Study: contractions help oxygenating brain

[trux]

Well, it was already stated here on DB several times in the past, but now it comes confirmed by a scientific study: contractions help you going through hypoxia by increasing the cerebral blood flow volume. A new study by Z. Dujic & co.: Involuntary breathing movements improve cerebral o... [J Appl Physiol. 2009] - PubMed result

We investigated whether the involuntary breathing movements (IBM) during the struggle phase of breath holding, together with peripheral vasoconstriction and progressive hypercapnia, have a positive effect in maintaining cerebral blood volume. The central hemodynamics, arterial oxygen saturation, brain regional oxyhemoglobin (bHbO(2)), deoxyhemoglobin, and total hemoglobin changes and IBM were monitored during maximal dry breath holds in eight elite divers. The frequency of IBM increased (by approximately 100%), and their duration decreased ( approximately 30%), toward the end of the struggle phase, whereas the amplitude was unchanged (compared with the beginning of the struggle phase). In all subjects, a consistent increase in brain regional deoxyhemoglobin and total hemoglobin was also found during struggle phase, whereas bHbO(2) changed biphasically: it initially increased until the middle of the struggle phase, with the subsequent relative decline at the end of the breath hold. Mean arterial pressure was elevated during the struggle phase, although there was no further rise in the peripheral resistance, suggesting unchanged peripheral vasoconstriction and implying the beneficial influence of the IBM on the cardiac output recovery (primarily by restoration of the stroke volume). The IBM-induced short-lasting, sudden increases in mean arterial pressure were followed by similar oscillations in bHbO(2). These results suggest that an increase in the cerebral blood volume observed during the struggle phase of dry apnea is most likely caused by the IBM at the time of the hypercapnia-induced cerebral vasodilatation and peripheral vasoconstriction.

 

[Don Paul]

Thank you I spearfish alone a lot, every little bit of info is a plus. thank you.
Cheers, Don Paul

 

[cdavis]

Very interesting! Thanks.

Could you extend the reverse situation, a diver who gets few or minimal contractions, and predict that such a diver would be more susceptible to B0? That's my experience, could this be the reason?

Connor

 

[trux]

Well, that's not an easy question. OK, the contractions help you going into deeper hypoxia, it means you can stay longer (though they consume some oxygen too, especially if you resist them and tense the muscles). However, it does not mean that you could not learn surfacing before the hypoxemia reaches the critical threshold anyway, regardless if the effect of contractions is positive or negative. I saw someone writing here, not such a long time ago, that he had the exact opposite experience - that freedivers without contractions learn better recognizing the hypoxic signals, while normal freedivers often use contraction as the signal, and that can be quite deadly.

 

[cdavis]

Could be a little bit of both. I train with a guy who doesn't get contractions and who almost B0ed early in his training history. Since then he's been very carefully exploring his limits and learning what it feels like as well as diving longer and deeper.

Connor

 

[wet]

I didn't see this message til now. Thanks Ivo, it agrees with what I'd speculated earlier, in reference to diaphragmatic contractions functioning as an oxygenation pump, induced by higher CO2. One could view this as a diving adaptation or simply a survival reflex; most specialized adaptations are reflexes that are naturally selected (strengthened) among members of a population in association with foraging sustenance.

 

[trux]

Yes, I remember hearing it first from you years ago, here on DB, David.

 

[efattah]

For years I've been saying that contraction's main purpose was to oxygenate the brain. Herbert doesn't get contractions unless he 'makes' them happen. He said that during static, if he doesn't let the contractions happen, he starts to black out. Once he lets the contractions happen, he gets another minute. So yes, a diver who doesn't get contractions could thus be assumed to black out one minute earlier than with contractions...

