Editing Cushing reflex (section)

== Definition ==
[[File:Bluthirnschranke nach Infarkt nativ und KM.png|thumb|Defect of the blood–brain barrier after stroke shown in T1-weighted MRI images. Left image without, right image with contrast medium administration showing evidence of [[brain ischemia]] ]]
The Cushing reflex classically presents as an increase in [[systole (medicine)|systolic]] and [[pulse pressure]], reduction of the [[heart rate]] ([[bradycardia]]), and irregular respiration.<ref name =Fodstad /> It is caused by increased pressure inside the skull.<ref name=Fodstad /> These symptoms can be indicative of insufficient [[blood flow]] to the brain ([[brain ischemia|ischemia]]) as well as compression of [[arterioles]].<ref name=Fodstad /><ref name= Dagal>{{cite journal | last = Dagal| first = A|author2=Lam AM| title = Cerebral blood flow and the injured brain: how should we monitor and manipulate it?| journal = Current Opinion in Anesthesiology| volume = 24| issue = 2| pages = 131–7| doi = 10.1097/ACO.0b013e3283445898| pmid =21386665 |date=April 2011 | s2cid = 6025444}}</ref>

In response to rising intracranial pressure (ICP), respiratory cycles change in regularity and rate. Different patterns indicate a different location of the brain where the injury occurred.<ref name=Grady>{{cite journal |vauthors=Grady PA, Blaumanis OR |title=Physiologic parameters of the Cushing reflex |journal=Surg Neurol |volume=29 |issue=6 |pages=454–61 |date=June 1988 |pmid=3375974 |doi= 10.1016/0090-3019(88)90140-1}}</ref> The increase in [[ventilation (physiology)|ventilation]] is exhibited as an increase in rate rather than depth of ventilation, so the Cushing reflex is often associated with slow, irregular breathing.<ref name=Dickinson /><ref name=Fox>{{cite journal |vauthors=Fox JL, Ransdell AM, Al-Mefty O, Jinkins JR |title=The Cushing reflex in the absence of intracranial hypertension |journal=Ann. Clin. Res. |volume=18 |pages=9–16 |year=1986 |issue=Suppl 47 |pmid=3813470 }}</ref> As a result of the now-defective regulation of heart rate and blood pressure, the physiologic response is decreased blood flow peripherally, which can present as [[Mayer waves]].  These are simply pathologic waves seen in HR tracings (i.e., arterial lines, electrocardiograph ([[ECG]], etc.), which reflect decreased intravascular blood flow. This decreased flow often causes reflexive [[vasoconstriction]], which leads to an overall increase in [[blood pressure]] despite the actual decrease in intravascular volume.<ref name=Dickinson />