Lecture 26 : Lung Volumes & Pressures

Question 1

What is the purpose of repiration?

Answer 1

External (lung): For gas exchnage
Internal (cellular): Cell metabolim and ATP production

Question 2

What are the non-respiratory functions of the respiratory system?

Answer 2

1. Defense against microorganisms
2. Phonation (sound)
3. Trapping and dissolving of blood clots
4. Ventilation of the airways contributes to body heat and body water loss

Question 3

What are the functions of gas exchange?

Answer 3

1. To provide oxygen to the body
2. To eliminate carbon dioxide from the body
3. Short-term regulation of the pH of blood

Question 4

What structures are included in the upper airways?

Answer 4

1. Nasal cavity
2. Nostril
3. Mouth
4. Pharynx
5. Larynx

Question 5

What structures are included in the lower airways?

Answer 5

1. Trachea
2. Bronchi
3. Lungs
4. Diaphragm

Question 6

What is the function of the nose?

Answer 6

• Moistens, clean and warms incoming air
• Contains mucus and cilia that wave 8-12x second

Question 7

What are the functions of cilia?

Answer 7

1. ‘Sweep’ mucus toward throat to swallow it
2. Removes foreign particles (dust/microbes)

Question 8

How much contaminates does the nose remove?

Answer 8

Healthy nose removes ~80% of contaminates
– Reduced in dry environments or with dehydration

Question 9

What are the functions of the pharynx (throat)?

Answer 9

1. Connects nasal and oral cavities
   – Respiratory and digestive roles
2. Soft collapsable tube
   – Aids movement of food (swallowing)
   – Can collapse during sleep (snoring)

Question 10

What are the functions of the larynx?

Answer 10

1. Allows speech (vocal cords/voice box)
2. Helps prevent choking
   – Vocal cords close
   – When ‘coughing up’ food the cords close and
   lungs contract, pressure ‘ejects’ the food
3. Allows increase in abdominal pressure
   – Pushing (labour and defecation)

Question 11

What type of compartment is the thorax?

Answer 11

Closed compartment
* Sealed at the neck (muscles, connective tissue)
* Separated from the abdomen by the diaphragm

Question 12

What does the thorax contain?

Answer 12

Lower part of trachea and lungs

Question 13

What makes up the wall of the thorax?

Answer 13

• Ribs
• Spinal column
• The sternum
• Intercostal muscles

Question 14

What are the functions of the thorax?

Answer 14

1. Ventilation
2. Protection of lungs

Question 15

What is a pleural sac composed of?

Answer 15

Two layers of membrane:
1. Parietal pleura = lining of the chest wall
2. Visceral pleura = surface of the lung

Question 16

How are the parietal and visceral pleura separated?

Answer 16

By pleural space filled with intrapleural fluid

Question 17

What is the role of the conducting zone?

Answer 17

• Dead air space
• Movement of air into and out of lungs
• Move ~10,000 litres of air/day

Question 18

What is the role of the respiratory zone?

Answer 18

Gas exchange

Question 19

How many airway divisions are there to the level of alveloli?

Answer 19

~20-23

Question 20

Describe how diameter and cross-sectional diameter changes during airway branching:

Answer 20

• Airway diameter decrease
• Cross-sectional diameter increases
• Peripheral airway resistance decreases

Question 21

Describe the relationship between diameter of a branch and number of alveoli:

Answer 21

• Longer airways = more branches and alveoli
• Larger diameter = greater airflow

Question 22

What are the 5 steps of respiration?

Answer 22

1. Ventilation
2. Gas exchange
3. Transport
4. Gas exchange
5. Cellular respiration

Question 23

What causes the elastic recoil inwards of the lungs?

Answer 23

Lungs have elastic elements

Question 24

What causes the recoil outwards of the lungs?

Answer 24

Chest wall has inherent elasticity

Question 25

What is generated due to the recoil inwards and outwards?

