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Year 1 - BRS > 6.8 - Ventilation and Gas Exchange > Flashcards

6.8 - Ventilation and Gas Exchange Flashcards

1
Q

What is minute ventilation (L/min)?

A
  • the volume of air expired in one minute or per minute
  • minute ventilation (L/min) = tidal volume (L) x breathing frequency (breaths/min)
  • typical range for 70kg healthy male is 0.5L x 12 breaths/min = 6L/min
  • gas entering and leaving the LUNGS
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2
Q

What is respiratory rate (Rf)?

A

The frequency of breathing per minute

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3
Q

What is alveolar ventilation (Valv) (L/min)?

A
  • volume of air reaching the respiratory zone/alveoli per minute
  • alveolar ventilation (L/min) = (tidal volume (L) - dead space (L)) x breathing frequency (breaths/min)
  • typical for 70kg healthy male is (0.5L - 0.15L) x 12 breaths/min = 4.2 L/min
  • gas entering and leaving the ALVEOLI
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4
Q

What is respiration?

A

The process of generating ATP either with an excess of oxygen (aerobic) or a shortfall (anaerobic)

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5
Q

What is anatomical dead space?

A

The capacity of the airways incapable of undertaking gas exchange

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6
Q

What is alveolar dead space?

A

Capacity of the airways that should be able to undertake gas exchange but cannot (e.g. hypoperfused alveoli)

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7
Q

What is physiological dead space?

A

Equivalent to the sum of anatomical and alveolar dead space (conducting zone + non-perfused parenchyma)

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8
Q

What is hypoventilation?

A

Deficient ventilation of the lungs; unable to meet metabolic demand (leads to increased PO2 - acidosis)

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9
Q

What is hyperventilation?

A

Excessive ventilation of the lungs atop of metabolic demand (results in reduced PO2 - alkalosis)

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10
Q

What is hyperpnoea?

A

Increased depth of breathing (to meet metabolic demand)

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11
Q

What is hypopnea?

A

Decreased depth of breathing (inadequate to meet metabolic demand)

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12
Q

What is apnoea?

A

Cessation of breathing (no air movement)

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13
Q

What is dyspnoea?

A

Difficulty in breathing

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14
Q

What is bradypnoea?

A

Abnormally slow breathing rate

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15
Q

What is tachypnoea?

A

Abnormally fast breathing rate

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16
Q

What is orthopnoea?

A

Positional difficulty in breathing (when lying down)

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17
Q

Why does the max inspiratory and expiratory effort plateau?

A

It takes a lot of effort from muscles of airways to hold in/squeeze out the last bit of air

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18
Q

What is tidal volume?

A

Volume of air going in and out with each breath - normally 0.5L

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19
Q

What is inspiratory reserve volume?

A

Extra volume of air that you can get into lung on top of tidal volume

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20
Q

What is expiratory reserve volume?

A

The volume of air that you can empty past your tidal volume

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21
Q

What is residual volume?

A
  • the volume of air left in the lungs
  • you cannot fully empty your lungs of air due to lungs holding their structure to prevent collapse via surfactants etc
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22
Q

What is vital capacity?

A

Difference between max air you can get into lungs and min air (IRV + TV + ERV)

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23
Q

What is functional residual capacity?

A
  • everything below default position of lung capacity (bottom of tidal volume) e.g. if you take in a deep breath and die, your lungs won’t empty all the way to bottom since that takes muscle effort, but to a baseline level due to elastic fibres of lung recoiling
  • ERV + residual volume
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24
Q

What is inspiratory capacity?

A
  • everything above baseline value (bottom of tidal volume)
  • IRV + tidal volume
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25
Q

What do volumes not do?

A

Volumes are discrete sections of the graph and do not overlap

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26
Q

What are capacities?

A

Capacities are the sum of two or more volumes

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27
Q

What factors affect lung volumes and capacities?

A
  • body size - height, shape
  • sex - male, female (average male has larger lung volume and total lung capacity)
  • disease - pulmonary, neurological
  • age - chronological, physical
  • fitness - innate, training (if you have athletic parents you tend to have larger lungs)
28
Q

What is the conducting zone?

