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Phonocardiogram

Visualization of heart sounds

The heart visualization presented by the Steth IO app is a phonocardiogram. In our software, we have significantly enhanced the phonocardiogram to make it very easy to understand.  In a phonocardiogram, you can visualize heart and lung sounds and their frequency spectrum.

A typical heart cycle shown here consists of an S1 (the first heart sound) and S2 (the second heart sound). These sounds correspond to the heart sounds commonly referred to as “Lub” (S1)  and “Dub” (S2) sounds.

Understanding the time series

The green line in the middle of the screen is the time series waveform representing the amplitude (or the strength) of the sound over time. The two high amplitude signal locations in a normal heart signal correspond to the S1 and S2 sounds.

The relative amplitudes of S1 and S2 usually depend on where the heart is auscultated, so you cannot reliably identify S1 and S2 based on amplitude alone.

To identify S1 and S2, we need to look at the relative distance between the two peaks in a single heart cycle. Usually, the S1 to S2 distance is shorter than the S2 to S1 (of the next cycle) distance. The S1 to S2 distance represents the systolic (pumping) phase of the heart cycle and the S2 to S1 distance represents the diastolic (filling) phase of the heart cycle.

Understanding the frequency spectrum

The colored graph on the bottom of the screen illustrates the frequency spectrum of the heart sounds. The frequency spectrum is displayed over time horizontally. Charted through time, the higher frequency sounds (higher pitch, measured in Hertz) are higher on the vertical axis and low-frequency sounds are lower. The color of the frequency spectrum indicates the amplitude (loudness, measured in Decibels) of the signal — the higher the signal strength, the redder its representation.

The frequency representation of the heart sound is really important because abnormalities like murmurs are high-frequency sounds and are easy to capture via the frequency representation. For a detailed overview of how common murmurs show up in our phonocardiogram visit our Visualizing Auscultation section.

 As an example, the visualization of a holosystolic murmur is shown below, where you can see the high-frequency part both in the time series as well as in the frequency spectrum.

 

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