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Biomedical subjects

D T Allen

Publications and source records attributed to D T Allen.

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

Flow characteristics of four commonly used mechanical heart valves.

The in vivo and in vitro fluid dynamic performance of 4 mechanical heart valves was reviewed: Starr-Edwards silicon-rubber ball valves (models 1200/1260 aortic and 6120 mitral valves), Björk-Shiley tilting disc valves (standard spherical model, modified and unmodified convexo-concave [60 degrees and 70 degrees C-C] models), the Medtronic-Hall (Hall-Kaster) tilting disc valve and the St. Jude Medical bileaflet valve. These valves were chosen because of their past or present popularity in clinical use and because they encompass most of the basic mechanical valve designs used during the past 2 decades. The flow measurements reported include in vivo and in vitro mean pressure drop, cardiac output or cardiac index, regurgitant volume, effective orifice area and performance index.

Cardiac Output↗
PubMed1986

Comparison of the effects of 3-ethoxycarbonyl-1,4-dihydro-2,4-dimethylpyridine and 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine on ferrochelatase activity and heme biosynthesis in chick embryo liver cells in culture.

3-Ethoxycarbonyl-1,4-dihydro-2,4-dimethylpyridine (EDP) was shown to lack the ferrochelatase-lowering activity of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) in chick embryo liver cells in culture. This was attributed to the inability of EDP to cause destruction of the heme moiety of cytochrome P-450 with concomitant formation of N-methylprotoporphyrin IX. EDP was less potent as a porphyrinogenic agent than DDC and caused the accumulation of uroporphyrin, heptacarboxylic porphyrin, and coproporphyrin in contrast with DDC which caused primarily protoporphyrin to accumulate. The inactivity of EDP as a ferrochelatase-lowering agent and its low porphyrinogenic potency was explained, at least in part, by its rapid transformation in aqueous solution to other nondihydropyridine products. The two ethoxycarbonyl substituents of DDC are therefore essential for N-methylprotoporphyrin formation, ferrochelatase-lowering activity, and optimal porphyrin-inducing activity.

Animals↗
PubMed1985

Neonatal outcome in planned v unplanned out-of-hospital births in Kentucky.

We conducted a survey of 1,064 out-of-hospital Kentucky births during 1981 to 1983 in order to classify each by planning status (planned or unplanned to occur out of hospital) and attendant. Among the 809 births for which we obtained information, 575 (71.1%) were planned. We examined birth outcome by low birth weight (LBW) and neonatal mortality (NM). Compared with planned births, unplanned births were associated with increased risk of LBW (odds ratio = 6.6; 95% confidence limits [CL], 3.9 to 11.2, adjusted for maternal age). Furthermore, after adjusting for maternal age and parity, LBW births occurred at less than expected frequency among planned births (observed to expected [O:E] ratio = 0.48; 95% CL, 0.29 to 0.73), but at greater than expected frequency among unplanned births (O:E ratio = 2.9; 95% CL, 2.2 to 3.8). A similar, but nonsignificant, trend was seen for NM and NM was much greater in the unplanned group (72.7 per 1,000 live births) than in the planned group (3.5 per 1,000).

Adolescent↗
PubMed1985

Suicidal destruction of cytochrome P-450 and reduction of ferrochelatase activity by 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine and its analogues in chick embryo liver cells.

The ferrochelatase-reducing activity and cytochrome P-450- and heme-destructive effects of a variety of analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) were studied in chick embryo liver cells. A group of DDC analogues was found in which an inability to reduce ferrochelatase activity corresponded with an inability to cause cytochrome P-450 and heme destruction. In a second group of DDC analogues, the ability to reduce ferrochelatase activity corresponded with the ability to cause cytochrome P-450 and heme destruction. These observations support the idea that the protoporphyrin IX moiety of N-alkylprotoporphyrin IX originates from the heme moiety of cytochrome P-450. A third group of DDC analogues caused cytochrome P-450 and heme destruction despite an inability to reduce ferrochelatase activity. With this third group of DDC analogues, the heme moiety of cytochrome P-450 is likely degraded to products other than N-alkylporphyrins. The inability of several lipophilic DDC analogues [4-benzyl, 4-isopropyl, 4-cyclohexyl, 4-(3-cyclohexenyl)] to reduce hepatic ferrochelatase activity may explain their low porphyrinogenicity. The pattern of porphyrin accumulation produced in response to two DDC analogues that did not inhibit ferrochelatase was investigated using high performance liquid chromatography. Coproporphyrin was the major porphyrin to accumulate in response to the 4-isopropyl analogue and uro- and heptacarboxylic acid porphyrins in response to the 4-benzyl analogue. These patterns of porphyrin accumulation are consistent with the inability of these analogues to inhibit ferrochelatase.

Animals↗
PubMed1984

Site-specific cancer mortality trends among Kentucky residents: comparison of 1971 to 1975 with 1976 to 1980.

We compared the average annual age-adjusted, sex- and site-specific cancer mortality rates among Kentuckians during two five-year time periods: 1971 to 1975 and 1976 to 1980. Lung cancer alone showed a statistically significant increase in mortality rates for both sexes, but significant increases were also found for skin cancer and leukemias among men and for pancreatic cancer and lymphomas among women. Significant decreases in mortality rates were observed for cancer of the rectum and stomach in both sexes, lymphomas among men, and leukemias and liver and uterine (corpus and cervix) cancer among women. Increased lung cancer mortality rates occurred for all age groups of women aged 35 and over, but in men, decreased lung cancer mortality rates were observed for ages 35 to 49 and increased rates only after age 50. All age groups of women experienced substantial declines in cervical cancer mortality rates. Without the dramatic increase in lung cancer mortality during this period, overall cancer mortality rates would have shown almost no change among Kentucky men and would have decreased among Kentucky women.

Adult↗
PubMed1982

Family planning and abortion: have they affected fertility in Tennessee?

In Tennessee between 1975 and 1978, birth rates among teenagers decreased while they increased among older age groups. This trend was unlike previous years and coincided temporally with the increased availability of legal abortion services in Tennessee and the special efforts to prevent unwanted pregnancies among teenagers. Increased use of family planning services was significantly associated with the drop in the fertility rate for Black teenagers; legal abortion use was significantly associated with the change in the fertility rate for Black females aged 20 years or older.

Abortion, Legal↗
PubMed1975

The epidemiology and interrelationship of cervical dysplasia and type 2 herpesvirus in a low-income housing project.

This report examines the association between cervical dysplasia and herpes simplex virus type 2 antibodies in a low-income housing project, Atlanta, Georgia. We established a clinic in this project at which women could receive a breast examination and Papanicolaou smear and have blood drawn to be tested for herpesvirus type 2 antibodies. Prevalence of herpesvirus rose sharply as age increased. There was a significant absence of antibodies in young, nulliparous women. Dysplasia showed a tendency to be related to age, age at first pregnancy, and total number of pregnancies. None of these associations was significant. The major finding of the study was that the 15- to 24-year-old women with herpesvirus had a relative risk of 5.44 of having cervical dysplasia compared to women without herpesvirus antibodies. these data are consistent with the concept that herpesvirus infections may be etiologically related to the initiation of cervical neoplasia. However, a cohort study is needed to determine whether herpes infection precedes or follows the earliest neoplastic changes.

Adolescent↗