Gas Exchange

Question 1

Describe how the nose, nasal passages and upper airways are adapted

Answer 1

• Moisten, warm and filter incoming air

- Hairs are the first line of defence

Question 2

Describe the trachea

Answer 2

• Large diameter
• Thin wall
• Reinforced with c-shaped rings of cartilage- this gives flexibility without wall collapse
• Negative pressure inside, so hyaline cartilage keeps it open

Question 3

What is the second line of defence in the airway?

Answer 3

• Muco-ciliary escalator

Question 4

What is the third line of defence in the airway?

Answer 4

• White blood cell moving through tissue and digesting proteins of connective tissue as they go
• Proteins include collagen and elastin

Question 5

What enzymes digest proteins of connective tissue in airways?

Answer 5

• Collagenase and elastase

- Found in neutrophils

Question 6

What is the overall function of the upper part of the airway?

Answer 6

To move the air down

Question 7

Describe the structure of the bronchi

Answer 7

• Similar to trachea
• Progressively smaller network of tubes
• Dichotomous branching until terminal bronchioles (16 generations)
• Progressively reduced cartilage and increased smooth muscle

Question 8

What is the conducting zone of the lungs?

Answer 8

• Mouth to bronchioles

- Do not take part in gas exchange and constitute dead space

Question 9

How does surface area increase down the airway?

Answer 9

• Total number of tubes rises in a binary fashion

- So, total cross-sectional area rises greatly

Question 10

What is the benefit of increasing surface area?

Answer 10

• Low resistance to air flow and a progressive reduction in linear velocity
• Most of the airway resistance is in the top part of the airway

Question 11

What is a spirometer?

Answer 11

A breathing tube to measure volumes

Question 12

What is functional residual capacity?

Answer 12

• Represents the volume of gas left in the lung at the end of a normal quiet expiration
• Neutral point from which inspiratory activity occurs

Question 13

What is tidal volume?

Answer 13

• Builds on FRC
• Volume of each breath (half a litre usually)
• Empty under lung’s own capacity
• Builds on neutral point

Question 14

vWhat is vital capacity?

Answer 14

Total volume of gas it is possible to inhale or exhale with a single breath

Question 15

What is residual volume?

Answer 15

The volume of gas left in the lung at the end of maximum expiration

• Includes dead space but also gas left in alveoli
• Cannot completely empty alveoli when breathing out

Question 16

What is the problem with assessing respiratory function?

Answer 16

• When trying to assess normal breathing, a patient may stop breathing normally

Question 17

What is the expiratory reserve?

Answer 17

What can be breathed out

Question 18

What is the calculation for minute volume?

Answer 18

Minute volume = tidal volume x rate

Question 19

What is alveolar ventilation?

Answer 19

The amount of air passing through gas exchanging parts of the lung per minute

Question 20

How do you calculate alveolar volume?

Answer 20

VA= (tidal volume - dead space) x rate/min

Question 21

How can you increase alveolar ventilation?

Answer 21

Better to increase depth of breathing rather than rate

Question 22

When might dead space increase?

Answer 22

Physiological dead space may increase in some disease states

- Clinically, care must be taken not to increase dead space by adding tubing

Question 23

What is the relationship between alveolar ventilation and arterial PCO₂?

Answer 23

• If alveolar ventilation doubles, arterial PCO₂ will half

- If alveolar ventilation halves, arterial PCO₂ will double

Question 24

How can PCO₂ be used to indicate ventilation?

Answer 24

• Raised arterial PCO₂- patient is hypo-ventilating (type 2 respiratory failure)
• Low arterial PCO₂- patient is hyperventilating

Question 25

In a normal healthy lung, what average alveolar PO₂ equal to?

Answer 25

PaO₂ (almost)- arterial

- If not, this means that alveolar and arterial gases are not in equilibrium

Question 26

What can cause alveolar PO₂ to be very different from arterial PO₂?

Answer 26

• Ventilation perfusion mismatch

- Shint

Question 27

How long will a red blood cell spend in a lung and how many alveoli will it pass?

Answer 27

• 1 second

- 3 alveoli

Question 28

Which parts of the lungs are better ventilated?

Answer 28

• Lower parts due to gravity

- Ensures lung bases are better perfused

Question 29

Describe the mechanism by which airflow to the base areas of the lungs is increased

Answer 29

• Oxygen in the lung is a vasodilator
• So, blood vessels in well-ventilated areas tend to dilate
• These areas receive high blood flow- high local carbon dioxide pressure
• CO₂ is a bronchodilator, so airflow to these areas will be increased

Question 30

Describe ‘Ventilation-Perfusion Mismatch’

Answer 30

• Reduced ventilation to certain parts of the lung
• Some pulmonary venous blood not fully oxygenated- passed through these parts
• Poorly saturated Hb
• Blood from well-ventilated area will have 100% Hb saturation
• Bloodstreams meet, final saturation is less than 100% and arterial PO₂ is reduced
• Body maintains normal PaCO₂ by over-ventilating areas in lung- so more CO₂ is blown off