Do Dive computer get you bent more than tables?

[Aquamore]

I was referring to the principles of Radio Wave propagation using an Isotropic antenna (a loss free antenna in free space) as an example.

Antenna Propagation: Basically, when a Radio Frequency is applied to the antenna a changing electro magnetic field is set up around the antenna which changes proportionally to the frequency of the applied RF which in effect is a fast AC (alternating current).

If the frequency is fast enough then the field which is set up initially tries to collapse but due to the short time constant of the wave it never fully collapses before the next cycle comes alongwhich pushes this collapsing field outwards. The direction of the EM wave changes again and another field is set up inside the first two, pushing the first and second waves further outwards.

This continues as long as the Radio Frequency is applied to the antenna. This is how radio waves get fro a transmit antenna to your recievers antenna.

The key factor in all of this is is time. As long as there is not enough time between the RF cycles for the field to fully collapse then Radio wave propagation occurs.

Now here's my analogy. Apply these laws of physics to the physiology of the human body:

The RF is like rapid changes in pressure (on a saw tooth profile or Yo-yo dive) applied to the Antenna (your body in this case). Your body tissues absorb gas at varying rates and also disapate gas at varying rates.

I think we can assume that we all agree that there are tissues in the body which absorb gases faster than they release them for a given symetrical change in pressure (these gases which are left over I will call residual gases for the purpose of explanation).

I'm suggesting that if the next increase in pressure is followed sharply by a decrease in pressure, then an increase again, the rate at which the gas is absorbed into the tissues will increase, (using the radio wave propagation principle as an example), because if the time constant is short between cycles being short and there always being some amount of residual gas left in the tissues before when the next compression cycle comes along.

This type of compression which I have heard described as Adiabatic compression (not Isothermal) occurs in a saw-tooth dive profile and I believe results in an increase of gas absorbed into the tissues compared to a straight line type of ascent and descent.

I hope the Doc can find some conclusive date to substantiate my theory which is based primarily upon pure physics and secondly upon our limited knowledge of barophysiology.

Thanks for your interest
Allan

 

[devilfish]

Which get you more bend, computers or tables? Neither. There's only two ways not to get bend.
1. Don't dive.
2. If you dive, don't come up.

What causes bends? No one really knows, there are many factors and contributors. But one thing is for sure. Saturation and pressure reduction.
So, given even situation, same diver, same circulation, same conditions, pushing dive tables and computer to the limit, because computer calculates based on multilevel bottom time, a diver with a computer will ongas more. From there it's history.

 

[devjr]

Hi Allan, I looked into rectified diffusion theory, but just a bit. Sofar, what I've found confirms Dr Deco's remarks, eg, the pressure variations attendant to a diver's normal depth excursions do not incur sufficiently high frequency or amplitude to promote rectified diffusion of bubbles. Furthermore, this phenomenon seems only to occur if bubbles are initially present, perhaps due to micronuclei being excited in some way. In the laboratory this excitation would typically be ultrasound. In the diver, perhaps, by rapid ascents followed by delayed resubmersion in violation of existing decompression criteria. (This could be a factor in making in-water recompression so problematical). I may look farther into this interesting subject if the math isn't too daunting.

Your EM wave analogy still baffles me but I'll think about it.

Dennis

 

[Aquamore]

Thanks for your interest and follow up,

You read:
-----------------><8
....the pressure variations attendant to a diver's normal depth excursions do not incur sufficiently high frequency or amplitude to promote rectified diffusion of bubbles.
-----------------><8
Well I can agree totally with that, the emphasis being on the word "Normal". First we have to define what 'Normal diving' or depth excursions are. My considered opinion is that Saw-tooth or Yo-yo profiles definitely do not fall into that category. I doubt very much that rapid changes in pressure which are caused by this irregular type of diving practice, are even considered considered by the researchers and developers of the Table and Computer algorythm producers

You also read:
-----------------><8
Furthermore, this phenomenon seems only to occur if bubbles are initially present, perhaps due to micronuclei being excited in some way
-----------------><8
Could it be that the micronuclei are actually being produced by this very action of rapidly changing the pressure on already compressed gasses (these exist in the body tissues due to Boyles Law and Henry's law)?

We all know and understand the Pressure/Volume relationships related to Boyles law but lets consider Henry's Law in conjunction with this.

Henry's law states:

The amount of any gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and the solubility coefficient of the gas in that particular liquid.

Think of a bubble bath, the foam is created by agitation of the surface of the water (causing compressions and rarefactions in the solubility co-efficient), which allows more gas into the liquid that usual and bubbles are formed. This accellerated effect is caused by direct intervention changing the surface area of the water where the gas is absorbed into the liquid.

It's my perception, (right or wrong), that rapid changes in pressure caused by the Sawtooth profile, have the same effect of stirring up the gasses in our tissues and this is where the micronuclei may be formed!

