Pulmonary function test interpretation

What it is

Testing before and after a bronchodilator answers two things in order: is there obstruction, and if there is, is it reversible. The flow-volume loop adds the pattern. It shifts to the left in patients with obstructive lung disease, where there is air trapping and decreased outflow, as in asthma, and it shifts to the right in patients with restrictive lung disease, where the lung volumes are smaller. The loop plots flow in L/sec against lung volume in L, and it has an expiration part and an inspiration part.