Several questions are raised in this paper:
1/ are whales on a ketogenic diet during aerobic metabolism (when they breathe regularly near the sea surface)?
2/ What is lunge feeding?
https://www.americanscientist.org/article/the-ultimate-mouthful-lunge-feeding-in-rorqual-whales
3/ Is whale bradycardia a diving reflex?
"As a cardiovascular surgeon, I was delighted to read this paper. My question is about whale metabolism as authors discussed it :
Whales don't have access to carbs. Krill contains very low amount of carbs:
Whales don't have access to carbs. Krill contains very low amount of carbs:
"Krill, Euphausia superba Dana, sampled from waters around South Georgia in 1978 contained 10–11% protein, 2–6% lipid, 0.3–0.6% carbohydrate, 2% chitin, and 3–4% mineral ash (all mean values, % fresh weight)." (https://www.sciencedirect.
Basically whales are on a ketogenic diet especially when they have plenty of oxygen. So the amount of glucose for glycolysis during diving would come from glycogen store in muscle and liver. Liver gluconeogenesis is apparently too slow to contribute to glycolysis during diving and diving time is too short. So I didn't understand the relationship they are searching between heart rate and metabolism during diving.
May I suggest another cause of the low frequency of cardiac contraction? Even if Whales do have a skeleton the pressure of water at this depth could perhaps explain that they save energy because systolic ejection is costly due to hydrostatic pressure? Is it the same diving reflex than in humans?"
Basically whales are on a ketogenic diet especially when they have plenty of oxygen. So the amount of glucose for glycolysis during diving would come from glycogen store in muscle and liver. Liver gluconeogenesis is apparently too slow to contribute to glycolysis during diving and diving time is too short. So I didn't understand the relationship they are searching between heart rate and metabolism during diving.
May I suggest another cause of the low frequency of cardiac contraction? Even if Whales do have a skeleton the pressure of water at this depth could perhaps explain that they save energy because systolic ejection is costly due to hydrostatic pressure? Is it the same diving reflex than in humans?"
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