Shizuo Hanya

A new method of evaluating the degree of stenosis using a multisensor catheter. Application of the pressure loss coefficient.

SummaryA new method of evaluating the degree of stenosis using the pressure loss coefficient is presented here. The pressure loss coefficient was obtained in patients with pulmonary or aortic stenosis by measuring the pressure and velocity of the blood simultaneously with a multisensor catheter. Although the pressure gradient across the stenosis was augmented by increasing the blood velocity with pharmacological loading, the pressure loss coefficient remained nearly constant. This confirmed that the pressure loss coefficient is more appropriate for evaluating the degree of stenosis than the pressure gradient, which depends on the blood velocity.The pressure loss coefficients obtained from the preoperative and postoperative catheterization data were compared to evaluate the effects of the surgical operation. A pressure loss coefficient of 15 was proposed as the critical value for the indication of operation.

Stenosis: Clinical Measurements

The purpose of this section is to illustrate the clinical application of the pressure-loss coefficient λ in quantifying the severity of stenosis in the heart and great vessels. It is well-known that the presence of a stenosis within a large artery gives rise to a region of turbulent flow downstream of the obstruction (Giddens et al. 1976). When the flow is highly disturbed or turbulent, the pressure loss (pressure gradient) across the stenosis is proportional to the square of the flow velocity V and to the blood density ρ (see Sect. 7.2).

Methods of Measuring Blood Velocity

The hot-film anemometer is based on heat transfer from a small body placed in the fluid flow. This is a very small metal film which is sputtered or burned on a substrate or a mount. This small film is connected to a bridge circuit (Fig. 13.1) for the generation of heat by an electrical current. A servoamplifier feeds back the error voltage of the bridge circuit, so that the electrical resistance, which is a function of the film temperature, is kept constant. This type of electrical equipment is called a constant temperature anemometer (CTA). If heat loss from the film increases, due to the high velocity of the surrounding fluid, the film temperature falls and the electrical resistance decreases, which leads to the increase of error voltage of the bridge. In this situation, the feedback current or output voltage of the servoamplifier becomes a nonlinear function of the fluid velocity. The metal film should be covered by a thin layer of insulating material, usually quartz, which does not interfere significantly with the heat transfer.

Fluid Dynamical Mechanism of Anacrotic Notch in the Great Arteries

There exist considerable texts on the anacrotic notch in the central arterial pulse wave, but little is known about the mechanism of the development of anacrotic notch.

Blood Flow in the Left Ventricle

There is a growing realization among physicians and scientists of the need to understand the physiology and pathophysiology of transmitral blood flow dynamics. This is due, in part, to an awareness that diastolic dysfunction may, in some patients and some disease states, precede systolic dysfunction. It is due also to the advent of sophisticated, noninvasive, diagnostic technology which makes it possible to explore the motion of blood and of cardiac structures. Doppler flowmetry, for example, is an extremely useful clinical and investigative technique, but it is apparent that, like most noninvasive techniques, it is often ambiguous and unclear. When combined with an understanding of the physiological principles derived from data obtained by invasive experimental approaches, however, modern technology offers greater information. In this section, we will present results from experiments on dogs; we will offer a conceptual framework with which to analyze the data and clarify the physiological mechanisms involved in transmitral blood flow. We hope that this approach will improve the clinical scientist’s understanding and interpretation of the data derived from the latest advances in technology.