1.2 Mechanics of Breathing - Physiology - Lecture

Question 1

List the main structures in the human respiratory tract

Answer 1

Upper: (above larynx)
- Nasal cavity
- Pharynx
- Larynx

Lower: (Below larynx)
- trachea
- bronchi (1, 2, 3)
- Bronchioles (terminal and respiratory)
- Alveoli (type I & type II)

Question 2

State the generational zones of the airway (the 23 Zones of Airway)

Answer 2

Conducting Zone: Z0-Z16
Z0: Trachea
Z1-Z3: Bronchi
Z4-Z16: Bronchioles —> Terminal bronchioles

Respiratory zone: Z17- Z23
Z17-Z19: Respiratory bronchioles
Z20-22: Alveolar ducts
Z23: Alveolar sacs

Question 3

Which zone marks the beginning of gas exchange

Answer 3

Z17: Respiratory bronchioles

Question 4

What is respiration?
Respiration

Answer 4

the series of exchanges that leads to:
- the uptake of oxygen by the cells,
- the release of carbon dioxide to the lungs

Question 5

What are the 5 stages/steps in respiration and what they involve?

Answer 5

1. Ventilation:
   - Inspiration & Expiration
2. External Respiration:
   - between alveoli (air) & pulmonary capillaries (blood)
3. Transport of gases:
   - via blood
4. Internal Respiration:
   - exchange between blood & body cells
5. Cellular Respiration:
   - ATP synthesis by using O2

Question 6

What are the exchange process involved in respiration

Answer 6

In these exchange process we follow the movement of the 2 main respiratory gases: CO2 and O2

Exchange I;
- ventilation
(atmosphere <–> alveoli)

Exchange II;
- External respiration
(alveoli <–> pulmonary capillaries)

Exchange III;
- Transport of gases & internal respiration
(Systemic capillaries <–> Cells)

Ultimately
Cellular respiration occurs:
- within the cells

Question 7

List the 6 main functions of the respiratory system

Answer 7

1. Provides O2 and Eliminates CO2
2. Regulation of blood pH
3. Phonation
4. Immune defence against pathogenic particles
5. Chemical modulation of arterial chemical messengers
6. Blood clot filtration: trap and dissolve

Question 8

What are the 4 Lung volumes

Answer 8

1. Tidal Volume (TV)
2. Inspiratory Reserve Volume (IRV)
3. Expiratory Reserve Volume (ERV)
4. Residual Volume (RV)

Question 9

What is meant by tidal volume and give the normal value for a 70kg adult

Answer 9

Volume of air exhaled or inhaled in a normal quiet breath

• 350 - 500 mL

Question 10

What is meant by Inspiratory Reserve Volume and give the normal value for a 70kg adult

Answer 10

Extra air inhaled after a max effort after tidal inspiration

• 2.5L

Question 11

What is meant by Expiratory Reserve Volume and give the normal value for a 70kg adult

Answer 11

Extra air forcibly exhaled after tidal expiration

• 1.5L

Question 12

What is meant by Residual Volume and give the normal value for a 70kg adult

Answer 12

Air left in the lungs after a max exhalation

• 1.5 L

Question 13

What is the signifcance of Residual volume

Answer 13

Prevents the lungs from collapsing

Question 14

Since Residual Volume (RV) and Functional Residual Capacity (FRC) cannot be measured using spirometry, What are the alternative methods to measure it?

Answer 14

1. Helium dilution
2. Body plethysmography

Question 15

What is meant by a capacity and List the 4 Lung capacities

Answer 15

Capacity is the addition of 2 or more Lung volumes

1. Inspiratory capacity (IC)
2. Functional Residual Capacity (FRC)
3. Vital Capacity (VC)
4. Total Lung Capacity (TLC)

Question 16

Which volume constitutes for each of the Lung capacities and give approximate value in a 70kg adult

Answer 16

1. Inspiratory capacity (IC)
   IRV + TV= 3L
2. Functional Residual Capacity (FRC)
   ERV + RV=3L
3. Vital Capacity (VC)
   TV + IRV + ERV= 4.5L
4. Total Lung Capacity (TLC)
   TV+ IRV + ERV + RV= 6L

