" Listening to your heartbeat to guide mindfulness. "
Heart rate variability (HRV), or the variations in time intervals between heartbeats, has been shown to be related to emotional arousal, elevated anxiety rates, physical activity and stress. There has been some research into whether measuring changes in HRV over time can be used as a physiological indicator for mindfulness therapy outcomes.
Project goal
Create a digital and interactive solution using heart rate variability measurements to aid users during mindfulness therapy.
Project details
Independent project completed as a student at Master Digital Design, Amsterdam University of Applied Sciences.
Target audience
Persons interested in improving their mindfulness meditation.
Pulse Sings is a biofeedback design that uses a pulse sensor and sound software to convey information about your heart beat. Listening to your heartbeat to guide mindfulness exercises is more conducive to closed-eye, mindfulness meditation.

I was inspired to start this personal project after reading The Sonification Handbook by Thomas Hermann which discusses practical implementations of using sound to convey information. Also, I had recently purchased some biofeedback devices for my Arduino including a pulse sensor that I was eager to experiment with. After a quick brainstorm session, I came up with an idea of how I might create sounds using a heart rate sensor as my input device.

A photo of a woman in a flower dress with over-ear headphones on listening to her pulse from a sensor which is on her finger.
audio-guided meditation

I began researching in Google Scholar and PubMed to find out which heart rate parameters are used as health indicators. The heart beat information which I decided to use is called "heart rate variability" (HRV). HRV is the variance in time between consecutive heart beats. Below are some of my research discoveries regarding HRV therapy:

  • Typically, lower HRV indicates higher stress levels and higher HRV indicates physical and mental well-being.
  • HRV monitoring is sometimes used to aid mindfulness meditation.
  • HRV biofeedback training has been known to help regulate the stress of athletes during competitions.
  • Some studies have explored using HRV training as a way to treat anxiety and depression.

HRV training typically make use of a Poincare plot. These plots graph the time intervals of your heart beat (RR intervals). The more spread out the points on the plot, the higher your HRV is.

A dark blue and white Poincare plot.
Problem space

Unfortunately, Poincare plots are not conducive to close-eye meditation. Staring at a bright screen for five or more minutes during a biofeedback session may also lead to increased anxiety, defeating the purpose of the training altogether.

  • How might I reliably convey heart rate variability information off-screen using sound?
  • How well will users interpret sonifications of HRV information compared to Poincare plot information?
A dark blue and white graph depicting heart rate variance.
Ideation & validation

The biggest challenge during this project was choosing which sound parameters to represent HRV and ongoing changes in HRV. Trusting my gut instinct, I began experimenting with sounds in the software Max MSP while trying my best to strike a balance between pleasant sounds and sounds that were able to convey changing information.

I had a lot of fun testing the design with my eyes closed to see whether I could relax enough to influence the sounds. My partner also tested the design and is apparently much better at meditating than I am.

For the final prototype, I used a tremolo effect (modulating amplitude) to represent the distance in time between heart beats and changing pitch/timbre to signify whether overall HRV was moving up or down. I created an on-screen visualizer as this was necessary to best demonstrate the proof of concept.

A man with a baseball cap on at a computer with a large monitor which is displaying a node-based code editor.
programming in max
Future direction

The Pulse Sings prototype has a lot of potential. My future goals for this design include:

  • Implementing a wireless pulse sensor so that users may lie down while meditating
  • Prototyping a mobile device version to allow for more freedom of movement
  • Visualizing user progress over time
PulseSings graphical user interface displaying in a tablet computer with a gradient purple background
tablet version