Turns out breathing strength training affects your blood pressure - most fascinating is the amount (~9mmHg).
I do wonder whether they have the causative effect right (a rabbit hole to fall into is the ecological fallacy). As we know from this, correlation doesn’t necessarily equal causation. My understanding is that the same effect is seen in meditation/relaxation techniques - so I wonder if the breathing exercises triggered a reflective state and whether it therefore is the act of consciously focusing on breathing or the strength training leading to the improvement?