Not sure if I've mentioned this before, but with the recent cold snap it's got really obvious.
Before PB, going from warm house to cold outdoors meant shortness of breath - a feeling of lungs constricted, only being able to fill them to half capacity. As for exertion in the cold? Er, no.
Post-PB... I've been cycling happily up and down hill in freezing temperatures, and it took me a while to remember that I 'ought' to be short of breath. No trouble at all.