Research Week 2 Part 2.docx

All right, well, you'll recall from A&P that there are corticospinal tracts. These are fibers that begin in the cortex. They descend through the midbrain, the pons, the medulla oblongata, and then they cross over to the contralateral side and they go all the way down to a specific part of the sp...

All right, well, you'll recall from A&P that there are corticospinal tracts. These are fibers that begin in the cortex. They descend through the midbrain, the pons, the medulla oblongata, and then they cross over to the contralateral side and they go all the way down to a specific part of the spinal cord itself. They then synapse with fibers that are present in the spinal cord and those fibers course all the way out to where the muscles are. So you know as well as I do that the right side of the brain controls the muscle set that's on the left side of the body and the left part of the brain controls those muscle sets that are on the right side of the body. But we should be able to pinpoint where lesions are found in these individuals depending upon the type of paralysis that we see. And there's two major types of paralysis that we see. One is spastic paralysis and one is flaccid paralysis. Whether you have spastic or whether you have flaccid, they're both bad because they can lead to the inability for the individual to move, including the individual's inability to ventilate. And that's why this is important to a registered respiratory therapist. So if there's any kind of a lesion in the upper motor neuron, we're really talking about those fibers in the cortex and down in the spinal cord. What that means is that the ability of these fibers to transmit action potentials is very, very minimal, if at all. When that happens, that means that the lower fibers, the ones that course out to the musculature, really have no governance. They have lost the control from the brain. And so these fibers fire all the time. They fire incessantly into the musculature, causing the muscle to remain in a state of spastic contraction. We refer to that as spastic paralysis because the patient can't move, ironically, because the muscles are contracted all the time without relaxation at all. If, on the other hand, it's a lower motor neuron lesion, then we're talking about a lesion in those fibers that arise in the spinal cord and course out to the musculature. In this case, the corticospinal fiber is intact. So there are impulses coming down from the brain, but they end at the level of the spinal cord. There is basically no connection at that point so that what we have is no action potential coursing all the way out to the musculature. And in this particular instance, we have what is known as a flaccid paralysis. Again, the patient can't move, so it's still paralysis, but it's flaccid paralysis. Some clinicians will refer to this as the muscles simply being limp, and they are because they're unable to contract no matter what. So in one case, you have spastic paralysis where the muscle is constantly contracted. That's spastic paralysis. And in the other case, you have a situation where the muscles can't contract at all, and this is flaccid paralysis. All right, well, here is a cross-section of a spinal cord, and you see a dark area toward the center of the spinal cord that looks kind of like a butterfly. That area is an area where the neuronal cell bodies abound. This is a very, very rich area when it comes to neuronal cell bodies. The other areas immediately on the outside of this are areas where you find axonal projections. Now, over to the left side of the slide, you're going to see three sections, and these three sections have areas shown in red that denote pathological changes as a result of a spinal cord injury. What I'd like you to realize is when we talk about a spinal cord injury, we're not talking about a homogeneous kind of injury. We're not talking about the exact same injury in every single patient. If we had three patients with spinal cord injury, we might have patterns that look like these three patterns. Very different presentations, very different patterns, and very different patterns of functional retention. So even though they're all the same kind of spinal cord injury, they are injuries that are different from patient to patient to patient. At the very top, you can see that this particular case, the spinal cord shows some hemorrhaging in the central part of the cord, but the peripheral part of the cord is relatively preserved. If you look at the second one, the second one shows that there is extensive hemorrhaging in the anterior portions of the cord, also in the lateral portions of the cord, and some aspects of the posterior cord. But the dorsal areas are relatively spared. No real pathological changes there. Finally, in the last section, you can see that on the patient's right side of the cord, it's relatively spared. There's no real damage there at all. And yet, as far as the left side is concerned, here we see extensive damage from the anterior to the posterior and every part in between. So think of the changes that are occurring with neurons in these areas, with astrocytes in these areas, and think of how each one of these three patients might have different preservation of function, even though they still all have spinal cord injury. So please don't make