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Respiratory System > Ventillation > Flashcards

Ventillation Flashcards

1
Q

Define minute ventilation

A

The volume of air expired in one minute (VE) or per minute (V̇E)

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2
Q

Define respiratory rate (Rf)

A

The frequency of breathing per minute

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3
Q

Define alveolar ventilation

A

The volume of air reaching the respiratory zone per minute

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4
Q

Define respiration

A

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

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5
Q

What is meant by anatomical dead space

A

The capacity of the airways incapable of undertaking gas exchange

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6
Q

What is meant by 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

Define physiological dead space

A

Equivalent to the sum of alveolar and anatomical dead space

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8
Q

Define hypoventilaiton

A

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

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9
Q

Define hyperventilation

A

Excessive ventilation of the lungs atop of metabolic demand (results in reduced PCO2 - alkalosis)

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10
Q

Define hyperpnoea

A

Increased depth of breathing (to meet metabolic demand)

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11
Q

Define hypopnoea

A

Decreased depth of breathing (inadequate to meet metabolic demand)

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12
Q

Define apnoea

A

Cessation of breathing (no air movement)

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13
Q

Define dyspnoea

A

Difficulty in breathing

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14
Q

Define bradypnoea

A

Abnormally slow breathing rate

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15
Q

Define tachypnoea

A

Abnormally fast breathing rate

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16
Q

Define orthopnoea

A

Positional difficulty in breathing (when lying down)

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17
Q

What is key to remember about lung volumes

A

Volumes are discrete sections of the graph and don’t overlap

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18
Q

What is key to remember about capacities

A

sums of volumes

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19
Q

Define tidal volume

A

Volume of air breathed in and out in a normal breath (0.5L)

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20
Q

Define inspiratory reserve volume

A

How much extra air you can draw in after a breath in (3.3L)

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21
Q

Define expiratory reserve volume

A

How much extra air you can breathe out after a normal breath out (1.0L)

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22
Q

Define residual volume

A

Volume of air left in the lungs at the end of a maximum expiration (1.2l)

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23
Q

Define total lung capacity

A

Vital capacity + residual volume
only a fraction used in total breathing (6.0L)
how much air can be adjusted - useful air

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24
Q

Define inspiratory capacity

A

TV + IRV
Volume of air breathed in by a maximum inspiration
The extra air you can take in on top of the FRC.
amount of air that can be forcibly inhaled from normal breathing
3.8L

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25
Q

Define functional residual capacity

A

Volume of air remaining in the lungs at the end of normal expiration. Acts as buffer between extreme changes in alveolar gas levels with each breath
2.2L
RV+ ERV

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26
Q

Define vital capacity

A 
Volume of air breathed that can be breathed in by a max inspiration following a max expiration 
4.8l
IRV + TV+ ERV
Useful air
can be regulated 
TLC- RV
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27
Q

What factors can affect lung volume and capacity

A

body size (height and shape - but obesity does not increase size of lungs), sex (males larger), disease (lung muscle/tissue disorders), age (decrease with age), fitness (innate&raquo_space; training)

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28
Q

Describe anatomical dead space

A 
16 generations
No gas exchange
Typicaly 150 mL in adults at FRC
Equivalent to anatomical  dead space
Not all the air reaches the alveoli
nose and mouth
pharynx
larynx
trachea
bronchi and bronchioles (including terminal)
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29
Q

What Does anatomical dead space vary with

A

size of subject

deep inspiration- greater expansion of the lungs lengthens and widens the conduction airways

30
Q

What can increase and decrease anatomical dead space

A

Decrease dead space: tracheostomy / cricothyrotomy

Increase dead space: snorkelling / anaesthetic circuits

31
Q

Describe alveolar dead space

A

non-perfused parenchyma (alveoli without a blood supply).
No gas exchange
Typicaly 0 mL in adults

32
Q

Why does alveolar dead space exist

A

Because gas exchange sits suboptimal in some parts of the lung
If each acinus were perfect- the amount of air received by each alveolus would be matched by the flow of blood through the pulmonary capillaries.
In reality:
Some areas receive less ventilation than others
Some areas receive less blood flow than others

33
Q

Describe the respiratory zone

A 
7 generations
Gas exchange
Typicaly 350 mL in adults
Air reaching here is equivalent 
to alveolar ventilation
34
Q

What re the distinct parts of the lung

A

 There are 2 distinct parts of the lungs called:
o Conducting zone – anatomical dead space.
o Respiratory zone – split into 7 generations.

