General recommendations
Adaptation to hypoxia and hypoxic training/hypoxic therapy have a broad range of indications in clinical, preventive and sports medicine, balneology and medical rehabilitation. Regardless of the type of exposure, the method can be considered safe for healthy people when adaptation is gradual, dosed and regulated, exposure regimens are appropriate and exercise tolerance is satisfactory. In patients with chronic diseases it is also effective and safe when procedure rules are observed, training is medically supervised, patients are monitored and those with contraindications are excluded. This lecture discusses the organisation of hypoxic training.
Guidelines approved by the Russian Ministry of Health have been developed and adopted for hypoxic therapy/training in treatment and rehabilitation, together with guidelines and instructional letters on its use in sport [1, 2, 4, 5].
For sports applications, whether the method is permitted is important. To prevent harm from certain drugs and ensure equal conditions for athletes, the World Anti-Doping Agency (WADA) established a list of substances and methods prohibited in training and competition. Hypoxic training is not on this list, is permitted at all stages of preparation for athletes of different qualifications and is not among the substances and/or methods prohibited in sport.
Indications for hypobaric and normobaric hypoxia are generally similar, while contraindications differ somewhat according to how hypoxia is generated. The previous lecture introduced the different exposure methods. Their indications and contraindications are considered below.
Indications
Hypoxic training (hypoxic therapy) is indicated in a number of pathological conditions and diseases. Russian (Soviet) and international authors have experimentally and clinically demonstrated its effectiveness in the following diseases and conditions [2, 4–6]:
Cardiovascular diseases: stage I–II hypertension, coronary heart disease, functional class I–II angina, atherosclerotic and post-infarction cardiosclerosis, hypercholesterolaemia, neurocirculatory dystonia, disturbances of free-radical oxidation and antioxidant defence;
Respiratory diseases: chronic bronchitis, pneumonia, conditions after acute pneumonia and bronchitis, occupational pulmonary diseases and non-hormone-dependent bronchial asthma;
Nervous-system disorders: transient cerebrovascular disturbances, neuroinfections and neurointoxications, consequences of closed head injuries, phobic forms of neurasthenia, asthenic and subdepressive states;
Endocrine diseases: diabetes mellitus, primary thyrotoxicosis and metabolic syndrome;
Blood-system diseases: hypoplastic and iron-deficiency anaemia and post-radiation disorders of haematopoiesis;
Allergic diseases and immunodeficiency states: allergic arthritis, dermatitis, neurodermatitis, eczema, drug-induced disease, frequent colds, autoimmune processes and immunosuppression after pharmacotherapy;
Gynaecological diseases: chronic nonspecific genital diseases, preparation for pregnancy in women with a complicated obstetric history and anaemia of pregnancy;
Gastrointestinal diseases in remission: peptic ulcer disease, cholangitis, chronic cholecystitis, chronic pancreatitis and chronic colitis;
Chronic inflammatory urogenital diseases, including prostatitis and urethritis;
Preparation for surgery and anaesthesia to increase organ and tissue resistance to ischaemia;
Increasing general resistance, particularly to environmental influences such as hypoxia and low or high temperatures;
Increasing resistance to chemical factors when permissible concentrations of chemicals are exceeded;
Reducing adverse effects of medicines and polypharmacy;
Increasing nonspecific resistance during combined treatment of malignant neoplasms. Normobaric hypoxic hypoxia produced by breathing a mixture containing 10.0 ± 1.0% O₂, or mixtures with still lower O₂ concentrations, reliably protects the cancer patient against adverse effects of ionising radiation during irradiation and thereby increases radiotherapy effectiveness;
Increasing tolerance of physical exertion, especially prolonged moderate-intensity activity and short maximum-power efforts;
Increasing performance under hypoxia after a training course and improving concentration during subsequent exposure to reduced O₂;
Accelerating recovery, including in chronic overfatigue;
Maintaining high aerobic performance in athletes during recovery from injury.
