Determinants of respiratory sinus arrhythmia in the vagotomized rabbit

After cardiac denervation, a small-amplitude respiratory sinus arrhythmia (RSA) has been described in animals and humans. Its mechanical and chemical determinants were investigated in 19 urethan-anesthetized, vagotomized, and mechanically ventilated rabbits. We measured the influence on RSA of arterial blood gases, beta-adrenergic blockade, and phasic and steady changes in right atrial pressure (RAP) induced by changes in tidal volume (VT, 20, 40, 60 ml), respiratory frequency (RF, 10, 20, 30 cycles/min), and dextran-induced RAP increases. Phasic changes in RAP during each recording were quantified as standard deviation of the first derivative of the RAP signal (dRAP) as a measure of magnitude of variations of the rate of change due to respiration. RSA was assessed by combined autoregressive power spectral analysis of R-R interval and respiration on sequences of 256 heart-beats. Despite vagotomy, RSA was present in all recordings in all animals. During room air breathing, RSA changes were dependent on RF and VT (P < 0.025 and P < 0.001, respectively) and correlated with dRAP (P < 0.001) and arterial PO2 (P < 0.001). beta-Adrenergic blockade did not change the amplitude of this residual RSA or its dependence on ventilatory mechanics. Dextran-induced increase in mean RAP from 2.9 to 11.9 mmHg did not modify RSA or dRAP. During 100% O2 inhalation, RSA changes were no longer significantly linked to RF and VT, and also the correlation of RSA with dRAP was reduced (P < 0.05). Changing the arterial PCO2 from 28 to 79 mmHg (induced by increasing dead space at fixed ventilation) did not modify RSA.(ABSTRACT TRUNCATED AT 250 WORDS)