DLCO Basics
This test evaluates the transfer of gas between the alveoli and pulmonary capillary blood.
DLCO (diffusing capacity)
During the single-breath DLCO maneuver, the patient holds their breath for approximately this long.
10 seconds
During quiet breathing, the majority of Raw is located in these airways.
Trachea and large airways
MIP evaluates primarily this group of respiratory muscles.
Inspiratory muscles, including the diaphragm, intercostals, and inspiratory accessory muscles
A patient with emphysema would commonly have an increased or decreased DLCO?
Decreased DLCO
These are the two major barriers O2 and CO2 must cross during lung diffusion.
alveolar-capillary membrane and blood plasma-RBC barrier
The DLCO test gas contains this percentage of carbon monoxide.
0.3% CO
This measurement represents specific airway resistance.
sRaw
MIP values are expressed as positive or negative pressure?
Negative pressure. The more negative the value, the stronger the inspiratory muscles.
A patient has polycythemia. Would you expect the uncorrected DLCO to trend high or low?
High. Increased hemoglobin can increase the DLCO.
Carbon monoxide is useful for DLCO testing partly because its affinity for hemoglobin is approximately this many times greater than O2
210 times
At least this many acceptable DLCO maneuvers are averaged for reporting.
Two acceptable maneuver. They should agree within ±10% or 3 mL/min/mmHg, whichever is larger.
Normal Raw is approximately this range.
To perform a MIP, the patient first exhales to this lung volume.
Residual volume (RV)
A patient’s Raw is 4.0 cm H₂O/L/sec. Normal or abnormal?
Abnormally high airway resistance. Adult Raw ≥ ULN, generally around 2.5 cm H₂O/L/sec, is abnormal.
Of steady-state, rebreathing, and single breath DLCO techniques, this is the most commonly used.
Single-breath technique
A DLCO Z-score of −3.0 falls into this impairment category.
Moderate impairment
These two measurements are more sensitive for detecting small-airway dysfunction than their nonspecific counterparts.
sRaw and sGaw
MEP is essentially this named maneuver performed against an occluded valve.
Valsalva maneuver
A patient with suspected Guillain-Barré syndrome has progressive respiratory weakness. Which two PFT measurements could directly evaluate respiratory muscle strength?
MIP and MEP. These tests are indicated for evaluating respiratory muscle weakness in neuromuscular disease.
Name four factors that affect diffusion across the primarily liquid barriers of the lung.
surface area, membrane thickness/distance, gas solubility, partial-pressure gradient, and gas density
Give four conditions/factors that can produce a decreased DLCO.
emphysema, pulmonary fibrosis/ILD, anemia/reduced Hb, pulmonary vascular disease such as PE, renal failure, small lung volume, respiratory muscle weakness, or smoking
As lung volume increases, Raw does this while Gaw does this.
Raw decreases and Gaw increases
How many MIP/MEP maneuvers should be obtained, and how close should the two highest values be?
At least 3 maneuvers, with the two highest values agreeing within 10%
A patient performs a MIP of −35 cm H₂O, followed by −52 cm H₂O and −50 cm H₂O. Which value should ultimately be reported if the maneuvers satisfy repeatability requirements?
−52 cm H₂O. For MIP, the highest value is the most negative repeatable result.