Pulmonary Function Equipment

Question-and-answer flashcards covering major equipment used in pulmonary function testing, including spirometers, flow sensors, breathing valves, gas analyzers, and plethysmographs.

What is the "gold standard" volume-displacement spirometer design?

The water-seal spirometer.

Name two major advantages of a water-seal spirometer.

High accuracy and few moving parts.

List two disadvantages of water-seal spirometers.

They are large/heavy and prone to leaks that require maintenance.

How much volume can a typical water-seal spirometer bell hold?

Approximately 7–10 L.

Why is temperature correction needed with water-seal spirometers?

Gas volume inside the bell changes with temperature, affecting accuracy.

What mechanical element converts bell movement into an electrical signal in many water-seal spirometers?

A potentiometer attached to the rotating drum or kymograph.

Describe the basic construction of a dry rolling-seal spirometer.

A lightweight piston moves inside a cylinder; the flexible seal rolls on itself instead of sliding.

State one advantage of dry rolling-seal spirometers.

They can interface with a paper recorder for easier calculations or rebreathing tests.

Give two disadvantages of dry rolling-seal spirometers.

Rolling seal sticking and increased mechanical resistance, both requiring maintenance.

What is the maximum cylinder volume for most dry rolling-seal spirometers?

About 10–12 L.

How does a bellows (wedge) spirometer measure volume?

A collapsible bellows expands and contracts, with movement recorded by a stylus on paper.

State one advantage and one disadvantage of bellows spirometers.

Advantage: can use a paper recorder. Disadvantage: bellows may stick and often measure only expiratory flows.

What type of flow-sensing device uses a rotating vane connected to precision gears?

A turbine respirometer (e.g., Wright respirometer).

Why are turbine respirometers generally unsuitable for full PFTs?

They do not meet ATS accuracy standards; they are mainly used for screening.

Name two advantages of turbine respirometers.

Compact size and the ability to measure a wide range of volumes with multiple scales.

Describe the working principle of a pressure-differential pneumotach.

Gas passes through a resistive element causing a pressure drop; the pressure difference is proportional to flow and measured by a transducer.

What are two common resistive elements used in pressure-differential pneumotachs?

Fleisch bundles of capillary tubes and Silverman/Lilly wire screens.

Give two advantages of pressure-differential pneumotachs.

Disposable options reduce infection risk and built-in heaters prevent condensation; they meet ATS standards.

State one limitation of pressure-differential pneumotachs.

Condensation can alter calibration, requiring frequent checks.

How does a heated-wire flow sensor detect flow?

Gas cools a heated platinum wire; the cooling rate is proportional to flow.

Why must heated-wire sensors be kept above 37 °C?

To avoid water condensation on the sensing wire, which would distort readings.

What correction is needed when using heated-wire sensors with gases other than room air?

Gas-specific correction factors for density and thermal properties.

Explain the Pitot-tube principle in spirometry.

Flow is inferred from the pressure of gas impacting small tubes; multiple tubes connect to a transducer to measure velocity-related pressures.

List one advantage and one disadvantage of Pitot-tube flow sensors.

Advantage: meet ATS standards and are easy to clean. Disadvantage: linearity must be routinely verified and electronic zeroing is needed.

What makes portable spirometers attractive for field testing?

They interface with small PCs, use disposable pneumotachs, and are easy to operate in diverse settings.

What is the simplest type of breathing valve used for SVC and VT maneuvers?

Free-breathing (demand) valve with two or more solenoid-controlled ports.

List two key concerns when selecting a breathing valve.

It must be leak-free and add minimal dead space to the breathing circuit.

How does a two-way non-rebreathing (directional) valve work?

T-shaped body with inspiratory and expiratory diaphragms that prevent gas mixing between the ports.

Which oxygen analyzer uses a polarographic electrode similar to blood gas analyzers?

The Clark-type polarographic oxygen electrode.

Give one drawback of polarographic O₂ analyzers in PFT labs.

Contamination can slow response and complicate calibration.

What oxygen analyzer employs a heated zirconium fuel cell?

The zirconium oxygen sensor used for breath-by-breath metabolic studies.

Why is helium the carrier gas in gas chromatography for pulmonary testing?

Its high thermal conductivity provides excellent sensitivity in the thermal conductivity detector.

Which analyzer technique is standard for single-breath DLCO CO measurement?

Infrared absorption analyzer for CO.

State two clinical uses for infrared CO₂ analyzers.

Exercise testing/metabolic studies and bedside capnography.

What analyzer method is preferred for nitrogen washout testing?

Emission spectroscopy with an ionization chamber.

How does a thermal conductivity analyzer differentiate gases?

By measuring the rate at which different gases conduct heat away from a heated filament.

What pulmonary measurements require thermal conductivity analyzers?

Closed-circuit FRC and DLCO tests that involve helium analysis.

Define "body box" in pulmonary function testing.

Whole-body plethysmograph used to measure thoracic gas volume (TGV) and airway resistance (Raw).

Which physical law underpins constant-volume plethysmography?

Boyle’s law: P₁V₁ = P₂V₂ at constant temperature.

Why is a pneumotach needed inside a plethysmograph?

To measure mouth flow for calculating airway resistance and verifying volume changes.

What role does the shutter mechanism play during Raw measurement?

It briefly occludes airflow so mouth pressure reflects alveolar pressure, enabling calculation of resistance.

Differentiate constant-volume (pressure) vs. flow plethysmographs.

Constant-volume boxes calculate volume from pressure changes, whereas flow boxes integrate flow through a wall pneumotach to obtain volume.

What maintenance issue often affects rolling-seal and bellows spirometers?

Mechanical sticking of the seal or bellows, increasing resistance and reducing accuracy.

Why must flow sensors often be calibrated between patients?

To correct for sensor drift, temperature/humidity changes, and ensure compliance with ATS accuracy standards.

What basic feature enables many modern portable spirometers to simplify infection control?

Use of disposable pneumotach cartridges or flow sensors.