EFFECTS OF AUTONOMIC BLOCKADE ON NON‐LINEAR CARDIOVASCULAR VARIABILITY INDICES IN RATS

1 The present study assesses the effects of autonomic blockade (a‐ and b‐adrenoceptor and cholinergic) on cardiovascular function studied by heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity in rats using non‐linear dynamics. Little is known about the influence of pharmacological autonomic nervous system interventions on non‐linear cardiovascular regulatory indices. 2 In 13 conscious rats, heart rate and aortic blood pressure were measured continuously before, during and after autonomic blockade with atropine, phentolamine and propranolol. Non‐linear scaling properties were studied using 1/f slope, fractal dimension and long‐ and short‐term correlation. Non‐linear complexity was described with correlation dimension, Lyapunov exponent and approximate entropy. Non‐linear indices were compared with linear time and frequency domain indices. 3 b‐Adrenoceptor blockade did not alter the non‐linear characteristics of HRV and BPV, although low‐frequency power of HRV was depressed. a‐Adrenoceptor blockade decreased the scaling behaviour of HRV, whereas cholinergic blockade decreased the complexity of the non‐linear system of HRV. For BPV, the scaling behaviour was increased during a‐adrenoceptor blockade and the complexity was increased during cholinergic blockade. The linear indices of HRV and BPV were decreased. 4 The present results indicate that the b‐adrenoceptor system has little involvement in the generation of non‐linear HRV and BPV in rats. 5 a‐Adrenoceptor blockade mostly influenced the scaling properties of the time series, whereas cholinergic blockade induced changes in the complexity measures. 6 The absence of the baroreflex mechanism can trigger a compensatory feed‐forward system increasing the complexity of BPV.