Plethysmography: history and recent advances.

A short historical development of pneumoplethysmography and its clinical usefulness has been given and the older instruments have been compared with a modern computerized pneumoplethysmograph. The computer aided plethysmogram, with proper programming, makes possible numerous computations which give new and useful information about the circulation. New applications of the CAP will quickly develop and the data collected will be only limited by the imagination.