35
Q

Describe the snorkel analogy

A

Essentially, a longer snorkel means more dead space which your lungs may not be able to shift and as according to Poiseuille’s law, a decrease in diameter by just a half means an increase in resistance by 16x!
Resistance is also proportional to length
Pressure is also inversely proportional to volume

36
Q

What happens with increased pressure

A

harder for the lungs to expand

37
Q

How do we measure pressure for respiratory gases

A

cmH2O

Air stops flowing at 0 cmH20

38
Q

Describe what happens in ventilation

A

Pressure at the entrance to the respiratory tract is Patm and pressure inside the lungs is alveolar pressure PA
Pa=Patm no air flow (FRC)
PAPatm- air flows out of lungs

pATM is constant, so alveolar pressure must change
Diaphragm flattens- increasing thoracic volume, lowers intra pleural pressure- air flows into lungs
Expiration, relaxation of the muscles of the chest wall allows elastic recoil of lungs to cause contraction of lungs, reducing thoracic volume and increasing intrathoracic volume (Boyle’s law) and thus expulsion of gas

39
Q

Summarise ventilation

A
  1. At the start there is NO transpulmonary pressure because there is no volume change.
  2. Chest wall expands and creates the negative pressure.
  3. Pressure gradient is established and air flows in.
  4. Pressure gradient equalises.
40
Q

Describe tidal breathing

A

Tidal breathing: vacuum leads to pressure gradient to generate flow; removal of inspiratory effort increases pressure due to recoil, compressing gas to push air out - no net change in volume
Ambient pressure: 0cm/H2O

41
Q

Describe the chest wall relationship

A

The chest wall has a tendency to spring outwards, and the lung has a tendency to recoil inwards
This creates a sub atmospheric (negative) pressure in the intrapleural space
These forces are in equilibrium at end-tidal expiration (functional residual capacity; FRC), which is the ‘neutral’ position of the intact chest.
the chest and lungs move as a unit

42
Q

What results in inspiration and expiration

A

Inspiratory muscle effort + chest recoil > lung recoil (results in inspiration)
Expiratory muscle effort + lung recoil > chest recoil (results in expiration)

43
Q

Describe the pleura

A

The lungs are surrounded by a visceral pleural membrane
The inner surface of the chest wall is covered by a parietal pleural membrane
The pleural cavity (the gap between pleural membranes) is a fixed volume and contains protein-rich pleural fluid

The chest wall and lungs have their own physical properties that in combination dictate the position, characteristics and behaviour of the intact chest wall

44
Q

Describe a haemothorax

A

intrapleural bleeding

45
Q

Describe pneumothorax

A

Pneumothorax: perforated chest wall or punctured lung leads to accumulation of air in pleural cavity

46
Q

Describe negative pressure breathing

A

Palv < Patm to cause air movement (sucking not forcing - physiological)
Normal breathing

47
Q

Describe positive pressure breathing

A

Palv < Patm to cause air movement (sucking not forcing - physiological)

48
Q

Describe the three compartment model

A

pressures in cmH2O
Palv = 0 at rest
Patm = 0 at rest
Ppl = -5 at rest

49
Q

Describe transmural pressures

A

ressure on inside - pressure on outside
PTT intraplural space and atmosophere (transthoracic) should be -5cmH2O Ppl- Patm
PTP (transpulmonary) should be 5cmH2O - Palv-Ppl
PRS (respiratory system) should be 0cmH2O - Palv-Patn

o Known as the pressure across tissues.
o POSITIVE transmural pressure leads to expiration.

50
Q

Describe the pressure gradient across the lungs

A

Because the alveoli communicates with the atmosphere- the pressure inside the lung is greater than the intrapleural pressure
This creates a pressure gradient across the lungs, known as transmural pressure
It is this transmural pressure (caused by a negative pressure in the pleural space) that ensures that the lungs are held partially expanded in the thorax
It effectively links the lungs (which are like suspended balloons ) with the chest wall

51
Q

Describe transpulmoanry pressures

A

 Transpulmonary pressure OR Transrespiratory pressure = difference between the alveolar and intrapleural pressure – IMPORTANT.
o This pressure dictates air flow.

Note: Transpulmonary pressure is a form of transmural pressure!
A negative transrespiratory pressure will lead to inspiration

52
Q

Describe the effects of the diaphragm

A

The effect of the diaphragm is like a syringe

A pulling force in one direction

53
Q

Describe the effects of the respiratory muscles

A

The effect of the other respiratory muscles is like a bucket handle
An upwards and outwards swinging force
Internal- pulls the ribs downwards
External- pulls the ribs upwards

54
Q

Describe the chest-wall relationship graphically

A

There are two components of the respiratory mechanics; the chest-wall and the independent lung.
 The orange line is the sum of the independent lines.
 FRC (functional residual capacity) is when the respiratory system is relaxed with -5cmH2O of chest wall pressure and +5cmH2O of lung pressure.
 It takes relatively little pressure to expand the chest wall to 6L because the chest-wall ‘wants’ to expand.
 With the elastic recoiling lung though, it takes more pressure to change the volume.
 This gives a net sigmoid shape.
It’s a trade off in breathing so we don’t use our whole vital capacity in exercise because we would expend too much energy in moving muscles.

