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Heart Sounds Research Lab
Physiologic Split S2
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The Heart Sounds and Murmurs Laboratory | 6560 Fannin St, Suite 1836| Houston, Texas 77030 | 832-355-2937
copyright 2017 © Houston MDs. All rights reserved.
The normal second sound is made of two components, the aortic and the
pulmonary, that follow each other in this order. Splitting of the second heart
sound (S2) during respiration is a normal phenomenon. Inspiration
increases blood return to the right side of the heart, increases the vascular
capacitance of the pulmonary bed, and decreases the blood return to the
left side of the heart. These physiological alterations are reversed with
expiration. As a consequence, aortic valve closure occurs slightly earlier,
and pulmonary valve closure significantly later, with inspiration. Accordingly,
the aortic and pulmonary components of S2 are closely juxtaposed in
expiration and split by 0.02 to 0.04 second normally with inspiration. This is a
cyclic phenomenon and should be observed during quiet respiration, or
perhaps minimally exaggerated, and is especially pronounced with the
patient in the sitting position. Forced inspiration, expiration or prolongation
of either of these components is an improper manner of eliciting this cyclical
event.
Listen to a couple of additional normal patient heart sounds and then
compare them to the simulated sounds. Pay close attention to the
simulated split second sound (S2)of 25msec since this is roughly around
the timing of a physiologic split second sound (S2).

Normal (physiologic) Split S2
Simulated Sounds