Scubapro Heart Rate Monitor

[montage]

@montage , have you tried replacing the battery?

Yes, had a brand new battery installed.

 

[CandiveOz]

I had three cut outs on my HR trace, two were very brief and recorded a spike and one read HR of 0 for just under one minute.

Thanks for the update Hatul. That is a disappointment but not unexpected from the feedback we are getting in this thread.

Moreover, even above water you should not expect that the combination of belt and G2 works properly, i. e. both the belt and the G2 (hardware or software) could be the culprit.

Yes, other divers can conduct a surface test themselves to confirm your observation. If you change the computer's setting to apnea mode, you can turn the G2 on and off at the surface. I did this with my Galileo Sol. I've attached screen shots from SmartTrak and LogTrak. I wore the polar HRM and Sol, and took my dog for a 15 min walk. The LogTrak image is a bit messy as the computer is measuring slight variations in pressure. As you can see from my readings, there is variation in heart rate, as expected, but no drop outs or spikes. It would be interesting to see the results from the G2 for the same surface test.

Nevertheless my observations might be useful and help to destroy any hope except of they develop a new version of the product:

Agreed. I certainly won't upgrade to a G2 with these outstanding issues. But I would suggest, rather than attempt to produce a new version, just go back to Polar and beg forgiveness. Reconfigure the firmware to capture the signal from a Polar HRM. Apparently the new H10 sends out the same 5 kHz signal as the T31. Lesson learned, if it works, don't mess with it!

 

[CandiveOz]

Yes, had a brand new battery installed.

@montage ,
Thanks for your feedback. You may want to try the apnea surface test just to see if the HRM even works properly at the surface. According to @VOGH it can't even do that! This begs the question; what happened to Scubapro's quality control? Surely they must have tested this piece of kit. Then again, as @VOGH has indicated, maybe its the G2 or a combination of both the computer and the HRM that is causing the problem. Who knows?

 

[Hatul]

I have a Polar M400 sports watch/monitor and found it also did not work consistently with the chest strap, but fortunately Polar came up with with the OH1. The OH1 is an optical HR sensor that works like the Apple Watch. It's on an elastic strap that goes around your arm and this system is much more reliable than the electric sensing chest strap. The OH1 works via Bluetooth which does not work under water, but I'm sure they could easily make one using low frequency radio waves that would work under water like the Galileo chest strap. The OH1 has breathed new life into my M400.

The optical sensor detect pulsation in blood flow under the skin rather than electric signals from the heart, and makes a much more dependable system, less prone to cutouts and interference.

 

[CandiveOz]

@Hatul
I couldn't agree with you more. The H10 and OH-1 (now called OH-1+) is one of the smartest moves Polar has made. For my land base activities, I'm Garmin centric and therefore rely on the Ant+ signal. These are the first Polar units that can broadcast Bluetooth as well as Ant+. In addition, the H10 can broadcast in 5 kHz. Its odd that the OH-1 can't broadcast 5 kHz. Maybe its a hardware/battery issue. Then again maybe they are working on a firmware upgrade. It would be great because the positioning of OH-1 on the upper arm would make it very close to the actual dive computer itself; reducing the risk of signal dropouts. In the meantime I'm contemplating purchasing the H10 since it can be used with my Garmin gear and potentially my Galileo Sol but I'm kind of waiting to see if they will upgrade the OH-1 to 5 kHz because I I like that form factor over the chest strap. I currently use a Scosche which is the same form factor as the OH-1.

 

[VOGH]

Yes, other divers can conduct a surface test themselves

@CandiveOz
Great idea to use apnea/freediving mode to trace the heart rate at the surface with the G2. I learned I have to do a kind of simulated dive (briefly expose the G2 to a higher pressure) as otherwise the log disappeared - or probably I am to clumsy.
I simply walked around with the G2 and the belt and later started to do some experiments. My first test produced the following results (Puls means heart rate, Haut means skin temperature, Temperatur means ambient temperature):

