Music of the Heart

The Music of the Heart is derived from electrocardiogram (ECG) data, actual digital recordings of the electrical signals of the human heart. These heart songs began as musical notes mapped from the heartbeat data. The composer then added harmonies and rhythm to make pleasant sounding music.

Listen to these heart songs MIDI files by clicking on the controls. Can you tell which 3 compositions are based on "healthy" heart data? (Hint: read below)

There was also a hands-on exhibit at the Boston Museum of Science that allowed museum-goers to record their own electrocardiogram and, in real time, listen to the music it produces. This 'heart music' created by museum-goers is different from the heart songs above which were 'interpreted' by a composer (i.e., chords and rhythm were added by the composer on top of the melody created from the data). Heart music you would hear at the museum exhibit which is based solely on the raw data sounds something like this:

How can your heart make music?

In the first of four stages, we obtained digital tape recordings of the heartbeat using a Holter monitor, a pocket-sized ECG recorder that can store thousands of consecutive heartbeats (as shown in the figure) over an entire day.

Next, using a computer, we measured the precise intervals between the heartbeats, creating a graph of the instant-to-instant changes in heart rate as a function of time.

While your pulse may feel perfectly regular, you actually have a great deal of subtle variability from one beat to the next. These fluctuations are produced by the normal functioning of the involuntary nervous system, which can cause your heart to slow down or speed up. The normal heartbeat, therefore, does not follow a metronomic or march-like beat---suprisingly, it has a dance-like plasticity and variability.

The third step in creating these heartsongs was to convert the time intervals between heartbeats into integers. We used a simple computer program to generate roughly 330 integers per data set. (We started with 10,000 recorded heartbeats, then calculated the average of every 300 beats. We averaged the beats to remove very short-term fluctuations caused by movement or breathing.)

The product of these musical mappings raises a fundamental question. Why does the healthy heart create musically pleasing or interesting note sequences, whereas the diseased heart create boring repitition?

The answer may lie in the origin of heart rate variability regulated by our nervous systems. The result is a complex pattern of variations present in normal heartbeats but absent in sick heartbeats that have been shown to have the mathematical structure of a fractal.

The term fractal describes objects such as snowflakes and coral formations, which are composed of smaller units resembling the larger scale form---a property called self-similarity. Fractals have been shown to be relevant to a wide range of natural phenomena. This term also applies to complex processes that are made up of different frequency components with a special type of scaling relationship to each other. Work by Richard Voss and John Clarke have shown that some classical music has this type of scaling pattern. These recordings are, to our knowledge, the first effort to use actual rhythms of the heart as the template for musical composition.

The musicality of these recordings raises a further question: could the composition of music involve, at least in part, the re-creation by the mind of the body's own naturally complex rhythms and frequencies? Perhaps what the ear and the brain perceive as pleasing or interesting are variations in pitch that resonate with or replicate the body's own complex (fractal) variability and scaling.

The musical pieces recorded here cannot resolve this question, but may challenge the imagination and delight the ear.

For more information, please contact Paul Trunfio.