55
Q

What are the implications of the chest-wall curve

A

There are two components of the respiratory mechanics; the chest-wall and the independent lung.
 The orange line is the sum of the independent lines.
 FRC (functional residual capacity) is when the respiratory system is relaxed with -5cmH2O of chest wall pressure and +5cmH2O of lung pressure.
 It takes relatively little pressure to expand the chest wall to 6L because the chest-wall ‘wants’ to expand.
 With the elastic recoiling lung though, it takes more pressure to change the volume.
 This gives a net sigmoid shape.
It’s a trade off in breathing so we don’t use our whole vital capacity in exercise because we would expend too much energy in moving muscles.

56
Q

Describe the volume-time curve as a lung function test

A

Protocol: FVC is the forced vital capacity.
Patient wears nose-clip and inhales to TLC.
Patient exhales as hard and fast as possible until RV is reached or 6 seconds have passed.
Inspect graph pattern and look for: slow starts, early stops or intramanouever variability.
(FEV_1)/FVC Ratio = (Volume of air forced out in 1 second)/(Volume of air at maximum inhalation)

57
Q

Describe abnormalities in the volume-time curve

A

 Obstructive Lung Disease (e.g. COPD) = FEV1 and FVC is much lower while FET is much higher (takes longer to expel).
 Restrictive Lung Disease (e.g. Sarcoidosis – think restrictive bar hug) – FVC is lower while FEV1 is relatively high as the airway conduction pathway is clear (not like in COPD).

58
Q

What can be obtained from the volume-time graph

A

 Obstructive Lung Disease (e.g. COPD) = FEV1 and FVC is much lower while FET is much higher (takes longer to expel).
 Restrictive Lung Disease (e.g. Sarcoidosis – think restrictive bar hug) – FVC is lower while FEV1 is relatively high as the airway conduction pathway is clear (not like in COPD).

59
Q

Describe peak flow lung function test

A

Patient wears noseclip
Patient inhales to TLC
Patient wraps lips round mouthpiece
Patient exhales as hard and fast as possible
Exhalation does not have to reach RV
Repeat at least twice. Take highest measurement

y-axis- peak expiratory flow rate
age x-axis
expected values for height and gender

60
Q

Describe the flow volume loop

A

Protocol
Patient wears noseclip
Patient wraps lips round mouthpiece
Patient completes at least one tidal breath (A&B)
Patient inhales steadily to TLC (C)
Patient exhales as hard and fast as possible (D)
Exhalation continues until RV is reached (E)
Patient immediately inhales to TLC (F)
Visually inspect performance and volume time curve and repeat if necessary. Look out for:
Inconsistencies with clinical picture
Interrupted flow data

61
Q

What happens to the flow-volume loop in obstructive disease

A

 Characterised by an indentation called ‘coving’ and a shift to the left.
 Deeper indent = more severe disease.
 The shift to the left indicates an increase in residual volume as air is trapped in the alveoli by small airway passages having collapsed.

62
Q

What happens to the flow-volume loop in restrictive disease

A

 Characterised by being a narrow flow-volume loop with much less TLC (shift to the right).

63
Q

What happens to the flow-volume loop in variable extra thoracic obstruction

A

 Flattening of the inspiratory curve section due to flow rate being limited by an obstruction outside the lungs.
 Only affected in inspiration.

64
Q

What happens to the flow-volume loop in variable intra-thoracic obstruction

A

 Expiratory curve blunted.

Remember that INtra is EXpiration and EXtrathoracic is INspiration.

65
Q

What happens to the flow volume loop in fixed airway obstruction

A

Blunted inspiratory cure
Blunted expiratory curve
Otherwise normal

66
Q

How might recovery from serious burns affect lung volumes/capacities?

A

Short- and medium-term recover from chest burns will lead to scar tissue formation, which is less elastic, restricting expansion of the chest at most volumes

67
Q

How does intrapleural pressure change at the start of tidal inspiration?

A

At the start of tidal inspiration, the diaphragm
contracts and pulls down (and the external
intercostals may contract and pull the ribs
upwards and outwards), which pulls the parietal
pleaural membrane away from the lung. This
‘stretches’ the intrapleural space as the lung fills.
Throughout this, the lung is trying to recoil back inwards,
so the visceral pleura is being pulled inwards too, increasing the partial vacuum in the intrapleural space.

Intrapleural pressure, usually -5 cm H2O across the lung, decreases to about -8 cm H2O

68
Q

How do we calculate alveolar ventilation

A

Va= (Vt (tidal volume)- Vd (volume of phsyiological dead space)) f
alveolar ventilation is air ventilating respiratory exchange surface

69
Q

Summarise the different lung function tests

A

Peak flow – tests airway resistance (how fast can air be expired?)
Time-volume curve – tests airway resistance and FVC
Flow volume loop – tests airway resistance, flow rates, TV, IRV, ERV and FVC

70
Q

Describe the muscles involved in different breathing patterns

A

Tidal breathing is predominantly diaphragm-induced (syringe movement)
Maximum ventilation involves full inspiratory muscle recruitment (syringe and bucket handle movement)

Respiratory System (23 decks)

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