Nitric oxide (NO) the vasodilator, is not the same as nitrous oxide (N2O) the anesthetic laughing gas, is not the same as nitrox, the oxygen enriched diving gas (O2 and N2 mixture). It’s the difference between to, too, and two. Maybe OP husband is just really excited about diving.
Good call. I missed the 2.
I was too busy laughing.