the mistake of thinking that just because someone has a spinal cord injury, they have the exact same type of spinal cord injury as any other patient. It's highly likely that it's going to be a patient-specific injury pattern. All right, so let's take a look now at the nervous system that enables the individual to take nice, big, deep breaths. If we look at this cartoon, what we see is that, of course, there's a heart, there are the lungs, and then underneath those organs is the diaphragm. So how is it that the diaphragm contracts? Well, it contracts because the phrenic nerve that courses down on the right-hand side innervates the right hemidiaphragm. The phrenic nerve on the left side innervates the left hemidiaphragm. But what makes up the phrenic nerve? Well, if we look at the phrenic nerve and we follow it all the way up to its headwaters, where it comes from, what we'll see is that it actually arises from three nerves on the right and the different three nerves on the left. Of course, inside of the vertebral motor unit shown here is the spinal cord. So ultimately, these fibers are all coming from the spinal cord, but they course out through C3, C4, and C5 on the right-hand side, becoming the right phrenic nerve, which courses out to the right hemidiaphragm. So if action potentials race down through the phrenic nerve, obviously what's going to happen is that the hemidiaphragm is going to contract. And when the hemidiaphragm contracts on that side, it's going to basically cause the lung to expand on the right side. Same thing with the left. If we look at C3, C4, and C5, those three spinal nerves, they coalesce together. They become one nerve, and that one nerve courses all the way down to where the left hemidiaphragm is situated. So once again, if we have action potentials coming down that phrenic nerve, we're going to have contraction of that left hemidiaphragm. So if we obviously have the same action potentials coming down the right phrenic nerve and the left phrenic nerve at the exact same time, we're going to have simultaneous contraction of both the right and the left hemidiaphragm. And as a result, this individual is going to take a nice, big, deep breath. So we can say that the diaphragm is innervated by bilateral phrenic nerves, C3, C4, and C5. So to remember that, we just say, hey, C3, C4, and C5, keep the diaphragm alive. It's just a little ditty that allows us to remember that. It's important to also keep in mind that these motor nerves innervate both hemidiaphragms and allow inspiration, not expiration. Well, with what we just studied as a background, let's look at what happens if an individual has a C5 spinal cord injury. Here we have an individual that has a C5 spinal cord injury. What I have done is I have put in a red line on the cartoon to denote where that injury occurs. That means that action potentials coursing down from the brain through the spinal cord cannot go down any further than C5. This type of injury might look like the spinal cord injury represented at the left in that white box. You can see that there's an area in there that is full of blood. It's hemorrhaged. And so the anterior portion of the spinal cord is involved. The posterior part of the spinal cord is relatively spared. And let's say that that is what the pathological picture looks like where that red line is. It's at C5. Well, if the patient has a C5 injury, what that means is that because action potentials can't get through, that's pretty bad. There are going to be some losses of some types of function. Fortunately for this patient, the diaphragm is going to be spared. The diaphragm will still continue to function just like it's always functioned. Let me show you why. If we go up and we look at C3, C4, and C5, the spinal nerves coursing out from underneath the vertebral motor units, you can see that they're still all intact. They haven't been cut in any way. They still coalesce together to become the phrenic nerve, both on the right as well as on the left. And those phrenic nerves come all the way down to where the diaphragm is, which means the diaphragm is still able to function. So we still have about 75% of the ability to take a big deep breath, and that's good. Because if you have that, well then you're basically still able to breathe to a fairly significant extent. On the other hand, if that injury, instead of being a C5, is a C4, that means that about 25% of our ability to ventilate is gone. So what we now have is 50% of our inspiration still intact. What if we go up one more level? Let's go up to C3. Well, with a C3 injury, we actually have only about 25% of our ability to inhale still intact. So you can look at this from a number of perspectives, but here's what we know. If you're going to get a spinal cord injury, and it's either going to be a C3, a C4, or a C5, the spinal cord injury that you want, not that anyone would want a spinal cord injury, but given the circumstances, a spinal cord injury that you want is a C5. Why? Because that means you have full preservation of the diaphragm. Go up just one level to C4, and now you have 50% preservation of the diaphragm. Go up one more level, and now you have 25% of the diaphragm preserved. Can you predict what would happen if you went up one more level, say to C2? Well, at C2, there is no preservation of the diaphragm. There is