Exercise induced hemoconcentration following spleen contraction in subjects with COPD

Background: The blood-boosting spleen contraction represents a potential protective response to hypoxia by raising the blood gas storage capacity. Human spleen contraction has been observed during exercise, apnea and simulated altitude resulting in ejection of stored red blood cells into circulation. High-altitude exposure has been shown to increase spleen contraction suggesting that long-term hypoxia may improve the response in humans. Subjects with COPD are often exposed to hypoxia, which limits their physical performance. However, it is not known if spleen contraction occurs in subjects with COPD. Our aim was to reveal whether subjects with COPD recruit the spleen erythrocyte reserve during mild exercise. Methods: SpO2, spleen volume and Hb were measured before and after 6 min walking test (6MWT) in 24 subjects with COPD. Results were analyzed for all subjects pooled and for subject groups with resting SpO2 above and below 90 % separated and expressed as mean. Results: 6MWT reduced SpO2 from 91 to 83 % and spleen volume from 254 to 181 mL, while Hb increased from 150 to 154 g/L (p = 0.001 for all). Compared to subjects with SpO2 > 90 %, the group with SpO2 < 90 % displayed the largest resting spleen volume (339 vs 202 mL; p = 0.001) and the most pronounced spleen volume reduction (139 vs 40 mL; p = 0.007). Conclusion: Exercise with hypoxia evokes spleen contraction in subjects with COPD and may represent a protective response during periods of hypoxia. The larger spleen volume and more pronounced contraction in the most hypoxic subjects may suggest long-term adaptation to hypoxia.