Ventilation

Question 1

Label graph with lung volumes and capacities

Answer 1

Capacities are the sum of two or more volumes

Volumes are discrete and don’t overlap

Question 2

What factors affect lung volumes and capacities?

Answer 2

Body size (height and shape)

sex male and female)

Disease (pulmonary and neurological)

age (chronological, physical)

fitness (innate and training)

Question 3

what are the 3 types of dead space?

Answer 3

Anatomical dead space and Alveolar dead space and Physiological dead space

Question 4

Anatomical dead space

Answer 4

capacity of the airways incapable of undertaking gas exchange, usually the conducting zone- the first 16 generations of airways (150ml) eg nose pharynx, larynx, trachea, bronchi and bronchioles
The conducting zone is dead space

Question 5

Alveolar dead space

Answer 5

capacity of the airways that should be able to undertake gas exchange by cannot
There could be alveoli that are not perfused or have collapsed within the respiratory zone - this makes up ALVEOLAR dead space (eg hypoperfused alveoli), should be 0ml in adults

Question 6

Physiological dead space

Answer 6

sum of the alveolar and anatomical dead space (around 150 ml)

Question 7

what is dead space?

Answer 7

Dead Space = the part of the airways and lung that DOES NOT PARTICIPATE IN GAS EXCHANGE

Question 8

What is respiratory zone

Answer 8

Respiratory zone: 7 generations, gas exchange, typically 350 ml in adults, ait reaching here is equivilant to alveolar ventilation

Question 9

Increase dead space

Answer 9

anaesthetic circuit snorkelling

Question 10

Decrease dead space

Answer 10

tracheostomy circothyrocotomy

Question 11

Chest wall relationship

Answer 11

The chest wall has a tendency to spring outwards, and the lung has a tendency to recoil inwards

Question 12

What happens at FRC?

Answer 12

These forces are in equilibrium at end-tidal expiration (functional residual capacity; FRC), which is the ‘neutral’ position of the intact chest.

Question 13

Chest recoil =

Answer 13

lung recoil

Question 14

inspiratory muscle effort + chest recoil >

Answer 14

lung recoil

results in inspiration

Question 15

Chest recoil

Answer 15

lung recoil + expiratory muscle effort

results in expiration

Question 16

What are the lungs surrounded by?

Answer 16

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

Question 17

Generating flow

Answer 17

Pressures drive flow - without a pressure gradient there would be no flow
NOTE: generally, when we’re talking about lung volumes, we use cm H2O instead of mm Hg or kPa - this is the default for measuring in respiratory physiology

Question 18

What os negative pressure breathing?

Answer 18

Palv is reduced below Patm
You inspire when there is lower pressure inside the lungs - this is NEGATIVE PRESSURE BREATHING (how we normally breathe)
It is also possible to ventilate using positive pressure breathing
This involves increasing the pressure outside by using a ventilator or CPR

Question 19

Transmural pressure

Answer 19

TRANSMURAL PRESSURES - this is the pressure across a tissue or several tissues
Pinside – Poutside

A negative transrespiratory pressure will lead to inspiration

Question 20

Mechanics of ventilation

Answer 20

The effect of the diaphragm is like a syringe
A pulling force in one direction

The effect of the other respiratory muscles is like a bucket handle
An upwards and outwards swinging force

Question 21

Transpulmonary pressure

Answer 21

There is a TRANSPULMONARY pressure = difference between alveolar and intrapleural pressure
NOTE: you always do the pressure inside MINUS the pressure outside to try and figure out the orientation of the gradient

Question 22

TRansrespiratory pressure

Answer 22

The TRANSRESPIRATORY PRESSURE is the important one - it tells us whether there will be airflow into or out of the lung

Question 23

Ventilation

Answer 23

At the start of the cycle there is no transpulmonary pressure (between alveolar and intrapleural pressure) because there is no volume change
The chest wall expands and creates negative pressure so more air flows in
This establishes a pressure gradient down which air flows
Eventually the pressure gradient will equalise again

Question 24

Chest wall relation, curve

Answer 24

We know that naturally the lung recoils inwards and the chest wall recoils outwards
Residual volume is the smallest volume of air that we can have in our lungs - if we put all the expiratory effort in, we are left with residual volume
FRC - chest wall pressure is -5 cm H2O and lung pressure is 5 cm H2O hence the FRC is 0
It takes relatively little pressure to expand the chest wall to 6L which is relatively easy because the chest wall wants to expand
However, to get the elastic lung to expand, the bigger the volume, the more pressure is needed
So the intact lung has a sigmoid shape in terms of its volume-pressure relationship
When we exercise, it is inefficient to use the whole of our vital capacity because a lot of energy and effort is expended to utilise the inspiratory and expiratory muscles to the maximum
You want to ventilate the lungs to achieve a higher ventilation performance but you don’t want to tire out your muscles

Question 25

Pulmonary function tests- volume time curve

Answer 25

Patient wears noseclip
Patient inhales to TLC
Patient wraps lips round mouthpiece
Patient exhales as hard and fast as possible
Exhalation continues until RV is reached or six seconds have passed
Visually inspect performance and volume time curve and repeat if necessary.
Look out for:
Slow starts
Early stops
Intramanouever variabiltiy

Question 26

Peak flow

Answer 26

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

Question 27

Flow volume loops

Answer 27

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

Question 28

FVC?

Answer 28

FVC = Forced Vital Capacity

Question 29

FEV1?

Answer 29

FEV1 = amount of air forced out of the lungs in 1 second

Healthy Person - around 75% of the air is out within the first second

Question 30

FET (Forced Expiratory Time)?

Answer 30

FET (Forced Expiratory Time) = the time taken to expel all the air from the lungs

Question 31

obstructive lung disease

Answer 31

increases residual volume, with reduced IRV, ERV and TV, flow into and out of lung is obstructed so lungs operate at higher volumes (eg asthma, COPD)
Obstructive Lung Disease (e.g. COPD):
FEV1 would be much lower (can’t expel air fast)
FET is much higher (takes longer to expel all air)
FVC is much lower

Question 32

restrictive disease

Answer 32

Restrictive Lung Disease (e.g. sarcoidosis, lung fibrosis
Imagine you are trying to breathe and then someone gives you a big bear hug from behind - it limits the expansion of the thorax (inflation/ deflation of chest/lungs are restricted and lungs operate at lower volumes)
FVC is lower
FEV1 is relatively high - because their conducting airways are quite clear they can expel air relatively easily

Question 33

Abnormal flow volume loops

Answer 33

see slides