rate response settings with Boston Scientific

I am 72 and am very active using a variety of aerobic activities.  I am a long time swimmer and swimming coach.

I had a Medtronic device implanted 12/18.  The rate response worked off an accelerometer only.  It did not work well for swimming, biking, paddling etc.  After numerous tweaks, it worked ok for running, hiking and some other things and if I tapped on it, it sort of worked in the pool.

In April, I broke the atrial lead and felt awful.  My new EP who is very tuned in to active older people, said this would be a good time to change to a Boston Scientific with the micro-ventilation and motion sensors.  

I am curious to know if anyone can tell me how the mv sensor works.  Is it respiration rate? some blood chemistry thing? CO2 level?

Since my surgery, I have had very positive results with biking and hiking.  My bike mph is typically in the 14s where for the past five years or so it's been in the 13s.  I feel very positive about hiking.  In the pool, however, I do not feel great.  I am not working that hard yet but there are many measurements that I am sensitive to that indicate I am well off form.  My respiration rate is, of course, a product of my stroke rate. Curiously, if I kick on my back when I can breath at will, my times are as fast or faster than before I broke the lead.  If the MV works strictly off respiration rate, it seems that might explain how I'm feeling.  

I have an appointment Thursday for possible tweaking so maybe there is something they can do.  If anyone has any information that might help me, I would really appreciate the input.

 


2 Comments

Boston Sci MV

by AgentX86 - 2021-06-22 23:58:58

Minute ventilation is the amount of air breathed per minute.  The sensor tries to estimate oxygen demand by guessing how much air you're sucking in.  This, with motion can give a better, or more balanced, estimation of demand.  No, it doesn't measure blood chemistry, as the SI node does, RR will always be a guess.  In theory, it's a better guess than an accelerometer alone but from what I've heard, the results are mixed.  It may just depend on the skill/knowledge of the PM tech.

Minute Ventilation on BostonSci

by crustyg - 2021-06-23 04:03:44

The MV feature measures chest impedance by using a tiny AC signal between the PM can (the outer metal case) and either of the leads available to it.  Trouble with this is that chest impedance also varies with each heartbeat, so there's some very clever dynamic filtering to tease apart variations in chest impedance due to HR and those due to breathing.

Once the chest impedance signal has been cleaned up, it measures the *depth* of each breath (a function of the amount by which impedance changes) and the *rate* of changes per minute, multiplies the two together (depth * rate) => Minute Ventilation.

This value is then fed into the Rate Response software algorithm to drive up HR: this is *usually* blended with data from the accelerometer, but doesn't have to be.

As Agent says, results are mixed: which is code for 'this feature doesn't work properly unless it's been tuned for *you*'.  I'm a keen road cyclist with BostonSci Accolade and had my PM's MV tuned for me using a static bike and it works nearly perfectly for road cycling (I have SSS+CI).  The BostonSci rep is the person to guide this tuning, as it requires a lot of prior experience to know the likely effect of each adjustment. Even tuning has some traps for the unwary that many reps aren't aware of.  But very well worth doing.

Swimming isn't so great: there's not a lot of upper body movement (so little response from accelerometer) and swim technique is all about breath management so MV doesn't help a great deal.  Pilates+Yoga is even more difficult: strength work in static poses (with the Instructor calling out when to breath in, breath out) doesn't work for me, so I'm quietly breathing a lot harder+faster to increase my HR.

BostonSci are pretty relaxed about their documentation and it's easy to find and download on the Web.  There's a lot of information about MV in Section 2-25 of the BradyReference Guide PDF.

Happy to help if you wish to share your settings via personal message.

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