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Work of Breathing – Breathing and Lung Mechanics

by Thad Wilson, PhD
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    00:01 The other item that we need to think about with both compliance and surface tension is how this affects the overall work of breathing.

    00:08 So this is how much energy it takes for a person to breathe.

    00:13 To do this, we have to know that the lungs themselves want to collapse.

    00:19 So to actually breathe, you’re going to have to overcome the elastic force necessary for there to be a collapsing of the lungs.

    00:29 We can use a diagram such as this in which we have the amount of pressure on the X-axis and volume on the Y.

    00:38 We’re going to have a number of different denotations on this graph just to help you orient what part we’re talking about.

    00:46 So if you’re trying to overcome elastic forces, that is the force between A, B, C, D, and 0, then back to A.

    00:58 So that’s all of that portion that is shaded in that kind of gray-blue.

    01:06 To overcome the non-elastic forces, that is this particular graph where we go from A, E, C, F, A.

    01:15 So it forms that kind of nice elliptical circle there.

    01:20 The inhalation component goes from A, E, C, B, A where that part that’s just on the right hand side.

    01:34 Or during exhalation, it’s A, B, C, F, A.

    01:42 Why this becomes important.

    01:44 If someone has a restrictive lung disorder, it’s harder for them to fully inflate their lungs because of resistance in inflation.

    01:55 Therefore, that person is going to need to generate a greater negative pressure to fully fill the lungs.

    02:02 So they are going to take more energy to fill the lungs.

    02:06 Therefore, when they go from A, E, C, F, A, it requires a greater pressure change and therefore, they have to exert a lot more effort to get in the particular air.

    02:22 Obstructive disorders also have a problem with work of breathing.

    02:26 But you’ll notice for this, it really just inflates this particular graph because they have a problem getting a lot of their air out.

    02:34 And so they’re overcoming a lot of resistance so they have to push air out of the lungs.

    02:41 And that can be seen in this diagram where you have A, E, C, D, F, back to 0 and then A.

    02:52 Where work of breathing comes in together with the rate of breathing, is that we’re trying to overcome both non-elastic and elastic work.

    03:02 And this creates a total work component.

    03:06 Most people’s respiratory rate is at the area of the lowest amount of total work.

    03:13 It can be seen here.

    03:16 In a pathophysiological state, such as someone that has a restrictive lung disorder, it creates a lot of work for them.

    03:26 So if it’s hard to inflate your lungs and taking a lot of effort to do so, how do you avoid doing that? Maybe just breathe more frequently.

    03:35 So someone with a restrictive lung disorder, oftentimes has a very high respiratory rate, simply because they’re trying not to work as hard to totally inflate their lungs.


    About the Lecture

    The lecture Work of Breathing – Breathing and Lung Mechanics by Thad Wilson, PhD is from the course Respiratory Physiology.


    Included Quiz Questions

    1. Absent breath sounds on the affected side.
    2. Dyspnea which gets worse with exertion.
    3. Use of accessory muscles during respiration.
    4. Increase in airway resistance.
    1. Increased total lung capacity.
    2. Increased vital capacity.
    3. Increased FEV1.
    4. Decreased total lung capacity.

    Author of lecture Work of Breathing – Breathing and Lung Mechanics

     Thad Wilson, PhD

    Thad Wilson, PhD


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