A little while ago I fielded a question about breath hold divers of the non human kind. The question was simple enough, “Do dolphins and whales also benefit from the effects of higher pressure of oxygen as they dive, as humans do in a hyperbaric chamber?”
The answer proved a little more complicated than the question, but to summarise it somewhat, the answer started out as, “I imagine they must do”, because the air in their lungs will also be subject to the same physics as ours. and in essence, their lungs contain compressed air, (which contains oxygen), at an increased ambient pressure. Henry’s law would apply, and greater amounts of the gasses in the breathing mix would dissolve into the blood and tissue. The same applies to human breath hold free divers who have, in some cases, developed decompression sickness following gas absorption on extended single breath dives. Ordinarily not a concern because breath hold diving seldom lasts long enough to cause a problem outside of the absolute elite. Considering marine mammals dive for considerably extended times compared with even the elite among human breath hold free divers, there would be some increase in oxygen tension in tissue. That said, they would also use that oxygen to stay down on a single breathe, which would then result in a low oxygen scenario, and a slowing of the metabolism. Paradoxical to say the least. A further kink in my theory is that HBOT usually takes maximal effect after fairly long uninterrupted exposure to pressure, with protocols lasting up to an hour or two a day and many treatments day after day, (anything from 20 to 80 in fact). Although, marine mammals and such dive all day, every day. Essentially they are on a permanent pressure regimen. But to them that would be the norm and they would evolve accordingly.
The explanation went on to include the size of their spleens and how much blood they could store. Ie, red blood cells in order to better transport oxygen. This is along similar lines of thinking when we referred to the Sherpa’s of the mountainous regions of Nepal and the Himalayas in the article ALTITUDE, THE HYPEROXIC HYPOXIA PARADOX, AND THE COMMON SENSE PARADOX which made mention of larger spleens which have developed over time by those individuals living at altitude. Apparently as much as 40% larger in fact according to various reports.
Needless to say, I don’t think the original question was entirely or convincingly answered, but it was an interesting one indeed, drawing many parallels with human physiology and the physiology of altitude, hypoxia, hyperoxia, and hyperbaric conditions.
As we know, in a hyperbaric chamber, we are only simulating depth. We increase pressure in the unit ‘atmospheres’ by adding air to the chamber which is supplied by a compressor, and which increased pressure is comparable to depth in sea water. That is, every one additional atmosphere over the one we’re already standing under, will add the equivalent pressure exerted by 10 meters of sea water. (Sea water has a slightly higher specific gravity than fresh water so we use sea water as the standard). Many technicians and operators refer to depth for this reason. Incidentally, one atmosphere (at), is equal to 1 kg/cm squared and also for practical purposes, mostly equal to one bar. It is the actual unit we measure pressure in. Expressed as an absolute pressure which includes the actual atmosphere we stand under, it is written as atmospheres absolute or ‘ata’.
In terms of physics and physiology, there is almost no difference between this pressure in the water and the pressure in the chamber. The body responds in the same way to simulated depth as it does to actual depth in water with only one exception. In water, the body interprets the water as an oversupply of water, and gravitational force differences cause the body to redistribute fluid as the external hydrostatic pressure, (water pressure), acts against the internal hydrostatic pressure in the body’s fluid systems. One effect is called immersion diuresis, or fluid loss when submerged. Many divers and swimmers report the need to urinate upon submersion, even if they just ‘went’. It’s a significant difference as it effects things like blood pressure, the renal system, heartbeat and oxygen tolerance, but as far as the gas laws go, there is no difference at all.
Marine mammals and reptiles are no different. Since they breathe air (a gas), the same gas laws apply to diving beneath the waves, increasing pressure and coming back to surface as those that apply to actual compressed air diving, or chamber ‘diving’.
Following all this bamboozlement, I sometime later coincidentally stumbled across an absolutely fascinating piece of research published by Shearwater Research.
As we’ve covered previously, one of the main and original purposes of hyperbaric chambers was to treat decompression sickness in caisson workers constructing the Brooklyn Bridge where decompression sickness was identified and labelled ‘the bends’. Also in divers suffering the same following dives. Read more on that here: HYPERBARIC OXYGEN THERAPY – SOME HISTORICAL PERSPECTIVE
It turns out that following the investigation into whether marine mammals and reptiles benefit from the oxygen as we do, which was never quite decided, it turns out they do moderate their dives to avoid decompression sickness. They have also been successfully treated for decompression sickness in hyperbaric chambers.
Some years ago, while working for the The South African Association for Marine Biological Research (SAAMBR), we frequently re-compressed fish and other marine animals after they had been brought into the facility with over expanded swim bladders and other embolism type problems. Specially constructed mini-chambers were pressurised with pure oxygen to significantly high enough pressures to ‘squash the bubble’ and remedy the situation. The oxygen would dissolve into the water according to Henry’s law, providing an oxygen enriched environment for our new residents. They would then be slowly decompressed back to normal atmospheric pressure. Essentially, we were treating them for decompression sickness/illness.
Seemingly, this learned behaviour, which allows marine mammals and reptiles to moderate their diving profile, has evolved to become part of the biological make up of these animals. Especially in those that do not benefit from “parental guidance”, Ie, the reptiles. The study suggests that marine mammals and reptiles do indeed do decompression. The same way divers, and in some circumstances, chamber occupants do.
Accordingly, we’re very pleased to have found this fun article to share on the subject. It ties in with all the physics and physiology we are subject to in hyperbarics as a direct extension of diving. It jut seems the natural world became well aware of all this eons before humans did. Too cool for words. Click through on the embedded link below to the original article.
© Hayden Dunstan