Breathing control and emotive control are two separate functions of the body that can be affected by brain state and emotion. While volitional control of breathing can affect emotion, emotive control of the facial muscles and breathing can exist independently in cases of locked-in syndrome.
The way we breathe can affect our emotional state, but our brain's state can also affect the way we breathe. Studies have shown that changes in brain activity as well as conscious breathing techniques can have a significant impact on our emotions.
Laughing can change your breathing pattern and have an impact on your breathing rate and oxygen levels, as shown in a study when a patient's ventilation increased when they laughed, and decreased when they held their breath or breathed faster.
The emotive control of breathing and facial expressions is distinct from volitional control and has a significant impact on how we communicate emotions to others.