Cardiorespiratory Coordination in Rats is Influenced by Autonomic Blockade

Abstract

Autonomic disturbance creates changes in the modulation of heart rate. In this study we analyzed the influence of sympathetic and vagal blockade on the interaction between cardiac and respiratory rhythms. In seven anaesthetized rats, electrocardiogram (ECG), and respiratory rate were recorded continuously before and after autonomic blockade with either methyl-scopolamine or atenolol. For the assessment of cardiorespiratory coordination, we analyzed the phase locking between heart rate, computed from the R-R intervals of body surface ECG, and respiratory rate, computed from impedance changes, using Hilbert transform. The procedure was carried out for different m:n coordination ratios where, m, is the number of heart beats and n, is the number of respiratory cycles. The changes in percentage of synchronization and duration of synchronized epochs before and after injection were assessed with one-way ANOVA. Sympathetic blockade with atenolol caused an increase (baseline: 0.49 ± 0.03s vs. blockade: 0.54 ± 0.06s) and vagal blockade with methylscopolamine caused a decrease (baseline: 0.49 ± 0.03s vs. blockade: 0.45 ± 0.08s) in the duration of synchronized epochs. Neither the overall percentage of synchronized epochs, (baseline: 10.76 ± 3.5% vs. blockade 9.44 ± 4.3%), nor the average locking ratio, 3:1, was significantly affected by autonomic blockade. In conclusion, the phase-locking between heart rhythm and respiration is modulated by both vagal and sympathetic efferences, in the opposite directions.