Optical Fiber Fabry-Perot Interferometer Based Spirometer: Design and Performance Evaluation

Spirometry enables the diagnosis and monitoring of multiple respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD). In this paper, we present an optical fiber-based device to evaluate the pulmonary capacity of individuals through spirometry. The proposed system consists of an optical fiber containing an intrinsic Fabry-Perot interferometer (FPI) micro-cavity attached to a 3D printed structure that converts the air flow into strain variations to the optical fiber, modulating the FPI spectral response. Besides providing the value of the flow, its direction is also determined, which enables a differentiation between inhale and exhale cycles of breathing. A simulation study was conducted to predict the system behavior with the air flow. The preliminary tests, performed with the FPI-based spirometer led to average values of forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) parameters of 4.40 L and 6.46 L, respectively, with an FEV1/FVC index (used as an airway function index) of 68.5%. An average value of 5.35 L/s was found for the peak expiratory flow (PEF). A comparison between the spirometry tests using the presented FPI system and a commercial electronic device showed that the proposed system is suitable to act as a reliable spirometer.