IOS(3) - Ain Shams University

Impulse oscillometry
Dr/ Hossam EL-din mohamed
Lecturer of chest diseases
Ain Shams university
Peripheral Airway Obstruction
Central Airway Obstruction
Restrictive Lung Disease
Very simple to perform
No special breathing necessary
Minimal (no) co-operation
Use with small children (down to 2 years)
Even with animals
No forced manoeuvre necessary
No box necessary
Peripheral and Central Resistance separated
Limits of oscillometry
• Detection of restrictive diseases is possible
only in higher degree of the disease
• Differentiation between distal obstruction and
restriction is only possible with additional
determination of VC (Spiromety) or
RV (body Plethysmography)
• Patient: Sitting in upright position while measured Head in neutral
position or slight extension (not in rotation or flexion)
• Nose clipped
• Cheeks supported with hands to avoid the "Upper Airway Shunt"
To avoid artifacts in the mouth chamber:
• Mouthpiece (plastic) tight between teeth,
• Tongue beneath mouthpiece
• Lips firmly closed around mouthpiece
• (even small gaps create remarkable pressure drops and therefore low
or zero resistance)
• Take care on tight belts and clothes (increases peripheral resistance)
Interpretation of IOS
• R5 total airway resistance normal if
Lower than 150% of R5 pred.
R20 poximal airway resistance normal if
Lower than 150% of R20 pred.
X5 Distal capacitive reactance normal if
Higher than X5 pred – 0.2 kps/l/s
lung function is abnormal if either R5 or
X5 or both parameters are in the
abnormal range
Assessment of bronchial hyperactivity
R5 (50% increase = 20% decease of FEV1)
Fres (40% increase = 20% decrease of FEV1)
When 2 parameters pass threshold, terminate
Assessment of bronchial
hyperreactivity (Dilatation)
R5 Total respiratory resistance
(20-25% decrease = 15% increase of FEV1)
Fres Resonant frequency
(20 % decrease= 15% increase of FEV1)
As soon as one of these two parameters passes the
threshold, the patient is hyperreactive