The brain is undoubtedly a complex organ that controls thought, memory, touch, motor skills, vision, breathing, temperature, and most other processes that regulate the body. As such, it needs a large amount of oxygen to function. The fact is that in a resting state about a fifth of the body’s total oxygen requirement is consumed through cerebral metabolism.
When the brain does not receive enough oxygen, brain cells can begin to die. Cell death can occur within 5 minutes of low oxygenation which quickly leads to various complications if oxygen is not redelivered. Since the brain is so complex and the process of hypoxia can occur so quickly, there is a great deal of preclinical research that goes into understanding these mechanisms and how to treat and mitigate damage due to cerebral hypoxia (or anoxia).
One way to investigate cerebral hypoxia caused by trauma (TBI) or lack of blood flow (stroke, MCAO) is to measure cerebral blood perfusion and pO2 directly within the area of interest. We at Oxford Optronix have been supporting brain research for 30+ years and helping researchers to answer these questions with our tissue vitality monitors to assess both parameters in real-time. Sensors start at a very fine 250 µm diameter making them minimally invasive.
This article looks at some of the major application areas in brain research and the large and small animal models used. We describe how our OxyLite and OxyFlo systems have been employed and we provide some supporting publications as reference material for the reader. Please note these systems can be used separately to garner microvascular blood flow or tissue pO2 information independently from separate tissue sites or in parallel using a unique combined sensor capable of reading pO2, blood flow and temperature from a singular site. There are also implantable sensors available for chronic studies and specialized sensors for use in an imaging setting like MRI and CT. These are discussed towards the end of this article.
Traumatic brain injury (TBI) is a sudden damage to the brain. It may happen when there is a blow, bump, or jolt to the head. Following head injuries there is reduction of cerebral blood flow (ischemia) which is detrimental to the brain’s ability to recover following the injury. Depending on the nature and severity of the injury, different approaches are often studied in animal models (of different sizes) to assess the feasibility and efficacy of a specific treatment.
The OxyLite™ and OxyFlo™ products have been used extensively over many years in these types of studies to assess brain health prior to, during, and following TBI. To further assess a treatment or the effect of a drug a researcher may look at the length of time it takes, following a traumatic event, for cerebral perfusion and brain pO2 return to a normal baseline.
A stroke, also known as a transient ischemic attack, happens when blood flow to the brain is blocked. This prevents a region of the brain receiving oxygen and nutrients from the blood. Without oxygen, brain cells begin to die within minutes.
As a stroke can cause lasting brain damage, long-term disability, or even death, it’s important to quickly mitigate the damage. This can be achieved by reperfusion (unblocking the stroke site) or using methods that extend brain cell survival, which is a focus for a large portion of translational research. Very much like in trauma studies where TBI researchers use the OxyLite™ and OxyFlo™ to assess brain health, in stroke models the same instruments and sensors can also be employed to assess (and quantify) the extent of the ischemic insult and to observe a potential or complete recovery to baseline following a drug or treatment intervention.
Cerebral vitality assessment using the OxyLite™ and OxyFlo™ devices can also provide valuable surrogate data during trauma elsewhere in the organism or to other vital organs, e.g., during episodes of sceptic shock and/or resuscitation. Since the brain is such an important organ overall, monitoring it even peripherally can provide researchers with useful information on general health or on the efficacy of a specific treatment.
Other ailments, like haemorrhage, seizures, and epilepsy that originate in the brain can often cause a change in intracranial pressure, cerebral perfusion, and oxygenation. Being able to monitor these vital physiological parameters is potentially of great value to the clinical scientist in models of drug treatment or other intervention.
Implantable sensors for tissue monitoring
For those performing chronic studies of the brain, implantable sensors offer a way to take serial measurements over time. In short, the sensors need to be surgically implanted into the brain. After a period of recovery measurements can be taken in awake, restrained, or anesthetized models by connecting the miniature exteriorized sensor ferrule to a dedicated adapter, itself attached to the OxyLite™ oxygen monitor.
MRI compatible sensors
Advanced imaging techniques, like magnetic resonance imaging, continue to be commonly used to examine the anatomy and physiological processes of the brain. Researchers using these imaging techniques commonly wish to validate their data. As the OxyLite™ and OxyFlo™ sensors utilize fibre optic technology, they are fundamentally MRI compatible, allowing for real-time blood flow and tissue oxygen measurement even during MRI. Dedicated, extended length sensors are available for this application.