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V Kahn

Publications and source records attributed to V Kahn.

At least 19 recordsLinked to original sources
PubMed2001

Infant temperament and the brainstem auditory evoked response in later childhood.

Brainstem auditory evoked responses (BAERs) were evaluated on 10-12-year-old children (N = 56) who had been classified as high or low reactive to unfamiliar stimuli at 4 months of age. BAER measurement was selected because high reactive infants tend to become inhibited or fearful young children, and adult introverts have a faster latency to wave V of the BAER than do extroverts. Children previously classified as high reactive at 4 months had larger wave V components than did low reactive children, a finding that possibly suggests greater excitability in projections to the inferior colliculus. The fact that a fundamental feature of brainstem activity differentiated preadolescent children belonging to two early temperamental groups supports the value of gathering physiological data in temperament research.

Age Factors↗
PubMed2000

Using data to improve medical practice by measuring processes and outcomes of care.

BACKGROUND: The purpose of this article is to help clinicians expand their use of data to improve medical practice performance and to do improvement research. Clinical practices can be viewed as small, complex organizations (microsystems) that produce services for specific patient populations. These services can be greatly improved by embedding measurement into the flow of daily work in the practice. WHY DO IT?: Four good reasons to build measures into daily medical practice are to (1) diagnose strengths and weaknesses in practice performance; (2) improve and innovate in providing care and services using improvement research; (3) manage patients and the practice; and (4) evaluate changes in results over time. It is helpful to have a "physiological" model of a medical practice to analyze the practice, to manage it, and to improve it. One model views clinical practices as microsystems that are designed to generate desired health outcomes for specific subsets of patients and to use resources efficiently. This article provides case study examples to show what an office-based practice might look like if it were using front-line measurement to improve care and services most of the time and to conduct clinical improvement research some of the time. WHAT ARE THE PRINCIPLES FOR USING DATA TO IMPROVE PROCESSES AND OUTCOMES OF CARE?: Principles reflected in the case study examples--such as "Keep Measurement Simple. Think Big and Start Small" and "More Data Is Not Necessarily Better Data. Seek Usefulness, Not Perfection, in Your Measures"--may help guide the development of data to study and improve practice. HOW CAN A PRACTICE START TO USE DATA TO IMPROVE CARE AND CONDUCT IMPROVEMENT RESEARCH?: Practical challenges are involved in starting to use data for enhancing care and improvement research. To increase the odds for success, it would be wise to use a change management strategy to launch the startup plan. Other recommendations include "Establish a Sense of Urgency. (Survival Is Not Mandatory)" and "Create the Guiding Coalition. (A Small, Devoted Group of People Can Change the World)." SUMMARY: Over the long term, we must transform thousands of local practice cultures so that useful data are used every day in countless ways to assist clinicians, support staff, patients, families, and communities.

Clinical Medicine↗
PubMed1998

N-acetyl-L-tyrosine (NAT) as a substrate for mushroom tyrosinase.

N-acetyl tyrosine (NAT) is hydroxylated by mushroom tyrosinase and the N-acetyl dopa formed is oxidized by the enzyme to N-acetyl dopaquinone (lambda max = 390 +/- 10 nm). H2O2 and NH2OH each shortened the lag period of NAT hydroxylation by the enzyme. H2O2 had an effect on the changes with time in the spectrum of product(s) formed and on the spectrum of the final product(s) obtained when NAT was hydroxylated by mushroom tyrosinase, in a manner suggesting that H2O2 converts N-acetyl dopaquinone to a pink-violet product(s) (lambda max = 490 nm), whereas such a product(s) was not formed in the absence of H2O2. A pink-violet product(s) (lambda max 490 +/- 20 nm) was also formed when NAT was hydroxylated by mushroom tyrosinase in the presence of NH2OH or para amino benzoic acid (PABA), probably as a result of an interaction between N-acetyl dopaquinone and NH2OH or PABA forming mono- or di-oximes. Kojic acid (5-hydroxy-2-hydroxymethyl)-4H-pyran-4-one) inhibited effectively the rate of NAT hydroxylation by mushroom tyrosinase in the absence or presence of H2O2. When NAT was oxidized by the enzyme in the absence of kojic acid, N-acetyl dopaquinone was formed at once and a shoulder at 490-530 nm appeared later. Under identical conditions but in the presence of kojic acid, a yellow product(s), characterized by a peak at 320 +/- 10 nm, was detected, suggesting that N-acetyl dopaquinone oxidizes kojic acid to the yellow product(s). Maltol (3-hydroxy-2-methyl-4H-pyran-4-one), a gamma-pyrone derivative structurally related to kojic acid, also inhibited the rate of NAT hydroxylation by mushroom tyrosinase. The addition of maltol at the plateau phase of the reaction resulted in an immediate decline in absorbance at 400 nm, suggesting that maltol conjugates with N-acetyl dopaquinone, yielding a product(s) characterized by a lower extinction coefficient at 400 nm than that of N-acetyl dopaquinone alone. The final brown-red product(s) formed when NAT was hydroxylated by mushroom tyrosinase was bleached in the presence of ascorbic acid or H2O2.

