Visualizing Auscultation

Interpretation of Heart Sounds

The Phonocardiogram is a spectrographic representation of sounds that contains information to help clinicians to arrive at a better diagnosis. The powerline or amplitude line represents the volume of the sound being recorded. The frequency is represented on the Y-axis and time is represented on the X-axis. The color spectrogram represents the amplitude of the sound recorded, and the height of the colored peaks represents the peak frequency. This information can be very useful in diagnosing heart and lung sounds. This is highlighted in the tutorial in the Steth IO application which is shown below.

Application Tutorial

Normal Heart Sounds

In this example normal first heart sound (S1) and second heart sound (S2) are clearly seen. S1 and S2 can be identified by examining the length of systole and diastole. Systolic phase is always shorter than the diastolic phase in any given cardiac cycle. Hence, the S1 is followed by S2 after a shorter systolic phase and S2 is followed by S1 after a relatively longer diastolic phase. Due to the absence of any murmurs, the systolic and diastolic phases of the cardiac cycle are free of energy signals.

Grade II Early Systolic Murmur

Early systolic murmur in a 74yr old female patient who recently underwent aortic valve replacement. In this example, the energy of the murmur recorded is represented as a bluish peak in the early systolic phase of the cardiac cycle and the height the peak is low due to the low-frequency peak of this murmur. This may represent a flow murmur.

Grade III Holosystolic Murmur

Holosystolic murmur in a 67yr old patient with severe aortic stenosis. In this example, the energy of the murmur recorded is represented as bluish-green peak (higher amplitude than in the earlier case) and the height of the peak is high due to high frequency of the murmur due to the presence of severe aortic stenosis. This example also shows that the murmur occupies the entire systolic phase of the cardiac cycle. Note the absence of murmurs in the diastolic phase.

Grade II Mid Diastolic Murmur

If a patient had a Diastolic murmur from moderate mitral stenosis, then the energy of the murmur recorded would be represented as a bluish peak in the mid-diastolic phase of the cardiac cycle. The example below shows this along with Atrial Fibrillation.

Extra Sounds, S3 and S4:

A normal cardiac cycle has first and second heart sounds (S1 and S2). Presence of S3 after S2 can be abnormal which can represent systolic heart failure and increased left ventricular filling pressures. S4 occurs before S1 in the diastolic phase of the cardiac cycle. S4 is almost always abnormal and is seen in left ventricular diastolic dysfunction.

Interpretation of Lung Sounds

Lungs sounds recorded are visualized as inspiratory and expiratory peaks. The width of the peaks represents inspiratory and expiratory phases of respiratory cycle separated by a respiratory pause.

Normal Lung Sounds:

In this example, normal inspiratory and expiratory phases of the respiratory cycle are seen as distinct peaks. The width of the peaks can represent the length of expiration and inspiration.


Wheezing, for example in a patient with mild exacerbation of bronchial asthma, would be seen as high-frequency energy in the expiratory phase of the respiratory cycle. If a bronchial obstruction is severe, wheezing may be seen in both the expiratory and inspiratory phases of the respiratory cycle.

Prolonged Expiration

In mild bronchial constriction, the earliest sign may be prolonged expiration. This is difficult to decipher when using a standard stethoscope. With visualization of lung sounds one can visualize the length of inspiration and expiration.



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