Perfused lung volume to thoracic gas volume ratio (perfused lung fraction) in patients with COPD and in controls.

Background: The deterioration of the ventilation-to-perfusion distribution in patients with chronic obstructive pulmonary disease (COPD) reflects structural changes affecting both the airways and the blood vessels. These changes result in lung perfusion abnormalities that may be quantified by lung perfusion single photon emission computed tomography (SPECT).
Objective: To compare the perfused lung fraction (PLF) in patients with airflow obstruction and controls.
Methods: Fourteen patients with COPD and 21 controls underwent spirometry, whole-body plethysmography, and lung perfusion SPECT. PLF was derived from the ratio of perfused lung volume (measured by SPECT) to thoracic gas volume (measured by whole-body plethysmography).
Results: In the whole study sample, there were 18 (51%) women and 17 (49%) men, mean age was 46.2 (±20.3) years, range: 18-80 years). In the COPD group, PLF was 0.74 (±0.08), whereas in the control group PLF was 0.99 (±0.18) (P<0.001). PLF correlated directly with forced expiratory volume in 1 s to forced vital capacity (r=0.597, P<0.001). Perfused lung volume was 3.66 (±0.64) l in the COPD group compared with 2.71 (±0.70) l in the control group (P<0.001).
Conclusion: The fraction of lung volume receiving blood from the pulmonary artery is reduced in patients with COPD. The degree of underperfusion seems to correlate with the degree of airflow limitation.