i am doing a project where i need to measure the breathing rate of a patient and display on a lcd .could you guide me on how to go about it since i couldn't find any sensor available in the market
Oi!
I am going to guess the patient breathes through a tube and you want to measure air flow?
Did you look up "hot wire anemometer"?
I use one as part of a person in the room detection system. Works great. Hard to fool the sensor when small movements cause the air to shift and the hot wire to change the current value.
The sensor I use can measure up to 60MPH of wind speed. You'll need to get the sensor offset. I wired up my sensor and put it under a glass, took a series of analog to digital readings got the 0MPH offset and went from there.
Patient?
Get an approved system! You don't want to be responsible for the person's death.
You may want to give this a read:
Standard pulse oximeters can be used to monitor respiratory rate
The full text of the article can be found here:
ORIGINAL ARTICLE
Pretty interesting stuff. Just keep in mind, as was mentioned I would not be using hobby parts to attempt making anything for reliable medical data or safety of life. We don't want to kill off the patients. 
I would also give strong consideration to "hot wire anemometer" as was suggested above. I only linked to the oximeter method because there are endless oximeter sensors available inexpensively. They work fine with Arduino or similar uC syatems.
Ron
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