Splenic contractions during breath-hold diving were already discussed here on DB several times. There are also number of studies about this topic - I have a dozen of them listed at spleen @ APNEA.cz
Few days ago, Elisabeth Kristoffersen published on her blog a new entry about her participation on the research of Erika Schagatay, a Swedish scientist from the Mid Sweden University, who is also the author of another older study listed in my database too.
However, I was rather surprised that Erika estimates the average increase of BHT (breath-hold time) to 20-30s. When calculating the possible effect of splenic contraction on the apnea time at humans, I do not see any possibility to get an improvement more than very few seconds (approx 2-4s in average). Since I guess that it may interest some of you, I posted a comment with the calculation on Elisabeth's blog, and am copying it below:
Personally, I am afraid that the breath-hold increase of 30s thanks to the splenic contraction is rather exaggerated. In the older study Erika found that in average the splenic contraction releases 49 ml of blood. Now the hematocrit is packed with the density twice so high as in arterial blood, so let's assume it corresponds to 100 ml. At ~5 l of blood in body, it would make about 2% hematocrit increase. That's consistent with the measurement from Erika's study (2.2% Hct increase).
However, spleen is used as a depository of old hematocrit, where it is then being destroyed. So quite likely this hematocrit released from the spleen has not the same oxygen transport capacity as new one. I wonder if this fact was taken in view in Erika's study.
Even if we speculate with the uncertain 2% increase of Hct, at the max breath-hold of 5 minutes (300s), the 2% would make only 6s. In fact even less, because although the higher Hct will allow saturating the blood with more oxygen during the breath-up, it won't help too much with pulling oxygen from lungs after the start of the apnea. Well, to certain extent the gas exchange with the dropping oxygen level in lungs during the apnea will be more efficient at higher Hct, but likely the difference will be much lower than the Hct increase. Blood pH will be a more important factor, so even with more Hct it won't allow much lower hypoxemia.
Considering the above mentioned facts, I am afraid that the splenic contraction will help with just some very few seconds (2-4s ?). I believe that the 20s or 30s observed in the study of Erika Schagatay can be only attributed to the other remaining factors of the progressing diving response (bradycardia, vasoconstriction, etc.), and unfortunately not to the splenic contraction.
I'd love though hearing from Erika or other experts on this topic. Of course, having the possibility to increase own breath-hold time by 30s thanks to the splenic contraction would be wonderful, but I am afraid it is just a dream originating probably in the studies of seals, who have indeed huge spleens containing several liters of blood highly packed with Hct.
Few days ago, Elisabeth Kristoffersen published on her blog a new entry about her participation on the research of Erika Schagatay, a Swedish scientist from the Mid Sweden University, who is also the author of another older study listed in my database too.
However, I was rather surprised that Erika estimates the average increase of BHT (breath-hold time) to 20-30s. When calculating the possible effect of splenic contraction on the apnea time at humans, I do not see any possibility to get an improvement more than very few seconds (approx 2-4s in average). Since I guess that it may interest some of you, I posted a comment with the calculation on Elisabeth's blog, and am copying it below:
Personally, I am afraid that the breath-hold increase of 30s thanks to the splenic contraction is rather exaggerated. In the older study Erika found that in average the splenic contraction releases 49 ml of blood. Now the hematocrit is packed with the density twice so high as in arterial blood, so let's assume it corresponds to 100 ml. At ~5 l of blood in body, it would make about 2% hematocrit increase. That's consistent with the measurement from Erika's study (2.2% Hct increase).
However, spleen is used as a depository of old hematocrit, where it is then being destroyed. So quite likely this hematocrit released from the spleen has not the same oxygen transport capacity as new one. I wonder if this fact was taken in view in Erika's study.
Even if we speculate with the uncertain 2% increase of Hct, at the max breath-hold of 5 minutes (300s), the 2% would make only 6s. In fact even less, because although the higher Hct will allow saturating the blood with more oxygen during the breath-up, it won't help too much with pulling oxygen from lungs after the start of the apnea. Well, to certain extent the gas exchange with the dropping oxygen level in lungs during the apnea will be more efficient at higher Hct, but likely the difference will be much lower than the Hct increase. Blood pH will be a more important factor, so even with more Hct it won't allow much lower hypoxemia.
Considering the above mentioned facts, I am afraid that the splenic contraction will help with just some very few seconds (2-4s ?). I believe that the 20s or 30s observed in the study of Erika Schagatay can be only attributed to the other remaining factors of the progressing diving response (bradycardia, vasoconstriction, etc.), and unfortunately not to the splenic contraction.
I'd love though hearing from Erika or other experts on this topic. Of course, having the possibility to increase own breath-hold time by 30s thanks to the splenic contraction would be wonderful, but I am afraid it is just a dream originating probably in the studies of seals, who have indeed huge spleens containing several liters of blood highly packed with Hct.
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