1 in 20 patients contracts an infection during hospitalization or surgery. Disposable items are one powerful tool to avoid cross-contamination between patients. In pulmonary function testing, the subject exhales through a mouthpiece into a sensor to measure lung function; hence contamination of surfaces is an ever-present risk, preventable by means
of a disposable flowmeter. In this study, we present a principle for a low-cost and disposable flow sensor for pulmonary function instruments, in particular for spirometers. The sensor is based on an optical detection principle. Light is coupled into a light guiding Polydimethylsiloxane fiber, that consists of a core and a cladding with similar refractive indices to ensure high bending sensitivity. A formulation that describes the relation between detected light intensity and fiber bending is established.