BO/samba mechanisms

[cdavis]

Is it possible that there is more than one mechanism that leads to B0?

Most B0s and sambas happen when divers are pushing their limits. However, it is possible to have a B0 when (apparently) no where near a diver's limit. I did not used to believe this could happen, but have seen it in a situation where the diver had taken a normal surface interval and breathup and we were quite sure there was no warning, the diver wasn't near his normal limits, and did not lose memory for any significant amount of time. This particular diver has experienced several B0s (over 4 or 5 years) and has not had any samba episodes that I know of. In contrast, although I have experienced samba type visual symptoms while doing stupid stuff a long time ago, I've never B0ed, even though I have a long history of go-for-broke spearo behavior. In recent years, when safety was perfect, I have pushed very hard trying to get to either samba or B0 but have never been able to intentionally push to either.

It seems pretty clear that some divers are more resistant to B0 than others. Could it also be that some divers are prone to a mechanism that leads to B0 and which is different from the normal, push the limits, B0 situation and maybe is not present in all divers? If so, any speculation on what it could be? Any other ideas on causation?

Connor

 

[trux]

Well, there are certainly plenty of factors that may play a role. Finally you have people who can faint even when not holding their breath at all. Blood pressure would be certainly one of the more important factors, so comparing the BP of the guy the day he had the BO would be interesting. And the BP can be influenced by many factors again too. Alcohol for example will have influence on the BO threshold and BP too, digestion will withdraw some blood from the primary circuit, so will contribute to an earlier BO. Drugs, hydration, temperature, tiredness, stress, etc, will play a role

 

[efattah]

I agree with trux. Low blood pressure (possibly caused by 1000 factors), can lead to extreme early unexpected blackouts. Also alkaline diet can delay the urge to breathe. Maybe the person only ate fruits for two days, which would both create alkalinity, plus low blood pressure.

 

[efattah]

Another huge factor is carbon monoxide inhalation. I myself suffered a CO induced samba in 2001. In a strange coincidence, I had actually brought a carbon monoxide monitor on the boat (as I believed CO could be a problem for freedivers).

On the boat, the motor malfunctioned and created a huge amount of blue smoke. The CO monitor went crazy, creating huge alarms and the CO ppm was off the scale. I tried as much as possible to hold my breath but it lasted for 15 minutes.

In the water, I kept getting a strange sudden onset of hypoxic symptoms long before any breathing reflex hit me. Then I dove a very easy target depth, 30m less than PB, with a sudden samba at the end.

This was not the only time. After this the CO problem happened again on another boat trip, but this time I recognized the symptoms and cancelled the deep dive.

I also was able to measure my COHb (carboxy hemoglobin %, = amount of hemoglobin bound to carbon monoxide). One breath of high CO air, from a boat or car motor exhaust, and my COHb level remained elevated for hours, and it took 24 hours to return to normal.

 

[Mullins]

Also there is the simple fact that some divers feel little urge to breathe before blacking out. So a spearo may be diving comfortably to 30m on a regular basis without knowing that they are close to a BO on each dive, while his/her buddies are less comfortable at that depth but have a much larger safety margin. Being close to BO all the time means that just a slight change (dehydration, fatigue, hyperventilation) can put the first diver over the edge and they'll have a seemingly inexplicable BO.

 

[cdavis]

I think Mullins is probably close to our explanation. My buddy has much less urge to breathe than I do. Take that, add a little C0, and a few other random factors and you're
there.

The C0 thing is one that has always concerned me. Boat going very slow or still, calm day, motor running and I can smell the exhaust. Always try to avoid it, but that's not completely possible. Sounds like its time to play with a battery powered C0 alarm. Anybody else have any experience along that line?

 

[efattah]

I got my carbon monoxide monitor on ebay new for around $350.

If you have the monitor (which measures ppm CO), you can measure your blood CO level.

To do so, inhale, hold your breath 30 seconds, then exhale into a ziploc plastic bag with the CO monitor in it. Seal the bag and wait. Watch the ppm reading. Then there are medical tables you can use to translate that into a blood %COHb value.