Intra-arterial blood pressure gradient is influenced by geometry of the arterial tree. In arterial systems with relatively long large branches considerable blood pressure drop takes place in large arterial branches, and in the systems with long small branches the blood pressure gradient is characterized by precipitous pressure drop in the arteriolar region. The difference is evaluated in association with different requirements of organ circulation.
A histometrical method is introduced into the quantitative analysis of the arterial muscular coat, and the effect of irregular post-mortem arterial constriction is averted. On account of different behavior of the muscular coat, every arterial system is divided into two, portions, conductive and regulatory, at an arterial radius of 100 μ. Medial hypertrophy is the anatomical expression of elevated blood pressure, and characteristic distribution of medial hypertrophy in arterial hypertension suggests high blood pressure in the conductive portion and abrupt pressure drop in the regulatory portion. This is presumably caused by functional arterial contraction of the regulatory portion.The blood pressure attains the normal level in the arteriolar region even in pronounced hypertension, so that organ blood flow is kept unchanged. The arterial narrowing required to suppress blood pressure to the normal level at arteriolar terminals differs according to the ratio of fixed to variable resistances in the whole vascular channel. In arteries with large fixed resistance arterial contraction to maintain normal blood flow is larger than in those with small fixed resistance, even under the common load of systemic hypertension.
The orientation of arterial and venous terminals in the organ determines the pattern of peripheral circulation. When the distances between the arterial and venous terminals are diverse, capillary blood flow is sustained only by alternate flow. Physiological blood flow regulation of the renal cortex by means of alternate flow is concluded from the renal vascular architecture.

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The pulse echo technique has been remarkably developed and it is now in wide use for the clinical diagnosis. As one of the methods of through-transmission imaging, ultrasonic holography seems to provide another new approach to noninvasive, dynamic and real time imaging of human tissues or internal organs.
We have been continuing the basic studies of this method for the practical applications in the medical field. The fundamental theory and principle of the practical apparatuses are outlined. Several examples of imagings by the liquid surface focused image type ultrasonic holography system are shown. Present technical problems and future aspects are discussed.

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It is well known that the epidermal stratum corneum has very large influence on the skin impedance. In the present paper, the formative mechanism of the skin impedance and the skin resistivity, and dielectric constant are discussed, with the structure of this part taken into consideration. The essential points of this paper consist of following items :
(1) The mathematical expression of the skin impedance Z taking into account the so-called multi-layer configuration of the stratum corneum is obtained by the following equation :
Z=∫^d₀2ρ (x) /1-jωε (x) ε₀ρ (x) ·dx/S
where, d : thickness of stratum corneum
x : distance measured from skin surface to inner tissue
ε (x), ρ (x) : specific dielectric constant ε (x) and resistivity ρ (x) of stratum corneum at point x
ε₀ : dielectric constant of vacuum
S : area of an electrode
(2) The formative mechanism of the frequency dispersion appearing on the average dielectric constant and the resistivity of the stratum corneum is analyzed with the above equation. In this case the existence of two dispersions, that is, the structural dispersion based on the multi-layer configuration and the dispersion of the another type, is made clear. The latter dispersion arises on the basis of the infinitesimal inhomogeneous structure, especially of the cell membranes, at the distance x and is like the so-called α, β dispersions appearing on the live tissues. The frequency characteristics of ε (x), ρ (x) are determined by this dispersion and the large specific dielectric constant appears.
(3) Specific dielectric constants and resistivities at every point in the stratum corneum of a living, human skin are experimentally determined and the multi-layer configuration characteristics of these values are made clear. Resistivities decrease exponentially with the distance from the skin surface, and specific dielectric constants decrease slightly in the beginning and then increase exponentially with the distance from the surface.

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The light scattering technique with a photoelectron counting method is applied to determine the average swimming velocities or the velocity distribution of spermatozoa. The results are in quantitative agreement with the ones which are obtained in other methods. This technique has proved useful in 'finding the accurate motility of spermatozoa in a very short observation time.

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Dynamic response of the fluid-filled catheter-manometer system was assessed by means of sinusoidal and rectangular pressure generator. The frequency response curves were found to be independent of the amplitude of the input sinusoidal pressure waves. Thus the evidence indicated that the catheter-manometer system was essentially linear. The performance of the catheter-manometer system suggested that it could be treated as an equivalent second order system at low frequencies. Typical pressure from various left ventricular pulses of the dogs obtained from a catheter-tip manometer were digitized and analyzed by Fourier analysis on a digital computer in order to determine the modulus of each harmonics and the number of harmonics necessary to construct accurate pressure waves. It was shown that resynthesis of the pressure recorded from the first 6-10 harmonics accurately reproduced systolic pressures. However resynthesis of the first 10-24 harmonics was necessary for accurate reproduction of waveform and first derivative of it.
Then, various left ventricular pressure waves of eight dogs obtained with eight catheter-manometer systems whose undamped natural frequencies were 19 to 64 Hz, were digitized and analyzed by Fourier analysis and the left ventricular pressure curves and their derivatives were resynthesized using the first 20 harmonics whose distortions of amplitude and phase lags were corrected according to the frequency response curve of the catheter-manometer system. Thus the pressure waves obtained from the catheter-manometer system were corrected and the comparison of the max dP/dt of the corrected pressure waves with the standard system resulted in a correlation coefficient of 0.987.

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Blood flow measurement based on the ultrasound Doppler effect has not yet advanced beyond the qualitative stage, and many theoretical and technical problems with regard to haemodynamics, ultrasound acoustics, measuring technique, equipment design and construction, signal processing, etc. must be investigated and overcome for quantitative measurement. This paper focuses especially attention on the following three problems concerning the zero-crossing counter widely used in the ultrasonic Doppler flowmeter.
(1) The ultrasound Doppler signal due to the blood flow is always accompanied with various kinds of noise such as internal noise generated in the equipment. The output value of the zero-crossing counter for this Doppler signal under the influence of the noise is necessarily different from that without the noise. Therefore, the output value of the zero-crossing counter for the Doppler signal with noise was analysed. Further, a noise-free counting method with the zero-crossing counter was newly developed, and the relationship between the output value of the zero-crossing counter based on this counting method and the actual zero-crossing number was investigated.
(2) Undesired signals caused by the vessel wall motion and artificial transducer movement must be rejected and a high-pass filter is usually employed for this purpose because the frequency bands of the undesired signals are lower than that of the Doppler signal. The relationship between the zero-crossing counter output for the Doppler signal fed through the high-pass filter and the actual mean flow velocity was theoretically analysed and experimentally confirmed.
(3) The zero-crossing counter output contains a signal due to the blood flow velocity change and a fluctuation due to, the random motion of blood cells. In order to determine the ratio of the random fluctuation to the output, an experiment was carried out, and an experimental equation was obtained from the result representing the dependence of the random fluctuation on the cut-off frequency of the low-pass filter in the zero-crossing counter and on the zero-crossing counter output.

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