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Bottom Time Based on Heart Rate

Nathan Vinski

Well-Known Member
Apr 19, 2015
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#21
Is the theory that HR would increase and decrease proportionally to effort induced oxygen consumption and allows for a calculation to be made or that each heart beat represents an x value of consumed oxygen?

The issues I see with this revolve around pressure enduced bradycardia. I've measured HR on shallow (30m dives).
  • CWT (45 resting, 60 active descent, 35 end of Freefall, 40 ascent until breathing)
  • VWT (45 resting, 40 from 0-15m, 30 bottom, 35 ascent until breathing)
At this point the theory is correct as a VWT dive is much easier than CWT.. but assuming, due to higher core blood volumes, HR would drop more on deeper dives (especially VWT dives) why is a 2:15 70m VWT harder than 2:15static with a higher HR or more heart beats (mine rises to 60 on static with a mask)
 
Mar 20, 2011
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Los Angeles
#22
Is the theory that HR would increase and decrease proportionally to effort induced oxygen consumption and allows for a calculation to be made or that each heart beat represents an x value of consumed oxygen?

The issues I see with this revolve around pressure enduced bradycardia. I've measured HR on shallow (30m dives).
  • CWT (45 resting, 60 active descent, 35 end of Freefall, 40 ascent until breathing)
  • VWT (45 resting, 40 from 0-15m, 30 bottom, 35 ascent until breathing)
At this point the theory is correct as a VWT dive is much easier than CWT.. but assuming, due to higher core blood volumes, HR would drop more on deeper dives (especially VWT dives) why is a 2:15 70m VWT harder than 2:15static with a higher HR or more heart beats (mine rises to 60 on static with a mask)
I agree, because of dive response HR is not actually a good indicator of O2 consumption. I think the OP was proposing that. However, by repeating say a full lung dive to the same depth and by changing only one variable, I think total beats could be a useful metric (ie testing different makes of longfins).
 
OP
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Jul 12, 2015
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#23
Is the theory that HR would increase and decrease proportionally to effort induced oxygen consumption and allows for a calculation to be made or that each heart beat represents an x value of consumed oxygen?

The issues I see with this revolve around pressure enduced bradycardia. I've measured HR on shallow (30m dives).
  • CWT (45 resting, 60 active descent, 35 end of Freefall, 40 ascent until breathing)
  • VWT (45 resting, 40 from 0-15m, 30 bottom, 35 ascent until breathing)
At this point the theory is correct as a VWT dive is much easier than CWT.. but assuming, due to higher core blood volumes, HR would drop more on deeper dives (especially VWT dives) why is a 2:15 70m VWT harder than 2:15static with a higher HR or more heart beats (mine rises to 60 on static with a mask)
My original proposal was definitely an oversimplification because of some of the factors you just pointed out. The problem I've run into is that there just isn't much qualitative data on how the cardiovascular system behaves while freediving. Every little bit of evidence is a huge help at this point, even if it blows the current theory out of the water. Right now I'm relying on anesthesia and sleep-apnea research for most of my ideas, because this seems to be the biggest pool of relevant data. Unfortunately, I don't have access to most of the professional journals, which slows things down quite a bit.

I don't think the basic HR monitor is going to provide enough data. I read a white paper describing how it is possible to predict VO2 Max with high accuracy based on analysis of the features of an ECG trace. Apparently it is possible to differentiate between HR changes due to metabolic change (exercise), vs changes due to stress/excitement. I wonder if it would be possible to use a similar analysis to account for the effects of the dive response.

I know it is possible to use noninvasive optical methods (like the fingertip pulse-oximeters you can buy for $20) to get info on blood oxygen, CO2 levels, blood pressure, and some other vital stats. The problem is, these senors are designed for hospital use, and cost thousands of dollars.

I'll keep plugging away at it. Until then, please keep weighing in with all the things I've overlooked, reasons this won't work, possible avenues of exploration, etc.
 
OP
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#24
The comment from @Nathan Vinski about the relative difficulty of a static vs VWT got me thinking. Under normal aerobic exercise conditions, blood pressure (BP) and heart rate (HR) both increase as the level of exertion goes up. Both apnea and the dive response act to drive BP up and HR down. So, without knowing BP, it's impossible to guess at the total cardiac output, which (I suspect) is really need.

There are other variables that affect cardiac output (heart size, overall fitness, body mass, etc.) but they all stay reasonably constant over the course of a day of diving. While it is impossible to measure BP on a continuous basis while diving, it is possible to track fluctuations in BP by looking at the lag between your heart beat (detected by chest strap), and when it shows up on pulse meter somewhere else on your body (the higher your BP, the faster the pulse wave travels through the arteries).

