///2009 Abstract Details
2009 Abstract Details2019-08-03T15:55:31-06:00

The effect of autonomic nervous system balance at rest and during parasympathetic challenge on heart rate and blood pressure following spinal anesthesia

Abstract Number: 8
Abstract Type: Original Research

Paloma Toledo M.D.1 ; Cynthia A Wong M.D.2; Sarah Olson M.D.3; Nirav K Shah M.D.4; John T Sullivan M.D.5

Introduction: Responses to autonomic nervous system (ANS) stimuli in term pregnant women suggest a reduction in baroreflex gain (1). Spectral analysis of respiratory sinus arrhythmia (RSA) signal provides an indication of where, within the frequency domain, the vagus nerve is influencing the heart (2). Continuous evaluation of wavelet transforms (CWT) of both RSA and heart rate variability (HRV) allows spectral monitoring of both autonomic branches. The purpose of this study was to evaluate whether ANS activity at rest and in response to a parasympathetic challenge (deep breathing) using CWT predict hemodynamic response to spinal anesthesia in healthy parturients scheduled for elective cesarean delivery.

Methods: Testing was performed using the ANX 3.0 testing system (Ansar Group, Inc., Philadelphia, PA). The testing sequence consisted of 5-min baseline rest period followed by 1-min of deep breathing. Data were analyzed by evaluating the low frequency (LFa) and respiratory frequency (RFa) domains of the HRV spectrum and the ratios of LFa/RFa. Subjects were classified as sympathetically dominant (SD) at rest if the LFa/RFa > 3.0 and a positive parasympathetic response (+PR) to deep breathing was defined as a LFa/RFa < 0.5. Mean sitting BP and HR were recorded just before spinal administration of hyperbaric bupivacaine 12 mg/ fentanyl 15 g/morphine 150 g, until the delivery of the infant. Baseline and post-spinal anesthesia data were compared between those who were SD and those not, and those with a +PR, and those without using grouped t-tests.

Results: 86 women were studied. Subjects demonstrating SD at rest (n=32)demonstrated higher basal HR and longer times to the lowest blood pressure following spinal drug administration than subjects with LFa/RFa s < 3 (Table). Failure to demonstrate an increase in parasympathetic dominance during deep breathing (n=42) was associated with lower mean pressures in response to drug administration.

Discussion: These findings suggest that resting SD alone cannot predict adverse hemodynamic changes associated with the induction of spinal anesthesia. The finding of a reduced hemodynamic response to an parasympathetic challenge is consistent with findings from previous studies (3). A better understanding of the ANS balance and response to challenges may help guide appropriate therapeutic interventions in parturients.


1)Br J Anaesthesia 2000; 84: 323-9

2)Clin Auton Res. 1996; 6:321-7

3)Anesthesiology 2007; A663

SOAP 2009