What is respiratory sinus arrhythmia?

Respiratory sinus arrhythmia (RSA) is a naturally occurring variation in heart rate that coincides with the breathing cycle. During inhalation, the heart rate speeds up, and during exhalation, it slows down. This is due to the movement of the diaphragm, which affects the size of the heart and the rate at which the blood flows through it. When you inhale, the diaphragm moves down, and there's more space in the thoracic cavity, making the heart larger and blood flow slower, prompting the nervous system to increase the heart rate. Conversely, when you exhale, the diaphragm moves up, reducing space in the thoracic cavity, making the heart smaller, increasing the speed of blood flow, and signaling the nervous system to slow the heart rate down. RSA can also be linked with heart rate variability (HRV), which is a measure of the variation in time between each heartbeat.

RSA reflects the healthy functioning of the heart and nervous system, and it can become more robust through practices like deliberate breathing techniques to emphasize longer exhales. People who have more descriptive granularity on their emotions also tend to show improvements in RSA and HRV, which correlate with better physical and mental health outcomes 1 2 3 4 5 6 7 8.