In the Cushing reflex, the central chemoreceptors are likely involved in the detection of ischemia, contributing to the sympathetic surge and hypertension in the first phase of the reflex, and work in opposition to the baroreceptors, contributing to the combined high sympathetic and parasympathetic activation. Function
Raised intracranial pressure can ultimately result in the shifting or crushing of brain tissue, which is detrimental to the physiological well-being of patients. As a result, the Cushing reflex is a last-ditch effort by the body to maintain homeostasis in the brain. It is widely accepted that the Cushing reflex acts as a baroreflex, or homeostatic mechanism for the maintenance of blood pressure, in the cranial region. Specifically, the reflex mechanism can maintain normal cerebral blood flow and pressure under stressful situations such as ischemia or subarachnoid hemorrhages. A case report of a patient who underwent a spontaneous subarachnoid hemorrhage demonstrated that the Cushing reflex played a part in maintaining cerebral perfusion pressure (CPP) and cerebral blood flow. Eventually, the ICP drops to a level range where a state of induced hypertension in the form of the Cushing reflex is no longer required. The Cushing reflex was then aborted, and CPP was maintained. It has also been shown that an increase in mean arterial pressure due to hypertension, characteristic of the reflex, can cause the normalization of CPP. This effect is protective, especially during increased intracranial pressure, which creates a drop in CPP.
Finally, the Cushing reflex may be one of many ways to identify if a patient has rejected a transplanted organ. Aside from the innate autoimmune response, ischemia in the cranial region has been detected with a transplanted organ that is being rejected. As such, the presence of a Cushing reflex due to ICP can indicate that ischemia may be occurring due to foreign organ rejection.As first postulated by Harvey Cushing, raised intracranial pressure is the primary cause of the Cushing reflex. Furthermore, continued moderate increases in cranial pressure allows for the Cushing reflex to occur. In contrast, rapid and dramatic pressure rises do not allow for the mechanism of the reflex to sufficiently take place. Elevated intracranial pressure can result from numerous pathways of brain impairment, including: subarachnoid hemorrhages, ischemia, meningitis, trauma, including concussions, hypoxia, tumors, and stroke. In one study, it was confirmed that raised ICP due to subarachnoid hemorrhaging causes mechanical distortion of the brainstem, specifically the medulla. Due to the mechanism of the Cushing reflex, brainstem distortion is then swiftly followed by sympathetic nervous system over activity. In addition, during typical neurosurgical procedures on patients, especially those involving neuroendoscopic techniques, frequent washing of the ventricles have been known to cause high intracranial pressure. The Cushing reflex can also result from low CPP, specifically below 15 mmHg. CPP normally falls between 70-90 mmHg in an adult human, and 60-90 mmHg in children.Brain plateau wave changes are also associated with the Cushing reflex.