Measurements of cardiac output of an isolated heart using a specially designed turbine

Cardiac output is one of the important parameters used in evaluation of hea rt function. A turbine which works on mechanical principles was designed. I t is also suitable for cardiac output measurements on isolated pig hearts i n cases where some other equipment is not, like on doppler effect based tra nsducers. The basic principle of measuring liquid flow through a turbine is based on measurement of the time that elapses when the rotor rotates by on e degree. For this purpose, the rotor is fitted with transparent foil with a ring of 360 short black lines printed close to its circumference. Two inf rared light-emitting diodes are mounted on one side of the foil and two pho to-transistors, used as sensors of the transmitted infrared light, are moun ted on the other. Voltage-regulated output ranging from 0 to +/-2048 V at o ne revolution per second gives 500 mV at the output (changeable by programm ing), calculating time 2 ms, 1 mV resolution (11 bits), with an external po wer supply of 5 V. The turbine showed a linear response at a continuous sal ine flow up to 3000 ml min(-1) at pressure loads of between 20 and 220 cm H 2O. Pressure drop across the turbine depends on the volume flow and was 1 m m Hg at 100 ml min(-1) and 3 mm Hg at 7000 ml min(-1). A rotating movement 1.25 x 10(-4) kg m(2) s(-1) was calculated. The lowest volume change of a b olus of saline solution, detected by the turbine, was 1.6 ml.