A Simple Non-Contact Optical Method to Quantify In-Vivo Sweat Gland Activity and Pulsation

Abstract

Most methods for monitoring sweat gland activity use simple gravimetric methods, which merely measure the average sweat rate of multiple sweat glands over a region of skin. It would be extremely useful to have a method which could quantify individual gland activity in order to improve the treatment of conditions which use sweat tests as a diagnostic tool, such as hyperhidrosis, cystic fibrosis, and peripheral nerve degeneration. Methods: An optical method using an infrared camera to monitor the skin surface temperature was developed. A thermodynamics computer model was then implemented to utilize these skin temperature values along with other environmental parameters, such as ambient temperature and relative humidity, to calculate the sweat rates of individual glands using chemically stimulated and unstimulated sweating. The optical method was also used to monitor sweat pulsation patterns of individual sweat glands. Results: In this preliminary study, the feasibility of the optical approach was demonstrated by measuring sweat rates of individual glands at various bodily locations. Calculated values from this method agree with expected sweat rates given values found in literature. In addition, a lack of pulsatile sweat expulsion was observed during chemically stimulated sweating, and a potential explanation for this phenomenon was proposed. Conclusion: A simple, non-contact optical method to quantify sweat gland activity in-vivo was presented. Significance: This method allows researchers and clinicians to investigate several sweat glands simultaneously, which has the potential to provide more accurate diagnoses and treatment as well as increase the potential utility for wearable sweat sensors.

Simultaneous imaging of multi-pore sweat dynamics and evaporation rate measurement using wind tunnel ventilated capsule with infrared window

“…The most prominent feature of dropwise sweating is its cyclic nature, which has been studied for at least 80 years 64 , 66 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 While observed using various techniques, the reported cycle period matches ours of 1.5–13 s (average of 6.2 s), which can be directly correlated to the oscillatory sympathetic nerve activation of the sweat glands. 77 As previously reported in the literature for thermal sweating on the forehead 74 , 78 and other body parts, 73 Figure 4 A shows that the number of active sweat pores increases with time.…”

“…Figure 1 B shows that the sapphire window is above the exposed skin area and enables high-resolution MWIR thermographic imaging. Out of the numerous sweat visualization approaches that range from applying water-sensitive coatings on skin 2 (or rolling films containing them across forehead 56 ) to advanced two or three-dimensional microscopy, 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 we selected MWIR thermography because it has several advantages demonstrated in prior imaging of mental sweating (i.e., rapid and short-lasting in response to non-thermal stimuli). 65 , 66 The peak in the absorption of water at 3 μm makes the technique sensitive even to thin films of the liquid, 67 , 68 while also providing fast imaging (10 Hz or more) over the relevant area (2 cm 2 ) with resolution sufficient to capture even small sweat pores (∼20 μm).…”

Variations of skin thermal diffusivity on different skin regions

“…As the skin's thermal properties dictate how the heat diffuses through the different skin layers, those parameters are particularly relevant when employing lasers for both cosmetic and non‐cosmetic applications 5 or cryogenic skin cooling 6 . They also play an important role in thermal imaging methods 7–9 …”

“…6 They also play an important role in thermal imaging methods. [7][8][9] Numerous devices have been proposed in the literature to measure the thermal properties of the skin in vivo. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] More recently, wearables have emerged as a solution for continuous monitoring.…”

Advances in Non-Electrochemical Sensing of Human Sweat Biomarkers: From Sweat Sampling to Signal Reading

“…Analyzing sweat offers a non-invasive means for health assessments and disease diagnoses. For instance, cystic fibrosis can be diagnosed based on sweat chloride concentration [8], and indirect assessment of blood glucose concentration can be made based on sweat glucose concentration [9], while the hydration status of the human body can be determined based on the concentration of potassium and sodium ions in sweat [10]. As such, detecting sweat biomarkers has garnered significant attention in recent years, yielding impressive research outcomes.…”