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PubMed1999

Issues in surgical randomized controlled trials.

As technology expands and health care resources become more limited, there is increasing pressure on surgeons to evaluate surgical procedures and technology to ensure they are effective. No longer is evidence from case series acceptable, and treatments must be evaluated in randomized controlled trials. The power of the randomized controlled trial is that because of its rigorous design the risk of random or systematic (bias) error is minimized and thus the risk of making an incorrect conclusion about the efficacy of a treatment is minimized. The randomized controlled trial has been widely accepted for evaluating the efficacy of medical treatments but less so for surgical procedures. Many cite methodologic issues related to surgical issues as the reason for this, including concerns related to standardization of the surgical procedure, timing of surgical trials, difficulties with blinding of subjects and investigators, ethics of surgical trials, and patient and surgeon acceptance of surgical trials. These issues are discussed in this paper as are possible strategies to minimize their effect.

Ethics, Medical↗

PubMed1997

Size principle and information theory.

The motor units of a skeletal muscle may be recruited according to different strategies. From all possible recruitment strategies nature selected the simplest one: in most actions of vertebrate skeletal muscles the recruitment of its motor units is by increasing size. This so-called size principle permits a high precision in muscle force generation since small muscle forces are produced exclusively by small motor units. Larger motor units are activated only if the total muscle force has already reached certain critical levels. We show that this recruitment by size is not only optimal in precision but also optimal in an information theoretical sense. We consider the motoneuron pool as an encoder generating a parallel binary code from a common input to that pool. The generated motoneuron code is sent down through the motoneuron axons to the muscle. We establish that an optimization of this motoneuron code with respect to its information content is equivalent to the recruitment of motor units by size. Moreover, maximal information content of the motoneuron code is equivalent to a minimal expected error in muscle force generation.

Animals↗

PubMed2007

A biomechanical model of mammographic compressions.

A number of biomechanical models have been proposed to improve nonrigid registration techniques for multimodal breast image alignment. A deformable breast model may also be useful for overcoming difficulties in interpreting 2D X-ray projections (mammograms) of 3D volumes (breast tissues). If a deformable model could accurately predict the shape changes that breasts undergo during mammography, then the model could serve to localize suspicious masses (visible in mammograms) in the unloaded state, or in any other deformed state required for further investigations (such as biopsy or other medical imaging modalities). In this paper, we present a validation study that was conducted in order to develop a biomechanical model based on the well-established theory of continuum mechanics (finite elasticity theory with contact mechanics) and demonstrate its use for this application. Experimental studies using gel phantoms were conducted to test the accuracy in predicting mammographic-like deformations. The material properties of the gel phantom were estimated using a nonlinear optimization process, which minimized the errors between the experimental and the model-predicted surface data by adjusting the parameter associated with the neo-Hookean constitutive relation. Two compressions (the equivalent of cranio-caudal and medio-lateral mammograms) were performed on the phantom, and the corresponding deformations were recorded using a MRI scanner. Finite element simulations were performed to mimic the experiments using the estimated material properties with appropriate boundary conditions. The simulation results matched the experimental recordings of the deformed phantom, with a sub-millimeter root-mean-square error for each compression state. Having now validated our finite element model of breast compression, the next stage is to apply the model to clinical images.

Biomechanical Phenomena↗

PubMed2006

Vocal dysperiodicities estimation by means of adaptive long-term prediction.

An adaptive formulation of the long-term bidirectional linear predictive analysis is proposed in the context of the acoustic assessment of disordered speech. Vocal dysperiodicities are summarized by means of a signal-to-dysperiodicity ratio (SDR) marker. It is shown that performing an adaptive forward and backward long-term linear prediction of each speech sample and retaining the minimal prediction error energy as a cue of vocal dysperiodicity results in an SDR that correlates with the perceived degree of hoarseness. The coefficients of the time-varying long-term linear predictive model are estimated by means of the recursive least squares algorithm. The corpora comprise sustained vowels and French sentences produced by male and female normophonic and dysphonic speakers. A perceptual assessment of speech samples, which rests on comparative judgments, is used to evaluate the ability of the acoustic marker to predict subjective measures of voice quality. Experimental results show that the adaptive approach gives rise to high correlations for sustained vowels as well as for sentences.

Case-Control Studies↗

PubMed2005

A comparison of external transducers and microtransducers in urodynamic studies of female patients.

