what is pulmonary function testing?
- to understand what is happening int he lungs
How is a pulmonary function test performed?
What is TLC? Total lung capacity?
- total amount of gas contained in the lung at full inspiration
WHat is FRC?
- - volume of gas ramining in the lung at the end of a normal expiration
- - the frc is the point (lung volume) at which all these forces are in equilibrium
What is RV? residule volume
- volume of gas ramining in the lung at the end of a maximal expiration
What is tidal volume?
- voume of gas inspired or expired during a normal breath
What is the VC? vital capacity
- maximal amount that can be expired aftera full inspiration
What is FRC affected by?
- - height
- - lung, chest wall and abdominal pathology (basically elasticity)
- - gravity
- - position
What is the significance of FRC?
- - prevents closure of the small airways and alveoli during expiration
- - reduces WOB- efficient
- - allows for continuous gas exchange during inspiration and expiration
What is closing volume?
- is volume at which small airways start to close
What happens if the closing capacity increases above the FRC?
then the small airway collapse is likely to occur during breathing - alveolar collapse- blood directed to non ventilated alvolie (V/Q mismatch) - hypoxaemia
What reduces FRC?
- - age
- - obestity
- - post surgery
- - anaesthesia
- - restricitve lung disease
- - increased abdominal pressure
What are measurements of static lung volumes?
- -measurement of volume of gas in the lung at fixed points during the breathing cycle
- - lab based
- - most commonly measured
- - TLC
- - RV
- - FRC
- - total body plethysmography- pt inside a closed pressure box and inspired and expires against a closed shutter- thoracic volumes can be worked out by pressure changes
- - helium dilution- a marker gas is used to measure RV or FRC, gas is rebreathed through a closed circuit and the final concentraion is used to calculate the accessible volume of the lung
What does it mean if TLC and FRC are greater than 120% of predocted
What does it mean if RV is greater than the 120% of predicted?
- gas trapping
What does it mean if TLC, RV and FRC are < 80% predicted?
- restrictive pattern
What is vital capacity?
- max expired air after full inspiration
What is spirometry?
- - involves the measurement of forced expiration from TLC
- - provides a great deal of infomration
- -pts readings are compared to age and height match to normal values
- - identifying pathology
- - assessing extent of respiratory compromise
- - monitoring lung disease
What are the measures that are commonly taken through spirometry
- - FVC- forced vital capacity
- - VC- slow (unforced) vital capacity
- - FEV1- forced vital capacity in one second
- - MMEFR (FER 25-75%)
- - the volume of gas that can be forcefully expired in the first second
- - FEV1 is a measurement of the flow rate at which air can beblwon out of the lungs
How can FEV1 be reduced?
- - narrowing of the airways
- - loss of expiratory power
- - inadequate expiratory effort
- - inadequate inspiratory volume
Spirometry FEV1 reported as
- - as an actual volume (eg 1.0L)
- - as a % redicted (eg 40% pred)
- - as a % of FVC (ratio)
FEV1- is after one sec
-FVC- is the highest point
-FVC- the total colume of gas that be forcefully expired from TLC. Measure of the accessible lung volume (apart from RV)
- - VC (slow vital capacity)
- - used if the pts airways have a tendency to collapse during forceful expiration eg emphysema (COPD)
- - in this situation VC is more acurate than FVC
How can FVC be reduced?
- - factors that reduce inspiratory volume- ie not enough volume to start
- - factors that limit airflow- airway obstruction, loss of lung elasticity
What is the FEV1/FVC ratio?
- an adult with normal respiratory system functioning can blow out at least 75% of FVC in the first second of forced expiration
What 2 groups lung disease may be categorised?
- -restrictive pattern
- - obstructive patterns
How can we tell through spirometry if a condition is obstructive?
- - low FEV1
- - FVC- normal, increase or decreased
- - FEV1/FVC ration <75%
How can you tell through spirometry if a condition is restricitive?
- - all lung volumes are reduced
- - FEV1 and FVC are down
- - FEV1/FVC may be preserved or sometimes elevated
What is maximum mid expiratory flow rate? (MMEFR)
- - maximum mid expiratory flow rate
- - forced expiratory flow- 25-75%
- - detects obstructive changes in small airways- often the first sign of obstructive lung disease
What are the safety precautions of spirometry?
- - due to being a forced technique- can generate high intrathoracic and abdominal pressure
- - unstable heart- IHD, angina, arythmias
- - AAA
- - hernias
- - paroxysmal coughing
- - very unstable airways
When must you stop spirometry?
- - dizzy/ faint
- - angina
- - increase SOB
- - coughing
- - pain in thorax
What is peak expiratory flow rate?
PEFR- effort dependent measurement which gives info about the calibre of airways
SEE NOTES ABOUT FLOW VOLUME LOOPS
What is diffusing capacity for carbon monoxide?
- - DLCO
- - the measurement of diffusing capacity for carbon monoxide is made when ever a diffusion problem is suspected
- - a reduced DLCO indicates a limitation to diffuse eg pulmonary interstitial fibrosis
CC= CV+ RV
if CC increases above FRC or FRC falls below CC collapse will occur