Ventilation and Compliance

Question 1

There is always residual air left in your lungs at the end of expiration. Why?

Answer 1

So patency of airways is maintained and smaller airways do not collapse, meaning the is less effort to inflate them.

Question 2

What does TV stand for?

Answer 2

Tidal volume: volume of air breathed in and out of the lungs in each breath

Question 3

What does ERV stand for?

Answer 3

Expiratory reserve volume: maximum volume of air that is expelled from the lungs at the end of a normal expiration

Question 4

What does IRV stand for?

Answer 4

Inspiratory reserve volume: maximum volume of air which can be drawn into the lungs at the end of a normal inspiration

Question 5

What does RV stand for?

Answer 5

residual volume: volume of gas at the end of a maximum expiration

Question 6

what does VC stand for?

Answer 6

vital capacity: the volume of air a person can expire

tidal volume+inspiratory reserve volume+expiratory reserve volume

Question 7

what does TLC stand for?

Answer 7

total lung capacity: vital capacity+residual volume

Question 8

what does IC stand for?

Answer 8

inspiratory capacity: tidal volume+inspiratory reserve volume

Question 9

what does FRC stand for?

Answer 9

functional residual capacity: expiratory reserve volume + residual volume

Question 10

what does FEV1/FVC stand for?

Answer 10

fraction of forced vital capacity expired in one second

Question 11

What does ventilation refer to?

Answer 11

the movement of air in and out of the lungs

Question 12

what is alveolar ventilation?

Answer 12

fresh air getting to alveoli and available for gas exchange

Question 13

what is pulmonary ventilation?

Answer 13

total air movement into and out of the lungs

Question 14

What is partial pressure?

Answer 14

the pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture

Question 15

what happens to the PAO2 and PACO2 during hyper-ventilation?

Answer 15

PO2 rises (120mmHg) and PCO2 falls (2ommHg)

Question 16

Describe changes of PAO2 and PACO2 in hypoventilation

Answer 16

PO2 falls (30mmHg) and PCO2 rises (100mmHg)

Question 17

describe the role of surfactant

Answer 17

surfactant helps reduce the surface tension of the water in the alveoli which is directed inwardly tending to collapse the alveoli. this means small alveoli useful for their large SA do not collapse increasing lung compliance and reducing the recoil. makes breathing easier.

Question 18

Describe infant respiratory distress disorder

Answer 18

premature babies have to battle collapsing alveoli with every breath as surfactant production does not start until 25 week of gestation and is only complete by week 36.

Question 19

What is compliance?

Answer 19

the change in volume relative to change in pressure. this represents the Add to strechability of lungs (not the elasticity), there fore does not explain air leaving the lungs.

Question 20

Describe what is meant by:
> High compliance
> Low compliance

Answer 20

> a large increase in lung volume for a small decrease in partial pressure
small increase in lung volume for a large decrease partial pressure

Question 21

Why does it take greater change in pressure to reach a particular lung volume in inspiration than it does to maintain in during expiration?

Answer 21

this id due to elastic recoil and surface tension that has to be overcome

Question 22

Why does expiration require a lot of work in emphysema?

Answer 22

due to loss of elastic tissues

Question 23

Why does inspiration require more effort in fibrosis?

Answer 23

due to inert fibrous tissue instead of elastic tissue

Question 24

Why does the pressure volume curve vary between the base and the apex of the lung?

Answer 24

The alveoli at the base of the lung are being squashed so have a higher compliance as can inflate more on inspiration. the alveoli at the top remain more inflated so the volume change is smaller for any given pressure change.

Question 25

What is static spirometry reading?

Answer 25

the only consideration that is made is the volume exhaled

Question 26

what is a dynamic spirometry reading?

Answer 26

where the time taken to exhale a certain volume is what is being measured

Question 27

what are the affects of obstructive lung disease on the FEV and FVC?

Answer 27

rate at which air is exhaled is slower total volume is also reduced FEV is reduced to a greater extent than FVC

Question 28

What are the affects of restrictive lung disease on FEV and FCV?

Answer 28

total volume is reduced due to limitations to lung expansion | ratio of FEV and FVC is constant of increases

Question 29

where are the respiratory centres found?

Answer 29

in the pons and medulla

Question 30

what does the dorsal respiratory group innervate?

Answer 30

inspiration

Question 31

what does the ventral respiratory group innervate?

Answer 31

expiration via the pharynx, larynx and tongue

Question 32

what modulates the rhythm of breathing?

Answer 32

> emotion, the limbic system > voluntary override by the cerebral cortex > mechano-sensory input from the thorax preventing over-inflation of the lungs stopping alveoli damage > chemical composition of the blood (PCO2, PO2, pH)

Question 33

where are central chemoreceptors found?

Answer 33

in the medulla

Question 34

what do central chemoreceptors respond to?

Answer 34

the H+ concentration in the CSF around the brain which directly reflecting the PCO2

Question 35

what would a rise in [H+] in CSF cause?

Answer 35

a stimulation of ventilation as a rise of [H+] is driven by raised PCO2 (hypercapnia)

Question 36

when is ventilation reflexly inhibited?

Answer 36

if there is a decrease in arterial PCO2 reducing CSF [H+]

Question 37

what is the blood brain barrier permeable to?

Answer 37

gases (not ions)

Question 38

what is the equation for carbon dioxide in the blood that the central chemoreceptors use to monitor PaCO2 ?

Answer 38

C02 +H2O = H2CO3 = H + HCO3

Question 39

Where are peripheral chemoreceptors found?

Answer 39

carotid bodies where the carotid artery splits in the neck | aortic bodies in the aortic arch

Question 40

what do the peripheral chemoreceptors respond to?

Answer 40

to the plasma [H+] and pO2 (less so to the pCO2)

Question 41

What changes would occur to cause a stimulation of ventilation by the peripheral chemoreceptors?

Answer 41

a significant fall in arterial PO2 | a rise in [H+], a fall in pH (acidosis)

Question 42

what affect would alkalosis of plasma (pH increase) have on ventilation?

Answer 42

ventilation would be inhibited by the peripheral chemoreceptors

Question 43

what can happen to chemoreceptors in chronic lung disease?

Answer 43

the chronic exposure to CO2 can lead to desensitisation of the receptors. the peripheral receptors are then used as the primary receptor but the peripherals can live with high levels of CO2 until ventilation changes. these circumstances are called hypoxic drive

Question 44

what drugs can depress the respiratory centre?

Answer 44

barbiturates and opioids

Question 45

in what cases can nitrous oxide be dangerous to a patient?

Answer 45

in patients with chronic lung disease who are in hypoxic drive as it blunts the peripheral chemoreceptors response to falling PaO2. administering oxygen to these individuals aggravates the situation as it reinforces the ide that everything is fine