Comparison of sweat gland output on the dorsal aspect of the forearm and foot

The quantitative sudomotor axon reflex test (QSART) relies on an approximate estimate of local sweat volume following iontophoresis of a 10% acetylcholine solution to the skin. This test relies on an axon reflex mediated by postganglionic sympathetic sudomotor nerves and is used to detect small fiber peripheral neuropathy. We have used intradermal electrical stimulation to elicit a direct local sweating response in a reliable and dose dependent manner in forearm skin. We applied this model of sweat induction to the dorsal foot to elucidate any dose response differences at these two skin sites. We hypothesize that the sweat volume response curve will be similar for the foot and forearm. The local sweat rate (LSR) was determined with a small sweat capsule (0.53 cm 2 ) flushed with dry air (100 ml/min) while monitoring air temperature and relative humidity of the air leaving the sweat capsule. A constant 5 mA electrical stimulus was applied to the intradermal space at 10 different frequencies (0.2, 1, 2, 4, 8,10, 12, 16, 32, and 64 Hz) to generate the stimulus-response curve. Subjects rested in a dental chair at an ambient temperature of 28°C. The data (mean ± 1 SD, n=8,4 F, 4 M) revealed that the stimulus-response curves were significantly different (p<0.001) in the foot and forearm. The response curve for the foot was shifted upward at the lowest three stimulus frequencies (0.2 Hz 0.042 ± 0.117 and 1.155 ± 0.955 mg•cm 2 ; 1Hz 0.039 ± 0.057 and 1.162 ± 0.805 mg•cm 2 : and 2 Hz 0.390 ± 0.406 and 1.596 ± 1.205 mg • cm 2 , forearm and foot respectively). The significantly higher baseline suggests indicates that the foot was slightly more sensitive to intradermal electrical stimulation than the forearm. Normalizing the sweat volume output to the peak sweat output did not alter the dose-response curve. Sweat output expressed as a % of max area under the curve revealed a 21 % increase in sweat output (AUC, % max) for the foot between stimulus frequencies 0.2, 1, 2, and 4 Hz. Our data indicate that using a single stimulus intensity to compare sweating capacity between the foot and forearm will be biased depending on the magnitude of the stimulus. Funding from the Department of Exercise Sciences This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.