CONTENTS Background............................................................... 948 Reference equations........................................................ 949 General issues............................................................ 949 Spirometry............................................................... 950 Lung volumes............................................................. 950 Diffusing capacity for carbon monoxide.......................................... 952 Types of ventilatory defects................................................... 953 General issues............................................................ 953 Obstructive abnormalities..................................................... 953 Restrictive abnormalities..................................................... 955 Mixed abnormalities........................................................ 955 Comments on interpretation and patterns of dysfunction............................ 955 Severity classification....................................................... 957 Bronchodilator response..................................................... 958 Central and upper airway obstruction........................................... 960 Interpretation of change in lung function......................................... 961 DL, CO interpretation......................................................... 962 Abbreviations.............................................................. 963