

The paper presents a method for calculating the minimal expenses of substrates from the medium necessary to compensate energy donor disbalances in an intracellular process under study (for instance, in the production of a unit biomass or in the synthesis of one mole of monomer) between the number of regeneration events and the number of events in which each energy donor is utilized. The method employs the performance tables of energetic processes and is based on linear programming method. The paper includes the performance tables RE, RU and RS describing the stoichiometry of energetic processes in Escherichia coli, and the results of calculation for the cases of E. coli growth on glucose and acetate as sources of carbon.

Acetyl Coenzyme A↗