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PubMed1989

Regional blood flow distribution during extracorporeal membrane oxygenation in rabbits.

To study regional blood distribution during extracorporeal membrane oxygenation, we stabilized three groups of five rabbits each (3 to 5 kg) on venoarterial bypass at a flow rate of 30 ml/kg/min. Albumin aggregates (15 to 30 microns) labeled with technetium 99m were injected into the left ventricle during bypass (ventricle), the perfusion cannula during bypass (cannula), and the left ventricle with no bypass (control). Animals were put to death, organs were removed, and the percent distribution was determined with a gamma camera. The Student Newman-Keuls test was used for statistical comparisons. Distribution to both the heart and brain in the cannula group were decreased from control by 55% and 35%, respectively. Distribution to the brain in the ventricle group was also decreased from control by 39%. Intestinal distribution was elevated above control in the ventricle group by 37%, whereas musculoskeletal distribution was elevated 33% above control in the cannula group. No significant changes were noted for the kidneys, stomach, or liver. These data suggest that overall perfusion of some vital organs may be significantly reduced during low-flow extracorporeal membrane oxygenation, specifically in the case of the heart and brain, which may be deprived of oxygenated blood.

Animals↗
PubMed1999

Management of adrenal cysts.

Adrenal cysts have been traditionally managed by excision to rule out malignancy. We reviewed the 613 cases of adrenal cysts (including 6 new cases of our own) to evaluate whether this is still appropriate. Descriptive statistics and distribution of each pathologic type have been updated, based on 515 cases, and have changed from statistics compiled on 155 cases by G. A. Absehouse et al. Only seven per cent of all adrenal cysts are malignant or potentially malignant. There is only one reported case of a malignancy found in a nonfunctioning adrenal cyst that was initially thought to be benign. In this case, no CT or aspiration was performed. There have been 19 cases of adrenal cysts managed with aspiration. All were nonfunctioning and benign. One had a bloody aspirate. Reaccumulation occurred in 32 per cent of the cases (six cases); six per cent were symptomatic, four per cent were excised. Follow up was available in 15 cases from 4 months to 3.5 years. Management of the patient with a suspected adrenal cyst should include a careful history and physical and biochemical screening to rule out a functioning lesion. A CT scan, and aspiration of the cyst with a cystogram should be performed to confirm a simple cyst of the adrenal. If the suspicion of malignancy is low, and the lesion is nonfunctional, the adrenal cyst may be managed by aspiration alone. If the cyst recurs and is asymptomatic, it may be observed. If a symptomatic cyst recurs, it may be reaspirated or excised.

Adrenal Gland Diseases↗
PubMed1995

Is it necessary to transform nutrient variables prior to statistical analyses?

The distributions of the intakes of many nutrients are skewed, yet this is often overlooked when standard statistical analyses are applied to nutrient data. The nutrient intakes of 5,123 men and 5,236 women, recorded by food frequency questionnaire in the Scottish Heart Health Study, were transformed to achieve approximately symmetric distributions. Power transformations were chosen using letter value analyses. A letter value analysis uses selected order statistics and their position around the median to assess symmetry. The effect that each transformation had on a comparison of nutrient intakes between those with and without prevalent coronary heart disease was determined from t tests on the untransformed and transformed variable. The effects of the logarithm and square root transformation and of the optimum Box-Cox transformation were also determined, and the results were compared with the nonparametric Mann-Whitney test. The conclusion of whether or not to reject the null hypotheses often varied, depending on the transformation and test used. The nonparametric test usually gave a conclusion similar to that of the t test on the letter value-transformed data, the Box-Cox-transformed variable, and after either the logarithm or square root transformation of the data, but not always both. The results from the untransformed variable were sometimes very different. Failure to account for skewness in nutrient variables may thus lead to spurious conclusions.

Aged↗
PubMed1979

Beta-structures of polypeptides with L-and D-residues. Part II. Statistical analysis and enrichment in enantiomer.

The possible formation of beta-structures from polypeptide chains with L-and D-Residues randomly distributed was statistically analyzed within the frame of two hypotheses. Firstly, only those segments containing residues of identical chirality can associate to form antiparallel beta-structures, and secondly these segments must have a minimum length. The influence of different factors was examined: initial ratio of the L-and D-monomer, minimum length required for the segments to be incorporated into beta-sheets, average length of the peptide molecules, and stereoselectivity in the course of the polymerization process. The results show that in all cases nuclei of beta-sheets surrounded by random coil segments are formed, the optical activity of which very increases to purity when the initial ratio of monomers deviates from the racemic mixture. This suggests experiments to enrich the system in one enantiomer. Comparison is made with the corresponding behavior and properties of the alpha-helical structure.

