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Biomedical subjects

A Baxter

Publications and source records attributed to A Baxter.

At least 37 records · Page 2Linked to original sources
PubMed1994

Affective expressions of toddlers with and without Down syndrome in a social referencing context.

Affective expressions of 11 toddlers with Down syndrome and 11 toddlers with no disabilities were compared. Each child participated, with one parent, in a social referencing procedure. Children's MAs ranged from 12 to 23 months. Parents posed positive or fearful expressions during presentations of ambiguous stimuli. Lability and intensity of children's expressions and regulation of affect were noted. Expressions of toddlers with and without Down syndrome were equally labile and intense. However, toddlers without Down syndrome tended to match their parents' expressions. Toddlers with Down syndrome did not match their parents expressions; instead, they responded with positive affect following fearful parental communications. Results were discussed in terms of the impact of emotional predictability and responsivity on caregiving interactions.

Affect↗
PubMed1994

An ordinal pattern analysis of four hypotheses describing the interactions between drug-addicted, chronically disadvantaged, and middle-class mother-infant dyads.

This study investigated mother-infant interactions in 18 dyads. All participants were African American and enrolled in an early intervention program because the infants (2-26 months of age) had developmental disabilities or were at high risk for developmental disability. Some mothers had used drugs during their pregnancy, and all mothers were of low or middle socioeconomic status. Dyads were videotaped interacting at 4 different times, separated by at least 5 months in time. Videotapes were rated in terms of infant involvement and maternal responsivity in the interaction. 4 hypotheses concerning the pattern of maternal interaction across time were tested using ordinal pattern analysis. The hypothesis that mothers would become less responsive to infants over time (HD) as a function of drug addiction, poverty, or serious developmental delay was supported for only 4 of the 18 dyads. There was support for the hypothesis (H(I)) that mothers naturally increase their responsivity over time (N = 6) and support for the hypothesis (HT) that mothers' interactive sensitivity fluctuates in relation to infants' involvement in the interaction over time (N = 7). Ordinal pattern analysis has advantages in determining how well competing hypotheses describe individuals within populations relative to approaches that identify differences that apply to entire populations.

Adult↗
PubMed1992

Squalestatin 1, a potent inhibitor of squalene synthase, which lowers serum cholesterol in vivo.

Squalestatin 1 is a member of a novel family of fermentation products isolated from a previously unknown Phoma species (Coelomycetes). Squalestatin 1 is a potent, selective inhibitor of squalene synthase, a key enzyme in cholesterol biosynthesis; in vitro, 50% inhibition of enzyme activity is observed at a concentration of 12 +/- 5 nM (range of 4-22 nM). Squalestatin 1 inhibits cholesterol biosynthesis from [14C]acetate by isolated rat hepatocytes (50% inhibition at 39 nM) and by rat liver in vivo. In marmosets, a species with a lipoprotein profile similar to that of man, squalestatin 1 lowers serum cholesterol by up to 75%. This compound will allow further investigation of the control of the sterol biosynthesis pathway and could also lead to the development of new therapies for elevated serum cholesterol.

Animals↗
PubMed1992

Improved method for i.r. determination of the degree of N-acetylation of chitosan.

Three published i.r. absorption band ratios for determining the % N-acetylation of chitosan have been used to follow the rate of alkaline deacetylation of chitin. Only one, the A1655/A3450 ratio, gives the expected rate of deacetylation curve. Consideration of the various i.r. ratios has led to a new relationship, % N-acetylation = (A1655/A3450) x 115, where the absorbance of the amide I band at approximately 1655 cm-1 is determined using the baseline proposed previously. The values obtained using this proposed relationship agree closely with those obtained from dye adsorption measurements for chitosans having % N-acetylation values in the range 0-55%.

Acetylation↗
PubMed1992

Comparison of vascular opacification after bolus injection of iodixanol-320 iohexol-350.

