QDIRT: quantitative direct and indirect test of sudomotor function

Area of Science:

• Physiology
• Biomedical Engineering
• Dermatology

Background:

• Current methods for assessing postganglionic sudomotor function, such as the quantitative sudomotor axon reflex test (QSART) and silicone impressions, have limitations.
• Advancements in high-resolution digital photography offer potential for developing novel, quantitative assessment techniques.

Purpose of the Study:

• To develop and validate a novel assessment of sudomotor function using digital photography, termed Quantitative Direct and Indirect Reflex Testing of Sudomotor Function (QDIRT).
• To compare the spatial and temporal resolution of QDIRT with established methods like QSART and silicone impressions.

Main Methods:

• Sweating was induced via acetylcholine iontophoresis in human subjects.
• Silicone impressions and digital photography of topical indicator dyes were used to capture sweat responses.
• QDIRT measurements were compared with silicone impressions and QSART on the forearm and dorsal foot.

Main Results:

• QDIRT's photographic sweat imaging showed strong correlation with silicone impressions for percent sweat area on both forearm and foot.
• The number of sweat droplets quantified by QDIRT correlated with silicone impressions, though QDIRT identified fewer droplets.
• QDIRT-assessed sweat response and onset latency correlated significantly with QSART measurements on the foot.

Conclusions:

• Quantitative Direct and Indirect Reflex Testing of Sudomotor Function (QDIRT) effectively measures both direct and indirect sudomotor responses.
• QDIRT provides spatial resolution comparable to silicone impressions and temporal resolution similar to QSART.
• QDIRT represents a novel and potentially valuable tool for evaluating postganglionic sudomotor function.