Induction of chronic non-inflammatory widespread pain increases cardiac sympathetic modulation in rats
- Source: Autonomic Neuroscience, Jan 21, 2012
By LR Oliveira, VJ Santana-Filho, et al.
[Note: The autonomic nervous system works below the level of consciousness to maintain the body’s balance – regulating blood pressure, pulse, breathing rates, etc. as needed in response to changing physical demands. Two parts of the system are sympathetic function, which involves ‘pushing’, balanced by parasympathic function, which involves relaxing. One type of autonomic dysregulation is when heart rate increases and blood pressure/volume decreases abnormally on standing, causing faint feeling (postural orthostatic tachycardia syndrome - POTS).]
Fibromyalgia (FM) is characterized by chronic non-inflammatory widespread pain (CWP) and changes in sympathetic function. In attempt to elucidate the pathophysiological mechanisms of FM we used a well-established CWP animal model.
We aimed to evaluate changes in cardiac autonomic balance and baroreflex function in response to CWP induction in rats. [Baroreflex function refers to the body’s mechanism for maintaining blood pressure.] CWP was induced by two injections of acidic saline (pH 4.0, n=8) five days apart into the left gastrocnemius muscle. Control animals were injected twice with normal saline (pH 7.2, n=6).
One day after the second injection of acidic saline or normal saline, the animals had pulse interval (PI) and systolic arterial pressure (SAP) variability, and spontaneous baroreflex sensitivity (BRS) evaluated.
After induction of CWP, there was an increase of power in the low frequency (LF) band of PI spectrum (12.75±1.04nu), a decrease in the high frequency (HF) band (87.25±1.04nu) and an increase of LF/HF ratio (0.16±0.01), when compared to control animals (7.83±1.13nu LF; 92.16±1.13nu HF; 0.08±0.01 LF/HF).
In addition, there was an increase of power in the LF band of SAP spectrum (7.93±1.39mmHg(2)) when compared to control animals (2.97±0.61mmHg(2)). BRS was lower in acidic saline injected rats (0.59±0.06ms/mmHg) when compared to control animals (0.71±0.03ms/mmHg).
Our results showed that induction of chronic widespread pain in rats shifts cardiac sympathovagal balance towards sympathetic [pushing] predominance and decreases BRS [blood pressure/flow]. These data corroborate findings in humans with FM.
Source: Autonomic Neuroscience, Jan 21, 2012. Department of Physiology, Federal University of Sergipe, Sao Cristovao, Brazil; Graduate Program in Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, USA. [Email: firstname.lastname@example.org]