Why does the tip of my nose and upper lip go white after I work out really hard? (photos)

When my heart rate is really high for longer periods of time (the picture is 15 minutes after a 5km run so the extreme white in the tip has gone isn't as extreme as while I was running) the tip of my nose and upper lip goes white like there is no blood going to it. This has only happened since my rhinoplasty 9 months ago.