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K I Yamakoshi

Publications and source records attributed to K I Yamakoshi.

10 recordsLinked to original sources
PubMed1979

Indirect measurement of instantaneous arterial blood pressure in the rat.

We devised a hydraulic servo-control system for indirect blood pressure measurement in the rat's tail, by which beat-to-beat systolic and diastolic blood pressure can be obtained. In this method the principle of "unloading vascular wall" proposed by Shirer (1962) is employed. The proposed system is composed of a transmittance photoelectric plethysmograph with an occluding cuff, a small diaphragm actuator for compressing and decompressing the segment by the hydraulic pressure, and an electromagnetic shaker driven by a volume servo circuit in accordance with the signal from the photoelectric plethysmograph. The plethysmographic signal is clamped at a proper value corresponding to the unload vascular volume by the instantaneous hydraulic servo control. The cuff pressure thus automatically controlled follows the intra-arterial pressure in the tail segment. The accuracy of this method was evaluated in comparison with direct measurement of blood pressure recorded simultaneously from 16 unanesthetized spontaneously hypertensive and normotensive rats. Close agreement between the simultaneous data from these two methods were observed.

Animals↗
PubMed1977

Reduction of the duration of isovolumic relaxation in the ejecting left ventricle of the dog: residual volume clamping.

1. The individual effects of stroke volume and speed of ejection on the duration of the isovolumic relaxation phase were analysed in the canine left ventricle with a constant end-systolic residual volume.2. A new technique was employed to maintain the ventricular end-systolic residual volume at a desired constant value regardless of wide changes in stroke volume and speed of ejection in a given inotropic background.3. The duration of isovolumic relaxation, which was defined to be the time taken for ventricular pressure to fall from its end-systolic level to its 75, 50 and 25% levels, markedly decreased with increases in stroke volume. The reduction amounted to as much as 30-50% when stroke volume was increased from zero (isovolumic) to 20-25 ml.4. The degree of shortening of the duration of isovolumic relaxation was largely independent of changes in speed of ejection which ranged from about 100-800 ml./sec at a constant stroke volume of 15 ml.5. It was therefore concluded that stroke volume itself could be a major determinant of the duration of isovolumic relaxation.6. It was speculated that the mechanism of the observed phenomenon might be a manifestation of the uncoupling effect of muscle shortening on contractile state.

Animals↗
PubMed1976

Transthoracic admittance plethysmograph for measuring cardiac output.

A plethysmograph for measuring ventricular stroke volume (SV) from the transthoracic admittance variation was developed. A correlation study between the SV values determined by this method (SVy) and those measured by Kubicek's transthoracic impedance method (SVz) was carried out on 24 healthy subjects; the correlation coefficient was r = 0.99 and the regression line of SVY on SVz was y = 1.03x - 0.47. Based on the results obtained through the study, it was concluded that the admittance method was more advantageous than the impedance method for measuring SV.

Cardiac Output↗
PubMed1976

Left ventricle as a compression pump.

Pressure-volume relationship of the left ventricle at endsystole was studied in three different series of experiment on the dog. Intraventricular pressure was measured with a miniature gauge at the apex. Intraventricular volume was accurately measured by three different methods: (1) plethysmographically with a cardiometer cup, (2) with an intraventricular balloon and a volumetric cylinder, and (3) with the same balloon and areciprocal pump which could clamp the endsystolic volume. We found consistently that as long as the contractile state was stable the endayatolic pressure-volume relationship curve was largely independent of the loading conditions such as enddiastolic volume and ventricular afterload pressure and also of whether the mode of contraction was isovolumic, auxobaric or physiologically ejecting. When the endsystolic pressure was kept unchanged in the ventricle with a stable contractile state, the intraventricular volume decreased to the same volume as given by the endsystolic pressure-volume relationship and the afterload pressure. When the endsystolic volume was maintained constant, the ventricle developed at the end of systole almost the same pressure as that predicted from the same endsystolic pressure-volume relationship. The endsystolic pressure-volume relationship, therefore, uniquely characterizes the degree of ventricular compression under a given contractile state.

Animals↗