Ask DAN
DAN medical specialists and researchers answer your dive medicine questions
Q: I would like to know if deep stops are always recommended for recreational dives, if the depth of the deep stop must be half of the maximum depth reached or half of the maximum pressure reached, and if, for multiday dives, it is always recommended to do this deep stop. A: The introduction of a deep stop at half of the maximum depth reached during recreational dives during the ascent phase seems to: - significantly decrease inert gas bubbles detected by a Doppler scan after a dive. - reduce tension of inert gas in ‘fast’ tissues, which is an important fact to correlate with gas exchange happening in the spinal cord. Authors of scientific publications regarding this topic concluded that a deep stop can decrease the likelihood of suffering from decompression sickness for recreational dives within the depth of 30m and without mandatory decompression stops. Q: When I am not wearing a hood, I have no problems equalising my ears. On the other hand, when I wear it, I
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always have great difficulty. Why is there a difference? A: When we pressurise the middle ear space using the Valsalva manoeuvre or another equalisation technique, the tympanic membrane (ear drum) bulges outward slightly. If the ear canal is uncovered and can transmit that pressure, the water in the ear canal moves easily in response. A hood that fits snugly against the outer ear can greatly restrict the movement of this water, hampering the diver’s ability to equalise. An easy remedy to this is to insert a finger under the hood near the ear, which will allow the water to move more easily. Another solution some divers choose to implement is to cut a hole from the inside of the hood, near the ear canal, through the inner lining and the neoprene, but leaving the outer fabric or covering intact. This hole allows the water to move with little restriction. Join DAN to get a number of benefits, including answers to all your diving-related medical questions: www.daneurope.org
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