Vascular and psychophysical effects of topical capsaicin application to orofacial tissues

Abstract

Aims: To characterize and contrast human sensory and vascular changes produced by topical application of the algesic chemical capsaicin to the glabrous lips and tongue.

Methods: Applications of 1% capsaicin or vehicle cream to the glabrous lips and tongue were randomized between two two-trial sessions. The capsaicin trial followed the vehicle trial for each session. Before and 5, 15, and 30 minutes after capsaicin or vehicle cream application, six parameters were recorded from the glabrous lips or the tongue dorsum: (1) burning pain intensity, as measured on a visual analog scale; (2) burning pain area, as indicated by subjects on an orofacial drawing; (3) mechanical sensitivity, as measured by a von Frey filament; (4) visual flare; (5) blood flow and temperature, as measured by laser-Doppler imaging and thermography, respectively; and (6) areas of increased temperature (hot spots), as calculated by a digital tracer from the thermographs. Data were analyzed by ANOVAs and Pearson's correlations.

Results: Compared to vehicle application, capsaicin elicited burning pain, increases in blood flow and temperature, but no change in mechanical sensitivity in the glabrous lips or tongue. Greater increases in blood flow and temperature paralleled more intense burning pain and larger areas of perceived pain for the lips compared to the tongue. The location of distinct areas of increased temperature within the orofacial area differed between the capsaicin-lip and capsaicin-tongue trials.

Conclusion: The several differences between these responses to noxious stimulation of the glabrous lips and tongue may have implications for examinations of orofacial somatosensory functions.

Fig 1

Illustration of the relative sizes, locations, and areas used for assessing changes in blood flow and temperature with respect to the capsaicin and vehicle application area (Drawing not to scale).

Fig 2

The burning pain intensity of the glabrous lips and tongue of all subjects for the capsaicin-lip and capsaicin-tongue trials, respectively. No burning pain intensity was reported for the vehicle-lip and vehicle-tongue trials (data not shown). *Represents significant difference between burning pain intensity for the lip and tongue trials. → Represents significant decrease in burning pain intensity with respect to time. All data are presented as mean (± SEM).

Fig 3

The mechanical sensitivity of the upper (a) and lower (b) lips and tongue site (c) before, 5, 15, and 30 minutes after capsaicin or vehicle application. All data are presented as mean (± SEM).

Fig 4

Correlation between blood flow and temperature with respect to time for the whole tongue (Pearson’s correlation = 0.18, P = .24), tongue site (Pearson’s correlation = 0.39, P = .003), and glabrous lips (Pearson’s correlation = 0.50, P = .003). All data are presented as mean (± SEM).

Fig 5

The life-sized areas of increased temperature, visible flare, and burning pain within the orofacial area before, 5, 15, and 30 minutes after capsaicin application to the (a) glabrous lips and (b) tongue dorsum. All data are presented as mean (± SEM).