Variations in heartbeat directly related to breathing; slower during inspiration and faster during expiration.

Respiratory sinus arrhythmia (RSA) is a natural variation in heart rate that occurs during the breathing cycle. It is characterized by an increase in heart rate during inhalation and a decrease in heart rate during exhalation. This phenomenon is most prominent in children and young adults, and generally becomes less pronounced as a person ages.

RSA is believed to be a sign of good cardiovascular health and efficient autonomic nervous system functioning. The autonomic nervous system is responsible for regulating involuntary bodily functions, such as heart rate, digestion, and respiration. RSA reflects the balance between the two branches of the autonomic nervous system: the sympathetic nervous system (which activates the “fight or flight” response) and the parasympathetic nervous system (which controls the “rest and digest” response).

In general, a higher degree of RSA is considered to be a marker of a healthy and well-functioning autonomic nervous system. However, it is important to note that RSA can be influenced by various factors, including age, fitness level, emotional state, and certain medical conditions.