rate response problems-rate curve?

I have posted several times about problems with rate response and swimming, first with a Medtronic, now a Boston Scientific.  Neither works well.  Lately I have had some more profound problems.  After a week or so of pretty disasterous sessions in the pool, I tried an experiment with a chest strap HR monitor.  I do not noramlly like to swim with any devices on and my not so smart watch is very inaccurate when wet.  I did some excercises on the deck and got my rate up to 110.  I then dropped in the pool and swam four lengths of freestyle.  The first two felt fine, the third deteriorated noticeably and the fourth was a struggle.  HR at the end showed 70.  Manual check confirmed it was pretty close. So I dropped a lot when moving.  Out of water activity may be slightly comproised but nothing like in the pool.


I conacted the EPs office to ask about what might be wrong.  In 24 hours+- I heard from three different people.  I asked on if it was possible for one of the rate response sensors (the motion) to go south while the ventialtion one was still working.  She thought know.  Another mentioned that my remote analysis in August showed a "slow rate curve" and that that could be an issue.  They asked me to send one on 10/20.  That also showed "slow rate curve" but said that the device was operating normally.  I checked past results and all others in the past 15 months or so show "normal rate curve".  I have sent a follow up message but being the weekend I do not expect to hear anything for a while.


Is anyone familiar with these rate curve terms and/or have any insight as to what might be going on.  I have emphasized to the doc's office that things are different that they were two weeks ago.  Either something is up with the device or with me.  Any help will be valued greatly.

Jeff Wren-age 73

Old Town, ME



Rate response

by AgentX86 - 2022-10-23 13:31:33

It sounds like you're close but have it backwards. The motion (accelerometer) seems to have working but the minute ventilation response may be turned office or at least need some serious tuning. This RR mode apparently doesn't work well for all but it's the place where I'd start beating my EP about the head and shoulders.

We've discussed this before

by crustyg - 2022-10-24 03:35:47

As a trained swimmer you'll know that swiming is all about breath management, so MV is never going to be easy as a feed into RR, so your HR will tend to stay low.

Ditto chest movement - competitive pool swimmers are taught to keep their chest as flat as possible in freestyle and do all of the breathing movements from the neck, so there's very little movement to drive the accelerometer.

I've now paired my new Garmin Swim 2 (does pulseox HR measurements) with the Garmin HR Swim strap which does a good job of recording HR - at least in fresh water.  And it confirms my feeling that I don't get much RR support whilst swimming (I can normally feel when my PM starts to drive my HR up).  Having my accelerometer sensitivity increased soon, but more in hope than expectation that it will give me a lot of HR support.

I'm told that open-water swimmers move their chest much more during breathing - a) to get more freeboard due to the splashing, and b) to be able to sight the marker buoys and that this might help to provide more chest motion to drive the accelerometer.

thanks for reading

by JWren - 2022-10-24 06:39:44

Thanks to AgentX86 and Crustyg for reading and commenting on my recent post.  With respect to why I suspect that the MV is working vs the accelerometer: When I had a Medtronic with only the accelerometer, it did not work well in the pool but I could get some reaction by tapping on it that would last me a few minutes.  I got so I could do 100-200 yard repeats and make some progress.  Both my EP and I thought the BS with the MV sensor would work better.  That turned out to be flawed reasoning since one only breathes as fast as you stroke when you swim.  The EP concluded that only the accelerometer was helping me in the pool.  The MV seemed to be a big help on things like hiking in which my breathing rate goes up rapidly when going up hill. Right now, I can run ok, and the hiking seems pretty good.  The pool feels like I have no help at all and the HR goes down quite rapidly as I swim.

With repsect to Crustyg's comment about chest movement in swimming.  I am a swimminer and also a swimming coach.  You should not try to keep your chest flat when swimming freestyle or backstroke.  Swimmers should rotate their whole body 35-45 degree in both directions.  Rotation should actually initiate from the hips as you can't rotate the middle of you without rotating the ends of you.  I had one tech early on suggest I switch to breaststroke since there would be more up and down movement of the torso.  That's not happening-I don't have the feet for that!

Thanks again for reading/commenting.  I home to hear from the EPs office today about the "rate curve" question.



What's wrong with blended sensor feed into RR

by crustyg - 2022-10-24 10:40:42

The BostonSci PMs support blended feed from the two sensors into RR.  It's not particularly well thought out as it averages the sensor feeds until MV is > accelerometer (I would have chosen greater of the two), but it works.

For anyone with SSS+CI, the alpha-and-omega is 'find some way to get Rate Response to increase HR when needed.'  How the device does that is down to the vendor and actually making something work that's predictable and reliable (no easy feat).  So, IMHO, taking the larger of two sensor feeds is the obvious choice when it comes to 'selecting' sensor input to the RR-algorithm.

It turns out that it's easier to avoid over-pacing the athletic heart than it is to provide the right level of rate support to cover ordinary daily living (stairs, bending down to tie shoelaces and then standing again) AND any form of 'athletic' activity - whether it's dancing, climbing flights of steps for sightseeing, running, road-cycling, swimming etc.  Running is easy for a PM - the accelerometer can do it all in 100m.  For swimming then you need more accelerometer sensitivity, short reaction time and low activity threshold.

Ideally we'd have a patient-activated switch to change modes - easily done with a magnet - but it won't happen in my lifetime. The technology is simple but the primary customers - the EP-docs - don't want it, and for the vendors that's the end of it.

How about short axis strokes?

by dogtired - 2022-10-25 13:38:30

What happens when you swim breast or fly?  Is the up and down motion enough to elicit a response from the PM?  Or what happens if you swim with poor form?  Say lift your head to breath and maybe swim a few strokes heads up free?

reply to dog-tired

by JWren - 2022-10-26 07:02:55

I have tried a bunch of different things, nothing has worked.  I am going to the device clinic today as they have summoned me.  I'm hoping they can do something.  I'm going to try swimming before I go in.  They can access my HR during that time so I can prove it's not my imagination.  Thanks for the feedback.

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