The net effect of vasopressin on cerebral blood flow depends on cerebral autoregulation status.

• A. False
• B. True
• C. CPP is independent of MAP
• D. CBF always decreases with vasopressin

Answer: (B)

Cerebral autoregulation is the ability of brain vessels to keep blood flow constant despite changes in pressure. When vasopressin raises mean arterial pressure, the brain’s autoregulatory mechanisms decide how much the flow changes. If autoregulation is intact, the cerebral vessels adjust their tone to offset the higher pressure, so cerebral blood flow remains roughly the same. If autoregulation is impaired, changes in MAP translate more directly into changes in cerebral perfusion pressure, making the net effect of vasopressin on cerebral blood flow depend on how much the flow pressure rises versus any direct vasoconstrictive action on cerebral vessels. Because the outcome hinges on whether autoregulation is functioning, the statement is true.