The Velocity Volume Loop: A Composite Pulmonary Function Test

¹ U. S. Naval School of Aviation Medicine, U. S. Naval Aviation Medical Center

1. Pulmonary function is ordinarily assesed by use of several test procedures. Since these tests are time consuming and some of them physically demanding, there is an obvious need for a simplified, composite pulmonary function test which provides a broad evaluation of pulmonary function. The breath velocity-volume (V-V) loop gives promise of being such a test.

2. The loop may be constructed by plotting temporally aligned breath volume and velocity values or it may be obtained by feeding the transduced velocity and volume signals into the two axes of the cathode my oscilloscope. To provide a permanent record, the loop traced on the oscilloscope screen is photographed.

3. Two V-V loops, a tidal loop, and a maximum (forced vital capacity) loop are superimposed and recorded. From these loops, analysis of pulmonary function may be made including a complete spirogram (i.e., vital capacity, expiratory reserve volume, inspiratory reserve volume, inspiratory capacity, tidal volume, and evidence of air trapping), a reliable prediction of the maximum breathing capacity, timed vital capacity, inspiratory reserve velocity, and expiratory reserve velocity.