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Bottom Time Based on Heart Rate

psimian

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Jul 12, 2015
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Does anyone know of any studies that link maximum breath hold times to average heart rate and/or number of heart beats during the hold?

I know that metabolic rate, heart rate, and O2 consumption rate are pretty closely correlated. Therefore, it seems like it should be possible to estimate how quickly you are burning through oxygen based on your heart rate preceding and during the dive.

It would be really handy to have a computer that could estimate how much time you have left before you are at risk for a blackout, particularly if you are going deep enough that ascent blackout is a concern.
 
Mar 20, 2011
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Yes, there have been seal studies but none on humans. I personally think it could be a good safety barometer for freedivers using HR equipped watches, just a change in firmware.

In the seal studies, seals showed a remarkable similarity in total number of heart beats, no matter the dive profile, on an individual basis. Meaning for a given animal, an athletic dive which was shorter in time was usually the same number of beats as that same animal's relaxed and slower dive.
 
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psimian

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Jul 12, 2015
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I thought about the HR watch as a starting place, but from what I've read, they have trouble picking the pulse at depth, particularly once blood shift starts to set in. EKG chest bands are better, but sometimes have trouble due to water conductivity. An ear clip might work, but running a wire down to your watch would be annoying.
 
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psimian

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Jul 12, 2015
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For what its worth, my resting heart rate is 38 to 40, and my breath hold sucks.
That's why you would need to calibrate it to the individual. What's important is how many beats you have before you run out of air. If you have a naturally slower heart rate, you'll have fewer beats.

Whether you're doing full lungs, FRC, or empty lung would also have a huge impact.
 

HoldFast

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Jan 22, 2015
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Also, your performance can shift from day to day, so it would be very hard to consistently predict an imminent blackout from HR or SaO2

https://rua.ua.es/dspace/bitstream/10045/69552/1/jhse_Vol_12_N_3_582-592.pdf

Not a very solid study. But he does claim a strong negative correlation between a diver's minimal HR during static and their overall competition performance, and no correlation between HR at rest and overall performance.

This is an intuitive result. Suggests that the stronger your dive reflex is, the stronger your performance overall.
 
Mar 20, 2011
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Funny this thread popped up. I just finished waterproofing a custom dive heartbeat logger prototype. I intend to begin testing it in the pool today. Since it is my machine and I wrote the software it will actually do a count of total heart beats among other things so I can track various correlations. First application will be a longfin shootout, testing 5 pairs against each other. Constant depth and distance but measuring total beats per dive.

Sent from my SM-G930T using Tapatalk
 
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psimian

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Jul 12, 2015
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That's fantastic. If it works would you care to share the plans? I've been doing more research that suggests a total heartbeat count, adjusted for overall aerobic fitness should give you a pretty good estimate of oxygen consumption. At least for running and cycling there is a linear relationship between heartrate, speed, and VO2 (this is the basis of most of the VO2max estimators). Basically, for a given level of fitness, distance=heartbeats. This is never going to be a perfect method, but it could add a margin of safety.
 
Mar 20, 2011
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I will provide a parts list... there is a lot of physical design in something like this though which is too involved to write up and sort of proprietary.


Primary components:
Adafruit 32u4 Bluetooth feather
Polar T34 Hear Rate Monitor educational starter pack
Adafruit MicroSD feather
Adafruit RTC feather
Blue Robotics altitude/depth/temp sensor

 
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psimian

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Jul 12, 2015
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I didn't know polar made a plug-in for their monitors. I'm curious to know how well that works in the water. I've been looking at building my own wired version to work with a raspberry pi since I don't want to run the risk of signal dropout during use.
 
Mar 20, 2011
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I didn't know polar made a plug-in for their monitors. I'm curious to know how well that works in the water. I've been looking at building my own wired version to work with a raspberry pi since I don't want to run the risk of signal dropout during use.
It is on the adafruit site. They sell a chest strap + receiver combo. You wire your receiver into your MCU. The reception is short range but in my dry testing so far very robust. I had thought about potting the receiver (which is size of a large coin) and tethering it to the MCU but reception has been fine. It uses an electromagnetic signal (not bluetooth) so it apparently works well in water.

Sent from my SM-G930T using Tapatalk
 

HoldFast

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Jan 22, 2015
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@Lance, brilliant project dude. Kudos. Looking forward to see what data it spits out. Keep us posted!

@psimian, Very interesting. So in theory, our hearts should be making the same total number of beats before we reach our hypoxic limit. Sounds like an easy thing to test :)
 
Mar 20, 2011
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I wore it line diving on Saturday, it seems to be working fine. I need sci graphing software though, 2 hour session creates too many data points and chokes Excel. I will post some sessions.

Sent from my SM-G930T using Tapatalk
 
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psimian

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Jul 12, 2015
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I was playing around with a pulse oximeter today and counting heartbeats for various breath holds. The problem with pulse oximeters is that the readout lags behind your actual spO2 by anywhere from 5-15 seconds, so all you can really get from a breath hold is a single data point--the lowest readout.

From the tests I did, I can conclude that the theory that heart beats = bottom time is at least partially incorrect. The results seem to be consistent for a given heart rate, but it is not a linear relation as heart rate increases. That is, 120 beats and 60bpm resulted in a spO2 of 91%, while 90 beats at 95bpm produced a spO2 of 88%. So, at the very least, you need to factor in both heart rate and total number of beats. It wouldn't surprise me if there is some variation between different types of activity as well since VO2MAX is activity specific. I was looking at various plans for arduino based pulse-oximeter dataloggers, and I think I can build something that will capture all the relevant data from an apnea event for $30-$40. It wouldn't be waterproof, but it would be a tool to start collecting data for a better version down the line.

I think my goal is to be able to accurately predict when you hit 80% spO2 just based on heart rate and total beats, since that is the average threshold for symptoms of hypoxia. Loss of consciousness doesn't happen until around 60% spO2, so that gives you a decent margin of safety (probably 15-30 seconds depending on exertion).
 

HoldFast

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Jan 22, 2015
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I can also recommend R. Excellent for both plotting and modeling.

What variables are you capturing? From your set up it looks like HR and depth.
 
Mar 20, 2011
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I can also recommend R. Excellent for both plotting and modeling.

What variables are you capturing? From your set up it looks like HR and depth.
A running total of beats since start of the session (from which HR can of course be computed), depth, time, and temperature.

Sent from my SM-G930T using Tapatalk
 
Mar 20, 2011
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Here are a couple graphs from the first day of shallow ocean testing. The plate was at 25M. I had not built a harness yet for the device and had it stuffed in my wetsuit so all the temperature info off the device logs was wrong but this is what came from the dive watches.

Surface temp: 58F/14C
Temp at 25M: 52F/12.8C

Some interesting results from a variety of dives... did a blind hang with no mask and since it came off, no noseclip, some touch and go drops, some half lung warm-ups, and for main set was kicking a 10lbs weight up from the plate. My normal resting HR is about 53BPM.



Sent from my SM-G930T using Tapatalk
 
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