I was experimenting with HRV as well.
Some time ago I did very intensive and long hypoventilation session, goal was to see if I can overload right ventricle without heavy cardio workout, as Juerg suggested we should be able to do it, but it sounds kinda "impossible" He was 100% right, it is more than possible and it is visible when looking at Moxy calibration.
On Jan 15th I had easy session, this shows on Jan 16th in my 10min calibration period:
tHb (brown 3rd from the top) nice amplitude and good recovery during 1 min stop at the end.
On Jan 17th, 5 hours before my cycling session I did intensive and long hypo-ventilation session, this affected my tHb quite a lot, no initial tHb dip and no increase after 1 min stop at the end, tHb went actually down...(legs were fresh so it was not related to muscle compression etc.)
I took fairly easy on Jan 17th, and we could see slight improvement(not big but better than day before) Jan 18th I also took easy on that day.
My RHV showed it as well, I have ithlete app and their ECG sensor as well HRV4training, will try CardioMood as well since it shows data real time.
I'm one of the people who extra stress increases HR variability, I'm always taking reading standing up right after I wake up.
What I really didn't realized until today, how my HRV increased since I bought Moxy, I use Moxy 10 min calibration routine to guide my day to day load since end of October:
Blue line represents HRV (higher more recovered I am) You can clearly see how my recover increased since I started using Moxy, I'm at the same 60min power and increased by sprint power by quite a lot.