Laser Doppler Assessment of Vasomotor Axon Reflex Responsiveness to Evaluate Neurovascular Function

Abstract

The vasomotor axon reflex can be evoked in peripheral epidermal nociceptive C-fibers to induce local vasodilation. This neurogenic flare response is a measure of C-fiber functional integrity and therefore shows impairment in patients with small fiber neuropathy. Laser Doppler flowmetry (LDF) and laser Doppler imaging (LDI) are both techniques to analyze vasomotor small fiber function by quantifying the integrity of the vasomotor-mediated axon reflex. While LDF assesses the flare response following acetylcholine iontophoresis with temporal resolution at a single defined skin point, LDI records flare responses with spatial and temporal resolution, generating a two-dimensional map of superficial blood flow. LDF is characterized by a high intra- and interindividual measurement variability, which is smaller in LDI due to its spatial resolution. Nevertheless, LDI still lacks standardized methods for image analysis. Consequently, use of the technique currently remains on an experimental level. Here, we sought to review the current literature on laser Doppler assessment of vasomotor function and discuss potential future applications of established techniques as well as those that are still experimental.

Assessment of autonomic innervation of the foot in familial amyloid polyneuropathy

“…Even if the results were analyzed only using the hF/rF variable, LDF did not show good diagnostic performance. This is clearly explained by a large inter‐individual variability, as previously acknowledged . In the present study, LDF assessment was performed in response to local heating but other provocative procedures may be applied, either local, such as painful electrical stimulation or acetylcholine iontophoresis, or general, such as deep inspiration or standing.…”

“…More recently, it was proposed to analyze the vasomotor axon reflex triggered by C‐fibers by using laser Doppler imaging rather than LDF . The quantification of the neurogenic flare response by laser Doppler imaging is a very promising technique to assess the existence of small‐fiber neuropathy with less intra‐ and inter‐individual variability than LDF, although the methods for image analysis remain to be standardized .…”

Autonome Small-Fiber-Neuropathien

“…Die Quantifizierung der im indirekten Areal vermittelten Vasodilatation kann mithilfe der beiden auf dem Doppler-Effekt beruhenden Verfahren "Laser Doppler Flowmetry" (LDF) und "Laser Doppler Imaging" (LDI) erfolgen [6,18]. [18].…”

“…Aktuell wird die LDF vor allem in der klinischen Forschung angewandt und aufgrund des großen technischen Aufwandes nicht routinemäßig in der klinischen Diagnostik. Die LDF eignet sich zudem nicht, um das Ausmaß der gesamtem Axonreflex-bedingten Vasodilatation zu erfassen, da nur an einigen definierten Punkten der Hautoberfläche die Veränderung der Perfusion ermittelt wird [18].…”

“…Die zeitliche Auflösung wird durch die Messung der Hautperfusion vor, während und nach der Iontophorese von ACh bestimmt. Anhand des LDI kann somit ein zweidimensionales Bild der dermalen Hautperfusion erstellt werden [18].…”