Work of Breathing — Breathing and Lung Mechanics

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.