MODEL RELEASED. Lung function test. Thirty-five year old woman breathing into a peak flow meter (spirometer). A peak flow meter is used to monitor lung function by measuring the maximum rate at which air is expelled from the lungs. The patient takes a deep breath and breathes out as hard as possible into the mouthpiece. This test is being used to determine the affect of volcanic activity on the island of Montserrat on the health of the residents' lungs. Photographed at Glendon Hospital, St John's, Montserrat.