Question about calcium channel blockers and ICP/CPP

[deleted1139416]

I understand that CPP and ICP are very complicated, so please forgive my dummbassery. Since calcium channel blockers increase cerebral blood flow (by arterial dilation) but also decrease blood pressure, would they then increase cerebral perfusion pressure without the need for higher blood pressure? Similarly, would it increase ICP since increased cerebral blood flow would lead to more volume in the intracranial space?

---

Members don't see this ad.

 

[CnsCrit]

You're on the right track. If cerebral autoregulation is working correctly, it shouldn't make a huge change either way. Autoregulation is the compensatory mechanism that keeps CBF constant despite changes in CPP (MAP - ICP). So, with a wide range of MAP, CBF will be pretty constant (even between MAPs in the 50-170 range). Autoregulation works by adjustments in the size of small arteries in the brain. With no autoregulation, increase in MAP leads to increases in CPP leads to increases in CBF. With proper autoregulation, increases in MAP ultimately lead to cerebral vasoconstriction to counteract the increase in MAP. Conversely, decreases in MAP will lead to decreases in CBF which causes cerebral vasodilation to counteract this and keep CBF constant.

All this to say, in a normal person, calcium channel blockers will decreased MAP peripherally, therefore will reduce CPP, but cerebral autoregulation will keep CBF relatively constant by causing a compensatory cerebral vasodilation You won't get increased ICP if the cerebral vessels are just compensating for a lower CPP, the cerebral dilation is in a sense evening things out. In a state of vasospasm in SAH, the cerebral vasculature is already clamped down due to the blood, thus throwing off the autoregulatory curve. Hence, we step in and increase the MAP thus reducing the chance of critically low CBF and ischemia.

 

[deleted1139416]

You're on the right track. If cerebral autoregulation is working correctly, it shouldn't make a huge change either way. Autoregulation is the compensatory mechanism that keeps CBF constant despite changes in CPP (MAP - ICP). So, with a wide range of MAP, CBF will be pretty constant (even between MAPs in the 50-170 range). Autoregulation works by adjustments in the size of small arteries in the brain. With no autoregulation, increase in MAP leads to increases in CPP leads to increases in CBF. With proper autoregulation, increases in MAP ultimately lead to cerebral vasoconstriction to counteract the increase in MAP. Conversely, decreases in MAP will lead to decreases in CBF which causes cerebral vasodilation to counteract this and keep CBF constant.

All this to say, in a normal person, calcium channel blockers will decreased MAP peripherally, therefore will reduce CPP, but cerebral autoregulation will keep CBF relatively constant by causing a compensatory cerebral vasodilation You won't get increased ICP if the cerebral vessels are just compensating for a lower CPP, the cerebral dilation is in a sense evening things out. In a state of vasospasm in SAH, the cerebral vasculature is already clamped down due to the blood, thus throwing off the autoregulatory curve. Hence, we step in and increase the MAP thus reducing the chance of critically low CBF and ischemia.

That makes so much sense! Thank you! What about when you have medications that are pharmacologically causing arterial vasodilation of cerebral blood vessels, would this interrupt the autoregulatory effect?