So, if we could track depth, relative BP, HR, and SaO2 after surfacing, it might be possible to build an on-the-fly model of your dive performance. Obvious limitations are that the model would be specific to a given type of dive, and you can only guess about your personal SaO2 threshold for loss of consciousness.
 
Mar 20, 2011
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#25
The comment from @Nathan Vinski about the relative difficulty of a static vs VWT got me thinking. Under normal aerobic exercise conditions, blood pressure (BP) and heart rate (HR) both increase as the level of exertion goes up. Both apnea and the dive response act to drive BP up and HR down. So, without knowing BP, it's impossible to guess at the total cardiac output, which (I suspect) is really need.

There are other variables that affect cardiac output (heart size, overall fitness, body mass, etc.) but they all stay reasonably constant over the course of a day of diving. While it is impossible to measure BP on a continuous basis while diving, it is possible to track fluctuations in BP by looking at the lag between your heart beat (detected by chest strap), and when it shows up on pulse meter somewhere else on your body (the higher your BP, the faster the pulse wave travels through the arteries).

So, if we could track depth, relative BP, HR, and SaO2 after surfacing, it might be possible to build an on-the-fly model of your dive performance. Obvious limitations are that the model would be specific to a given type of dive, and you can only guess about your personal SaO2 threshold for loss of consciousness.
That is a lot to track! I think we will have an ear lobe UW pulse oximeter in the next 5 years. I know Omer has been developing one. I may do some research on it, since they are light driven I do not think the water interferes, I think it just is a matter of making something which is useable by everyone and probably the waterproofing...

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Nathan Vinski

Well-Known Member
Apr 19, 2015
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Canada
#26
I still think main issues with creating a reliable method of prediction revolve around the fact that during a freedive we 1: are dealing with a closed cardiovascular system and 2: have a bradycardic response.

The reason this creates a problem is that blood O2 desaturation in any particular area of the body for any particular volume of blood can happen without changing cardiac output. For example if 10 heart beats of blood pass through the legs during static we only assimilate a very small amount of the available O2. This isn't the case during a deep ascent and even with blood shift, our legs still get some blood flow and we will assimilate more of the available O2 from those 10 heart beats. Due to DR we might have a similar HR/total beats during both of these time periods with drastically different O2 consumptions.

The same can apply to fin-testing for example. A super stiff fin might produce lots of CO2 and improve bradycardia (less total beats) on a mid length dynamic but your non-bloodshifted muscles will be consuming more O2 than a soft fin with (maybe) more total beats due to less CO2 enduced bradycardia but much slower blood O2 desaturation.

Just FYI I'm rooting for the possibility of a reliable prediction method to be made, mainly for testing different approaches. I've been doing lots of 55m bi fins dives with different methods (different weighting, no freefall, "extreme" hyperventilation, fast/slow ascents..).

Based on ease of recovery my best results have come from the combination of (extreme hyperventilation, deep neutral point (30m w/1kg), no freefall, and medium speed ascent.

My worst results are (minor breath up/hypoventilation, shallow neutral point (20m w/2kg), freefall (30m), and medium speed ascent.

Although I'm sure I have a much worse HR on the first approach I still have the best results. Unfortuatly I never train with a computer so I'm unaware of dive time but my feeling/ buddy feedback is that approach 1 is quite a bit faster. So I would be curious to see the relationship between recovery, divetime, and total heart beats.
 
Mar 20, 2011
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#27
That is very interesting Nathan, with your different bifin dives. I have not tested with my HR computer but over years of testing different diving styles my own are very different. I do well with a long freefall or hang, and when I weight extremely light my dives are very difficult. There is definitely a sweet spot of course, being too heavy is grueling.

I have not tried a hyperventilation but I get very uncomfortable during descent when I overbreathe.

My ascent speeds are usually mediumish for a competitive diver.

What I always 'felt' was that I needed a freefall or hang to lock in DR, and once locked in it would remain steady even on ascent. All of my HR graphs from my training session reflect that, and while I did not do any underweighted, I can see my HR drop at the point when I would ordinarily begin freefall (I tend to freefall very soon after my neutral point). When doing deep dives here in a 5mm, I do best when weighted neutral at 12M. In warmer water thinner suit I am usually neutral around 15M.

