Explain simple spirometry
- Pt takes larges forces inspiration and blows as hard as they can for as long as they can
- The results are plotted on a volume vs time on a vitalograph
- Measurements are compared to standards accounting for age, sex and height (normogram)
- Gives you many different readings such as TLC, FEV1/FVC etc
What is the normal picture of a vitalograph? What does it show?
- Initial rapid rise with plateau
- Shows forced vital capacity and forced expiratory volume in 1 second
- FEV1:FVC = 70%
What is FVC?
- Forced vital capacity
- Maximum volume which can be expired from full lungs
What is FEV1?
-Forced expiratory volume in 1 second
Describe an obstructive pattern on a vitalograph
-Same FVC but with decreased slope so FEV1:FVC
Give 3 diseases which produce obstructive vitalographs
- COPD
- Asthma
- Emyphysema
Describe a restrictive pattern on a vitalograph
-Decreased FVC with not effected FEV1 producing a normal or high ratio
(lungs cannot fill)
Give 3 causes of restrictive lung diseases
- Fibrosis
- Interstitial lung disease
- Pneumothorax
Define tidal volume
-Volume of air in and out with each breath (typically 0.5L)
Define Inspiratory reserve volume
-Extra vol which can be breathed in over that at rest
Define expiratory reserve volume
-Extra vol which can be breathed out over rest
Define residual volume
-vol remaining in lungs after maximum expiration
What is a capacity?
-two or more volumes added together
define vital capacity
-max inspiration to max expiration (TV+IRV+ERV)
Define inspiratory capacity
-maximum inspiration from resting expiration (TV+IRV)
Define functional residual capacity
-vol air in lungs at resting expiratory level (ERV+RV)
Define total lung capacity
-Vol of air after maximal inhalation (VC+RV)
What factors influence vital capacity?
Inhalation factors -Lung compliance -Force of inspiratory muscles Exhalation factors -airway resistance
What is a disadvantage of single breath spirometry?
-technique greatly effects result ie very user dependant
What are the advantages of lung-function tests?
- Non-invasive
- Cheap
- Technically simple
- Measures volume and flow
If the obstructive pattern on a vitalograph is reversible what does it indicate?
-Asthma
What is Peak expiratory flow rate?
-Simple cheap measurement screening for airway narrowing by measuring the peak flow rate when the lungs are full so there is minimal resistance
What is a flow volume curve?
-A graph which plots volume vs flow using the measurements from a vitalograph
Why when the lungs are full is flow the fastest?
-Airways stretched meaning minimal resistance with maximum recoil -> fastest flow
What are the advantages of volume flow curves?
- Sensitive
- Can detect problems early in disease
- Can discriminate where in the tract the problem lies
Describe and explain an obstructive pattern of disease on a volume flow curve
- Normal upwards slope with an indented downwards slope
- As exhalation occurs and the airways begin to narrow, the obstruction greatly increases resistance more than usual and the flow declines
- the narrower the airways to start the more rapidly it falls
Describe a restrictive pattern of disease on a volume flow curve
-Narrowed flow volume curve as there is no problem with flow but an overall decrease in volume
How do you measure residual volume? Describe this test
- Helium dilution
- helium is a non-toxic inert gas which cannot cross capillary membrane
- Pt. breaths in helium from container with known He conc until equilibrium is reached
- The new conc of He in the chamber is used to calculate FRC from which you can calcuate RV
Describe Nitrogen washout
- Measures anatomical deadspace
- Patient takes max inspiration of 100% O2
- O2 reaching alveoli mixes with residual volume where as air in conducting portion will be 100% O2
- Pt exhales through one way valve and %N2 in inhaled air and volume of air calculated
- A graph of n2 vs exhaled vol is plotted
- initially n=0% but as alveolar air exhaled and mixes with deadspace air a plateau is reached after which only alveolar air exhaled
- Deadspace determines from graph where area A = Area B
Describe a test used to measure diffusing capacity of the lung
- CO transfer factor
- Measures rate of transfer of CO from alveoli to blood in ml/min/kPa
- CO has increased affinity for Hb so only limiting factor is diffusion capcity
- Pt. takes rapid and full inspiratory vital capacity of air containing low CO conc.
- Breath held for 10 seconds
- Alveolar sample collected mid expiration (discard dead space)
- remaining conc of CO in sample measured