Höfuðflæði

Höfuðflæði, English commonly referred to as cerebral blood flow, describes the amount of blood that circulates through the brain’s vascular system per unit time. It represents the net delivery of oxygen and nutrients necessary for neuronal and glial function and is tightly regulated by autoregulatory mechanisms that maintain cerebral perfusion across a range of systemic blood pressures and metabolic demands.

The key vessels involved in höfuðflæði are the internal carotid arteries, which supply the anterior circulation, and the vertebral arteries, which feed the posterior circulation. The intracranial circulation includes a network of arteries, arterioles, capillaries, venous sinuses, and the dural venous sinuses that drain into the internal jugular veins. Regulation occurs through a combination of myogenic, metabolic, and neurogenic responses, with critical contributions from nitric oxide and endothelin-1 signaling.

Measurement of höfuðflæði in the clinic is commonly performed with transcranial Doppler ultrasonography, which estimates blood velocity in large cerebral arteries, and with magnetic resonance imaging techniques such as arterial spin labeling, which directly measures perfusion. These modalities provide indices like mean flow velocity, pulsatility index, and cerebral perfusion values expressed in millilitres per 100 grams of brain tissue per minute.

Normal cerebral perfusion ranges between 50 to 80 millilitres per 100 g of brain tissue per minute, though values vary by age, sex, and systemic conditions. Deviations from normal flow—whether hypoperfusion or hyperperfusion—are implicated in stroke, traumatic brain injury, cerebral small vessel disease, and vascular dementia. Monitoring changes in höfuðflæði informs prognosis, guides therapeutic decisions such as blood pressure management or revascularisation procedures, and serves as a biomarker in neurovascular research.