January 2002 newsletter

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Children and diving

The diving organisations are under pressure to lower the age limit for diving. Much has appeared recently in the internet message boards about the benefit experienced by children who take up diving as a recreational sport. There are important medical concerns however, and the UKSDMC needs to be clear about the message for parents, instructors and advisors.

An important issue is that of consent and it is worth noting that there are differences between Scottish and English law in terms of the age of consent, and the need for parental permission. Some instructors feel that children should only be allowed to dive with their parents in attendance. Certainly children should not be regarded as equal diving partners and cannot be relied on to provide emergency assistance.

From a medical perspective however, there are several unanswered questions. We know that adults have large quantities of venous gas bubbles after even innocuous shallow dives and the concern in children is the effect such bubbles might have on spinal cord function, bone growth plate maturation and cerebral function. Decompression tables were not designed for children who have different metabolic patterns, tissue composition and thermal conduction from adults.

Is it possible to set a minimum age limit? There are so many variables to consider for individual fitness to dive that any age limit must be a compromise. However unless this is set with very specific guidelines, we will be accused of transferring responsibility inappropriately to non-medically qualified diving instructors.

Understandably feelings run high. Looking at the BSAC internet forum recently there have been scores of postings and widely differing opinions with enthusiasts and detractors equally definite in their opinions. This is the problem– there is very little evidence to help here.

Should a lack of evidence be interpreted as showing that allowing young children to dive is safe, or should we advise caution, outlining the medical concerns and accepting that we are unlikely to progress from this position because it will not be possible to conduct prospective safety studies ethically.

Responsible parents will be less likely to consent to allow their children to dive if we present the physiological arguments coherently and in a language understandable to them. As ever, we appreciate your views and experience.

The current BSAC limit is 14 years although 12 year olds are being trained via the Ocean Diver programme. Depth restrictions are in place as are guidelines for instructing. SSAC members need to be 15 years old before starting SCUBA training. SAA members can start SCUBA training at 12 years. The PADI Bubblemaker course is aimed at children as young as 8-9 years.

There is confusion therefore and this needs to be clarified. Watch this space for developments.

Diving after stapedectomy

Stapedectomy is a relatively common operation performed for sensorineural deafness related to otosclerosis. The first operation was performed in 1960 and a recent small survey of 22 SCUBA divers following stapedectomy found that four had experienced symptoms during diving including otalgia (3), tinnitus (1) and transient vertigo (1). One patient developed a sudden onset sensorineural hearing loss with vertigo, and this was found to related to a perilymph fistula. No symptoms of labyrinthine injury were reported by the divers suggesting a low incidence of inner ear barotrauma. The authors concluded that SCUBA diving did not appear to increase the risk of inner ear barotrauma provided that adequate Eustachian tube function had been confirmed by clinical examination following surgery.

For more information:
Diving after stapedectomy: clinical experience and recommendations. Otolaryngol Head Neck Surg 2001;125(4):356-40. House JW, Toh EH, Perez A.

Diving and back injury

Carrying SCUBA equipment and weights can be regarded as a fitness test or a potential mechanism for back injury. A study of 24 military divers and matched controls examined the incidence of cervical and thoracic disc protrusion by MRI scanning and identified protrusions in 14 divers and 9 controls. The authors concluded that there was no significant difference between the groups and felt that diving was not associated with an increased risk of back injury.

Certainly there are concerns about diving following spinal surgery and disc prolapse. Theoretically there may be disturbance of local circulation following injury, and this may increase the risk of local bubble accumulation. The venous drainage system from the spinal cord is unusual, forming a venous plexus, and this may encourage coalescence of bubbles and possibly increase the risk of venous infarction within the spinal cord. This was found in animal studies and some post-mortem examinations. The other issue is the pre sence of neurological deficit following back injury or spinal surgery and this should be carefully documented before returning to diving. This helps to avoid confusion with new neurological signs resulting from decompression injury. Currently no specific limits or restrictions are imposed on divers following back injury or spinal surgery.

