Lung volumes Flashcards
What is a lung capacity
Sum of two or more lung volumes
What is an average tidal volume
7ml/kg
500mls
Define tidal respiration
the volume of gas inhaled or exhaled during normal respiratory cycle
Define inspiratory reserve volume
is the maximum volume of additional air that can be inspired over and above VT after normal end inspiratory level during tidal breathing
What is an average inspiratory reserve volume
45ml/kg
3150mls
What affects IRV
Kyphosis
Rib fractures
COPD
Anything reducing range of movement of diaphragm and chest wall
Expiratory reserve volume define
maximum volume of additional air that can be expired from the end expiratory level following normal tidal exhalation
What is an average value for expiratory reserve volume
15ml/kg
1050mls
Residual volume define
the volume remaining in the lungs at maximum exhalation
What is an average volume for residual volume
15ml/kg
1050mls
What is FRC
‣ The volume of gas present in the lung at end expiration during normal tidal breathing
What is FRC made up of - what is its volume therefore
ERC + RV
2100mls
30ml/kg
Vital capacity
Maximum volume change between full inspiration and full expiration
67ml/kg
4.8L
ERV + VT + IRV
Inspiratory capacity
VT + IRV
Maximum inspiration capacity from FRC
What is an average inspiratory capacity
52ml/kg
3.6L
TLC define
Volume of gas in the lungs after maximal inspiration
What is an average value for TLC
82ml/kg
5.7L
How do lung volumes change with age 4
TLC increases until reaching maximal heigh then remains similar
FRC increases until maximal growth and slowly increases
Residual volume increases until maximal growth and then slowly increase throughout life, is responisble for all of the increase in FRC with a fall in ERV later in life
Draw and label a volume loop
What can spirometry measure in terms of lung volumes
◦ All lung volumes with the exception of residual volume can be measured in this way
What other ways of measuring lung volumes are there 3
Gas dilution
Body plethysmography
Multiple breath nitrogen washout test
What gas is used in the gas dilution method of assessing lung volumes? Why?
5% helium, does not diffuse across alveolar capillary barrier so any drop is due to redistribution in the lung
How does the gas dilution of lung measurements work
◦ Patient breathes 5% helium, through a spirometer (known volume and concentration)
‣ does not diffuse across alveolar capillary barrier (insoluble), any drop is due to redistribution in the lung
◦ At the end of tidal expiration a spirometer containing a known concentration is opened ot the patient
◦ The patient breathes in an out until He equilibrates
◦ The new concentration is then used to work out volume
‣ Concentration of helium x volume in spirometer (prior to opening) = concentration at equilibrium x (volume in spirometer + FRC)
‣ C1 x V1 = C2 x V2 (where V2 is V1 + FRC)
‣ If the same spirometer is opened to the patient after full inspiration the TLC can be calcualted
What equation is the foundation of the gas dilution method
◦ Patient breathes 5% helium, through a spirometer (known volume and concentration)
‣ does not diffuse across alveolar capillary barrier (insoluble), any drop is due to redistribution in the lung
◦ At the end of tidal expiration a spirometer containing a known concentration is opened ot the patient
◦ The patient breathes in an out until He equilibrates
◦ The new concentration is then used to work out volume
‣ Concentration of helium x volume in spirometer (prior to opening) = concentration at equilibrium x (volume in spirometer + FRC)
‣ C1 x V1 = C2 x V2 (where V2 is V1 + FRC)
‣ If the same spirometer is opened to the patient after full inspiration the TLC can be calcualted