An Improved Method of Blood Pressure Measurement by Catheter Insertion

Abstract

Recently, accurate blood pressure measurements have been required for many purposes. For example, if the blood pressure can be measured accurately at various points of an aorta, a great deal of information about the cardiovascular system can be obtained. The most reliable method measuring the blood pressure is the direct method by catheter insertion. This method has been applied for long time as the most reliable method, despite involvement of considerable error. There are many causes for the errors, such as (1) wave distortion due to the resonance phenomenon of measurement system, (2) changes in physiological state of the subject due to the insertion of a catheter into the arterial system, (3) pressure wave reflection at the tip of the catheter. The second cause is too complicated to discuss, and the third cause has already been reported1). The first cause is the most serious one, and is discussed in this paper.
The resonance phenomenon occurs in the usual blood pressure measurements due to the inertia of saline in the catheter and the compliance of the electrical manometer. Many researchers have been trying to reduce the error due to the resonance phenomenon, but no method which is effective for clinical and experimental application has yet been made available.
In this paper, a simple damper device is proposed for the reduction of the resonance phenomenon. This damper device is inserted between the catheter and the electrical manometer. This blood pressure measurement system is discussed theoretically and experimentally and it has been verified that this system can measure the blood pressure waveform accurately enough for clinical and experimental application. This system is quite useful for the measurement of dp/dt because of the high measurement accuracy of the rising edge of blood pressure waveform. The behavior of this system is compared with that of of other error reduction methods.
It is shown that this system is the best one and is as good as catheter tip manometers.