Breath holding and oxygen consumption

[jiveturkey]

I just read in the Encyclopedia of Recreational Diving that your body only uses 10% of the oxygen it inhales in a breath. This is why AR is so effective. My question is if you hold your breath longer than normal (as in the case with skin diving), does your body use up the rest of that oxygen? It seems like that is the case. If your body uses more oxygen at depth because of increased partial pressure, that oxygen has to come from somewhere right? Your lungs? As far as I know the oxygen normally expelled from your body comes from your lungs and not your blood. I'm not aware of a surplus of oxygen in the blood. Does anyone have any clarification on this?

 

[canuckdiver]

holding your breath between breaths is commonly called "skip breathing". It does force your body to use more of the oxygen from each breath.

It also a DRASTIC increase in carbon dioxide retension, which causes bad headaches, neurological damage, and can cause greater amounts of nitrogen in the tissues, leading to DCS

 

[pescador775]

Jive, breath hold divers consume oxygen in the lungs. This oxygen, plus whatever reserves are in the blood and tissues, support life. There is a huge mythology which has evolved around breath holding. There is no connection between breath holding and neurological damage, DCS or headaches in normal individuals provided that the diver does not reach the point of fainting. At that point, depending on the water temperature and metabolic rate such damage could ensue within minutes.

Skip breathing is another subject, one not specifically asked. There is some slight danger that a diver could experience embolism with this and there is no real reason to do it. Some divers attempt to control buoyancy by suspension of breathing. I think it's overkill and unnecessary. It is claimed that at very deep depths, the practice of skip breathing could interfere with gas exchange or uptake or somehow cause CO2 retention leading to some unspecified or claimed consequences. I haven't personally tested this and don't intend to.

 

[pescador775]

I overlooked one of your questions. Jive, oxygen consumption depends on a lot of factors but PP of O2 is not normally one of them. Basically, it depends on metabolic rate, blood supply, chemistry of the body and preferential mode of the mitochondria, eg whether direct ATP conversion, or alternately, fermentation where mitochondria are distressed or inefficient. A simpler explanation is exercise level. However, although high PP is not an issue except in extremis caused by high O2 PP toxicity, LOW PP is of direct concern to freedivers when ascending. This is blamed for some instances of diver 'blackout'. Obviously, when partial pressure approaches zero the diver's brain will be struggling to maintain consciousness.

 

[jiveturkey]

canuckdiver once bubbled...
holding your breath between breaths is commonly called "skip breathing". It does force your body to use more of the oxygen from each breath.

It also a DRASTIC increase in carbon dioxide retension, which causes bad headaches, neurological damage, and can cause greater amounts of nitrogen in the tissues, leading to DCS

This has almost nothing to do with my question. I'm not talking about skip breathing.

 

[jiveturkey]

pescador775 once bubbled...
I overlooked one of your questions. Jive, oxygen consumption depends on a lot of factors but PP of O2 is not normally one of them. Basically, it depends on metabolic rate, blood supply, chemistry of the body and preferential mode of the mitochondria, eg whether direct ATP conversion, or alternately, fermentation where mitochondria are distressed or inefficient. A simpler explanation is exercise level. However, although high PP is not an issue except in extremis caused by high O2 PP toxicity, LOW PP is of direct concern to freedivers when ascending. This is blamed for some instances of diver 'blackout'. Obviously, when partial pressure approaches zero the diver's brain will be struggling to maintain consciousness.

You're only supposed to hyperventilate 2-3 time before a skin dive. If you hyperventilate more, your body gets rid of too much Co2 and you're body loses it's stimulus to breath. This principle is what skin divers use to stay down longer but if too much carbon dioxide is removed, it causes problems. At depth the ambient pressure allows your body to use more than it's "normal" share of oxygen. As you surface, and the pp drops and leads to shallow water black out (hypocapnia). What I'm wondering is, where does the extra oxygen that is used come from? Is your body allowing too much oxygen to be used from the blood or is it depleting the oxygen in the lungs? If not, why can't your body use the rest of the gas in your lungs? It seems kind of wasteful to have all the o2 sitting if your body is starving for it.

 

[scubadoc]

Blood is normally saturated with O2 to about 98%. It is not stored but is metabolized [used up]. The physiological limits of breath holding in human beings are based almost entirely on the oxygen reserves in the lungs, and the oxygen consumption. Big lungs give bigger reserves.

Oxygen consumption is directly related to the exercise of swimming. While the amount of oxygen used for a given speed through the water may be slightly improved through training, the change is really quite small. The time to blackout from hypoxia varies from individual to individual and time to time, but is in the order of 60-90 seconds with moderate activity. Oxygen consumption goes up disproportionately with the increase in speed.

What happens is that the amount of oxygen in the blood steadily falls as you swim holding your breath. This reduces the oxygen going to the brain. Once it drops below a certain level, you black out.

 

[pescador775]

Jive, get it out of your head that the body is using 'more than its fair share' while at depth. The blood, as Scubadoc explained, attempts to remain at saturation. It is only slightly inhibited from doing this by attached carbon monoxide of about 2%, hence 98% saturation. The blood will have become desaturated on the venous circuit due to prior uptake by cells. The rate of absorbtion from the lungs is mostly constant for a given metabolic level. This uptake can be impaired when the PP of oxygen is reduced to very low levels, below 16% fraction at atmospheric pressure. However, the reverse is not true, the blood hemoglobin does not take up more oxygen due to increased O2 pressure. When partial pressure of O2 is increased the uptake returns to normal levels even though the fraction may be deficient. The red cells are limited at the molecular level and there is no where to deliver more O2 anyway. The cells do not require more oxygen due to high PP. The body does not take up more oxygen and 'store' it.

As to the hyperventilation remarks; in my experience, breathing up makes one dizzy, that's it. However, some divers have a lower 'set point' for breath impulse and hyperventing may be dangerous for them. I believe the theory of this has to do with CO2 tolerance and does seem to vary or be suppressed among some breath hold divers. However, the real danger has to do with focus. A diver, spearfisherman, will lock in on a target and stay down too long while fighting a fish or simply chasing quarry. They belatedly kick hard for the surface when the 'fuzzies' set in. Tunnel vision and blackout are not far away.

 

[canuckdiver]

apologies, the way I read the question, I thought you were holding your breath between breaths.

my bad

 

[Laurence Stein DDS]

I would like to add to Scubadoc's answer. Everything he said is correct. In addition, when free diving, the PPO2 goes up at depth. This creates a situation in which there is more oxygen available at depth than at the surface.

With practice, the free diver is able to "overcome" the CO2 driven breathing response. At depth, the diver may actually feel like there is "more" air available to breathe.

Unfortunately, when surfacing following a long breathhold, the PPO2 falls below a minimum and hypoxia then occurs. The result may be shallow water blackout. In addition, the PPCO2 also goes up and increases the urge to take a breath. Once unconscious, the CO2 reflex kicks in and a sudden inhalation of water is possible.

Scubadoc, I think I've gotten this correct n'est pas?

Larry Stein