What are the causes of a raised hemidiaphragm?
The causes are numerous and varied and can be divided into: (1) Above the diaphragm - e.g. lobar collapse; (2) diaphragmatic - e.g. phrenic nerve palsy; (3) subdiaphragmatic - e.g. gas-filled stomach or colon.
What is the likely cause in this case?
Iatrogenic injury of the phrenic nerve in cardiac surgery.
How could this be confirmed?
Fluoroscopic "sniff test" is a cheap and non-invasive test. Ultrasound and manometry are alternative tests.
Hemidiaphragm is not elevated. Note sternotomy wires and aortic valve replacement is not present.