Mammalian diving reflex

Heart rate plummeted from 72 BPM (resting) down to 39. It was pretty cool to see

I think it's to do with the diving reflex, that's the only reason I can think of.

https://www.youtube.com/watch?v=L0KTqPloUiU

[Side note: DO NOT read any of the comments. They are particularly obnoxious and there is nothing worthwhile. You have been warded.]

I wonder if this is why seals, whales evolved flippers instead of big limbs less warm blood wasted in big limbs.

Our daughter was born a few weeks early. Her lungs weren't mature enough yet, so she was in the NICU for a while. One day we were changing her diaper right before her evening feed, around 8 p.m. She was already fussy because she was hungry, and then she got really upset because she pooped halfway through the diaper change, so we had to start over. She was really mad, screaming at the top of her little lungs.

In the middle of all of this, I looked over at the monitor (babies are always on monitors at the NICU) and noticed that her heart rate had jumped from ~160 bpm (typical for a newborn) to ~320 bpm. I asked the nurse about it and she said it was a little high, but that it was probably just because she was upset. After we wrapped things up, our daughter started eating and quickly calmed down. Strangely, though, the monitor hadn't budged: still ~320 bpm.

I asked the nurse if the monitor was correct, and apparently it was, because things quickly turned serious. Double-check with a stethoscope. EKG ordered. Doctors we'd never met appeared out of nowhere. Pediatric cardiologist called. Another IV started. 10 people crowded around our tiny daughter.

The neonatologist texted the EKG printout to the cardiologist (at a hockey game with her daughter, we later learned), and she and diagnosed a supraventricular tachycardia. Untreated, it would result in organ failure within hours.

The top priority became getting the heart rate back to normal. I assumed they would use drugs or some kind of electrical stimulation, but they told me about their preferred treatment, and it seemed almost like quackery: sticking ice packs on our daughter's face and forehead.

They got their bags of ice water ready, applied them simultaneously, waited precisely 6 seconds, and removed them. A few seconds later, still ~320 bpm. It hadn't worked.

They planned to try once more, and then try with drugs through the IV. Ice packs ready. Applied. 6 seconds. Again, nothing. Disappointment, anxiety, fear, worry.

And then it happened: five or six seconds after they removed the ice packs, our daughter's heart rate instantly dropped back to ~160 bpm. There was no gradual decline: it was a step function. It almost seemed like magic. The quackery wasn't so quackish after all.

That was my introduction to the diving reflex.

(Postscript: our daughter has been on medication since that day, but she's getting old enough that they're starting to taper it off, and soon she'll be medication-free. The idea is that if she has a reoccurrence, she'll notice and tell us. Then, guess what the prescribed treatment is? Yep: stick her face in a bowl of ice water.)

Further reading:

http://www.ncbi.nlm.nih.gov/pubmed/22389355 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1544966/ http://www.webmd.com/heart-disease/tc/supraventricular-tachy...

And free dive fins are the best. If you've never tried any, try to get hold of a pair. It's fun zooming through the water like a seal.