Reverse blocking

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The reverse blocking is a term from the diving . It can occur with ascending divers as well as with passengers of an aircraft taking off and arises as a result of a drop in ambient pressure . In this case, gas (usually breathing gas) cannot escape from a cavity, which prevents pressure equalization with the environment and an overpressure builds up in the cavity concerned. Gas-filled cavities in the body that are relevant for recreational divers are the lungs, paranasal sinuses, frontal sinuses, middle ear, but also carious teeth and the digestive tract. Reverse blockages are sometimes very painful and in extreme cases can lead to serious injuries such as tearing the eardrum.

Symptoms

As different cavities in the body can be affected, different symptoms also occur. Reverse blocking is associated with mild pressure to severe pain in the affected areas and only occurs when you surface.

Reverse blockages are easy to identify by the fact that symptoms disappear when the ascent is stopped and then descended again. This does not apply to glottic cramp.

Causes and consequences

Example of a blockage:
You can ascend from a depth of 10 m to 5 m. The pressure difference is 0.5 bar . Since in this case the resulting forces act directly on the nerve, the diver would in reality suffer considerable toothache even a little over 10 m depth and interrupt the ascent.

During diving, the diver's body is exposed to the external pressure that increases with increasing depth. The pressure can first be felt on the sensitive eardrums and already above 1 m diving depth. All divers, including apnea divers , must actively perform pressure equalization , in which the pressure in the cavities behind the eardrum is raised to the level of the external water pressure. With scuba diving, there is also the fact that the lungs are unable to fill against external pressure. The breathed air is supplied by the regulator with exactly the ambient pressure, which is why the lungs also have an internal pressure that corresponds to the ambient pressure and still maintains its volume. When you surface, the ambient pressure drops and the air expands again. This behavior can be traced back to Boyle-Mariotte's law , which states that the pressure and volume of a gas in a closed system are inversely proportional. Normally, the excess gas escapes automatically through the breath. For this reason, a scuba diver should never hold his breath, but breathe continuously so that excess gas can escape, especially from the lungs. The middle ear is connected to the pharynx via the eustachi tube , which is why air can also exit the ear.

In the case of reverse blocking, one of the paths through which the air reaches the throat is at least partially blocked or completely closed. The air cannot escape, which creates an overpressure in the affected cavity. There are forces acting on the surrounding tissue, which lead to pain and deformation.

  • The most common reverse blockages occur in the middle ear. They can usually be explained by inflammation or colds , which lead to swelling of the mucous membranes and accumulations of mucus. The mucus blocks the connection to the throat. A reverse blockage in the middle ear results in a painful protuberance of the eardrum, which in extreme cases can lead to overstretching or even tearing.
  • Cavities can form in carious teeth or under leaky tooth fillings . Here, too, it can happen that the pressure in the tooth is not reduced quickly enough. One possible cause is the small diameter of the hole. Forces can be exerted on the dentin or directly on the nerve, some of which are very painful.
  • Overpressure can also build up in the digestive tract. They can be traced back to the formation of digestive gases or inhaled air.
  • An extremely dangerous form of reverse blocking occurs as a result of glottic spasm . Water droplets cause the larynx to cramp and prevent breathing. This condition leads to serious injuries such as overstretching or even tearing of the lungs on further ascent . Furthermore, the blockage leads to suffocation . With a glottic cramp there is extreme danger to life. The rescue measures are completely different from the behavior with other reverse blocking.

Countermeasures

In the case of acute reverse obstruction, the only option is to increase the external pressure again. The ascent process must be canceled. The diver should sink to a depth at which the symptoms subside, then emerge very slowly with pauses and then stop looking for greater depths or, if necessary, cancel the dive. The symptoms usually go away after a few minutes. This does not apply to a glottic cramp .

If the symptoms occur on a plane taking off , a reverse Valsalva attempt can help by closing your nose and mouth and carefully sucking in the air.

If the symptoms recur, the consultation of a doctor who is familiar with diving medicine is strongly recommended. There is a possibility that there are chronic organic causes. These need to be dealt with. In rare extreme cases, the illnesses that cause it can also lead to a person not being able to dive.

Reverse blocking of the teeth is clear evidence of leaky teeth. Visiting a dentist as soon as possible is essential.

It has happened that in caissons, when there was a sudden drop in pressure (“blow-off”), workers who had an accident had to have their eardrums pierced in order to be able to move them quickly enough out of the danger zone into a decompression chamber . This method is only useful when there is acute danger to life and as a last resort, as there is a risk of irreparable damage to the ear.

What to do if you have a glottic cramp

Glottic cramp is a natural protective reflex that is designed to prevent fluid or foreign bodies from getting into the lungs. The lower airways are completely closed. It is an uncontrollable reflex that causes the person concerned to fear death and the uncontrolled desire to climb as quickly as possible, which on the one hand would not release the blockage and on the other hand can lead to fatal injuries to the lungs.

The situation of a glottic cramp is life-threatening.

The only way of rescue is to use force to keep the drowning person at the current depth level until he faints due to the lack of oxygen. In the event of unconsciousness, the muscles relax and the cramp should also be released so that the breathing reflex starts again. Then you have to surface slowly.

Resuscitation measures such as chest compressions and mouth-to-mouth resuscitation must be performed immediately after surfacing . Rescue workers are to be called as soon as possible via the emergency number .

Prevention and precaution

  • A dehydrating regulator can be a cause of glottic cramp. A regular revision of the safety-relevant technology is mandatory and strongly advised.
  • When planning the dive, the prescribed reserve pressure of the cylinder must be included and only marked during the dive in emergencies. Reverse blockages delay the ascent and therefore require unpredictable additional air.
  • Pressure equalization must not be forced when diving. If there are already problems descending, reverse blockages are not unlikely.

Explanations

  1. ↑ Even in the apnea diver, the internal pressure of the lungs corresponds to the external pressure. But the volume sinks. The lungs are compressed. When ascending, the air does not have to escape. The amount of air corresponds exactly to the lung volume at normal pressure. This does not apply to the middle ear as it is not compressed.