PubMed Health⌕ Search

Biomedical subjects

P M Kulkarni

Publications and source records attributed to P M Kulkarni.

11 recordsLinked to original sources
PubMed2000

Maximum likelihood estimation for longitudinal data with truncated observations.

We obtain maximum likelihood estimates of the parameters when the observations on the response variable in a repeated measures design are truncated above a cutpoint. The maximum likelihood equations are solved iteratively using an EM-like procedure. It is observed that these estimates have smaller mean squared error than recently proposed iterative weighted least-squares estimates. The results are applied to data arising from a study of dioxin elimination in Air Force veterans. Published in 2000 by John Wiley & Sons, Ltd.

Aerospace Medicine↗
PubMed1999

Analysis of in vitro migration patterns of human spermatozoa by a petri dish-based horizontal column.

Spermatozoa are required to travel a considerable distance in vivo to meet the oocyte at the fertilization site. However, none of the existing in vitro tests critically evaluates migration of sperm to assess their potential of reaching the oocyte. On the other hand, an in vivo model is not suitable for this type of study because of ethical and technical constraints. In the present study we utilized a horizontal column technique to analyze sperm migration. Migratory characteristics of fresh, unwashed semen sperm and sperm undergoing various treatments were examined in vitro using a Petri dish-based horizontal fluid column. The procedure involved loading a sperm sample into the column and determining sperm concentration, motility, and viability at different column segments for different migration durations (6, 12, 24, 48, and 72 h). All sperm samples produced an exponential migration pattern in all durations of migration. Propagation along the column edge, tendency to exit from the column, and hiding in the blind pouches were some of the important characteristic features exhibited by the migratory sperm. Variations in migration patterns were documented among semen donors, between fresh and frozen semen, and between washed and unwashed sperm. Prolonged postejaculation time diminished migratory potential. The recovery of sperm in the column end was independent of seminal variables with the exception of oligozoospermia. These observations suggest that the Petri dish-based horizontal column is effective for analyzing sperm migration characteristics for prolonged periods. The potential of this migration assay in predicting the in vivo potential of spermatozoa to reach the fertilization site will be worth exploring.

Humans↗
PubMed1998

Maximum (Max) and Mid-P confidence intervals and p values for the standardized mortality and incidence ratios.

The authors present algorithms to compute the confidence interval for a Poisson parameter (lambda) and the p value for testing the hypothesis that lambda is equal to a constant, which can be used to make inferences about the standardized mortality ratio and the standardized incidence ratio. The p value and confidence interval always agree, despite the discrete nature of the Poisson distribution. The authors also give simple equations to compute numeric approximations of the confidence limits that do not require the use of any probability distributions. An example based on data arising from a study of cancer incidence is given.

Algorithms↗
PubMedDate not supplied

Lack of significant morphological differences between human X and Y spermatozoa and their precursor cells (spermatids) exposed to different prehybridization treatments.

Human X and Y spermatozoa were previously compared by several nonmolecular techniques. Recent studies show that in many of the previous investigations, the methods used to identify the spermatozoa were nonspecific and thus produced contradictory findings. In the present study, the comparison of the 2 germ cell types, X and Y, were performed following fluorescence in situ hybridization (FISH), which is the most reliable genotyping technique currently available. The FISH technique was performed under 3 different treatments: permeabilization with liquid N2, fixation with Carnoy's, and chromatin decondensation with lithium di-iodosalicylate. Mature and immature germ cells (spermatozoa and spermatids) were compared. Lithium showed higher hybridization efficiency, while liquid N2 and Carnoy's fixative maintained better morphological integrity of cells with lower hybridization. The sperm exhibiting hybridization signals were not different in any of the morphometric or qualitative comparisons from those that did not exhibit signals. No significant deviation of the sex ratio from 1:1 was seen in either the mature or immature germ cell population. The spatial distribution of X and Y chromosome-specific signals in the sperm head were identical. The hybridization treatments did not have any preferential effect on the cells of specific genotype (X or Y). Neither head parameters (length, HL; width, HW; area, HA) nor tail length (TL) significantly differed between X and Y populations of spermatozoa under any of the treatments. Similarly, the haploid, X-specific round cells did not differ from Y-specific ones by their size (diameter) and shape. These results indicate that neither mature sperm nor their precursors possess significant morphological differences between X and Y genotypes.

Cell Separation↗
PubMedDate not supplied

The reliability of the serum dioxin measurement in veterans of Operation Ranch Hand.

A study was conducted on the reliability of the serum dioxin measurement of enlisted Ranch Hands veterans participating in the Air Force Health Study using paired serum dioxin measurements. The 46 veterans were not randomly selected, but their demographic characteristics, health, and dioxin levels were similar to those of 404 other enlisted Ranch Hand veterans who had a single dioxin measurement made in 1987. The average time between the measurements was 0.61 years, the first measurement made from blood drawn on 10 April 1987 and the second from blood collected at a subsequent physical examination. In original unit, the coefficient of reliability was 0.87 (95% confidence interval: 0.76, 0.94) when the first measurement was at or below 50 parts per trillion. The measurement had no reliability in original units when the first measurement was greater than 50 parts per trillion. After a logarithmic transformation, the coefficient of reliability was 0.96 (95% confidence interval: 0.93 to 0.98). These results suggest that the serum dioxin measurement should not be used in original units for any purpose when the value exceeds 50 parts per trillion. The measurement is, however, highly reliable after a logarithmic transformation over the entire range of concentrations. Other studies using the same analytical method to measure dioxin in serum could similarly benefit if the measurement used is on the natural logarithm scale.

Aerospace Medicine↗
PubMedDate not supplied

Levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 1,302 unexposed Air Force Vietnam-era veterans.

We summarize the distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in 1,302 Air Force veterans who serve as controls in a 20-year prospective epidemiologic study of health and exposure to herbicides and their dioxin contaminant in Air Force veterans of Operation Ranch Hand, the unit responsible for aerial spraying of Agent Orange and other herbicides in Vietnam. We present statistics summarizing the dioxin distribution overall and by stratum of age and body mass index of these veterans. The average dioxin measurement was 4.23 and the standard deviation was 2.53 parts per trillion. With 95% confidence, 99% of the distribution is less than or equal to 10.4 parts per trillion.

Adult↗