The effect of posture on diaphragmatic movement and vital capacity in normal subjects with a note on spirometry as an aid in determining radiological chest volumes.

Since earliest times the diaphragm has attracted attention from philosophers as well as anatomists and physiologists. Hailer (1738) summarized the opinion of the Renaissance anatomists when he described the diaphragm as nobilissimus post cor musculus. Buffon, quoted by Bell (1826), reiterated a medieval superstition by describing its central tendon as a nervous centre, the place of all emotions and the seat of the soul: " in sickness and oppression, lowness and sighing, weeping and laughing, in joy or in fear, all our feelings seem to concentrate in this part." At the beginning of the nineteenth century Bell (1826) and Astley Cooper (1839) demonstrated that life could be maintained by diaphragmatic breathing alone after injuries to the cervical spinal cord in man. Duchenne (1867) used the newly discovered faradic current to investigate the action of the diaphragm in respiration of men and animals. He stimulated the phrenic nerve in dogs, horses, and men, and found it caused the diaphragm to descend and the costal margin to rise upwards and outwards. In dead animals he made similar observations, but when he had opened the anterior abdominal wall and removed the viscera he found phrenic stimulation caused the diaphragm to descend, drawing the costal margin inwards and downwards. He believed that in life the diaphragm in its descent lifted the lower edge of the costal margin upwards and outwards by leverage against the abdominal viscera. Although the mode of action of the diaphragn was the subject of controversy among physiologists (Magendie, 1825; Duchenne, 1867; Bert, 1870), it was accepted that the diaphragm was the most important muscle of respiration.