For a PubMed search using the term “Q-Sweat”, only two related articles [8, 10] can be found. Although QSART is an important tool for ANS evaluation, its clinical utility is still limited by its requisite of specialized equipment and its cost [1, 2]. Compared with QSART, the Q-Sweat has a much simpler physiologic set-up. In the meanwhile, the Q-Sweat is reliable, reproducible, and easier to use, operate and maintain. Its study results can be used to estimate the expected QSART findings . However, despite its importance in post-ganglionic sudomotor function evaluation, its clinical use is still limited, at least partially, due to the lack of normal values for reference, particularly among Asians, including the Chinese, who lack a normative database.
As shown in Tables 6
7 and 8, the onset latencies of sweat response are around 2.0 min, which is similar to that reported by Sletten et al. . This may suggest that there is no ethnicity difference in sweat onset time. In the present study, the total volume of sweat responses was generally smaller than that reported by Sletten et al. . It is known that different environmental conditions of study may contribute to the different sweat responses. The present study environment has a larger relative humidity (56% [49%, 61%]) than that of Sletten et al. (25-35%) (Tables 5 and 8) . The room temperature of this study environment is 23°C (19°C, 27°C) compared to 23°C of Sletten et al. . The influence of relative humidity on physiologic condition has also been reported recently by Maughan et al. , who found a similar sweat loss of 60% but higher sweat rate of 80% in relative humidity. In the meanwhile, the mean skin temperature was higher in a relative humidity at 80%. Thus, the physiologic responses may explain the relatively higher skin temperature of 35.5-36.0°C in the present study compared to the 31.1-32.6°C of Sletten et al. . Therefore, the difference in the total volume of sweat response may imply that there is an ethnicity difference in sweat response.
There are studies [13–18] that examine racial or ethnic differences of ANS in different study methods. Although there may be differences in the number of sweat glands among different racial groups, other factors such as acclimatization may also influence the onset and type of sweating processes . In the study of Johnson et al. , there was no significant difference in number of active sweat glands between black and white male subjects. The possible ethnicity difference in sweat response in the Q-Sweat test warrants further large-scale comparison study for better delineation. Nonetheless, the present study shows that the total volume of sweat response recorded at the foot is consistently the smallest when compared to those recorded at the forearm, proximal leg, and distal leg. This finding is also consistent with that reported by Sletten et al.  and is important for a relative comparison in an individual if no normal database is available for reference.
Gender difference is an important factor that may influence the total volume of sweat response (Tables 2 and 6), and this effect on sweat response is also noted in other reports [7, 8, 19]. In the present study (Table 6), the total volume of sweat response in males is about 2.0 times larger than that of females. This difference may be explained by the larger eccrine sweat gland droplets in men despite the same sweat gland density in both sexes .
The BW effect on ANS has been reported before  but all of the reported studies focus on cardiovascular responses that show a hyper-active sympathetic response and a hypo-active parasympathetic response. This change of ANS activity can also be observed in weight changes (weight gain or weight loss) [22–24]. The effect of BW on the sweat response has not been previously reported but in the present study, the BW is another factor that may influence the total volume of sweat response. As shown in Table 7, the total volume of sweat response of the participants with BW ≥62 Kg is about 2.0 times larger than those of the participants with a BW <62 Kg. However, there is an uneven distribution of male participants in the body weight groups, with a high percentage (86%, 64/74) in BW ≥62 Kg group and low percentage (16%,12/76) in BW <62 Kg (Table 7). This uneven distribution of gender percentage in these two different BW groups may have an influence on the sweat response. Further large scale and more even gender distribution studies are needed to establish a better delineation of the BW influence on sweat response.
The total volume of sweat response has a significant negative regression with age only in the foot site recording (Table 3). Based on analysis of the five separated age groups, aging causes lower total volume of sweat response in the foot site recordings (Table 8). Although this finding did not reach statistical significance, this effect of age on total volume of sweat response is also noted in others studies [7, 19] whereby there is a progressive decline in the total volume of sweat response with age in all three lower extremity sites but not the forearm sites. In Table 4, the influence of age may have a similar effect on sweat response, but this difference cannot be drawn from the analysis shown in Table 8 because of the limited participants aged >60 years. In the report of Low et al. , aging has been shown to have selective influence on ANS activities. Of these, cardio-vagal function is known to be influenced significantly but not sweat response . But as shown in the reports of Holowatt et al.  and Kihara et al. , aging may influence the sweat function.
The present study has limitations. First, the case number in the aged participants with complete normal ANS is limited. Second, there is an uneven distribution and gender and BW difference in the study groups. Third, the difference in laterality or sidedness is not examined. Lastly, participants of other ethnicities have not been included for comparison. Further large-scale study is needed to examine the sweat response of different groups of participants.