Why not sleep during surface interval?

[alexeames]

Dear Dr Deco,

You told us a couple of days ago...

Gas loads are governed by time and pressure exposure. They are also controlled by activity levels upon surfacing (e.g., do not go to sleep during the surface interval). To control tissue nuclei, strenuous activity with upper and lower extremities is to be avoided.

I understand the reasoning behind not doing any strenuous activity - control of nuclei.

Could you briefly explain the reasoning behind not sleeping? I've not heard that advice before - and I'm sure that many people on liveaboard boats do sleep between dives.

Thank you in advance - and sorry if this has been covered before.

p.s. If you are going to have an extended surface interval (eg. overnight) is it important to not sleep for a couple of hours after diving?

 

[Drew Sailbum]

I'm not a doctor, but my doctor :doctor: told me the same advice.

If I understood his explanation, it is because during sleep :snore: the heart rate and repiratory rate fall. This results in slower elimination of residual nitrogen than when you are awake.

Net result is that if you :snooze: sleep, you may not offgas as much nitrogen and that can throw off your calculations for repetitive dives.

Of course, I may not have understood a damn thing my doctor said.

 

[pipedope]

Also during sleep you don't notice signs of DCI.

If you get a DCI hit you want to know about it as soon as possible.

michael

 

[Dr Deco]

Dear alex:

The washout of inert gas is governed to the greatest extent by the flow of blood through the tissues. This washout is promoted when the flow of blood is large and hindered when it is small. At NASA, we have studied the effect of gas washout as a function of body activity. This effect is determined not by actually measuring blood flow in tissues (very difficult) but rather by studying the response to decompression. The effect on blood flow is inferred, but the effect of exercise on DCS risk is very large as can be determined from depressurization experiments. This effect of exercise in DCS is directly quantifiable. It is not theoretical and/or qualitative. We are not talking about generalities such as “exercise and activity to promote blood flow is good.”

This has been worked out in an algorithm (= calculation method to allow our astronauts to decompress in a fraction of the time previously. The activities and workloads must be carefully tracked and thus the system is not directly applicable to divers on the ground. Nevertheless, the principle is there.

When one is up and around, blood flow is greater than when seated, and it is much greater than when you are sleeping. Blood flow, and therefore gas washout, is lowest during sleep. It is for this reason that I do not recommend that divers sleep during the surface interval between dives. Nighttime sleep at the end of the day is a different matter. That sleep is necessary, but then one has 7 to 8 hours for gas washout.

Dr Deco:doctor:

 

[alexeames]

Excellent answers. Thank you...

:doctor: Dr Deco
Drew Sailbum
:rasta: pipedope

...I've got a friend who's coming back from a liveaboard trip in :egypt: Egypt.

Last time he told me that all there was to do between dives was talk to other divers, read or sleep.

Now I'll be able to tell him why he should not be sleeping between dives...

Or, for that matter, doing a lot of snorkelling either.

I'm surprised that these things are not in the training manuals. Or at least if they are, they were not stressed much in my courses (PADI OW/AOW).

I will certainly be adapting my habits around this advice. Thank you guys, you have made a difference

 

[AllenG]

Dr. D -

Is the effect of sleep on offgassing clinically significant or just statistically significant (i.e., the former meaning that yes there could be some clinical effect and the magnitude of differential effect is enough to make one say, "hey, only an idiot would take on this risk!" e.g., 1% incidence of observed DCS hit in comparison to a 25% incidence; vs. a statistician got a significant finding which, while consistently found, may nonetheless be of little consequences)?

 

[blacknet]

Dr Deco,

Can you cite your source please so I can read them?

Ed

 

[waterdogs]

I understand the information regarding sleeping during surface intervals, but what about the "snorkling" part of the thread.

Should you not, limited or at all during surface intervals. What if you planned a morning dive, then SI, then snorkled a few hours before your night dive?

Thanks, interesting information.

waterdogs.

 

[alexeames]

Originally posted by waterdogs
I understand the information regarding sleeping during surface intervals, but what about the "snorkling" part of the thread.

I mentioned snorkelling because it is exercise and Dr Deco told us that nuclei will form if we do strenuous exercise.

I guess gentle snorkelling might be OK. But Dr Deco mentioned avoiding lugging tanks around too much. OK they are heavy, but I get the impression that we should take it fairly easy during surface intervals, but not go to sleep.

 

[earl]

So when exactly is it safe to exercise -- I don't understand. Look at, for example, GUE's curriculum. They want folks to exercise at least 3 days a week, and 6 is better. Yet you aren't supposed to exercise around diving... how does that work?

That is to say, I lift 3 to 6 days a week (depending on my cycle), run, and do karate. When is it OK to exercise -- before diving, after diving, or never?

Thanks for any help,

-earl-