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PHM BSc - Applied Science > Respiratory Physiology > Flashcards

Respiratory Physiology Flashcards

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1
Q

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

A

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

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

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2
Q

What does a left shift mean and what can cause it

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

What does a right shift mean and what can cause it

A 
Hb has reduced affinity for oxygen
Raised PCO2
Acidosis
Hot 
Raised 2,3DPG
Exercise
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4
Q

Why do we used 92% saturations as a cut off

A

At this point the curve starts to drop off

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5
Q

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

A

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

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6
Q

How is CO2 transported

A

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

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7
Q

Describe the location and function of central chemoreceptors

A

In the medulla near the floor of the 4th ventricle

They detect the pH of CSF therefore indirectly measuring PCO2

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8
Q

Describe the location and function of peripheral chemoreceptors

A

Carotid and aortic bodies

They detect plasma O2

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9
Q

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

A

Peripheral chemoreceptors actually detect plasma pO2 not arterial blood

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10
Q

What would the effect of haemorrhage be on peripheral chemoreceptors

A

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

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11
Q

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

A

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

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12
Q

What is the role of irritant receptors

A

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

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13
Q

How is alveolar ventilation calculated

A

(Tidal volume - physiological deadspace volume) x RR

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14
Q

What is the oxygen delivery equation

A

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

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15
Q

What is pre-oxygenation and what is its role

A

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

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16
Q

Why is there a reduced PaO2 in anaesthesia

A

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

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17
Q

What is the normal response to hypoxia

A

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

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18
Q

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

A

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

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19
Q

What is the oxygen cascade

A

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

20
Q

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

A

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

21
Q

What are the 2 types of V/Q mismatch

A

Deadspace - ventilated but not perfused - VQ»1

Shunt - perfused but not ventilated - VQ«1

22
Q

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

A

Pressure collapses the blood vessels leading to dead space

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

What are some lung pathologies that exacerbate a shunt

A

Atelectasis, consolidation, pulmonary oedema

26
Q

What is hypoxic pulmonary vasoconstriction

A

Minimises pulmonary shunting

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

27
Q

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

A

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

28
Q

What are the 4 types of hypoxia and give some examples

A

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

29
Q

What is the role of nitrogen

A

Stop the alveoli collapsing when O2 is extracted

30
Q

What is positive end expiratory pressure

A

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)

31
Q

When is positive end expiratory pressure raised

A

Hyperventilation
Obstructed or narrow airway
CPAP
Pursed lip breathing

32
Q

What pathologies lead to increased compliance

A

Emphysema

Elderly

33
Q

What can lead to decreased compliance

A

Tension pneumothorax
Fibrosis
Obesity
Supine position

34
Q

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

A

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

35
Q

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

A

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

36
Q

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

A

This increases the concentration of oxygen dissolved in the blood

37
Q

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

A

Initiates inspiration

Receives and integrates information

38
Q

What is the role of the ventral respiratory group

A

Expiratory aspect of breathing
Rhythm generation
?Inactive during restful breathing

39
Q

What is the role of the pneumotaxic centre (Pons)

A

Inhibits the apneustic centre to limit inspiration

40
Q

What is the role of the apneustic centre (Pons)

A

Controls the depth of breathing by prolonging inspiration

41
Q

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

A 
Medulla = rhythm
Pons = depth
42
Q

What is lung compliance

A

Change in volume of the lung per unit force

43
Q

What is the role of surfactant and where is it produced

A

Type 2 pneumocytes

Decreases the surface tension of alveoli meaning they don’t collapse as easily

44
Q

Which nerve innervates the carotid body chemoreceptors

A

Glossopharyngeal

45
Q

What nerve innervates peripheral chemoreceptors in aortic bodies

A

Vagus

PHM BSc - Applied Science (12 decks)

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