A
  • 16 generations
  • no gas exchange
  • consists of the structures that provide passageways for air to travel into and out of the lungs e.g. nasal cavity, pharynx, trachea, bronchi, most bronchioles
  • typically 150 mL in adults at FRC
  • equivalent to anatomical dead space
29
Q

What is the respiratory zone?

A
  • 7 generations
  • gas exchange
  • corresponds to lung parenchyma and includes some bronchioles, alveolar ducts and alveoli
  • air reaching here is equivalent to alveolar ventilation
30
Q

What are non-perfused parenchyma?

A
  • alveoli without a blood supply
  • no gas exchange
  • typically 0 mL in adults
  • called alveolar dead space
31
Q

Name two procedures that can decrease the volume of someone’s dead space?

A
  • tracheostomy
  • cricothyrotomy
32
Q

Name two procedures that can increase the volume of someone’s dead space?

A
  • anaesthetic circuit
  • snorkelling
33
Q

What does the chest wall have a tendency to do?

A
  • chest wall has a tendency to spring outwards, and the lung has a tendency to recoil inwards
  • these forces are in equilibrium at end-tidal expiration (functional residual capacity, FRC) which is the neutral position of the intact chest
  • changes in external forces are needed to change the equilibrium
34
Q

What changes in these forces would result in inspiration?

A

inspiratory muscle effort + chest recoil > lung recoil

35
Q

What changes in these forces would result in expiration?

A

chest recoil < lung recoil + expiratory muscle effort

36
Q

Describe the anatomy of the chest wall.

A
  • lungs surrounded by a visceral pleural membrane
  • inner surface of the chest wall is covered by a parietal pleural membrane
  • the pleural cavity (gap between pleural membranes) is a fixed volume and contains protein-rich pleural fluid - lubricates surface
  • chest wall and lungs have their own physical properties that in combination dictate position, characteristics and behaviour of intact chest wall
37
Q

What drives the flow of air in and out of the lungs?

A

High pressure –> low pressure

38
Q

What is negative pressure breathing and give an example?

A
  • alveolar pressure is reduced below atmospheric pressure
  • this is normal breathing
39
Q

What is positive pressure breathing and give examples?

A
  • atmospheric pressure is increased above alveolar pressure
  • e.g. mechanical ventilation, CPR, fighter pilots
40
Q

What is the effect of the diaphragm when breathing?

A
  • diaphragm is like a syringe
  • pulling force in one direction
  • when diaphragm pulls down = increases volume and decreases alveolar pressure = negative pressure = inspiration
41
Q

What is the effect of the other respiratory muscles when breathing?

A
  • other muscles e.g. external intercostal muscles are like a bucket handle
  • upwards and outwards swinging force
42
Q

Key terminology - prefix symbols

A
  • P - partial pressure (kPa or mmHg)
  • F - fraction (% or decimal)
  • S - Hb saturation (%)
  • C - content (mL)
  • Hb - volume bound to Hb (ML)
43
Q

Key terminology - middle (subscripts) symbols

A
  • I - inspired
  • E - expired
  • A - alveolar
  • a - arterial
  • v(line) - mixed venous
  • P - peripheral
  • D - dissolved
44
Q

Key terminology - suffix symbols

A
  • O2 - oxygen
  • CO2 - carbon dioxide
  • N2 - nitrogen
  • Ar - argon
  • CO - carbon monoxide
  • H2O - water vapour
45
Q

What is Dalton’s Law?

A

Pressure of a gas mixture is equal to the sum of the partial pressures (P) of gases in that mixture

46
Q

What is Fick’s Law?

A

Molecules diffuse from regions of high to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)

47
Q

What is Henry’s Law?

A

At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid

48
Q

What is Boyle’s Law?

A

At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas

49
Q

What is Charles’ Law?

A

At a constant pressure, the volume of a gas is proportional to the temperature of that gas

50
Q

What gases make up the air and at what % at sea level?

