Dr Oli: Diving and unusual noises at depth

Q: Hi. I've recently started tech diving and have just done the TDI extended range course and am diving around 45-65m on air (I'm fully aware of the dangers of such air dives following a huge amount of research!). I'll be doing the Advanced Trimix course in a few weeks and won't do the air dives after that.

However, I have noticed something rather strange when I go beyond 45m: I hear a very loud beat in my head. If I clear my ears with a small blow, the sound disappears, and once I ascend, it stops. I've just done a couple of 30m dives and no beat in my head. It has only started since I've done deep dives. I've done over 300 dives above 40m and never heard it before.

The sound is like a propeller: thud, thud, thud. It sounds like it's my heart beat or pulse, but really loud, and it gets louder the deeper I go (below 45m). Is this narcosis, O2 toxicity or (as my buddy thinks) could my Eustachian tube be pressing on a vein due to the increased pressure? Do you have any other ideas as to what it could be?

A: From your description of the sound, it would appear to be a heightened awareness of your pulse, technically termed pulsatile tinnitus. Quite why this should have arisen now and not on previous dives is anyone's guess, but with increasing depth your Eustachian tubes are likely to be compressed nearer to the blood vessels that are causing the sound, and so I can see some merit in your buddy's explanation. It tends to be louder with exertion (as your blood is being pumped around with more force), which would also tie in with deeper diving. If you have any middle ear congestion, then the sound will get louder too, as the congestion conducts sound much better than air. It can sometimes be due to high blood pressure, or rarely to vascular tumours in the middle ear - but in these cases I'd expect you to be aware of the symptoms much more frequently, including at night, and when you're not diving.
So on balance I don't think you need worry unduly. A lot of people get this from time to time, non-divers as well as divers, and it is simply an elevated perception of the big arteries pulsing away in the neck. It is, basically, nothing to worry about.

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