Altitude before diving

[Chris]

One of the students in on the sports diver course stumped me the other day with the following question :

Can anyone explaing why flying or going over a mountain BEFORE diving has effects on your Nitrogen loading. Less preassure means that you should off-gas some Nitrogen, however if you check the BSAC 88 tabes for example if you go over a moutain you end up with a Current Tissue Code (CTC) of B1.
Micro Bubbles / Stress are the only thinks I can think of?

[PeteM]

Micro Bubbles / Stress are the only thinks I can think of?

Spot on. Going up the mountain you will off gas, coming down you will on gas again. But off gassing will produce micro bubbles which can then get compressed. Doing a dive could make these micro bubbles themselves on gas and grow, when you ascend these could grow to a dangerous size.

Add into this the fact that rarely do you go straight up a mountain and down the other side. Normally roads will go up a bit, down a bit etc. so you are doing what is effectively a saw tooth profile with an ascent and immediate re-descent. If this was in the water everyone would say its an aggressive profile - in the air its still aggressive but less of an issue because of the smaller pressure changes

HTH

Oete

[Chris]

Thanks

[derek perry]

Further to this.
If you read the tables further you will see that if you fly and the journey is more than 90 minutes you revert to table A1 and are actually benefiting by the flight. It is felt the micro bubbles have subsided. If you then descend and go diving you are on loading nitrogen but as you start the dive you will (may) have less nitrogen in you blood than if you hadn't flown. In effect you've detoxed some of the nitrogen out of your blood and in theory it will be a safer dive as you are starting with less nitrogen in your system than you would normally. Obviously it all depends on how long it takes to get from the plane to the dive site and I would imagine any benefit is minimal. Hope this makes sense.

Derek


:=Micro Bubbles / Stress are the only thinks I can think of?

Spot on. Going up the mountain you will off gas, coming down you will on gas again. But off gassing will produce micro bubbles which can then get compressed. Doing a dive could make these micro bubbles themselves on gas and grow, when you ascend these could grow to a dangerous size.

Add into this the fact that rarely do you go straight up a mountain and down the other side. Normally roads will go up a bit, down a bit etc. so you are doing what is effectively a saw tooth profile with an ascent and immediate re-descent. If this was in the water everyone would say its an aggressive profile - in the air its still aggressive but less of an issue because of the smaller pressure changes

HTH

Oete

[David J Smith]

Further to this.
If you read the tables further you will see that if you fly and the journey is more than 90 minutes you revert to table A1 and are actually benefiting by the flight. It is felt the micro bubbles have subsided. If you then descend and go diving you are on loading nitrogen but as you start the dive you will (may) have less nitrogen in you blood than if you hadn't flown. In effect you've detoxed some of the nitrogen out of your blood and in theory it will be a safer dive as you are starting with less nitrogen in your system than you would normally. Obviously it all depends on how long it takes to get from the plane to the dive site and I would imagine any benefit is minimal. Hope this makes sense.

Derek


:=:=Micro Bubbles / Stress are the only thinks I can think of?
:=
:=Spot on. Going up the mountain you will off gas, coming down you will on gas again. But off gassing will produce micro bubbles which can then get compressed. Doing a dive could make these micro bubbles themselves on gas and grow, when you ascend these could grow to a dangerous size.
:=
:=Add into this the fact that rarely do you go straight up a mountain and down the other side. Normally roads will go up a bit, down a bit etc. so you are doing what is effectively a saw tooth profile with an ascent and immediate re-descent. If this was in the water everyone would say its an aggressive profile - in the air its still aggressive but less of an issue because of the smaller pressure changes
:=
:=HTH
:=
:=Oete


Appreciating the question was about nitrogen loading in particular. Any benefit mentioned above with regards to off gassing giving you a better 'starting load' of nitrogen would almost surely be negated by the other physiological effects of flying, for example dehydration and the cramped conditions of flight, restricting circulation etc.... So it is still a reasonable idea to have a rest after flying and before diving.