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 heart function. A turbine which works on mechanical principles was designed. It is also suitable for cardiac output measurements on isolated pig hearts in cases where some other equipment is not, like on doppler effect based transducers. The basic principle of measuring liquid flow through a turbine is based on measurement of the time that elapses when the rotor rotates by one 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 infrared light-emitting diodes are mounted on one side of the foil and two photo-transistors, used as sensors of the transmitted infrared light, are mounted on the other. Voltage-regulated output ranging from 0 to +/- 2048 V at one revolution per second gives 500 mV at the output (changeable by programming), calculating time 2 ms, 1 mV resolution (11 bits), with an external power supply of 5 V. The turbine showed a linear response at a continuous saline flow up to 3000 ml min-1 at pressure loads of between 20 and 220 cm H2O. Pressure drop across the turbine depends on the volume flow and was 1 mm Hg at 100 ml min-1 and 3 mm Hg at 7000 ml min-1. A rotating movement 1.25 x 10(-4) kg m2 s-1 was calculated. The lowest volume change of a bolus of saline solution, detected by the turbine, was 1.6 ml.