Red cell distribution and the recruitment of pulmonary diffusing capacity

Area of Science:

• Physiology
• Pulmonary Medicine
• Biophysics

Background:

• Red blood cell distribution in alveolar capillaries is typically nonuniform.
• This nonuniformity is observable via intravital microscopy and in fixed alveolar tissue.

Purpose of the Study:

• To determine the effects of red blood cell distribution on pulmonary diffusive gas transport.
• To compute the uptake of carbon monoxide (CO) across a two-dimensional geometric capillary model with variable red blood cell numbers.

Main Methods:

• A finite-element method was used to calculate total CO diffusing capacity (DLCO) and membrane diffusing capacity (DmCO).
• Red blood cells were modeled as uniformly spaced, randomly distributed, or clustered without overlap within the capillary.

Main Results:

• Red blood cell distribution significantly affects capillary CO uptake at a fixed hematocrit.
• Uniform distribution yielded the highest DmCO and DLCO, while clustered distribution yielded the lowest.
• Nonuniform distribution within a segment reduced CO uptake by up to 30%, and across segments by over 50%.

Conclusions:

• Pulmonary microvascular recruitment for gas exchange depends on more than just capillary number or hematocrit.
• Red blood cell redistribution within capillaries can account for a substantial portion of physiological DLCO recruitment during exercise.