no ability to breathe. This individual is going to be on the mechanical ventilator for a very long period of time, possibly even a lifetime. Now, fortunately, what happens is that sometimes areas like the one that I showed you here to the left inside the white box, those areas have a tendency to change. They can improve, or they can actually get worse. And whether they improve or whether they get worse is really dependent upon what we do as therapists, both physical therapists as well as respiratory therapists. And, of course, the rest of the transdisciplinary team is also very definitively involved. Let's turn our attention now to the autonomic nervous system. You'll recall that the autonomic nervous system has not only a sympathetic division but also a parasympathetic division. Let's begin by looking at the parasympathetic division first. In this cartoon, you'll see that there is a spinal cord running down the length of the cartoon. That's over to the left. And then you'll notice some blue fibers that arise from the spinal cord and course out to lots of different organs and organ systems. One of these blue fibers courses out to what appears to be an icon for the heart and an icon for the lung showing the larynx, the trachea, the bronchi, et cetera. And what this is showing is that, of course, it's from this site that parasympathetic fibers course out to the heart and lungs. Now let's look at the sympathetic part. The sympathetic part or the sympathetic fibers arise from thoracic segments in the middle of the spinal cord. They then course out to what's known as a parasympathetic ganglion. You can recall from your AMP that there's one on the right side, there's one on the left side. And these red fibers also course out to a number of organ systems, once again, including the heart and the lungs. So the heart and the lungs are going to receive parasympathetic fibers and sympathetic fibers. And that is as it should be. That is the normal state of affairs. It's a lot like having this teeter-totter that we have on the right-hand side, where sometimes the parasympathetic is in the ascendancy, sometimes the sympathetic part of the autonomic nervous system is in the ascendancy. So there's a balance. There's a balance so that the sympathetic doesn't get away with controlling all the function, and the parasympathetic doesn't get away with controlling all the function. That is what is normal. Now, when we have a cervical spinal cord injury, as shown up at the top of the cartoon, there's a little oval that shows where that injury is. What happens is that the fibers coming down from the brain are unable to get into the spinal cord because there's some sort of a problem. There's hemorrhaging. There might be laceration. There will be lots of contusion. And so if you look at the fibers that are present below this point, the only fibers that are present below this point are the sympathetic fibers. Well, if action potentials can't get through this area because there's damage where the oval is, that means that for all intents and purposes, the sympathetic nervous system is basically out of commission. If you look at the blue fibers, they arise from the upper portion where the injury is. And because they are above the injury, they're spared. So they are able to continue to provide parasympathetic influences. Now, we then see that because the parasympathetic influences have been preserved and the sympathetic influences have been blocked, there's going to be a predominance of parasympathetic function. What does that mean? Well, in order to determine that, you have to remember what both of these sympathetic and parasympathetic divisions do. Let's review that. The sympathetic nerves promote bronchodilation and also normal airway secretion production. Parasympathetic fibers, on the other hand, promote bronchoconstriction--not a good thing-- and increased airway secretion production. Again, not a good thing. But as long as sympathetic and parasympathetic are balanced, the control of the system is preserved. However, when there's a cervical spinal cord injury, as shown here, the sympathetic nervous system is basically out of commission. The parasympathetic nervous system is the only nervous system that remains intact. Because of this, we refer to this as parasympathetic predominance. And that also means, for the registered respiratory therapist, that if you're dealing with a spinal cord injured patient, they're going to have tremendous bronchoconstriction all the time. And they're going to have an increase in airway secretion production all the time. Because it's all the time, because it's never abating, you're always going to have to be doing something to manage this individual's lung function. And it's important to keep this in mind as we go forward and we study methods that we've developed in the past for addressing these problems, like chest optimization protocol. And we'll have more to say about that in later units. We've been talking about spinal cord injuries and cervical spinal cord injuries, and now I'd like to show you what an MRI of a spinal cord injury actually looks like. You can see that this is the upper part of the cord, this is the lower part of the cord, and here's where we have some twisting or torsion of the spinal cord. This is the most common kind of spinal cord injury. Very rarely