This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'Sinus arrhythmia is due to- \nSelect and explain. \nA. Sinus node disease, B. Exaggerated response to sympathetic system, C. Fluctuating parasympathetic response during respiration, D. Decreased hea rate in inspiration', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Answer-C. Fluctuating parasympathetic response during respirationSinus rhythm with a beat-to-beat variation in the P-P interval (the time between successive P waves), producing an irregular ventricular rate.Sinus arrhythmia is a normal physiological phenomenon, most commnonly seen in young, healthy people.The hea rate varies due to reflex changes in vagal ( parasyntpathetic ) tone during the different stages of the respiratory cycle,Inspiration increases the hea rate by decreasing vagal tone.With the onset of expiration, vagal tone is restored, leading to a subsequent decrease in hea rate.', 'role': 'assistant'}]