Dynamic Analysis of Blood Flow Measurements to the Brain, Brainstem, Cervical Spinal Cord, and Cranial Nerves
At the Hauser Neck Center at Caring Medical Florida, we can utilize transcranial doppler (TCD) and extracranial doppler (ECD) ultrasound examination to assess proper blood flow during positional changes of the neck. Compromised blood supply due to cervical dysstructure (destruction of the cervical supporting structures and loss of cervical lordosis) and cervical instability cause a wide array of symptoms. Dynamic transcranial doppler (TCD) and extracranial doppler (ECD) ultrasound provide documentation of any decreases in blood supply when the neck is in motion or in various positions.
Ultrasound examinations involve insonation, the process by which sound waves are emitted from a probe and reflected back from the tissue(s) and then converted to an image on the screen. These sound waves can be directed toward a blood vessel and the wave reflected back by moving red blood cells within the vessel. The amount of reflection and speed of reflection can then be used to measure the speed of blood flow in centimeters per second (cm/s). The doppler effect can be observed when a person’s voice gets louder as they walk toward you and softer as they walk away from you. The amount of sound waves heard increases (thus increase frequency of sound waves) or sound is amplified when sound it is coming toward you; while sound is dampened (or the waves are less frequent) when it is going away from you. In color doppler examinations, this doppler effect is shown by sound coming toward the probe is seen as a red color and sound going away from the probe as blue!
Sound waves can be emitted into blood vessels and then reflected back to determine the speed at which blood is flowing toward or away from the probe. Transcranial doppler determines the blood flow inside the cranium and extracranial doppler is used to determine it in vessels outside the cranium. The main vessels tested in the neck include the vertebral, common carotid, external carotid, internal carotid, and ophthalmic arteries. Those inside the cranium (brain) include the Circle of Willis, vertebral, basilar, posterior cerebral, middle cerebral and anterior cerebral arteries. The speed of the blood flow correlates with vessel diameter and can be used to determine obstructions to blood flow, such as a clot, atherosclerosis, compression (from bone or bone spur), and vasospasm. The blood flow in the brain, brainstem, neck, head, eye, and face can be compared when a person is lying down or upright and with their neck in various positions. Changes in a person’s cervical curve and cervical instability can cause decreases in blood flow in important arteries and cause various symptoms.
According to Bernoulli’s Principles, there is an increase in blood flow velocity at and/or immediately beyond the point of constriction of a vessel, because of either compression or stretching of the vessel. At the point of compression or stretching, there is a reduction in the diameter of the vessel, which causes an increase in flow velocity. Poiseuille’s Law states that flow is proportional to the fourth power of the radius of the vessel. Blood flow is extremely sensitive to the radius or size of the blood vessel. At points of restriction of blood flow, there is an increase of blood flow velocity until approximately 95% occlusion, when blood flow can dramatically drop until it ceases completely. There can be turbulence of flow in the artery immediately down-stream from the region of distortion (stretch or compression). This results in a decrease in blood flow velocity a short distance distal to the point of constriction and blood flow can return to normal laminar flow in the more distal parts of the vessel. Because of the unique path the vertebral artery takes to go from the skull to the brain, it is especially vulnerable to compression and stretch at the C1 and C2 vertebrae. The internal carotid artery is subject to compression and stretch lies just anterior to the transverse processes of the C1, C2, and C3 vertebrae before entering the skull via the carotid canal. The carotid canal contains the internal jugular artery and the sympathetic nerves from the superior cervical sympathetic ganglion (which by the way vasoconstrict the blood vessels of the brain). Of interest, is the carotid canal is just anterior to the jugular foramen through which the vagus nerve enters and leaves the brain! Whether due to long-term forward head posture, a face-down lifestyle (extended cell phone use), or upper cervical instability, positional abnormalities of C1 and C2 can compromise both the anterior circulation of the brain (internal carotid artery) and the posterior circulation (vertebral artery).
