3 Ventiliation Flashcards
Q: Describe the movement of normothermic ex vivo ventilated perfused lungs. (2)
A: There is no restriction to the movement and so they expand freely in all directions
The movement is not limited by the chest wall
Q: Define minute ventilation.
A: The volume of air expired in one minute (VE) or per minute (V̇E).
Q: Define respiratory rate (RF).
A: The frequency of breathing per minute
Q: Define alveolar ventilation (Valv).
A: The volume of air reaching the respiratory zone
Q: Define respiration.
A: The process of generating ATP either with an excess of oxygen (aerobic) and a shortfall (anaerobic)
Q: Define anatomical dead space.
A: The capacity of the airways incapable of undertaking gas exchange
Q: Define alveolar dead space.
A: Capacity of the airways that should be able to undertake gas exchange but cannot (e.g. alveoli that are not perfused or have collapsed within the respiratory zone)
Q: Define physiological dead space. (2) Normal value? Depends on?
A: Equivalent to the sum of alveolar and anatomical 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
Q: Define hyperventilation,
A: Excessive ventilation of the lungs atop of metabolic demand (results in reduced PCO2 - alkalosis)
Q: Define hypoventilation.
A: Deficient ventilation of the lungs; unable to meet metabolic demand (increased PO2 – acidosis)
Q: Define hyperpnoea.
A: Increased depth of breathing (to meet metabolic demand)
Q: Define hypopnoea.
A: Decreased depth of breathing (inadequate to meet metabolic demand)
Q: Define apnoea.
A: Cessation of breathing (no air movement)
Q: Define dyspnoea.
A: Difficulty in breathing
Q: Define bradypnoea.
A: Abnormally slow breathing rate
Q: Define tachypnoea.
A: Abnormally fast breathing rate
Q: Define orthapnoea.
A: Positional difficulty in breathing (when lying down)
Q: What are the components of the chest wall? Describe the recoil property of them.
A: TWO components to the chest wall:
- Bone + muscle + fibrous tissue
- Lungs
- the rib cage would naturally recoil outwards
- tThe lungs have a tendency to recoil INWARDS
Q: What is functional residual capacity (FRC)? How? Marked by?
A: 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
end of a tidal breath marks the Functional Residual Capacity (FRC)
Q: When the lungs and ribcage are in equilibrium, what do you need to cause movement in either direction?
A: muscular effort to push the equilibrium in one direction or the other
Q: What is the pleural cavity? Pressure?
A: (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
Q: What links the lungs and the chest wall?
A: When we think about changing pressures, the pleural cavity is going to be the link between the lungs and the chest wall
Q: How do we do a full inspiration? (including diaphragm, lung, pleural cavity, chest wall)
A: 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
Q: What happens if the chest wall separates from the lungs?
A: lungs will deflate
Q: What happens if you puncture the chest wall or lung? Haemothorax?
A: the fixed volume pleura is compromised - air will fill the pleural cavity and elastic recoil will take over and the lung will collapse
If you have a haemothorax then this happens much slower
Q: What is tidal breathing? Mouth or nose usually? Exercise? End marks?
A: the amount of inspiration and expiration that meets metabolic demand - usually nasal
tidal volume INCREASES
the Functional Residual Capacity (FRC)
Q: What is residual volume? What causes it?
A: 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
Q: What are the 4 main volumes?
A: -Tidal Volume
- Inspiratory Reserve Volume
- Expiratory Reserve Volume
- Reserve Volume
Q: What is total lung capacity (TLC)?
A: 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 TLC
Q: What is vital capacity (VC)? Equation?
A: how much air is within the confines of what we are able to inspire and expire
i.e. TLC - RV
Q: What is functional residual capacity (FRC)? Equation?
A: 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
i.e. ERV + RV
Q: What is inspiratory capacity? Equation?
A: how much extra air you can take in on top of the FRC
i.e. TV + IRV
Q: What drives flow? No flow when?
A: Pressures drive flow - without a pressure gradient there would be no flow (ie pressure between the atmosphere and the inside of the lung is EQUAL and hence there is no NET movement of air)
Q: What units are used in lung volumes?
