S1 L1 Lung Mechanics and Ventilation 1 Flashcards
Respiratory tract - order air moves through
- 2 sections of the resp tract
- *Define:**
- Ventilation
- Respiration
- Intrapulmonary pressure
- Intrapleural pressure
- Transpleural pressure
Ventilation: The process of inspiration and expiration (Mechanical and involves the movement of air)
Respiration: Physiologic and involves gas exchange
Intrapulmonary pressure: Pressure inside alveoli/intrathoracic respiratory tract
Intrapleural pressure: Pressure between visceral and parietal pleura
Transpleural pressure: Intrapulmonary pressure minus intrapleural pressure
Breathing…
- Normal breathing, is called _______
- Volume of air being moved _______
- Breathing is rhythmic and involuntary process, where do the neurones originate?
- How is air moved?
‘quiet’ inspiration and expiration
tidal volume
Neurones in respiratory centre of the brain automatically generate impulses to inspiratory muscles
Move air by changing lung pressure - gas moves from greater to lower pressure
Boyle’s Law
- Equation
- Example
Boyle’s Law = inverse relationship between pressure of a gas and volume it occupies
P1 x V1 = P2 x V2
Example: A volume increases, the pressure exerted by a gas decreases
Also, if a volume decreases, the pressure increases
INVERSLY PROPORTIONAL
Lung Mechanics in Quiet Inspiration
- Define intrapulmonary pressure
- Process of quiet inspiration
Contraction of the diaphragm and external intercostal muscles -?
Expands the thoracic cavity outwards ->
The pleural seal ensures that the lungs expand along with the thorax ->
Intrapulmonary pressure falls below atmospheric prssure (as the lung volume increases) ->
Air then flows into the lungs
Lung Mechanics in Quiet Expiration
- Process of quiet expiration
- Lungs returning volume depends on what____?
Air expelled from the airways passively, by relaxing muscles used in inspiration ->
reduces volume of thoracic cavity ->
reduces volume of lungs as they return to original volume, this increases pressure inside lungs (intrapulmonary pressure) relative to atmosphere and air expelled
Depends on: Elastic recoil (ER is the ability of a stretched organ to return to its resting position)
- *How come - When the thoracic cavity returns to its original size, the lungs don’t just collapse?**
- > Afterall, there are no fibres or muscles connecting the chest wall to the lungs - so why do they move together?
- Definitions associated with this
PLEURA and PLEURAL CAVITY
- *Pleura:** Each of a pair of serous membranes lining thorax and enveloping the lungs.
- *Parietal pleura** lines the inside of each hemi-thorax (the bony thoracic cage, diaphragm & mediastinal surfaces)
- *Visceral pleura** lines the outside of lung
Intrapleural space = space between visceral and parietal pleura, (potential space) - contains about 15 ml fluid
Fluid in pleural space IMPORTANT!
In a healthy person. the pleural cavity is a ‘potential space’
- *Pleural seal**
- What is this?
- Forces?
- Analogy
- What does the PS ensure?
- What is this?
Surface tension between the pleural surfaces created by the presence of thin film of pleural fluid holds outer surface of lung to inner surface of chest wall
- Forces?
Surface tension
- Analogy
Presence of thin film of pleural fluid holds outer surface of lung (base of cup/bottle) to inner surface of chest wall (coaster standing in for intrathoracic wall)… When lift the cup, also lift the coaster
- What does the PS ensure?
Pleural seal ensures the chest wall and lungs move together
The ‘pull’ of the lungs and chest wall
- What direction is this pull?
- What does this lead too…., in which space…..
When looking at pressures, what do the following mean:
- Atmospheric pressure
- Negative pressure e.g. -4
- Positive pressure e.g. +5
Lungs have a natural inward elastic recoil (pulls visceral pleura inward towards the lungs)
Chest wall have a natural outward elastic recoil (pulls parietal pleura outwards)
These two opposing forces create a negative pressure in the intraPLEURAL space
When looking at pressures, what do the following mean:
- Atmospheric pressure:
Designated at 0, it is a conventrion to be set at 0mmHg (anything with 0mmHg, has the same pressure as atmospheric pressure)
- Negative pressure e.g. -4:
This means the pressure is -4mmHg less than atmospheric pressure
- Positive pressure e.g. +5
This means the pressure is +5mmHg more than atmospheric pressure
What happens to intraPULMONARY pressure during inspiration and expiration?
What is the intraPLEURAL pressure always……
Why does the intraPLEURAL pressure alawys stay ____ than atmospheric pressure?
What happens to intraPULMONARY pressure during inspiration and expiration?
Intrapulmonary pressure negative to atmosphere (so air moves into lungs)
What is the intraPLEURAL pressure always……
Intrapulmonary pressure positive to atmosphere (so air moves out of lungs)
Why does the intraPLEURAL pressure alawys stay ____ than atmospheric pressure?
IntraPLEURAL pressure stays negative during expiration and inspiration.
