Chronic obstructive pulmonary disease was the fifth highest cause of death in 2002 and it is projected to be the fourth highest cause of mortality by 2030 [1]. It is a heterogeneous disease, but the basic abnormality in all patients is airflow limitation, a value that could be easily assessed by pulmonary function tests. These tests are not readily available in low and middle income countries. Reasons include high equipment costs and the need for trained personnel. In this work, we present a lung function test that measures three highly relevant values: the forced vital capacity; the forced expiratory volume in one second and their ratio; the Tiffeneau-Pinelli index. The sensor is based on an optical detection principle. Light is coupled into a silicone fiber, that consists of a core and a cladding with low refractive index contrast to ensure high bending sensitivity. All parts of the sensor are low-cost, the silicone fiber can be both disposed and autoclaved.