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Biomedical subjects

A Hillis

Publications and source records attributed to A Hillis.

At least 37 records · Page 2Linked to original sources
PubMed1986

The Markov process as a general method for nonparametric analysis of right-censored medical data.

The product limit method of Kaplan and Meier for estimating survival functions and the logrank test of Mantel are widely employed for analysis of longitudinal medical data. Developed for analysis of one-time events such as death, survival analysis is also commonly adapted to more complex states such as loss of vision or cancer remission by restricting analysis to first occurrences. The nonparametric discrete time nonhomogeneous Markov process is proposed as a better model for any applications of the latter type. This simple stochastic model allows for an arbitrary number of possible states and for transitions in any direction. Maximum likelihood estimators are easily computed for the stochastic model and are identical to the product-limit estimates in the special case represented by the Kaplan-Meier model. The logrank test extends to evaluation of differences between populations with respect to any specified transition.

Actuarial Analysis↗
PubMed1985

Comparison of sequential anterior and posterior rhinomanometry.

This study was conducted to test the validity in adult subjects of the commonly used technique of summing anterior nasal measurements to describe the patency of the total nose. We measured the total nasal conductance in 36 nonallergic, nonsmoking subjects by use of posterior rhinomanometry (PRM) and compared the results with sequential summed unilateral conductances in the same subjects based on anterior rhinomanometry (ARM). Linear regression of the relationship between the two measures demonstrated significant differences. Variation between these two measures is composed of two parts: random time variation and a component attributable to the difference between methods. Random time variation was estimated from five serial posterior nasal conductances in nine of the subjects in a second experiment. We observed significantly greater variations between ARM and PRM than between PRM measures separated by similar time intervals (F 36.36 = 2.30, p less than 0.01). We conclude that PRM is significantly more accurate than summed ARM when the goal is to quantitate precisely the patency of the nose as a whole at a given instant in time, and yet summed ARM measurements may be acceptable in clinical studies wherein large changes in nasal patency occur.

Adolescent↗
PubMed1985

Tests for departure from normal in laboratory data.

This study was undertaken to compare several methods of evaluating the common assumption that laboratory data may be treated as if they had been drawn from an underlying Gaussian distribution. As had been described earlier, the usual Kolmogorov-Smirnov test was found to be unsatisfactory due to its sensitivity to rounding. In addition, a recently suggested modification also was shown to be unsuitable, because it was quite insensitive when applied to simulated data known to be positively skewed. The authors suggest the following: that the coefficients of kurtosis and skewness are valuable for use against specified alternatives; that the traditional Kolmogorov-Smirnov test is appropriate if the degree of rounding is minimal; and that a satisfactory "omnibus" test is not yet available.

Blood Chemical Analysis↗
PubMed1983

The second eye of patients with senile macular degeneration.

Patients with senile macular degeneration and exudative maculopathy in one eye and drusen in the second eye have a 3% to 7% risk per year of exudative maculopathy developing in the second eye during the first three years following their initial presentation. The risk is the same for patients with new vessel membranes or other types of exudative maculopathy in the first eye. Second eyes in which exudative changes develop are more likely to have larger numbers of drusen or greater confluence of drusen (or both) initially. The data from this study were analyzed using the Kaplan-Meier technique of estimation, a method (to our knowledge) not previously employed by other investigators. The demographic features of the overall study population, as well as the photographic features associated with increased risk of development of exudative maculopathy, were in agreement with those previously reported.

Aged↗
PubMed1982

Scleropachynsis maculopathy.

To our knowledge, this is the first clinicopathologic report of a previously unrecognized maculopathy in which there is thickening and mucopolysaccharide deposition in the sclera subjacent to the macula. A healthy 50-year-old man had bilateral mottling of the retinal pigment epithelium (RPE) in the macular region. The left eye was enucleated because of a choroidal melanoma. Histopathologic examination disclosed a thickened sclera with abnormal collagen fibrils with diameters up to 5,800 A and compressed choroid. The overlying RPE had areas of hypopigmentation, hyperpigmentation, and hyperplasia and contained intracytoplasmic lipofuscin.

