Background & Aims
An interaction between descending pain modulation (DPM) and the autonomic nervous system (ANS) has been reported [1]. For example, healthy individuals showed a significant correlation between ANS activity and DPM [2]. Patients with fibromyalgia and irritable bowel syndrome were also examined [3]. However, individuals with chronic knee pain (CKP) have not been examined.
This observational study examined the association between DPM and ANS activity. We hypothesized that sympathetic and parasympathetic nervous system activities are associated with DPM as measured by conditioned pain modulation (CPM) protocol.
Methods
Participants were recruited from the International University of Health and Welfare Narita and Ichikawa Hospital between February and November 2023. Women with CKP aged 20–80 years were included. Patients with cardiopulmonary, vascular, or nervous system disorders were excluded.
Following 15-min REST period, the participants immersed the right hand into 8–12?C water (3 min, COLD). Pressure pain threshold (PPT) was measured in the left upper trapezius. The CPM effect was calculated as PPT(COLD) -PPT(REST). Heart rate variability was simultaneously measured during the CPM protocol. Low/high frequency (LF/HF) and HFnorm indicated sympathetic and parasympathetic nervous system activities, respectively [4]. Similar to the CPM effect, differences from COLD to REST in autonomic activities were expressed as ?LF/HF and ?HFnorm. Associations between the CPM effect and ?LF/HF (or ?HFnorm) were analyzed by simple linear regression with statistical significance at p<0.05.
Results
Forty-two females were screened, and 10 were excluded because they were aged >80 years (n=3) or had no chronic pain (n=7). There were 32 participants (mean age; 64.4±10.1). In the numerical rating scale, average pain intensity was 3.8±1.8. Four participants had negative CPM effect (-0.3±0.2), indicating central sensitization [5].
Simple linear regression analysis showed a significant association between CPM effect and ?LF/HF (p<0.01, B=-3.83 [95% CI; -6.38–-1.27], R2=0.238). However, ?HFnorm was not significant in the regression analysis (p=0.178, B=12.8 [95% CI; -6.18–31.9], R2=0.060).
Conclusions
Our results suggest an association between DPM and sympathetic nervous system activity. However, parasympathetic nervous system activity was not associated with CPM. Because an association between DPM and elevated blood pressure has been reported [6], only sympathetic nervous system activity may interact with DPM. Further studies are required to explore the etiology of CKP.
References
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Presenting Author
Hironobu Uzawa
Poster Authors
Hironobu Uzawa
PhD
International University of Health and Welfare
Lead Author
Kenichiro Takeshima
MD
Department of Orthopedic Surgery, International University of Health and Welfare Narita Hospital
Lead Author
Toshiro Otani
MD
Department of Orthopedic Surgery, International University of Health and Welfare Ichikawa Hospital
Lead Author
Yusuke Nishida
PhD
Department of Physical Therapy, International University of Health and Welare
Lead Author
Topics
- Specific Pain Conditions/Pain in Specific Populations: Rheumatology, Arthritis, and Other