Hysteresis in the relation between diffusing capacity of the lung and lung volume

Area of Science:

• Pulmonary Physiology
• Respiratory Medicine

Background:

• The diffusing capacity of the lung for carbon monoxide (DLCO) is a key measure of gas exchange efficiency.
• DLCO typically varies with lung volume (VA), but the relationship can differ based on measurement technique.

Purpose of the Study:

• To investigate the hypothesis that hysteresis, or a volume history-dependent effect, influences the relationship between DLCO and VA.
• To determine if DLCO measurements differ when lung volumes are achieved via inhalation versus exhalation.

Main Methods:

• DLCO was measured using breath-holding techniques at specific lung volumes.
• Measurements were performed at three lung volumes, achieved both by inhaling from residual volume (RV) and exhaling from total lung capacity (TLC).
• DLCO during slow exhalation was also recorded to compare with the breath-holding data.

Main Results:

• DLCO was significantly higher when lung volumes were reached by exhalation compared to inhalation at both 72% TLC (22% higher, P < 0.02) and 52% TLC (19% higher, P < 0.005).
• Measurements during slow exhalation aligned with the exhalation limb of the DLCO/VA curve, confirming the hysteresis effect.

Conclusions:

• The study provides evidence for hysteresis in the diffusing capacity of the lung for carbon monoxide with respect to lung volume.
• This hysteresis indicates that the method of achieving a specific lung volume (inhalation vs. exhalation) affects DLCO measurements.