The urodynamic catheter and its transducer play a significant role in the performance of good urodynamic studies. The fluid-filled (perfusion) catheter with its external strain gauge transducer and the microtransducer catheter with a transducer built directly into the catheter are the two most prevalent catheters used in urodynamic studies today. Either functions differently with regard to how pressures are measured during testing. Both are unique with regard to their requirements for handling and management during testing. Proper transducer calibration, maintenance of standardized reference levels, and attention to catheter zeroing procedures as outlined by the International Continence Society are vital to good study technique and quality testing results. When used in a manner consistent with the catheter's performance characteristics, study error is minimized and meaningful clinical data can be obtained.

Equipment Design↗

PubMed1986

Epidemiology of hydatidiform mole during early gestation.

Different methodologic approaches have resulted in a wide variability in the reported incidence of hydatidiform mole in the United States. We studied the epidemiology of hydatidiform mole among 84,318 women obtaining legal abortions in the United States during the period 1975 to 1978. Our estimated rate of 7.5 hydatidiform moles per 10,000 pregnancies was similar to most reported rates for the United States. The rate was significantly higher for women 14 years or younger and those 45 years or older. Race, number of previous pregnancies, and number of previous spontaneous abortions were not found to significantly affect the risk of having the disease. The incidence was slightly (but not significantly) higher for women obtaining abortions during the first trimester than for those obtaining abortions during later gestation. This study minimizes the errors encountered in estimating the total number of pregnancies and the number of hydatidiform moles at later stages of gestation. Hydatidiform mole, although relatively the number of hydatidiform moles at later stages of gestation. Hydatidiform mole, although relatively uncommon, represents a complication of pregnancy that is of public health importance.

Abortion, Induced↗

PubMed1983

Improved methods for calculating formation constants for nucleotide--cation complexes.

Two data reduction methods that can be used to calculate formation constants for nucleotide-cation complexes are described. Both methods are used to analyze data obtained by an anion-exchange resin method, and either method can improve the accuracy of the calculated formation constants by more than 50%. The key to this significant improvement in accuracy is the realization that the equation for the mathematical model describing such systems is always nonlinear in terms of the formation constants and, in the general case, is higher order in the cation concentration. There are two major reasons for the improved quality of the results associated with the new model. First, successive linear extrapolations are eliminated, and error propagation is reduced. Second, all of the data are used for the simultaneous calculation of all formation constants, and the uncertainty due to random experimental errors is minimized.

Anion Exchange Resins↗

PubMed1993

The practicability of finite-element analysis for assessing changes in human craniofacial morphology from cephalographs.

The usefulness of a finite-element analytical (FEA) method for studying changes in facial form was investigated. The material was lateral cephalographs of 19 patients who had undergone surgical correction of the chin. FEA was used to assess changes in bony form brought about by surgery. Replicate digitization of cephalographic landmarks was used to minimize measurement error. Random and systematic errors were examined and their influence on the finite-element method was assessed. However, the sensitivity of FEA is such that the level of residual measurement error affects the reliability of the method and makes the technique unsuitable for individual cases. However, for pooled data from a group of cases the effect of measurement error is reduced and the reliability of the analysis is satisfactory for intergroup comparison.

Cephalometry↗

PubMed1995

Evaluation of the i-STAT system: a portable chemistry analyzer for the measurement of sodium, potassium, chloride, urea, glucose, and hematocrit.

OBJECTIVE: To evaluate the analytical performance of the i-STAT system, which is designed for point of care testing and employs a hand-held chemistry analyzer and disposable cartridges, which in the configuration tested, are capable of measuring sodium, potassium, chloride, urea, glucose, and hematocrit in approximately 65 microL of blood in 90's. METHODS: Linearity and imprecision in hematocrit measurement were assessed using whole blood, while that for the other analytes were evaluated with aqueous solutions. The accuracy of the i-STAT system was judged by assay of patient specimens obtained both by venipuncture and fingerprick and correlated with the Kodak Ektachem 700XR and the microhematocrit methods. RESULTS: Linearity was obtained over the clinically relevant range for all analytes. Total imprecision as expressed by the coefficient of variation (CV) was less than 3.5% for all analytes at both high and low concentration except for a low concentration of urea where a CV of 9.4% was obtained. Linear regression analysis revealed minimal systematic errors. The standard error about the regression line (Sy/x) ranged from 0.017 for hematocrit to 2.262 for chloride in the assay of venous blood, whereas in the assay of capillary blood the Sy/x ranged from 0.018 for hematocrit to 0.755 for glucose. CONCLUSIONS: The analytical performance of the i-STAT was deemed acceptable by calculation of total error and comparison with published performance standards. Our study has shown the i-STAT system to be reliable, robust, and simple to operate. Moreover, the compactness of the analyzer and the requirement for only small volumes of whole blood will make it a valuable diagnostic tool in point of care settings.

