Application to skin physiology using optical coherence tomography

Background and aims: The sweat glands and peripheral vessels beneath the skin surface act as minute organs governed by the skin sympathetic nerves and have important physiological functions for body temperature control and nutrition support along with maintenance of a peripheral organization. Dynamics of the mental sweating of sweat glands and the peripheral vessels reflect the activity of a sympathetic nerve. The purpose of this paper is to study the dynamic observation and analysis of sweat glands and a peripheral vessels by optical coherence tomography (OCT). Materials and Methods: In the dynamic analysis of mental sweating of sweat glands, after confirmation of the resting state of the volunteer, mental stress was applied in the form of unpleasant sound for 0.5 sec; piled-up en-face OCT images of sweat glands were then obtained time-sequentially, with the frame-spacing of 3.3 sec. A swept-source (SS) OCT was used for in vivo en-face OCT of a group of sweat glands on the subject's fingertip. Furthermore, we conducted in vivo dynamic analysis in response to external mental stress of a peripheral vessel in the second joint of the subject's third finger using 1.3-µm SS OCT. Results: We analyzed time variation in the amount of excess sweat produced by a group of sweat glands and found a large difference in the amount of sweat stored by each sweat gland in the spiral lumen. Mental stress was also shown to cause the small artery of the finger to contract, reducing blood flow. In particular, the thickness of the tunica media of the small artery changed abruptly in response to the sound stress, increasing and then decreasing so that the artery contracted and expanded, respectively. Conclusions: Dynamic analysis of mental sweating in the eccrine sweat glands and changes in peripheral vessels was performed using time-sequential OCT imaging. For mental sweating, time variation in the amount of excess sweat produced could be simultaneously evaluated for a few tens of eccrine sweat glands. Furthermore, we performed the dynamic analysis of a peripheral vessel in a human finger in response to external mental stress and found that the small artery contracted and expanded in response to sound stress while continuing to pulse in synchronization with the heartbeat. These studies have the potential for establishing new knowledge about skin physiology.