is there complete cutting or transection of the cord. By far, torsion and twisting of the cord is the most common type of cervical spinal cord injury. Now, what makes working with patients that have spinal cord injury difficult is that, of course, they need to be on the mechanical ventilator until they stabilize. However, as a general rule, we need to be able to wean them as promptly as possible from the mechanical ventilator. So those two missions are kind of at odds with each other. The reason for that is because if you look at a quadriplegic patient or a tetraplegic patient, those are the exact same types of patient. We can say a patient is a quad or a patient is a tetra. We're really talking about a person who has a cervical spinal cord injury. What we know is that their survival rates over the long term are dependent upon whether or not they have been weaned from the ventilator. Weaning from the ventilator for these patients is particularly important if we're able to wean someone from the ventilator. Their five-year survival rate is right around 84%, according to the best available scientific literature that we have. But if we do not wean patients from the mechanical ventilator, their five-year survival rate drops to 33%. And in some authors, some papers, it's actually lower than that. So mechanical ventilation increases morbidity and mortality in this specific patient population. When weaning patients with cervical spinal cord injury, we want to be able to resolve their lung problems, their heart problems, any electrolyte derangements they may have, etc. If they have nutrition problems, we need to be able to replete their protein stores. We need to optimize their pulmonary function. We need to be able to optimize their muscular function. That's why we do resistance strength training both on the vent and off the vent. We do endurance training on the vent and off the vent. We do progressive increase and strength training in order to try to help them recover their functionality. And this is best done in a well-structured neurorehabilitation program that uses protocols that are based on the best available scientific evidence. Let's talk for just a moment about how we can measure and rate spinal cord injuries. There are rating scales. I'm sure you've used the Borg scale. I'm sure you learned about the Glasgow Coma scale. There are lots of different scales that we use clinically to try to rate where a patient's functionality resides. Well, here is the ASIA scale, which stands for American Spinal Injury Association scale. So very often we will say this person is C3 ASIA A. This person is C5 ASIA B. ASIA A is the worst possible designation because it means that there is trauma and hemorrhaging and changes in the neurons and astrocytes from one side of the spinal cord to the other. Completely involved. There's no area that is spared. That's a complete injury. Very, very bad. ASIA B is a little better. ASIA C is even better than that. ASIA D is significantly better than that. And ASIA E is normal. So the worst possible injury an individual could have is an ASIA A because that's a complete injury as opposed to being an incomplete injury. And I'm not going to go into all of the different details of this. I just want to introduce you to this concept and make you sensitive to the fact that it exists. All right. Now, as you're going to see several figures that I can point out that this first figure is a paraplegic patient. This third figure is also a paraplegic patient. And right away, if we look at both of those, you can see that the lower half of the body seems to be paraplegic. On the other hand, if we look at a quadriplegic patient, shown here, or quadriplegic patient shown here, and if you look at the third one, that's just the lower half. In fact, it's the lower half and the pattern is quite different. So the big, remarkable feature of the left foot, the paraplegic spirit, you can see the lower aspect of the arms. Whereas in the first case, that paraplegic individual has involved quadriplegic in his arms, not just the lower aspect, but also the arms. So in both the paraplegics, all the way up to and including their presentation, this is a typical presentation of a paraplegic. And if you look at this quadriplegic model relative to this one, you can see that this one is by all definitions, of course, these areas in red, the areas of functional loss. This individual, at least, is a quadriplegic, but there is some sparing of perhaps sensory or motor function. At this area right here, we have a thigh, and that's because this quadriplegic had a complete spinal cord injury, whereas this quadriplegic patient had an even worse spinal cord injury. Same sort of things with the paraplegic individual. There is a portion of the individual who has a complete spinal cord injury, and he not only has his legs involved, but as a matter of fact, he has the lower aspect of his arms as well. Here's a paraplegic patient that has an incomplete spinal cord injury. So it just depends on how the injury has occurred for that specific injury, and there is not a fully intact floor. So the take-home message again is the worst possible thing you can have is the over-arter plegia, of course, of the aorta, which is injured. The spinal cord injury has this type of actually worsening of their spinal cord injury.