Lets get a second opinion on this theory from the Doc:doctor: because if this was electronics I could prove this in a test area but sadly I am just an space industry engineer and don't have a laboratoty to perform any sort of testing of this nature.

Regards
Allan

 

[devjr]

Let's not get too excited by "froth". Even an athletic diver shouldn't transfer enough bodily energy to cause excitation of micro nuclei and stimulate a small bubble, at least not through rectified diffusion. I also get the impression that Dr Deco is ambivalent about the role, if any, that micronuclei might play in depth deviations and alleged consequences for DCS.

There is a tiny, very tiny, possibility that ultrasound produced by the regulator could initiate this. The sound waves could easily penetrate the body. This might be compounded by changes in blood chemistry and gas exchange through exercise. Anyway, if it could be shown that even the smallest bubbles are initiated by some mechanism then the argument for rectified diffusion could proceed to the next step, dealing with the relatively low cycling of depth and pressure. Worst case, this might take on the appearance of water recompression gone wrong or a freediver going to extreme depths.

I'm puzzled by your statement that propagation of EM waves is dependent on freq. After all, in free space ELF and EHF waves travel at one speed, the speed of light. Even light waves arrive at the same time and can only be separated by a prism or something similar which optically forces a differentiation in speed.

Dennis

 

[Aquamore]

To be absolutely honest I personally don't see any signifigant connection between Micronuclei and ultra sonic noise experienced in normal SCUBA diving.

Secondly Frequency is an integral part of the relationship between propagation of an EM wave and the actual Wave length.

The formulae is:

V = F x La.

Where:

V (Velocity) is a constant, in metric 300 x 1,000,000 metres per second.

La. (Lambda) is the wavelength

F (Frequency) is the rate of change of the EM wave.

I hope you are less puzzled now.? If you are still puzzled try and think od AC and DC. DC is direct current and will not radiate from and antenna. It is only AC (Alternating current) that causes a change in the EM wave.

The link is: AC has a frequency, it is usually sinusoidal in waveform and the Voltage or Current componant of the EM wave change between positive and negative during one complete cycle.

I hope this helps you.

Allan

 

[The Chairman]

but this was a hobby in Junior High School... If I remember rightly... a pulsing DC current can emit EM waves as well. There has to be a change in voltage, but there does not have to be a "negative" to emit EM waves. This is how the coil in an automobile works off of battery voltage... It is merely a high output transformer... when the electronics cut the voltage to the low tension side of coil, it produces an EM wave which is picked up and amplified by the high tension side of the coil... up to several thousand volts. If you don't have the right attenuating capacitors (somtimes called condensors in the automotive arena), you can expect a hum out of your radio.

One of the biggest pains in designing any DC power supply is to eliminating the "noise" from the output top an acceptable level. Am I really that off track here?

 

[devjr]

Aquamore, I agree about the ultrasound, but bear in mind that ultrasound is used in laboratory experiments to initiate rectified diffusion (bigger bubbles).

About the formula, all that says is that frequency and wavelength are inversely proportional. So, what's new? Does sound a bit like Boyles law, though. Heh, heh. OK, OK, I promise not to bug you about the EM analogy anymore.

Carry on, there is an answer out there somewhere. Even if nobody has seen it. (G)

Dennis

 

[Aquamore]

You are correct about a pulsing DC current can emit EM waves as well. It can then be considered as AC, all be it a square wave and not sinusoidal.

The change in voltage, is the 0 Volt 12 volt change as it pulses so the zero volt could be considered as a "negative" to emit EM waves (as it is negetive with respect to + 12 volts and the axis here would be around +6 volts).

Your coil in an automobile analogy is a good example of this. The changing voltage causes a changing current to flow (Alternating Current) which sets up the changing EM field (Faradays Law of induction).

Getting back to the original point though, I still sincerely believe their is a connection between Saw-tooth profiles (rapid changes in ambient pressure around a divers body) and DCS and DCI that has occasionally occurred whilst diving within the limits of the dive computer Algorythm or the tables. Sadly I still haven't found any conclusive research on the subject, but nearly all divers I talk to agree Saw tooth profiles are not good for the body tissues.

It is a fact that the human body has a time constant for tissues to saturate and desaturate with gas. It is arguably the case that if there is residual gas in the tissues which never fully disapates that each time this gas is compressed again because the full time constant is never reached (as in the case of a saw tooth profile), there is another different rate at which gas is absorbed, and this leads to bubbles being formed in the tissues more rapidly than on a conventional dive.

My mind is open but unless someone can prove otherwise I tend to look at the laws of physics which have already been researched and documented and apply them as a logical guide to help me understand why this DCS phenomena occurs whilst diving within the limits of the tables and the computer.

This posting has been interesting and fun to say the least - from DCS to Electronis Engineering to Auto Mechanics and back to DCS in 3 easy steps!


regards
Aquamore
Allan