Session 2 - Lecture 1 - Ventilation and Lung Mechanics Flashcards
1 - SKIP
Lung Mechanics and Ventilation of the Lungs
2 - Overview
• Mechanics of quiet inspiration and expiration vs forced inspiration and forced expiration
• Importance of the pleural seal, in allowing the lungs to expand with the thoracic cavity
• Defining the resting expiratory level
• Relationship of volume and pressures changes within the lungs and thoracic cavity that enable movement of air into and out of lungs during inspiration and expiration
• Relate volumes moved during inspiration and expiration to spirometry
• Work of breathing and defining lung compliance
- Surface tension and elasticity of the lungs
• The critical role of surfactant in reducing surface tension and preventing small alveoli
collapse
• Airway resistance
- Why we have so many tiny airways rather than a few big ‘tubes’
- Effects of forced expiration on airway resistance
“1. mechanics of how we expand, inspire and expire – so when we take a breath, and to do that we have to think about important volume changes, pressure changes
- pleural seal that ensures the chest wall expands when our lungs xpanded
- mapping mechanincs of ventilation – terms we use there, to spirometry
- Thinking quietly with the compliance, the stretchiness – what makes the lungs stretchy and what makes them difficult to stretch
- also links into role of surfactant which is rly critical to allowing you to breathe in resp system
- think about getting air to lungs – alveoli getting to where gaseous exchange will actually occur.”
3 - What is ventilation?
Ventilation is the process of inspiration and expiration
The physical action of breathing and moving air into and out of the lung
Ventilation ≠ respiration
“Ventilation is the process, it’s mechanical – moving volumes, changing pressures – it’s not actually what happens at the cellular level at the alveolus, at the capillary – that is gaseous exchange/resp – movement across the alveoli, so what we’re focusing on is the mechanics, the breathing.”
4 - Note your breathing…
Note your breathing…
• This is ‘quiet’ inspiration and expiration
- Volume of air being moved = tidal volume
• Breathing is a rhythmic and involuntary process
- Neurones in respiratory centre of brain automatically generate impulses to inspiratory muscles
“So while you’re sitting here relatively relaxed, now consciously take note of what you’re doing when you breathe – breathe then continue breathing as you would normally – consciously think about whats happening as you take a breath in and take a breath out. So what you’re doing aat rest is quiet inspiration and expiration – something that moves a volume of air called tidal volume – talking about volume of air moving in and out of your lungs as you’re sat there, quietly breathing in and out. Now a you’re quietly breathe in and out, you’re not relying on conscious movement – it just happens – doesn’t stop working when you fall asleep. So the control you’re breathing is completely involuntary – automatic control in resp centre sits in brainstem, around the medulla. And there’s this rhythmic fibre of neurones that trigger muscles in your chest wall, your diaphragm to contract – and that relaxation we do – now whilst this is involuntary – consciously decide to take a deep breath, so we can consciously influence this process, but actually we don’t need to be consciously controlling our breathing, it just happens automatically.”
5 - Lung Mechanics in Quiet Inspiration
Lung Mechanics in Quiet Inspiration
Air is drawn into the airways by ACTIVE expansion of the thoracic cavity, which in turn expands the lungs
Boyle’s Law = inverse relationship between pressure and volume of a gas
“What’s actually happening to allow air to move into and out of our lungs, we have to start changing some volumes inside the thoracic cavity – and that will start to do things with pressures- so we know the airwill actually move from high pressures to lower pressures. so if on this img here, here isyour chest wall – this is your thoracic cavity, not got anything in it, just bones muscles fascia etc., and bone shaped low portion, so before you take a deep breath in, this is the size of your thoracic cavity – deep breath in and size of thoracic cavity increases, so volume increases. So how is it we expand the thoracic cavity? What musclesa re we using? External intercostal muscles and diaphragm. So diaphragm flattens those down the way by its contracting, and the external intercostal muscles draw the ribs up and outwards – so there’ll be expansion outwards of your chest wall, but flattening of your diaphragm, the volume inside your thoracic cavity goes up. So when we say active expansion, so there’s an active process to actually expand the chest wall and do work. So, why are we wanting to increase the volume in thoracic cavity? To lower pressure, bc we want more air in don’t we – air likes to move from higher pressure to lower pressure – want to lower pressure inside chest to lower atmospherically – expanding thoracic cavity, intrathoracic pressure goes down, air goes into thoracic cavity. Doesn’t actually go into thoracic cavity, goes into something else – what would draw air into our lungs? So fi we draw the lungs on, so can you see that when we expand the thoracic cavity, we not only increase the volume inside thoracic cavity, we increase volume inside lungs, therefore dropping pressure, intra pulmonary pressure into our lungs. So pressure goesdown. Now remember in BL we went over a lot of these principles and I think we lookeda t ht learn models, so this represents the chest wall – floppy balloons that are deflated are your lungs, and as you flatten the diaphragm, change th pressure einside the bottle and thoracic cavity, therefore expand lungs. But these balloons are not stuck up inside sides of the bottle – not sort of pushed up against sides of bottle – in life, in us, our lungs are v much of the side of the thoracic cavity, so every time our thoracic cavity expands, our lungs will expand with it.Just put the physics thing at the bottom reminding you of inverse relationsjip involved in the pressure, a the volume increase, pressure goes down.”
6 - Lung Mechanics in Quiet Expiration
Lung Mechanics in Quiet Expiration
Air expelled from the airways PASSIVELY, by relaxing muscles used in inspiration–> reduces volume of thoracic cavity –> reduces volume of lungs
“Okay, so that’s when we’re taking a quiet breath in, and what happens when we then breathe out? So quiet expiration – so just that normal breath out we do at rest, how does that happen? Is it involving a muscle? So it’s completely passive, so taking that natural breath out, purely passive – all the muscles used to expand your chest when we breathe in just relax – natural elastic recoil inside your lungs, that will pull the chest wall back in, okay so air is expelled passively bc the muscles used to expand your chest have just started to relax – so expend more energy in actually breathing out of quiet resp. So go from bigger volume to small volume – so what will happen to pressure – goes up, volume smaller so pressure goes up so all air/pressure inside lungs will be higher than atmospheric pressure, so the air is expelled. Okay, so you’re breathing in, you expand volume of thoracic cavity and lungs, bigger volume, lower pressure, air drawn into muscle. Relax those muscles, expand chest wall – drawn back in by elastic recoil, and then volume of thoracic cavity small, pressure rises and it then comes above atmospheric pressure so air then leaves.”
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