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Results for “Error minimization”

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At least 253 records · Page 14Linked to original sources

PubMed1998

Hemodynamic patterns of pharmacologically induced erection: evaluation by color Doppler sonography.

PURPOSE: Penile erection is achieved through hemodynamic mechanisms that can be assessed best with color flow imaging and Doppler waveform analysis. We performed dynamic studies using computer assisted analysis to assess the hemodynamic patterns of pharmacologically induced erection. MATERIALS AND METHODS: A total of 73 color Doppler ultrasound studies was performed in 66 patients with erectile dysfunction. Various blood flow parameters, including peak systolic velocity, end diastolic velocity, mean flow rate, resistive index and artery diameter, were observed continuously and recorded frequently for about 30 minutes after intracorporeal injection of papaverine/phentolamine/prostaglandin E1 mixture. A computerized Doppler waveform analysis of 3 curves or greater was performed for each recording to minimize error. A second injection was administered if the first injection failed to induce a rigid erection. Status of the erection was observed and recorded throughout the study. A computerized graph was generated for each corpus. RESULTS: After intracorporeal injection the time to reach normal or peak velocity varied from 1 to 24 minutes. Among 146 corpus units in 73 color Doppler ultrasound studies we observed the following hemodynamic patterns: I-normal maximal peak systolic velocity (35 cm. per second or greater), sustained; Ia-end diastolic velocity 0 or less with complete erection response (19 units); Ib-end diastolic velocity greater than 0 or incomplete erection response (14 units); II-normal maximal peak systolic velocity (35 cm. per second or greater), transient; IIa-end diastolic velocity 0 or less with complete erection response (21 units); IIb-end diastolic velocity greater than 0 or incomplete erection response (12 units); III-borderline maximal peak systolic velocity (30 to 35 cm. per second); IIIa-end diastolic velocity 0 or less with complete erection response (10 units); IIIb-end diastolic velocity greater than 0 or incomplete erection response (8 units); IV-low maximal peak systolic velocity (less than 30 cm. per second); IVa-end diastolic velocity 0 or less with complete erection response (24 units); and IVb-end diastolic velocity greater than 0 or incomplete erection response (38 units). CONCLUSIONS: Erection is a complex and dynamic process. A new classification of hemodynamic patterns is presented that aids in assessing and interpreting more thoroughly blood flow parameters to stratify more precisely the hemodynamic patterns of erectile dysfunction.

Adult↗

PubMed2001

Improved sea ice parcel trajectories in the Arctic via data assimilation.

An assimilated sea ice motion product is used to track ice parcels in several regions of the Arctic over time periods of one day to several weeks during 1992-1993. Motions simulated using a two-dimensional, dynamic-thermodynamic sea ice model are combined with motions derived from daily 85 GHz special sensor microwave/imager (SSM/I) imagery using an optimal interpolation method that minimizes error covariance. Assimilation attenuates the tracking error over the stand-alone model in comparison to buoy trajectories with the same starting location and time. The average 14-day assimilated trajectory's displacement error is as much as 34% lower than the model trajectory, while the RMS direction error is decreased by up to 10 degrees (24%). Assimilation can also yield an estimate of dispersion, which is not retrievable by point buoy observations. An assimilation approach improves estimates of ice drift and has the potential to further the understanding of ice mass flux, freshwater flux, and pollutant transport in the polar regions.

Arctic Regions↗

PubMed2003

A simulated annealing algorithm for maximum likelihood pedigree reconstruction.

The calculation of maximum likelihood pedigrees for related organisms using genotypic data is considered. The problem is formulated so that the domain of optimization is a permutation space. This is a feature shared by the travelling salesman problem, for which simulated annealing is known to be effective. Using this technique it is found that pedigrees can be reconstructed with minimal error using genotypic data of a quality currently realizable. In complex pedigrees accurate reconstruction can be done with no a priori age or sex information. For smaller numbers of individuals a method of efficiently enumerating all admissible pedigrees of nonzero likelihood is given.

Algorithms↗

PubMed2003

Effect of repeated administration of phencyclidine on spatial performance in an eight-arm radial maze with delay in rats and mice.

