Cholinergic blockade with atropine eliminated respiratory heart rate variations, showing that vagally mediated heart rate variations normally reduce fluctuations in cardiac output and arterial pressure.
Does cholinergic blockade by atropine alter respiration-synchronous fluctuations in stroke volume, heart rate, and arterial pressure in healthy young adults?
Vagally mediated heart rate variations normally counteract mechanically induced stroke volume fluctuations during respiration to stabilize cardiac output and arterial pressure.
Simultaneous recordings of beat-to-beat left cardiac stroke volume (SV, pulsed ultrasound Doppler), mean arterial pressure (MAP) and heart rate (HR) were obtained in ten healthy young adults during spontaneous respiration at supine rest, before and after cholinergic blockade by atropine (0.035 mg kg-1). 2. Respiration-synchronous fluctuations in SV, HR, cardiac output (CO) and MAP were quantified by spectral analysis of the recordings of each of these variables. 3. Before atropine administration, respiration-synchronous fluctuations in HR and SV were prominent. The changes in HR and SV were inversely related and variation in SV was the main source of respiratory variability in CO. Respiration-synchronous fluctuations in MAP were mainly caused by variations in CO. 4. After cholinergic blockade, respiratory HR variations were eliminated, whereas the respiratory fluctuations in SV persisted. The fluctuations in CO and MAP increased. In this situation, mechanically induced variations in SV were not counteracted by inverse HR fluctuations and the influence on CO thus increased. 5. The main source of respiratory fluctuations in MAP in supine humans is thus variation in SV, while inverse, vagally mediated HR variations tend to reduce the fluctuations in CO and MAP.
Toska et al. (Wed,) conducted a other in Healthy (n=10). Atropine vs. Baseline (before atropine) was evaluated on Respiration-synchronous fluctuations in SV, HR, CO and MAP. Cholinergic blockade with atropine eliminated respiratory heart rate variations, showing that vagally mediated heart rate variations normally reduce fluctuations in cardiac output and arterial pressure.