Blood Chemical Analysis↗

PubMed1990

Computer integrated measurement of respiratory compliance.

Respiratory compliance is obtained from the ratio of lung volume change to change in differential pressure across the chest wall, and is classically derived from the slope of the static, transrespiratory pressure-volume relationship. The need to remove subjectivity from the derivation of respiratory compliance, has prompted the development of a computer-based system which facilitates compliance measurement with minimal experimenter error. This paper outlines the basic algorithms necessary to analyse static, quasi-static and dynamic pressure-volume data, and describes how these data may be entered into a graphics package (Sigmaplot) to derive best-fit polynomial curves.

Algorithms↗

PubMed1985

Finite centroid and helical axis estimation from noisy landmark measurements in the study of human joint kinematics.

Recent work on joint kinematics indicates that the finite centroid (centre of rotation) and the finite helical axis (axis of rotation, screw axis, twist axis) are highly susceptible to measurement errors when they are experimentally determined from landmark position data. This paper presents an analytical model to describe these effects, under isotropic conditions for the measurement errors and for the spatial landmark distribution. It appears that the position and direction errors are inversely proportional to the rotation magnitude, and that they are much more error-prone than the relatively well-determined rotation and translation magnitudes. Furthermore, the direction and rotation magnitude errors are inversely proportional to the landmark distribution radius, and the position and translation magnitude errors are minimal if the mean position of the landmarks coincides with the centroid or helical axis. For the planar centroid, the use of rigid-body constraints results in considerable precision improvement relative to the classical, finite Reuleaux method for centroid reconstruction. These analytical results can be used to define suitable measurement configurations, and they are used in this paper to explain experimental results on Röntgenphotogrammetrically acquired in vitro wrist joint movement.

Biomechanical Phenomena↗

PubMed1991

Accurate measurements of coupling constants from two-dimensional nuclear magnetic resonance spectra of proteins and determination of phi-angles.

A new and simple method to measure 3JHNH alpha coupling constants of proteins by adding and subtracting traces from corresponding two-dimensional nuclear Overhauser enhanced spectroscopy and two-dimensional correlated spectroscopy cross peaks after scaling is proposed. The optimal scaling for the addition and the subtraction of the two traces is obtained by minimizing an error function. The method was proven to give accurate and precise measurements of coupling constants when tested with a series of simulated spectra. The accuracy of the method was better than 0.1 Hz for all test cases including the limiting case of J = 2.0 Hz and line-width = 11.0 Hz. The accuracy of the method was better than 0.1 Hz for all test cases including The 3JHNH alpha coupling constants were measured in two-dimensional nuclear magnetic resonance spectra of the two proteins barley serine proteinase inhibitor (CI-2) and the bacterial ribonuclease (barnase) of Bacillus amyloliquefaciens. The experimentally measured coupling constants were used to calculate the constants in a Karplus equation to be: 3JHNH alpha = 6.7 cos2(phi-60) -1.3 cos(phi-60) +1.5. These constants are in good accordance with those obtained for basic pancreatic trypsin inhibitor (BPTI). In addition, special emphasis is given to the measurements of positive phi-angles, and to the contribution of molecular dynamics on the apparent coupling constants.

Bacillus↗

PubMed1991

A note on efficient estimation of mutation rates using Luria-Delbrück fluctuation analysis.

The maximum likelihood and Luria-Delbrück P0 methods for the estimation of spontaneous mutation rates are compared. The maximum likelihood method is fully efficient, utilizing all available information in a fluctuation experiment, but can be numerically cumbersome. Under certain conditions, there is little loss of efficiency using the P0 method, which is readily implemented numerically. Design considerations should aid investigators in minimizing statistical errors associated with the statistical analysis of fluctuation experiments.

