Pulmonary function tests (PFTs) determine the presence, nature, and extent of pulmonary dysfunction caused by obstruction, restriction, or both. When ventilation is disturbed by an increase in airway resistance (Raw), the ventilatory defect is called an obstructive ventilatory impairment. When ventilation is disturbed by a limitation in chest wall excursion, the defect is referred to as a restrictive ventilatory impairment. When ventilation is altered by both increased Raw and limited chest wall excursion, the defect is termed a combined or mixed defect. Table 14.1 presents the conditions that affect ventilation.
PFTs may reveal locations of abnormalities in the airways, alveoli, and pulmonary vascular bed early in the course of a disease, when the physical examination and x-ray studies still appear normal.