Respiration and Electrocardiograms [HAPP-L]

[Ken Saladin <ksaladin@xxxxxxxxxx>]

Dear HAPSters,

Can anyone help me out here?

I am about to run the Biopac electrocardiography exercises for the first
time, and I am wondering about the physiological relationship between
breathing and the ECG. In the "ECG I" chapter, there is an
experiment in which the students are to observe and measure changes in
the ECG during deep inspiration and expiration. However, in the data
analysis section and lab report questions, there are no further
references to this, much less any physiological explanation of why
the ECG should change during deep breathing -- the whole phenomenon
just seems to disappear from further consideration in the lab manual and
in the students' writeup. Nor do I find any discussion of the effects of
respiration on the ECG in Guyton & Hall, Berne & Levy,
Harrison's, or Cheitlin's Cardiology, nor was the
vertebrate comparative physiologist in my college department able to
help. (There's only one to consult; we're not a large
department.)

I offered him the conjecture that the thoracic pressure changes during
respiration may affect the arterial baroreceptors and thus activate
transient baroreflexes, to be reflected in changes in heart rate. He at
least thought that was a reasonable hypothesis. But the screen capture in
the Biopac lab manual shows (but does not discuss) what appear to be
changes in voltage rather than heart rate. My feeble intellect can't
imagine why the respiratory rhythm would cause voltage changes in the
ECG, or what that would mean physiologically.

I am running this in my two lab sections at 1:00 (EST) Mon & Wed this
coming week. I'd be very appreciative of whatever explanations anyone can
offer before then, but even afterward, it would be useful to have more
insight into this for the benefit of my future classes. I hate just
exhorting students to measure something and compare numbers with no
insight into what the numbers and comparisons mean.

Many thanks for any help you can offer.

Ken