4-Aminobenzoic Acid↗
PubMed1997

Effect of maltol on the oxidation of DL-DOPA, dopamine, N-acetyldopamine (NADA), and norepinephrine by mushroom tyrosinase.

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one) appears to inhibit the rate of oxidation of DL-DOPA, dopamine, NADA and epinephrine by tyrosinase when assayed spectrophotometrically but not when assayed polarographically. Maltol has an effect on the spectrum of product(s) formed when each catecholamine was oxidized by tyrosinase showing that maltol hastens the disappearance of the quinones, possibly by conjugating with them. Indeed, at relatively high concentrations, maltol prevented the conversion of DL-DOPA, dopamine, and norepinephrine to their corresponding melanins via tyrosinase.

Basidiomycota↗
PubMed1995

Effect of kojic acid on the oxidation of DL-DOPA, norepinephrine, and dopamine by mushroom tyrosinase.

Kojic acid inhibits effectively the rate of formation of pigmented product(s) and of oxygen uptake when DL-DOPA, norepinephrine and dopamine are oxidized by mushroom tyrosinase. In addition to the direct effect of kojic acid on the enzyme, kojic acid also affects the UV-VIS spectrum of the final product(s) formed, this being due to the ability of the o-quinones of these substrates to oxidize kojic acid to a yellow product(s). Kojic acid can thus prevent the conversion of the o-quinones of DL-DOPA, norepinephrine and dopamine to their corresponding melanin.

Basidiomycota↗
PubMed1992

Effect of different isomers of dihydroxybenzoic acids (DBA) on the rate of DL-dopa oxidation by mushroom tyrosinase.

Dihydroxybenzoic acids (DBA), such as 3,4-DBA, 3,5-DBA, and 2,4-DBA--at all concentrations tested--inhibited the rate of DL-DOPA oxidation to dopachrome (lambda max = 475 nm) by mushroom tyro0sinase. 2,3-DBA and 2,5-DBA at relatively low concentration had a synergistic effect on the reaction, whereas at relatively high concentrations they inhibited the rate of DL-DOPA oxidation. The synergistic effect of 0.6-13.3 mM 2,3-DBA on the rate of DL-DOPA oxidation to dopachrome (lambda max = 475 nm) was found to be due to the ability of 2,3-DBA-o-quinone (formed by the oxidation of 2,3-DBA by mushroom tyrosinase or by sodium periodate) to oxidize DL-DOPA to dopachrome (via dopaquinone) non-enzymatically. A similar explanation is likely to be valid for the synergism exerted by 2,5-DBA on the rate of DL-DOPA oxidation by mushroom tyrosinase.

Basidiomycota↗
PubMed1992

Synergism exerted by 4-methyl catechol, catechol, and their respective quinones on the rate of DL-DOPA oxidation by mushroom tyrosinase.

4-Methyl catechol and catechol, at concentrations ranging from 0.03 to 9 mM and 0.066 to 20 mM, respectively, have a synergistic effect on the rate of DL-DOPA oxidation by mushroom tyrosinase to material absorbing at 475 nm. The synergism results from the ability of 4-methyl catechol-o-quinone (4-methyl-o-benzoquinone) and of catechol-o-quinone (o-benzoquinone) to oxidize DL-DOPA non-enzymatically to dopaquinone, with the later being immediately converted to dopachrome (lambda max = 475 nm).

Basidiomycota↗
PubMed1986

Effect of methimazole on the activity of mushroom tyrosinase.

Methimazole (1-methyl-2-mercaptoimidazole) inhibits both the mono- and the o-dihydroxyphenolase activities of mushroom tyrosinase when assayed spectrophotometrically. With DL-3,4-dihydroxyphenylalanine as substrate, the inhibition was found to be a mixed-type one with Ki 4.6 X 10(-6) M. We found that methimazole can interact with the oxidation products of o-dihydroxyphenols, probably with o-quinones, to form a conjugate. The conjugate formed between methimazole and o-benzoquinone was separated by chromatography on Sephadex G-10 and was characterized by an absorption maximum at 248-260 nm. Our data suggest that methimazole inhibits mushroom tyrosinase activity in two ways: by conjugating with o-quinones, thereby causing an apparent inhibition in pigmented product formation as judged by the spectrophotometric assay; and by chelating copper at the active site of the enzyme, as judged by assaying the release of 3HHO from L-[3,5-3H]tyrosine.

Basidiomycota↗
PubMed1976

The teaching of child psychiatry in U.S. medical schools: results of a survey.

The major results of this survey are that most schools have special programs in child psychiatry and that these are distinct from the adult psychiatry course. The course content involves clinical evaluation of children, information on child development and psychopathology, assigned reading, and liaison with pediatrics. Most schools have full-time psychiatrists on their faculty, and the child psychiatry course is taught by child psychiatrists; but less than 20 percent of the psychiatric faculty are child psychiatrists in a majority of the schools in the country. Finally, although evaluation by students and faculty is common in most of the schools, only slightly more than one-third of the institutions gave grades in child psychiatry and slightly fewer than one-third gave examinations in this subject.

Child Psychiatry↗