Abstract
This study will identify that patients with chronic neck pain have an altered autonomic functioning compared to a control group, and that manipulation might directly influence the autonomic nervous system as measured by using a fully automated pupillometry system. Subjects. 100 chronic pain patients and 50 control subjects participated in this study to achieve a power of 0.80, effect size of 0.5, and a type I error rate of 0.05 for two-tailed hypothesis testing. Method. A quasi-experimental design was be used. The ANOVA and Chi square test were used to establish homogeneity of baseline characteristics. The Mann-Whitney U test was performed to compare the pre-intervention pupil diameter amongst the groups. The Friedman's test was used to determine the pupil diameter change during the three measurements. The Wilcoxen Signed-ranks test was used to analyze the difference in pupil size between the pre- and post-intervention measures and to determine if there was a difference in pupil diameter between the two groups undergoing the thoracic manipulation. The Kruskal-Wallis test was used to compare the pupil diameter change to the presence of joint sounds. And the Fisher's Exact test was used to determine the relationship between the number of pops and the VAS change score > 13mm. Results . This study demonstrated that the chronic pain group had a statistically significant smaller pupil diameter than the healthy control group (P=0.022). Manipulation resulted in a relative increase in pupil diameter following the manipulation, however this was not statistical significant. There was a statistical significant decrease in pupil diameter in the placebo group (p<0.001). This study showed that the presence of joint sounds during manipulation does not affect the change in pupil diameter or the change in pain perception. There was no relationship demonstrated between the Neck Disability Index and the pupil diameter change. Conclusions. It appears that a T3-T4 manipulation results in a relative non-specific increase in sympathetic activity. Recommendations. Manipulation may be used by physical therapists to affect the autonomic nervous system. Visual pupil assessment may become part of the evaluation process to identify patients that might present with autonomic dysfunction and to determine the effect of treatment modalities.