lung function testing Flashcards
what are the devices used for lung function testing?
peak flow meter
vitalograph
spirometer
peak flow meter
measures peak expiratory flow rate
rapid exhaled puff from full inspiration
normal peak flow range
500-600L/min
vitalograph
sustained forced expiration from full inspiration
what does vitalograph measure?
measures volumes exhaled
FVC
FEV1
cannot measure residual volume
what is the slope on a vitalograph?
PEFR - measured by peak flow meter
normal vitalograph
FEV1/FVC greater than 0.75/ 75%
spirometer
measures continuous trace
work of breathing
2 factors to overcome = resistance and compliance
resistance
ease with which gas flows through conducting airways
compliance
expandability of lungs and chest wall
increasing resistance
obstructive disease
what happens to vitalograph in obstructive disease?
same volume but takes longer to reach, gentler initial slope and plateaus later . FVC is same FEV1 decreases and ratio of FEV1:FVC decreases
decreases compliance
restrictive disease
what happens in obstructive disease?
increasing resistance
what happens in restrictive disease?
decreasing compliance
what happens to vitalograph in restrictive disease?
lungs cannot expand normally because of restriction . FVC decreases, FEV1 decreases and the ratio stays the same . the line is the same shape as the normal line but lower
what causes variation in lung function test results?
gender
height
age
example of obstructive diseases
asthma
COPD
example of restrictive diseases?
pulmonary fibrosis
sarcoidosis
what does a spirometer measure?
IRV
VC
Vt
ERV
what does a spirometer calculate for the height/ gender/ age of the person but is unable to measure?
FRC
RV
TLC
what is Vt
tidal volume
what is IRV
inspiratory reserve volume - how much more can be breathed in on top of tidal volume
what is ERV
expiratory reserve volume - how much can be breathed out on top of tidal volume
what is RV
residual volume
what is TLC
total lung capacity
what is VC
vital capacity
what is FRC
functional residual capacity
what are capacities
the sum of 2 or more volumes
mixed obstructive and restrictive disease
reduced FEV1
reduced FVC
reduced ratio
COPD produces a similar trace for different reasons
gentler initial slope, plateaus later and is lower
COPD
lungs are hyperinflated at end of expiration and limits inspiratory reserve so IRV decreases
FRC
quantity of gas in the lungs at the end of a normal expiration
results from the balance of forces acting inwards (lung elastic) and outwards (diaphragm and intercostal muscle tone)
FRC in COPD
elastin in the lung is normally broken down by proteases but there are protease inhibitors that limit this . In COPD the balance is disturbed causing elastin destruction and hyperinflation (raised FRC) and alveolar destruction
what protease breaks down elastin
elastase
e.g. of protease inhibitor
alpha 1 anti-trypsin
alveolar destruction
causes coalescence into large air spaces - bullae
severe COPD
hyperinflation limits inspiration and airway closure limits expiration
hyperinflation
due to breakdown of elastin there is nothing limiting the chest wall pulling the lungs outwards
vitalograph trace for COPD
similar to mixed obstructive and restrictive disease
reality of COPD vitalograph
stops after a second as most COPD patients are unable to sustain expiration for much longer
sign of COPD on chest x–ray
hyperinflation, normally able to see 10 ribs max but can see more (11 or 12)
what are the methods used to measure RV or FRC?
helium dilution
body plethysmohraphy
helium dilution
known quantity of He is distributed throughout the lungs
FRC calculated from final concentration
body plethysmography
inspiratory effort against a closed shutter produces measureable pressure and volume changes in box and lungs
FRC derived using boyles law
what is wheeze?
from lower airway obstruction at level of bronchioles
heard on expiration
inside thoracic cavity
what is stridor?
from upper airway obstruction
situated outside thoracic cavity
normally heard on inspiration
what causes wheeze?
inflammation or smooth muscle spasm
greater expiratory effort increases positive intrapleural pressure, compressing small intrathoracic airways and limiting expiratory flow
what happens in inspiration in relation to wheeze?
negative intrapleural pressure generated helps increase bronchiolar diameter, improving air flow
what causes stridor?
tumours, infection, swelling, vocal cord palsy or foreign bodies
greater inspiratory effort creates a more negative pressure in thorx, which further narrows the obstructed part of the airway
what happens in expiration in relation to stridor?
the greater positive pressure generated within the airways helps increase upper airway diameter, improving air flow
how long does ventilation take?
0.75 seconds
how long does full oxygenation take?
0.25 seconds
difference in time for ventilation and fully oxygenation
allows a reserve in healthy lungs for exercise
impaired diffusion
there may not be time for full oxygenation, especially during exercise
how is diffusion capacity measured?
transfer factor - TLco
how does TLco work?
carbon monoxide used, CO binds to haemoglobin, keeping plasma partial pressure at 0
single vital capacity inhaled with 0.3% CO and 10% He
breath held in for 10 seconds then exhaled and gases measured
what is the purpose of He in transfer factor measurement?
to calculate initial volume and partial pressure of CO
what happens to CO in TLco?
known starting volume and partial pressure of CO, CO readily binds to haemoglobin and then the final volume and partial pressure of CO is measured. The reduction in volume of CO enables rate of transfer to be calculated
what is TLco measured in?
mL/kPa/min