It stays negative during inspiratory phase, due to expansion of the thorax
- *Which properties affect ability to expand lungs, lungs to return to orgininal volume and ‘resting lung’ volumes?**
- 2 and explain them
- How are they related (equation)
- Examples
- 2 and explain them:
Compliance: Stretchiness. A measure of distensibility - change in volume relative to change in pressure (the capacity to swell as a result of pressure from inside)
Elastance: A measure of elastic recoil = the tendency of something that has been distended to retrun to its original size
- How are they related (equation):
Compliance = 1 / Elastance
INVERSELY PROPORTIONAL
- Examples:
–> In tissue tissues with a high compliance (easier to stretch), the elastic recoil is less
–> In tissues with a low compliance, elastic recoil (tendency to return to original size) is high
Compliance
To stretch the lungs, the elastic recoil of the lung must be overcome. The elastic recoil, arises from:
- 2 sources
- what is the relationship between compliance and these two listed above?
- *2 sources:**
- Elastic tissue in the lungs (connective tissue - elastic fibres incl collagen and other matrix elements within the lung parenchyma)
- Surface tension forces of the fluid lining the alveoli
They are INVERSELY related (think about the equation on the last flashcard)
- *Lung Elastic Recoil**
- Directly related to… 2 sources
- Directly related to connective tissue surrounding alveoli - elastic fibers including elastin & collagen and other matrix elements within the lung parenchyma
- Directly related to alveolar fluid surface tension
Lung compliance and elastic recoil cont.
- Name for when we have just expired and before we start inspiring…
- Volume air at _______ is called…
Name for when we have just expired and before we start inspiring…
Resting Expiratory level
At this stage:
• Lungs collapse inwards (lung elastic recoil)
• Chest wall pulls “out” (chest elastic recoil)
• Forces are equal and opposite so balance out (=no movement chest wall)
i.e. state of equilibrium
Volume air at _______ is called…
Functional Residual Capacity (FRC)
The Resting Expiratory Level:
- What happens when elastic recoil is weaker than physiologically normal because of pathology - where will equilibrium be reached?
- What happens when elastic recoil is stronger than physiologically normal becuase of pathology - where will equilibrium be reached?
- e.g. if lung recoil is weaker, chest recoil will be strong than lung recoil, this means the equilibrium will be reached closer to the wall
- e.g. ig lung recoil is stronger, chest recoil is weaker in comparison (note - chest recoil hasn’t changed), equilibrium will be closer to the chest
Alveoli is lined by fluid, this fluid creates _______________
What is surface tension? Explain the forces
What is surface tension like in alveoli? What does this mean?
What happens with more ST?
What helps to reduce surface tension?
Surface tension
Due to charges in the water moelcules, water molecules are attacted to other water moleucles. At the air-water interface: all water moelcules below the surface are attracted by surrounding water molecules, equally, in all directions. However, at air-water interface, these water molecules are pulled ‘downwards’, no pull upwards. This creates a vaccum on the surface = surface tension.
In alveoil - water molecules at this surface are under tension, like an elastic band - tries to have the smallest surface area possible -> WANTS THE ALVEOLI to collapse (to reduce surface area)
The more surface tension = harder it is to expand the lungs
Surface tension decreases compliance of lungs
Surfactant
In pic: Blue = water, causing surface
Pink triangles = surfactant (next flashcard)
- *Surfactant**
- How and why does it affect surface tension?
- When is it more effective? (think about emphysema)
- Which cells secrete it?
- What type of molecule is surfactant?
- How and why does it affect surface tension?
Reduces surface tension by disrupting the interaction between fluid molecules on the surface
- When is it more effective? (think about emphysema)
More effective at disrupting surface tension when its molecules are closer together (i.e. around smaller alveoli)
Smaller alveoil WOULD HAVE higher surface tension, except that in smaller alveoli the surfactant molecules are closer together, so are more effective at disrupting surface tension of fluid
THIS LEADS TO ALL ALVEOLI SIZES HAVING SAME PRESSURE
- Which cells secrete it?
Type II pneumocytes
- What type of molecule is surfactant?
Mixture of phospholipids and proteins
- *Airway resistance**
- For ventilation to occur, aiway resistance needs to be overcome. This depends on
1) Surface tension within airways
2) Airway diameter - small diameter have higher resistance to flow (Poiseuille’s Law)
R = resistance
n = viscosity
L = length
r = radius
a) Many airways in lung are small
i. Individual resistance is high - but all together is low
b) Diameter airways also affected by
i. Mucous in airways
ii. Intrapulmonary pressure gradients - inspiration vs expiration
iii. Radial Traction
How does the arrangement of bronchioles lead to a lower resistance as possible?
Like a watering can.
Many broncioles all arranged in parallel, compensates for increase in their ‘individual resistance’
- *Forced inspiration and expiration: Uses lung reserves, but require more effort**
- Beyond quiet inspiration and expiration
Which muscles is involved in forced inspiration?
Which muscles are involved in expiration?
Which muscles is involved in forced inspiration?
Which muscles are involved in expiration?
- *Lung volumes and capacities**
- Graph showing the names of different breathing…