Choroid↗
PubMed1982

Ocular findings in osteogenesis imperfecta congenita.

Osteogenesis imperfecta is a rare, inherited, connective-tissue disorder. The three main signs of this disease are multiple bone fractures, blue scleras, and deafness (osteosclerotic type). In our research, only a few reports of the morphologic studies of the eyes of patients with osteogenesis imperfecta were found. This report describes the ocular histopathologic condition of four cases of osteogenesis imperfecta congenita, with emphasis on the ultrastructural characteristics of the collagen in the cornea and sclera.

Cornea↗
PubMed1982

Natural course of choroidal neovascular membranes within the foveal avascular zone in senile macular degeneration.

We divided 96 eyes (93 patients) with senile macular degeneration and choroidal neovascular membranes into two groups--those with juxtafoveal membranes (1 to 250 mu from the center of the foveal avascular zone) and those with subfoveal membranes (0 mu from the center of the zone). After an average follow-up period of 21 months, one of 38 eyes in the juxtafoveal group (3%) had improved two or more lines on the Snellen chart, three eyes (8%) had remained the same, and 34 eyes (89%) had lost two or more lines on the Snellen chart. Although 35 of the 38 eyes (92%) had had initial visual acuities of 6/30 (20/100) or better, 27 eyes (71%) had become legally blind. Of the 58 eyes in the subfoveal group, 18 (31%) had remained the same or improved and 40 (69%) had lost two or more lines on the Snellen chart; 41 (70%) had final visual acuities of 6/60 (20/20) or worse. Of the 26 eyes in the subfoveal group that had had initial visual acuities of 6/60 (20/100) or better (45%). four (15%) had stayed the same and 22 (85%) had lost two or more lines on the Snellen chart. Fourteen of the 26 eyes (54%) had final visual acuities of 6/60 (20/200) or worse. Exudative maculopathy developed in the second eye in 13% of patients who initially had unilateral choroidal neovascularization after 12 months, in 22% after 24 months, and in 29% after 36 months, using life table analysis.

Adult↗
PubMed1982

Branch vein occlusion. Retinal neovascularization outside the involved segment.

Three hundred sixty-six cases of branch vein occlusion entered within the multicenter Branch Vein Occlusion Randomized Clinical Trial have been reviewed. Four cases that developed retinal neovascularization outside of the retinal area involved with the occlusion have been documented by photography and fluorescein angiography.

Aged↗
PubMed1981

HLA antigens and HBV infection: evaluation in the chronic carrier state and in a large family.

HLA antigens were determined in 65 apparently well chronic carriers of HBsAg, in race-matched controls and in 42 members of a family with a high frequency of hepatitis B virus infection. The only apparent significant association in the chronic carriers was negative, i.e., no HLA-B7 specificities were found among whites. B7 may confer resistance for whites to chronic infection with hepatitis B. In the family neither active (HBsAg) nor prior (anti-HBs) hepatitis B infection was associated with HLA specificities. HLA antigens in this family failed to provide a clue to the genetics of hepatitis B infection.

Carrier State↗
PubMed1981

Hepatitis B infection in patients with end stage renal disease: some characteristics and consequences.

Susceptibility to hepatitis B infection appears to be in part genetically determined. The HLA specificity Bw35 is commonly associated with a higher frequency of both transient and persistent hepatitis B surface antigen in the serum. Persistent hepatitis B surface antigenemia occurring in patients with end stage renal disease while on dialysis is associated with a poor prognosis and markedly decreased survival regardless of whether the individual is treated subsequently by chronic dialysis or by transplantation. We conclude that persistent hepatitis B surface antigenemia is not a contraindication to transplantation since outcome is not improved by management on hemodialysis.

Hepatitis B Surface Antigens↗