Shortness of Breath on starting to exercise

Just thought I would pass on some information to all those people that have shortness of breath starting their exercise.

I mentioned to my cardiologist (one of three) that I was wondering whether my hypertrophic cardiomyopathy ( thickening of the heart muscle) was responsible for my shortness of breath on initiating exercise ( the heart muscle is known to be 'stiff' [lacking compliance] with this condition). The result was a referral to have my PM settings checked. Yesterday, and 3 months later, I have had a chat with the PM tech. 

I am on the fastest onset for rate response (RR). I was told the RR effect is a sinusoidal curve and that maybe increasing the basal rate would help. Although offered 70 bpm. I opted for 65 bpm. It remains to be seen whether this will stop the breathlessness on climbing stairs and starting to cycle with determination! 

According to my PM tech. both of these activities ( stairs, cycling) are a problem for the older PM technologies ( mine is 12 years old).  The newer PMs seem to be a bit better. If anyone has any suggestions, other than change to a newer model ( and may I say the wife and I are 'adjusted' to each other), then I would be pleased to hear.

Best wishes for 2021.



SOB (Shortness of Breath) on starting exercise

by Gemita - 2021-01-05 12:53:15

Hello Selwyn, lovely to hear from you and to know that you are well and wanting to do more.  

Thank you for sharing this information.  I don’t seem to have any sudden breathlessness on starting my exercises, but I certainly develop it as my heart rate climbs.  I feel this is due to my arrhythmias.  It happened again last night and I was fighting for air and noticed an irregular pulse.  

I hope the adjustments they made for you will help alleviate some of your SOB.  I wonder whether you would mind answering a few questions:

Did your cardiologist confirm that the likely cause for your SOB on starting exercise was hypertrophic cardiomyopathy?

In simple language could you please define RR effect is a sinusoidal curve.

When you say you are on the fatest onset for RR, may I ask what your rate is set at ?

I am assuming the basal rate is the resting heart rate or minimum heart rate? 

Last question, did they explain how an increase in the basal rate could help with the SOB ?

As to how to improve your situation Selwyn, have your doctors checked for all other causes for your SOB on exertion and treated them where possible?

Yes forget all about a newer model.  Make the most of what you have.   Hubby and I often talk about trading each other in but then we haven’t been able to find anything better.  I send my best wishes for 2021 to you too.  

Speed of increase of HR with RR

by crustyg - 2021-01-05 12:57:03

Hi Selwyn: I'm interested in what you say.  My PM is less than 2years old and apart from a couple of minor tweaks (leaving aside min- and max-HR) it's on pretty much factory settings.  For me too, RR is critically important.

The accelerometer is set to 30s reaction time (and for me, when running I can normally get from 70-80BPM to maxHR in less than 300m) so that's not an issue.  For cycling it takes a full 2min to get from a starting HR (about the same as above) to maxHR, since there's not much accelerometer input from road cycling, and the MV contribution to RR is only supposed to deliver 2BPM per second rate of change, up or down.  So I'm moderately sedate when I set off because it's easy for my legs to oustrip their blood supply at this stage.  Then, if I'm sensible, I can keep my HR around 115-120 which makes it very quick to get to maxHR if I reach a hill.

Overall my HR histogram is massively in the <70BPM three sections, which is perfect.  Long-term excessive HR has already caused me a small problem, so I'm keen to avoid being overpaced.

*IF* I understand correctly what the BostonSci folk have told me, the rate of change of the RR is fixed in the firmware: what we modify with the accelerometer/MV 'sensitivity' feeds into RR is the delta-HR that will be delivered in total - not the speed that the PM will get there.  It's a PITA when coming a long downhill (HR drops like a stone) and then we hit another hill climb - the RR isn't fast enough to stop my legs turning to jelly.  But it's not easy to argue against a fixed delta of 2BPM per second.  Perhaps for some 2.5BPM per second would be better.  But you have to have really good atrial & ventricular filling to support that rate of change of HR.  Yes, I do know you have a different vendor's device...

