COVID-19
Covid-19, also called Coronavirus, is a newly identified virus that causes contagious disease. The Coronavirus led to a worldwide pandemic with respiratory illness and cerebrovascular diseases.
The Covid-19 pandemic became internationally widespread in early 2020. This contagious disease was initially thought to affect only respiratory illness and pulmonary function, but very quickly, it became evident that this disease is primarily a vascular disease with detrimental effects on the complete cardiovascular circulation. The cerebrovascular circulation is of primary interest because it has been shown that the incidence of stroke resulting from Covid-19 has increased, and particularly alarming is the fact that young adults became susceptible to stroke.
It is evident that cerebral embolization is a high-risk factor for stroke and neurological deficits.
Intracranial Stenosis
Intracranial Stenosis is a narrowing of a cerebral artery, which can develop primarily due to intracranial atherosclerosis or acute thrombus. It is a significant risk factor for Transient Ischemic Attack (TIA) and ultimately a Stroke.
Stroke Management
Stroke is the result of the death of brain cells due to lack of cerebral perfusion, which in turn causes serious functionality problems that may even lead to death.
The two main types of stroke are:
- Ischemic stroke as a result, for example, of cerebral embolization, and
- Hemorrhagic stroke as a result, for example, of cerebral bleeding due to aneurysm rupture.
Vasospasm and SAH
Cerebral Vasospasm is one of the major complications after Subarachnoid Hemorrhage (SAH) as a result of an aneurysm rupture or head injury. The outcome of vasospasm is the reduction of the arterial cross-sectional area due to extended arterial vasoconstriction or external mechanical forces.
Significant arterial narrowing resulting from SAH may take around a week to develop and present detrimental clinical conditions. Early detection of vasospasm is critical since it allows timely intervention. TCD is rather specific for this condition since it allows simple, non-invasive, and continuous bedside monitoring of vasospasm development.
Arteriovenous Malformation
Arteriovenous Malformation (AVM) relates to an anomaly whereby the arterial flow bypasses the capillary circulation and connects directly to the venous drainage circulation, thus not allowing for appropriate tissue perfusion.
AVM is characterized by low resistance to blood flow due to direct communication between the arteries and veins, which bypasses the micro-circulation with vasomotor capabilities. Thus, blood flow through an AVM anomaly is a high volume flow, hyper-perfusion, which in turn results in relatively high mean blood flow velocities.
Collateral Capacity
Similar to cerebral autoregulation and vasomotor reactivity, cerebral collateral flow reflects an alternative compensatory mechanism to pathological flow conditions
The cerebral collateral pathways include side-to-side via the anterior communicating artery, posterior-to anterior via the posterior communicating artery, and external-to-internal via the ophthalmic artery. TCD can detect reverse velocities in the collaterally perfused arteries, indicating the viability or absence of this compensatory mechanism.
The Viasonix Dolphin’s highly sensitive M-mode display identifies forward or reversed blood flow, throughout the depth range, for analysis of this brain protection mechanism.