For more information
Cervico-thoracic disc protrusions in controlled compressed- air diving: clinical and MRI findings. Bartsch T, Cordes P, Keil R, Reuter M, Hutzelmann A, Tetzlaff K, Deuschl G. J Neurol 2001:248(6):514-6

Eustachian tube function and free radicals

Free radicals are implicated in various disease pro cesses including atherosclerosis, tissue injury during sepsis, and tissue injury during hypoxia or reperfusion (eg during myocardial infarction or stroke). A recent study hypothesised that free radicals may be involved in Eustachian tube dysfunction possibly as the result of inflammation during infection. Laboratory studies of rats confirmed a reduced incidence of myringosclerosis after administration of free radical scavengers following myringotomy. Vitamins C and E are naturally occurring antioxidants with free radical scavenging activity. This study examined the effect of high dose administration on 15 police special task divers performing training dives on pure oxygen. Typmanometry was performed before the dive and again at 2 and 24 hours following diving. The study involved divers using pure oxygen because such divers often have difficulty with ear clearing and there are studies confirming the development of negative pressure within the middle ear following this type of diving. The authors found a low incidence of abnormal tympanometry with only one subject having a significantly negative pressure the morning after the dive. The study did not demonstrate any significant difference between the group treated with vitamins C and E, compared with controls although the incidence of problems was obviously very low. In fact the only significant difference between groups suggested that the group treated with vitamins had a tendency to negative middle ear pressures following the dive but this was not at a level to cause clinical pro blems. Overall then it is not possible to recommend the prescription of high dose vitamin C and E to try to overcome Eustachian tube dysfunction.

For more information
Can Eustachian tube ventilatory function impairment after oxygen diving be influenced by application of free radical scavengers Vitamins C and E? Mutzbauer TS, Neubauer B, Mueller PHJ, Sigg O, Tetzlaff K. Laryngoscope 2001;111:861-866

The pleasures of diving

Heart rate variability refers to the beat to beat variation in heart rate seen in healthy subjects. Such variability reflects a balance between sympathetic and parasympathetic activity, and is lost in those at risk of sudden cardiac death. A study of 25 amateur divers found increased heart rate variability related to increased parasympathetic activity during pool diving. The study was designed to examine the effect of diving in controlled conditions on various measures of heart rate variability to determine the relative role of sympatheticand parasympathetic stimulation. In this group of experienced divers there was no evidence of sympathetic stimulation, suggesting that pool diving was an entirely pleasurable activity without stress. The UKSDMC look forward to seeing a further study performed during winter diving off the UK coastline to re-examine this hypothesis.

For more information
Effect of immersion, submersion, and scuba diving on heart rate variability. Schipke JD, Pelzer M. Br J Sports Med 2001;35:174- 80

Headache in divers

A useful review of the differential diagnosis and management of headache in divers was published recently. Drs Cheshire and Ott from the Mayo Clinic reviewed the vast array of causes of headache in divers and classified these in broad terms (see below):

Headache due to changing gas volume
-decompression illness including arterial gas embolus
-barotrauma including mask squeeze (particularly in novice divers), dental squeeze, sinus squeeze, external ear barotrauma, middle ear barotrauma, inner ear barotrauma, alternobaric vertigo, and rarely pneumocephalus (probably due to rupture of the tegmen tympani).
Carbon dioxide retention
This leads to cerebral vasodilatation and raised intracranial hypertension and may result from skip breathing or inadvertent hypoventilation when maintaining buoyancy control.
Carbon monoxide toxicity
Divers are trained to position the compressor inlet away from the exhaust to avoid contamination, but there are still regular incidents involving carbon monoxide poisoning with potentially lethal outcomes.
External trauma
The limited field of visibility makes divers prone to collision and there is a risk of cervical spinal trauma on entry although better training has reduced the incidence of this.
Toxins
There are relatively few venomous creatures in UK coastal waters although poisonous jellyfish are a regular feature in the summer.
An unusual cause of headache is described involving a wader who sustained a temporal bone fracture, vertigo, cerebrospinal fluid otorrhea and pneumocephalus after being struck by a flying fish.
Pre-existing conditions including migraine, tension, temporomandibular joint dysfunction (see page 5 for information on alternative mouthpiece design), benign exertional headache, cold stimulus headache. Tension headache may result from a poor fitting mask or helmet leading to scalp muscle contraction. Supraorbital neuralgia (goggle headache) may result from excessive tightening of the mask straps particularly in novice divers. Trigeminal neuralgia may be worsed by exposure to cold or contact from a diving mask. Cervicogenic headache may result in divers with cervical spine disease because of the unnatural posture of diving involving hyperextension of the cervical spine.

In most cases a careful history will clarify the cause but in severely ill divers this may not be possible. It can be difficult to distinguish between migraine symptoms and decompression illness and the authors recommend that such divers should be recompressed as part of the diagnostic process.

For more information
Headache in divers. Cheshire WP, Ott MC. Headache 2001;41:235-247