Descent of 2000 Meters in Five Minutes – Hands-on Training in the Altitude Climate Simulation Facility of the German Air Force

Markus Tannheimer ^a,b, Raimund Lechner ^c,d, Thomas Küpper ^e,f, Andreas Werner ^e,g,h

^a Section of Sports and Rehabilitation Medicine, University of Ulm

^b General and Visceral Surgery, ADK-Hospital Blaubeuren

^c German Society for Mountain and Expedition Medicine

^d Medical Service, Police of Baden-Württemberg

^e Institute for Occupational, Social & Environmental Medicine, RWTH Aachen

^f Faculty of Travel Medicine, Royal College of Physicians and Surgeons, Glasgow (U.K.)

^g Medical Group Occupational Medicine, Medical Support Center Munster

^h Institute for Physiology/Center for Space Medicine and Extreme Environments, Charité Universitätsmedizin Berlin

Abstract

Military operations at high altitudes are of significant importance, as approximately 85 % of all armed conflicts worldwide occur in mountainous regions. Above an altitude of 2,500 meters, the risk of acute mountain sickness (AMS) increases markedly. Soldiers are significantly more affected than civilian mountaineers. The hyperbaric rescue bag provides an effective emergency medical measure under field conditions. By creating an overpressure in an airtight chamber, a physiological descent of approximately 2,000 meters can be simulated, often leading to rapid clinical improvement.

Practical training is required for safe application. The Altitude Climate Simulation Facility at the German Air Force’s Center for Aerospace Medicine offers optimal conditions for this. It enables a realistic depiction of high altitudes (15,000 feet, equivalent to 4,572 meters) in a controlled and safe environment.

During a training course, the effect of the hyperbaric rescue bag is impressively demonstrated. The simulated descent and the associated rapid improvement of physiological parameters, such as oxygen saturation and heart rate, are immediately tangible to the participants. This hands-on training enhances understanding of the pathophysiology of altitude sickness and the handling of available emergency measures during military operations at altitude.

Keywords: Military operations at high altitudes, acute mountain sickness (AMS), hyperbaric rescue bag, Altitude Climate Simulation Facility, emergency medical training, physiological parameters

The Altitude Climate Simulation Facility of the German Air Force

The Altitude Climate Simulation Facility (ACSF) in Königsbrück, now operated by the Center for Aerospace Medicine of the German Air Force, has a long history in the training and research of flight physiology [18][19], dating back to its use by the National People’s Army of the former German Democratic Republique [17]. Since its commissioning in 1987, it has been used to specifically prepare flying personnel for the effects of oxygen deficiency (hypoxia) and altitude conditions (low pressure). These measures are an essential component of flight safety [4]. Over the years, the chamber has undergone several modernizations to meet the latest technological standards [5]. The chamber is equipped with comprehensive safety measures to respond in an emergency quickly. Trained personnel can immediately intervene if complications occur during training. The HKS is a unique facility in Europe. It is not only used for military purposes but can also be utilized for scientific cooperation and research in the civilian sector.

Performance Data and Functions

The ACSF is a technical facility that enables the realistic simulation of the physiological effects of low pressure (altitude simulation) and, to some extent, climatic conditions (air temperature and humidity) on the human body. With a length of 6.60 meters, a width of 3.70 meters, and a height of 2.20 meters, the chamber is large enough to train six people simultaneously. Depending on the profile, longer simulations (up to 21 days) can also be conducted [10]. For safety reasons, an interior companion is generally present during ascents in the chamber, who is permanently supplied with 100 % oxygen as a paramedic or emergency medical technician and can intervene appropriately in case of complications until the pressure in the chamber has returned to ground level and further medical measures can be initiated. Additionally, a smaller chamber (with two seats) is attached to the main chamber to simulate rapid decompression.

Key Data of the ACSF

1. Altitude Simulation: In the ACSF, low pressure can be generated, equivalent to an altitude of up to 82,000 feet (≈ 25 km). This is well above the maximum flight altitudes of military aircraft (≈ 55,000 feet).
2. Climatic Ranges: Temperatures between 15 and 50°C and humidity between 30 and 80 % relative humidity can be generated in the chamber, which is of great importance for testing equipment and technical devices. In the small chamber, temperatures as low as -45°C can be generated, although this involves dehydrated air.
3. Hypoxia Training: One of the primary training objectives in the HKS is the simulation of oxygen deficiency (hypoxia), which becomes increasingly prevalent at altitude due to the reduction in O₂ partial pressure. Flying personnel can recognize their individual symptoms of oxygen deficiency here in a safe environment and learn how the symptoms change with the use of oxygen masks.