Isomerism↗
PubMed2005

Robust genomic control for association studies.

Population-based case-control studies are a useful method to test for a genetic association between a trait and a marker. However, the analysis of the resulting data can be affected by population stratification or cryptic relatedness, which may inflate the variance of the usual statistics, resulting in a higher-than-nominal rate of false-positive results. One approach to preserving the nominal type I error is to apply genomic control, which adjusts the variance of the Cochran-Armitage trend test by calculating the statistic on data from null loci. This enables one to estimate any additional variance in the null distribution of statistics. When the underlying genetic model (e.g., recessive, additive, or dominant) is known, genomic control can be applied to the corresponding optimal trend tests. In practice, however, the mode of inheritance is unknown. The genotype-based chi (2) test for a general association between the trait and the marker does not depend on the underlying genetic model. Since this general association test has 2 degrees of freedom (df), the existing formulas for estimating the variance factor by use of genomic control are not directly applicable. By expressing the general association test in terms of two Cochran-Armitage trend tests, one can apply genomic control to each of the two trend tests separately, thereby adjusting the chi (2) statistic. The properties of this robust genomic control test with 2 df are examined by simulation. This genomic control-adjusted 2-df test has control of type I error and achieves reasonable power, relative to the optimal tests for each model.

Case-Control Studies↗
PubMed2005

Power-law correlated processes with asymmetric distributions.

Motivated by the fact that many physical systems display (i) power-law correlations together with (ii) an asymmetry in the probability distribution, we propose a stochastic process that can model both properties. The process depends on only two parameters, where one controls the scaling exponent of the power-law correlations, and the other controls the degree of asymmetry in the distributions leaving the correlations unaffected. We apply the process to air humidity data and find that the statistical properties of the process are in a good agreement with those observed in the data.

Algorithms↗
PubMed1981

Comparison of three distribution-free procedures in the establishment of assigned values in control sera. The establishment of assigned values in control sera, III.

Distribution-free statistical procedures should be applied to the establishment of assigned values and uncertainty intervals in a control serum. The two problems, how to find an appropriate statistical evaluation procedure and how to find an optimized experimental design, are simultaneously dealt with here: Three distribution-free procedures are presented, each based on elimination of extreme values, and 60 designs are considered differing with respect to the number of reference laboratories, of independent series, and single or double determinations. Using the data of the study described in part 1 of this series (Passing, H. et al. (1981) this j. 19, 1137-1144) we simulated these designs and the pertaining assigned values and uncertainty intervals given by each evaluation procedure. From this study one evaluation procedure is shown to be superior to others. This optimized procedure had the following characteristics: Extreme values are eliminated so that the width of the uncertainty interval is as small as possible. The median of the remaining values is the assigned value. Moreover, 6 reference laboratories are shown to be appropriate.

Alanine Transaminase↗
PubMed2001

Improved inference of mutation rates: I. An integral representation for the Luria-Delbrück distribution.

The estimation of mutation rates is ordinarily performed using results based on the Luria-Delbrück distribution. There are certain difficulties associated with the use of this distribution in practice, some of which we address in this paper (others in the companion paper, Oprea and Kepler, Theor. Popul. Biol., 2001). The distribution is difficult to compute exactly, especially for large values of the random variable. To overcome this problem, we derive an integral representation of the Luria-Delbrück distribution that can be computed easily for large culture sizes. In addition, we introduce the usual assumption of very small probability of having a large proportion of mutants only after the generating function has been computed. Thus, we obtain information on the moments for the more general case. We examine the asymptotic behavior of this system. We find a scaling or "standardization" technique that reduces the family of distributions parameterized by three parameters (mutation rate, initial cell number, and final cell number) to a single distribution with no parameters, valid so long as the product of the mutation rate and the final culture is sufficiently large. We provide a pair of techniques for computing confidence intervals for the mutation rate. In the second paper of this series, we use the distribution derived here to find approximate distributions for the case where the cell cycle time is not well-described as an exponential random variable as is implicitly assumed by Luria-Delbrück distribution.

