Design and Development of Miniature Turbine Based Flow Sensing Device for Respiratory Flow Diagnosis

Pulmonary diseases form an important part of the national burden of diseases. Respiratory flow testing is integral to management of pulmonary diseases. The paper presents exploratory study and design of a flow sensing device that is used to diagnose the respiratory flow. It is helpful in reliable and fast screening of respiratory diseases, so that appropriate action can be taken to cure the diseases. The system is designed in a modular way and consists of: mouthpiece, interfacing hardware and software unit. A spirometer is a medical instrument designed to measure the flow of air inspired or expired by human lungs. The device is designed to perform a spirometry test which provides us with two important parameters: Forced Vital Capacity (FVC) and Forced Expiratory Volume in the first second (FEV1). These parameters are helpful in determining the results. Primary focus is not to identify the type of respiratory disease but to calculate the parameters FVC, FEV1 and their ratio so that a comparative analysis can be done based on the different readings of the same test object for each individual. For a normal person the ratio FEV1/FVC is 75 % or more. The device consists of a mouthpiece, inside which a miniature turbine is fixed. Hall sensor sense the rotations of turbine and& gives the output voltage proportional to the magnetic field strength, which is proportional to rotations of turbine. The purpose of the AT89s52 is to convert the rotations of turbine to a particular volume by as per the input air flow. Flow rate is calculated and can be used by physicist to diagnose the patient.