Breathe easy

(L-R) Ex-LACW Alex Willett and WOFF Andy Hislop receive direction from AVMED Hypoxia trainer SGT Craig Keane who, in a night vision demonstration in the hypobaric chamber, outlines the difficulties of map reading under various coloured lights and at altitude. (Photograph by SGT Ian Gosper and LAC Ian Hurlock).

In a world-first, the Royal Australian Air Force's Institute of Aviation Medicine (AVMED) has introduced a revolutionary technique to eliminate the risk of decompression illness for aircrew under instruction in the facility's hypobaric chamber.

The technique, which involves aircrew breathing air containing a reduced level of oxygen to simulate being at an altitude 25,000 feet, allows for effective hypoxia training in a safe environment.

Hypoxia is the single most serious physiological risk an aviator will face at altitudes above 10,000 feet. This is because the partial pressure of oxygen above that is too low to allow for normal physical and mental function.
AVMED, at RAAF Base Edinburgh in South Australia, may be one of the RAAF's smallest units, but without it, aircrew would be less prepared and aware if one of their worst nightmares came true - if they became hypoxic, or starved of oxygen, while flying.

The symptoms of hypoxia are highly individual and can be reproduced. This means it can be demonstrated to aircrew in a controlled environment and they will tend to get the same symptoms if hypoxia occurs in the aircraft. They will also know how to recover.

Commanding Officer AVMED, Wing Commander Suresh Babu, who has been involved with aviation medicine for more than 22 years, said hypoxia is traditionally demonstrated in the hypobaric chamber at a simulated altitude of 25,000 feet.

The Time of Useful Consciousness (TUC) at this altitude is normally about three minutes,' he said.

'This period of time allows for ease of demonstration of individual hypoxia symptoms as well as the importance of TUC when the aviator takes recovery action and starts breathing 100 per cent oxygen.

'The altitude of 25,000 feet is not without risks - the most serious risk being Decompression Illness (DCI).'

The affects of DCI can include skin rashes (commonly called the creeps) and joint pains (known as the bends) that are usually resolved once emergency action has been taken. Sometimes, people experience lung problems (chokes) and neurological problems (staggers) that require hyperbaric treatment (recompression).

WGCDR Babu said several cases of DCI had occurred at AVMED during the 42-year history of the institute.

'These cases have been associated with the traditional hypoxia training at 25,000 feet,' he said. 'As a result, AVMED ceased using the traditional procedure in January 2001 and alternatives were researched.'

In December 2001, AVMED began hypoxia demonstrations in the hypobaric chamber to simulate an altitude of 10,000 feet.

Aircrew in the chamber then breathe air that contains a reduced level of oxygen to simulate being at an altitude of 25,000 feet.

'This newly-developed technique is referred to as "Combined Altitude Depleted Oxygen (CADO) Hypoxia Awareness Training Protocol" which eliminates the risk of decompression illness while at the same time providing excellent training benefits.'

WGCDR Babu said under CADO, hypoxia exposure was limited to five minutes so aircrew are able to get two to three symptoms.

'At this time, we instruct them to take immediate action, as they would in the aircraft, by selecting 100 per cent oxygen and emergency pressure on their personal regulator. This recovery procedure is commonly called "gang-loading".' The chamber is then descended to ground level and a debrief takes place.

AVMED will soon be using biological monitoring equipment that will facilitate further research, testing and evaluation of the CADO protocol, again proving the facility's personnel truly believe in their motto - 'Safety through Knowledge'.