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The research shows that there is wide individual variation in the response to IHE and altitude. This variation exists in both humans and animals, and appears to be due to mechanisms beyond simple iron insufficiency.
==Research from the USSRIHE and Athletic Performance==*A lot of research on IHE has come from the former USSR<ref name="USSR"/>. ** Expose subjects to 15,000 feet for 1 hour per day over several days for 7 to 11 sessions showed increased blood O<sub>2</sub> saturation compared with initial exposure and the benefits were detectable for up to 4 weeks.** Exposure of 30 min to 3 hours every 2 to 3 days for 9 exposures increased hemoglobin by 12% and red blood cells by 22%** Exposure of 3x (6 min low O2, 4 min normal air) per day for 14 days increased breathing volume at altitude by ~50%. Partial pressure of O<sub>2</sub> started at 50 mmHg (20,000 ft) dropping to 35 mmHg (28,000 ft). Several studies have shown similar results. ** 5x (15 min 11% O<sub>2</sub> + 15 min recovery) for 14 day produced changes to the metabolic pathways that optimize the use of oxygen.* Studies in rats suggest that continuous exposure to altitude reduces anti-oxidant defenses, but IHE improves them.* Other studies in rats indicate that IHE changes the ratio of fat to protein burning in favor of fats by 80%.* A study of workers that cleaned up after Chernobyl nuclear reactor explosion showed that they had higher levels of oxidant stress where higher than normal. Exposing the workers to IHE of 3x (5 min 7-8% [28,000+ ft] O<sub>2</sub> with 5 min normal air) for 14 days significantly reduced the oxidant stress. * Studies have shown IHE reduces the oxidant stress associated with bronchial asthma, however, the study had large variations in individual response. (See below for more on asthma.)* Recent studies indicate that IHE stimulates NO (Nitric Oxide) production, with the excess stored in the vascular walls. This improves blood pressure. * Research indicates that there is a very wide variability in the response to altitude (IHE or other) and tolerance of extreme hypoxia. Future research may provide methods of overcoming the lack of response in some individuals. ==Other Research==
* Research<ref name="jack"/> using highly trained runners showed no running improvement with IHE. However, this study used IHE for 4 weeks and had O<sub>2</sub> saturation values of 89.9, 86.3, 85.9, and 81.4 for each week. The value of IHE is dependent upon the O<sub>2</sub> saturation levels, with little effect until values under 89%<ref name="HTI"/>. The athletes in the study therefore only received significant hypoxia for about one week. The athletes were given 5 min hypoxic, 5 min normal for 70 minutes total for five days per week, 4 weeks total.
* A similar research<ref name="junis"/> study showed a significant improvement in 3K running performance. This study used 90 minutes of IHE (5 hypoxic:5 normal) for 15 days over a three week period, using 13,000 feet at the start to 19,000 feet at the end.
==Intermittent Hypoxic Exposure and Diseases==
IHE has been looked at for a number of diseases.
===Intermittent Hypoxic Exposure and Asthma===
Studies have reported an improvement in asthma, with reduced attacks, reduced severity of attacks and reduced need for medication. Note that none of these studies has looked at specifically at exercise induced asthma.
* IHE increased lung force in asthmatic and non-asthmatic athletes<ref name="asthmatic"/>. There was no deterioration in asthma status from the trial, and half of the asthmatics reported a reduction in the need for medication. The trial used 15 sessions over three weeks, with each session being 5 min hypoxia followed by 5 min normal air, repeated for 60 minutes. The hypoxia was equivalent to 22,500 ft.
* IHE has been shown to reduce the shortness of breath and congestion of childhood bronchial asthma, reducing or eliminating the attacks<ref name="Serebrovskaya-2012"/>. The protocol was 4 repeats of 5-7 minutes with 12% O<sub>2</sub> which resulted in a [[SpO2|SpO<sub>2</sub>]] of 89-92%.
* IHE reduced the bronchial resistivity by 31–37% in bronchial asthma patients<ref name="Levashov-2012"/>. IHE also increased reserves of lung ventilation, restored the physiological level of alveolar ventilation in 78% of patients with chronic obstructive pulmonary disease (COPD)<ref name="Levashov-2012"/>.
* Studies have shown IHE reduces the oxidant stress associated with bronchial asthma, however, the study had large variations in individual response<ref name="USSR"/>.
===Intermittent Hypoxic Exposure and Parkinson's Disease===
===Intermittent Hypoxic Exposure and Cancer===
A study of mice with [http://en.wikipedia.org/wiki/Acute_myeloid_leukemia Acute Myeloid Leukemia] (AML) showed an increased survival time and an inhibition of the [http://www.cancer.gov/dictionary?cdrid=46349 infiltration] of the cancerous cells, and improved [http://www.cancer.gov/dictionary?cdrid=46445 differentiation]<ref name="Chen-2012"/>. Note that this is an animal study on one specific type of cancer.
===Intermittent Hypoxic Exposure and Oxidative Stress===
* Studies in rats suggest that continuous exposure to altitude reduces anti-oxidant defenses, but IHE improves those defenses<ref name="USSR"/>.
* A study of workers that cleaned up after Chernobyl nuclear reactor explosion showed that they had higher levels of oxidant stress where higher than normal. Exposing the workers to IHE of 3x (5 min 7-8% [28,000+ ft] O<sub>2</sub> with 5 min normal air) for 14 days significantly reduced the oxidant stress.
==A note on terminology==
