Re: Respiration and Electrocardiograms [HAPP-L]

["Phil Stephens" <phil.stephens@xxxxxxxxxxxxx>]

I do the same experiment using a finger pulse unit instead of ECG 
electrodes.  It's quicker to set up for students (and cheaper for us) 
and it allows them to see changes in blood flow, which are dramatic in 
some individuals.

Phil. Stephens

----- Original Message -----
From: Alan Magid <amagid@xxxxxxxxx>
Date: Sunday, January 26, 2003 1:00 pm
Subject: Re: Respiration and Electrocardiograms [HAPP-L]

> > 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.)
>
> Ken and Katja-
>
> The "Bainbridge reflex" (which I believe to be too slow and 
> insensitive to
> be a likely cause) may not be involved at all.
>
> Here's a link to the abstract of the paper which identifies the 
> mechanism of
> 'respiratory sinus arrhythmia' as due to direct effects of atrial 
> distensionon the SA node.
>
> Vagotomy + sympathetic blockade had no effect on rate, ruling out 
> reflexmechanism! Here's the citation:
>
> http://www.pulsus.com/europe/04_01/knud_ed.htm
>
> -Alan
>
>
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