Three Hearts... Beat As One(?)

You're taking the other side? O2, Bruté?

I'm not on any side.

What about that famous song

Never heard that song. it must not be that famous

Looking around on this topic, it seems that there are significant differences between hypoxia (low oxygen) and hypercapnia (high CO2).

I dont know if I experienced hypoxia or hypercapnia. I never thought about it until now. It was an occasion were I was the passenger in a small plane. we were flying in the mountains. the pilot was wearing a O2 mask and I was not. At one point we were high enough that I basically just fell a sleep, then when the plane went lower I woke back up. Nice little nap. I think that it was Hypoxia.
 
CaptFish;160666 said:
I dont know if I experienced hypoxia or hypercapnia. I never thought about it until now. It was an occasion were I was the passenger in a small plane. we were flying in the mountains. the pilot was wearing a O2 mask and I was not. At one point we were high enough that I basically just fell a sleep, then when the plane went lower I woke back up. Nice little nap. I think that it was Hypoxia.

It sounds like it. I am reminded of the Helios Airways flight 522, for which a memorial service was held in the last day or so. The crew did not recognize that they had forgotten to pressurize the aircraft (and even silenced the alarm); all were impaired and the aircraft ultimately crashed, killing all on board.

Heartbeats are hard to tell from observation, but the mantle activity seems readily observable. Have you observed a "distressed breathing" response in octopuses or squid that you associated with low oxygen levels?
 
We have seen excessive breathing that was eliminated when the water was areated. This is most likely to be high CO2 but also low O2. I am not sure I fully grasp the difference when I think about it though. In the case of low O2, something would be displacing it in the water, if not CO2 then nitrogen or other gases as I don't think (but don't know) the gas levels would just get thin like being higher in the atmosphere.
 
As far as the hearts slowing down in response to less oxygen in the water, it might be that a common mechanism both slows the heart and reduces general muscle activity/behavior in response to hypoxia. This could be adaptive because it would keep the animal from over-exerting itself and running out of oxygen in these conditions, and the heart slowing could either directly limit muscle contraction (and thus oxygen use) or these two things could be limited by some common third mechanism. I have no idea how one would go about proving this. I think this may have already been said.

Also, respiration rate and heart rate might not be directly coupled in octopus. It seems sensible to me that in low-oxygen conditions, the respiration rate speeds up to get more oxygen flowing across the gills, and the heart rate slows down so that each unit of hemocyanin has more time to pick up oxygen while it's in the lungs.

Now I wish I knew more about cardiac physiology.
 

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