| abstract |
Cardiac output is ascertained by measuring the cross-sectional area of a blood vessel and the velocity of fluid flowing through the vessel. The cross-sectional area is determined from the measured resistance within the vessel, derived from the known injected signal and the differential voltage generated between first and second measuring pairs of electrodes. A velocity sensor consists preferably of a Doppler shift type optic fibre (16, 18), and the accuracy of the velocity measurement is improved by focusing light emissions from the optic fibre(s) by either providing a Fresnel plate (80, 82, 84, 86) on the terminal end of the fibre or by forming the terminal end of the fibre in a generally conical shape (70, 72). |