The heart rate signal starts after 10 to 15 seconds after I started the dive with the menu button. No Problem. Then the heart rate varies a little bit, but seems to be OK as long as you do not do much. I compared the heart rate with the reading of a good automatic blood pressure monitor. The low rates were always in agreement, the high rates not, e. g. instead of 140 shown on the G2 the real rate was 65 (over a sufficiently long time to avoid any influence of the measuring interval). So the overall picture shows unreasonably high peaks that did not exist in reality. I could not check all peaks in comparison, of course, but the examples that I checked supported this conclusion.
It seems that the heart rate shown by the G2 strongly depends on what happens with the belt. And this effect seems to be much more pronounced than with the old Galileo Sol and the Polar belt. After minute 5 I prepared a simulated dive having the G2 in a plastic bag. So I had to move my arms and bend them. This seemed to increase my heart rate.. Then I observed the G2 a while and decided to have a cup of coffee. And I just put the coffee pot back when I realized that around minute 11 until 12 the G2 did not show the heart rate any more. In the diagram you see a horizontal line for skin temperature and heart rate. But it came back again, so I was still alive.
Then I decided to see what other movements or manipulations might result in. Most successful was when I embraced myself strongly. The high peaks from minute 18 to the end are essentially due to embracing myself in different ways. I could produce virtually any heart rate value I wanted to have and which was well above my actual heart beat.
I could also produce peaks by pressing the belt, but they were less significant.
Not shown in the above protocol:
Just to simulate the interaction of a diving suit and the belt: I produced major heart rate peaks by knocking on the belt. And they increased a while even after I stopped knocking. And the increase was not correlated with the frequency of knocking (so this knocking was not a simulated heart beat but stimulated something in the belt). - And simply pressing the belt on my body in many cases increases the heart rate. However, I did not find a special problem trying to press the battery containment.
Moreover, if I put my fingers between my body and the center of the belt to simulate that it might be pushed away by some movement, the heart rate increased significantly. Bending the belt also influenced the heart rate, although I was amazed that there was a (reasonable and not constant) signal for a few seconds even after I detached the electrodes.
If I moved the belt a little bit upwards on top of my breast, the effects seemed to be more pronounced. So it is certainly wise to adhere to the prescribed position.
I know that all these manipulations are not what you would do. But I think they simulate effects you might have while diving or free diving. To sum up: This is not a satisfactory result. Or you better move only very slowly and hope that the signal does not disappear.

 

[CandiveOz]

@VOGH
Wow, what a comprehensive review. Thanks for posting. I've used heart rate monitors for a number of years and I don't think I have put them through a battery of tests like you have. On occasion, HRM's do spike, but I have found, they do settle down as you continue your activity. But if my heart rate continues to be erratic, I determine its usually the battery and replacing it with a new one resolves the problem. Unfortunately, this doesn't seem to be the case with the Scubapro heart rate monitor. But to be fair, I decided to conduct another "apnea" surface test using my Galileo Sol and Polar T31 HRM. I've incorporated some of your tests to determine if they produce a similar effect. Note, to ensure good electrical conductivity, with all my HRM's, I soak them and the elastic band in water. I also wet my chest area with water. This preparation is effective in ensuring a good reading. The Galileo apnea surface interval times out in 15 min so this is the time limit for my test. It is broken down as follows:
0 - 5 min; walking
5 - 6 min; walking with bear hugs
6 - 7 min; walking with chest/HRM thumping with fist
7 - 8 min; walking with forward arm windmills
8 - 9 min; walking with backward arm windmills
9 - 10 min; walking with hand claps in front of chest and behind back
10 - 15 min; running

So the idea was to start walking to get the heart rate up and establish a base. Then I started folding my arms around my chest and squeezing about 20 times during a minute. These self bear hugs were followed by thumping the heart rate monitor with my fist for a minute. This was then followed by forward arm windmills. Another way to describe it would be freestyle if you were swimming. The forward windmills were followed by backward windmills (like the back stroke in swimming). At the 9 minute mark, was alternative stretching my arms in front and clapping my hands followed by reaching behind my back and clapping my hands. Finally, I ran for the last 5 minutes. Here are the results.

Walking is as expected. With the bear hugs, there are three jumps. I wouldn't call them spikes because they are within an acceptable range. It could be the case that with my arms wrapped around my chest compressing, my heart rate may actually increase. On the other hand the fist thumping on the HRM did increase the heart rate substantially. In fact 189 is my maximum heart rate. Once I stopped the thumping, the heart rate dropped to normal. Under normal conditions this wouldn't happen so the thumping isn't a fair test of the unit. The unit is trying to monitor an electrical impulse while the PCB (printed circuit board) and battery compartment are being hit by an external force; its bound to misread. As for the extreme arm movements - no real impact. And the running is as expected. So in conclusion, the Polar HRM is functioning within specification.

@VOGH, one thing I didn't quite understand from your post is why did you have to put the G2 in a plastic bag?

 

[VOGH]

one thing I didn't quite understand from your post is why did you have to put the G2 in a plastic bag?

