Lung Volume Measurement & Diffusing Capacity Flashcards

The single-breath diffusing capacity (DLCO) test primarily measures the transfer of which gas across the alveolar-capillary membrane?

Answer: Carbon monoxide

DLCO uses carbon monoxide (CO) as a tracer because its high affinity for hemoglobin makes pulmonary capillary blood effectively an infinite sink, so diffusion is the rate-limiting step.

During a single-breath DLCO maneuver, how long does the patient hold their breath at TLC after a rapid inhalation of test gas?

Answer: 10 seconds

The standard breath-hold time is 10 seconds (range 8–12 s per ATS/ERS guidelines), which allows sufficient CO uptake for accurate calculation.

Which of the following conditions is most likely to cause a DECREASED DLCO with NORMAL spirometry?

Answer: Pulmonary arterial hypertension

Pulmonary arterial hypertension reduces pulmonary capillary blood volume and surface area for gas exchange, lowering DLCO despite preserved airflow.

The DLCO result must be adjusted (DLCO/VA or KCO) when a patient cannot perform a full inhalation to TLC. What does VA represent in this equation?

Answer: Alveolar volume calculated from the helium dilution during the breath hold

VA is the effective alveolar volume derived from the dilution of the tracer gas (usually helium) inhaled during the same DLCO breath, reflecting the volume actually participating in gas exchange.

A patient with significant anemia is found to have a low DLCO. What correction should be applied to interpret the result accurately?

Answer: Correct DLCO for hemoglobin concentration

Because hemoglobin carries CO, low hemoglobin reduces CO uptake independent of lung pathology; DLCO should be corrected to a standard Hb (e.g., 14.6 g/dL for men) to isolate the membrane component.

Which of the following is an absolute contraindication to performing a DLCO test?

Answer: Carbon monoxide poisoning or recent exposure to high CO levels

If the patient has elevated carboxyhemoglobin from CO poisoning or heavy smoking, the test gas CO cannot be accurately measured, making the result invalid and potentially dangerous.

According to ATS/ERS quality criteria, the minimum number of acceptable DLCO maneuvers required for a valid test session is:

Answer: 2

ATS/ERS guidelines require at least 2 acceptable maneuvers that agree within 2 mL CO/min/mmHg (10%) to report a mean DLCO.