A standardized bedside test for assessment of peripheral sympathetic nervous function using laser Doppler flowmetry

In spite of increasing knowledge about the role of the sympathetic nervous system in autonomic disturbances like reflex sympathetic dystrophy, no functional test for the peripheral sympathetic system has been introduced into the clinical routine so far. In the development of a standardized bedside test, effects of arousal stimuli [inspiratory gasp (IG) and contralateral cooling (CC)] on blood flow in the fingertips (FTBF) were studied, using laser Doppler flowmetry (LDF). Fifty-two healthy subjects (ages 17 to 75) and 15 patients with sympathetic reflex dystrophy (SRD) underwent the diagnostic procedure. FTBF of healthy subjects during arousal maneuvers showed a reproducible decrease, which is related to a sympathetic vasoconstrictor response. The standardized test procedure with external body heating made interindividual test results comparable. Examination trials with 4 healthy subjects on 10 subsequent days showed good reproducibility. Mathematical analysis of the LDF curves was performed to calculate the degree of FTBF decrease (SRF = (Fmean - Fmin)/Fmean, QI = integral pre/integral post). In contrast to absolute flow values like Fmean and Fmin or time-related parameters like tdecrease and tregeneration, SRF and QI values presented small coefficients of variation (IG test, SRF 25.7, QI 21.7; CC test, SRF 20.0, QI 15.3). The typical decrease of the LDF signal after sympathetic stimulation was absent or diminished in patients with SRD. SRF and QI values showed statistically highly significant differences (P < 0.001) compared to healthy subjects. The presented test appears reliable for the assessment of peripheral sympathetic nervous function. The narrow physiological range of SRF and QI values enabled the differentiation of pathological sympathetic reactions. The test procedure is easy to perform, noninvasive, and practical even in patients with injuries of the upper limbs.