BLOOD SUPPLY IN THE HEAD, FACE, NECK, AND BRAIN
At the base of the brain, the carotid and vertebrobasilar arteries form a circle of communicating arteries known as the Circle of Willis. The arteries that form this circle, including the anterior, posterior and middle cerebral arteries can be analyzed with TCD. TCD is used in intensive care units around the globe to monitor people noninvasively who suffer a subarachnoid hemorrhage, stroke, and traumatic brain injury. Not only can vasospasm and other decreases or changes in brain blood flow be monitored, but TCD can also show if the person has blood clots called emboli affecting their brain circulation!
Two-thirds of the blood supply to the anterior and middle parts of the brain (anterior blood supply) is through the carotid arterial system and one-third from the vertebrobasilar arteries (posterior blood supply). The common carotid and vertebral arteries are present on the left and right sides of the neck. The common carotid arteries branch off in the mid-cervical region into the internal and external carotid arteries. The external carotid arteries supply the structures of the face and neck including the cranial nerves. The internal carotid arteries lie in the carotid sheath with the internal jugular vein and vagus nerves. The carotid arteries lie very close to the anterior portion of the transverse process of the cervical vertebrae. The internal carotid artery ends inside the skull (cranium) as the middle and anterior cerebral arteries. These supply the middle and anterior parts of the brain, respectively. The blood flow in these arteries can be checked in real-time with TCD. The ophthalmic artery which supplies the eye and retina is a branch of the internal carotid and its blood flow can be checked with TCD.
Because the vertebral arteries lie within the cervical vertebrae, they become compromised with neck conditions like instability, change of cervical curve, and various bone spurs (which can compress the arteries). The cervical vertebral arteries go into the brain via the foramen magnum to form the basilar artery of the Circle of Willis and, ultimately, the posterior cerebral arteries. These arteries supply the posterior part of the brain, brainstem, and cerebellum.
While all types of cervical dysstructure and cervical instability can compromise blood flow, both the anterior (carotid) and posterior (vertebral) arterial systems are vulnerable at the level of C1 (atlas) and C2 (axis). Anyone with documented upper cervical instability, especially with cervical kyphosis (reversal of cervical curve), is prone to periodic decreases of blood flow with certain movements.
WHY DO HOSPITAL TRANSCRANIAL DOPPLER OR EXTRACRANIAL DOPPLER TESTS OFTEN MISS ABNORMALITIES?
Most ultrasound technicians who examine the neck are trained to find atherosclerotic plaque in the common and internal carotid arteries via the carotid doppler duplex examination. This examination involves both B-mode and doppler ultrasound examinations. It is a non-motion test and does not test the blood vessels in the eye or brain. Plaque is assessed by the B-mode or brightness mode of the ultrasound that can detect subtle differences in acoustic impedance (resistance to sound wave propagation) in tissues or fluid so they display a different brightness or shades of gray. Sound waves bounce back quickly off of bone, so they are hyperechoic and appear white on the ultrasound screen. Tissues such as the liver appear gray because some of the sound waves go through the liver and others bounce back. Fluid doesn’t reflect much of the sound wave back, so it appears darker (black) with B-mode ultrasound. This can give information on the character of plaque including smoothness, texture, size and whether it is ulcerated or not. The doppler examination is then performed to determine the speed at various places in the arteries, this gives an indication in the amount of stenosis. Carotid stenosis from plaque is a risk factor for stroke and this is generally why the test is ordered. Unfortunately, a person can have intermittent stenosis or narrowing of a blood vessel without significant plaque. There are many patients who have transient ischemic attacks, and even strokes, yet no compromise of blood flow is seen by CT or MRI angiography. Remember, CT and MR angiography are typically done with the patient in the supine neutral head position. These tests are also just a moment in time. If there is no decrease in the diameter of the blood vessel (or blood flow) at the exact moment in time that the person is getting scanned, the test will come up negative.
Another important point is that transcranial doppler or extracranial doppler tests that are performed at the hospital, typically have the person lying in the supine position. This is when the blood flow in the arteries to the brain are maximum. Even when looking for vertebrobasilar insufficiency or ischemia, the person is normally tested in a supine or side-lying position. Therefore, a lot of abnormalities are missed since blood flow is lower in the vertebral artery in the upright position as well as when the head is rotated. Since patients with neck problems, including instability, have symptoms when they are upright, standing, or with various neck motions, a supine blood flow test is most likely going to miss the issue. Ultimately, the blood flow test has to be performed in the position(s) that recreates a patient’s symptoms in order to really visualize and understand what is happening to that patient.
