Week 6: Pulmonary ventilation, alveolar ventilation and circulation

Question 1

What are the 4 steps of respiration? which of these steps are functions of the respiratory system and which are steps if the cardiovascular system?

Answer 1

Rispirartory Steps:

1. Movement of air in/out of the lungs
2. Exchange of gases between alveoli and pulmonary capillaries

Cardiovascular steps:

3. Transport of O₂ and CO₂ to and from the tissues
4. Exchange of O₂ and CO₂ between blood and tissues

Question 2

What is pulmonary ventilation?

Answer 2

Aire being moved in and out of lungs

Question 3

What is gas exchange?

Answer 3

Movemetn of oxygen and carbon dioxide between air in the alveoli and pulmonary capillaries in the lungs. This also occurs between th e blood capillaries and tissues of the systemic circulation.

Question 4

What is meant by ther term “partial pressure”?

Answer 4

Represents the concentration of a gas in both its gaseous or dissolved form

Question 5

How do the muscles of inspiration assist in briging air into the body?

Answer 5

The diaphragm and the external intercostals assist in helping to decrease the intrapulmonic pressure by reducing volume of the thorax which results in a increased pressure gradient which causes air to flow into the lungs to equilibrate pressure.

Question 6

What does the term normal (quite) expiration mean?

Answer 6

• Passive process with no muscle action
• Lungs return to their original size due to elastic recoil and surface tension forces in alveoli
• alveolar pressure increases and air is pushed out

Question 7

What is forced expiration?

Answer 7

Muscles actively assist lungs

Question 8

What is the pleura? what does it compose of? what is its main function?

Answer 8

Two components:

• Parietal pleura: Lines the inside of thoracic cavity
• Visceral pleura: Covers the lungs

Function:

• Contains a few ml’s of serous fluid to provide a frictionless environment for lung expansion and contraction. The cohesive forces between the fluid and pleural surfaces allows lung expansion to mirror chest expansion.

Question 9

“the lungs have an elastic nature” explain why this is important? how does ralate to negative pressure?

Answer 9

Due to the elastic nature, the lungs have a tendency to recoil to a smaller volume. This collapsing force is opposed by the expansion of the chest wall which causes a negative pressure to develope in the pleural cavity. This pressure is held at around negative 3-4mmHg to intra-alveolat pressure to oppose the collapsing force of the lungs and also assist with the machanics of pulmonary ventilation.

Question 10

How does the intrapleural pressure assist pulmonary ventilation?

Answer 10

The “jacket” of negative pressure surrounding each lung assists with inspiration and expiration by:

Inspiration: Encouraging inspired air to travel to the periphery of the lung to fully inflate the more distal alveoli in the bronchial tree

Expiration: On expiration, encouragees some air to remain in the alveoli so that they do not completely empty (collapse)

Essentially this negative pressure is just an energy saving mechanism, making it easier to inflate the lungs; essentially increasing efficiency

Question 11

Having some remaining oxygen in the alveoli is beneficial in many ways including the filling efficiency and avoiding collapsing, what is the is the other beneficial reason involving blood flow?

Answer 11

Because blood flow doesnt stop when we expire, capillary exchange must still be taking place so therefore having some “left over” oxygen is beneficial in that systemic circulation can continue for a limited ammount of time until the alveoli are filled with more oxygen again.

Question 12

Simply explain what the intrapleural cavity allows the alveoli to do during inspiration and on expiration?

Answer 12

On inspiration:

• Allows alveoli to fully inflate

On expiration

• Prevents alveolar collapse (energy saving)

Question 13

What is a pneumothorax?

Answer 13

An injury to the chest wall that has let air enter the intrapleural space.

• Surface tension in the alveoli and recoil of elastic tissues equalise with the atmospheric pressure outside the body causing the lung on that side to collapse

Question 14

What are dynamic lung volumes? What are they derived from?

Answer 14

A measurement of lung volume over time

Derived from a forced vital capacity

Question 15

What is FEV_1sec ?

Answer 15

The forced expiratory volume in 1 second (part of FVC)

Question 16

What is FEF_25-75% ?

Answer 16

Forced Expiratory flow, 25-75% is the mean forced expiratory flow during the middle half of FVC

Question 17

What is FEV_1%?