Contraindications
Hypoxic training can be used in all age groups. There are no separate contraindications solely for younger or older ages or for pregnancy. In pregnant women, inspired mixtures containing no less than 14.5% O₂ are recommended. For young children, the restrictions are the same as in adults, including gradual adaptation. In older people, contraindications and risks are mainly associated not with simulated or natural hypoxia itself but with chronic diseases that impair tolerance. Hypoxic therapy should be used cautiously in patients with chronic diseases or congenital disorders.
Absolute contraindications to any continuous or intermittent hypoxic exposure are:
Recent myocardial infarction within one year; functional class III–IV angina with rhythm and conduction disturbances; paroxysmal arrhythmias carrying a high cardioembolic risk; uncontrolled or stage III hypertension; congenital anomalies of the heart and great vessels; acquired valvular defects; thrombophilic states; erythrocytosis;
Acute somatic diseases, including myocardial infarction, stroke, hypertensive crisis, pneumothorax and status asthmaticus;
Decompensated chronic diseases, including chronic renal failure requiring haemodialysis and anasarca;
Acute infections, marked exacerbation of chronic inflammatory processes and diseases accompanied by fever, including resorption syndrome;
Tuberculosis at any phase and exercise-induced bronchial asthma;
Epilepsy, including partial and secondarily generalised forms;
Individual intolerance of oxygen deficiency.
For hypobaric hypoxia, contraindications are somewhat broader. In addition to those already listed, they include:
Obstruction of the Eustachian tubes and passages connecting the paranasal sinuses to the outside, caused by polyps, inflammatory processes in the nasopharynx, middle ear or sinuses, or developmental anomalies;
Diseases of the veins of the lower limbs;
Hernias at any location;
Head injury within the preceding year;
Uterine bleeding;
Pregnancy;
Claustrophobia.
Organising hypoxic training
Compared with the methods discussed in the previous lecture, normobaric hypoxic training offers advantages over natural and artificial hypobaric hypoxia. Natural hypobaric exposure does not allow regulation of the hypoxic dose for individualisation and safety or continuous monitoring. Other factors are the high cost of spa treatment or training camps at moderate altitude, remoteness of mountain areas and environmental influences such as low temperature, solar radiation and unstable weather.
Artificial hypobaric exposure in a chamber involves relatively rapid reductions of atmospheric pressure. These can cause discomfort during ascent, and especially descent to normal pressure, because of changes in the spacing of air molecules in the frontal and maxillary sinuses and middle ear. Pressure changes increase the risk of reverse block: air expands in the middle ear but cannot escape through an obstructed Eustachian tube. The eardrum is then excessively distended and the mucosa lining the middle ear may be injured.
Thus normobaric hypoxia is the safest, simplest and relatively inexpensive method compared with trips to moderate altitude or pressure chambers. Many portable hypoxicators are available, producing mixtures with adjustable inspired O₂ concentrations from 16% to 10%.
For any hypoxic training or therapy method, regimen selection is based on age, physical performance, functional status, chronic diseases, the stage and characteristics of the primary disease, comorbidities and the phase of both primary and concomitant diseases.
Before starting, the protocol should be individualised for exposure intensity, session duration, changes in intensity between sessions, the number and frequency of procedures and total course duration.
The screening flowchart in Figure 1, mainly for exercise or prolonged stays in hypoxic conditions, and a pre-training hypoxic test help determine an appropriate individual starting dose. Correct dosing is critical for both patients and athletes of different qualifications [4, 5]. Exposure must trigger adaptation without becoming excessive and causing pathological structural or functional changes in tissues, organs or the whole body. To obtain the adaptations described in the first lecture, oxygen saturation during continuous or intermittent hypoxia should reach 90–80%.
Effective, well-tolerated dosed hypoxia develops when breathing mixtures with 11–12% O₂. SpO₂ falls below 90%, but generally not below 77–80%. Experimental and clinical studies show that this degree of hypoxaemia and tissue hypoxia is optimal for initiating adaptive cascades yet insufficient to induce adverse damaging changes [7, 8].
