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* If my O<sub>2</sub> saturation drops below about 65% I tend to phase out, and it’s easy to drop into a strange dream like state for a few moments. This is almost a shamanistic experience, but I try to avoid this situation as it's probably quite unhealthy.
* Reading a book while using the AltoLab is tricky because you need to hold the tube in your mouth.
* You need to keep the mouth piece angled upwards to prevent saliva flowing into the system. If you don't the anti-bacteria filter will be hard to breathe through and the tube will fill up!
* For the first couple of bouts of AltoLab training, the initial sessions seemed to leave me a little weakened and slower than normal. I also found that the altitude training tended to give me a headache that would come back periodically.
* I found there is quite a bit of lag in using AltoLab. When you start breathing through the AltoLab, it will take a couple of minutes before your O<sub>2</sub> saturation drops, and when you have the rest period, it can also take a minute or more before your O<sub>2</sub> saturation returns to near normal. However, I also found that the feeling of low O<sub>2</sub> saturation seemed to lag even further behind the reading from the meter (Pulse Oximeter). My assumption is that the O<sub>2</sub> saturation of your blood can change, but the tissues your blood is supplying will take time to change to match the O<sub>2</sub> saturation of your blood. The practical implication is that my blood O<sub>2</sub> saturation could drop to 65% quickly and I would feel more or less okay for a short time. Once my blood O<sub>2</sub> saturation had been low for a minute or so, the impact would kick in and I'd start to feel light headed. Likewise, when I had a rest period, my blood O<sub>2</sub> saturation would rise to normal but my head would still be feeling the effects.
* I wrote some software that would interface with a USB enabled pulse oximeter. This gave me a graph of how my blood O<sub>2</sub> saturation was changing over time. It also allowed me to calculate the 'Hypoxic Training Index' so I could compare different training sessions.
==Conclusion==
Overall, I think the AltoLab is a cost effective and useful way of training for high altitude conditions, and possibly for improvements at sea level. I suspect that the downsides of using other intermittent systems will be similar to AltoLab. From what I understand from other people who've slept in altitude tents, there are different, but equally significant downsides to that approach, including poor sleep quality.