Lung Volumes and Gas Distribution - Testing Equipment RET 2414L Pulmonary Function Testing Module 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