Introduction: Chronic Obstructive Pulmonary Disease (COPD) is responsive to bronchodilator (BD). However, it is unclear how BD alters ventilation distribution.

Aims: To determine the effect of BD on the extent and distribution of ventilation in COPD measured by Single Photon Emission Computed Tomography (SPECT)/Computed Tomography (CT). 

Methods: 10 participants (6M) with physician diagnosed COPD underwent baseline spirometry and a SPECT/CT pre and post BD. A significant BD response was an increase of 200mL and 12% in FEV1 or FVC. Both lungs were segmented into outer, middle, and inner shells, from the CT which were 40%, 30%, and 30% of each lungs? volume respectively. From fused SPECT/CT, we calculated ventilation as; 1) percentage of total CT lung volume (Vent_Total), 2) percentage in each shell (Vent_Shell) and 3) each shell?s ventilation as a proportion of total ventilation (Shell_Total).

Results: 3/10 participants had significant BD responses. Vent_Total did not change following BD (p=0.13). Vent_Shell decreased in the inner shell exclusively (p=0.004). Shell_Total significantly increased in the outer shells (Shell_Total ?=1.19, p=0.003) and decreased in the inner shells (Shell_Total ? =-1.31, p=0.001). Shell_Total did not undergo significant change in the middle shells (Shell_Total ? = 0.06, p=0.8). % change in Shell_Total in the middle shells correlated significantly with % change in FEV1 (p=0.003, r=-0.86) and FVC (p=0.02, r=-0.74).

Conclusion: SPECT imaging is sensitive to changes in the pattern of ventilation following BD in COPD, showing that ventilation is redistributed from the central to the peripheral areas of the lungs.