RATIONALE AND OBJECTIVES: The vascular opacification characteristics of a new nonionic, dimeric contrast agent, iodixanol, have been compared with a nonionic, monomeric agent, iohexol, using ultrafast computed tomography (UFCT). METHODS: In 10 experiments with mongrel dogs, the contrast agents were alternately injected into the animal's left atrium, and UFCT images were obtained at four cross-sectional levels through the carotid arteries. Time-density curves were then obtained for each carotid artery and each agent. The peak height and area under the curves were compared for each agent. RESULTS: Iohexol provided significantly (P < or = .05) greater opacification, determined by paired Student's t tests. CONCLUSION: This result was predicted from the greater iodine concentration of iohexol (350 mg/mL) compared with iodixanol (320 mg/mL); the difference was greater than expected based on iodine content alone.

Animals↗
PubMed1991

Contingent provision of social referential information by parents of children with and without developmental delays.

Social referencing involves using information from other persons to guide behavior and affect in ambiguous situations. Children's behavior toward a stimulus paired with positive affective messages was compared to behavior toward a stimulus paired with fearful messages. Normally developing children, but not those with delays, showed evidence of behavior regulation, touching positive-message more than fearful-message toys. Parental communications were more regularly preceded by children's looks in dyads with normally developing children. Parents of children with delays often initiated unsolicited communications in addition to responding to children's initiations. Children with delays regulated behavior only when messages were contingent upon looks. Parental contingency was not associated with behavior regulation in dyads with normally developing children.

Affect↗
PubMed1990

Substrate and inhibitor studies with human gastric aspartic proteinases.

The separation of pepsin isoenzymes 1, 2, 3 and 5 (gastricsin) in human gastric juice was effected by chromatography on Mono Q ion-exchanger, and slow-moving proteinase was purified to homogeneity by using a modified procedure incorporating a novel affinity-chromatography step. The pH-activity profiles of these enzymes with mucus glycoprotein and basement-membrane substrates were determined; the profiles for pepsin 2 were noticeably different, and, in general, the pH optima for the hydrolysis of basement membrane were more acidic. Pepsin 1 expressed larger specificity constants (kcat./Km) than pepsin 3 with a series of synthetic peptide substrates, reflecting greater binding (smaller Km) by pepsin 1. Inhibitor studies at pH 1.7 and 4.5 with a series of P2-substituted lactoyl-pepstatins implied that valine at position P2 was optimal for inhibiting pepsins 1, 2 and 3 but detrimental for pepsin 5, whereas lysine at position P2 was tolerated well by pepsin 5 but not by pepsins 1, 2 and 3. The potency of lactoyl-pepstatin with lysine at position P2 did not increase as a function of pH. P2-substituted lactoyl-pepstatins failed to show any inhibitory selectivity among pepsins 1, 2 and 3.

Basement Membrane↗
PubMed1989

Proteolytic activities of human Campylobacter pylori and ferret gastric Campylobacter-like organism.

The levels of proteolytic activity in cell washes, lysates and pellets of C. pylori and gastric Campylobacter-like organisms isolated from humans and ferrets, respectively, have been studied using porcine mucus glycoprotein and bovine haemoglobin substrates. The total haemoglobin degrading activity, expressed by 10(12)-10(13) cfu of either organism, was no greater than 3 micrograms chymotrypsin equivalents. The mucolytic specific activity (rate of mucus peptide bond hydrolysis by bacterial protein) of the fractions tested from both organisms did not exceed 2nmol/min/mg protein. This value is 1000-fold lower than expected from published data. Electrophoretic profiles suggested that the mucolytic activity assessed by fluorimetry was insufficient to alter the quaternary structure of mucus and hence may not significantly contribute to the undermining of gastric mucus integrity.

Animals↗
PubMed1989

The effect of context and age on social referencing.

