DISTINCT BRAINSTEM ORIGINS OF CARDIAC VAGAL TONE AND RESPIRATORY SINUS ARRHYTHMIA

Abstract

Cardiac vagal tone is a major determinant of health. Its brainstem origins are unknown, but can be investigated in the working heart‐brainstem preparation (WHBP), which shows cardiac vagal tone with a normal pattern of respiratory sinus arrhythmia (RSA). Ongoing activity in the cardiac vagal branch peaks in late inspiration/postinspiration, correlating with the minimum heart rate of RSA. Bilateral inhibition of the pontine Kölliker‐Fuse nucleus (KF) with isoguvacine (GABAA receptor agonist; 10 mM, 40‐60nl) abolished RSA at the same time as removing postinspiratory phrenic activity. Mean heart rate rose modestly (mean +13 bpm). Transection of the caudal pons also abolished RSA and raised hear..