Most studies of the diaphragm are made with the subject standing, sitting or lying prone or supine. Such consideration ignores the fact that in health, as well as in disease, much time is spent lying on the side, and that the position and activities of this muscle and adjoining organs are greatly changed by shifts of posture. Although the literature is not without more or less detailed reference to these changes, their magnitude and clinical importance are popularly underestimated. As they affect directly physical signs, and as convenience or necessity frequently demands examination of a patient lying on one or the other side, it follows that an understanding of the action of the diaphragm in lateral positions of recumbency possesses an interest of practical value.
The relaxed diaphragm, in health, assumes a height and position dependent on forces exerted from below as well as from above. Recumbent on the back
ADAMS RD, PILLSBURY HC. POSITION AND ACTIVITIES OF THE DIAPHRAGM AS AFFECTED BY CHANGES OF POSTURE. Arch Intern Med (Chic). 1922;29(2):245-252. doi:10.1001/archinte.1922.00110020104005