Effect of Partial Air-leak on Respiratory Resistance using the Airflow Perturbation Device (APD)

A mouthpiece used in spirometry is modified to produce a partial air leak while the patient is breathing into the device. Tubes were mounted on the left and right sides of the standard mouthpiece. Three different size tubes were used to produce high, moderate, and low leaks through the mouthpiece. The subjects were asked to use the Airflow Perturbation Device (APD) under identical conditions; with no leak (control), low, moderate, and high leak mouthpieces. Their average respiratory resistances were evaluated in each case. The results show that respiratory resistance decreases as more leak was allowed. It is therefore important that the respiratory technician takes additional steps to ensure that the patient completely holds and seals the mouthpiece with his/her lips so that all the breathing takes place through the mouthpiece and no leak is allowed from around the lips.