Traumatic brain injury can cause dangerously raised intracranial<unk> .<unk>  or PRx is tool for monitoring cerebral autoregulation in the intensive care setting for patients with severe traumatic brain injury or subarachnoid haemorrhage, in order to guide therapy to protect the brain from dangerously high or low cerebral blood flow. PRx uses mathematical algorithms to calculate the correlation between arterial blood<unk>  and intracranial<unk> . PRx assesses for correlations at low frequencies, below 0.5 Hz, and thus ignores individual pulses while capturing the effects of respiratory-driven variation in arterial<unk>  as well as other longer-acting stimuli. Under normal conditions, cerebral autoregulation ensures that cerebral blood flow is unchanged despite variations in blood<unk>  by regulating the cerebral vessels. For example, if the blood<unk>  increases, the cerebral vessels vasoconstrict to keep cerebral blood flow normal, whereas a decrease in blood<unk>  would lead to vasodilation of the cerebral vessels to increase blood flow. The cerebrovascular reactions to changes in blood<unk>  generates a corresponding effect on the intracranial<unk> . When the blood<unk>  increases and the vessels vasoconstrict, the cerebral blood volume is reduced. According to the Monro-Kellie doctrine, less cerebral blood volume leads to a reduction in the intracranial<unk> . If the blood<unk>  instead would decrease, the cerebral vessels would vasodilatate, with a resulting increase in cerebral blood volume.
Pressure reactivity index
Instantaneous wave-free ratio
Fractional flow reserve
Arterial resistivity index
Coronary flow reserve
Arterial input function
Flow-mediated dilation
Cold pressor test