Ventilation Flashcards
What is ventilation?
Movement of air
What is tidal volume?
volume of air inspired and expired during regular breathing
500 mL in a 70 kg man.
What is inspiratory reserve volume (IRV)?
volume of air that can be inspired after a tidal inspiration
2.7 L in a 70 kg man
What is the expiratory reserve volume (ERV)?
volume of air that can be expired after a tidal expiration
1.3 L in a 70 kg man
What is residual volume (RV)?
volume of air that cannot be emptied from the lungs
1.2 L in health adults
What is total lung capacity (TLC)?
maximum capacity of the lungs
(TLC) = RV + IRV + TV + ERV
6 L in a 70 kg man
What is functional lung capacity (FRC)?
volume of air in the lungs following a tidal expiration at rest
(FRC) = RV + IRV
• Equilibrium of mechanical forces of lung
• Needs to be imbalanced to stimulate ventilation
What is inspiratory capacity (IC)?
maximum volume of air the lungs can draw in from the equilibrium FRC point
(IC) = TV + IRV
What is vital capacity (VC)?
volume of air between the maximum and minimum achievable volumes
(VC) = TLC – RV; or, TV + IRV + ERV
How does a normal inspiratory trace look? What happens in a respiratory trace when a deep breath is taken?
see notes
What factors cause differences in lung capacity?
Height, body size, sex, age, genetic, areobic fitness, disease
What is the conducting zone?
- 16 generations
- No gas exhange
- Ca. 150ml
- anatomical dead space
What is the function of the conducting zone?
Defense (mucus)
Speech (layrnx)
Warming and humidying air for gass exchange
How does the speed of air change as it moves down the airway?
Slowed as cross sectional area increases
What is the respiratory zone?
Alveoli (parenchymal airway tissue)
Mostly terminal but some repiratory bronchioles have some
What is dead space?
parts of the airways that do not participate in gas exchange
What are the types of dead space?
- Anatomical:
- All of conducting airway and upper respiratory tract (nasal cavity to larynx) - Alveolar dead space/non perfused parenchyma
- respiratory tissues unable to participate in gas exchange
- Usually due to absent blood flow
- In healthy person 0 - Physiological dead space:
- Sum of anatomical and alveolar dead space
How would you decrease deadspace?
Trachestomy
How would you increase deadspace?
Snorkelling
Anaesthetic circuites
What is alveolar ventilation?
difference between tidal volume and dead space
Valv = VT – VD
What are the natural direction of recoil of the chest wall and lungs?
Chest wall: out
Lungs: in
When are the chest wall and lung forces at equilibrium?
FRC
What balances of forces causes inspiration?
Inspiratory muscle effort and chest recoil is larger than lung recoil
What balances of forces causes expiration?
lung recoil and expiratory muscle effort is more than chest recoil
What is the intrapleural cavity pressure in healthy individuals?
Negative
-5 cmH2O
How is airflow stimulated?
- Increasing atmospheric e.g positiv pressure breathing (ventilator)
- Decreasing intrapleural pressure e.g negative pressure breathing (normal)
How does negative pressure breathing occur?
- diaphragm contracts downward towards the abdomen (decrease in intrapleural pressure)
- the external intercostals pull the ribcage outwards and upwards
- Creates partial vacuum
- decrease in pressure
- visceral pleura is pulled outwards which inflates the lungs
- Alveolar pressure below atmospheral pressure
- Expand until pressures equal out
What happens during positive pressure breathing?
- increase in alveolar pressure
- expansion of lung tissue against the resistance of the thoracic wall
- increase in pleural pressure which causes an expansion of the chest wall
intra-pleural volume is fixed and resistant to change
What is haemothorax?
- accumulation of blood in the pleural cavity
- Accumulates slowly
- Reduces space to inflate
- Increases effort to inhale
- Limits overall achievable volume
What is pneumothorax?
- Puncture
- Lung tension compromised
- Resistance of outward and inward force disappears
- Lung recoils and chest expands
What are the 3 transmural pressures (across tissue pressures)?
pressures inside relative to the pressure outside: always pressure inside minus pressure outside
- transpulmonary pressure: difference in pressure between the alveolar sacs and the pleural cavity
- (PTP= Ppl– Palv)
- transthoracic pressure: difference in pressure between the pleural cavity and the atmosphere
- (PTT= Patm– Ppl)
- transrespiratory system pressure: difference in pressure between the alveolar sacs and the atmosphere
- Dictates ariflow
- (PRS= Patm– Palv)
What are atmospheric, alveolar and pleural cavity forces at rest?
P(atm)=0
P(alv)=0
P(pl)= -5
How are lung volumes calculated?
- breathing in and out with a nose clip to recreate the spirometry trace
- maximal expiration from TLC as “hard and fast” as possible
What does spirometry measure?
- forced vital capacity (FVC)
- forced expiratory volume in 1 second (FEV1)
What is FVC/FVC1 used for?
- Diagnosis of obstructive and restrictive lung disease
What causes OLD?
- structural abnormalities in the airway that increase resistance to airflow
How does an OLD curve look?
- have a shallower curve
- FVC is reduced because RV is larger than normal due to air trapping and emphysema
How does a RLD curve look?
- initial rate of expiration is largely unchanged
- FVC is markedly reduced.
What is required for effective gas exchange?
- atmospheric air in alveolar sac
- Adquate perfusion from pulmonary capillary close to it
What is wasted ventilation?
Ventilated alveoli with no blood supply
What is wasted perfusion?
Pulmonary capillaries that perfuse non-ventilated alveoli
What part of the lung ventilates more readily?
- Base
- Effect of gravity on transmural pressure
- makes basal lung tissue more compliant
What is peak expiratory flow (PEF)?
maximum rate that the lungs can be emptied
Tested using noseclip
How is PEF measured?
Wright peak flow meter
done three times and the highest value is used
compared with the charts
How is peak expiratory flow rate calculated?
Gradient of graph
L/min
What is the difference in PEF in asthma and COPD?
COPD would have stable PEF
asthma would have variable PEF.