Before prescribing training, obtain the history, perform complete physical and instrumental examinations including ECG, blood pressure, heart rate and spirometry, and obtain a full blood count and biochemical tests. Athletes generally have clearance from a sports medicine clinic or dispensary based on an in-depth examination. Healthy active people should undergo a resting ECG to exclude congenital cardiac abnormalities such as Wolff–Parkinson–White syndrome, sinus-node dysfunction or conduction disorders, complete a questionnaire and consult a cardiologist.
Hypoxic test
A hypoxic test establishes individual tolerance and is important for programme design. Several variants exist. Before testing, measure blood pressure, heart rate and SpO₂ and ask about wellbeing, complaints and unusual circumstances: no food for over six hours, nervousness, sleep deprivation or less than six hours of sleep, recent infectious or viral illness and emotional distress. Baseline systolic pressure should be no higher than 140 mmHg, heart rate 110–120/min and SpO₂ at least 94–96%. A 5–10-minute test is recommended, with ECG recording in cardiovascular patients. Comparison with an ECG under the same conditions after the course permits objective assessment of normobaric hypoxic therapy, including in people with occult cardiovascular disease [1].
Testing is performed at rest, seated, using a hypoxicator mask with continuous monitoring of arterial oxygen saturation and heart rate. Inspired O₂ is 10%, equivalent to an altitude of 6400 m.
Explain the protocol beforehand and warn the patient or athlete about possible dizziness, palpitations, sweating, tingling or unusual limb sensations. Emphasise calm breathing without increasing depth or rate, breath-holding or talking; breathe through the nose and immediately report discomfort or unusual sensations to the specialist.
For athletes, a modified test follows the same instructions but records only SpO₂, heart rate and the time in seconds for saturation to fall from baseline to 80% (fall time, Tf). At 80%, the mask is removed and ambient-air breathing begins; the time to recover to 96% (Tr) is measured. The hypoxic tolerance index I-Hyp = Tf/Tr is calculated: 0–1.9 arbitrary units indicates low tolerance, 2–3 moderate and over 3 high tolerance [7]. If poor wellbeing, pronounced tachycardia or inappropriate blood-pressure changes occur, use 13–14% inspired O₂ for the next test and therapy. This concentration can also be used at the first test if the specialist considers it safer, usually in cardiovascular patients.
Individuals may be unaware of their intolerance and therefore unable to report it before testing.
Signs of intolerance include loss of consciousness when hypoxic breathing starts, seizures, dyspnoea, marked tachycardia, an abrupt blood-pressure fall or rise and profuse sweating, including beads of sweat on the forehead. The room should have an emergency kit containing an oxygen inhalation device, mouth opener, tongue forceps, defibrillator, ammonia solution, sterile disposable 2.0 ml syringes, sterile needles, 1 ml ampoules of 10% caffeine, 1 ml ampoules of cordiamine, nitroglycerin tablets and alcohol wipes. The kit should be supplemented according to the principal diseases of patients undergoing training [2].
Course design and monitoring
During a course, repeat tolerance testing periodically or adjust mixture O₂ after each session using heart rate and SpO₂. The target SpO₂ remains 90–80%, achieved through cardiovascular compensation. Reduce O₂ gradually in steps as adaptation develops. More severe disease or symptoms require longer steps, up to 6–7 sessions. This applies to all exposure types except repeated hypoxic sprints, used only for qualified athletes, where the target inspired O₂ is 12–14% (Figure 2).
For artificial hypobaric exposure in chambers, session duration and starting altitude matter. Allowing for gradual ascent and slow descent, O₂ levels are somewhat lower, 12–15%, than with normobaric exposure.