Importance and Use

The ACSF in Königsbrück is one of the central facilities for training flying personnel of the Bundeswehr. Its main tasks include:

1. Pilot Training: Pilots are prepared in the chamber for the physiological challenges associated with high-altitude flights. In particular, they learn how to recognize the symptoms of hypoxia early and take countermeasures.
2. Aeromedical Research: The ACSF is used for scientific investigations into the effects of low pressure, temperature, and humidity on the human body. This also includes studies on altitude sickness, acclimatization, and the limits of human performance in this extreme environment.
3. Testing of Survival and Protective Equipment: Equipment for emergencies, especially breathing masks and oxygen systems used in the event of a sudden drop in pressure at high altitude, is tested in the ACSF. Real conditions can be simulated here to ensure that the equipment functions reliably under extreme conditions.
4. Emergency Scenario Training: The ACSF also allows training for emergencies, such as a sudden drop in pressure or failure of the oxygen system in an aircraft.
5. Altitude Medicine Training for Medical Personnel: This course was initiated at the request of foreign deployments by the Surgeon General of the German Medical Service, Lieutenant General Bernhard Nakath, MD, and by the Surgeon General of the German Air Force, Brigadier General (ret) Erich Roedig, MD, and took place almost annually until 2022.

Basics of Altitude Sickness and Hyperbaric Oxygen Therapy

Military operations at high altitudes are of great importance, as approximately 85 % of all armed conflicts worldwide occur in mountainous regions. Acute mountain sickness (AMS) occurs when the body is not given sufficient time to adapt to the lower oxygen partial pressure at high altitudes [13]. This can lead to headaches, nausea, fatigue, and in more severe cases, pulmonary or cerebral edema [7][14]. The susceptibility of soldiers to altitude sickness is about twice as high as that of civilian mountaineers [16]. In such symptoms, especially in severe forms, the best therapy is immediate descent [6]. However, this often cannot be carried out due to the patient‘s condition, adverse weather conditions, poor lighting and visibility, challenging terrain, or lower camps that have already been dismantled, thus lacking necessary infrastructure [3][9]. In the military context, mission fulfillment and the military threat often do not allow for descent [8].

The hyperbaric rescue bag offers a mobile option for an initial and temporally limited treatment option [2], enabling an artificially created overpressure environment to increase oxygen availability in the breathing air. Although the patient remains at the exact location and terrestrial height, they are „transported“ to a lower altitude level, which physiologically corresponds to a descent.

Functionality of the Hyperbaric Rescue Bag

A hyperbaric rescue bag operates on a simple principle: the patient is placed in an airtight bag, which is then pressurized using a pump. This significantly reduces the simulated altitude inside the bag by about 1,500 to 2,500 meters, increasing oxygen availability for the patient. This provides quick relief from altitude sickness symptoms, especially life-threatening forms such as high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE) [9][15].

The most commonly used models are the Gamow Bag^®and the CertecBag^®. Another model, the PAC Bag^®, according to the Australian manufacturer, is not delivered in Europe and has the design disadvantage that patients must be slid in lengthwise, which is extremely difficult if a patient cannot actively cooperate. The following discussion, therefore, focuses on the first-mentioned models:

Gamow Bag^® : This is a widely used, robust hyperbaric bag manufactured by Chinook Medical Gear Inc. (USA), which has been in use for decades. It has proven to be a reliable option for treating AMS, HAPE, and HACE. It can be inflated relatively quickly (in about 2 minutes) and allows the simulated altitude to be reduced by up to 2,000 meters. Due to the numerous crossing straps, it can be challenging to place non-cooperative patients into the bag.

CertecBag^®: This model by the French company Certec is characterized by its lightweight design and ease of handling, making it particularly attractive for mountaineers and expedition teams. The CertecBag^® is also more compact than the Gamow Bag^®, which can be advantageous in extreme ventures where weight and pack size are critical. There are two variants with different internal pressures (180 mbar and 220 mbar), each achieving a greater reduction in simulated altitude compared to the Gamow Bag. During the course in the ACSF, we used the 180 mbar (Trekking) variant. The exemplary calculations (Figures 3 and 4) were performed with the 220 mbar variant (MAM’OUT).

Recommendations of International Professional Societies

Leading professional societies such as the International Society for Mountain Medicine (ISMM), the Union Internationale des Associations d’Alpinisme Medical Commission (UIAA MedCom), and the Wilderness Medical Society (WMS) recommend the use [1][11][12] of a hyperbaric rescue bag in cases where descent is not immediately possible [6]. Typical symptoms for its use include severe headaches, vomiting, signs of pulmonary edema (e.g., shortness of breath and performance decline), or neurological symptoms such as confusion [9][15]. The recommended duration of treatment varies but typically ranges between 1 and 2 hours per session [11]. Repeat sessions may be necessary, especially if circumstances continue to delay descent. Rapid improvement of symptoms is often expected after 30–60 minutes. This should ideally be used to assist with descent with the patient, if possible, or to transport them [3].

Application of the Rescue Bag

To perform the procedure, the patient is placed in the rescue bag, which is then sealed and pressurized using a pump until the integrated pressure valve opens. Pumping must continue to supply the patient with fresh air. Mountaineers have died due to insufficient air supply and CO₂ buildup because the group failed to continue this maintenance pumping. The patient‘s condition should be regularly monitored during treatment. Ideally, a pulse oximeter is attached to the patient, and a barometric altimeter is included in the rescue bag for success control [11]. Additionally, therapy in the bag can be supplemented with oxygen insufflation and medications against altitude illness. Sufficient insulation from the ground should also be ensured. Since significant nausea often exists, a bag for potential vomiting during therapy should be provided to the patient. If available, decongestant nasal drops can be applied beforehand to facilitate pressure equalization. Continuous psychological support of the life-threateningly ill patient and constant monitoring through the viewing window are self-evident. Even though the principle is simple, practice is required for practical application [11], primarily since real-life application situations are often associated with high stress and the patient‘s companions usually also experience altitude symptoms.

