There is general agreement that evaluation of ventilatory function by spirometry is the first step in the clinical assessment of pulmonary function. Terminology, methodology, and standards for the prediction of spirometric indices have been outlined in a recent report.1
The vital capacity (VC) is a measure of the stroke volume of the thoracic bellows, and many factors may decrease it. Some, such as kyphoscoliosis, neuromuscular disorders, and destruction of lung tissue, are permanent; others, such as left ventricular heart failure, pleural effusion, and ascites, are reversible and their course may be followed by serial measurement of the VC.
Unlike the VC, indices which relate time and volume provide a measure of breathing capacity and of airway obstruction. The maximal voluntary ventilation (MVV) is a good measure of ability to move air and, when reduced proportionately more than the VC, indicates airway obstruction. However, the test is fatiguing, requires a