My exciting and educational field trip to the Singapore Aeromedical Centre!

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Hi again, dear readers.

Today I am back with another blogpost! I am super excited to write today’s post because the military is something that I've been rather interested in ever since I joined the National Police Cadet Corps (NPCC) in secondary school.

So I had a chance to visit the Singapore aeromedical centre. Boy, was it security tight! Oh, just in case some of you are wondering, this was part of my field trip for my module: LSM4215: Extreme Physiology. As what many of you would know, I am very curious about the human body since I was a kid and it is just so fun and exciting to understand how the body works and how the body react to extreme conditions! My fascination of how the human body functions has led me to appreciate the complexity of physiological anatomy of the human body and this is what prompted me to learn human physiology!

So today, I will be sharing what I learnt from my fun and exciting educational trip. I hope some of you will be just as inspired as me after reading this blogpost! :D May be for the male readers out there, this might even give you a glimpse of what you might be up to when you are enrolled to be an  RSAF pilot.

So we first started out with the human centrifuge. This is a very big and intimidating looking centrifuge that generates high G-force that replicates the G-forces which a fighter pilot has to endure, in a safe and controlled environment. Most advanced fighter jets can pull a maximum of 9Gs. In comparison, a person experiences 1G on the ground, and a rollercoaster typically generates 2 to 3Gs. Meanwhile, a normal human tolerance is about 4G, before he or she experiences a blackout, also known as G-LOC, or gravitational force-induced loss of consciousness, which is what happens when insufficient oxygen reaches the brain because high G-forces cause blood to rush to the legs.  G-LOC has been a continuing threat in tactical fighter operations and is still one of the most frequent causes of fatal aircraft mishaps. Therefore, the human centrifuge aims to replicate the setting in which the fighter pilots will experience when in the jets and train them to be ready and execute the anti-G straining manoeuvre (AGSM).

A good and effective anti-G straining manoeuvre can give increase G-tolerance by about 3-4G. AGSM increases aortic blood pressure, maintaining brain perfusion thereby maintain pilot consciousness. There are two components to AGSM:

1.     Isometric Contraction:  Flexion or tensioning of skeletal muscles of legs (calf and thigh) and abdomen.  This step increases pressure in the chest and displaces blood away from these contracted muscles into the arms, chest, and brain. In other words, it causes the blood vessels at the lower limbs to constrict thereby preventing blood pooling, avoiding the occurrence of blood deprivation in the brain.

2.      Respiratory component which serves the purpose of countering the downward G force by increasing chest pressure by expanding the lungs. Breathing techniques were taught which involves rapid (< 1 sec) exhalation/inspiration cycles every 3-4 seconds. This maintains oxygen content and decreases carbon dioxide in the blood, while also relieving increased pressure of chest, and allowing the heart to refill with blood and also forces blood to flow from the heart to the brain.

According to Dr. Ganesh Anbalagan, the Head of Aviation Physiology Simulations and Safety at Singapore Aeromedical Centre, the straining step involves breathing out without letting the air escape so as to increase intra-thoracic pressure, which will increase mechanical pressure to squeeze blood to the brain. According to him, the most effective way to do this, in order to yield the highest increase in chest pressure, is to breathe out against a closed glottis. This way, the blood in the head and torso is prevented from flowing into the body’s lower extremities, thereby enabling the pilots to maintain consciousness.

On top of that, there is also the anti-G suit or trousers that contain 5 air bladders located over the abdomen, one over each thigh, and one over each calf. These air bladders will inflate to reduce the amount of blood that can pool in the lower limbs during high-G manoeuvres. This allows more blood to be pumped to the brain so that aviators are less likely to experience G-induced Loss of Consciousness.

While such conventional anti-G suits provide 1 to 1.5Gs of protection, the Full Coverage Anti-G Trousers (FCAGT) that all RSAF fighter squadrons don on, can provide 2 to 2.5Gs of protection. This is because the FCAGT's air bladders fully cover the limbs, offering 95 percent lower body coverage compared to the five-bladder suit which only provides 40 percent lower body coverage. This means 50 percent less energy expenditure for the aircrew when using the FCAGT (Figure 1).

Figure 1: Full Coverage Anti-G Trousers that is donned by the RSAF fighter pilots (Neo, 2015).Photo was taken from Mindef website.

