How does having copd affect a vq scan?

Yes: If a patient has bullous emphysema it will affect the flow then the v/q scan.

See below: The ventilation part of the v/q scan will show air trapping which may be patchy. The perfusion is usually not affected much but bottom line is the v/q scan will be more difficult to read and the results may be inconclusive.

Markedly: The VQ (ventlation/perfusion) lung scan can have many defects in its homogeneous density related to abnormal air trapping and shunting of blood to areas of better ventilation. COPD and asthma can cause difficulty in interpretation of scan with confusion with pulmonary embolism. Usually lung scans are compared with chest radiographs, but interpretation can still be difficult.