Asthma attacks brought with them a fear of death. These attacks were triggered in the fall, around dogs, and in the horse hair seats at church. I also had food allergies. I ended up with an old HEPA filter/purifier, an ionizer (which turned the wall black), and an old carbon filter machine all running at the same time in my bedroom. I went for allergy shots each week and took medications to prevent and/or relieve asthma attacks.
These machines weren't specifically designed for asthma, but since my triggers were airborne (mostly) I wanted to try and help my lungs. Did my asthma air purifier really help? At that time I honestly didn't know whether the relief was psychological or physiological but I did sleep better and feel better.
HEPA - HEPA filtration is the #1 technology for asthma since it removes the most airborne particles. Most allergists will recommend a HEPA asthma air purifier first for allergy-induced asthma. HEPA is a cloth-like filter that has to be replaced every 4-9 months on average. It is best for capturing and removing dust, pollen, dirt, and most airborne particles. If your asthma is allergy-based asthma start with HEPA. But don't stop there. If you're allergic to (or "also allergic to") mold HEPA will not do the job.
UV - Ultraviolet (UV) light kills most germs, bacteria, mold, mildew, and viruses. Because asthmatics often have a weakened immune system and these foreigners or pathogens stress the immune system adding UV, while not primary, can be an inexpensive and helpful addition.
PreFilter - A Pre-filter looks like a screen door, is usually washable, and captures hair and dust. HEPA does a much more complete job and the washable prefilter in front of it is primarily to save money by extending the life of the HEPA. If you have dog or cat the hair captured will be worth its inclusion.
Carbon - Carbon filters are treated charcoal minerals which have millions of tiny cell pockets. These pockets are very effective at trapping gas, odor, and toxic chemical fumes. If you are chemically sensitive, and /or chemical fumes bring on asthma, Carbon would be added to your list. Because these toxins affect and weaken the immune system it can help the body.
Electrostatic - Also called "truman cells", grids, ionic cleaners, or ionic plates. These type of air purifiers capture particles using positively and negatively charged "washable plates" or grids. Oreck is one example. Most do not have HEPA filters. The washable part is great (and great for marketing), but the effectiveness is limited. Good for smoke it will not remove pollen, dust and airborne particles like HEPA. Also, some models with flat plates and no holes in the plates can cause asthma which can trigger asthma attacks.
Tio2 - Used in conjunction with UV it simply magnifies the effectiveness of the virus, germ, and bacteria killing of ultraviolet light.
1) Getting my liver cleansed of toxins which were causing me to create too many histamines.
2) Special treatments to the brain which had to do with the mind-body causes of allergies. Many allergies (and hence asthma attacks) are caused by patterns in the brain which cause energy blockages in the nervous system.
3) Building up my adrenal glands which relieved the muscle spasms of asthma.
The Comparison Chart on the site may be of help.