Ventilation Flashcards
What has the chest wall have a tendancy to do?
What has the lungs got a tendancy to do?
These forces are in ……………. at end-tidal expiration (functional residual capapcity; FRC), which is the ‘neutral’ position of the intact chest.
When the two components are in this equilibrium, you need …………….. effort to push the equilibrium in one direction or the other
The pleural cavity (space in between parietal and visceral pleura) is of a …………. ………….and contains protein-rich pleural fluid
The pleural cavity is at …………. pressure
The 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 capapcity; FRC), which is the ‘neutral’ position of the intact chest.
These forces are in equilibrium at end-tidal expiration (functional residual capapcity; FRC), which is the ‘neutral’ position of the intact chest.
FUNCTIONAL RESIDUAL CAPACITY (FRC) = when we are at the end of tidal expiration. At the end of that tidal expiration you’re at FRC where the rib cage and the lungs are in equilibrium.
The elastic recoil of the lungs inwards and the outward recoil of the rib cage are IN EQUILIBRIUM
When the two components are in this equilibrium, you need muscular effort to push the equilibrium in one direction or the other
The pleural cavity (space in between parietal and visceral pleura) is of a FIXED VOLUME and contains protein-rich pleural fluid
The pleural cavity is at negative pressure
When we think about changing pressures, the pleural cavity is going to be the link between the lungs and the chest wall
If we do a full inspiration, we will be expanding the chest wall as well as pulling the diaphragm down
So the chest wall needs to pull the lung with it (though they aren’t physically attached) - the negative pressure of the pleural cavity allows the chest wall to pull the lungs with it
If the chest wall separates from the lungs, the lungs will deflate - they must move as one
If you puncture the chest wall or lung, then the fixed volume pleura is compromised - air will fill the pleural cavity and elastic recoil will take over and the lung will collapse
What are the lungs surrounded by?
What is the inner surface of the chest wall covered by?
•The pleural cavity (the gap between pleural membranes) is a ……………. …………… and contains protein-rich pleural fluid
Chest-wall relationship
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
Breaching the Pleural Cavity
If you get a puncture in the chest wall or lungs, then the ………… ………… pleural cavity is compromised
What will then happen to the pleural cavity, and what will happen to the lungs aswell and why will that happen to the lungs?
If you have a …………………… then this happens much slower
Breaching the Pleural Cavity
If you get a puncture in the chest wall or lungs, then the fixed volume pleural cavity is compromised
Air will fill the pleural cavity, elastic recoil will take over and the lung will collapse
If you have a haemothorax then this happens much slower
Lung Volumes and Capacities
What is Tidal Breathing?
What happens to your tidal volume whilst excercising?
The end of a tidal breath marks the …………….. ……………… ……………..
Due to the …………….. in the alveoli, you can’t empty the lungs fully because you don’t want the alveoli to stick together and not reopen
This remaining volume is the…………….. ……………..
There are FOUR main volumes: Name them
Volumes can be combined into capacities:
Total Lung Capacity (TLC) = …………………… combined
When you inspire all the way in and fill your lungs up as much as possible, the volume of air in the lungs is the …………………. ………………. ………………..
Define Vital Capacity and write an equation for it?
Define Functional Residual Capacity and write an equation for it?
Define inspiratory capacity and write an equation for it?
Lung Volumes and Capacities
Tidal Breathing = the amount of inspiration and expiration that meets metabolic demand
NOTE: when you’re exercising, your tidal volume INCREASES
The end of a tidal breath marks the Functional Residual Capacity (FRC)
This patient inhaled deeply and then did a full expiration - empty the lungs as much as possible
Due to the surfactant in the alveoli, you can’t empty the lungs fully because you don’t want the alveoli to stick together and not reopen
This remaining volume is the RESIDUAL VOLUME
There are FOUR main volumes:
Tidal Volume
Inspiratory Reserve Volume
Expiratory Reserve Volume
Reserve Volume
Volumes can be combined into capacities:
Total Lung Capacity (TLC) = EVERYTHING combined
When you inspire all the way in and fill your lungs up as much as possible, the volume of air in the lungs is the Total Lung Capacity (TLC)
Vital Capacity (VC) = Vital capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation.
