- Pulmonary (lung) function test: The child blows very hard into a tube attached to a machine to measure the airflow from the child's lungs. This test measures airflow from the lungs. (all visits) The children are given small plastic device called a peak flow meter - a device used to measure lung function - to use at home. Children whose lung function is less than 80% of the predicted value for their age may be given medicine to see if their lung function improves.