Does the aortic smooth muscle wall undergo rhythmic contractions during the cardiac cycle?
Classically, the smooth muscle walls of the aorta and other large conduit arteries are
believed to behave as passive elastic tubes undergoing periodic distension with the pulse wave.
This is in contrast to data that suggest that an active contraction-relaxation cycle occurs in
synchrony with the cardiac cycle. In this paper data are reviewed, and the conclusion is
reached, that the aorta undergoes an active contraction in synchrony with the heartbeat. These
contractions show an upstroke in tension during the rising phase of the pulse wave, prompting
the nomenclature pulse synchronized contractions, or PSCs. PSCs are eliminated by blockers of
neural transmission, and the pacemaker for these events resides in the right atrium, potentially
allowing for coordination between cardiac and vascular contractility. Understanding the
contractile behavior of the aortic smooth muscle wall may both yield new targets for
therapeutics as well as help to further explain the etiology of cardiovascular disease processes.