AJP - Heart and Circulatory Physiology, Vol 257, Issue 4 1292-H1305, Copyright © 1989 by American Physiological Society
Nonlinear mechanics of the heart's swinging during pericardial effusion
D. R. Rigney and A. L. Goldberger
Department of Medicine, Beth Israel Hospital, Boston, Massachusetts.
When excessive fluid accumulates in the pericardial space, the heart,
suspended by the great vessels, is then free to swing as a pendulum. The
swinging may occur at either the same frequency as the heart rate (1:1
oscillation) or at half the heart rate (2:1 oscillation), the latter
frequency often arising during cardiac tamponade. We show that these two
frequencies of oscillation may be explained by the nonlinearity of Newton's
equation of motion as applied to the heart. Terms in the equation
correspond to gravitational and buoyancy forces, forces due to ejection of
blood into the great vessels, and damping forces. A transition between the
1:1 and 2:1 swinging is found to occur when particular parameters of the
model are changed, notably when there is an increase of heart rate. This
finding is compatible with previous clinical reports.