In other words, I have my doubts about whether a later PM (or just later firmware in an existing PM) will deliver a higher *rate* of RR delta.  But I'm happy to be told otherwise.

Sinusoidal RR curve

by crustyg - 2021-01-05 13:02:28

Put simply, a small feed into the rate response algorithm produces only a little increase in HR at first.  Add a bit more and the ratio between sensor feed in and increased HR out increases quite sharply.  As you near the maximum sensor inputs, the additional effect on HR is much smaller again, so quite big changes in sensor input near the maximum don't have much effect on HR - and the same at the lower end.  You don't want climbing the stairs in a house to take you to maxHR, and you don't want a small change in chest movement when running hard to produce a 50% drop in HR - you'd fall over in a faint.


Sinusoidal RR curve

by Gemita - 2021-01-05 13:29:50

Thank you so much crustyg for your explanation.  That is really so helpful and fairly easy to understand.  I expected a far more complicated definition.  Maybe I am making some progress at last.

My doctor died...

by runpacer - 2021-01-05 15:15:21


I have copied and pasted your message about the death of your doctor back to you in a private message, so you can copy and re-post under your own new post.  Please see crustyg and my comments below.  

Thank you,


Please post in a new thread

by crustyg - 2021-01-05 15:31:04

Hi Phillip: I'd suggest you repost your crie de coeur in a new thread otherwise we'll end up hijacking Selwyn's original thread.

In short, I think you need a more comprehensive evaluation than just focussing on PM and heart.  There are *lots* of things that could produce a massive drop in athletic ability and I'm not going to try and start listing them here.  You need a proper work-up.


by Gemita - 2021-01-05 15:37:37

Hello Phillip, 

I am so sorry to hear the sad news of the death of Dr. Fujimura.  The loss of continuity care must be so worrying for you and for so many of his other grieving patients.  

I am wondering whether your post, which is obviously important to you, would be better copied and pasted into a new message from you to the PM Club, so that others will see it and answer you directly rather than placing it here under Selwyn's message?  I hope you will agree it might be best

Sinusoidal RR curve

by AgentX86 - 2021-01-05 17:36:08

I assume "Sinusoidal RR curve" means that the PM's RR function acts similar to the sinus (SI) node.

As far as Selwyn's exercise question goes, these are the same exercises that bother me.  Both stairs and cycling are similar in that the PM doesn't get the same input as it would from running or walking.  I've had them try everything but my stair climbing stilll sucks.  I can make one flight with no problem but by the second, I'm puffing, and the third, well...  Bringing our arifical Christmas tree out of the basement was a problem too.  I had it on a hand truck and pulled it ouside around the house on a fairly gentle grade.  I was really out of gas by the top of the little hill.  My PM had no idea that I was towing a hundred or so pounds, so didn't kick in the turbos.


No, nothing to do with SA-node

by crustyg - 2021-01-06 10:48:26

Agent: Selwyn was explaining that you, and thee and me, don't get much chronotropic support in the early phases of moderate movement.  We either have to move around for longer or more vigorously.  I have exactly the same problem on walks with my wife - despite her worn-out knees and fixed great toe-joints (no push-up from the feet), she can climb stairs to cathedrals/restaurants/observation points more easily that I can because I get almost no increase in HR from my PM.  But I can exercise at far higher levels than she can, once I get going.

I imagine that the precise shape of the sensor=>RR algorithm output can be, and has been, tweaked between PM models over time, as patients like us complain about lack of PM support at modest levels of movement - and still avoid overpacing, which is a big worry for the PM manufacturers now, especially as there are so many patients with dual-chamber PMs driving an RV-apical lead (damn you DANPACE....).

Shortness of Breath on starting exercise.

by Selwyn - 2021-01-06 16:50:46

Thanks guys for your thoughts.

The sinusoidal curve is an S shape curve -  crustyg explains the rationale for this so well. 

I don't know the slope of the curve for the fast setting of the rate response. I presume it is factory set. 

The idea of increasing the basal rate (resting rate)  was just to give a little more oxygen as I start exercise ( such as belting up stairs). I think this has helped a bit. 