Question 17

Describe the difference in effect and examples of Restrictive & Obstructive Lung Diseases

Answer 17

1. RESTRICTIVE:
   - causes reduced lung volumes (all the volumes esp TLC & VC)
   - eg: 1. Pulmonary fibrosis
   2. ARDS
2. OBSTRUCTIVE:
   - causes obstruction to airflow (so RV increases, VC decreases (or remain normal))
   - eg: 1. Asthma
   2. Emphysema
   3. Chronic bronchitis

Question 17

What is meant by FVC & FEV1

Answer 17

FVC: Forced Vital Capacity
- Total volume of air FORCIBLY exhaled after a maximal inspiration (VC: TV+ IRV+ERV)

FEV1: Forced Expiratory Volume in 1sec
- Total volume of air expelled in the 1st sec of Forced VC

Question 18

What useful ratio is derived from FEV1 and FVC

Answer 18

FEV1/FVC

Question 19

State the diagnostic ratios of FEV1/FVC in normal and diseased, both obstructive and restrictive Lung Diseases

Answer 19

Normal: 0.8

Restrictive:
normal or higher than 0.8 (because both FEV1 and FVC reduced in almost the same ratio)

Obstructive
lower than 0.8
(because FEV1 reduced alot more than FVC)

Question 20

Define Dead Space

Answer 20

Volume of airways and lungs that does not participate in gas exchange

Question 21

What are the 3 types of dead spaces and define them

Answer 21

1. Anatomic DS:
   volume of the conducting airways (until the terminal bronchioles)
2. Functional (alveolar) DS:
   volume in lungs that does not participate in gas exchange ( basically the alveoli which are ventilated but not perfused - aka wasted ventilation) PATHOLOGICAL
3. Physiological DS:
   volume of the anatomic and functional DS

Question 22

What is a normal value for anatomic DS out of the 500 mL TV

Answer 22

150 mL fills the conducting airway
(350 mL only reaches alveoli)

Question 23

What is the most important inspiratory muscle and how does it initiate airflow into lungs

Answer 23

Diaphragm,

it contracts, abdominal muscles are pushed downwards –>

Increased intrathoracic pressure as the ribs move outward and upward (increase in vertical diameter)–>

this increase in intrathoracic VOLUME results in a decrease in intrathrocic PRESSURE hence air flows into the lungs, down the PRESSURE gradient

Question 24

When exercising which other muscles are also involved in inspiration

Answer 24

1. External intercostal muscles 2. Intrachondral part of internal intercostal muscles 3. Accessory muscles such as: a. Sternocleidomastoid muscle b. Scalene muscles i. Anterior ii. Middle iii. Posterior

Question 25

What is the purpose of using these other muscles during inspiration while exercising

Answer 25

Higher O2 demand, so need to increase - breathing frequency (RR) - Tidal volume (TV) to increase the rate and amount basically

Question 26

What is the main function of the accessory muscles during forced inspiration

Answer 26

1. Sternocleidomastoid: elevates STERNUM 2. Scalene muscles: elevates and fixes the UPPER RIBS

Question 27

What are the muscles involved in quiet and active EXPIRATION

Answer 27

1. Quiet: elastic recoils of lungs 2. Active: a. Ineral intercostal muscles (except for the interchondral part) b. Abdominal muscles: - compresses abdominal contents and depresses the lower ribs - muscle names: i. Rectus abdominis ii. External/Internal oblique iii. Transversus abdominis

Question 28

What is the mechanism of Expiration

Answer 28

Decrease in intrathoracic volume --> Increase in intrathoracic pressure --> air flows out of the lungs

Question 29

What is meant by compliance

Answer 29

Change in Volume/ change in transpulmonary pressure it describes the distensibility

Question 30

Compliance of which 2 structures are important in respiration

Answer 30

1. Lungs 2. Chest wall

Question 31

What is the relation between compliance and elastane

Answer 31

inversely proportional

Question 32

What is meant by INCREASE in lung compliance and in which conditions does it occur, give examples

