Pressure transmission device

Claim 1

In a device for use in measuring blood characteristics, particularly blood pressure or the like, having a catheter tube for insertion into the blood stream of a body and a transducer apparatus for picking up and converting pressure variations into proportional electrical voltage variations susceptible of measurement, a combination comprising a pressure transmission tube having two spaced end portions and adapted to be filled with a substantially immobile liquid pressure transmission medium, said end portions respectively communicating with said catheter tube and said transducer, and said pressure transmission tube defining an internal passaGe free of turbulence-producing projections and composed of at least two communicating main sections, one of said main sections having a constant inner diameter of between 0.5 and 2.5 mm and having a first selfresonant frequency, and the other of said main sections having a second self-resonant frequency and being of narrower diameter than said one main section and having a constant inner diameter of between 10 through 85 percent of said inner diameter of said one main section, whereby the self-resonant frequencies of said catheter tube and said pressure transmission tube are shifted away from the frequencies of the pressure variation signals to be measured so as to provide error-free measurement of the latter; and joining means forming a continuous internal channel located intermediate said sections of said pressure transmission tube and communicating with said internal passage so as to accommodate said liquid medium therein in a non-turbulent manner.