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Biomedical subjects

L Stevens

Publications and source records attributed to L Stevens.

At least 145 records · Page 8Linked to original sources
PubMed1986

In vitro and clinical studies on intravenous feeding mixtures comprising fat emulsion, amino acid and electrolytes.

This paper describes the effect of the amino acid mixture Freamine II on the physical stability of Intralipid fat emulsion. The amino acid-fat emulsion mixture was also administered to patients requiring intravenous nutrition and its clinical and biochemical effects were assessed. The amino acid-fat emulsion mixture was stable on storage for 48 hours as judged by flocculation and particle growth measurements made in the presence of 20 mmol/1 monovalent cations at 2 mmol/1 diavalent cations. Long-term storage of mixtures containing Freamine II is not recommended because of an interaction between the emulsifier and the amino acids. In a small open trial patients maintained their serum albumin concentrations. There was no evidence of impaired pulmonary function even in those subjects with impaired fat clearance.

Journal Article↗
PubMed1986

Can noncardiac muscle provide useful cardiac assistance? Preliminary studies of the properties of skeletal muscle.

The treatment of end-stage cardiac disease is the focus of extensive investigation. Both cardiac transplantation and mechanically powered assist devices are currently in use. However, transplant recipients are at constant risk of infection and rejection, and patients with mechanical assists are tethered to external driving devices. These limitations have led to the investigation of methods of cardiac support that rely on autogenous tissue. The current study tests the ability of skeletal muscle to produce cardiac-type work. The cephalic half of one rectus abdominis muscle was mobilized (taking care to preserve the attachment to the superior epigastric vessels) in 12 canines. The muscle was formed into a cylindric pouch around a bladder device. This allowed the determination of the pressure and flow produced by the muscle. The muscle was stimulated to contract at a rate of 60 contractions per minute using twin stimuli of 80 ms duration. The muscle pouch yielded a maximal isovolumetric pressure of 282 mm Hg, which equalled 245 per cent of the dog's systolic blood pressure. In addition, the pouch produced a flow of 1.88 L per minute (73% of the dog's cardiac output) and a power output of 0.22 watts (39% of the dog's left ventricular power), while pumping against an afterload of approximately 2/3 the systemic resistance. Also, the muscle demonstrated an ejection fraction of 62.7 per cent. These data indicate that a hydraulic pouch formed from rectus abdominis muscle is capable of pumping function that may be able to assist the compromised ventricle. However, total replacement of cardiac function does not seem feasible.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Muscles↗
PubMed1986

Previous alcohol intake and residual cognitive deficits in detoxified alcoholics and animals.

A common assumption is that protracted alcohol consumption is causally related to the intellectual impairment seen in sober recovering alcoholics. However, attempts to demonstrate consistent and significant relationships between alcohol intake and cognitive-perceptual functioning in such alcoholics have been inconclusive. A review of the human studies indicates that the inconsistent results cannot be accounted for by potentially confounding variables such as age, education, sex, days abstinent, years of abuse, type of hospital and number of tests used. In detoxified mice and rats there is clear evidence for a causal relationship between duration of alcohol intake and learning and memory tasks, although limited mainly to studies of relatively high levels of alcohol intake and performance on a few types of tasks. These studies suggest a duration threshold for impairment before which impairment does not occur and after which there is a systematic inverse relationship between duration and quality of performance. Finally there is an asymptote effect where, with increase in duration and increase in age, there is no corresponding decrement in performance. A number of promising areas to be investigated using the rodent model are discussed. Findings from such investigations should have heuristic value for human studies. Reasons for the inconsistent results in humans are detailed and suggestions offered to facilitate further research in this area.

Adult↗
PubMed1985

Microorganism mediated reproductive isolation in flour beetles (genus Tribolium).

Reproductive isolation is induced by microorganisms in diverse geographic strains of the flour beetle Tribolium confusum (Coleoptera:Tenebrionidae). The incompatibility between populations is due to nongenetic cytoplasmically inherited factors. Males of infected strains produce no progeny when crossed with females of noninfected strains; however, they produce "normal" numbers of progeny when crossed with infected females. Males from noninfected strains show no reproductive isolation. Infected strains of T. confusum can be cured when tetracycline or other antibiotics are added to the flour medium. "Cured" strains become partially reproductively isolated from all noncured strains including the source strain

Animals↗
PubMed1985

Surgery for discrete subvalvular aortic stenosis: actuarial survival, hemodynamic results, and acquired aortic regurgitation.

