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Noise trauma after inflation of air bags in low speed car crashes

BMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7195.1421 (Published 22 May 1999) Cite this as: BMJ 1999;318:1421

Article was unclear and possibly misleading

  1. S S M Hussain (Musheerhussain{at}btinternet.com), Consultant otologist
  1. Directorate of Otolaryngology, Ninewells Hospital and Medical School, Dundee DD1 9SY
  2. Department of Otolaryngology (Head and Neck Surgery), St James's University Hospital, Leeds LS9 2TF

    EDITOR—Buckley et al draw attention to possible noise trauma and sensorineural hearing loss and tinnitus as a result of the inflation of air bags in low speed car crashes.1 Their report is unclear on several issues and may be misleading.

    In neither of the two cases reported is mention made of how soon after the accident the audiometry was carried out. The accident in case 1 occurred in the United States, and audiometry was carried out in Leeds by one of the authors. There is no record of any hearing assessment in the United States, which is surprising given that the patient experienced bilateral hearing loss, tinnitus, and unsteadiness (the unsteadiness lasting two weeks). Patients' perception of hearing loss does not imply that such a loss was simply sensorineural; indeed, conductive loss may have occurred and been transient. The small high frequency hearing loss depicted on the left side in case 1 is not one that most patients will notice and may have been present before the accident. There is the added factor of a flight from the United States.

    Sensorineural hearing loss has been reported after minor trauma to the ear2; it usually involves high frequencies and is transient. The hearing loss depicted in case 2 mainly involved low frequencies, and readers are not told if it was reversible. This patient had had high frequency hearing loss noted 18 months before the accident. It is unclear if the small additional loss in the high frequencies was in fact related to the trauma. This patient was receiving treatment for hyperlipidaemia and was 68.

    It would be useful to know if the associated tinnitus in both cases was bilateral and whether, with the undocumented improvement in hearing in the left ear in case 1, tinnitus on that side stopped.

    References

    Author's reply

    1. Graham Buckley (JGrahamBuckley{at}compuserve.com), Consultant otolaryngologist
    1. Directorate of Otolaryngology, Ninewells Hospital and Medical School, Dundee DD1 9SY
    2. Department of Otolaryngology (Head and Neck Surgery), St James's University Hospital, Leeds LS9 2TF

      EDITOR—In both cases audiometry was carried out more than three weeks after the injury; it was not carried out in the United States in case 1. The suggestion of a transient conductive hearing loss is pure speculation and is largely irrelevant since the audiometrically measured loss is clearly sensorineural. The high frequency loss in the left ear may have been present before the accident, but this is also speculation. We disagree that it is a hearing loss that most patients would not notice. In a 38 year old patient it is significant and probably symptomatic. The damage to cochlear outer hair cells implied by such a loss affects frequency resolution and speech perception as well as simply volume of sound. Hussain's point about the flight from the United States being an added factor is a curious one. Flying may cause barotrauma to the middle ear with a temporary conductive hearing loss, but the loss here is sensorineural. Is he suggesting that it is due to flying?

      Hussain's comments about case 2 repeat the points we discussed in the article. Deterioration due to age and other factors is always a possibility, but the deterioration seen is greater than would be likely in the time frame. Hussain also seems to miss the point in the article that the hearing loss occurred at both 1 kHz and 4 kHz. Since the audiogram was obtained three weeks after the event the hearing loss is unlikely to be a transient effect. The “small” additional loss at high frequencies amounted to 25 dB at 3 kHz and 4 kHz. We suspect that Hussain would not think this small if it affected him.

      The initial tinnitus in the left ear in case 1 did indeed settle, but that in the right did not. The patient in case 2 had bilateral tinnitus, which was not present before the injury.

      One final point should be made. Both subjects presented because they noticed a persistent hearing loss and tinnitus after inflation of the air bags. Other potential contributory factors always exist, but the evidence in the cases that we reported is compelling. The important issue is whether these cases are isolated occurrences or indicate a more widespread problem. Although the danger of overinterpretation always exists, we fail to see how the paper could be regarded as misleading.

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