Assessment of cardiac sympathetic regulation by respiratory‐related arterial pressure variability in the rat

1 Mechanical ventilation evokes a corresponding arterial pressure variability (APV) which is decreased by β‐adrenoceptor antagonism. Therefore, in this study we set out to determine whether the respiratory‐related APV can be used to assess cardiac sympathetic tone. 2 Computer‐generated broad‐band mechanical ventilation (0–3 Hz) was applied to Sprague‐Dawley rats that had been anaesthetized with ketamine and paralysed with pancuronium. APV and its relationship to lung volume variability (LVV–APV) was systematically quantified with auto‐ or cross‐spectral frequency domain analysis. 3 APV and LVV–APV transfer magnitudes between 0.5 and 1.5 Hz showed dose‐dependent suppression by propranolol from 0.01 to 1 mg kg−1, while the static value of arterial pressure remained unchanged. Stroke volume variability, assessed by the use of a pulse contour method, exhibited a similar pattern of suppression by propranolol. In contrast, heart rate variability was not lowered with propranolol. 4 The effect of propranolol on respiratory‐related APV persisted even in the presence of combined α‐adrenoceptor and muscarinic receptor blockade by phentolamine and atropine. 5 The frequency range of 0.5–1.0 Hz was optimal for LVV–APV transfer magnitude to correlate with cardiac sympathetic tone. 6 We conclude that respiratory‐related APV may provide a valid assessment of cardiac sympathetic regulation which is independent of parasympathetic and vascular sympathetic influences in ketamine‐anaesthetized and positive pressure‐ventilated rats.