Answer 25

Negative pressure within pleural space relative to atmospheric pressure - intrapleural pressure Pip - When chest expands the lungs expand with it

Question 26

What is intrapleural pressure?

Answer 26

Pip is the pressure within the pleural space relative to atmospheric pressure

Question 27

What is alveolar pressure?

Answer 27

Palv is the pressure within the alveoli relative to the atmospheric pressure

Question 28

What is Patm?

Answer 28

The atmospheric pressure which is ~760 mmHg at sea level

Question 29

What is transpulmonary pressure?

Answer 29

Ptp (TP) is the pressure difference between the alveoli and the pleural space - Force acting to expand the lungs

Question 30

What is the function of Pip and what is required for inspiration?

Answer 30

Provides ‘suction’ to keep lungs from collapsing * Inspiration requires more negative Pip to expand the lungs

Question 31

What is quiet expiration?

Answer 31

A passive process requiring no muscle contraction, just elastic recoil

Question 32

Describe the 7 steps of inspiration:

Answer 32

Active 1. “Inspiratory” intercostal muscles and diaphragm contract 2. Thorax expands (increases in volume) 3. Pip (“suction”) changes from -4 mmHg to -7 mmHg 4. Ptp increases from 4 to 7mmHg → lungs expand 5. Palv changes from 0 to –1 mmHg at mid-inspiration 6. Palv < Patm→ air moves into the lungs 7. At the end of inspiration Palv = 0 mmHg

Question 33

What is forced expiration?

Answer 33

Requires use of expiratory muscles e.g. expiratory intercostals, abdominal muscles

Question 33

Describe the 6 steps of expiration:

Answer 33

1. Inspiratory muscles relax 2. Thorax shrinks, pulled by elastic recoil of the lungs 3. Pip rises from -7 to -4 mmHg 4. Palv rises from 0 to +1 mmHg at mid-expiration 5. Palv > Patm→ air flows out of the lungs 6. Palv at the end of expiration is 0 mmHg

Question 34

Describe the 4 stages of the breathing cycle:

Answer 34

1. End of expiration: Palv - Patm = 0 so no flow of oxygen 2. Mid-inspiration: Palv - Patm = -1 so oxygen flows into lungs 3. End of inspiration: Palv - Patm = 0 so no flow of oxygen 4. Mid-expiration: Palv - Patm = 1 so oxygen flows out of lungs

Question 34

What is tidal volume?

Answer 34

Amount of air inhaled or exhaled in one breath during relaxed, quiet breathing ~500mL

Question 35

How does pressure and volume of the lungs change during respiration?

Answer 35

* Volume increases during inspiration and decreases during expiration * Pressure decreases during inspiration and increases during inspiration

Question 36

What is alveolar volume?

Answer 36

Tidal volume – anatomic dead space volume = 500 – 150 = 350 mL

Question 37

What is alveolar dead space?

Answer 37

Part of the alveolar volume in alveoli which are inadequately perfused with blood - Gas exchange is reduced - Healthy = small dead space

Question 37

How is physiological dead space calculated?

Answer 37

Anatomical dead space (150mL) + alveolar dead space (~5mL)

Question 38

What is minute ventilation?

Answer 38

Total gas flow into the lungs per minute or minute volume

Question 39

How is minute ventilation calculated?

Answer 39

Minute ventilation = tidal volume x frequency of breathing * VE = VT x f e.g. 6000 mL/min = 500 mL x 12 breaths/min

Question 40

How is dead space ventilation calculated?

Answer 40

VD = dead space x frequency of breathing = 150mL x 12/min = 1800 mL/min

Question 41

How is alveolar ventilation calculated?

Answer 41

VA = (tidal volume - dead space) x frequency of breathing = (500mL - 150mL) x 12/min = 4200 mL/min

Question 42

What type of ventilation is most important when assessing efficiency of breathing?

Answer 42

Alveolar ventilation