Phencyclidine (PCP) is an N-methyl-D-aspartate (NMDA) glutamate receptor channel noncompetitive antagonist that produces some of the symptoms of schizophrenia, including delusions, hallucinations, and negative symptoms as well as cognitive impairment. Thus, administration of PCP to rodents and nonhuman primates has been suggested to provide a potential animal model for schizophrenia. There have been some reports that 7-14 days of PCP administration can bring about enduring impairments in working memory in rodents but not all studies have been consistent in this regard. The present study determined whether repeated PCP administration impaired spatial performance in rats or mice trained to make minimal errors in an eight-arm radial maze task with a delay. Male Sprague-Dawley rats and C57BL/6J mice received 14 daily injection of vehicle or PCP (10 mg/kg, s.c.) followed by a withdrawal period of 1 week. The number of arm reentry errors and the distance traveled to complete the task were not significantly different between PCP-treated and vehicle-treated rats on 2, 8, and 14 days of PCP administration or 8 days following withdrawal of PCP. Mice treated with PCP for up to 2 weeks also had no significant differences in the number of arm reentry errors, travel distances, the numbers of visits to different arms during the first eight choices, or latencies to take all eight pellets compared to the vehicle-treated group. Thus, the present study failed to demonstrate that repeated administration of PCP to rats or mice produces enduring memory impairment. Factors potentially contributing to the discrepancies between various studies are discussed.

Animals↗

PubMed2002

[Comparison of three methods to calculate adherence in patients receiving antiretroviral treatment].

INTRODUCTION: Knowledge of the patient's adherence to antiretroviral treatment is extremely useful for monitoring HIV infection. Several methods have been proposed to calculate adherence, but they all have certain problems at application. The aim of this study was to compare three of the available methods for assessing medication adherence in order to determine their accuracy for this purpose. PATIENTS AND METHODS: Three methods for evaluating medication adherence were prospectively studied: 1. Remaining pill count (RPC), 2. Structured interview (SI), and 3. Pharmacy registry of drug refills (DR). The RPC was considered the gold standard and sensitivity and specificity of the other methods was calculated according to the RPC. The study included 100 consecutive patients and had a follow-up of one year. RESULTS: We were able to assess all three methods in 69 cases. The percentages of patients taking 95% or more of the prescribed dose according to the three methods were 72.5% (RPC), 85.5% (SI) and 81.2% (DR). Taking the RPC as gold standard, there was 75.1% concordance with the DR and 75.1% with the SI method. The sensitivities of the DM and SI were 52.6 % and 42.1 %, respectively. After one year of follow-up, patients with > 90% adherence (RPC) had a 1.29-times higher probability of achieving good virological response (CI 95% 1.04-1.62, p 5 0.0138). CONCLUSION: Although concordance among the methods was acceptable, the SI and DR overestimated adherence as compared to the RPC. Since there is currently no ideal method for determining treatment adherence, it is important to combine several methods to minimize errors and provide results that are as close to the true situation as possible.

Adult↗

PubMed2005

[Definition of a reproducible method for acetabular anteversion measurement at CT].

PURPOSE: To demonstrate the variability of acetabular anteversion angle measurement at CT and suggest a new and reproducible method of measurement. MATERIAL AND METHODS: Sawbone pelvis based study: We first realized a series of helical CT of the pelvis, with gradual increase in tilt angle, and measured acetabular anteversion angles on axial sections, then on sections parallel to the superior S1 endplate. Then, we made a series of radial sections centered at the acetabulum, and the anteversion angle was measured on each section. Finally, a test series of five in vivo pelvis was performed to evaluate the feasability of our method. RESULTS: The acetabular anteversion angle varies with pelvis tilt, whereas measurements obtained from sections parallel to the S1 endplate are constant. CONCLUSION: Acetabular anteversion angle should be measured from sections parallel to the S1 endplate, in order to minimize errors during total hip arthroplasties.

Acetabulum↗

PubMed1996

Development of computer-assisted patient control for use in the hospital setting during mass casualty incidents.

Hospital resolution of mass casualty incidents can have difficulties involving "command and control" and information management, ineffective use of triage classes, and missed diagnostic procedures, leading to lower quality of care. A computer system has been developed to supply continuously updated group and patient data. The system uses barcoded identifiers to represent patients, injuries, facilities, and locations, in order to minimize errors and make exchange of data possible. The system communicates with the permanent hospital information system. This article reports the use of this technology during several experiments and real incidents. Computer registration based on bar codes, despite the greater number of items entered, still showed 25% fewer inaccuracies when compared with handwritten medical charts. Extensive training was shown to be unnecessary. Paramedical personnel judged the automated procedures to be an improvement during the admission of 143 evacuated patients.