My cardiomyopathy doctor took the easiest course of action and thought my PM was the problem ( It may well be).

 Compliance is difficult to measure. ( see If this measurment involved personal discomfort, I may well just have to put up with the problem. Also, there is no point in knowing if there is no effective treatment. There is no way I will take a beta-blocker again due to side effects.  I think beta blockers are likely to be the treatment if compliance is the problem. 

Can any one tell me whether the Boston Scientific PM, using transthoracic impedance, is better for the initiation of exercise?

Sinusoidal RR curve

by AgentX86 - 2021-01-06 19:53:29

Yes, I was reading the word wrong, as sinus-oidal rather than sine-u-soidal. As an EE, I should be able recognize that word.  ;-)  ...and I even looked at it several times to convince myself of it (and was wrong anyway).

I find it strage that a simple watch can count stairs but a pacemaker can't.  I've had my RR tweaked up about as far as it'll go and still get no joy on stairs (hills are OK but I'm moving forward).  I'm not worried about ventrical overpacing since it's all I've got.



by Gemita - 2021-01-07 07:52:08

Thank you for your response to my questions.  Yes crustyg provided a very helpful, fairly simple explanation for the sinusoidal curve and I have copied and pasted this into my pacemaker folder of useful information(!)

It is reassuring in a way that your cardiologist even attempted to take the easiest course of action and considered the pacemaker might be the problem for your SOB on starting exercise.  I do not believe he would have done this if he felt it was futile to even try to look for a potential pacemaker cure for your symptoms.  And even if the pacemaker adjustments do not help, it will be a step nearer to getting the help you may need to overcome this problem.  If that means a new pacemaker, then so be it.  Quality of life is important at our age and you sound as though you still want to achieve much more.  

I will have a closer look at your link on “Compliance”.  Thank you for this.  I appreciate hypertrophic cardiomyopathy may not be treatable unless compliance is the problem and I further understand that you do not wish to take beta blockers.  I think one of the side effects might be insomnia and both hubby and I are getting lots of this at the moment on Bisoprolol, otherwise a very good med for us . . . I think.

I hope someone can help you with Boston Scientific/using transthoracic impedance.  Good luck Selwyn

BostonSci for faster/better RR?

by crustyg - 2021-01-07 10:06:32

Hi Selwyn:

The short answer is NO, in my experience.  The Minute Ventilation (MV) feed into RR for my Accolade definitely *lags* behind the RR feed from the accelerometer - and the PM reference manual tacitly admits this (there's a discussion section about how the RR algorithm handles dual-sensor input).  MV takes about 2min to get me to maxHR, but the accelerometer can do it in 40-50s in my experience (hence my comment about being able to achieve maxHR when running in a few hundred yards, cycling I expect to take 0.5-1mile (alright, 1600m) before I can be sure of reaching maxHR - and then I need to be pushing hard to get there.

In fact, the BostonSci reps have confirmed that MV is (partly) designed to prevent a bit of deliberate over-breathing from pacing too hard, so it's much easier to drive up HR by paddling the PM than sitting down deliberately hyperventilating.

This lack of RR support drives me nuts when swimming.  I just can't get my HR up high enough to allow me to swim f/c properly for any length of time.  What is needed, is patient control - two profiles, one for normal living and one (for me, swimming) with different sensitivities for the various sensors, different recovery times etc. It would be really easy to allow a patient to control a switch between two different profiles with a magnet, and easy to design in a way to allow anyone - with no tech - to distinguish between the two modes.  But no-one has done this and no-one will because the primary customers (the EP-docs, not us, the patients, dear readers) who choose the PMs inside us, and they don't want us to have that control.  Too much risk and time to adjust the settings.  And for the manufacturers, there's no money in it.  Only about 10-12% of current PM users are seriously athletic, and that's too small a segment for the huge costs of R&D and certification.

Patient-centred EP-cardiology: I don't see it happening in my lifetime.

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So, my advice is to go about your daily routine and forget that you have a pacemaker implanted in your body.