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Biomedical subjects

K J Falk

Publications and source records attributed to K J Falk.

7 recordsLinked to original sources
PubMed1999

M-DNA: A complex between divalent metal ions and DNA which behaves as a molecular wire.

M-DNA is a complex of DNA with divalent metal ions (Zn(2+), Co(2+), or Ni(2+)) which forms at pH conditions above 8. Upon addition of these metal ions to B-DNA at pH 8.5, the pH decreases such that one proton is released per base-pair per metal ion. Together with previous NMR data, this result demonstrated that the imino proton in each base-pair of the duplex was substituted by a metal ion and that M-DNA might possess unusual conductive properties. Duplexes of 20 base-pairs were constructed with fluorescein (donor) at one end and rhodamine (acceptor) at the other. Upon formation of M-DNA (with Zn(2+)) the fluorescence of the donor was 95 % quenched. Fluorescence lifetime measurements showed the presence of a very fast component in the decay kinetics with tau</=10 ps. The fast component was absent in B-DNA and in M-DNA lacking an acceptor chromophore; a result which is only consistent with electron transfer. Efficient signal transduction was also observed between the two fluorophores separated by 54 base-pairs (over 150 A) in an M-DNA duplex. The addition of a sequence-specific DNA-binding protein prevented the flow of electrons and this was reversed by protease digestion. Therefore, M-DNA behaves as a molecular wire and could be manipulated to prepare self-assembling electronic circuits.

Base Sequence↗
PubMed1982

A program for processing of multiple-lead exercise ECGs in real time.

A computer program for continuous recording and real-time processing of 8-channel exercise ECGs is presented. Current average ECG complexes and trends of various morphological and rhythmic parameters can be displayed on a TV monitor during the stress test. Average complexes computed every 10 s, the time of occurrence and 6 morphological coefficients of all detected tentative QRS complexes, and data manually entered by the operator are stored in a file on disk. The operational procedures and the principal signal processing are briefly presented. The main attention is given to a description of the software structure, explaining the subdivision of the program into dedicated autonomous sections and the system for the coordination of simultaneous activities of different priority.

Computers↗
PubMed1982

Computerized exercise ECG in the diagnosis of critical coronary lesions.

Different ECG criteria are evaluated with respect to their ability to identify individuals with critical lesions of the coronary arteries in a population of patients with severe angina. Six chest leads and the the limb leads were recorded in 85 patients by computer during maximal, symptom-limited exercise ECG testing. Averaging of ECG complexes enhances the signal quality and makes it possible to use measurements of the limb leads recorded during exercise. 14 patients with abnormal Q waves in lead V2 were excluded from ST analysis. In the remaining 71 patients, more than 1/3 mm ST depression in lead I and/or more than 2.0 mm ST depression in any of the chest leads had a sensitivity of 85% and a specificity of 67% for lesions in the main stem and/or proximal LAD and/or three-vessel disease. The predictive value of a positive test was 83%. This and other criteria were evaluated for different disease groups and a different stages during the exercise test.

Adult↗
PubMed1982

Real-time processing of multiple-lead exercise electrocardiograms.

A system for continuous recording and real-time processing of eight-channel exercise ECGs is presented with emphasis on the algorithms performing the principal signal processing. The hardware and the operational procedures are briefly described. New methods have been developed for the detection, alignment, and selection of complexes to be used in the creation of eight-dimensional average ECG complexes every 10 s. These algorithms are based on digital filter functions approximating low-order Legendre polynomials in order to be robust in the presence of noise.

Computers↗
PubMed1975

Improved method for the simultaneous determination of phenobarbital, primidone and diphenylhydantoin in patient's serum by gas-liquid chromatography.

A quantitative gas-liquid chromatographic method for the simultaneous determination of phenobarbital, primidone and diphenylhydantoin in human serum is described. A double extraction is employed to improve the removal of interfering substances. The N,N-dimethyl derivatives of the compounds are prepared by "oncolumn" methylation with 50% Methelute. Decomposition of phenobarbital to N-methyl-a-phenylbutyramide was negligible if the contact time with Methelute was less than 10 min. The drugs were stable in serum for at least two weeks. This procedure provides a rapid, sensitive, selective and accurate method for the routine determination of serum concentrations of three of the most commonly prescribed anticonvulsant drugs.

Anticonvulsants↗
PubMed1975

Effect of dosage regimen on natriuretic response to furosemide.

We have examined the differences in urinary excretion of water, sodium, potassium, chloride, urea, and creatinine produced by different dosage regimens offurosemide in normal volunteers. Three oral dosage regimens were compared: 20 mg daily, 20 mg twice daily, and 40 mg daily. Furosemide, 20 mg, did not produce a significant weight loss, diuresis, or natriuresis in 12 normal subjects. With 40 there was a significant weight loss, diuresis, natriuresis, and chloruresis over 24 hr. Comparison of the divided regimen with 40 mg daily revealed significantly greater sodium excretion, and chloride excretion with 20 mg twice daily. The divided dosage regimen produced a different pattern of diuresis with most of the sodium and water excretion occurring after the second dose. These differences in response to different regimens are predictable from pharmacokinetic considerations and may have clinical significance.

Administration, Oral↗