Re: Respiration and Electrocardiograms [HAPP-L]

[Ken Saladin <ksaladin@xxxxxxxxxx>]

Thank you very much, Katja. A very timely and helpful response,
since I am writing up my instructions and lab report forms for the
students "even as we speak." I've located the discussion in
Berne & Levy and I'm "good to go" now. This will
substantially enrich the lab experience for the class this week. Now I
can conceive of some meaningful questions to ask about the numbers they
record.

I was wondering if the voltage change was an electromyography artifact,
but it seems that would be minimal to nonexistent with limb
leads.

Ken


> Hi Ken!
>
> The effect that is observed in these Biopac experiments is called
> respiratory sinus arrhythmia.  It is described on p. 384 of Berne
> and
> Levy's 4th edition Physiology text.  I have found it to be 
> very
> reproducible in this Biopac experiment if the students take care to
> keep
> track of and record inspiration and expiration carefully and
> exaggerate
> their breathing.
> The heart rate increases during inspiration and decreases during
> expiration.  This is due to the change in intrathoracic
> pressure.  During
> inspiration intrathoracic pressure decreases and this aids venous
> return.
> The increased venous return stretches the right atrium, setting off
> the
> Bainbridge reflex (which is an increased heart rate upon stretching of
> the
> atria).
> In addition to this, apparently stretch receptors in the lungs may
> also
> somehow result in a relflex increase in heart rate and there may be
> central
> factors involved as well.
>
> The change in voltage observed in the Biopac figure could simply be due
> to
> movement of the electrodes during the repiration so that their
> positions
> relative to the ECG vector have changed.  I doubt that that is
> reproducible, but the change in heart rate is almost always
> present.
>
> I hope this helps.  (Marieb also mentions the Bainbridge reflex on
> p. 707
> 5th edition.)
>
> Katja Hoehn
> Mount Royal College
> Calgary, AB, Canada
> (Site of HAPS 2004)
>
>
>
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