Respiratory Physiology

Question 1

What are the axis on the oxygen dissociation curve and what does it look like

Answer 1

X axis - partial pressure of oxygen
Y axis - oxygen saturation of Haemoglobin

Sigmoidal shape, higher partial pressures of oxygen lead to higher haemoglobin saturations

Question 2

What does a left shift mean and what can cause it

Answer 2

Hb has increased affinity for oxygen 
Reduced PCO2
Alkalosis
Cold
Reduced 2,3DPG
CO poisoning

Question 3

What does a right shift mean and what can cause it

Answer 3

Hb has reduced affinity for oxygen
Raised PCO2
Acidosis
Hot 
Raised 2,3DPG
Exercise

Question 4

Why do we used 92% saturations as a cut off

Answer 4

At this point the curve starts to drop off

Question 5

Does myoglobin have a higher or reduced affinity for oxygen compared to Hb and what does this mean

Answer 5

Much higher affinity meaning it will hold on to its oxygen until partial pressures are very low. This means there is delayed onset anaerobic respiration and lactic acid production

Question 6

How is CO2 transported

Answer 6

Bound to Hb
Dissolved in water and transported as a solution
Diffused into erythrocytes (Co2 + H2O = HCO3 + H+)

Question 7

Describe the location and function of central chemoreceptors

Answer 7

In the medulla near the floor of the 4th ventricle

They detect the pH of CSF therefore indirectly measuring PCO2

Question 8

Describe the location and function of peripheral chemoreceptors

Answer 8

Carotid and aortic bodies

They detect plasma O2

Question 9

Why can arterial PaO2 drop extremely low before being detects in cases of anaemia or CO poisoning

Answer 9

Peripheral chemoreceptors actually detect plasma pO2 not arterial blood

Question 10

What would the effect of haemorrhage be on peripheral chemoreceptors

Answer 10

Localised stagnant hypoxia due to reduced blood flow stimulates them leading to a sympathetic drive

Question 11

What are the stretch receptors (respiration control) and where are they found

Answer 11

Pulmonary - airway smooth muscle they inhibit inspiration and increase expiration when distended (Hering Breuer reflex)
J - alveoli walls they cause rapid shallow breathing
Golgi tendon organs - intercostal muscles they inhibit inspiration when the chest wall is distended

Question 12

What is the role of irritant receptors

Answer 12

Bronchoconstriction and apnoea to stop you breathing in any more of the irritant

Question 13

How is alveolar ventilation calculated

Answer 13

(Tidal volume - physiological deadspace volume) x RR

Question 14

What is the oxygen delivery equation

Answer 14

Oxygen delivery = CO x arterial oxygen content (which is determined by Hb, arterial O2 saturation and amount of O2 dissolved in blood)

Question 15

What is pre-oxygenation and what is its role

Answer 15

100% O2 given for 3 minutes to fill the functional residual capacity therefore increasing oxygen stores

Question 16

Why is there a reduced PaO2 in anaesthesia

Answer 16

Hypoventilation (anaesthetic agents, opioids, sedatives)
Raised metabolic rate increases oxygen demand
Inhibition of the normal response to hypoxia
Loss of tone of respiratory muscles
Hypoxic-pulmonary vasoconstriction inhibited

Question 17

What is the normal response to hypoxia

Answer 17

Carotid and aortic bodies stimulate the sympathetics leading to hyperventilation and increased CO

Question 18

What is diffusion hypoxia and what needs to be done to prevent it

Answer 18

This describes reduced alveoli PaO2 when nitrogen (if patient allowed to breath air) and nitrous oxide (which diffuses out of the blood to the alveoli when discontinued at the end of anaesthesia) mix
Need to give 100% O2 when stopping anaesthesia

Question 19

What is the oxygen cascade

Answer 19

Stepwise reduction in PaO2 as O2 passes from the environment to tissues

Question 20

Why is there a drop in PO2 between
A) air to alveoli
B) alveoli to pulmonary capillaries

Answer 20

A) addition of water vapour and mixing with CO2

B) either there is a V/Q mismatch or due to diffusion across the alveolar-capillary membrane

Question 21

What are the 2 types of V/Q mismatch

Answer 21

Deadspace - ventilated but not perfused - VQ»1

Shunt - perfused but not ventilated - VQ«1

Question 22

What happens if alveoli pressure >pulmonary artery pressure and when could this happen?

