Effects of changing air pressure
When an aircraft climbs during take off the air pressure inside the cabin decreases and the air and other gases expand by 30%. Similarly, as the aircraft descends for landing, the volume of a gas will decrease. These changes do not cause any problems where gas movement can take place freely, such as in the lungs, but may cause discomfort or damage where gas is trapped or restricted
The middle ear
- As the aircraft takes off, air in the middle ear (behind the ear drum) expands and some escapes down a tube into the back of the mouth - you often feel a 'popping' sensation as it happens. As the plane lands air has to pass back into the middle ear to equalise the air pressure.
- Yawning or swallowing can help to clear the ear but if this doesn't work then pinching the nose and attempting to blow out gently with your mouth closed may do the trick.
- You can help babies and infants by giving them a feed or a dummy to suck on.
- If you have a cold and the tube is blocked, you may get problems which may be worse during landing. The pressure in the middle ear becomes lower than that in the outer ear, the eardrum is pushed inwards, causing discomfort and sometimes can lead to the eardrum rupturing.
The sinuses
- The sinus cavities lie within the bones of the face and skull and are connected to the nose and the back of the mouth by narrow ducts. The sinus cavities contain air, which expands and contracts on ascent and descent.
- Congestion due to a head cold (or conditions such as hay fever) can cause partial or complete blockage of these ducts, which may result in considerable pain during descent to lower altitude. Decongestant nasal sprays may help by reducing congestion and opening up the ducts.
Trapped air in teeth and the gut
- If you have air trapped in pockets of dental decay or dental abscesses you may experience discomfort, which is usually worse during take off.
- The stomach and intestines contain gases, which may lead to a sense of fullness or bloating.
Cabin air quality
- The control of the cabin air system is automatic and is designed by the aircraft manufacturer to comply with the requirements of the regulatory authorities.
- Onboard oxygen availability (because of the lower pressure) is less than at sea level, it is more than adequate for normal healthy individuals.
- The total volume of air in the cabin is exchanged every 2 to 3 minutes, compared with an exchange rate of 5 to 10 minutes in an air-conditioned building.
- In modern aircraft, all the recirculated air is passed through high efficiency particulate filters which remove more than 99% of particles, including bacteria and viruses.
- Research by the World Health Organisation (WHO) has found no evidence that air recirculation facilitates transmission of infectious disease aboard aircraft.
- The cabin air, although dry, does not make you dehydrated or harm your health. Dry skin and eyes can lead to discomfort, which can be alleviated by the use of moisturising creams and eye drops.
- Onboard oxygen availability (because of the lower pressure) is less than at sea level, it is more than adequate for normal healthy individuals.
Jet Lag
Jet lag occurs when the body clock is disrupted by crossing a number of time zones. The symptoms can include fatigue, disorientation and an inability to sleep.
Your body clock
Deep in your brain there is a 24-hour master clock governing every aspect of the body's functioning. Called the circadian clock (circ = about and diem = day), it synchronises the following internal systems so they function smoothly with each other and with the external world:
- sleep and wake cycle
- levels of alertness
- performance
- mood
- hormone levels
- digestion
- body temperature
- light is one of the primary cues that the clock uses to maintain this link with the outside world
Crossing time zones
This confuses the body clock because it has to adjust to a new time and new patterns of light and activity. To make matters worse, not all internal body functions adjust at the same rate. So your sleep/wake cycle may adjust more quickly than your temperature. Your digestion may be on yet another schedule. Confusing the clock like this causes the mental and physical upset we call jet lag.
Go west
Though the body clock has difficulty adjusting to time zone travel, it prefers flying in an east to west direction. This is because although we live on a 24-hour day, the natural rhythm of our clock is programmed to operate on a day that is longer than 24 hours. So our internal clock can naturally extend our day but it finds it very difficult to reduce the hours in our day.
When flying west you are adding hours and going in the natural direction of your internal clock. For example, flying westward from London to New York involves extending your day by five hours, while the eastward flight from New York to London results in shrinking your day by five hours
Managing jet lag
Because it can take the body clock anything from several days to several weeks to fully adjust to a new time zone, it may be less disruptive to keep yourself on your home time schedule if you are only going to be away from home for a short time (about 48 hours or less).
If your trip is going to be longer, you should start to adjust to your new time zone as soon as you board the plane.
How to keep your body clock on home time
You need to do a bit of advance planning, but these steps will help:
- Calculate the time difference between your home time and the time at your destination.
- Consider when you normally would be asleep and awake on your home time compared to the times at the new destination.
- Make a note of the destination times that correspond with times when your body clock would be at maximum sleepiness at home (3-5am and on a lesser level 3-5pm).
- Try to avoid important business meetings scheduled at these times of maximum sleepiness at home.
- Try not to be in the light at your destination if you would normally be in darkness at home. You can do this by staying indoors or wearing sunglasses when you go out.
- When planning meals try to keep your stomach on home time. So if it is dinner time at your destination, but breakfast on your home time, try to have something light, rather than a full heavy dinner that your stomach may not be ready to digest.