With live-low–train-high methods, hypoxic dose and load can be closely controlled. Initial inspired O₂ for passive intermittent hypoxic training is approximately 10–12% in healthy people and 13–15% in patients with pronounced disease. For active hypoxic training and intermittent hypoxic exposure during exercise, additional physical load requires higher targets: 12–14% in healthy people and 14–18% in patients. Courses should include at least 10 procedures, optimally 20. Passive training may be daily or on alternate days; active training, exposure during exercise and repeated hypoxic sprints should be no more than three times weekly. Sessions last 45–60 minutes for healthy people.
Patients should begin with 20–25 minutes, progressing to 35–40 minutes; children and adolescents should also begin with 20–25 minutes and increase gradually. Target SpO₂ is 90–80% regardless of training type.
For live-high–train-high, live-high–train-low and live-high–train-low-and-high methods, mainly used by professional athletes, starting exposure is crucial. According to testing, low-tolerance individuals start at 1500 m, moderate-tolerance at 1800 m and high-tolerance at 2100 m. Altitude is increased in steps whose length depends on adaptation. The target is 3000–3500 m for healthy people and patients alike. Athletes training over 20 hours weekly need closer recovery monitoring to prevent maladaptation. Natural moderate-altitude stays should last at least two weeks, optimally 18–21 days. The same duration applies to tents and hypoxic rooms, with exposure of at least 10, optimally 12–13 hours daily to elicit a haematological response; in some cases the simulated altitude also needs increasing.
Documentation must record examination and initial testing, protocols for initial/repeated hypoxic tests and every procedure, SpO₂ and heart-rate changes, complaints and adverse effects. Before each procedure the doctor or nurse performs instrumental assessment and clearance, explains the test/training protocol and possible unpleasant sensations, monitors the person during the programme, adjusts exposure or stops a session if wellbeing worsens, checks equipment and hygienically treats masks, tubing and other equipment. The specialist must also maintain training protocols and reporting documentation.
Training programmes in hypoxic methods are offered by equipment manufacturers such as ReOxy (http://www.reoxy.lu) and Hypoxico Russia (http://www.hypoxico.ru), working with leading national and international specialists in clinical, preventive and sports medicine, balneology and medical rehabilitation.
References
1. Горанчук В.В., Сапова Н.И., Иванов А.О. Гипокситерапия. СПб.: ЭЛБИ-СПб; 2003.
2. Методические рекомендации Медицинского центра Олимпийского комитета РФ. Применение дополнительного искусственного гипоксического воздействия в спорте высших достижений. Москва; 2013.
3. Постановление Правительства Российской Федерации от 28.03.2017 № 339 «Об утверждении перечня субстанций и (или) методов, запрещенных для использования в спорте, для целей статей 2301 и 2302 Уголовного кодекса Российской Федерации».
4. Стрелков Р.Б. Нормобарическая гипокситерапия: Методические рекомендации Министерства здравоохранения Российской Федерации. М.: ПАИМС; 2001.
5. Утехина В.П., Куртаев О.Ш., Утехин Е.В., Ищенко Г.Н. Методы нормобарической гипоксии в реабилитации больных ишемической болезнью сердца. Сочи; 2003.
6. Chizhov A.Ya., PotievskayaV.I. Intermittent normobaric hypoxia in prevention and treatment of the hypertensive disease. Moscow: Russian Peoples’ University Press; 2002.
7. Serebrovskaya T.V., Xi L. (еds.) Intermittent Hypoxia: From Molecular Mechanisms to Clinical Application. New York: Nova Sci Publishers, Inc.; 2009.
8. Küpper T., Milledge J.S., Hillebrandt D., Kubalova J., Hefti U., Basnyat B. et al. Work in hypoxic conditions – Consensus Statement of the Medical Commission of the Union Internationale des Associations d’Alpinisme (UIAA MedCom). Ann. Occup. Hyg. 2011, 55(4): 369–86.
Full main-text translation of: Образовательный курс «Гипоксическая тренировка». Занятие № 3. Общие рекомендации по организации гипоксических тренировок: показания и противопоказания, регламентирующие документы, аппаратура, подготовка специалистов. Физиотерапия, бальнеология и реабилитация. 2017;16(3):160–166.
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