What is respiratory sinus arrhythmia?

Respiratory sinus arrhythmia is characterized by a variation in heart rate that occurs in synchrony with the respiratory cycle. Specifically, when a patient inhales, the heart rate typically decreases, and when they exhale, the heart rate increases. This phenomenon is a normal physiological response and is most commonly observed in healthy individuals, particularly children and young animals. It results from the influence of the vagus nerve on the heart and is a reflection of autonomic nervous system activity during respiration.

The other options do not accurately describe respiratory sinus arrhythmia. For instance, the option stating that heart rate remains constant regardless of breathing does not capture the essence of how the heart rate varies with breath cycles. Similarly, the options concerning heart rate changes during sleep and elevated heart rates during rest reflect different physiological processes and do not pertain to the cyclical nature of heart rate changes associated with respiration. Thus, the selection of heart rate decreasing during inhalation and increasing during exhalation is indeed the correct depiction of respiratory sinus arrhythmia.