Respiration VI

Question 1

Draw and describe the apperance of the pleural space.

Answer 1

The visceral pleura is continuous with the layer attached to the rib cage, the thoracic pleura. There is a separate space for each lung.

Question 2

What is the pneumothorax?

Answer 2

It represents what would happen if we had no pleural space. The lungs would collapse inwards and the ribcage would expand outwards, with the pressure being 0 everywhere.

Question 3

To evaluate the elastic properties of the respiratory system (chest wall and lungs), we measure changes in the […] of each structure for a given change in […]

Answer 3

Recoil pressure, lung volume

Question 4

Lung volumes can be measured by […]

Answer 4

spirometry

Question 5

Respiratory system pressures are measured using […]

Answer 5

manometers

Question 6

Pleural space pressure can be measured with a […]

Answer 6

flexible balloon introduced into the esophagus

Question 7

What is transpulmonary pressure? How is it measured?

Answer 7

The transpulmonary pressure is calculated as the difference between the alveolar pressure and the pleural pressure.

Question 8

What is chest wall pressure and how is it measured?

Answer 8

This is the pressure drop across the rib cage. It is calculated as the difference between pleural pressure and the body surface pressure, which is equal to atmospheric pressure (treated as 0).

Question 9

What is respiratory system pressure and how is it calculated?

Answer 9

This is the pressure across the entire respiratory system. It is calculated as the difference between the alveolar pressure and the body surface pressure, which is equal to atmospheric pressure (treated as 0).

Question 10

What is the compliance of the lungs? What is the formula?

Answer 10

Compliance of the lungs refers to the ease with which they can be distended.

C = dV/dP (v = volume, p = pressure)

Question 11

Describe the pressure-volume curve for the lungs only.

Answer 11

At higher volumes, the slope is less. It gets harder at high lung volumes to inflate the lungs.

Question 12

Explain how fibrosis affects the respiratory system.

Answer 12

In fibrosis, fibrotic tissues on the alveolar walls make them stiff and difficult to inflate. Compared to the normal subject, a given pressure leads to less inflation. Therefore, the pressure-volume curve for the lungs (isolated) has a lower slope than normal.

Question 13

Explain how emphysema affects the respiratory system and total lung capacity.

Answer 13

Emphysema causes breakage of alveolar walls, so they’re very easy to inflate. The problem in emphysema is that it’s hard to deflate the lungs. You get more inflation for a given pressure.

Therefore, the pressure-volume curve for the lungs alone has a higher slope than normal.

Question 14

Emphysema and fibrosis alter the […] of the lungs.

Answer 14

compliance

Question 15

What is the formula for the compliance of the lungs?

Answer 15

C = dV / (dPalv - dPpl)

Question 16

What is elastance and how is it calculated?

Answer 16

Elastance is the inverse of compliance.

Question 17

Describe the pressure-volume curve of the chest wall.

Answer 17

We start when the rib cage is at rest. This is at 60% vital capacity and the pressure is 0. This is when the rib cage is at equilibrium.

If I take that ribcage to total lung capacity, you have to push air inside that ribcage, so you get a positive down. The rib cage wants to recoil down, so it generates a positive pressure. That’s what you see in C.

What if you take the ribcage below its resting position? This will generate a negative pressure (left side of the pressure axis).

Question 18

How do you calculate the compliance of the chest wall?

Answer 18

Cw = dV / dPpl

Question 19

Describe the volume-pressure curve of the whole respiratory system.

Answer 19

To obtain this curve, it’s just the sum of the two pressures of the chest wall and lung. The rib cage and the lungs work in series; you’re adding up their pressures to move the system to that given volume.

Note the point where the lung and TLC cross. This is resting position of the rib cage. This TLC pressure is equal to 0 + the pressure needed to get the lungs there.

Note the FRC (functional residual capacity) value. This is the point where the positive pressure of recoil of the lungs is equal and opposite to the pressure of rib cage wanting to spring out. This is why you naturally expire to here without making any additional effort.

Question 20

Where is functional residual capacity (FRC) on the pressure-volume curve for the respiratory system? Explain why.

Answer 20

It is located at the point where the pressure of the recoil of the lungs is equal and opposite to the pressure of the rib cage wanting to spring out. This balance is the reason why you naturally expire to that volume without effort.