I should note for those who live at higher elevations, it is normal to see lower saturations. I live at 5500' (1676m), but travel to sea level and also sleep at elevations as high as 10500' (3200m). I wear a ring that records SpO2 (and heart rate) every 4 seconds overnight. At home, it is common to see an average saturation around 94 or 95% with maybe 1 drop per hour of 4% and a few minutes under 90%. Average heart rate 50 BPM. At sea level, average SpO2 is 96 or 97 with 0 drops per hour and 0 minutes under 90%.Average heart rate 51 BPM. At 7500' (2286m), average is 91 or 92%. Drops per hour might be 2, but time under 90% is 84 minutes with the lowest at 82%. Even with these numbers, my average heart rate was 52 BPM. As I routinely do extended exhaled breath holds dropping my SpO2 to 70% or below, none of this is worrying.
I specifically train CO2 tolerance through slow breathing and breath holds. Because of the
Bohr effect, when CO2 levels are higher, hemoglobin releases O2 into the cells more readily. One of the ways I train is to keep my lips taped during sleep. This insures nasal breathing and lower probability of hyperventilation, which would lead to reduced serum CO2 levels. In this
post, you can see the impact on beat to beat heart rate in me with and without mouth tape.
