How long Accelerometer active while cycling?

Greetings Fellow Pacers,

I am intetested in learning more about: length of time sustained, and heart rate achieved when activating the accelerometer while cycling.  The accelerometer seems to really work when manually tapped in advance of a cycling effort such a climbing a steep hill.  Does the accelerometer cause the HR to reach the upper limit (140bpm in my case) but how long will it last until reverting back to the base rate (60bpm) while climbing longer and steeper hills?  Also, how does the accelerometer function for sustained efforts such as during "gravel griding" ?  Does the pacemaker sense the oxygen demand during the whole effort episode or is there a particular amount of time such as 3 minutes from the start of manual activation?  Thanks for any information or suggestions.






by IAN MC - 2019-07-17 14:48:05

The rate at which your HR returns to normal after exercise is one of the RR setting adjustments which can be made.

Accelerometers cannot "sense: anything  other than responding to motion / vibration in the upper body.

Cycling produces inadequate upper body motion to fully activate your accelerometer , manual tapping does

The more sustained motion which is detected then the more sustained a rise in HR will occur. It is not time-limited.

Also bear in mind that there are 2 maximum settings , the max tracking rate and the RR max sensor rate ( which is usually the lower of the two )




Rate responsive PMs and cycling

by crustyg - 2019-07-18 04:55:32

Hi: As far as I know, none of the rate-responsive PMs stop using the accelerometer to drive increased HR after a certain time - if you keep producing movement at a level where the accel output is big enough this input feeds into the software routine that calculates what your HR should be.  PMs generally have a maximum sensor rate (MSR) - how high can HR be driven by the accel + software routine - and for active cyclist/runners like yourself this is likely to be your effective HR ceiling.

I have a BostonSci unit that has an accel *and* measures Minute Ventilation (respiration rate * respiration depth) as upper body movement is generally not enough for road cycling to drive you to max HR - there's not enough accel input.  For offroad work (MTB etc.) this can often produce enough accel input to drive you to MSR == max HR.  And as long as you're providing input (bumps, potholes, jumps) it keeps your HR up.

Recovery time is controlled by a separate setting on your box - standard is usually 2min but it's adjustable.

Most EP docs aren't athletes and the thought of a max HR of 160 for a 60+ year old makes them very nervous.  More than that will probably give *them* a heart attack - but it all depends on how good is your heart's blood supply, how you feel, and how much confidence they have in your common sense - if it hurts I slow down!  And yes, I did check your dob!

AFAIK no-one is marketing a PM that senses oxygen demand!  It's all much simpler than that.  SCUBA diving friends of mine have seen so many technical divers die in mysterious circumstances on very deep Helium/Oxygen re-breather circuits - where the oxygen sensor is the *only* thing keeping the diver alive - that they won't use them.  Portable coffins.  So I think we're some way from oxygen sensor-driven PMs (even though the environment where the O2 sensor would work is very different).

But I may be wrong....

Many Thanks for Input

by FaustoC49 - 2019-07-18 12:50:11

Thanks very much for the helpful responses regarding the nuances of the accelerometer in my Medtronic PM.   Grateful for the forum.  I had the PM implanted in 2013 and it is appreciated as a solution for my bradycardia and diminishing HR;  but the PM and 60bpm really put a crimp in my cycling quality of life and reduced me to solo riding since I was perpetually gassed.  It was only recently that I learned from the nice Pacer tech of the existence of an accelerometer and how it can be manually activated by tapping on it.  The sad irony is that road cycling typically promotes a "calm, quiet" upper body to conserve energy and ride efficiently.  I will have to experiment to find out the effects of sustained effort once the AC is activated by tapping.  My chief concern now is what fellow riders will think when they observe frantic mea culpas just prior to a pull at the front or a big hill.



And next time get a better PM!

by crustyg - 2019-07-19 09:44:51

Hi Fausto: Good luck with the 'paddling' - tapping on your PM to fool the accelerometer into driving your heart rate up.  I can do it with mine, but it takes some time before the box decides 'oh, he's actually moving' and starts to push up the HR.  It really does work, even if it looks totally bizarre to the uninitiated!

Guidant (a company based in Belgium - national sport==cycling) brought a PM to market in about 2000 that also measures Minute Ventilation specifically for cyclists.  I've recently learned that it also checks that the respiration rate is appropriate for the HR and if not, discards the data (so sitting in a chair and pretending to blow up party balloons doesn't increase HR - and yes, I've tried that too).

When you have your box replaced, if you're still keen on cycling, charm your EP into giving you a replacement box that has this capability - I'm sure that any patents covering it will have expired so it won't necessarily be limited to Guidant (now BostonSci).

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