i.e. TLC - RV
Functional Residual Capacity (FRC) = the volume of air in the lungs when the outwards recoil of the rib cage and the inward recoil of the lungs are in equilibrium or Functional Residual Capacity (FRC) is the volume of air present in the lungs at the end of passive expiration.
i.e. ERV + RV
Expiratory reserve volume- expiratory reserve volume. : the additional amount of air that can be expired from the lungs by determined effort after normal expiration
Inspiratory reserve volume. : the maximal amount of additional air that can be drawn into the lungs by determined effort after normal inspiration
Inspiratory reserve volume?
Inspiratory Capacity = how much extra air you can take in on top of the FRC
i.e. TV + IRV
What factors affect LUNG VOLUMES AND CAPACITIES?
List 5
What is negative pressure breathing- state if it is healthy or Artifical?
What is positive pressure breathing- state if it is healthy or Artificial?
What is transmural pressure?
What is Transpulmonary Pressure?
The ……………………….. …………………….. is the important one - it tells us whether there will be airflow into or out of the lung
A ………………. transrespiratory pressure will lead to inspiration
A ……………….. transmural pressure leads to expiration
Palv is reduced below Patm- Healthy- Negative Pressure Breathing
Patm is increased above Palv- Ventilation or CPR- Positive pressure breathing
TRANSMURAL PRESSURES - this is the pressure across a tissue or several tissues
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
The TRANSRESPIRATORY PRESSURE is the important one - it tells us whether there will be airflow into or out of the lung
Transmural pressures-(Pinside – Poutside)
A negative transrespiratory pressure will lead to inspiration
A positive transmural pressure leads to expiration
Ventilation
At the start of the cycle there is no …………………… pressure (between alveolar and intrapleural pressure) because there is no volume change
The chest wall expands and creates …………………. pressure so more air flows in
This establishes a pressure gradient down which air flows
Eventually the pressure gradient will equalise again
Ventilation
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
What is the dotted line in the image below?
Define Dead Space?
Give an example of a zone which is dead space?
What is alveolar dead space?
What is physiological dead space equal to?
In most healthy individuals, the alveolar dead space is ……… and hence the physiological dead space is more or less equal to anatomical dead space
Dead Space
Dotted Line = border between the conducting zone and the respiratory zone
Dead Space = the part of the airways and lung that DOES NOT PARTICIPATE IN GAS EXCHANGE
The conducting zone is dead space
There could be alveoli that are not perfused or have collapsed within the respiratory zone - this makes up ALVEOLAR dead space
Alveolar Dead Space = the parts of the lung that could participate in gas exchange but do not
Physiological Dead Space = Anatomical Dead Space + Alveolar Dead Space
In most healthy individuals, the alveolar dead space is zero and hence the physiological dead space is more or less equal to anatomical dead space
Normal physiological dead space = 150 mL
This varies depending on the size of your conducting zone
QUESTION: State two reversible procedures that can alter a patient’s dead space.
Tracheostomy - cutting off the upper part of the airway so it is no longer dead space
Ventilator - the extra tubing becomes dead space
What is a diaphragm and a respiratory muscles similar to?
What are the two components of respiratory mechanics?
We know that naturally the lung recoils ……………. and the chest wall recoils ……………
………………… 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
Purple line is the sum of the other two lines
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 …………….. shape in terms of its volume-pressure relationship
When we exercise, it is inefficient to use the whole of our ………… 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
We must consider the TWO components of respiratory mechanics:
Chest wall
Independent lung
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
Purple line is the sum of the other two lines
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
Volume-Time Curve
What is the protocol to generate this Volume-Time Curve?
Give a brief description in what happens in a healthy person?
What does FVC stand for?
What is FEV1 and why is it important?
State how FVC, FEV1 and FET is affected in Obstructive Lung Disease (COPD)?
State how FVC, FEV1 is affected in Restrictive Lung Disease (e.g. sarcoidosis)?
State if the FEV1/FVC ratio is higher or lower compared to normal in the aforementioned conditions?