Answer 32

lungs stretch more easily - occurs in conditions where elastic recoil is lost. - eg: 1. Emphysema: destruction of the elastic fibres 2. Old age: natural degeneration of lung tissues

Question 33

What is meant by DECREASE in lung compliance whats the complication of it and in which conditions does it occur

Answer 33

Lungs become stiffer and harder to expand - increased risk of lung collapse (atlectasis) - eg: pulmonary fibrosis

Question 34

Why are small alveoli so prone to collapse

Answer 34

due to the high surface tension

Question 35

What is the role of surfactant

Answer 35

it reduces this surface tension, lines the alveoli to prevent collapse and keeps them open

Question 36

What are the 3 main interlinked consequences of absence of surfactants

Answer 36

1. Alveolar collapse 2. Reduced lung compliance 3. Can lead to pulmonary edema

Question 37

Which cells produce the surfactants and whats the main component of surfactants

Answer 37

Cells producing: Type II pneumocytes Main component: DPPC: (Di Palmityoyl Phosphatidyl Choline)

Question 38

What establishes the pulmonary pressure gradient

Answer 38

the difference between intrapulmonary (alveolar) and atmospheric pressure

Question 39

What are the 4 key pulmonary pressures

Answer 39

1. Atmospheric pressure: - pressure exerted by the weight of the air in the atmosphere - almost 760mmHg 2. Intra-alveolar (intrapulmonary) pressure: - Pressure inside the lungs 3. Intrapleural pressure (within pleural cavity) -Inside the pleural space (between visceral and parietal pleura) 4. Transpulmonary pressure (difference between intra- alveolar & intrapleural pressures)

Question 40

Why does no airflow occur in the "at rest" stage of the breathing cycle

Answer 40

because the atmospheric pressure= the alveoli pressure

Question 40

What are 3 phases of Breathing

Answer 40

1. Inspiration (start) 2. Expiration (end) 3. At rest (between expiration of 1st breathing cycle and inspiration of 2nd breathing cycle)

Question 41

What is the reason for the negative interpleural pressure of -5cmH2O

Answer 41

due to the opposing forces of: 1. Lungs trying to collapse - inward elastic recoil of lungs 2. Chest wall trying to expand - outward recoil of lungs

Question 42

What is the expanding force of lungs at rest

Answer 42

its +5cmH20 which is equal to the transpulmonary pressure: intra-alveolar - intrapleural

Question 43

What is the mechanism behind Inspiration phase of the breathing cycle

Answer 43

- as the diaphragm contracts the intrathoracic volume increases - therefore the airway and alveolar pressure decreases and drops below atmospheric pressure - this establishes a pressure gradient between the atmosphere and alveoli - so air will flow down the pressure gradient until it is neutralised, into the lungs

Question 44

What is the 2 main reason for the intraplueral pressure to become even more negative than at rest (-5cmH2O to -8cmH2O)

Answer 44

1. increased elastic recoil strength of lungs due to increased lung volume 2. Increase in intrathoracic VOLUME results in even more negative alveolar and airway pressure

Question 45

Describe the mechanism of expiration in the breathing cycle in terms of pressure and volume

Answer 45

- Elastic recoil of lungs causes compression of air - this leads to more positive alveolar pressure (greater than Patm) - therefore air flows out of the lungs (down the pressure gradient)

Question 46

What happens to the intrapleural pressure in the expiration phase of breathing

Answer 46

the intrepleural pressure becomes more positive and returns to its normal value of -5cmH2O as the lungs recoil back to its resting volume

Question 47

What is meant by the "Work of Breathing"

Answer 47

Amount of energy expended or used during ventilation

Question 47

What are the 3 types of work done or energy used for during Breathing

Answer 47

1. Compliance work: to expand elastic tissue of lungs and chest wall 2. Tissue resistance work: work done to overcome the viscosity of inelastic structures of Lungs and Chest wall 3. Airway resistance work: work done to move air against the resistance (friction) of the airways

Question 48

What is the contribution of "Work of Breathing" on total energy expenditure

Answer 48

2-3%