pump rate p 0 is increased by a factor corresponding to an increase of 5 100 preferably by 10 50 most preferably by 15 30 thus the pump speed during increased flow or pulse mode is after a time u03b4t when the reaction in the reactor is complete the pump speed is reverted back to the initial value p 0 then control reverts to the computer for either a programmed new measurement at a preselected point in time or an operator initiated measurement in fig2 a connector device for connecting to a patient suitable for use in connection with the system according to the invention is illustrated the connector device generally designated 100 comprises a male part generally designated 102 and a female part generally designated 104 the male part 102 is provided on the distal end of a catheter 106 that has been inserted in e g a blood vessel of a patient the female part 104 comprises a narrow tube 108 of e g steel the inner diameter of which is larger than the inner diameter of the lumen 110 of the catheter 106 the ratio between diameters is preferably 2 3 1 furthermore the steel tube 108 is milled or ground on its outer proximal end such that a sharp cutting edge 112 is formed i e the outer surface is made slightly conical at the proximal end the tube 108 is inserted in and fixed centrally of a concentric socket structure 114 forming said female part 104 the socket 114 thus comprises a cylinder like element having a circular cylindrical opening.