Pulmonary Function Testing Flashcards

The flow-volume loop in a patient with a fixed upper airway obstruction shows:

Answer: Flattening of both the inspiratory and expiratory limbs

Fixed upper airway obstructions (such as tracheal stenosis) truncate both inspiratory and expiratory flows equally, producing a flattened box-like loop.

A variable extrathoracic obstruction (e.g., vocal cord dysfunction during inspiration) flattens which portion of the flow-volume loop?

Answer: Inspiratory limb

Variable extrathoracic obstructions worsen during inspiration because negative pressure draws the obstruction into the airway, flattening the inspiratory limb.

The maximum voluntary ventilation (MVV) test measures:

Answer: The maximum volume breathed in and out over 12–15 seconds, extrapolated to one minute

MVV assesses the maximum minute ventilation achievable with maximal effort, reflecting overall ventilatory capacity including respiratory muscle strength and airway patency.

Which PFT finding is most consistent with pulmonary fibrosis?

Answer: Reduced TLC, reduced FVC, normal or elevated FEV1/FVC, reduced DLCO

Pulmonary fibrosis causes restrictive physiology with reduced TLC and FVC, elevated FEV1/FVC ratio, and reduced DLCO due to loss of alveolar-capillary surface.

Nitrogen washout and helium dilution are techniques used to measure:

Answer: Functional residual capacity (FRC)

Both nitrogen washout and helium dilution techniques measure FRC by using inert tracer gases to calculate the volume of gas in communication with the open airways.

Acceptable spirometry requires that the technician ensure the patient performs a maneuver that is:

Answer: Repeatable within 150 mL for the two best FVC and FEV1 values

ATS/ERS acceptability criteria require reproducibility of the best two FVC and FEV1 values within 150 mL to ensure test reliability.