“Enlarged cardiac silhouette may be secondary to the patient’s poor respiratory effort as well as portable AP technique.”
Respiration is the act of breathing and includes both inspiration and expiration. It would be better to say “inspiratory effort.” However, it’s not possible to judge a patient’s effort by radiography. It could be the patient was in pain and made a great, albeit unsuccessful, effort.
I’d say “Enlarged cardiac silhouette accenuated by hypoinflation.”