Body processes

Cushing’s Reflex – Function, Task & Diseases

Cushing-Reflex

Basically, the Cushing reflex is not a real reflex , but a connection between intracranial pressure , blood pressure and heart rate . When intracranial pressure increases, blood pressure increases to keep the brain supplied with O2 . The perfusion pressure in the brain corresponds to the difference between mean arterial pressure and intracranial pressure.

What is the Cushing reflex?

In 1901, the American neurologist Harvey Cushing discovered a connection between the increase in intracranial pressure, the drop in heart rate and the increase in blood pressure. The connection has borne his name in his honor since it was first described and is therefore referred to as the Cushing reflex.

The formula of the reflex is CPP = MAP – ICP. ICP stands for the intracranial pressure (brain pressure), MAP stands for the mean arterial pressure and CPP for the cerebral partial pressure. In other words, the perfusion pressure in the brain is made up of the difference between the mean arterial pressure and the intracranial pressure. The latter opposes the arterial pressure and is overcome by it as resistance.

Sometimes, instead of the Cushing’s reflex, the Cushing’s triad is mentioned, which is made up of hypertension , bradycardia and irregular, insufficient breathing .

In the true sense, the increase in blood pressure and the drop in heart rate following an increase in intracranial pressure are not a true reflex arc .

Function & task

Elevations in intracranial pressure can be due to a variety of contexts. For example, masses in the brain parenchyma can increase the pressure, such as a brain tumor . The same applies to any swelling of the brain, such as that present in the form of cerebral edema . Cerebral edema is often the result of traumatic brain injury .In addition, stroke and inflammation can increase intracranial pressure in the brain. Other causes are increases in the liquor volume, as is the case with outflow disorders of the cerebrospinal fluid.

If the intracranial pressure increases because of one of the phenomena just described, the perfusion pressure of the brain automatically decreases. For this reason, the brain is less supplied with blood. The blood transports vital oxygen to the brain. Therefore, when the perfusion pressure falls , the nerve cells are no longer sufficiently supplied with oxygen and there is a risk of irreversible damage to the nerve tissue.

The body wants to prevent this. The organism therefore tries to keep the mean arterial and intracranial pressure at a certain level. To this end, the body sharply increases blood pressure. Elevations of up to 300 mmHg in systolic blood pressure can be expected. As blood pressure increases, so does ICP. This causes the arterial pressure to rise even higher. At the same time, the heart rate drops. Because the organ has to recover from the increased stress. The pressure pulse arises on the basis of these relationships , it is caused by a suddenly increased sympathetic activity in the medulla oblongata .

After a certain time, self-regulation of blood pressure is to be expected. Therefore, the administration of antihypertensive drugs in the described situation is contraindicated. Only in the case of active bleeding into the brain, such as a ruptured aneurysm , does the doctor need to lower the systolic blood pressure to below 160 mmHg.

In summary, the Cushing reflex describes the falling perfusion pressure, the decrease in cerebral blood flow and the compensatory measure of systemic blood pressure increase, which the body takes after an increase in intracranial pressure in order to keep the MAP-to-ICP ratio constant. Due to the subsequent increase in the ICP, the arterial pressure rises again and in this way creates a vicious circle .

Diseases & Ailments

The Cushing reflex gains clinical relevance with all increases in intracranial pressure and can therefore be relevant in the context of bleeding, cerebrospinal fluid disorders, strokes, edema formation, after trauma or in tumors.Signs of increased intracranial pressure are, for example, symptoms such as more or less severe headaches , vomiting or edema within the optic disc. The edema can be diagnosed using an ophthalmoscope.

If several of the symptoms are present at the same time, there is a so-called intracranial pressure triad. The triad is often associated with side effects such as dizziness , paralysis of the eye muscles , bradycardia or respiratory and consciousness disorders . An absence up to coma can occur in the context of increased intracranial pressure. In most cases, patients initially suffer from increased restlessness and experience a general increase in blood pressure and a drop in heart rate as part of the Cushing reflex.

Patients with high intracranial pressure are monitored in intensive care and placed in bed with their upper body elevated by 30 or 45 degrees. Your head must be as straight as possible so that the venous drainage can take place without obstruction. With slight hyperventilation , the blood vessels constrict . In this way, a slight reduction in the ICP can be achieved therapeutically.

Further treatment depends on the cause of the increased pressure. Edema can be resolved or reduced by administering diuretics . In the event that the autoregulation of blood pressure in the brain does not become effective, patients with increased intracranial pressure are closely monitored with regard to their blood pressure. Invasive blood pressure measurements are often used for this purpose . In this way, intervention can be carried out in the event of a missing Cushing reflex. Various medications are available for intervention that can keep the blood pressure physiological and in this way have an effect on intracranial pressure and can ensure the blood supply to the brain tissue. Increased intracranial pressure can be a life-threatening situation.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.