L15 Flashcards
Lung compliance is increased in emphysema
BECAUSE
chronic emphysema increases airway resistance.
Both statements are true but are not causally related
what does Spirometry measure
Lung volumes – How much?
Air flow rates – How fast?
what do you use to mesure lung function
Pulmonary Function tests, Lung Function tests
define tidal volume (VT or TV)
Volume of air moved in and out during normal quiet
breath
what is the approx value of tidal volume
~ 500 ml
define Inspiratory reserve volume (IRV)
Extra volume that can
be inspired with
maximal inhalation - external intercostal
muscles.
define Expiratory reserve
volume
Extra volume that can
be exhaled with
maximal effort - internal intercostal and
abdominal muscles.
define residual volume (RV).
Volume remaining
in lungs after maximal
exhalation.
when exercising what lung volumes will increase
When you are exercising you need to breath in more O2 (inspiratory reserve) and breathe out CO2 (expiratory reserve)
define Inspiratory capacity
maximal breath in
Vt + IRV
define Vital capacity
Maximal breath into out
Volume of air can shift
in/out of lungs (IC +ERV)
define functional residual capacity
• Lung volume at the end of a normal
expiration when there is no inspiratory
or expiratory muscle contractions (ERV +RV)
define total lung capacity
Total volume in lungs
when maximally full =
(VC + RV)
which of the lung capacities is not clinically relevant
inspiratory capacity
which of the lung capacities is the most clinically relevant
vital capacity
because it is vital
what is the “resting equilibrium” position for the lungs + thorax (in “elastic” combination)
functional residual capacity
what are the normal values for functional residual capacity
Normal large FRC ~2.4 L (~40% of TLC),
“Topped up” each breath by the smaller
resting Vt ~500 ml (only ~20% top up!)
what is the importance of large FRC
At all times during the breath cycle O2 and CO2 exchange can occur between alveolar gas and the pulmonary capillaries.
Prevents large fluctuations in the composition of alveolar gas
eg you don’t want to go from 0% O2 - 100% O2 or from 0% CO2 to 100% CO2
when you have a restrictive lung disease what does that do to your breathing
breathe more shallowly and rapidly
what happens in terms of lung volumes in restrictive lung disease
decrease in compliance means that you need to do a lot of work to get air in
Therefore people with this breath more shallow
The whole spirometry trace has gone down
This is because the lung is not expanding
VC ↓ IRV ↓ ERV ↓ RV↓ FRC ↓ TLC↓
what happens to the way someone breathes in OBstructive lung disease
Increased work due to increased airway resistance,“narrow pipes”, breathe more slowly and deeply