Physiological Reactivity to Functional Tests in Patients with Chronic Low Back Pain

Abstract

Objectives: The aim of the present study was to investigate autonomic regulation at rest and in response to functional laboratory tests in patients with chronic low back pain [CLBP], as well as its possible relations to different characteristics of the clinical picture.

Methods: Ninety-three CLBP patients [47 females, 45 males; age 38 ± 7 years] and 32 healthy normal control subjects [15 females, 16 males; 36 ± 9 years] participated. Subjects were examined according to the McKenzie procedure, and filled in Short Form 36 and Oswestry Disability Questionnaires in addition to self-reports of pain. An electrocardiogram, finger plethysmogram, respiration, and skin conductance were recorded. Functional tests included the Stroop Color-Word test, orthostatic test, paced breathing, and handgrip. A five-minute baseline recording was followed by four counterbalanced functional tests, separated by two- to three-minute long pauses.

Results: An analysis of variance revealed higher baseline heart rate [P = 0.011 in females only], low frequency spectral power [P = 0.001] and electrodermal activity [P = 0.048], and lower high frequency spectral power [P = 0.001]. Each functional test evoked a response, without any group differences in physiological reactivity. There were no significant differences with respect to physiological reactivity between subgroups formed on the basis of prior diagnoses, McKenzie evaluation, VAS pain estimates, Short Form 36, and Oswestry Disability Questionnaire data. The patients did not show high levels of individual response specificity.

Conclusions: Presented data show that patients with CLBP exhibit increased sympathetic tonus in comparison with the control group, regardless of CLBP patients' level of pain, functional disability, or clinical status indices.

KEYWORDS:

• Chronic low back pain
• functional tests
• stress
• stressors
• physiological reactivity