Cell Cycle↗
PubMed2006

[Abecedary of the "Annales". Part 14].

The terms included and detailed in the present part are: Median, Medline, MeSH, meta-analysis, fixed effects model, random effects model, Mean.

Clinical Trials as Topic↗
PubMed2004

Mixture distribution analysis of a computer assisted diagnostic method for the evaluation of pulmonary nodules on computed tomography scan.

RATIONALE AND OBJECTIVES: To compare the effectiveness of a new computational scheme for pulmonary nodule detection in computed tomography images against human observers. MATERIALS AND METHODS: The study involved evaluation of 81 potential nodules by four radiologists. Each radiologist separately evaluated the potential nodules and provided a confidence level for the presence of pulmonary nodules. Their performance was compared with that of the new computational scheme by mixture distribution analysis. RESULTS: Mixture distribution analysis of the results of the four radiologists demonstrated a relative proportion agreement of 0.84. The kappa statistic was used to compare the agreement of the computational scheme with the results of the four radiologists. A kappa value of .65 (se = .11) was shown to be significantly different from chance (P = .99). CONCLUSION: The new computational scheme correlates well with the radiologists' subjective rankings of pulmonary nodules on computed tomography scans and may prove a useful tool in the evaluation of algorithms for the screening and diagnosis of lung cancer.

Humans↗
PubMed1991

Mapping the distribution of amobarbital sodium in the intracarotid Wada test by use of Tc-99m HMPAO with SPECT.

The intracarotid amobarbital sodium, or Wada, test has been used to localize speech and memory function prior to surgical treatment of temporal lobe seizures. The authors mixed technetium-99m hexamethyl-propyleneamine oxime (HMPAO) with amobarbital sodium and injected the mixture in 25 patients with epilepsy. Single photon emission computed tomography (SPECT) of the brain was then performed to determine intracerebral distribution of the amobarbital sodium. Results of SPECT were compared with those of conventional and digital subtraction angiography (DSA). The distribution of Tc-99m HMPAO and, presumably, amobarbital sodium varied from patient to patient. SPECT revealed a statistically different distribution from that predicted with conventional angiography. The distribution also often differed from that of DSA, although the difference was not significant. SPECT revealed infrequent delivery to mesial temporal lobe structures. This emphasizes the need for caution in the use of the intracarotid amobarbital sodium test to predict the outcome of removal of these areas.

Adolescent↗
PubMed2000

The effect of dose calculation uncertainty on the evaluation of radiotherapy plans.

Monte Carlo dose calculations will potentially reduce systematic errors that may be present in currently used dose calculation algorithms. However, Monte Carlo calculations inherently contain random errors, or statistical uncertainty, the level of which decreases inversely with the square root of computation time. Our purpose in this study was to determine the level of uncertainty at which a lung treatment plan is clinically acceptable. The evaluation methods to decide acceptability were visual examination of both isodose lines on CT scans and dose volume histograms (DVHs), and reviewing calculated biological indices. To study the effect of systematic and/or random errors on treatment plan evaluation, a simulated "error-free" reference plan was used as a benchmark. The relationship between Monte Carlo statistical uncertainty and dose was found to be approximately proportional to the square root of the dose. Random and systematic errors were applied to a calculated lung plan, creating dose distributions with statistical uncertainties of between 0% and 16% (1 s.d.) at the maximum dose point and also distributions with systematic errors of -16% to 16% at the maximum dose point. Critical structure DVHs and biological indices are less sensitive to calculation uncertainty than those of the target. Systematic errors affect plan evaluation accuracy significantly more than random errors, suggesting that Monte Carlo dose calculation will improve outcomes in radiotherapy. A statistical uncertainty of 2% or less does not significantly affect isodose lines, DVHs, or biological indices.

Algorithms↗
PubMed1990

Applicability of Pascal distribution to quantal analysis for non-stationary release of neurotransmitter.

In order to assess the applicability of theoretical distributions to statistical analysis of neurotransmitter release, we made mathematical approaches such as derivation of frequency-generating function of the distributions, and obtained a result that a frequency distribution of the number of quanta released by the consecutive stimulations is described by a Pascal distribution when the Poisson parameter m varies temporally according to a gamma (gamma) distribution. Therefore, if the experimentally obtained distribution fits with a Pascal distribution, this suggests that non-stationary nature of the release mechanism.

Animals↗