GB863535A - Micromanometer particularly adapated for use with a cardiac catheter - Google Patents

Abstract

863,535. Measuring electrically. ALLARD, E. M. L., and LAURENS, P. G. L. July 23, 1959 [Aug. 7, 1958; Feb. 25, 1959], No. 25299/59. Class 40 (1). [Also in Groups VI and XXXIX] In a manometer intended particularly for cardiac catheterization diaphragms 18a and 18b support in the centre of a coil 16, a core 30 composed of two parts, one 17a of material having high magnetic permeability, and the other, 17b, of material having low permeability. 'The part 17b has a temperature coefficient of expansion at least 4 times as great as that of 17a so that movement of core 30 due to thermal expansion will compensate the increase in inductance of coil 16 due to temperature increase. Further methods of temperature compensation include making diaphragm 18a larger than 18b so that thermal expansion of air trapped between them will act differentially on the two diaphragms, or, making passage 25 larger than required for leads 2 and blocking it some distance from the head, e.g. at 27, to form a chamber in which air is trapped which, on rise in temperature, applies a compensating pressure to diaphragm 18b. Ring 28 may be of metal and may be used as an ultra-cavity electrode in electro-cardiography. In an alternative form, Fig. 5 (not shown), for use in determining blood velocity the cap 20 has holes provided at the rear of the core and its diaphragms in which case these holes admit static pressure to diaphragm 18b while hole 22 admits dynamic pressure to diaphragm 18a. Deflection of core 30 therefore being a function of the speed of blood flow. Measuring circuit, Fig. 1 (not shown). The output of an oscillator whose frequency determining circuit includes the coil 16, is limited and passed to a frequency discriminator the signal may then be passed to an optional integrator, an impedance transformer and high and lowpass filters in parallel. The output of the highpass filter, cut-off 30 c.p.s., is connected to apparatus to indicate or record intra-cardiac sound whilst the low-pass filter connects to apparatus for indicating or recording intracardiac pressure. The integrator circuit referred to above is included in circuit if it is desired to average the pressure rather than record -instantaneous values.