If tissue pressure is higher than intravascular pressure, transmural pressure is which state?

• A. High transmural pressure
• B. Negative transmural pressure
• C. Zero transmural pressure
• D. Low transmural pressure

Answer: (D)

Transmural pressure is the pressure difference across a vessel wall, calculated as intravascular pressure minus tissue (outward) pressure. If tissue pressure is higher than intravascular pressure, the outside pressure exceeds the inside pressure, so the difference becomes negative. In other words, the transmural pressure is driven to a low (and in strict terms negative) value. This reduced gradient means the wall is less stretched by the internal pressure and can even be pushed inward by the external force. If pressures were equal, the transmural pressure would be zero; if the outside pressure were lower than inside, the transmural pressure would be positive and higher.