2. Lung Ventilation

Question 1

How do bronchioles allow air to move into the lungs?

Answer 1

They dilate, increasing their volume and lowering the pressure inside the lungs.

Question 2

How are the two pleural layers held together?

Answer 2

By the fluid secreted by the parietal layer, the surface tension of which adheres the layers.

Question 3

What is the relevance of the two pleural layers being held together?

Answer 3

When the chest wall expands, the parietal pleura (attached to the chest wall) pulls the visceral pleura (attached to lung) with it, so the lung expands.

Question 4

How do the external intercostals account for 30% of chest expansion in quiet respiration?

Answer 4

They elevate the ribs in a bucket handle type movement.

Question 5

What accounts for 70% of chest expansion during quiet respiration?

Answer 5

The diaphragm, it contracts and descends.

Question 6

Which muscles are involved in inhalation during quiet breathing?

Answer 6

The diaphragm and external intercostals.

Question 7

Which muscles are involved in exhalation during quiet breathing?

Answer 7

None.

Question 8

Which muscles are involved in inhalation during forced inhalation?

Answer 8

Diaphragm, external intercostals, scalene, pectoralis minor, sternocleidomastoid, and serratus anterior.

Question 9

Which muscles are involved in exhalation during forced expiration?

Answer 9

Internal intercostals, innermost intercostals, and abdominal muscles.

Question 10

Which three factors affect gas exchange?

Answer 10

Area available for the exchange, resistance to diffusion, and gradient of partial pressure.

Question 11

How are the lungs adapted for optimal gas exchange in terms of the area available for gas exchange?

Answer 11

The alveolar surface is large due to a huge number of alveoli so the exchange area of the normal lung is around 800m^2. This means area is not a limiting factor of gas exchange in the normal lung.

Question 12

Which layers must gas diffuse through from the alveolar gas to alveolar capillary blood?

Answer 12

Alveolar epithelial cell, interstitial fluid, capillary endothelial cell, plasma, red blood cells membrane.

Question 13

How long is the path of diffusion between alveolar gas to alveolar capillary?

Answer 13

Less than one micron.

Question 14

Why does carbon dioxide diffuse much faster than oxygen?

Answer 14

It is more soluble.

Question 15

How are the partial pressures of oxygen and carbon dioxide in the alveolar gas kept close to their normal values?

Answer 15

By ventilation.

Question 16

What can measure the movement of air during breathing?

Answer 16

Spirometry.

Question 17

What is the lung tidal volume?

Answer 17

The lung volume that represents the amount of air that is displaced between normal inspiration and expiration, when extra effort is not applied.

Question 18

What is the lung inspiratory reserve volume?

Answer 18

The extra volume that can be breathed in when extra effort is applied.

Question 19

What is the lung expiratory reserve volume?

Answer 19

The extra volume that can be breathed out when extra effort is applied.

Question 20

What is the lung residual volume?

Answer 20

The volume left in the lungs at maximal expiration. This cannot be measured with a spirometer.

Question 21

How is lung residual volume measured?

Answer 21

By helium dilution.

Question 22

What is the lung vital capacity?

Answer 22

The biggest breath that can be taken in, measured from the maximum inspiration to maximum expiration.

Question 23

What is the typical vital capacity of the lungs in a healthy adult?

Answer 23

5 litres.

Question 24

What is the lung functional residual capacity?

Answer 24

The volume of air in the lungs at resting expiratory level. Expiratory reserve volume + residual volume.

Question 25

What is the typical functional residual capacity of the lungs in a healthy adult?

Answer 25

2 litres.

Question 26

What is the lung inspiratory capacity?

Answer 26

The biggest breath that can be taken from resting expiratory level. Lung volume at the end of quiet expiration.

Question 27

What is the typical inspiratory capacity of the lungs in a healthy adult?

Answer 27

3 litres.

Question 28

What is the serial/ anatomical dead space?

Answer 28

The air that is the last in and first out so doesn’t reach the alveoli so is unavailable for gas exchange.

Question 29

What is the normal volume of the serial dead space?

Answer 29

150ml.

Question 30

How can serial dead space by measured?

Answer 30

By a nitrogen washout test.

Question 31

How is a nitrogen washout test performed?

Answer 31

The patient takes a maximum inspiration of 100% oxygen. The oxygen that reaches the alveoli will mix with alveolar air, and the resulting mix will contain nitrogen. However, the air in the conducting airways (dead space) will still be filled with pure oxygen. The person exhales through a one way vale that measures the percentage of nitrogen in and volume of air expired. As alveolar air begins to move out and mix with dead space air, nitrogen concentration gradually climbs from zero to where is plateaus.

Question 32

What is the physiological dead space?

Answer 32

The volume of air in alveoli not taking part in gas exchange.

Question 33

Why does some air in the alveoli not take part in gas exchange?

Answer 33

Because some alveoli receive inadequate blood supply, or are damaged by accident or disease. So even if air reaches the alveoli, there can’t be any gas exchange.

Question 34

How are anatomical, alveolar, and physiological dead spaces linked?

Answer 34

Anatomical dead space + alveolar dead space = physiological dead space.

Question 35

How can physiological dead space be measured?

Answer 35

Measure pCo2 of expired alveolar air. The degree of dilution from dead space air is measured to give the physiological dead volume.

Question 36

What is the alveolar ventilation rate?

Answer 36

The amount of air that reaches the alveoli.

Question 37

How is alveolar ventilation rate calculated?

Answer 37

Alveolar ventilation rate = pulmonary ventilation rate (tidal volume x RR) - dead space ventilation rate (dead space volume x RR).