Dyspnea: Causes

by Carlo Raj, MD

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    00:01 Now, the control center.

    00:02 And there is quite a bit of detail here. Let me just set it up for you so that we will refer to the different components of this when the time is right. We will take a look at, well, we have the motor area and the sensory cortex. I would like for us to pay attention on your far right side where it says sensory cortex. Okay. Now, in physiology, would you please tell me, what is the most important chemoreceptor? Is it central or peripheral? Central. Good.

    00:30 Right now, as you are sitting there, watching me, perhaps. Me, right now, it is my central chemoreceptors that are always going to then detect whom? Oxygen or carbon dioxide? What are the central chemoreceptors more sensitive to? Carbon dioxide changes.

    00:46 Apparently, carbon dioxide. Remember, on your arterial side, what's your PCO2? At 40, right? Whereas on the venous side, what is PCO2? Only 7, excuse me, 47. So, there is only a difference of 7 there. Okay, so, carbon dioxide is very important in terms of sensing or being sensed by chemoreceptor, central type. So, sensory cortex is then going to sense the carbon dioxide that is in your blood, but how does it do it? Your chemoreceptors are located in the medulla. And in the medulla, it's going to measure the cerebrospinal fluid.

    01:22 Correct? Cerebrospinal fluid. And what do you know about carbon dioxide? Why is there only difference of 7 between the arterial and the venous side? Because carbon dioxide, how quickly does it diffuse across the membrane? Like that. Carbon dioxide and carbon monoxide is even faster, isn’t it? So, oxygen is pretty good in terms of diffusion, but what’s the heck of a lot faster is going to be carbon dioxide and later on, we will talk about carbon monoxide. So carbon monoxide, which we are either trying to blow off or if you are retaining it, well, it is in the blood and so, therefore, it passes across the blood brain barrier and is then sensed by the central chemoreceptors. Is that clear? Once that occurs then what happens? It is going to then trigger through the motor cortex, come over to your left now. In the motor cortex, see where it says chemoreceptors, it's hungry for air, because now, it sensed an increased amount of carbon dioxide. How did that occur? Maybe there is dyspnoea. You are holding on to carbon dioxide. What was that called? Hypercapnia or hypercarbia. What's your level? Greater than 40. Are you building upon the foundation that we are placing for you? Good. So now, this is sensed by the central chemoreceptors through your blood brain barrier in the cerebrospinal fluid and as soon as you hear about carbon dioxide, what’s the formula that you are thinking? Good. Carbonic anhydrase, aren’t you? Carbon dioxide plus water, with the help of carbonic anhydrase, will then yield your bicarb and your hydrogen. So hence, carbon dioxide equals hydrogen, hence a decrease in pH. Lot of stuff there and as you can see here, it's integration making sure that you understand what is triggering that air hunger. And once you get that air hunger going, then you are going to start breathing as long as you have proper muscles that are working. So, what you are seeing in the bottom portion there would be the most important muscle obviously, just breathing back and forth will be your diaphragm.

    03:18 When your diaphragm contracts, which direction? Down. Good. And when you are expiring, you are exhaling, it's passively moving up, diaphragm.

    03:28 But, then you also have involvement of intercostal artery, excuse me, intercostal muscles and so forth. Sternocleidomastoid, that will become important to us, when we talk about a condition that a child might be suffering from known as status asthmaticus. And why it is so important to make sure that you understand when these muscles are kicking in and why.

    03:50 After muscle fatigue, your patient might die and you don’t want that on your clock.

    03:55 Let's continue. So, pulmonary problems, dyspnoea. Cardiac problems, we just talked about this.

    04:00 Pulmonary problems may result in edema. What kind? Exudate, because of increased capillary permeability. Cardiogenic, could result in dyspnoea. Of course, give me some examples.

    04:13 Left-sided heart failure, mitral stenosis. Metabolic disturbances. What about the medulla? What if the individual is taking an opiod, okay, a narcotic. What happens now? The respiratory center in the medulla has been knocked out. It's gone. What do you end up having? The patient has hypoventilation. Welcome to CNS issues. Anxiety, absolute panic attacks, anemia, lack of hemoglobin, exercise, well, that would be normal. So, dyspnoea could occur even with enough exercise, in which what happens? The skeletal muscles are really starving for oxygen. It's a nice little list here to go through different problems or differentiation of dyspnoea.

    About the Lecture

    The lecture Dyspnea: Causes by Carlo Raj, MD is from the course Introduction to Pulmonary Pathology.

    Included Quiz Questions

    1. CO2
    2. O2
    3. Blood pressure
    4. Ventilation
    5. H+
    1. Readily crosses the blood brain barrier.
    2. Pressure changes at different altitudes.
    3. Low environmental pressure means higher internal pressures.
    4. Does not bind to RBCs.
    5. Moves freely between arterial and venous blood.
    1. Alveoli
    2. Chemoreceptors
    3. Chest wall
    4. Upper airway
    5. Brainstem
    1. Sleep
    2. Left sided heart failure
    3. Metabolic disturbances
    4. Decreased drive to breath from CNS
    5. Anemia

    Author of lecture Dyspnea: Causes

     Carlo Raj, MD

    Carlo Raj, MD

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