A
  • N2 - 78.09%
  • O2 - 20.95%
  • Ar - 0.93%
  • CO2 - 0.04%
  • Ne, He, H2, Kr etc - <0.01%
51
Q

How is high-altitude air different to sea level air?

A

It has the same % of gases as sea level but lower partial pressures of each

52
Q

How is inspired gas modified in the airways?

A
  • the air is warmed, humidified, slowed (so alveoli do not burst) and mixed to help protect respiratory exchange surface as air passes down the respiratory tree
  • dry air at sea level –> conducting airways –> respiratory airways
53
Q

What is total O2 delivery at rest?

A
  • 16 mL/min
  • at rest we need approx. 250 mL/min, so relying on diffused O2 alone is not conducive with life
54
Q

What are haemoglobin monomers made of?

A

A ferrous iron ion (Fe2+, haem-) at the centre of a tetrapyrrole porphyrin ring connected to a protein chain (-globin); covalently bonded at the proximal histamine residue

55
Q

What is the positive cooperative effect?

A
  • as O2 binds to Hb, this leads to a conformational change that increases affinity of Hb for O2 which allows it to bind more easily - allosteric behaviour of Hb
  • this change in the protein also creates a binding site for 2,3-DPG which facilitates unloading of O2 at tissues where it is needed
  • the amount of 2,3-DPG increases proportionally to metabolic demand as you need to release more O2 at tissues
56
Q

What causes left shift?

A
  • left shift = increased affinity (loading)
  • decreased temperature
  • alkalosis
  • hypocapnia (low CO2)
  • reduced 2,3-DPG
57
Q

What causes right shift?

A
  • exercise
  • increased temperature
  • acidosis
  • hypercapnia (high CO2)
  • increased 2,3-DPG
  • Bohr effect
58
Q

What causes upwards shift?

A
  • upwards shift - increased oxygen-carrying capacity
  • polycythaemia
59
Q

What causes downwards shift?

A
  • downwards shift - impaired oxygen-carrying capacity
  • anaemia
60
Q

How does carbon monoxide change the oxygen dissociation curve?

A
  • downwards and leftwards shift
  • decreased capacity
  • increased affinity
61
Q

What is the oxygen dissociation curve for foetal haemoglobin?

A

Greater affinity than adult HbA to ‘extract’ oxygen from mothers’ blood in placenta

62
Q

What is the oxygen dissociation curve for myoglobin?

A

Much greater affinity than adult HbA to ‘extract’ oxygen from circulating blood and store it

63
Q

How is oxygen loading in lungs?

A
  • RBCs entering from left are not deoxygenated - should be called mixed venous blood - is actually at 75% saturation
  • from lungs –> RBC
64
Q

How is oxygen unloaded at tissues?

A
  • partial pressure of O2 has decreased as venous supply dumps blood with less O2 into blood at tissues which mixes and dilutes it, but amount of Hb same
  • 5mL/dL of oxygen flux means 250mL/min is transferred to tissues - which is how much the body needs
65
Q

How is CO2 loaded in tissues?

A
  • CO2 moves into blood where it binds very slowly (as non-enzymatic) with H2O –> carbonic acid
  • carbonic acid is weak so dissociates into HCO3- and H+
66
Q

How is CO2 loaded into RBC?

A
  • most CO2 leaving tissues goes into RBCs where it reacts with water in presence of carbonic anhydrase to produce carbonic acid
  • H2CO3 –> H+ + HCO3-
  • HCO3- moves out into blood and Cl- moves in (chloride shift) through AE1 transporter to maintain resting membrane potential
  • Cl- binds to Hb allosterically causing right shift
  • CO2 is mainly transported as bicarbonate in blood via RBCs but also binds to Hb at amine end to produce carbaminohaemoglobin (HbCO2)
  • Hb is a good buffer so can bind protons that H2CO3 dissociates into to maintain pH inside RBC so carbonic anhydrase can work optimally
67
Q

What changes happen in pH and other measures of CO2 levels during CO2 loading in tissues?

A
  • slight pH decrease
  • for the amount of O2 we are using, we do not produce a proportional amount of CO2 due to formation of water in respiration

Year 1 - BRS (73 decks)

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