A system for processing by digital computer spirograms acquired in field surveys

Instrumentation and techniques are described for recording expiratory spirograms in the field and analysing them with a digital computer in the laboratory. A commercially available spirometer is modified, to give an oscillating electrical output signal which is recorded on a cassette tape recorder. The computer displays the spirogram, calculates the forced vital capacity, one-second forced expiratory volume, maximum mid-expiratory flow, and time to expire 25%, 50%, 75%, and 90% of the vital capacity.