Sent from my SM-G930T using Tapatalk
 
OP
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#28
There are 3 main problems with using a pulse-ox as a kind of early warning system.
  1. They are less reliable when you have decreased blood flow to the skin. So cold water + dive response could really mess up your readings. Having one on the ear, instead of the finger, will help a lot, but it may not be enough for all conditions.
  2. There is always a delay in the reading. The amount of delay depends on your heart rate and the location of the pulse-ox, but it can easily be 15-30 seconds since the blood has to travel from your lungs to the meter. This means you could potentially black out from hypoxia before the meter even detects a problem. Again, having the meter on the ear will shorten this delay, but it won't eliminate it.
  3. Here's the real sticking point: your blood O2 saturation will remain above 90% as long as the partial pressure of O2 in your lungs is above 60mmHg. At the start of a breath hold, the partial pressure of O2 in the lungs is usually about 100mmHg, maybe a little more depending on breathing technique. Below 60mmHg, O2 saturation drops rapidly, and blackout hits at around 30mmHg (60% O2 saturation). So, suppose you have a reading of 95% on your pulse oximeter at 30 meters. This means the partial pressure of O2 in your lungs could be anywhere from about 70mmHg to 300mmHg. If it's 70mmHg, you're in serious trouble since you will probably black out as you surface (70mmHg @ 30m = 27mmHg @ surface).
In short, the pulse-ox won't tell you anything useful during a dive, but it might be able to tell you how close you came to blackout after the fact. I say "might" because the pulse-ox gets increasingly inaccurate below 80%.
 
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#29
I wonder how consistent the profiles are within a given type of dive? If you use the same gear, weight, and technique for multiple dives, how much variation is there in HR, BP, and ending SpO2?
 

cdavis

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Jan 21, 2003
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#30
Fascinating stuff. Any idea why the spike in heart rate when getting to depth in most of the dives? The spike is much smaller on half lung dives. Same question. Looks like your DR is breaking on ascent with the 10 lb weight. Any other reason? What did it feel like?
 
Mar 20, 2011
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#31
@psimian a pulse ox based computer would not replace a safety or really be much use in competition where divers are frequently riding the line between samba/BO and not. But recreationally you could set it with a wider safety margin and it would be in theory programmed to be more 'intelligent'-- it would know that reduced O2 sat at 30M is much bigger deal than reduced O2 sat at 5M. Combined with a freedive recovery vest it could even be designed to go off if it detects O2 sat below a certain point, likesay 80%...

I think dive profiles would be relatively consistent (I did not post all my results because many were basically identical).

Connor my HR spikes at depth on a lot of those at depth I think were because of the turnaround.. I was sort of goofing around and playing with the bottom plate or shadowing less experience divers and don't have a record of what happened on every dive but on the shadow dives I had to fin around on the bottom (very metabolically expense at depth, hence spike in HR). The weight dive doesnt have a bottom spike because I used the rope and paused to check rigging before bringing the weight up. Spikes on ascent with the weight were related to workload I would assume, work response overcame dive response at some points. That particular drill becomes significantly more difficult the deeper I do it, and the effort involved compounds quickly with repetition. The half lung dive was mixed FIM and finning. My safety commented that my lips on breaking the surface were blue for an instant. 25M on an exhale in our water is pretty deep and I was wearing my regular weight so the whole way up I am very heavy.

Seb Murat published some HR graphs a long time ago of full vs half lung drops he was doing. He had little to no bradycardia on a full lung and giant bradycardia on exhale; for me on cold water facial immersion full lung vs half lung makes not much difference (hence why I never did much FRC diving outside of as a training exercise).

The giant spikes on the no mask dive are very interesting to me. I am going to repeat that but manually check my pulse at carotid artery at depth and have my safety flash a lighy every 10 secs to make sure then chest strap was recording accurately. I am told that below 30bpm a lot of machines get confused and start to see the components of a single beat as multiple heart beats.

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OP
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#32
I'm going to bet on machine error. It seems highly unlikely that your heartrate would spike 100bpm and you wouldn't notice. It could also be some kind of pressure induced arythmia, but I think your right about it double counting some of the beats. It could also be fluctuations in the strap contact pressure. Even if the strap seems to be staying put, varying levels of impedance could confuse the sensor, especially at low HR.
 
Mar 20, 2011
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#33
I'm going to bet on machine error. It seems highly unlikely that your heartrate would spike 100bpm and you wouldn't notice. It could also be some kind of pressure induced arythmia, but I think your right about it double counting some of the beats. It could also be fluctuations in the strap contact pressure. Even if the strap seems to be staying put, varying levels of impedance could confuse the sensor, especially at low HR.
Yeah, it was a little strange. Towards the second half of the hold when I started to count my heart beats and it shows the spike was when I felt most relaxed. I do know from past experiments that feeling relaxed has very little bearing on my actual heart rate or O2 readings during a breathhold, and my passage of time was extraordinarily off during the dive; I had told my safety I was doing a 60 sec hang at 10M, and when I surfaced I thought that I had aborted very early, hanging for barely 30 secs very short of the target depth. He had eyes on me during the dive and said I was very relaxed looking, but I am of course trained to be physically relaxed underwater even when mentally I am not.

