Inter-individual differences in control of alveolar capillary blood volume in exercise and hypoxia

• We evaluated the change in pulmonary capillary blood volume during exercise at sea level and at high altitude.
• We found an increase in some subjects but a decrease in others.
• We measured the corresponding changes in respiratory reactance as index of lung fluid perturbation.
• Reactance was significantly more negative when capillary blood volume decreased.
• We conclude that subjects showing decrease in capillary blood volume are more prone to lung water perturbation.

We compared by non-invasive technique the adaptive response of alveolar capillary network to edemagenic conditions (exercise and high altitude [HA, PIO2 107 mm Hg] in subjects with different resting sea level (SL) capillary blood volume (normalized to alveolar volume, Vc/Va): Group 1 (N = 10, Vc/Va = 16.1 ± 6.8 ml/L- mean ± SD) and Group 2 (N = 10, Vc/Va = 25 ± 7.7). In Group 1 Vc/Va remained unchanged in HA at rest and increased during exercise at SL (26.3 ± 8.6) and HA (28.75 ± 10.2); in Group 2 Vc/Va significantly decreased in HA (19 ± 6) and did not increase in exercise at SL and HA. We hypothesize that Group2 exerts a tight control on Vc/Va being more exposed to the risk of lung edema due to inborn greater microvascular permeability. Conversely, Group 1 appears more resistant to lung edema given the large capillary recruitment in the most edemagenic condition. The 4-fold increase in frequency dependence of respiratory resistance in Group2 in HA stems for greater proneness for lung water perturbation compared to Group 1.