Answer 17

Forced Expiratory volume exhaled during the first second to forced vital capacity ratio and expressed as a percentage

Question 18

What would be good indicators of airway obstruction? What values would suggest restriction and would values would suggest obstruction?

Answer 18

An FEF_25-75% decrease suggests the possibility of small aiwary obstruction

An FEV_1% is an indicator of a restirctive obstuction abnormality

Restriction is suggested when both values are low and the ratio is normal

Obstruction is probably when the ratio is decrease

Question 19

What are the two main categories of pulmonary diseases?

Answer 19

Restrictive and obstructive

Question 20

Explain how a restrictive lung disease effects volume?

Answer 20

Restrictive lung diseases causes decreased compliance, resulting in a more negative intrapleural pressure. They make it harder to bring in efficient volume and increase the elastic work of breathing.

Question 21

What happens during pulmonary fibrosis?

Answer 21

Loss of compliance in lung tissue due to elastic fibers becoming fibrous

Question 22

What is adult respiratory distress syndrome (ARDS)?

Answer 22

Severe hypoxaemia and progressive loss of compliance of the lung tissue

• Capillary congestion causing fluid to leak into pulmonary interstitium and eventually into alveoli

Question 23

What are the two classes of obstructive diseases ?

Answer 23

Emphysema: Loss of lung tissue decreases elastic recoil

Asthma: Where bronchiolar constriction and increased mucous secretion, increase airway resistance.

Question 24

What is surface tension?

Answer 24

The air/water interface, the water molecules are more strongly attracted to other surrounding water molecules than to the air molecules aboe the surface.

Question 25

What does surfactant do?

Answer 25

Counteract surface tension forces by interspersing between the water molecules

Question 26

Explain what is meant by: Alveolar surface tension

Answer 26

Thin layer of fluid in alveoli causes inwardly directed force; surface tension: which causes:

• The liquid layer to resist any force that increases its surface area (oppose expansion of the alveolus)
• The liquid surface area tends to become as small as possible because the surface water molecules try to get as close as possible to each other

Question 27

How does surfactant work? what cells produce it?

Answer 27

Prevents the collapse of alveoli from the effects of surface tension on expiration. (saves energy)

produced by Type II alveolar cells.

Question 28

Explain how the larger and smaller alveoli are able to have the same “collapsing” force?

Answer 28

According to LaPlace’s law if we have a small alvioli and a large alveoli, the pressure will greater in the smaller alveoli. HOWEVER, surfactant produced by the Type II alveolar cells is much more abundant in smaller alveoli and therefor is able to break up the water molecules reducing the surface tension and overall resulting in all alveoli having the “same” collapsing force.

Question 29

How do neighboring alveoli help with a collapsing alveoli?

Answer 29

The tendency for an alveolus to collapse is resisted by the surrounding alveoli which recoil in resitance to being stretched.

Question 30

What do concepts does pulmonary elasticity rely on?

Answer 30

Elastic recoil: A measure of how readily lungs rebound after being stretched

Compliance: A measure of how readily lungs can be stretched or distended

Question 31

Would a highly compliant lung or a less compliant lung require more work to acheive inflation?

Answer 31

A Less compliant lung would require more work as it has less stretchability

Question 32

What 2 factors do pulmonary elasticity rely on?

Answer 32

• Highly elastic connective tissue in the lungs
• Surface tension of alveoli

Question 33

Why is surfactant important in regards to elastic recoil and pulmonary compliance?

Answer 33

• Reduces elastic recoil by lowering surface tension
• Increases pulmonary compliance therefore reducing the work required to inflate the alveoli

Question 34

What are the main pathological factors that can decreases pulmonary compliance?

Answer 34

• Pulmonary congestion and oedema that accompanies left hand side heart failure.
• Replacement of normal lung tissue with fibrous connective tissue
• Excess production of pleural fluid

Question 35

explain this statement: “Flow resistance of the pulmonary circulation is almost completely indepepndent of changes in cardiac output”

Answer 35

• When CO₂ increases, pulmonary pressure increases and blood vessels that were previously collapsed begin to open and allow blood to flow through them. This is known as recruitment.

Question 36

Why is the mean low pulmonary pressure in the lungs a good thing?