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Nathan Vinski

Well-Known Member
Apr 19, 2015
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Canada
#34
@growingupninja I'll take a look around Dahab and see if I can find someone with and willing to lend me a good HR monitor and maybe repeat the 55m tests with different breathups, weighting, and freefall depths and see what one looks worse/ better.

I might need to ask for advice on making my own if I can't find one already.

Also. This got me thinking and could sidetrack this thread.. so I'll make a new one about another potential test around CO2 levels.
 
Mar 20, 2011
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#35
@growingupninja I'll take a look around Dahab and see if I can find someone with and willing to lend me a good HR monitor and maybe repeat the 55m tests with different breathups, weighting, and freefall depths and see what one looks worse/ better.

I might need to ask for advice on making my own if I can't find one already.

Also. This got me thinking and could sidetrack this thread.. so I'll make a new one about another potential test around CO2 levels.
I would be curious what you find although I would not expect my dive style to work for everyone.

I am always seeing blog posts and talking to divers who prove on paper that one should strive to put their neutral point as deep as possible but in my experience that has not been beneficial, mainly because for me DR kicks in good and strong with freefall point and once established leg workload doesnt affect it much. I do need to test it further though.

As far as making your own there is a Garmin watch, I think the Fenex, which measures HR and has an open source platform. You might want to look into that. I have been doing underwater and dive electronics for a while, not to discourage, but it is a rough learning curve.

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cdavis

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Jan 21, 2003
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Sarasota, Fla
#36
I'd suspect machine error on some of those spikes, too. Once my DR has set in strong, I don't see much increase in heart rate, even kicking up a long way (for me) untill I hit the surface. Interesting idea that work response may overcome DR , even after DR is strong.
 
Jun 30, 2018
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#37
I'm sure that everybody noticed it, but i didn't see anyone commented on it.
most dives bpm from growingupninja data was above 50bpm, besides the ones without a mask.
Does that mean that diving masks have negative effect on diving response?
and if so, arn't freedivers better diving with something else besides the masks?
i remember something about the region of face close to the nose to be the most sensitive point for body to feel and react to immersions
did someone else or a study tried to compare the drop of HR between mask and no mask?
and if so, what would be a better alternative to diving masks? googles arn't safe for depths, or can we use them by filling them with fresh water?
 
Mar 20, 2011
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#38
I'm sure that everybody noticed it, but i didn't see anyone commented on it.
most dives bpm from growingupninja data was above 50bpm, besides the ones without a mask.
Does that mean that diving masks have negative effect on diving response?
and if so, arn't freedivers better diving with something else besides the masks?
i remember something about the region of face close to the nose to be the most sensitive point for body to feel and react to immersions
did someone else or a study tried to compare the drop of HR between mask and no mask?
and if so, what would be a better alternative to diving masks? googles arn't safe for depths, or can we use them by filling them with fresh water?
You are a bit late to the party, friend, that is one advantage to fluid goggles. In cold water facial immersion tests I have done in the past on myself the mask cuts bradycardia by about 50%. Real depth (ie below RV) however may start to overcome the mask's interference in cold water receptors around the eyes and above the lips.

Sorry, I havent had time to do more tests, waiting on a sleeve to properly mount the HR computer.

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Jun 30, 2018
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ghardaia, Algeria
#39
Sorry, i only joined this forum the past few days.
I guess this explains why fluit goggles are being used, but if you said depths overcame the mask, then i guess using them for VWT or no-limits woudn't help much, but i guess they are used to eliminate the mask volume egalisation
so, i guess mb fluit goggles are the future of moderate depths?
 

Nathan Vinski

Well-Known Member
Apr 19, 2015
176
107
58
23
Canada
#40
Sorry, i only joined this forum the past few days.
I guess this explains why fluit goggles are being used, but if you said depths overcame the mask, then i guess using them for VWT or no-limits woudn't help much, but i guess they are used to eliminate the mask volume egalisation
so, i guess mb fluit goggles are the future of moderate depths?
The main disadvantage of the mask is equalization. Therefore, fluids, or just not wearing goggles benefits VWT/NLT the most since they are the 2 most dependant on equalization.

In depth diving (to any depth) the dive response advantages of no mask vs w/mask are actually quite small. Probably the main benefit of diving with a nose clip is that you don't need your arm for equalizing. This allows for a more streamlined body position and general relaxation of the neck and shoulders which can give better results.

Of course in the pool disciplines where there is an absence of pressure, the main DR trigger is facial immersion affecting mainly heart rate, so loosing the mask can make a significant difference.

All that being said, slower HR isn't a perfect measure of dive response or lower oxygen consumption. For example on a CWT dive I would rather have 1) Weak bradycardia and strong blood shift VS. 2) Strong bradycardia and weak bloodshift. When swimming muscle O2 consumption is probably more important to deal with than metabolic O2 consumption if you had to choose between the two. On a static I would prefer the opposite.
 
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