A: 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
Q: What is transpulmonary pressure?
A: difference between alveolar and intrapleural pressure
Q: What is transmural pressure?
A: pressure across a tissue or several tissues
Q: What is transrespiratory pressure?
A: the important one - it tells us whether there will be airflow into or out of the lung
Q: How do you calculate the pressure gradient? When do you inspire in normal breathing?
A: you always do the pressure inside MINUS the pressure outside to try and figure out the orientation of the gradient
when there is lower pressure inside the lungs - this is NEGATIVE PRESSURE BREATHING
Q: How is it possible to ventilate using positive pressure breathing?
A: involves increasing the pressure outside by using a ventilator or CPR
Q: Draw a ventilation graph including volume and pressure. Describe.
A: 2 lines
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
Q: On a diagram of a ‘bronchi->alveloi’ outline, draw a line separating the conducting zone and the respiratory zone. Label. What is the conducting zone?
A: line between cartilaged parts and not (labels: physiological dead space, conducting zone (anatomical dead space), respiratory zone, non-perfused perenchyma (alveolar dead space))
dead space
Q: What is dead space?
A: the part of the airways and lung that DOES NOT PARTICIPATE IN GAS EXCHANGE
Q: State two reversible procedures that can alter a patient’s dead space.
A: Tracheostomy - cutting off the upper part of the airway so it is no longer dead space
Ventilator - the extra tubing becomes dead space
Q: Draw a graph of pressue (x) and volume (y) for independent chest wall, intact lung and independent lung. Describe the intact lung line shape and explain.
A: REFER
intact lung has a sigmoid shape in terms of its volume-pressure relationship
Q: When we exercise, it is inefficient to use?
A: 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)
Q: How do you create a volume time curve? What should you look out for when visually inspecting it? (3)
A: 1. 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
- Slow starts
- Early stops
- Intramanouever variabiltiy
Q: Draw an example volume time curve. Define and label FVC, FEV1, FET.
A: REFER
FVC = Forced Vital Capacity
FEV1 = amount of air forced out of the lungs in 1 second
FET (Forced Expiratory Time) = the time taken to expel all the air from the lungs
Q: How would a volume time curve differ if you had an Obstructive Lung Disease (e.g. COPD)?
A: FEV1 would be much lower (can’t expel air fast)
FET is much higher (takes longer to expel all air)
FVC is much lower
Q: How would a volume time curve differ if you had a Restrictive Lung Disease (e.g. sarcoidosis)?
A: (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
Q: What is the peak expiratory flow test? Method? Exhalation does not have to reach?
A: Another way to assess lung function is to use the Wright Peak Flow Meter
- 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)
Q: What are flow volume loops? Draw an example diagram. Label A to B. Label PEF, IRV, TV, ERV, VC.
A: combines peak expiratory flow test and volume time curve
- Inspiration = Downwards
- Expiration = Upwards
- Y axis is the flow rate - the further it deviates from the x-axis, the greater the rate of flow
A: Tidal inspiration
B: expiration
->makes the small ring seen in the middle
D: 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
E: As you get closer to the residual volume, the air flow rate becomes SLOWER
F: There is then a maximal inspiration which brings the lungs back to TLC - this is dome shaped
Q: How can residual volume be measured in a closed circuit?
A: 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
Q: How does a flow volume loop change with mild obstructive lung disease? (5)
A: 1. 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 (E) -> 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
- The inspiratory curve is more or less the same
- Loop moves to the LEFT
Q: How does a flow volume loop change with restictive lung disease?
A: 1. Narrower flow-volume loop (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
- Loop moves to the RIGHT
Q: In a flow volume loop, what happens if the airway becomes obstructed?
A: flow rate would be limited
Q: How does a flow volume loop change with a Variable EXTRAthoracic Obstruction?
A: 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
Q: How does a flow volume loop change with a Variable INTRAthoracic Obstruction?
A: The expiratory curve is blunted but the inspiratory curve is the same
Q: How does a flow volume loop change with Fixed Airway Obstruction?
A: BOTH the inspiratory and expiratory curves will be blunted
