The blunted pulmonary capillary blood volume (VC) response to an upright-to-supine postural change in moderate-to-severe COPD is consistent with reduced alveolar-capillary reserve and may be useful when measurements during exercise are not possible.
Key Findings
Results
The upright-to-supine change in DL,CO5s was reduced in moderate and severe COPD compared with healthy controls, but not in mild COPD.
Total sample: 50 participants (35 with COPD and 15 healthy controls)
Control vs. moderate COPD difference in upright-to-supine DL,CO5s change: median [IQR] 0.6 [0.3, 0.9] mmol/min/kPa, P < 0.001
Control vs. severe COPD difference: 0.9 [0.2, 1.5] mmol/min/kPa, P = 0.006
Control vs. mild COPD difference: 0.3 [-0.1, 0.7] mmol/min/kPa, P = 0.13 (not statistically significant)
Results
The upright-to-supine change in pulmonary capillary blood volume (VC) was reduced in moderate and severe COPD compared with healthy controls, but not in mild COPD.
Control vs. moderate COPD difference in upright-to-supine VC change: 8.3 [3.9, 12.8] mL, P < 0.001
Control vs. severe COPD difference: 10.7 [1.2, 20.2] mL, P = 0.021
Control vs. mild COPD difference: 5.3 [-0.2, 10.8] mL, P = 0.063 (not statistically significant)
The blunted VC response is described as consistent with reduced alveolar-capillary reserve in moderate-to-severe COPD
Results
The upright-to-supine changes in DL,NO, DM,CO, and alveolar volume (VA) did not differ between COPD patients and healthy controls.
Upright-to-supine change in DL,NO: P = 0.271 (no significant group difference)
Upright-to-supine change in DM,CO: P = 0.068 (no significant group difference)
Upright-to-supine change in VA: P = 0.934 (no significant group difference)
These findings suggest that the postural response differences between groups are primarily captured by DL,CO5s and VC rather than membrane diffusing capacity or alveolar volume
Results
A 12-week supervised high-intensity interval training (HIIT) intervention had no effect on any of the measured diffusing capacity metrics.
HIIT subset included 12 COPD patients and 12 healthy controls
No significant effect of the 12-week HIIT intervention was observed on DL,NO, DL,CO5s, DM,CO, VC, or VA
The intervention was described as supervised and high-intensity interval training in format
Duration of the intervention was 12 weeks
Discussion
The transition from upright to supine posture was proposed as a potential alternative to exercise-based assessment of alveolar-capillary reserve in COPD patients for whom exercise measurements are not feasible.
Exercise-based measurement of DL,CO,NO may pose difficulties in COPD patients with reduced alveolar-capillary reserve
The postural change method measures the recruitment of pulmonary capillary blood volume via gravitational redistribution of blood rather than exercise-induced increases in cardiac output
The blunted VC response to postural change in moderate-to-severe COPD was interpreted as consistent with reduced alveolar-capillary reserve
Authors suggest this approach 'may be useful when measurements during exercise are not possible'
What This Means
This research suggests that the lungs' ability to recruit additional blood vessels during increased demand — called alveolar-capillary reserve — can be tested in patients with chronic obstructive pulmonary disease (COPD) by simply measuring lung function in two body positions: sitting upright and lying flat. When a person lies down, blood naturally shifts toward the lungs due to gravity, which normally causes an increase in the amount of blood in the tiny lung capillaries. The study found that this increase was significantly blunted in patients with moderate-to-severe COPD compared to healthy individuals, suggesting their lungs have less capacity to expand their blood volume when needed. This difference was detected in the measures of carbon monoxide diffusion (DL,CO) and pulmonary capillary blood volume (VC), but not in measures related to the lung membrane itself or lung air volume, pointing specifically to a vascular limitation.
This research suggests that the upright-to-supine postural test could serve as a practical alternative to exercise-based lung function testing, which can be difficult or unsafe for patients with more advanced COPD. Currently, exercise testing is the standard way to assess this type of lung reserve, but many COPD patients struggle to exercise adequately. The simple act of changing body position from sitting to lying down offers a passive, low-effort way to stress the pulmonary circulation and reveal similar information about reserve capacity.
The study also found that 12 weeks of supervised high-intensity interval training did not change any of these diffusing capacity measurements, suggesting that this type of lung vascular limitation may not be easily reversed by exercise training alone in COPD patients. Taken together, the findings highlight that moderate-to-severe COPD involves not just airway obstruction but also a meaningful reduction in the lung's vascular reserve, detectable through a simple postural maneuver.
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Rasmussen I, Nymand S, Hartmann J, Thomsen R, Hartmeyer H, Andersen A, et al.. (2026). Alveolar-capillary reserve in COPD assessed by the pulmonary diffusing capacity response to an upright-to-supine postural change.. Experimental physiology. https://doi.org/10.1113/EP093384