Oct 4, 2006, 10:37 AM
Post #1 of 17
Useful Information About Air Pressure
I did some research a few weeks ago and sent a few emails to some doctors, because I wanted to know what is going on during the ride to altitude and the descent, especially after I experienced some problems with my left ear drum on my first dive. This is an email I got as a response from one source. I thought others might find it useful so I posted it here.
Below is an article which may help you. We have also sent your email to Gareth Holder who wrote the article and to a skydiving doctor. Hopefully they will provide more specific advice.
Best wishes Lucie
Lucie Fenton, Editorial, The Mag, 5 Station Road, Ailsworth, Peterborough PE5 7AH UK
No Wind Situation A subject close to every skydiver is the expansion of gases within the human body.
So, when you have all finished giggling about the wind problem we are all aware of, read on for useful information about the more serious effects that failure to understand the subject can produce
As Mr Scott was wont to remind Captain Kirk on occasion, "You canna change the laws of physics, Captain!" In this particular case, the laws that govern the rate of the expansion of gases. Although complex in detail, they basically state that a body of gas will expand if the surrounding pressure drops. We decrease the air pressure around us every time we ascend to altitude and we do it without the niceties of controlled cabin pressure. This means that any gas contained with our bodies will start to expand. Air is found in several areas of the body; most obviously the lungs, but also the sinuses, stomach, bowel, and middle ear. There are also other places it can be found and where problems can arise. In a nutshell, as long as these gases can escape to the outside, their expansion should not pose problems. However, complications such as pain, disorientation and even damage can occur should they remain trapped. Let's look at the troublesome areas:
The Ear The ear is the place where we most feel the effects of the slow ascents and rapid descents of skydiving. It's a very complex but surprisingly fragile piece of biology, subject to a lot of stress during a day of skydiving. The middle ear is the part we are concerned with. It is separated from the outside world by the eardrum but it also has a passage to the outside via the Eustachian tube which connects it to the back of the throat. As we ascend to altitude, the air in the middle ear expands, pushing against the eardrum and causing it to bulge out. This is the cause of the slightly full feeling that you get as we climb. Once the pressure is sufficient, air can escape through the Eustachian tubes, allowing the eardrum to settle back, causing the 'pop' we all know. This expansion and settling will take place all the way to altitude. It can be aided by yawning, swallowing, sucking sweets or any other activity which opens the Eustachian tube.
On the descent, the opposite is true. Pressure increases on the outer surface of the eardrum, causing it to bulge inwards. Again the Eustachian tubes will equalise this pressure. However, because the freefall descent is so rapid compared to the ascent, and also because the Eustachian tubes are better at emptying the inner ear than filling it, ear pain and discomfort is more likely to be caused. A properly executed 'valsalva' manoeuvre where the nose and mouth are pinched shut, and air forced into the middle ear by blowing can alleviate this - but don't attempt this until you know what you are doing or you could cause damage to your ear. The problems here are nothing that every skydiver has not dealt with but they are dramatically compounded when pressure equalisation is disabled by something as simple as the common cold blocking the Eustachian tube with phlegm. The eardrum will bulge inward or outward until, depending on the circumstances of the ascent or descent, it ruptures, causing severe pain and sometimes disorientation. Vertigo experienced by a failure to equalise pressure in the middle ear can range from mild to severe and can pose a serious safety concern to any skydiver struck with it during freefall.
Avoiding problems Do not jump with a cold, flu, sinusitis, or any other ailment that may affect your ability to equalise pressure efficiently. What may seem only a mild bother on the ground can become a serious problem in the air. Most commercial pilots will ground themselves for these ailments - and they have the luxury of being able to control their descent rates and cabin pressures. We should do the same.
The Sinuses The sinuses are air-filled cavities within the bones of the face. I have absolutely no idea of what they are supposed to do other than to keep decongestant manufacturers in business. They have a passageway into the back of the nose through tunnels in the bones of the face. In a similar fashion to the inner ear, expansion and contraction of trapped air during ascents and descents will take place, with pressure equalisation happening through the nose. As it is a little more efficient than the venting of the Eustachian tubes, most people are not aware of it happening until the system fails to work, such as when the jumper has a cold or sinusitis. When the equalisation cannot take place, severe pain in the affected sinus can be felt, accompanied by profuse tearing in some cases. It can happen quickly too and without prior warning, as I can personally attest. The loss of equilibrium can be alarming and sudden.
