From a physiological perspective, heartbeats and breathing do not operate independently in the human body. Cardiac rhythm varies with the respiratory cycle, and the close interaction between the two is known as cardiopulmonary coupling (CPC). CPC reflects the regulatory state of the autonomic nervous system and serves as an important physiological indicator for evaluating sleep quality, cardiovascular health, and stress levels.
For decades, however, cardiopulmonary coupling has been assessed almost exclusively using electrocardiogram electrodes, respiratory belts, or other contact-based sensors. While effective, these devices can compromise comfort and limit their use in home environments, long-term monitoring, and applications involving sensitive populations such as infants or post-operative…