Attitude of Health Personnel↗

PubMed2000

Organization of personnel and resources for airway management in the hospital and office environment.

Good airway management depends on a system that emphasizes teamwork to expedite care and minimize errors. By understanding the accreditation and licensing requirements, appropriate personnel and equipment can be allocated along cost effective guidelines. Newer techniques for management of the difficult airway, such as the laryngeal mask airway (LMA; LMA North America, San Diego, CA) and flexible fiberoptic bronchoscope, provide alternatives to the emergency cricothyrotomy. A program of continuous quality improvement and clinical guidelines will enhance patient care and suggest intelligent use of airway resources.

Airway Obstruction↗

PubMed1992

[A study of 11 ventilators for anesthesia: laboratory testing].

Eleven anaesthesia ventilators were instrumentally tested under various conditions. They included: Excel and Modulus II Plus (Ohmeda); 710 and Servo anaesthesia circle 985 (Siemens); Jollytronic (Soxil) and Elsa (Engström); SA2 and Cicero (Dräger); ABT 4,300 (Kontron); Monnal A and the prototype Alys (Taema). The test circuit comprised a two compartment model lung, a pneumotachograph, a pressure gauge in the "airway". The volume was calculated as the integral of flow rate. Each machine was calibrated by the firms' technicians. Before each test, the pneumotachograph was calibrated using a 11 air syringe and the pressure gauge with a 5 cm water column. Each machine ventilated the model lung for 30 min before starting the tests. There were five tests: 1) reliability of the machine's spirometer, 2) reliability of the ventilation rate, 3) reliability of pressure measurements, 4) effect of increasing fresh gas flow on spirometry, 5) effect of increasing downstream resistances. In usual simulated ventilatory conditions, all the machines accurately delivered the setted ventilation and spirometric measurements were with minimal error only. Several ventilators (SA2, Excel, 710, Elsa, ABT 4,300) did not succeed in maintaining their performances when compliance was strongly decreased or resistance of the test lung notably increased. Resistance in the circuit during simulated spontaneous ventilation was < 3.6 cmH2O.l-1.s-1. Increasing fresh gas flow raised the minute volume delivered in six ventilators. It is concluded that, during extreme ventilatory conditions, the inspired volume must be adjusted so as to maintain the inspired tidal volume. However, ventilators which increase inspiratory time in response to an increased mechanical load cannot be adjusted by this way.

Anesthesia, Closed-Circuit↗

PubMed2002

Measuring corneal power for intraocular lens power calculation after refractive surgery. Comparison of methods.

PURPOSE: To find a more accurate and predictable method for intraocular lens (IOL) power calculation in eyes after refractive surgery. SETTING: Department of Ophthalmology, Kangnam St. Mary's Hospital, Seoul, Korea. METHODS: The accuracy of the following methods for calculating IOL power in 132 eyes after PRK or LASIK was compared: manual keratometry, hard contact lens, refraction-derived keratometry at the corneal plane, and the refraction-derived keratometry at the spectacle plane. Based on this comparison, the IOL power was calculated in the 2 eyes of a patient using refraction-derived keratometry at the spectacle plane with the SRK II formula. Cataract surgery with IOL implantation was then performed. RESULTS: The largest corneal power values were obtained using a manual keratometer and the smallest using refraction-derived keratometry at the spectacle plane (P <.001). In the patient having cataract surgery with IOL implantation, near target refraction was achieved with minimal error in IOL power. CONCLUSIONS: If the corneal power is known before refractive surgery, the use of the smallest value of those obtained using refraction-derived keratometry and the hard contact lens method is recommended. However, if the corneal power before refractive surgery is unknown, the use of the hard contact lens method is recommended.

Adult↗

PubMed2001

Bayesian approach for neural networks--review and case studies.