Mathematics↗

PubMed1982

Behavioral kinetics: dynamics of the unconditioned response to footshock.

The purpose of this paper is to present an instrument and behavioral assay for monitoring the unconditioned response to footshock in the rat. The instrument provides measures of the total force exerted by a subject in response to a footshock, the duration of the subject's response, and the subject's latency to respond to the stimulus. The assay is developed to minimize the error variance inherent in behavioral measurements. In the second part of this paper, the relationships between the response and the physical parameters of the stimulus are investigated. The total force exerted by a subject, and the duration of the subjects response are linearly related to the multiplicative interaction of stimulus current and stimulus duration. The subject's latency to respond is curvilinearly related to stimulus current alone. The form of this relationship is hyperbolic. These results are discussed in the context of the measurement of behavioral and psychophysical processes in psychobiological research.

Animals↗

PubMed1985

Self-stimulation of the lateral hypothalamus and ventrolateral tegmentum: excitability characteristics of the directly stimulated substrates.

Recovery from refractoriness in the neural substrate for self-stimulation of the ventrolateral tegmentum (VLT) was estimated using psychophysical techniques, and compared to recovery in the substrate for self-stimulation of the lateral hypothalamus (LH). A computer-controlled testing setup was developed to minimize experimenter error and testing time. In order to assess the performance of this setup, refractory period estimates obtained in the newly designed, computer-controlled equipment were compared to those obtained in the hand-operated equipment used in previous experiments of this type. No meaningful differences were found. Thus, the more convenient computer-controlled setup was used to collect refractory period estimates from the VLT and LH. A comparison of these values revealed differences in the slopes of the recovery curves, and in the C-T intervals bracketing their rising portions. The VLT curves rose more gradually, and both began to rise and levelled off at longer C-T intervals than the LH curves. One explanation of these results is that the distribution of excitability in the LH substrate is shifted towards higher values than the VLT distribution. The overlapping portions of the recovery curves could reflect the contribution of a common bundle of reward-related fibers.

Animals↗

PubMed1982

A method to estimate cardiac volume by two-dimensional echocardiograms recorded from one extracorporeal point.

This paper presents a method for estimating the volume of a cardiac region from its oblique sectional images recorded with a sector scanner. The probe of the scanner is attached to the chest wall and an ultrasonic beam is cast from a fixed intercostal space. In a previous paper a method of calculation for the above recording technique was reported. The present method is superior to the previous one because it minimizes calculation error and is applicable to organs of intricate shape.

Cardiac Volume↗

PubMed1990

Evaluation of Euler's angles with a least squares method for the study of lumbar spine motion.

To analyse intervertebral movements, methods with a high level of accuracy are required. Stereoradiographic methods have been used for a number of years to describe intervertebral movements, but their major problem is to identify the same anatomical landmarks, not only on the pair of radiographs used for three-dimensional reconstruction, but also on all the pairs used to analyse the displacements. To minimize the errors due to the incorrect identification of anatomical landmarks, a least squares method to resolve the parameters of Euler's angles was validated by means of measurements made on a spine obtained from a cadaver. The accuracy of this method varied between 0.69 degrees and 0.71 degrees in rotation and between 0.28 mm and 0.77 mm in translation. In addition, this method significantly corrected the position of the anatomical landmarks. Euler's angles, used with a least squares estimate, can provide accurate and precise results.

Aged↗

PubMedDate not supplied

Optimum spectral windows to minimize quantum noise of ratiometric intracellular fluorescent probes.

When fluorescent indicators are used to measure intracellular ligands in single cells, the quality of the data is usually limited by quantum (shot) noise. For indicators which shift excitation or emission wavelengths upon ligand binding, a ratiometric method is usually employed. In choosing the spectral windows for excitation or collection of fluorescence, there is a trade-off between maximum sensitivity to ligand binding, and maximum collection of light. We show that there is a well-defined optimum choice of windows which minimizes the error caused by quantum noise in the estimated ligand concentration. An algorithm for determining these optimum windows is presented. As an example, we consider the measurement of intracellular calcium by indo-1 fluorescence emission ratio in cardiac myocytes. The optimum wavelength bands for collection of fluorescence are considerably wider than those commonly employed. The use of these windows in a pulsed-excitation time-resolved calcium measurement instrument resulted in improved signal to noise ratio of the calcium signal.

Calcium↗