lecture 2: ventilation Flashcards
what are the two main components to the chest wall?
- bone and muscle and fibrous tissue
- the lungs
ribcage and lungs
what are the natural tendencies of both the rib cage and the lungs?
- the ribcage recoils outwards
- the lungs recoil inwards
what is the volume and pressure of the pleural cavity?
- fixed volume
- and contains protein-rich negative fluid
- there is negative pressure
what is the functional residual capacity?
- when we are at the end of tidal expiration
- at the end we are at FRC when both the lungs and the ribcage are in equilibrium
what is the importance of the pleural cavity?
- it is the link between the lungs and the chest wall
- if we do a full inspiration we are expanding the chest wall as well as pulling the diaphragm down
- so the chest wall needs to pull the lung with it
- the negative pressure of the pleural cavity allows the chest wall to pull the lungs with it
what happens to the pleural cavity with a punctured lung?
- if you have a puncture in the chest wall
- the fixed volume pleural cavity is compromised
- air will fill the pleural cavity the elastic recoil will take over and the lung will collapse
what is the difference with a haemothorax?
- this occurs much slower
what is hyperventilation?
excessive ventilation of the lungs atop of metabolic demand
what is hypoventilation?
Deficient ventilation of the lungs; unable to meet metabolic demand
*show a diagram of a labelled lung volume and capacity graph :
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what is the tidal volume?
normal breathing volume - it can increase during exercise
what is inspiratory reserve volume?
how much extra air you can draw in after a breath in
what is expiratory Reserve volume?
how much extra air you can breathe out after a normal breath in
residual volume?
the volume left in the lungs after normal expiration
what factors affect the lung volume and capacity?
- body size - sex (men are bigger) - fitness - disease - age
what is dead space?
these are areas on the airway that do not participate in gas exhange
what are the two types of dead space?
anatomical dead space -
alveolar dead space -
non perfused parenchyma (alveoli without a blood supply)
the conducting zone is dead space
what are the two distinct parts of the lungs?
- conducting zone - anatomical dead space - respiratory zone - split into 7 generations
*show a diagram of dead space:
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how to increase dead space ?
- use a ventilator
how to decrease the dead space?
- tracheostomy
what is
transmural pressure
transpulmonary pressure
transrespiratory pressure
transmural = across several tissues
transpulmonary = difference between alveolar and intrapleural pressure
transrespiratory pressure = tells us if there is airflow into or out of the lung
what is the snorkel analogy saying?
a longer snorkel means more dead space which means the lungs may not be able to shift - poiseuilles law: a decrease in diameter by a half increases resistance by x16
how does the alveolar volume and pressure in alveolar change ?
- at the start there is no transpulmonary pressure - there is no pressure change - the chest wall expands and creates the negative pressure - the pressure gradient is established - the pressure gradient equalises
how to work out the orientation of the gradient?
inside - outisde
how do we normally inspire?
in terms of pressure
- we inspire when there is a lower pressure inside the lungs
- it is possible to ventilate using positive pressure breathing
this is when we increase the pressure outside by using a ventilatory or CPR
what is the chest wall relationship?
- the elastic recoil of the lungs inwards and the outward recoil of the rib cage are in equilibrium - the lungs are surrounded by a visceral pleural membrane whilst the inner surface in covered in a parietal membrane
what does breaching in the pleural cavity result in?
- haemothorax - bleeding in chest cavity - pneumothorax - perforated chest wall
how is air flow generated?
- goes from high pressure - to low pressure *****
what is negative pressure breathing?
this is inspiration with a lower pressure in the lungs (NORMAL)
what is positive pressure breathing?
- this is pressure increased abnormally in situations like CPR and ventilation
what is transmural pressure?
pressure inside - pressure outside this is the pressure across the tissues a positive transmural pressure leads to expiration
what is transpulmonary pressure?
- this is a difference between the alveolar and interpleual pressure this pressure dictates the airflow
what is the chest wall relationship graph?
*** will go over in later lecture
how are lung function tests carried out?
- patient wears nose clip and inhales to total lung capacity - the patient exhales as hard and fast as they can until 6 seconds have passed - inspect the graph and look for -slow starts - early stops or - intramanouver variability
how to calculate the FEV1/ FVC ratio? (forced vital capacity)
volume of air forced out in 1 second / volume of air at max inhalation
what does obstructive lung disease do to the lung function tests?
FEV1 and FVC is much lower while FET is much higher (takes longer to expel). - forced expiratory time
what do restrictive lung diseases do to the lung function tests?
FVC is lower while FEV1 is relatively high as the airway conduction pathway is clear (not like in COPD).
what does the volume time graph look like?
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what peak flow test?
this measures the force of exhalation instead of the volume or time taken
how to measure the peak flow?
look at the graph which is peak expiratory flow rate / age and look at the max point
how to calculate alveolar ventilation
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how to calculate alveolar ventilation
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