Technology has also made it easy to check that the pilots are executing both parts of the AGSM. The radar pedals in the human training centrifuge are installed with sensors that can measure how much the pilot is straining and also a camera that monitors the respiratory aspect of AGSM.

To mini-conclude for this section, the 9G that a fighter pilot may experience in the aircraft can be cushioned and alleviated due to protection by executing the anti-G straining manoeuvre (AGSM) as was trained in Human Centrifuge and donning on the Full Coverage Anti-G Trousers (FCAGT):

Next, we went to the Somatogyral Turntable. Before I continue to explain about this machine, let me just recap briefly (through pictorial) about what we know about the vestibular system.

Figure 2: Semicircular canal system mechanism

Figure 3: Otolith mechanism

The Somatogyral Turntable demonstrates the limitations of the human vestibular system (which is the sensory system that is responsible for coordination of movement and balance) in the air and shows how the balance organ systems can misinterpret aircraft motion and potentially confuse the aircrew controlling the aircraft. This is because, while the sensory organ for movement on the ground is accurate, the same sensory organs can give inaccurate information when in the skies and this may lead to spatial disorientation. Spatial disorientation is a condition in which an aircraft pilot's perception of direction does not agree with reality. This is particularly dangerous during poor weather conditions with low or no visibility because the pilot may not have an external visual horizon and may not know the plane’s true position, motion and altitude relative to the surroundings. As such, it may lead to inaccurate judgments and decisions and the pilot may veer the aircraft in a wrong direction.

According to Dr. Ganesh, spatial disorientation was reported as the largest human factor that causes fatal accidents. Therefore, if the pilots can recognize that he is going through spatial disorientation, he should learn to not trust his deceiving senses but instead, rely on his instruments.

Personally, I got the chance to try the Somatogyral Turntable, which is a rotating black box designed to make one lose all sense of spatial orientation when seated within. And, that is exactly what I experienced. I literally could not perceive any sort of motion from inside. I followed the operator’s instructions to tilt my head slightly to the right and I felt the world turning upside down.

I was informed that I was suffering from vestibular illusion, where my eyes were telling my brain that I was not moving, even though I was spinning at 12 rounds a minute. Tilting my head had activated the sensory organs in my ear canals that told my brain otherwise and this created a confusion.

I was then told to tilt my head to the left, then up at the ceiling before stretching out to “get that $10 bill on the floor”. Nope, it was definitely not worth the imaginary $10 bill because my head was spinning and I felt dizzy after that. I really felt the disorientation and it took me a while to regain my sense of balance without veering off the path.

The third place that we went to was the altitude chamber or the hypobaric chamber. The altitude chamber can take up to 80 000 feet to simulate the effects of high altitude on the human body, especially hypoxic hypoxia. Hypoxia, by definition, is the lack of sufficient oxygen in the blood, tissues, and/or cells to maintain normal physiological function. The most common form of hypoxia encountered in aviation is called hypoxic hypoxia, which results from a deficiency of O2 (or reduced partial pressure) in the air being inspired. Pilots may experience hypoxic hypoxia when flying at altitude in an unpressurized aircraft. With increasing altitude, the partial pressure of oxygen gets lower and the lungs cannot effectively transfer oxygen from the ambient air to the blood to be carried to all tissues in the body. Hypoxia can lead to a loss of cognition, which can be detrimental, particularly for pilots who have to make important decisions that affect the safety of all passengers and crewmembers onboard. And this is where the altitude chamber comes in. The primary purpose of the altitude chamber is to train the pilots to recognize physiological symptoms of hypoxia, thereafter enabling them to react in actual flight so as to avoid emergencies.

The final place we visited was the Ejection Seat Trainer, which helps pilots train to adopt the correct posture should they need to eject. This is because pilots may need to abandon their aircraft at high speeds during emergencies and the violence of the motion may result in the pilot suffering from permanent disabilities. Thus, the right posture to adopt was a tucked-in posture, body kept as rigid as possible and the spine kept straight.

After my giddiness at the somatogyral turntable, I knew I do not have the stomach for flying, but the experience certainly left me with a newfound respect for those who do. This trip really made me appreciate all the advances in technology we have to help people cope with extreme conditions.

Till then, I’m Nabilah signing off!

See you at my next blogpost!