Transcript lung-function

PULMONARY FUNCTION TESTS
• Effort dependent tests
- Forced expiratory volumes/flow rates
• Effort independent tests
- Relaxed vital capacity
- Helium static lung volume
• Gas diffusion tests
- CO transfer factor
- Arterial blood gases (resting)
- SaO2 during exercise
DYNAMIC LUNG VOLUMES (SPIROMETRY)
Volume (L) vs Time (s) curve
- Forced expiratory manoeuvre: from TLC to RV
• Forced expiratory volume in 1 s : FEV1 (L)
• Forced vital capacity
: FVC (L)
• Forced expiratory ratio
: FER (FEV1/FVC%)
EXPIRATORY FLOW RATES
Flow-volume curve: dv/dt (flow-rate) from volume time curve
- Flow rate (L/s) plotted against forced expiratory volume (L)
- from TLC to RV
EXPIRATORY FLOW RATES
Shape of expiratory flow-volume curve:
• Volume dependent expiratory airway closure
- asthma, chronic bronchitis
• Pressure dependent expiratory airway closure
- emphysema
EXPIRATORY FLOW RATES
From flow-volume curve:
• Peak expiratory flow rate (PEFR)
- expressed in L/min (L/s x 60)
- also measurable with simple linear peak flow meter
• Forced expiratory flow rate (FEFR) at a % of FVC
- FEFR 50%, FEFR 75%
Obstructive Restrictive
PEFR
FEV1
FVC
FEV1/FVC ratio
FEV1 response
to 2-agonist


Normal(Asthma)
(COPD)
< 75%
> 15% (Asthma)
<15% (COPD)
Normal


> 75%
No response
BRONCHIAL CHALLENGE TESTING
• Exercise
• Methacholine/Histamine
- marker of airway hyperreactivity
- concentration to produce 20%  FEV1
• Allergens/Chemicals
- early and late responses
- diagnosis of occupational asthma
EXERCISE TESTING
• FEV1 or PEF post exercise - Asthma
• SaO2 during exercise in interstitial lung disease
- to monitor treatment response
• Differentiate cardiac vs respiratory dyspnoea
- heart rate vs oxygen uptake vs ventilatory rate
STATIC LUNG VOLUMES
• Effort independent test
• Helium dilution / N2 washout : functional residual capacity
• (RV = FRC - ERV)
(TLC = VC + RV)
• TLC in hyperinflation (Emphysema)
TLC in restrictive lung disease
• Gas trapping in COPD:
(RV/TLC%)
(RVC - FVC/RVC%)
• TLC adds little to RVC and FVC
TRANSFER FACTOR (DIFFUSION CAPACITY)
• CO diffusion across alveolar-capillary barrier
• TLCO - total lung transfer for CO
• TLCO: Anaemia, Emphysema, Int lung disease, Pulmonary
oedema, Pulmonary emboli
• To monitor treatment response in In lung disease
SUMMARY OF LUNG FUNCTION PATTERNS
Parameter
PEFR
FEV1
FVC
FEV1/FVC%
Gas transfer (TLCO)
FEV1 response to
 2-agonist
Obstructive
Restrictive

Normal


Normal in asthma

Reduced in COPD
<75%
>75%
 in Emphysema

Normal in Asthma
> 15% in asthma
< 15% in COPD
No response