In a supine patient, hydrostatic pressures across major body regions tend to be approximately equal.

• A. All regions are approximately equal
• B. Head higher than feet
• C. Feet higher than head
• D. Chest higher than abdomen

Answer: (A)

Hydrostatic pressure in the circulation is determined by gravity acting on blood columns. When the body is lying flat, the vertical distances from the heart to the head, chest, abdomen, and feet are small, so the gravitational term (rho g h) contributing to pressure differences becomes negligible. This makes arterial and venous pressures across major body regions essentially the same in the supine position. Small residual differences can arise from factors like breathing, intrathoracic pressure changes, or abdominal pressure, but they do not create a meaningful gradient across regions. In contrast, standing would produce higher pressure in dependent portions (like the feet) and lower pressure in the head, which is not the case when supine.