Answer 22

Pressure collapses the blood vessels leading to dead space

Seen in haemorrhage (reduced artery pressure), PE and +ve pressure ventilation (increases alveoli pressure)

Question 23

In a pneumothorax should you put the affected lung up or down and why

Answer 23

Bad lung up so that good lung is getting better perfusion (gravity)

Question 24

Why can the body not compensate very well for a pulmonary shunt

Answer 24

Well ventilated alveoli can’t compensate because of the capacity of Hb to carry oxygen

Question 25

What are some lung pathologies that exacerbate a shunt

Answer 25

Atelectasis, consolidation, pulmonary oedema

Question 26

What is hypoxic pulmonary vasoconstriction

Answer 26

Minimises pulmonary shunting | Blood vessels vasoconstrict to hypoxia meaning blood flow is redirected to well ventilated areas of the lung

Question 27

Compare the upper and lower zones in terms of their V, Q and VQ ratio

Answer 27

Lower zone is better perfused (gravity) and ventilated (sits right next to diaphragm so increased compliance) Upper zone is relatively more ventilated than perfused so has a much higher V/Q ratio

Question 28

What are the 4 types of hypoxia and give some examples

Answer 28

Hypoxic (PO2 too low to saturate Hb)- altitude, hypoventilation Anaemic (not enough functioning Hb) - anaemia, CO, methemogobinaemia Hystotoxic (tissue can’t use available O2) - cyanide Stagnant (poor flow to tissues) - HF, shock

Question 29

What is the role of nitrogen

Answer 29

Stop the alveoli collapsing when O2 is extracted

Question 30

What is positive end expiratory pressure

Answer 30

The pressure left in the lungs at the end of expiration which enables the alveoli to stay open. This increases their compliance (blowing up a balloon)

Question 31

When is positive end expiratory pressure raised

Answer 31

Hyperventilation Obstructed or narrow airway CPAP Pursed lip breathing

Question 32

What pathologies lead to increased compliance

Answer 32

Emphysema | Elderly

Question 33

What can lead to decreased compliance

Answer 33

Tension pneumothorax Fibrosis Obesity Supine position

Question 34

Define tidal volume, inspiratory and expiratory reserve volume, residual volume

Answer 34

A) Volume of air inhaled and exhaled during one respiratory cycle B) Volume of air that can be forcibly inhaled/exhaled after a normal tidal volume C) Volume of air remaining in the lungs after maximal exhalation

Question 35

Define inspiratory capacity, functional residual capacity, vital capacity, total lung capacity

Answer 35

A) Volume of air than can be inhaled from a resting state B) Volume of air left in the lung following a tidal expiration C) Volume of air that can be exhaled after maximal inhalation D) Maximum volume of air the lungs can accommodate

Question 36

What is the role of increasing atmospheric pressure (hyperbaric chambers)

Answer 36

This increases the concentration of oxygen dissolved in the blood

Question 37

What is the role of the dorsal respiratory group (located in medulla)

Answer 37

Initiates inspiration | Receives and integrates information

Question 38

What is the role of the ventral respiratory group

Answer 38

Expiratory aspect of breathing Rhythm generation ?Inactive during restful breathing

Question 39

What is the role of the pneumotaxic centre (Pons)

Answer 39

Inhibits the apneustic centre to limit inspiration

Question 40

What is the role of the apneustic centre (Pons)

Answer 40

Controls the depth of breathing by prolonging inspiration

Question 41

In short what are the roles of the medulla and pons in central respiratory control

Answer 41

``` Medulla = rhythm Pons = depth ```

Question 42

What is lung compliance

Answer 42

Change in volume of the lung per unit force

Question 43

What is the role of surfactant and where is it produced

Answer 43

Type 2 pneumocytes | Decreases the surface tension of alveoli meaning they don’t collapse as easily

Question 44

Which nerve innervates the carotid body chemoreceptors

Answer 44

Glossopharyngeal

Question 45

What nerve innervates peripheral chemoreceptors in aortic bodies

Answer 45

Vagus