Volume-Time Curve
Patients are asked to inspire all the way in and then expire all the way out as hard and fast as possible from TLC to RV
Healthy Person - the first bit comes out very quickly and then it becomes very difficult to expel the last little bit of air
FVC = Forced Vital Capacity
FEV1 = amount of air forced out of the lungs in 1 second- tells us if the airways are constricted
Healthy Person - around 75% of the air is out within the first second
FET (Forced Expiratory Time) = the time taken to expel all the air from the lungs
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
Restrictive Lung Disease (e.g. sarcoidosis):
Imagine you are trying to breathe and then someone gives you a big bear hug from behind - it limits the expansion of the thorax
FVC is lower
FEV1 is relatively high - because their conducting airways are quite clear they can expel air relatively easily
In this example - FEV1/FVC ratio
NORMAL = 73
Restrictive = 87
Obstructive = 53
Peak expiratory flow
How would you assess the peak expiratory flow?
Peak expiratory flow
Another way to assess lung function is to use the Wright Peak Flow Meter
You blow through the mouthpiece and are interested in the first big expiration
Flow-Volume Loops
Flow-volume loops combines the other two tests and does almost everything
Inspiration = Downwards
Expiration = Upwards
Y axis is the flow rate - the further it deviates from the x-axis, the greater the rate of flow
Tidal inspiration and expiration makes the small ring seen in the middle
A fast hard expiration is shown by the green line - there is a quick peak because the first 60% of volume takes very little effort
As you get closer to the residual volume, the air flow rate becomes SLOWER
The amount of flow right at the end of expiration is tiny
There is then a maximal inspiration which brings the lungs back to TLC - this is dome shaped
The parts of real importance are the maximum flow rate - D, E and F
In this scenario, there is an assumption that we already know the patient’s residual volume, because the maximum expiration ends at around 1.3 L
EXPERIMENTAL NOTE: Residual volume can be measured in a closed circuit by inhaling and exhaling something with a known concentration of an inert gas in it (as it is inert, none of it leave the lungs and enter the circulation) - by measuring the concentration difference after we’ve kept breathing it in and out, we can determine the residual volume
Some scales start at 0 where you haven’t measured residual volume
TV, IRV and ERV can be measured from the pressure-volume loop
Describe the differences in the flow-volume loop in patients with Mild obstructive disease, severe obstructive disease and restrictive disease?
The bold green curve is the normal FV loop
Mild Obstructive Disease - the top right line representing the last bit of expiration is usually a straight line but in people with mild obstructive disease, there is an indentation
The deeper the indentation the more severe the disease
Residual volume is EXPANDED in obstructive lung disease - because there is air trapped in the alveoli as the small airways linking the alveoli to the outside world have collapsed
TLC might increase
As emphysema degrades the alveolar walls you just get one large alveolus instead of one with several separate segments and hence there is an increase in the volume of the lungs
The inspiratory curve is more or less the same
Main changes in obstructive lung disease:
INDENTATION of the upper right line (end of expiration)
Loop moves to the LEFT
Restrictive Disease:
Narrower flow-volume loop
This is because getting up to a high TLC is difficult because of the restriction to the expansion of the lungs
Because of this, there may be some decrease in flow rate but it may not be affected
Main changes in restrictive lung disease:
Loop is NARROWER
Loop moves to the RIGHT
State the differences in the Flow volume loop for variable extrathoracic obstruction, variable intrathoracic obstruction and Fixed airway obstruction?
Extrathoracic- think of a peice of paper wrapped around your lips. When you breath out it is eassy when you breath in it is hard
Intrathoracic is opposite
More Flow-Volume Loops
If the airway becomes obstructed then the flow rate would be limited
Variable EXTRAthoracic Obstruction - you get flattening of the inspiratory curve because the flow rate is being limited by something in the way of it
The flow-volume loop is only affected during inspiration
Variable INTRAthoracic Obstruction
The expiratory curve is blunted but the inspiratory curve is the same
REMEMBER:
INTRAthoracic - EXpiration
EXTRAthoracic - INspiration
If you have Fixed Airway Obstruction, BOTH the inspiratory and expiratory curves will be blunted
Do the quiz at the end of panopto
