Are bradypnea and hypopnea the same thing?

No, they are different. Bradypnea occurs if a patient's respirations slow from their normal rate. Hypopnea occurs when the depth of respiration changes from their norm. The definitions are listed below.

Bradypnea: Abnormal slowness of respiration.

Hypoventilation: Abnormally slow and shallow respiration, resulting in an increased level of carbon dioxide in the blood.

Hypopnea: Literally, underbreathing. Breathing that is shallower or slower than normal.

Apnea: no respirations.