[Power spectral analysis of heart rate and peripheral blood flow variations during total spinal anesthesia]

We evaluated the effect of total spinal anesthesia (TSA) on the heart rate and peripheral blood flow variations to evaluate if TSA could influence these parameters as indicators of autonomic nervous function (ANF). Four patients with intractable pain were treated by TSA by administration of local anesthetics (lidocaine or mepivacaine) into the C7-Th1 vertebral interspace. Power spectrum of heart rate before TSA showed three peaks; low (LO-FR, 0.04-0.095 Hz), mid (MID-FR, 0.095-0.15Hz) and high frequency areas (HI-FR, 0.15-0.3Hz). Spectral peaks of LO-FR and MID-FR disappeared during TSA (P less than 0.001). HI-FR area decreased to 3.3% of the control level (P less than 0.001). Mean peripheral blood flow was changed to 59.9% of the control level (not significant). However, peripheral blood flow variations of LO-FR decreased to 11.3% of the control level (P less than 0.001) after TSA. Furthermore, the vagal discharge disappeared promptly after TSA in dog. These results suggest that TSA depresses the vagal activity as well as the sympathetic activity innervating the cardiovascular system and therefore, heart rate and peripheral blood flow variations are totally eliminated. Thus, we conclude that heart rate and peripheral blood flow variations can serve as valid markers of ANF activity.