Lung function tests Flashcards
what is peak expiratory flow?
maximal speed of airflow as the patient exhales in L/min
what does (1) increase or (2) decrease in PEF value reveal
increase:
- lung function is better
decrease:
- lung function has gotten worse
what is FVC (forced vital capacity)
maximal amount of air (L) that a patient can forcibly echale after taking in maximal inhalation
what does a spirometer record and what can it generate
- records:volume of air that is breathed in and out
- generates: tracings of air flow called a pneumotachograph
what 3 things can tracings on a pneumotachograph allow you to observe
- tidal volume
- vital capacity
- flow rate of air movement
what is always bigger, FVCstanding or FVCseated
FVCstanding is always larger than FVseated
what 2 things can high intrathoracic pressure result in and what can this lead to when observing FVCstanding of patients?
- reduced cardiac output
- reduced cerebral blood flow
can lead to patients becoming unsteady on their feet in FVCstanding patients
outline 4 steps of how a spirometer works
Think:
1. water seal
2. Pressure and jar
3. Pen
4. Relationship to pen and volume breathed in and out
- expired gas passes into water seal
- increased pressure causes jar to rise
- movement is then transmitted to a pen
- pen movement is proportional to volume breathed in and out
how is inspiration displayed as on a spirometer pen trace?
it is displayed as an upward deflection
how is expiration displayed as on a spirometer pen trace?
it is displayed as an downward deflection
how do you calculate inspiratory capacity from a spirogram?
Tidal volume (Vt) + Inspiratory reserve volume (IRV)
how do you calculate functional residual capacity from a spirogram?
Expiratory reserve volume (ERV) + residual volume (RV)
what 5 things can forced flow volume measurements show us (FVC and FEV1)
think:
- blowing out
- expelling air from lungs
- treatment
- diases
- age/growth
can show us:
- how much air can the subject blow out
- how fast the air is expelled from lungs
- response to treatment
- progression of disease
- change with age/growth
what 2 things reduce how much air a subject can blow out in forced flow-volume measurements
For second part think narrowing and closure
- restrictive disorders
- airwary narrowing precipitating early airway closure (asthma or CF)
what can a pattern change in flow-volume curve indicate?
can indicate site of obstruction
- what is FEV1 on spirogram
maximal volume exhaled in the first second
what are the 3 typical patterns of Forced flow-volume measurements in obstructive airway diseases and give a reason for why
think FVC, FEV1 and FEV1/FVC ratio
for the reason think speed of air
- FVC nearly normal
- FEV1 markedly reduced
- FEV1/FVC ratio is less than 70%
1 reason why is that narrowed airways reduces the speed at which air can be breathed out
what obstructive disease does it indicate someone has if there is improvement of a volume-time graph curve, towards the normal, after treatment with a bronchodilator?
it indicates the person has Asthma
what obstructive disease does it indicate someone has if there is NO improvement on a volume-time graph curve after treatment with a bronchodilator?
it indicates the person has COPD
what are the 3 typical patterns of Forced flow-volume measurements in restrictive airway diseases
think FVC, FEV1 and FEV1/FVC ratio
- low FVC
- low FEV1 but is proportionality to FVC is normal
- FEV1/FVC ratio is ≥ 70% (elevated)
why is there low FVC in restrictive diseases like lung fibrosis?
because lungs are stiff so cannot expand adequately
what does the width of a volume flow loop show?
- shows the vital capacity/forced vital capacity
what does the rapid rise at the beginning of the expiratory portion of the flow volume loop show?
shows large airway movement
what type of airway movement does the sloped section of the expiratory section of a flow-volume loop show?
shows small airway movement
outline the differences in a flow volume loop between someone with an obstructive disease (e.g COPD, asthma, tracheal-stenosis) and a normal flow volume loop
hint: think:
- expiration line
- think what does this look like if the small airways are obstructed
- think waht this line looks like if the large airways are obstructed
NORMAL flow-volume loop:
- relatively linear expiratory slope
- normal/expected steep rise in the inital portion of the expiration line
OBSTRUCTIVE disease flow-volume loop:
- if **smaller/lower airways ** are obstructed, there is a smaller angle or caving in of the usually linear expiratory slope on the flow-volume loop
- if upper/large airways are obstructed, initial portion of expiration line can also have shorter steep line.
what is the physiological reason for why flow-volume loops are narrowed in restrictive lung diseases
- This is because the lungs suffering from restrictive diseases are not able to expand to the same volume as healthy lungs, meaning the Vital capacity/Forced vital capacity is reduced, thus narrowing the loop.
outline the differences in a flow volume loop between someone with a restrictive disease (e.g lung fibrosis, interstitial lung disease) and a normal flow volume loop
hint:
- difference lies in the width of the flow volume loop
NORMAL flow-volume loop:
- relatively linear expiratory slope
- normal/expected steep rise in the inital portion of the expiration line
- normal width of the flow-volume loop, meaning normal VC/FVC
RESTRICTIVE disease flow-volume loop:
- relatively linear expiratory slope
- normal steep rise in initial portion of expiration line
- Difference is that there is low VC/FVC, therefore the width of the flow-volume loop is lower, narrowing the loop
what is the physiological reason for why flow-volume loops have a shorter steep line and/or caved in slopes in obstructive diseases?
this is because the obstruction to the upper and/or lower airways reduces the speed at which air in the airways can be breathed out.
