Lung Function Measurement & Testing Flashcards
What is FVC & FEV1.0?
FORCED VITAL CAPACITY = maximum volume that can be expired from full lungs = ~5l
FORCED EXPIRATORY VOLUME IN 1S = volume expired in 1st second (affected by how quickly air flow slows down) = >70% FVC
How is single-breath spirometry done? What information does this provide?
Subject completely fills lungs from atmosphere and then breathes out as far and fast as possible through a spirometer
Results plotted on a vitalograph - calculate FVC & FEV1.0 & extrapolate PEFR
How are FVC and FEV1.0 affected in restrictive & obstructive deficits?
RESTRICTIVE: lungs difficult to fill e.g. stiff lungs, weak muscles, problem with chest walls -> reduced FVC but normal FEV1.0
OBSTRUCTIVE: narrowed airways but lungs still easy to fill (airways stretch as well as lung) but resistance will increase in expiration so air comes out more slowly -> reduced FEV1.0 but normal FVC
What is PEFR? Why is this significant?
PEAK EXPIRATORY FLOW RATE = maximal flow rate
Insensitive measurement but used as a screening test for airway narrowing (graph of flow rate v.s. volume expired can show what part of the airway has narrowed)
Reduced PEFR indicated a problem with the large airways e..g tracheal tumour
What is helium dilution used to measure? How is it done?
Breathe in known concentration of helium and see how much the concentration of helium is reduced by mixing with air already in the lungs
Measures residual volume
Helium is insoluble, so not exchanged into the blood
What is nitrogen washout? How is it done?
Breathe in one normal breath of pure oxygen and breathe out via meter measuring % oxygen. Mixture of oxygen & air (including nitrogen) breathed out. Transition indicates when all of the serial dead space has been expired (change in % nitrogen)
Note: different airways empty at different times, therefore variation in gas composition indicates different areas of airways (can identify differences in gas exchange in different areas of the lungs - indicates ventilation/perfusion mismatch)
What is diffusion conductance? What factors affect it?
How easily carbon monoxide crosses from alveolar air to blood
TLCO = CO is insoluble and so cannot move out of the blood by binding to Hb - therefore exerts no partial pressure
Factors: pCO in alveolar gas, pCO in mixed venous blood (0kPa in this case), amount of CO which moves into the blood, lung volume
note: KCO = TLCO/alveolar volume (corrects for lung volume, e.g. diffusion conductance on person with one lung removed)
What is the vital capacity?
Maximum inspiration to maximum expiration i.e. biggest possible breath that can be taken
~ 5l
What is the tidal volume?
Volume in & out with each breath
~ 0.5l
What is the definition of the inspiratory/expiratory reserve volumes?
Extra volume that can be breathed in/out over the tidal volume at rest
What is the definition of the residual volume?
Volume left in lungs at maximal expiration
~ 0.8l
What is the inspiratory capacity?
Biggest breath that can be taken from the resting expiratory level (at end of quiet respiration)
~ 3l
What is the functional residual capacity?
Volume of air in lungs at resting expiratory level
~ 2l
What does arterial blood gas analysis measure? How is it performed? What are some advantages and disadvantages of using this?
Measures arterial pO2, pCO2, & pH (kPa/mmHg)
Puncture artery with needle and draw blood (usually radial artery)
Advantages:
- provides lots of important information
Disadvantages: - risk of infection - painful - risk of needle-stick injury etc.
What does a pulse oximeter measure? How does this work? What are some advantages and disadvantages of using this?
O2 saturation (proportion of binding sites on Hb occupied as % of maximum)
Place on thin part of body e.g. fingertip. Two wavelengths of light pass through & photodetector measures change in absorbance
Advantages:
- non-invasive
Disadvantages:
- no information on pO2, pH, pCO2
