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Biomedical subjects

T Sonobe

Publications and source records attributed to T Sonobe.

84 records · Page 5Linked to original sources
PubMed1980

Digoxin degradation in acidic dissolution medium.

The release of digoxin and its simultaneous conversion to digoxigenin bisdigitoxoside, digoxigenin monodigitoxoside, and digoxigenin in a USP dissolution test medium were followed by high-pressure liquid chromatography. Two products, Tablets A and B, were manufactured by solvent deposition and simple blending methods, respectively. Tablet A released digoxin faster than Tablet B in distilled water and in artificial intestinal juice, and no decomposition was observed. In the USP dissolution test medium, the rate of hydrolysis to digoxigenin bisdigitoxoside was almost equal to that of hydrolysis to digoxigenin monodigitoxoside, and a comparatively large formation rate of digoxigenin was observed. Concentrations of digoxin and its decomposition products were described by differential equations that included dissolution rates of digoxin (rapidly dissolving digoxin and digoxin crystals) and an apparent hydrolysis rate. In the earlier stage of dissolution, hydrolysis was rate determining; in the later stage, dissolution became the rate-determining step for overall digoxin degradation. To suppress digoxin hydrolysis in the USP dissolution test medium, a developmental formulation study was performed. The incorporation of magnesium oxide and magnesium hydroxide-aluminum hydroxide in the tablet formulations inhibited digoxin hydrolysis by 15.3 and 14.5%, respectively, after dissolution for 30 min without serious delay of drug release.

Acids↗
PubMed1977

Synchronized crystal dissolution behavior for tooth enamel and synthetic (NBS) hydroxyapatite.

The synchronized cyrstal dissolution hypothesis previously proposed to explain the unusual dissolution behavior of human dental enamel and hydroxyapatite in partially saturated acidic media has been critically examined with dissolution-dialysis transport experiments. The findings are in accord with the hypothesis. A model based upon a variable effective solubility for the hydroxyapatite crystal is proposed.

Chemical Phenomena↗
PubMedDate not supplied

Fundamental rhythm of sympathetic nerve discharges in animals with total artificial hearts.

To evaluate the effect of total artificial heart replacement on the autonomic nervous system, sympathetic neurograms were analyzed by power spectrum and coherence function. Two pneumatically driven, sac type ventricular assist devices were implanted as biventricular bypasses (BVB) in adult, mongrel dogs. After initiation of BVB pumping, the natural heart was electrically fibrillated to form a BVB TAH model. Renal sympathetic nerve activity (RSNA) was recorded using a bipolar electrode attached to the left renal sympathetic nerve. RSNA was amplified and integrated by use of an R-C integrator. Power spectra of the RSNA and values of squared coherence between the arterial pressure wave form and the RSNA were calculated by computer. In animals with total artificial hearts (TAHs), coherence at the cardiac rhythm frequency was decreased, and coherence at the TAH pumping rhythm frequency was increased. These results indicate that the arterial pulse wave observed in TAH animals contributed to the sympathetic neurogram.

Animals↗
PubMedDate not supplied

The newly designed univalved artificial heart.

A univalved artificial heart (AH) powered electromagnetically in the frequency range of 1-30 Hz was developed to obtain a totally implantable AH. This small sized AH consisted of a vibrating tube, coils, magnets, and a jellyfish valve as an outlet AH valve. The fluid mechanical, hemodynamic, and hematologic properties were evaluated in a mock circulation and 10 animal experiments using adult goats. This vibrating electromagnetic AH could generate more than 10 L/min as an output volume, with 10 Hz vibration using 20 volts supplied voltage. It could also provide two kinds of flow and pressure patterns, in constant-peak and periodic-peak patterns. The values of free hemoglobin remained within acceptable limits. The authors concluded that this new type of pump was useful as a totally implantable AH, ventricular assist, or organ assist system.

Blood Flow Velocity↗
PubMedDate not supplied

Deterministic chaos in the hemodynamics of an artificial heart.

To analyze the hemodynamic parameters during prosthetic circulation as an entity, non linear mathematical techniques were used. To compare natural and prosthetic circulation, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in chronic animal experiments using adult goats to consitute the biventricular bypass complete prosthetic circulation model with ventricular fibrillation. After implantation, these goats were placed in a cage and extubated after waking. All hemodynamic parameters with the natural circulation without biventricular bypass pumping, and the artificial circulation with biventricular bypass pumping under ventricular fibrillation were recorded under awake conditions. By the use of a non linear mathematical technique, the arterial blood pressure waveform was embedded into a four dimensional phase space and projected into three dimensional phase space. The Lyapunov numeric method is used as an adjunct to the graphic analysis of the state space. A phase portrait of the attractor showed a high dimension complex structure, with three dimensional solid torus suggesting deterministic chaos during natural circulation. However, a simple attractor, such as a limit cycle attractor, was observed during artificial circulation. Positive Lyapunov exponents during artificial circulation suggest the lower dimensional chaotic system. Thus, hemodynamic parameters during prosthetic circulation must be carefully controlled when unexpected stimuli are fed from outside.

Animals↗