Respiratory Sinus Arrhythmia: A literature review

Respiratory sinus arrhythmia (RSA) is a natural variation in heart rate that occurs in synchrony with breathing and serves as a noninvasive indicator of vagal tone. This literature review summarizes current knowledge of RSA and its relevance in physiological and psychological contexts. We review the physiology of RSA, describing how the vagus nerve modulates heart rate variability and how RSA is measured. RSA increases during inhalation and decreases during exhalation, reflecting complex interactions between cardiac and respiratory processes. An evolutionary benefit of RSA has been proposed, as RSA may optimize cardiac efficiency by minimizing cardiac work for a given respiratory demand. We will also examine RSA in emotion regulation. High RSA (greater heart rate variability) has been associated with better emotional regulation and stress resilience, whereas low RSA is often observed in stress and anxiety. Studies are highlighted linking maternal stress and infants’ RSA, suggesting early-life stress can dampen an infant’s RSA and emotion-regulation capacity. Finally, we explore RSA in dyadic interactions. Research in parent–child and romantic pairs shows that synchronized RSA (physiological synchrony) relates to better social engagement and emotional connection. In therapeutic settings, a client’s RSA may indicate openness and a strong therapeutic alliance. Understanding RSA in these domains underscores its potential as a biomarker for emotional and relational health.