Hmmm, this sounds interesting. Tell me some more about respirocytes, how they work, and how someone like Superman would have them.
Well
this site explains them far better than I could. I recommend checking it out. As for how Superman would have them, well, it's very unlikely but a similar structure could have evolved in Kryptonian blood. It might even be a prerequisite for life evolving on such a high g world. Either that or super advanced K-Science could have created them and then introduced them as the norm for their entire species. It's also cool that that page mentions other capabilites for them that could apply to our favorite Man of (Carbon) Steel.