WHAT IS VASOSPASM?
Vasospasm is when an artery goes into spasm causing vasoconstriction or a decrease in blood flow. Vasospasm can be very little or shut off a blood vessel completely causes a transient ischemic attack. Someone with drop attacks or sudden-onset loss of balance or dizziness could be having vertebrobasilar ischemia from neck instability. Almost all vascular headaches have some type of vasospasms and rebound vasodilation. A vascular headache can actually be seen on color doppler. You can see the blood vessels dilated! So, the vasospasm and/or vasodilation which occurs with various headaches can be seen and measured. The cause (cervical instability) then can be determined and treated with Prolotherapy!
Not all vasospasm causes a problem as the body has collateral blood vessels that can be called upon to give blood supply when an artery is cut off. While vasospasm is well known for conditions such as brain hemorrhage as in subarachnoid hemorrhage, it is often overlooked for such conditions as transient ischemic attack or for people that have intermittent symptoms such as migraine headaches, loss of vision (or vision changes), speech changes, imbalance, mental fatigue, swallowing difficulty, tachycardia and many others. Basically, any type of pulsatile headache has as part of its pathophysiology, changes in the diameter of an artery. Depending on which artery is changing diameter will determine the symptoms. Some patients have hemiplegic migraines where they become paralyzed on one half of their body as part of their migraine symptoms. This vasospasm can occur because of cervical instability.
Vasospasms can occur with changes in neck positions especially in people with cervical instability or severe changes in their normal cervical curve. Vasospasms are detected to the arteries in the brain by TCD and those outside of the brain and in the neck by extracranial doppler ultrasound analysis. Baseline values of blood flow through arteries such as the anterior cerebral, posterior cerebral, middle cerebral, internal and external carotid, as well as their branches such as the ophthalmic artery while the person is supine (laying down) and then compared to those while upright and in various neck positions. Vasospasm is documented by an increase in blood flow velocity as the blood flows into a blood vessel that is narrowed. As the blood vessel narrows by vasospasm, the blood pressure causes the blood to rush into the smaller space at a greater speed. It is the same principle that occurs in a riptide in the ocean by us. If the water is to go into a much narrower space (channel or small space in the sand bar), the speed of water rushing into the smaller space increases drastically and becomes very dangerous for swimmers who might happen upon a riptide.
COULD INTRACRANIAL PRESSURES BE TOO HIGH?
Many people feel an enormous pressure in their brain. Some people have it there all the time and others periodically. It is often there when a person is upright. It feels like there is too much pressure in the brain and it causes headaches, facial pain, focusing issues, brain fog, and overall fatigue. One of the parameters measured with dynamic TCD and ECD vascular testing that is done at the Hauser Neck Center is the pulsatile index (PI).
|Pulsatile Index =||peak systolic flow velocity – peak end diastolic flow velocity|
|mean flow velocity|
When intracranial pressure is high, pulsatile index is often high. An increase in pulsatile index and intracranial pressure means the resistance to blood flow in the brain is increased. This ultimately reduces blood flow (medically called a decrease in cerebral perfusion pressure). One factor that decreases brain blood flow is a drop in CO2 pressure. In general, for every drop of CO2 pressure by 1mm hg the cerebral blood flow decreases by 2%. During vasospasm, the blood vessels show an increase in PI (and thus a drop in CO2 levels). If blood flow to the brain is reduced enough, neurons start to die. The optic nerve sheath (the nerve that allows us to see) diameter as measured by ultrasound may be enlarged on one or both sides (greater than 5mm). With increased intracranial pressure the pupils may not constrict normally to light. This can be evaluated by shining light into one eye and measuring the amount of constriction of the pupils under ultrasound guidance.
