The following examples of heart sound analysis are from pediatric patients, and they demonstrate the validity of modern phono-spectrocardiographic imaging techniques. The software used includes corresponding audio recordings and marker measures (Fig. 2–3).
In these phono-spectrograms (Figs. 2–4, 2–5, 2–6, 2–7, 2–8, 2–9, 2–10, 2–11), timing is read from the time scale (at the bottom of the figures) by visually examining both the phonocardiogram and the spectrogram and then deciding the duration of a sound event or murmur and dragging the marker over the selected time segment. The intensities of S1, S2, and murmurs are read from the scale (to the right in the figures, percentages of the recording capacity of the stethoscope) by positioning the marker over the phonocardiogram. The loudness of a murmur is estimated from the phonocardiogram by comparing the maximum amplitude of the murmur to the average value of the maximum amplitude of the first and second heart sounds. Finally, the frequencies (in hertz) are read by moving the marker over the spectrogram. The intensity level (on the left of the figures, the color scale) of the marked and nonmarked frequency limits of the sounds is between 45 and 50 dB (yellow color in the figures).
Hence, this system is able to display and reproduce cardiovascular sound events. For example, a musical murmur caused by harmonic movements of the heart and vasculature, such as an innocent vibratory murmur (Still's murmur) is usually visualized as a well-defined area or line on the spectrogram. Innocent systolic murmurs appear to have a lower peak frequency (below 200 Hz) and a shorter duration (below 80% of the duration of "audible systole" from the end of S1 to the beginning of S2) compared with recordings of pathologic murmurs. Also, innocent systolic murmurs always fade before the second heart sound. In contrast, the higher velocity blood flow of a pathologic cardiac lesion produces a more intense murmur and a wider frequency scale (in hertz). This phenomenon is clearly demonstrated on the spectrographic recordings.