Surface anatomy (diaphragm)

The posteriorinferior margin of the diaphragm is the T12 vertebra. The anteroinferior margin is the costal margin. Hence, the posterior origin is inferior to the anterior origin.

The superior margins of the diaphragmatic domes are dependent upon:

• the relative pressures within the thoracic and abdominal cavities
• the angle at which the patient stands, sits or lies; the more erect the posture, the more downward pressure is exerted on the diaphragm from above and the flatter it becomes
• the degree of muscular contraction

When contracted and flattened, they approximate the level of their tendinous origins. When fully relaxed at the end of respiration, the normal upper limits of superior margins are:

• the fourth intercostal space for the right dome
• the fifth intercostal space for the left dome
• the xiphisternum for the central tendon