Journal of Applied Physiology, Vol 45, Issue 1 24-32, Copyright © 1978 by American Physiological Society
Effects of hydrostatic pressure on conduction and excitability in rabbit atria
T. J. Doubt and P. M. Hogan
The effects of hydrostatic pressure on cardiac conduction and excitability
were studied in 39 rabbit right atrial preparations. Increases in pressure
significantly increased atrial conduction time, i.e., 41% at 150 ATA.
Excitability, determined from strength-duration (S-D) curves, was depressed
by pressure. The slope constant of the S-D curve increased 64% at 150 ATA.
Rheobase and the X-asymptote were not affected significantly. The
depression of excitability partially accounted for the slowed conduction.
Frequency stress and pressure had an additive effect to produce even
greater decreases in excitability and increases in conduction time. Atrial
refractoriness to premature stimuli also increased as a function of
pressure. Nitrous oxide (2.5 ATA) partially reversed the effects of 150 ATA
of pressure on conduction time and excitability. The results suggest that
pressure acts by altering basic functional components of the myocardial
cell membrane. Some of these changes, particularly when combined with
frequency stress, i.e., rapid heart rate, may pose a serious threat to
humans exposed to hyperbaric environments.
