RPFT Lung Volume Measurement & Diffusing Capacity

Question 1

Which technique measures total lung capacity (TLC) by having the patient breathe a known concentration of helium in a closed circuit until equilibration?

Accepted Answer

Helium dilution

Answer

Helium dilution uses an insoluble tracer gas (helium) breathed in a closed circuit; TLC is calculated from the dilution factor at equilibration.

Question 2

During body plethysmography for FRC measurement, the patient performs panting maneuvers against a closed shutter. This technique measures:

Accepted Answer

Both communicating and non-communicating (trapped) gas

Answer

Body plethysmography uses Boyle's Law to measure total thoracic gas volume, including trapped (non-communicating) gas that dilution methods miss.

Question 3

In the nitrogen washout technique for measuring FRC, the patient breathes 100% oxygen, and FRC is calculated from:

Accepted Answer

The total volume of nitrogen exhaled until end-tidal N2 reaches <2%

Answer

Nitrogen washout collects all exhaled N2 over successive breaths until < 2% N2 remains; FRC is back-calculated from the known initial alveolar N2 (~80%) and total N2 exhaled.

Question 4

Which lung volume compartment represents the volume of air remaining in the lungs after a maximal forced exhalation?

Accepted Answer

Residual volume (RV)

Answer

Residual volume (RV) is the volume remaining after maximal exhalation and cannot be measured by simple spirometry; it requires gas dilution or plethysmography.

Question 5

An elevated RV/TLC ratio in a patient's pulmonary function results most commonly indicates:

Accepted Answer

Air trapping consistent with obstructive lung disease

Answer

A high RV/TLC ratio (>35–40%) indicates that a disproportionate fraction of TLC is trapped gas, a hallmark of obstructive conditions such as COPD or emphysema.

RPFT - Registered Pulmonary Function Technologist Practice Test

RPFT - Registered Pulmonary Function Technologist Practice Test

RPFT Lung Volume Measurement & Diffusing Capacity