I used the plastic bag (with water, pressure tests without water are not allowed according to the manual) just to simulate a dive by blowing into the bag to produce a 0.8 to 1 m dive. (I was simply too lazy to activate the test chamber.) If I did not simulate a dive the log of the complete activity always disappeared, was not stored. Maybe I should have read the manual to learn why. But I only wanted to have the log files.
Just to add another experience: During a real dive yesterday I had no drop-out of the signal, but several intervals with more than 200 BPM for about two minutes and some additional spikes. As this was the kind of dive I did at least a hundred times before I know that the real BPM should not have been above 100 even in extreme cases. But because of the very poor visibility and therefore fishes showing up suddenly we certainly had some very erratic movements to stay with the fishes. This might suggest that the belt reacts to the movements, not to the heart rate - just as it did during the surface experiments I described above.
To try to learn more I compared the Scubapro belt and the old Polar belt once more. The Scubapro belt consists of three parts whereas the Polar belt is essentially just a single piece. The Polar belt is flat and fits quite well to the body and does not provide too much attack surface to the suit. The middle part of the Scubapro belt with the battery containment is a little bit thicker and connected via a kind of hinges with the flat outer parts. This makes the Scubapro belt a little bit more flexible, but it might just as well follow movements of the body or be attacked by the suit and that might lead to wrong BPM. This effect might be increased by the thickness and weight of the middle part. Since this part is quite heavy (when compared to the neighboring parts or the Polar belt) the flexibility gives way to moving the center part of the belt away from your body in a horizontal position (face looking down) or it gives way to a torque that tends to move the belt away from the body in an upright position of the body (the upper edge of the belt going away from the body and downwards while the lower edge stays at the body in an upright position). Yes, I fully agree with Scubapro that you should carefully put the belt around your body! (But after the dive I prefer not to have a deep red stripe around my body.) However, the belt is not glued to your body and it may move together with the strap or even a little bit independent, in particular with the hinges and the unbalanced weight distribution. In addition, due to my anatomy and although I am male, the center part of the belt does not touch my skin (this is true for both the Polar and the Scubapro belts) and makes movements together with a moving diving suit even more easy. Just as in the case of pretty sharp bends to follow the fishes coming out of nowhere because of the poor visibility. So if the Scubapro belt is more sensitive to movements in a direct way (it should follow the heart beat that might change due to movements of the body, but should not react on movements themselves) then we might have a possible explanation for unreasonably high BPM values.
To support this view I would like to mention that in many cases I observed spikes or even longer extreme signals while entering and in particular leaving the water. (I observed similar spikes with the polar belt, but not so many.) You can see that in the logs in this forum, too. At the end of the dives, at depth 0 m, you usually observe high spikes. And yes, all divers are probably busy to take off parts of the equipment or move up the cliffs or ... with some extraordinary movements that cheat the sensor and/or the software of the computer. Yes, and you might really have a very high load (and consequently BPM) in these cases, but not always.
Just an idea that might help to understand the problems, not a proof!

 

[CandiveOz]

During a real dive yesterday I had no drop-out of the signal, but several intervals with more than 200 BPM for about two minutes and some additional spikes.

Hi @VOGH
On this particular dive, with the 200 BPM for two minutes, did the computer record an increase in workload? I've been testing my Sol with regards to workload and I noticed that the increase in heart rate has to be sustained for a period of time (ie over 10 min) before the computer will start adding more deco time to compensate for the increased workload. I need to conduct more tests to validate this finding but the important thing is that random spikes in heart rate will not impact your workload or planned decompression profile; the increase in heart rate must be sustained to have an impact.

There actually is a simple software coding solution to this problem and that is the computer to ignore any instantaneous jump in heart rate unless that increase is recorded for a period (say 15 or 30 seconds).

 

[VOGH]

I noticed that the increase in heart rate has to be sustained for a period of time

Sorry, CandiveOz, I have to disappoint you. To be honest, I am not interested in the workload.
Moreover, because of the problems with the heart rate I set the Workload for the G2 as follows:

WL: Respiration
HR monitor:On
Use skin temp.: On

Although I know that "Respiration" had some problems depending on your respiration characteristics with the Galileo Luna and Sol I thought "Respiration" might be more trustworthy. Nevertheless I dive with breathing sensitivity -12 (least effect on workload).
The result for the dive two days ago was a constant and very low workload ("Arbeitsleistung" in German):

Nevertheless, if the BPM goes beyond 200 for two minutes or more you would expect an effect on the respiration. But as I already mentioned in my previous contribution these high BPM values are definitely outside any realistic limits for this dive.
However, I used a different workload setting for some time in the past. Unfortunately, I do not remember the setting exactly. Probably I selected "Always highest". Max and Base HR could have been 220 and 100, respectively, as this is still stored on the G2, but these values might just be from another test. In the log I found several dive profiles with high BPM and a significant change in workload. Maybe the following example helps to contribute partly to an answer to your question:

It is obvious that the workload increases some time after a high BPM shows up. For the first two bumps it took some 40 seconds. For the third bump or double-spike it is interesting to see that the workload rises after the heart rate was back to normal. And finally my standard observation: There was a broad bump when back to the surface. - Maybe I should mention that this was a dive with a dry suit (December 2017).
If I have some spare time I shall check my old logs with the Galileo Sol and the Polar belt to check whether there are some interesting observation with regard to your question.