Could there be negative affect on lung function slightly below average performance 1yr after being on heart and lung machine for open heart surgery?

Yes, brain, heart &: lungs, etc. because clots form in blood while being moved through the long plastic, non-endothelium lined tubing between your chest & within the heart lung machine a few feet away from your body. Thus heparin is infused into the blood shortly after leaving your body (too much would ↑ bleeding) yet can never prevent all microscopic clots which block microcirulation after blood is returned to body.

Unusual: There are multiple reasons for lung dysfunction after cardiac surgery especially if significant transfusions were needed and time on bypass was long. Most of these factors resolve over 1-3 months if healing is adequate and rehab is successful. Diaphragm dysfunction or lung trapping may be reasons for prolonged problems. Get a pulmonary evaluation at this point unless recovery slowed by some issue

To a degree: depending on ore existent situation: obstructive lung disease,recent smoking, heart failure and congestion. It is common to have peri operative atelectasis, fluid shifts, blood or fluid in pleural spaces