Obstructive and Restrictive Ventilatory Defects

Pulmonary function testing separates two different problems: difficulty moving air out of the lungs and difficulty expanding the lungs in the first place. An obstructive ventilatory defect is defined by a reduced FEV1/FVC ratio. FEV1 is the volume forcibly exhaled during the first second; FVC is the total volume exhaled during a properly performed forced manoeuvre. In current ERS/ATS interpretation, obstruction is present when FEV1/FVC falls below the lower limit of normal, usually the 5th percentile or a z-score below -1.645, using appropriate GLI reference equations. Airway narrowing from asthma, COPD, or bronchiectasis reduces expiratory flow. In emphysema, destruction of alveolar walls also removes elastic recoil, so small airways lose the support that normally keeps them open during forced expiration. FEV1 therefore falls disproportionately to FVC. Expiration becomes prolonged, air remains trapped, and residual volume and the RV/TLC ratio may rise. Hyperinflation can make the patient feel unable to take a satisfying breath even though the immediate problem is impaired emptying. A restrictive ventilatory defect reflects reduced total lung capacity. Pulmonary fibrosis and other parenchymal disorders make the lungs less...