 

[wet]

Eric, I didn't mean to claim precedence, it is very likely your writings (and some others) inspired my understanding. I meant only that the oxygenation mechanism of diaphragm contractions, despite their widely known discomfort, can be understood as not-widely-known optimal peripheral-central pumping, where CO2 is the trigger for the reflex, and oxygen conservation is a goal.
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I just saw these, tangential to the subject but interesting:

A Clarke & H-O Poertner 2010 Biol.Rev.PRESS
Temperature, metabolic power, and the evolution of endothermy (warmbloodedness)

Endothermy has evolved at least twice, in the precursors to modern mammals and birds. The most widely accepted explanation for the evolution of endothermy has been selection for enhanced aerobic capacity. We review this hypothesis in the light of advances in our understanding of ATP generation by mitochondria and muscle performance. Together with the development of isotope-based techniques for the measurement of metabolic rate in free-ranging vertebrates, these have confirmed the importance of aerobic scope in the evolution of endothermy: absolute aerobic scope, ATP generation by mitochondria, and muscle power output are all strongly temperature-dependent, indicating that there would have been significant improvement in whole-organism locomotor ability with a warmer body. New data on mitochondrial ATP generation and proton leak suggest that the thermal physiology of mitochondria may differ between organisms of contrasting ecology and thermal flexibility. Together with recent biophysical modelling, this strengthens the long-held view that endothermy originated in smaller, active eurythermal ectotherms living in a cool but variable thermal environment. We propose that rather than being a secondary consequence of the evolution of an enhanced aerobic scope, a warmer body was the means by which that enhanced aerobic scope was achieved. This modified hypothesis requires that the rise in metabolic rate, and the insulation necessary to retain metabolic heat, arose early in the lineages leading to birds and mammals. Large dinosaurs were warm, but were not endotherms, and the metabolic status of pterosaurs remains unresolved.
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Torsion of ventricular (heart) musculature & rotary bloodflow
Torsional Ventricular Motion and Rotary Blood Flow
I note that among the pictures in Figure 1 is tao-like image #14, and others appear snail-like. The heart functions as a rhythmic flow control device, responsive to both external and internal stimuli, moving gases etc. around the body. I don't know how/if diaphragmatic contractions link to that specifically.

 

[wet]

(OT, not linked to contractions, just hemoglobin, respiration, cold)

Mammoth hemoglobin, cold tolerance in respiration

(Mammoths & manatees are genetically closely related, their common ancestor was semi-aquatic herbivore somewhat beaver-like)

KL Campbell cs 2010 Nature Genetics PRESS
Substitutions in woolly mammoth hemoglobin confer biochemical properties
adaptive for cold tolerance

We have genetically retrieved, resurrected and performed detailed
structure-function analyses on authentic woolly mammoth hemoglobin to reveal
for the first time both the evolutionary origins and the structural
underpinnings of a key adaptive physiochemical trait in an extinct species.
Hemoglobin binds and carries O2; however, its ability to offload O2 to
respiring cells is hampered at low temperatures, as heme deoxygenation is
inherently endothermic (that is, hemoglobin-O2 affinity increases as
temperature decreases). We identify amino acid substitutions with large
phenotypic effect on the chimeric ¦Â/¦Ä-globin subunit of mammoth
hemoglobin
that provide a unique solution to this problem and thereby minimize
energetically costly heat loss. This biochemical specialization may have
been involved in the exploitation of high-latitude environments by this
African-derived elephantid lineage during the Pleistocene period. This
powerful new approach to directly analyze the genetic and structural basis
of physiological adaptations in an extinct species adds an important new
dimension to the study of natural selection.
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Manatees, mammoths, stellar sea cows:
Ozawa et al. 1997. Phylogenetic position of mammoth and Stellar's sea cow within Tethytheria demonstrated by mitochondrial DNA sequences. J. Mol. Evol. 44:406-413. ... trichotomy among Steller's, manatee, and dugong, estimated divergence 22ma.

Manatees crossed the Atlantic from South America to West Africa ~10ma
http://scienceblogs.com/tetrapodzoology/2010/05/those_transatlantic_manatees.php