■Middle Ear

When the ear, normally adjusted to surface pressures, is exposed to increased pressure during diving, the middle ear’s eardrum can feel painfully disturbed. In this case, we use the Valsalva maneuver to equalize pressure. The Valsalva maneuver is performed by forcibly exhaling at the same time you are pinching your nose while keeping your lips tightly closed.

The action forces air into the middle air via the Eustachian tube. However, you should take care not to overdo the maneuver to avoid auditory damage form over-pressurization.

Swallowing and a yawning motion are some of the gentler methods that can work as well.

In order to prevent squeeze, you should equalize frequently and in advance of any pain developing. If you find it difficult to equalize, slowly ascending to a shallower depth should resolve the issue. As well, equalization is easier if you descend feet first from the surface. If discomfort or pain is ignored and you continue to descend, there is a risk of a perforated eardrum, which allows water to enter the middle and inner ear regions. Water’s chilling effect on the cochlea causes excessive dizziness and malaise. In the case of this happening, grab hold of a rock or anchor-line to stabilize yourself, and once the water is warmed and balance somewhat restored, make an emergency assent.

■Sinus

Sinuses are joined to the nasal cavity via small orifices called ostia. These remain open and so pressure equalizes under normal conditions. However, these become blocked relatively easily by colds and allergic inflammation, causing sinusitis. For divers, this can present a problem with pain due to unequal ear pressure equalization. Most commonly, the sinus cavities in the forehead area become painful. In the worst case scenario, the pressure causes capillaries to break, causing bleeding in the sinus areas that pools in the throat area.

If you have a cold with blocked sinuses, don’t dive.

■Lungs

Even though at 40m depth lungs compress to 1/5 their normal size, pliable lungs can suffer squeeze. This is due to the unique phenomenon called “Blood Shift”, where the blood gathers in the areas of the body due to pressure.

■Teeth

Dental care, such as fillings, can create spaces in teeth in which nerves get pulled due to squeeze. This can be corrected by visiting your dentist.

■Mask

If you feel mask squeeze, you can equalize by blowing air out from your nostrils into the mask. This is called “Mask Blow”. If you neglect to complete a necessary mask blow, the pulling can cause blood vessels in your eyes to rupture. In the worst case, this pooled blood can cause bruising in the eyes or around the face.