1. Impulse oscillometry By Dr/ Hossam EL-din mohamed
Lecturer of chest diseases
Ain Shams university

2. At the end of this lecture you would be able to:
List the different components of IOS.
Interpret IOS results.
Compare the variations in IOS results among different disease states.
Describe the limitations of IOS.
Describe the assessment of bronchial hyperreactivity using IOS.

3. Impulse oscilomety (IOS)
Ohm‘s Law:
Resistance = pressure
flow

4. AIRWAY RESISTANCE
The relationship between pressure and flow tells us about airway resistance.
Flow
Pressure
Low Resistance
High Resistance

5. IOS Methods of measurement of airway resistance Occlusion technique
Impulse oscillometry
Bodyplethysmography

6. OCCLUSION
occlusion  pressure
PT  flow

7. Forced Oscillation Technique (FOT):
Apply frequencies from outside to the airways
measure pressure changes
Range: from 1 Hz to 30 Hz

8. One frequency

9. Two frequencies

10. Sum of two frequencies

11. Rectangular pulse: all frequencies

12. Simplified approach: pressure waves generate pressure in the lungs
waves are reflected in the lungs
reflected waves carry information about the pressure at different places in the lungs
flow measured via PT
reflected waves are analysed in respect of pressure and frequency
 Resistance = pressure/flow
can be calculated for different frequencies (= areas)

13. Different Frequencies
High frequencies: low penetration
upper (central) airway
Low frequencies: deep penetration
total airways (central and peripheral)

14. Impulse Penetration
Slow Impulses 5Hz
Fast Impulses 20 Hz

15. Impedance Z = R + jX
Impedance describes a complex (mathematical sense) airway resistance which includes two components, the real resistance R and the imaginary reactance X.
Reactance X (Capacitive-inertial storage of energy)
Reactance consists of two components. The positive
inertial portion increases with frequency and the negative
capacitive portion decreases frequency

16. X at 5 Hz: X5 Distal capacitive reactance f at X=0: Fres Resonant frequency The ability to store energy in the capacitance (elastic recoil) is prerequisite for passive expiration. Inertance has minor clinical relevance Impedance Z Respiratory impedance, i. e. the interaction between resistive and reactive properties of the respiratory system, is primarily measured by the oscillometric method.