We give a short review on the Bayesian approach for neural network learning and demonstrate the advantages of the approach in three real applications. We discuss the Bayesian approach with emphasis on the role of prior knowledge in Bayesian models and in classical error minimization approaches. The generalization capability of a statistical model, classical or Bayesian, is ultimately based on the prior assumptions. The Bayesian approach permits propagation of uncertainty in quantities which are unknown to other assumptions in the model, which may be more generally valid or easier to guess in the problem. The case problem studied in this paper include a regression, a classification, and an inverse problem. In the most thoroughly analyzed regression problem, the best models were those with less restrictive priors. This emphasizes the major advantage of the Bayesian approach, that we are not forced to guess attributes that are unknown, such as the number of degrees of freedom in the model, non-linearity of the model with respect to each input variable, or the exact form for the distribution of the model residuals.

Algorithms↗

PubMed1999

Cervical screening in Africa: discordant diagnosis in a double independent reading. DYSCER-CI Group.

Interobserver variation in the cytological diagnosis of cervical lesions poses a problem for public health screening programs. This study assessed the frequency of discordant diagnoses between two independent cytopathologists in the screening of African women. In Abidjan, Côte d'Ivoire, 2157 women were recruited from three outpatient gynecology clinics and screened for cervical abnormalities and genital and human immunodeficiency virus (HIV) infections. The degree of agreement between the cytopathologists was assessed by kappa statistics. The overall agreement was poor (kappa = 0.33); however, the degree of agreement increased with the severity of the lesions and was fairly good (kappa = 0.53) for high-grade and invasive lesions requiring curative treatment. Discordance was associated with HIV infection but not with genital infections. For a prevention program of cervical cancer in this African context, strategies must be developed to minimize errors in cervical screening. Particularly, HIV-infected women require a systematic rereading to reduce false-negative results.

Adult↗

PubMed2001

Intercomparison of 131I and 99mTc activity measurements in Brazilian nuclear medicine services.

This work outlines the quality assurance program for the activity measurements of the most used radionuclides at Brazilian Nuclear Medicine Services (NMS). The program aims to guarantee that the patient is given the correct prescribed amount of activity in diagnostic or therapeutic applications. This accurate administration depends upon proper use and calibration of the activity meters by the NMS. Underestimation of administered activity in diagnostic practices could delay correct diagnosis disturbing the value of the investigation. On the other hand, the overestimation would be worse, mainly in therapeutic applications, because an unnecessarily high absorbed dose would be delivered to the patient. The preliminary results of intercomparison for 131I and 99mTc showed that many activity meters used at NMS's present problems giving results up to 41% greater than the reference values determined at the National Metrology Laboratory for Ionizing Radiation (LNMRI) which is recognized as the Brazilian authorized metrology laboratory for ionizing radiation. These results have demonstrated that the NMS should improve the accuracy of the activity measurements of the radionuclides administered to the patients and establish the traceability to the national standards of measurements. These standards are based on a pressurized well-type ionization chamber installed at LNMRI and calibrated with reference sources standardized by absolute methods. The protocol of the intercomparison and recommendations made in order to minimize errors in measuring procedures are described and results are discussed.

Brazil↗

PubMed2002

Comparison of measurement accuracy between two wrist goniometer systems during pronation and supination.

Pronation and supination have been shown to affect wrist goniometer measurement accuracy. The purpose of this study was to compare differences in measurement accuracy between a commonly used biaxial, single transducer wrist goniometer (System A) and a biaxial, two-transducer wrist goniometer (System B) over a wide range of pronation and supination (P/S) positions. Eight subjects moved their wrist between -40 and 40 degrees of flexion/extension (F/E) and -10 and 20 degrees of radial/ulnar (R/U) deviation in four different P/S positions: 90 degrees pronation; 45 degrees pronation; 0 degrees neutral and 45 degrees supination. System A was prone to more R/U crosstalk than System B and the amount of crosstalk was dependent on the P/S position. F/E crosstalk was present with both goniometer systems and was also shown to be dependent on P/S. When moving from pronation to supination, both systems experienced a similar extension offset error; however R/U offset errors were roughly equal in magnitude but opposite in direction. The calibration position will affect wrist angle measurements and the magnitude and direction of measurement errors. To minimize offset errors, the goniometer systems should be calibrated in the P/S posture most likely to be encountered during measurement. Differences in goniometer design and application accounted for the performance differences.

Adult↗

PubMed2002

A dynamic model for simulating a trip and fall during gait.

