1. PNEUMOTACHOMETERS

2. Differential manometer:
Small resistance
Pressure drop
Change in pressure is measured using differential pressure transducer.

3. Hot wire anemometer: Small heated element in flow path
current maintain the element at constant temperature
Output proportional to the gas flow that cools the element

4. FLEISCH PNEUMOTACHOMETER:
Rolling a thin sheet, corrugated metal with a plain strip of metal.
Inserted within a metal cover.
Small, parallel metal channels
O/p : pressure drop across the element is proportional to the flow rate of the gas.

5. Fleisch pneumotachometer:

6. Transducers: Capacitive type pressure transducer More stable
Less vibration sensitive
The viscosity of a mixture of gases,
X =fraction of gas
= viscosity

7. Calibration:
Volume flow rate can be done by passing a known gas flows through it.
Reported as BTPS
Body temperature
Ambient pressure
Saturated with water vapour
37o C , to prevent condensation
Warmer is electrically isolated

8. Venturi type pneumotachometer:
Replaces the linear resistance element
Pressure drop is square of volume flow
Drawbacks:
non-linearity of calibration
Requirement of laminar flow

9. Turbine type pneumotachometer:
Air flowing through the transducer rotates a very low mass (0.02 g) turbine blade
Rotation of the turbine interrupts the light beam from LED.
Phototransistor produces a train of pulses.

10. Turbine type pneumotachometer:

11. Measurement of volume:
Volume in single breath
Total volume in a given time
Output voltage is proportional to the pressure difference at the manometer input
The output

12. Measurement of flow and volume:

13. Flow volume curve:
Instantaneous maximum expiratory flow rate versus volume
Shape of the curve obstructive airway
disease
Time consuming and expensive

14. Area of the flow volume:
Area under the maximum expiratory flow volume curve (AFV) is a sensitive indicator of lung function impairment.
VT = total volume exhaled during the time.

15. Nitrogen washout technique:
Indirect determination
Nitrogen concentration is plotted versus volume during the expiration.

16. Pulmonary function analyzer:
Nitrogen analyzer
Vacuum pump
X-Y recorder
Digital displays
Other electronic circuits

17. Pulmonary function analyzer:

18. Impedance pneumography:
Indirect measurement
Measurement of thoracic impedance change signal

19. Impedance pneumography:

20. Impedance pneumography:
Disadvantages:
Electrode position, body posture
Accuracy is still inferior to other methods