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
Define functional residual capacity
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
26
Define vital capacity
``` 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 ```
27
What factors can affect lung volume and capacity
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 >> training)
28
Describe anatomical dead space
``` 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) ```
29
What Does anatomical dead space vary with
size of subject | deep inspiration- greater expansion of the lungs lengthens and widens the conduction airways
30
What can increase and decrease anatomical dead space
Decrease dead space: tracheostomy / cricothyrotomy | Increase dead space: snorkelling / anaesthetic circuits
31
Describe alveolar dead space
non-perfused parenchyma (alveoli without a blood supply). No gas exchange Typicaly 0 mL in adults
32
Why does alveolar dead space exist
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
Describe the respiratory zone
``` 7 generations Gas exchange Typicaly 350 mL in adults Air reaching here is equivalent to alveolar ventilation ```
34
What re the distinct parts of the lung
 There are 2 distinct parts of the lungs called: o Conducting zone – anatomical dead space. o Respiratory zone – split into 7 generations.
35
Describe the snorkel analogy
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
What happens with increased pressure
harder for the lungs to expand
37
How do we measure pressure for respiratory gases
cmH2O | Air stops flowing at 0 cmH20
38
Describe what happens in ventilation
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
Summarise ventilation
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
Describe tidal breathing
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
Describe the chest wall relationship
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
What results in inspiration and expiration
Inspiratory muscle effort + chest recoil > lung recoil (results in inspiration) Expiratory muscle effort + lung recoil > chest recoil (results in expiration)
43
Describe the pleura
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
Describe a haemothorax
intrapleural bleeding
45
Describe pneumothorax
Pneumothorax: perforated chest wall or punctured lung leads to accumulation of air in pleural cavity
46
Describe negative pressure breathing
Palv < Patm to cause air movement (sucking not forcing - physiological) Normal breathing
47
Describe positive pressure breathing
Palv < Patm to cause air movement (sucking not forcing - physiological)
48
Describe the three compartment model
pressures in cmH2O Palv = 0 at rest Patm = 0 at rest Ppl = -5 at rest
49
Describe transmural pressures
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
Describe the pressure gradient across the lungs
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
Describe transpulmoanry pressures
 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
Describe the effects of the diaphragm
The effect of the diaphragm is like a syringe | A pulling force in one direction
53
Describe the effects of the respiratory muscles
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
Describe the chest-wall relationship graphically
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
What are the implications of the chest-wall curve
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
Describe the volume-time curve as a lung function test
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
Describe abnormalities in the volume-time curve
 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
What can be obtained from the volume-time graph
 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
Describe peak flow lung function test
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
Describe the flow volume loop
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
What happens to the flow-volume loop in obstructive disease
 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
What happens to the flow-volume loop in restrictive disease
 Characterised by being a narrow flow-volume loop with much less TLC (shift to the right).
63
What happens to the flow-volume loop in variable extra thoracic obstruction
 Flattening of the inspiratory curve section due to flow rate being limited by an obstruction outside the lungs.  Only affected in inspiration.
64
What happens to the flow-volume loop in variable intra-thoracic obstruction
 Expiratory curve blunted. | Remember that INtra is EXpiration and EXtrathoracic is INspiration.
65
What happens to the flow volume loop in fixed airway obstruction
Blunted inspiratory cure Blunted expiratory curve Otherwise normal
66
How might recovery from serious burns affect lung volumes/capacities?
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
How does intrapleural pressure change at the start of tidal inspiration?
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
How do we calculate alveolar ventilation
Va= (Vt (tidal volume)- Vd (volume of phsyiological dead space)) f alveolar ventilation is air ventilating respiratory exchange surface
69
Summarise the different lung function tests
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
Describe the muscles involved in different breathing patterns
Tidal breathing is predominantly diaphragm-induced (syringe movement) Maximum ventilation involves full inspiratory muscle recruitment (syringe and bucket handle movement)