Lung Volumes and Gas Distribution- Testing Equipment

RET 2414LPulmonary Function TestingModule 3.1

Lung Volumes / Gas Distribution

Open-Circuit N2 Washout

Lung Volumes / Gas Distribution

Open-Circuit N2 Washout Equipment Required

Spirometer Tissot; a water-sealed spirometer

with a volume of approximately 100 liters. Designed for collecting large volumes of exhaled air

Pneumotachometer

Lung Volumes / Gas Distribution

Open-Circuit N2 Washout Equipment Required

Free- Breathing valve Valve is opened or closed either

manually or by computer control to allow patient to be switched from breathing room air to breathing gas from spirometer or special circuit

Deadspace of valve is determined by closing off all ports and filling the valve with water. The volume of water is the deadspace volume

Oxygen source

Lung Volumes / Gas Distribution

Open-Circuit N2 Washout Equipment Required

Nitrogen analyzer Giesler Tube Ionizer

Measurement on the basis of photointensity (emission spectroscopy)

Sample is pumped (vacuum pump) into an ionizer chamber where a light is emitted and monitored by a phototube. Intensity of light is directly proportional to the percent of N2

Lung Volumes / Gas Distribution

Open-Circuit N2 Washout Equipment Required

Nitrogen analyzer Measurement range (0 – 80%) Calibrate to zero using 100% O2

(0% N2) and a known concentration of N2

Troubleshooting Sporadic or erratic zero readings

which return to the expected value are caused by aspiration of water through the needle valve

Lung Volumes / Gas Distribution

Single-Breath N2 Washout Equipment Required

Same as equipment used for open-circuit N2 washout

Lung Volumes / Gas Distribution

Closed-Circuit He Dilution

Lung Volumes / Gas Distribution

Closed-Circuit He Dilution Equipment Required

Spirometer Volume displacement

Directional breathing circuit Free breathing valve He source O2 source

Allows addition of O2 during test to replenish O2 consumed by patient

Maintains constant system volume

Lung Volumes / Gas Distribution

Closed-Circuit He Dilution Equipment Required

He analyzer Thermal conductivity analyzer

(wheatstone bridge) Measurement range (0 – 10%) Calibrate to room air (0% He) and a

know amount of He (10%), then re-zero.

CO2 and water vapor must be removed from gas prior to being analyzed

Lung Volumes / Gas Distribution

Closed-Circuit He Dilution Equipment Required

Fan or Blower Promotes gas mixing within a

rebreathing circuit

CO2 absorber (Scrubber) Needed for tests requiring rebreathing Sodium hydroxide (NaOH) – “Soda lime”

Light brown to white - exhausted Barium hydroxide (BaOH2) – “Baralyme”

White to purple – exhausted By product is water

Place upstream from H2O absorber

Lung Volumes / Gas Distribution

Closed-Circuit He Dilution Equipment Required

H2O absorber Removes moisture as patient

breaths through the system Moisture adversely affects

analyzer Calcium sulfate (CaSO4) Place in-line after CO2 absorber Desiccant color changes from blue

to pink when exhausted

Lung Volumes / Gas Distribution

Body Plethysmograph AKA: “Body Box”

Lung Volumes / Gas Distribution

Body Plethysmograph Two types

Constant-volume, variable-pressure

“Pressure Plethysmograph” Flow or variable-volume

“Flow Plethysmograph”

Both measure thoracic gas volumes and airway resistance and it derivatives

Both use a pneumotachometer to measure flow and a mouth transducer with a shutter to measure alveolar pressure

Lung Volumes / Gas Distribution

Body Box Calibration

Mouth pressure is verified with a mercury or water barometer

Flows are verified with a rotometer (flow-metering device) or a 3-liter syringe

Box pressure is calibrated by using a sine-wave rotary pump

simulates inspiratory/expiratory volumes