Sound advice for tunnel travellersBMJ 1994; 309 doi: http://dx.doi.org/10.1136/bmj.309.6952.426 (Published 13 August 1994) Cite this as: BMJ 1994;309:426
- D W Proops
The Channel Tunnel will soon be open and millions of people are expected to use it. But are there any health risks associated with travelling through the tunnel? Eurotunnel have recently issued guidelines for doctors (available from Eurotunnel*, and these have focused on the effects of such travel on the ears.
Everyone experiences some slight discomfort when entering a tunnel in a train or when flying. Rapid changes in ambient pressure occur when entering a tunnel at speed, or when two trains pass each other in a tunnel. This increase in pressure deflects the intact tympanic membrane medially.
The tympanic membrane is, of course, designed to move, and most people can equalise the relative pressures each side of it by swallowing to allow air to pass through the eustachian tube. Other measures such as the Valsalva manoeuvre, yawning, or rapidly moving the tongue against the soft palate (the Frenzel manoeuvre) also open the eustachian tube, and achieve the same effect.
These mechanisms are important for adapting to the sustained changes in pressure that occur when flying.1 The more rapid change of pressure experienced on a train may not give time for these natural measures to equalise the pressure. But what are the chances that this will damage the ear? Otic barotrauma depends on the amount of pressure change along with other predisposing factors such as acute and chronic infections of the nose such as coryza and rhinosinusitis.
The changes are vascular in origin and include mucosal congestion, oedema, haemorrhage, effusion, and polymorph infiltration.
The extent of otic barotrauma depends on two factors; the size of the pressure change, and the ability of the eustachian tube to open. When there is a sudden external rise in pressure it may “lock” the eustachian tube, and Armstrong and Heim showed that a positive extra tympanic pressure of 90 mm Hg (12 kPa) is enough to lock the tube.2
*Eurotunnel, The Adelphi, John Adam Street, London WC2N 6JT and 112 Avenue Kleber, BP 166-Trocadero, 75770 Paris Cedex 16.
Locking produces pain from the many unmyelinated fibres in the tympanic membrane but can also lead to rupture. Tears commonly occur in the anteroinferior portion, and also at the sites of previous scars. Fortunately most traumatic perforations heal quickly. A more serious injury is rupture of the round window membrane. In 1971 Goodhill reported spontaneous rupture of the round window membrane caused by rises in intracranial pressure from coughing, sneezing, or straining.3 A sudden change in middle ear pressure from an outside source could have a similar effect.
A person who has undergone a stapedectomy, in which an otosclerotic stapes is replaced by a prosthesis, does have a theoretical increased risk of ear damage if exposed to sudden pressure changes, and this was investigated in flying by Rayman in 1971.4 Those with middle ear effusions will not notice pressure changes, and the same is true of patients with perforations or grommets who will have a natural system of equalising pressure.
What should doctors tell patients about using the Channel Tunnel? Tunnel travel seems unlikely to damage the ear. While travellers may be aware of the sensation of pressure in their ears when entering the tunnel, those with normal tympanic membranes and eustachian tubes should expect no problems. People who usually have problems when flying may also experience discomfort in the tunnel, but only those who have recently (within two months) undergone ear surgery, especially stapedectomy, should be advised to cross above rather than below the waves.