Avoiding problems Basically, don't jump if you have sinusitis or a cold or flu. Even with common decongestants you are at risk, as these are not formulated with skydiving in mind. As a sobering example, a fatality occurred some years back on a major record attempt which was believed to have started because a jumper continued to jump with a severely blocked sinus. The ensuing rupture at altitude and loss of vision due to blood and subsequent disorientation, led to a freefall collision that resulted in that jumper's death. It's just not worth it.
The Digestive Tract Okay, here's the bit you really started reading this article for (which I why I put the more important stuff ahead of it.) Our digestive systems can contain anywhere up to around a litre of gas. This is comprised of the by-products of digestion, swallowed air, and all the carbon dioxide in that Diet Coke that you gulped down whilst packing. You don't have to be a rocket scientist to work out that, as the gases expand, they have to go somewhere. Go somewhere they do, through the outlets traditionally supplied for this purpose; the mouth and the anus. Depending on the amount of gas present and the altitude you are at, anything from mild to extreme discomfort can be experienced. It may be socially polite to hold it in but this just may not be an option. Show me the jumper who claims that they have never given in to temptation on the way the altitude and I'll show you a liar!
Avoiding problems Adjust your diet to reduce the amount of gas-producing food that you eat. Anything from the cabbage family, pulses, beans, and carbonated drinks are the main offenders. Do yourself and the others on the load a favour. I realise that some jumpers owe their entire notoriety in the sport for their prowess in this field but I really don't need to experience it every time I ride to altitude. You can stop laughing now.
Teeth We've covered the main areas where air and gas traditionally lurk but there are other areas where it can crop up unexpectedly and cause problems. One of these is in the teeth. Gas can be lurking in fillings, abscesses you didn't realise that you had, or in the gums. If you start to experience mild to severe tooth pain on a ride to altitude, there's not much you can do about it then. However, it is a timely warning to get a dental check-up as soon as possible.
Injuries There are other ways that air can get introduced into the body, mainly through injury. In a serious medical evacuation by air, sometimes the persons transporting the patient will insist on sea-level pressure in the cabin. This can be to avoid unnecessary damage caused by air expansion in a fracture or wound. Obviously we are not looking at such an extreme but if, for instance, you have an eye injury such as small sliver, you may find yourself at risk from damage due to expansion of introduced gas. If you are jumping with any injury and feel pain on the way to altitude, it's probably a good idea to stop jumping until it clears up, as you're not doing yourself any good.
In Summary Basically all we're saying here, is that there is a lot of gas inside us and it's fighting to get in and out of the body all day, in a way that not even most experienced aviators get to experience. We have to make sure that we are in a physical condition which allows us to achieve the necessary equalisation in a controlled and comfortable manner - before it happens in a painful and potentially damaging one. To put it bluntly, don't jump with a cold, flu, sinusitis or a suspect injury.
Oct 8, 2006, 10:58 PM
Post #14 of 17
Re: [skytash] Useful Information About Air Pressure
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If Gareth wrote it, it MUST be true.
That sarcasm or do you actually know who this person is?
Hot tip: this is a very small sport. If it appears in Skydiving magazine, chances are a lot of people know who the author is.
Another Hot Tip, it's SKYDIVE Mag (UK) NOT SKYDIVING (USA)
Yes, but Gareth lives in Berkeley, CA.
and like you and me, he's a Brit-abroad!
And I'll have you all know that I offerd my sage words to Skydiving first and they passed on it, mainly becuase I think there was too much about farting in it. As it's a subject near and dear to a Brit's heart, Lesley at Skydive Mag had it in a flash, bless her. Farting is always funny, no exception. Americans fail to realise this.
Anyway, I wrote it as a consequence of what happened to me when I jumped with a blocked ear. I stroked out my left ear, and lost all hearing in it. I was profoundly deaf for two months on that side, had to have steriod therapy (not fun), and no jumping. Only 30% of people so injured ever get their hearing back, I was one of the lucky ones.