The purpose of this study was to develop an analytical model to simulate a trip and fall during gait. The human body was modeled as a 12 degree-of-freedom linkage system. The kinematics of the lower extremity for one cycle of gait were obtained for a healthy subject using an optoelectronic three-dimensional data acquisition system. Inverse dynamics was used to compute the moments about the hip, knee and ankle joints of the lower extremity. These moments were then used as input actuators to the joints in to a forward dynamics model to simulate the swing phase of gait from toe-off to heel-strike. An optimization procedure to minimize errors associated with the computed experimental torque was applied to correct for mathematical instability. An experiment was performed to measure the three-dimensional foot--obstacle contact force for a healthy subject tripping on an obstacle during gait. The contact force was applied to the swing limb of the forward dynamics model for 0.09 s beginning at 0.04 s after toe-off. Tripping on an obstacle followed by a muscle-relaxed fall was simulated. The simulation results were visualized with animation software.

Accidental Falls↗

PubMed2000

Kinaesthetic judgements and refinement of striking action.

Little is known about the developmental course of striking action. This cross-sectional study explored the refinement of striking in 28 children aged between 4 and 12 years and investigated how well they could use kinaesthesis to gauge the length of an unseen bat. The kinematic data (including smoothness of movement) showed quantitative differences between the age groups. In contrast, no differences were found in the children's ability to judge the length of the unseen bat: within three strikes all of the children had made a clean hit, indicating that they had successfully judged bat length. The children then appeared to memorize the bat with which they had accurately hit the target and made: (1) minimal errors when using this bat in later trials and (2) predictable errors when using two other bats of different sizes. The results show that the striking action becomes optimized over childhood, with smoothness of movement providing an index of this refinement. The findings also suggest that young children have a higher level of kinaesthetic sensitivity than has been assumed previously on the basis of static limb positioning tasks. The results suggest that the striking task used in this study might be a useful tool for investigating the development of movement skills in children with developmental disorders.

Age Factors↗

PubMed1993

A linkage study of schizophrenia with DNA markers from the long arm of chromosome 11.

We report the results of a collaborative linkage study using 12 polymorphic markers (9 loci) from the long arm of chromosome 11, and 24 families multiply affected with schizophrenia and other closely related disorders. This region is of interest because several families have been reported in which balanced translocations involving 11q apparently co-segregate with psychotic illness. In addition, the dopamine D2 receptor, porphobilinogen deaminase, and tyrosinase genes map within the region studied and may be aetiologically involved in schizophrenia. We have primarily analysed genotypic data by the LOD score method using a range of single gene models. In order to minimize error due to mis-specification of genetic parameters we have analysed data from markers at candidate gene loci by the non-parametric extended sib-pair method in addition to the LOD score method. Our results suggest that most of the region can be excluded from containing a gene of major effect in the aetiology of this disease.

Alleles↗

PubMed2002

Metabonomic assessment of physiological disruptions using 1H-13C HMBC-NMR spectroscopy combined with pattern recognition procedures performed on filtered variables.

Metabonomic characterization of long-lasting although weak physiological events such as anabolic disruptions remains poorly investigated. We have validated 1H-13C HMBC-NMR as a suitable generator of instrumental variables that are strongly linked to the concentration of endogenous metabolites in biological fluids. This method is interfaced to multivariate pattern recognition procedures. Fingerprints established from urine sample collected on cattle treated with anabolic steroids were used to validate this method. Four main results arise from this study. (i) 2D NMR is as informative as 1D NMR. (ii) 2D NMR variable clustering highlights successfully a contingent redundancy of variables, although a relevant hierarchical model of statistical correlations covering from structural relationships to physiologic links can also be evidenced. (iii) To enhance pattern recognition performances, we have validated a variable selection algorithm for accurate prediction of unknown individuals belonging to predetermined groups achieved by linear discriminant analysis (LDA). This algorithm synthesizes the whole information contained in the data set by selecting preferentially nonredundant variables. Parameters generating variable subsets are validated by predicted variance efficiency obtained when minimizing error rates calculated by cross-validation methods. (iv) Provided variables are correctly filtered, LDA fairly competes with partial least-squares methods for both classification of individuals and statistical interpretation of metabolic responses obtained in such a physiological disruption context.

Algorithms↗