Validation of the Measure of Sympatho-vagal Effect in Lambs Through Autonomic Blockades and Heart Rate Variability Indexes

The validity of heart rate variability (HRV) indexes for autonomic studies in conscious lamb was assessed by the way of autonomic pharmacological blockades. In addition we have calculated the index of the net vago-sympathetic effect (VSE). These indexes could be usefull for the study of animals` emotions and stress. Eight lambs received an injection of either atenolol (0.5mg kg-1), atropine sulfate (0.2 mg kg-1), a mixture of atenolol and atropine (0.5 and 0.2 mg kg-1 respectively) or saline. Time-domain indexes of HRV were calculated: mean heart rate (HR), mean of RR intervals (MeanRR), standard deviation of all RR intervals (SDRR), and standard deviation of differences between adjacent RR intervals (SD RR). Frequency-domain indexes were extracted: total power (0-1 Hz; TPW), low frequency power (0.04-0.15 Hz; LF), high frequency power (0.15-1 Hz; HF) and the ratio LF/HF. VSE was obtained by dividing MeanRR (for each drug injected) by RR0 (MeanRR after injection of atenolol and atropine together). Atenolol injection had no effect on cardiac activity, whereas atropine induced large modifications which were reduced when atenolol was administered at the same time. All explored indexes vary during autonomic blockade and contribute significantly to the variance of the model in our lambs. VSE appears a valid indicator of the net vago-sympathetic effect. SD RR or HF can be used for qualitative estimation of parasympathetic activity. Since no measure reflected directly the sympathetic tone, it is suggested that measures of SD RR or HF together with VSE could conduct, by logical deduction, to an estimation of sympathetic activity.