Ventilation Flashcards
Inspiration volume equals?
Expiration volume
The amount we breathe in, equals the amount we breathe out (a simple concept)
What is tidal volume (TV)?
Normal volume of air displaced between normal inhalation and exhalation
This is around 500ml in a healthy adult
What is residual volume?
What is left in the lungs after breathing out as much as you can
Lung volume is never 0L, only becomes 0L with a pneumothorax (lung collapse)
What is vital capacity (VC)?
The greatest volume of air that can be expelled from the lungs after taking the deepest possible breath
What is total lung capacity (TLC)?
It is the totality of the capacity of the lung, including residual volume
How can ventilation be calculated?
Minute ventilation
Alveolar ventilation
What is the equation for minute ventilation?
Tidal volume (ml/breath) x Respiratory rate (breaths/min)
What does the term ‘alveolar ventilation’ refer to?
Respiration which is happening deep in the lungs in the alveoli
What is the equation for alveolar ventilation?
(Tidal volume – dead space) x respiratory rate
What is ‘dead space’?
Conducting airways where no gaseous exchange takes place
What is the difference between minute ventilation and alveolar ventilation?
Alveolar ventilation corrects for air in the upper airways, as there is no gaseous exchange there
Alveolar volume is more prescriptive
What is the average volume of the conducting airways?
Around 150ml
What are the typical lung function tests performed?
Spirometry
Peak flow meter
When are lung function tests particularly important?
In asthma diagnosis
What are the 2 key volumes used to look at lung function?
Forced vital capacity (FVC)
Forced expiratory volume in 1 sec (FEV1)
What is FVC?
Maximum volume exhaled
Gives an indication of the size/capacity of the lungs
What is FEV1?
Amount that you can force out of your lungs in 1 second
Around 80% of FVC in a healthy patient
What is obstructive lung disease?
Obstructive meaning airways are obstructed
What happens to these volumes in obstructive lung disease?
FEV1 is reduced due to increased resistance in the airways
FEV1 is <80% of FVC
FVC is around normal (over time the amount of air you can force out is normal)
Give 2 examples of obstructive lung disease.
Asthma, cystic fibrosis
What is restrictive lung disease?
Affects how easily the lungs inflate and deflate
What happens to these volumes in restrictive lung disease?
FEV1 is reduced
FVC is reduced
FEV1 >80% of FVC (as both are reduced, ratio is not altered)
What is lung compliance?
A measure of how easily the lungs and thorax expand
Relationship between ΔV and ΔP
In healthy individuals this happens easily, in some disease states, this is not possible
Explain what is happening in high compliance.
When this person has the exact same ΔP, the ΔV is much larger
There is a loss of alveolar and elastic tissue, this loss of elastic recoil means the lungs are floppy/stretchy, like a loose elastic band, they are easily stretched hence the large change in volume
In which conditions would you see high compliance?
Emphysema, old age
Explain what is happening in low compliance.
When this person has the exact same ΔP, the ΔV is much smaller
There is an increase in collagen expression due to inflammation, this stiffens the lungs and makes them more difficult to inflate
In which conditions would you see low compliance?
Oedema, pneumonia, fibrosis
Disorders affecting the movement of the chest, particularly the ribs and spinal column (e.g. arthritis, ankylosing spondylitis)
Premature infants
What else can cause reduced compliance?
Normally, type II cells in the lung produce surfactant
This surfactant is a type of phospholipid
Reduced surfactant production leads to problems as it increases surface tension (force across a liquid area)
If we don’t have enough surfactant, this tension pulls on tissues
What is new-born respiratory distress syndrome?
Premature infants quite often suffer from this condition
These patients have underdeveloped type II cells in the lungs meaning reduced surfactant production, higher surface tension and alveolar collapse
What is the equation for lung compliance?
CL = ΔVL / ΔTP
What is the equation for change in transpulmonary pressure?
ΔTP = TP (END) – TP(START) ΔTP = [Palv – Pip]end - [Palv – Pip]start
What is ventilation-perfusion inequality?
A mismatch between ventilation and blood flow, reduces the amount of oxygen entering the body
Give an example of where ventilation-perfusion equality can be seen.
Lung diseases where alveoli are in very poor condition, can breath in but oxygen can’t pass through the tissue in the alveoli into blood vessels
There is a mismatch in ventilation and what you can actually take into the body
This is seen in emphysema, where degeneration of alveolar and bronchiole walls and capillaries occurs
