designing & development of flow sensor for breathing measurement

I want to develope a flow sensor with thermal time of flight technology thatwill work bidirectional & will be able to measure per minute respiration, forced vital capacity & forced expiration for 1st second. you have to use 3 nickel wires or pallets of 5mm length & diameter of not more than 1 mm (need to determine resistance) placed at 2mm distance apart in parallel inside a 2 cm dia and 4 cm lenth tube. later we will connect all this wires to 3 seperate weastone bridge 3rd leg and create a balaced bridge in normal condition by choosing other leg resistances, only diffrence in those 3 wires will be: we will excite middle nickel wire with 30hzs, 10mamp sinosoidal supply(this is a sending send) and other 2 wires will act as a detector or recieving end. after this we have to measure the heat flow from sending point to both of the detector points(by measurening voltage drop when every weastone bridge gets unbalaced) also we need to determine the time in micro-seconds when bridges gets unbalaced and need to calculate time diffrence between sending(middle )end to detector end. then by deviding this time electronically with spacing between sending end and detector end we will get the air velocity and from the constant area from where air is flowing we will measure flow rate. this way for every inhalation and exhalation we need to measure this paratemeters and from this we can measure the volume of air flow in total time