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Biomedical subjects

O Okai

Publications and source records attributed to O Okai.

17 recordsLinked to original sources
PubMed2000

Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat.

In this study, the inhibiting action of theanine on the excitation by caffeine at the concentration regularly associated with drinking tea was investigated using electroencephalography (EEG) in rats. First, the stimulatory action by caffeine i.v. administration at a level higher than 5 micromol/kg (0.970 mg/kg) b.w. was shown by means of brain wave analysis, and this level was suggested as the minimum dose of caffeine as a stimulant. Next, the stimulatory effects of caffeine were inhibited by an i.v. administration of theanine at a level higher than 5 micromol/kg (0.781 mg/kg) b.w., and the results suggested that theanine has an antagonistic effect on caffeine's stimulatory action at an almost equivalent molar concentration. On the other hand, the excitatory effects were shown in the rat i.v. administered 1 and 2 micromol/kg (0.174 and 0.348 mg/kg) b.w. of theanine alone. These results suggested two effects of theanine, depending on its concentration.

Animals↗
PubMed1998

Implication of the systolic hump in systemic arterial pressure waves.

The systolic hump in the aortic blood pressure wave is defined as the aortic-resistance component proportional to the aortic blood flow superimposed on the windkessel component. An electrical analogue comprising a series resistance (aortic resistance) plus a resistance (peripheral resistance) and capacitance (aortic compliance) in parallel (i.e. windkessel component) is used for analysis. Curve fitting using the least-squares method is performed on calculated and measured blood pressure waves from dogs under haemodynamical conditions induced by infusion of three drugs (noradrenaline, isoproterenol and acetylcholine). The curve fitting RMS (root mean square) errors are < 3% for blood pressure waves and < 30% for blood flow waves, with good agreement between measured and calculated blood flow waveforms. Infusion of noradrenaline and acetylcholine is found to induce a significant decrease and increase in the aortic resistance, respectively. Although only a small fraction of the blood pressure wave, the systolic hump has a marked effect on the systolic pressure waveform.

Animals↗
PubMed1977

Modified magnetorheography. Measurement of cardiac output by a catheter and an externally applied high magnetic field.

This study is dealt with a design for measuring cardiac output using a catheter and an externally applied magnetic field with the most minimized trauma. Many trials have yielded the following results. When a high static magnetic field is applied externally to the body and a catheter carrying electrodes at the tip is inserted from the carotid artery cutdown, 2 sensing electrodes, across the lumen of the aortic arch, at a little larger electrode distance than the lumen can detect the greatest flow signal. Since the biggest noises in the signal are ECG, they can be cancelled to a great extent by the reversed deflection of the ECG which is detected with cancelling electrodes placed at the left chest surface point geometrically symmetrical to the ascending aorta with respect to the center of the heart. Clamping the flow signal to zero level during diastole leads to the remodulation of D-C level in the flow signal and to the reduction of zero drifts. The flow signal produced by giving known volume to the ascending aorta via a catheter can be used for the calibration of the flow measuring system.

Animals↗
PubMed1975

Magnetorheography; calculation of blood flow from surface induced potentials.

This research is an attempt to measure blood flow without doing any hurt to the body. When the body is placed in a high magnetic field the blood-flow-induced electromotive force (EMF) can be detected with the surface electrodes using the same principle as an electromagnetic flow-meter. This blood flow measurement is named magnetorheography (its recording: MRG). A theoretical analysis of the potential in the tissue shows that blood flow can be calculated from the surface-induced EMF (MRG) without measuring the radius and the depth of the vessel from the skin surface, when the surface is fairly flat in the vicinity of the vessel. A model experiment verified the theory. In order to apply the theory to the measurement in an in situ situation, a structural coefficient was introduced which is related to the external shape, internal tissue compositions and their impedance of the body. Using such a coefficient the flow calculated from MRG, by an equation including the coefficient, agreed with the flow actually recorded. In experiments on the thighs of 8 dogs weighing 7 to 17 Kg, MRG proved to be proportional to arterial flow and the coefficients were approximately constant. These results indicate that blood flow may possibly be estimated by the calculation from MRG.

Animals↗