The present study investigated social referencing in 2 settings, familiar child-care centers and an unfamiliar university laboratory. 48 children from 6 to 40 months, divided into 3 age groups (6-12, 13-23, and 24-40 months), participated with 1 parent. Looking at parents varied with age and setting. Younger children looked more often when parents expressed positive reactions, whereas middle children looked more at fearful expressions, and the oldest children looked equally at positive and fearful expressions. Children looked at their parents sooner and were more involved with parents in the child-care setting. Behavioral regulation--less play with the fearful-message than the positive-message toy--was observed in both settings. Affect was not influenced by setting and showed regulation only for the oldest children. These results indicate that some effects of social referencing, such as behavior regulation, may be generalizable across some settings, but that parent proximity and looking at parents are sensitive to the context in which referencing occurs.

Affect↗
PubMed1984

Leukocyte-depleted blood: a comparison of available preparations.

Febrile nonhemolytic transfusion reactions due to leukoagglutinins are frequently seen in patients who have been given multiple blood transfusions. To prevent or reduce the severity of these reactions, leukocyte-poor blood (that containing fewer than 0.3 X 10(9) leukocytes per unit) is frequently requested by clinicians. Four methods commonly used in Canada to produce leukocyte-poor blood were examined for their relative effectiveness and appropriate use. The mean total leukocyte count per unit was reduced to 0.22 X 10(9) in buffy-coat-poor red blood cell preparations produced by centrifugation with the blood bag inverted, to 0.19 X 10(9) by perfusion through an Imugard filter, to 0.21 X 10(9) by the use of an IBM 2991 automated cell washer and to 0.13 X 10(9) with the use of frozen blood. The proportion of red cells recovered varied from 62% with the inverted-spin method to 85% with the use of frozen blood. Comparison of these data and the percentage of leukocytes removed, the shelf life of the product, the cost of supplies and the preparation time indicated that the use of sophisticated machinery, such as the IBM cell washer, or of glycerolization plus washing of frozen cells is not warranted for most patients. Instead, patients who have febrile nonhemolytic transfusion reactions should initially be treated with a leukocyte-poor red cell preparation produced by the inverted-spin method; only if such reactions recur should the blood bank be requested to provide filtered, washed or frozen red cells.

Blood Transfusion↗
PubMed1982

Patient management problems. Issues of validity.

Patient management problems (PMP) are being used in medical examinations with increasing frequency despite evidence which throws doubt on their validity as measures of clinical competence. This study investigated the construct validity of a PMP constructed in both written and interview formats. Each test was administered to groups of students of different seniorities and to two groups of doctors, interns and post-interns. The pattern of scores for the different groups was not that expected of a valid test of competence. The most competent groups (the post-interns) generally scored less well on the calculated indices than the senior students and interns. These findings were similar for both formats of the test so cueing was not thought to be the major factor. It appears that the scoring system is at fault. A comparison of performance on the written and interview (uncued) formats showed that many more options were chosen by all groups tested on the written PMP. It was concluded that written PMPs cannot yet be regarded as a valid simulation of clinical performance. Although content validity is high this does not appear to be so for construct validity or concurrent validity.

Australia↗
PubMed1981

Preparation of leukocyte-poor blood: a comparison of IBM 2991 washing and Huggins freeze-thawing.

Frequently, forzen blood is requested in order to provide a leukocyte-poor red cell transfusion and a reduced level of exposure to hepatitis virus rather than in an effort to find serological compatible red blood cells. However, this usage of frozen blood is expensive and, as recently reported, does not eliminate the risk of transmission of hepatitis. To assess the feasibility of substituting washed cell preparations, we have compared the Huggins frozen blood process with the IBM 2991 cell washing technique and have evaluated the efficiency of leukocyte removal and red cell recovery from homologous pools of fresh blood. The results of these experiments combined with the greatly decreased cost (approximately 1/3) and time required (approximately 1/6) indicate that many of the requests which blood banks receive for frozen blood could, in fact, be better met by using cells which have been washed in the IBM 2991.

Blood Preservation↗