This training took place during the course „Altitude Medicine for Medical Personnel.“ The ACSF provided an ideal and safe, as well as a very illustrative and practical, demonstration for this purpose. This will be presented below.

Training and Testing in the HKS

During the “Altitude Medicine Course for Medical Personel”, participants experienced an oxygen deficiency demonstration at 15,000 feet (4,572 meters) in the HKS. In addition to tests for color vision and concentration ability, a hyperbaric rescue bag (CertecBag^®) was tested in practice. The handling was trained the day before. A course participant, equipped with a pulse oximeter and a barometric altimeter, lay down in the rescue bag. It was sealed and inflated by the other course participants, maintaining the fresh air supply thereafter (Figure 1).

Fig. 1: CertecBag (R hochgestellt), trekking version with 180mbar internal pressure (Origin of photo material: Raimund Lechner).

Once a relevant pressure had built up in the rescue bag through pumping, the altitude inside the bag dropped noticeably for the course participants, as observed through a viewing window on the barometric altimeter placed inside. With some delay, the subject‘s oxygen saturation increased by about 25 percentage points to nearly 100 %. The pulse rate, increased due to altitude hypoxia, decreased in parallel. Within just 5 minutes, a physiological descent of 2,000 meters was achieved. At the end of the demonstration, the pressure in the rescue bag was slowly released, and the chamber altitude was regained. During this process, the SpO2 dropped again, and the pulse increased (Figure 2).

Fig. 2: Use of the hyperbaric rescue bag (CertecBag^® Trekking) at 15,000 ft (4,572 m): Within 5 minutes, the person inside „descends“ physiologically by 2,000 m. Once a relevant pressure has built up in the bag, the SpO₂ increases by about 25 percentage points.

Discussion

The extent of the achievable physiological descent depends on the starting altitude and the rescue bag used. The higher the starting altitude, the greater the effect (Figure 3). There are also technical differences between the various hyperbaric bags, listed in Table 1, which affect the achievable descent altitude.

Tab. 1: Specifications of Gamow and CertecBag^®

Fig. 3: Comparison of Gamow and CertecBag^® (220 mbar version): The higher the starting altitude, the greater the descent effect; exemplary at 3,000 m: 1,450 m with the Gamow Bag vs. 2,200 m with the CertecBag^® or at 7,000 m: 2,130 m with the Gamow Bag vs. 3,175 m with the CertecBag^®.

Hyperbaric rescue bags are typically used at altitudes between 3,000 meters and 7,000 meters above sea level. Severe forms of altitude sickness are sporadic below 3,000 meters, and above 7,000 meters, the effort required for necessary pumping becomes so great that application is generally no longer possible. Since the internal pressure of the CertecBag^®is higher at 220 mbar than that of the Gamow Bag (138 mbar), a greater descent altitude is achieved with the CertecBag^®. At 3,000 meters, a descent of 1,450 meters is achieved with the Gamow Bag and 2,200 meters with the CertecBag^®. At 7,000 meters, a descent of 2,130 meters is achieved with the Gamow Bag and 3,175 meters with the CertecBag^®.

From a user‘s perspective, this does not play a significant role, as the descent altitude achieved with the Gamow Bag is entirely sufficient. For real descent, a descent of 300–500 meters or to the altitude of the last symptom-free night is recommended [2]. In life-threatening forms such as high-altitude pulmonary edema or high-altitude cerebral edema, a descent of at least 1,000 meters should be undertaken [6]. In the military context, for example, if the altitude relocation occurred through rapid air transport to altitude, even the Gamow Bag still has sufficient safety reserves.

Fig. 4: Inspiratory O₂ partial pessure achieved in the corresponding atitude in the Gamow Bag and CertecBag^® (220 mbar Version) compared to the natural environment.

Conclusion

Hyperbaric rescue bags are a fascinating example of how practically applied physiology can save lives. Although their application is fundamentally simple, user training is still required. For this, the ACSF in Königsbrück offers ideal conditions, as the technical handling of such a rescue bag can be practiced in a safe environment, and the impressive physiological effect can be experienced live. The visualization of increasing oxygen saturation, decreasing pulse, and real physiological descent significantly enhances learning success.

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Manuscript Data

Citation

Tannheimer M, Lechner R, Küpper T, Werner A: [Descent of 2000 Meters in Five Minutes – Hands-on Training in the Altitude Climate Simulation Facility of the German Air Force.] WMM 2025; 69(10-11E): 8.

DOI: https://doi.org/10.48701/opus4-761

For the Authors

Lieutenant Colonel (MC Res.) Prof. Dr. Markus Tannheimer

Department of General Surgery, ADK-Hospital Blaubeuren

Ulmer Str. 26, D-89143 Blaubeuren

E-Mail: m.tannheimer@adk-gmbh.de