WHEN TO SUSPECT DECREASED BLOOD FLOW TO THE BRAIN/BRAINSTEM/HEAD/FACE/NECK
Many people experience transient symptoms, such as dizziness or brain fog, which come on quickly then subside when lying down. Why does this happen? One of the reasons is that the blood supply to vital neuronal tissue is compromised in the upright posture but increased when a person lies down. Anyone who suffers from a symptom that is significantly greater in the upright position or with a certain head movement and relieved by lying down is likely experiencing intermittent ischemia in some blood vessels due to cervical instability and a dysfunctional cervical curve.
Consider some of the blood vessels that can be seen with ECD and TCD and what these blood vessels supply:
The common carotid artery branches into the internal carotid artery and external carotid artery. The external carotid artery supplies the face, thyroid, neck and many of the cranial nerves, including the vagus (via several branches, including the ascending pharyngeal). The internal carotid artery supplies the eye (via the ophthalmic artery branch), anterior spinal cord (anterior spinal arteries), trigeminal ganglion and then terminates in the brain to supply the middle and anterior cerebral arteries.
The anterior cerebral artery (ACA) extends upwards and forwards from the internal carotid artery. It supplies the front lobes, the parts of the brain that control logical thought, personality, and voluntary movement, especially the legs. Tapping the toes forcefully, for instance, can increase ACA flow by 10 cm/second as seen on TCD! When the ACA blood supply is compromised some of the symptoms can be slow movement, poor coordination, tremor, dystonia, weakness, personality changes, agitation, memory impairment, emotional lability (know anyone like that?), and decreased self-awareness.
The middle cerebral artery (MCA) is the largest branch of the internal carotid artery. The artery supplies a portion of the frontal, temporal and parietal lobes, as well as basal ganglia and parts of the internal capsule, including the primary motor and sensory areas of the face, throat, hand, and arm. It is also extremely important for speech. Squeezing a ball vigorously, for instance, can increase flow through the MCA by 10 cm/second. When the MCA blood supply is compromised, one can have decreased sensation or strength on one side of the body, difficulty remembering words, slurred speech, brain fog, and/or poor judgment.
The posterior cerebral arteries (PCA), in most people, arise from the basilar artery (and thus vertebral arteries) and supply the thalamus, internal capsule, choroid plexus, hippocampus, and parts of the temporal and all (or most of) occipital lobe (vision center), brain stem, and cerebellum. If a person is in a dark room and then a bright light is shone in their eyes (hyperlight), blood flow in the PCA can increase 20 cm/second! A decrease in the PCA blood supply can have catastrophic effects on a person and cause drop attacks, seizures, slurred speech, impaired swallowing, incredible stress, inability to relax, abnormal respiration, decreased level of consciousness (extreme brain fog), poor ability to focus, intermittent darkening or blindness in an eye, nausea, vomiting, headaches, nystagmus (objects appearing moving when they are actually stationary), poor blood pressure control, and lack of balance.
ASK THE HAUSER NECK CENTER ABOUT YOUR CASE
Dr. Hauser and our team at Caring Medical Florida would love to help you resolve your chronic pain and neurological symptoms! For many of our new neck patients, blood flow studies are an important part of the testing and treatment process.
Blood flow studies can assist in healing for several reasons:
- Compromises in blood flow can cause strokes and permanent brain, brainstem, and cranial nerve injury.
- Decreases in blood flow can lead to brain nervous tissue injury and ultimately to increases in intracranial pressure.
- Knowing why a symptom occurs means the diagnosis is finally found!
- It is necessary to know which neck positions optimize blood flow to the brain, brainstem, head, face, and neck, and which ones compromise it. During treatment, positions of optimum blood flow are chosen.
- Depending on the severity of vasospasm or blood flow compromise, cervical bracing (wearing a neck collar) may be instated. It is important to choose a neck and head posture for bracing that optimizes blood flow.
- Knowing which motions compromise blood flow also helps determine if anything needs to be done during sleep, including altering sleep position, neck position, or pillow selection.
- Blood flow analysis can also be used to make sure treatments are working. The neck position(s) that caused compromises in blood flow can be rechecked periodically to make sure blood flow is returning with treatment.
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