Sympathovagal Effects of Spinal Anesthesia Assessed by Heart Rate Variability Analysis

Abstract

Heart rate variations (HRV) result from moment-to-moment changes in sympathetic and parasympathetic activity in response to many conditions. These two neural inputs to the heart can be identified by analyzing power spectra of HRV for frequency components at the vasomotor (low-frequency [LF]) and the respiratory (high-frequency [HF]) rhythms. HRV analysis has been used successfully in humans to noninvasively evaluate the autonomic responses to specific maneuvers and drugs, as well as responses to more chronic preexisting pathologic conditions. The effects of an isolated "acute" withdrawal of sympathetic activity in humans, however, have not as yet been evaluated using an autoregressive (AR) technique. We examined HRV using this technique in a group of patients receiving subarachnoid block for abdominal surgery. The sensory levels achieved were within the range of those reported to interrupt sympathetic outflow to the heart. Electrocardiograms were recorded and subjected to AR analysis. AR analysis of HRV after spinal anesthesia revealed significant decreases in both dominant frequency components (LF and HF) that occur between 0.03 Hz and 0.5 Hz. These reductions coincided with blockade of cardiac sympathetic outflow after cephalad spread of the spinal block. The power spectra were almost abolished in patients with sensory blocks reaching T1-2. The decreases in amplitude of the LF and HF components, therefore, act as markers of diminished sympathetic and parasympathetic activity to the heart, while the ratio of LF:HF indicated that sympathovagal balance was predominantly maintained during most of the block.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the effects of hyperbaric and isobaric bupivacaine spinalanesthesia on hemodynamics and heart rate variability

“…Sympathetic preganglionic fibers are more sensitive towards the effects of local anesthetics because of small fiber diameters, and sympathetic blocks are a few segments above sensory blocks (34). Cephalic progression of spinal block causes a quantitative decrease in HRV in parallel with block height (16). Although the median sensory block height was only one segment higher in the hyperbaric group, we thought that it could be the reason for the difference in LF/HF ratios.…”

“…Studies comparing hyperbaric and isobaric bupivacaine reported variable results on spinal anesthesiainduced hypotension (11)(12)(13)(14). In addition to their role in predicting hypotension due to spinal anesthesia, HRV parameters also undergo significant changes following spinal anesthesia (9,10,15,16). However, there are no reports that have compared the effects of hyperbaric versus isobaric bupivacaine on HRV.…”

Slow oscillations in blood pressure via a nonlinear feedback model

“…In comparison with the power of the faster oscillation in heart rate associated with respiration, there have been numerous papers reporting changes in sympatho-vagal balance in such varied conditions as anesthesia (20), sleep (3), and the menstrual cycle (36). A mounting number of studies indicates that this hypothesis is flawed on several points, and it is more probable that the 0.1-Hz oscillation in heart rate provides an index of baroreflex gain (5,38,39).…”

The effectivness and simpthoms of spinal anaesthesia depending on the influence of the applied local anaestetic

“…Simpatički blok [4] dovodi do arterijske i venske dilatacije krvnih sudova donjih ekstremiteta i refleksne kompenzatorne povećanosti simpatičke aktivnosti iznad bloka. Parasimpatička inervacija srca preko nerva vagusa nije blokirana, čak i usled viših nivoa spinalnog bloka [4,5].…”

“…Simpatički blok [4] dovodi do arterijske i venske dilatacije krvnih sudova donjih ekstremiteta i refleksne kompenzatorne povećanosti simpatičke aktivnosti iznad bloka. Parasimpatička inervacija srca preko nerva vagusa nije blokirana, čak i usled viših nivoa spinalnog bloka [4,5]. Rezultati studije Roberta i saradnika [4,5] ističu ređu pojavu direktnog uticaja spinalnog bloka na aktivnost n. vagusa jer su doze lokalnih anestetika aplikovanih intratekalno veoma male i ne omogućavaju adekvatnu krvnu koncentraciju za nastanak patofizioloških efekata.…”