The Heartbeat Amplifier (HBA) is a viscerally interactive art project that passively monitors the participant’s heartbeat, via electrocardiogram (ECG) signal. The human-sensitive papasan chair amplifies and condition the participant’s ECG to drive audio, haptic (touch sensation), visual and thermal transducers to stimulate those respective perceptual pathways in the participant.
The HBA is easy to use. The participant sits in the papasan chair, places their hands on the curved silver surfaces, and relaxes. Within a few seconds, the HBA optimizes its amplification for the participant. The participant begins to hear the sound of their heartbeat and the simple red light, above their head, begins to flash with the advent of each beat.
The HBA is comprised of a papasan chair with incorporated ECG sensors, amplifiers and feedback transducers. As soon as the participant sits in the HBA, the HBA adjusts its amplification and visceral feedback to match the participant’s ECG. The ECG signal level is about 1mV (1/1000th of a volt). The HBA amplifies this signal, about 30,000 times, to drive low frequency subwoofers in the chair.
The HBA provides clear feedback as to the relationship between heart and breath. As one inspires, the expanding lungs compress the heart and also subtly reduces the level of the heart’s electrical signal (ECG). Upon expiration, the heart expands, as the lungs deflate, and the heart’s signal increases. Variations in heart rate (BPM) also happen during the changes from inspiration to expiration.
A Primer on the ECG and Respiratory Activity
There are two influences of respiratory activity on the electrocardiogram. The first influence is characterized by the mechanical relationship between the diaphragm and heart. The second influence is a consequence of respiratory action on the vagus nerve and is known as Respiratory Sinus Arrhythmia (RSA).
1) The position and movement of the diaphragm determine the position of the heart because the pericardium is firmly attached to the central tendon of the diaphragm. With deep inspiration, the diaphragm contracts and becomes flatter and less dome-shaped. As it does, the heart descends, moves backward, and rotates to the right so that it becomes narrower and more vertical. The apex beat is lower and more medial. During deep expiration, the diaphragm relaxes, elevates, and becomes more dome-shaped, and movements of the heart are the converse of those that occur during deep inspiration. The degree of the directional movements of the heart during quiet breathing is similar, but reduced, compared to deep breathing and, in some persons, may be hardly noticeable. Thus, diaphragmatic breathing cyclically affects the position of the heart thus modifying the electrical signal “seen” by the HBA.
2) Heart rate increases during inhalation and decreases during exhalation. Heart rate is normally controlled by centers in the medulla oblongata. One of these centers, the nucleus ambiguus, increases parasympathetic nervous system input to the heart via the vagus nerve. The vagus nerve decreases heart rate by decreasing the firing rate of the sinoatrial (SA) node. The SA node is the “pacemaker” of the heart. Upon expiration, the cells in the nucleus ambiguus are activated and heart rate slows down. In contrast, inspiration triggers inhibitory signals to the nucleus ambiguus and consequently the vagus nerve remains unstimulated. When sitting in the HBA, this phenomenon is experienced as subtle changes in the R-R interval that appears synchronized with respiration. This is the time period between two “R” waves on an electrocardiogram. The R-R interval associated with the ECG is shortened during inspiration and prolonged during expiration. Meditation and relaxed breathing techniques can temporarily induce RSA.