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S Kikkawa

Publications and source records attributed to S Kikkawa.

48 records · Page 3Linked to original sources
PubMed1986

Technique with lock-in amplifier for real-time measurement of tricuspid valve annulus area.

A new measuring system that permits real-time registration of the tricuspid valve annular area (TVA) using lock-in amplifier is devised and applied in open-chest anesthetized dogs. The tricuspid valve annulus was stitched with a fine, pliable, metal thread made of 10 30-micron urethane resin-coated copper wires during inflow occlusion. Both ends of the thread were guided out from the right atrium through a single pinhole in the right atrial wall. The signal intensity induced in the sense loop is linearly related to the area encircled by the thread, i.e., the area of the tricuspid annulus. During control state, TVA varied by an average of 24.5% (3.8-46.5%) of its maximum. Presystolic peak and valley of TVA due to atrial contraction and a decrease in TVA during ventricular ejection were generally observed. An increase in TVA during the initial portion of isovolumic contraction phase was prominent in dogs with filariasis, whereas in the other dogs it was not.

Acetylcholine↗
PubMed1984

Application of Taylor's hypothesis to an unsteady convective field for the spectral analysis of turbulence in the aorta.

Two types of unsteadiness must be considered when spectral analysis is applied to unsteady turbulence such as that found in the aorta. Firstly, the statistical properties of the turbulence itself change in time and so the definition of spectral density must be reconsidered. Secondly, the turbulent velocity fluctuations, whether they are steady or unsteady, are carried by an unsteady convective velocity which alters their properties as seen by a stationary observer. In the present study, unsteadiness of turbulence in the latter sense is discussed by applying Taylor's hypothesis of 'frozen turbulence' to turbulence with an unsteady convective velocity. If both a 'frozen' pattern of turbulence and a constant convective velocity are assumed, measured frequency spectra can be easily transformed into wavenumber (spatial) spectra, usually as a trivial part of normalisation. In the case of unsteady turbulence, however, the convection velocity is no longer constant and the conventional method can not be used. A new method of estimating the spatial properties of unsteady turbulence is proposed in which the temporal fluctuations of the turbulent velocity are transformed into spatial fluctuations using a nonlinear transformation based upon the unsteady convective velocity. The transformed data are then Fourier analysed to yield a wavenumber spectrum directly. The proposed method is applied to data obtained in the canine ascending aorta. Spectra calculated by the proposed method differ significantly from those obtained by the conventional method, particularly in the high wavenumber (or frequency) range. This difference is discussed as an 'aliasing' phenomenon that has also been known in steady turbulence.

Animals↗
PubMed1983

Measurement of turbulence intensity in the center of the canine ascending aorta with a hot-film anemometer.

The blood flow velocity near the central axis of the canine ascending aorta was measured with a hot-film anemometer. The cardiac output and the heart rate were controlled at will by means of an extracorporeal circulation and by atrial pacing. The turbulent component of the blood flow velocity was calculated using an ensemble average technique. Ensemble average turbulent intensity was also calculated to show the time course of turbulence in the aorta. The ratio of the mean turbulence intensity to the time mean sectional average velocity in the aorta was constant in most animals regardless of the changes in fluid mechanical parameters. The correlation between the frequency parameter and the relative mean turbulence intensity was weakly positive. The power spectrum of the turbulence was also calculated.

Animals↗
PubMed1977

Maximum rate of tension fall during isometric relaxation at end-systolic fiber length in canine papillary muscle.

We measured the characteristics of the decline in tension during isometric relaxation of canine papillary muscle. In the intact heart, relaxation begins with the isovolumic phase, but in experiments on papillary muscle previously reported the isotonic phase preceded the isometric phase during the course of relaxation. In our experiments, however, the isotonic bar was locked at the instant the muscle reached the end-systolic fiber length in order to hold the fiber at the length during the succeeding relaxation process. Therefore, we obtained a relaxation process similar to that occurring in the intact heart. The major results of these experiments are: (1) Maximum rate of the decline in tension (-dT/dtmax) is linearly related to the magnitude of total load. (2) -dT/dtmax is augmented by positive inotropic interventions and diminished by negative inotropic interventions. (3) An increase in preload results in only a slight increase in -dT/dtmax. (4) End-systolic fiber length itself is not a principal determinant of -dT/dtmax. (5) -dT/dtmax divided by total load is independent of the amount of muscle shortening. We, therefore, suggest that -dT/dtmax divided by total load cand be a useful index of the relaxation characteristics of cardiac muscle.

Animals↗