The finished DIY hypoxicator.

The heart of my DIY Altitude Training system is the 'hypoxicator'. The principle of this altitude system is that you rebreathe your exhaled air, and each time you do so the oxygen level drops. This creates air that has less oxygen, which simulates high altitude. However, you can't simply breathe into a bag because as the oxygen level drops, the carbon dioxide levels rise. This rise in CO2 will cause you to breathe deeper and faster, leading to dramatic panting without any drop in your blood oxygen level (SpO₂). To overcome this problem, your breath must go through a CO2 scrubber, which is the function of the hypoxicator. This hypoxicator is essentially a box filled with a chemical CO2 scrubber, plus attachments for the breathing hoses and filters to keep the scrubber in the box. I made mine for less than $20 plus the cost of the CO2 scrubber.

1 Tools and materials needed

You will need the following:

Box. An air tight box, which should be about a pint/half liter in size. The box should be clear, as the CO2 scrubber changes color when it needs replacing. Ideally the lid of the box should fit into the box rather than creating a dome above so that there is no air gap above the CO2 scrubber. This Flip-Tite container is ideal and is the one I use.
Hose connector. I used some viral filters cut in half, but you might be able to use a plumbing connector. (You will need viral filters for the overall altitude training system.) I got my filters from Allegro Medical for around $3 each.
Air Filter. I used parts of an air conditioning filter to stop the scrubber going into the holes for the hoses. I think you could use other materials, such as open cell foam.
Drills. You will need to cut a hole into the box that's about an inch/2cm or so wide. The box I used is polycarbonate, which is tough, but you need to cut it carefully.
Saw. I cut the viral filters in half with a hacksaw designed for metal and it worked quite well. A vice to hold the viral filter still is handy.
Glue. It's hard to glue polycarbonate, but I found that if you sanded the parts, an epoxy resin worked well and created an air tight seal. If you use other glues, you may need some type of sealant.
CO2 scrubber. The CO2 scrubber is a consumable as it uses a chemical reaction to absorb the CO2. The scrubber will change to a violet color when it's used up, but the change is no permanent so check after you finish using the hypoxicator rather than before. I use 'JorVet J-553 Soda Lime', produced by Jorgensen Laboratories which I get from shopmedvet.com. They tend to change their URLs so you may have to search for 'soda lime' on their site. Each 3 pound bag is $7.80 (plus $10 shipping per order), and each bag tends to last me for a few weeks. There are some newer CO2 scrubbers available, such as Amsorb plus that have a permanent color change. I have not tried these, but they are available on line at surgical tools, and Hull Anesthesia. There is an interesting write up at http://www.armstrongmedical.net/absorbent/amsorb-plus/amsorb-plus

2 Construction

The steps to construct the Hypoxicator are reasonably simple.

2.1 Cut the viral filters

The viral filters are cut in half so that you have an attachment for the breathing hose.

I cut two filters so I could have a male fitting on both sides, something I found unnecessary in practice, so just cut a single filter.

2.2 Cut holes in the box

I used a small drill to create a pilot hole, then used the hole cutter. You need to cut polycarbonate slowly and gently to prevent it either melting or cracking. Cut the holes closer to the bottom than shown.

2.3 Glue the viral filters in place

I used an epoxy resin, which worked quite well, but you need to sand the contact surface of the box to create some roughness the resin can adhere to. I tried to glue both ends on at the same time, which was a mistake; glue one, then the other when the first is set. You will need an air tight seal, so use plenty of resin. I had to go back a few times to seal holes I'd missed.

2.4 Add the air filter

Cut some air filter material to size and cover the open holes.

2.5 Fill with CO2 scrubber

Just fill the box with CO2 scrubber and close the top. Store the hypoxicator in a sealed plastic bag when not in use.

DIY Hypoxicator

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