Lesson

Lub Dub (Dupp)

Ever wonder why the heart sounds the way that it does? Opening and closing of heart valves makes the heart rhythm come alive with its lub dub (Dupp) beats.

The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle (Figure). The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole. Both the atria and ventricles undergo systole and diastole, and it is essential that these components be carefully regulated and coordinated to ensure blood is pumped efficiently to the body.

Overview of the Cardiac Cycle

The cardiac cycle begins with atrial systole and progresses to ventricular systole, atrial diastole, and ventricular diastole, when the cycle begins again. Correlations to the ECG are highlighted.

The cardiac cycle begins with atrial systole and progresses to ventricular systole, atrial diastole, and ventricular diastole, when the cycle begins again. Correlations to the ECG are highlighted.

Heart Sounds

One of the simplest, yet effective, diagnostic techniques applied to assess the state of a patient’s heart is auscultation using a stethoscope.

In a normal, healthy heart, there are only two audible heart sounds: S1 and S2. S1 is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as a “lub,” or first heart sound. The second heart sound, S2, is the sound of the closing of the semilunar valves during ventricular diastole and is described as a “dub” (Figure). In both cases, as the valves close, the openings within the atrioventricular septum guarded by the valves will become reduced, and blood flow through the opening will become more turbulent until the valves are fully closed. There is a third heart sound, S3, but it is rarely heard in healthy individuals. It may be the sound of blood flowing into the atria, or blood sloshing back and forth in the ventricle, or even tensing of the chordae tendineae. S3 may be heard in youth, some athletes, and pregnant women. If the sound is heard later in life, it may indicate congestive heart failure, warranting further tests. Some cardiologists refer to the collective S1, S2, and S3 sounds as the “Kentucky gallop,” because they mimic those produced by a galloping horse. The fourth heart sound, S4, results from the contraction of the atria pushing blood into a stiff or hypertrophic ventricle, indicating failure of the left ventricle. S4 occurs prior to S1and the collective sounds S4, S1, and S2 are referred to by some cardiologists as the “Tennessee gallop,” because of their similarity to the sound produced by a galloping horse with a different gait. A few individuals may have both S3 and S4, and this combined sound is referred to as S7.

Heart Sounds and the Cardiac Cycle

In this illustration, the x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.

In this illustration, the x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.

The term murmur is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood. Murmurs are graded on a scale of 1 to 6, with 1 being the most common, the most difficult sound to detect, and the least serious. The most severe is a 6. Phonocardiograms or auscultograms can be used to record both normal and abnormal sounds using specialized electronic stethoscopes.

During auscultation, it is common practice for the clinician to ask the patient to breathe deeply. This procedure not only allows for listening to airflow, but it may also amplify heart murmurs. Inhalation increases blood flow into the right side of the heart and may increase the amplitude of right-sided heart murmurs. Expiration partially restricts blood flow into the left side of the heart and may amplify left-sided heart murmurs. Figure indicates proper placement of the bell of the stethoscope to facilitate auscultation.

Stethoscope Placement for Auscultation

Proper placement of the bell of the stethoscope facilitates auscultation. At each of the four locations on the chest, a different valve can be heard

Proper placement of the bell of the stethoscope facilitates auscultation. At each of the four locations on the chest, a different valve can be heard

 

Attribution

Creative Commons License The Khan Academy video is shared with permission and under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. For more content and activities related to this activity see the associated lesson.

Creative Commons License The text was modified from OpenStax, Anatomy & Physiology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License 4.0 license.

Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. If you would like  to use this material, please provide attribution as follows: Marini, S. (2016). http://www.ceces.ca/courses/circulatory-system-introduction/. Continuing Education Centre for Emergency Services.

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