Discrete membranous subaortic stenosis (DMSS) accounts for 8 to 30% of congenital left ventricular outflow obstruction. The immediate effectiveness of surgical resection of this discrete obstructing membrane has been well documented, but little has appeared regarding late clinical and hemodynamic follow-up. Fifty-three patients with DMSS underwent operation at our institution from 1957 to 1983. Most (78%) were symptomatic, 79% had left ventricular hypertrophy (LVH) by electrocardiogram, and 92% had roentgenographic evidence of cardiomegaly preoperatively. Catheterization revealed a mean preoperative left ventricular-aortic gradient of 89 mm Hg. Twenty-eight patients had associated aortic insufficiency (AI) on the initial aortogram. Seven patients acquired AI in the interim between the first and second preoperative catheterization. Our patients have been followed for up to 12 years postoperatively. There have been 2 early and 3 late deaths. (Actuarial analysis revealed 5- and 10-year survival of 95% and 83%, respectively.) Seventy-one percent of the previously symptomatic patients noted relief of their preoperative complaints, and 45% of those with LVH had a regression in voltage. Cardiomegaly as determined by chest roentgenogram decreased in 45%. The left ventricular-aortic gradient fell to an average of 35 mm Hg a year postoperatively. Surgical treatment of congenital subvalvular aortic stenosis is effective in reducing the preoperative symptoms and the left ventricular-aortic gradient. It appears that DMSS causes AI.

Actuarial Analysis↗
PubMed1985

Heart transplantation at a private institution: a two year experience.

Since October 1982, 45 patients were referred and 15 underwent orthotopic heart transplantations. Eleven patients are presently alive. The donor heart ischemic time averaged 104 minutes for locally procured hearts and 183 minutes for hearts harvested in distant cities. Ninety-three percent of the patients survived the perioperative period. Survival rate at six months was 84%, at one and two years 72% and 52%, respectively. The one year survivors spent 80% of their time out of the hospital. The average cost for the transplant admission was $58,023. Four patients died 11 days, 57 days, 8 and 12 months after the operation. During the first three months there were 0.75 rejection episodes, 1.13 infections and 1.40 other complications per patient. We conclude that heart transplantation can be successfully carried out at a private institution, with excellent survival rates and at reasonable costs. In spite of progress, infection and rejection still account for most of the mortality and morbidity.

Adolescent↗
PubMed1984

Transformation and tumor promoter sensitive phosphoproteins in JB-6 mouse epidermal cells: one is also sensitive to heat stress.

JB-6 mouse epidermal cells undergo irreversible transformation when exposed to tumor-promoting agents such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Phosphoprotein changes related to transformation were sought in four tumor cell lines related to JB-6 cells. Two dimensional polyacrylamide gel electrophoresis showed altered abundances of five phosphoproteins in the tumor cell lines compared with five untransformed clones. The mol. wt. in Kilodaltons and isoelectric points in pH units were: 120/6.0, 80/4.5, 55/6.5, 37/5.0 and 23-25/4.5. In all four transformants pp80 was markedly decreased and the pp23-25 doublet increased. In two of the four transformants pp120 and pp55 were increased and pp37 decreased. Treatment of untransformed clones with TPA affected only one of the phosphoproteins altered in the transformants. Treatment of untransformed clones with TPA produced a 2-fold increase in pp80 after 5 h. pp80 returned to baseline levels by 24 h and changed little in the continuous presence of TPA for up to 96 h. The increase in pp80 with short term TPA treatment occurred in all of the untransformed clones but none of four transformants. Late preneoplastic (P+) JB-6 cells only require treatment with a tumor promoter to transform. Early preneoplastic (P-) JB-6 cells require prior transfection of DNA from late preneoplastic JB-6 cells to transform in response to tumor promoter treatment. Quantitative analysis of pp80 in early preneoplastic, late preneoplastic, and tumor cell lines showed an inverse relationship between the level of pp80 and degree of preneoplastic progression in these cells. pp80 represents approximately 2% of total cellular phosphoprotein in JB-6 cells, shows microheterogeneity of both mol. wt. and isoelectric point, occurs in the particulate fraction of cells and is readily solubilized by 1% Triton. pp80 is increased by heat stress and shares other properties with the recently described mammalian heat stress protein, hsp 80. pp80's decrease in four out of four tumor cell lines, inverse correlation with stage of preneoplastic progression and responsiveness to TPA in preneoplastic but not in tumor cell line suggest that pp80 may be closely linked to biochemical mechanisms underlying transformation in this cell system.

Animals↗
PubMed1984

Comparative study of the neutral proteinases from fungi and actinomycetes using polyacrylamide gel electrophoresis.

Neutral proteinases from mycelial extracts of fungi and actinomycetes may be readily detected by polyacrylamide gel electrophoresis in which azocasein is incorporated into the gels. Most of the proteinases detectable at pH 6.5 were sensitive to both phenylmethanesulphonyl fluoride and to mercuric chloride. In all the species examined, except for one, the proteinase activities in the mycelial extracts increased during storage at 19 degrees C.

Electrophoresis, Polyacrylamide Gel↗