Answer 36

The low pulmonary pressure in the lung cappilaries promotes absorption of fluid in the interstitual fluid which protects the lung from oedema. It also helps keep the diffusion distance in the respiratory membrane to a minimum. WE DONT WANT INTERSTITUAL FLUID AS THIS MEANS LESS EFFICIEANT EXCHANGE!

Question 37

What is a pulmonary oedema?

Answer 37

Accumulation of fluid in the tissues (interstitual and alveolar) of the lung.

Question 38

How do we calculate the rate of alveolar ventilation?

Answer 38

Alveolar minute volume/Cardiac output

Question 39

What is the effect of body posture on V(dot)_A / Q (dot)?

Answer 39

Lying down: V(dot)_A / Q (dot) is roughly equal through the lung tissue

Standing up: The hydrostatic pressure component of blood pressure in pulmonary capillaries decreases above the level of the heart but increase below it. (due to gravity and compliance)

Question 40

Which is more pronounced; the effect of gavity on blood flow, or the effect of gravity on air flow?

Answer 40

Blood flow:

Due to its weight

Question 41

Explain both the air and blood gradients in a standing person?

Answer 41

• Air in the alveoli decreases from apex to base; but “newer air” occupies those alveoli nearer the base
• Blood in the pulmonary capillaries decreases from base to apex

Question 42

Explain the differences in blood flow in the following areas:

Apex of lung

Mid Lung

Base of lung

Answer 42

Apex of lung: Pulmonary arteries are compresses as vascular resistance is high therefore causing blood flow to be low

Mid lung: Pressure in pulmonary arteries is higher so blood flow increases.

Base of lung: Blood vessels are completely open so blood flow is high.

Question 43

Explain this diagram?

Answer 43

This graph shows the ratio relationship between blood flow and ventilation as we get further up the lung.

Base of lung is well perfused, but underventilated, ratio rises slowly up the lung.

Rib 3 has a 1.0 reatio

Apex has 3.0

Question 44

Which zone (1,2 or 3) is most efficient in the lungs?

Answer 44

Zone 2 as V(dot)_A / Q(dot) is = to 1.0

This means that zone 2 is well-ventilated and well-perfused allowing for the blood to equilibrate with alveolar air.

Question 45

Explain what is meant by the term “mismatch” in relation to ventilation and perfusion?

Answer 45

Known as V(dot)A / Q(dot) missmatch:

This can be caused by ventilation of part of the lung that is not being perfused, or perfusion of lung regions that are not being ventilated.

Question 46

What is meant by the term “physiological dead space” in relation to V-P matching?

Answer 46

Alveolus is ventilated, but no blood perfusion offurs (ususally due to a pulmonary embolism)

Question 47

What is meant by the term “Physiological Shunt” in relation to V-P matching?

Answer 47

Alveolus is perfused, but no ventilation occurs (due to an air obstruction)

Question 48

How does pulmonary circulation deal with V-P matching of poor ventilating alveoli?

Answer 48

Constrict the blood flow so that it will not go to these alveoli with high pressures of CO₂ , and therefore that will increase the blood flow to better ventilated alveoli.

Question 49

What are the intrinsic and extrinsic controls of the airways?

Answer 49

Intrinsic:

• Increase in CO₂ results in dilatation of airways
• Decrease in CO₂ results in constriction

Extrinsic: ANS

• PNS: dominates in quite/relaxed situations and stimulation of PNS promotes bronchiolar smooth muscle contraction
• SNS: Stimulation and adrenaline promote brochodilation and decreased airways resistance which is important for when the body requires more Oxygen.

Question 50

How do the airways respond to an increase in CO₂ ?

Answer 50

An increase in CO₂ causes nearby bronchioles to enlarge thus redirecting inspired air toward relatively under-ventilated alveioli.

Question 51

How do the blood vessels respond to a decrease in O₂ ?

Answer 51

A decrease in O₂ causes local blood vessel vasoconstriction and shifts blood away from underventilated portions of the lung. THIS IS DIFFERENT TO SYSTEMIC BECAUSE THE WHOLE AIM OF PULMONARY CIRCULATION IS TO PICK UP OXYGEN EFFICIENTLY FOR THE WHOLE BODY.

Question 52

Fill in the blanks:

Answer 52

Question 53

What receptors are responsible for detecting changes in CO₂ and O₂ ?

Answer 53

Chemoreceptors