Quantitative measurement of sweating rate is a useful indicator of the state of autonomic nerves and related factors such as stress response or body temperature regulation. Specifically, it is known that mental stress increases mental sweating, and deep body temperature and dehydration increase thermal sweating. Therefore, continuous sweat measurement with a small sweating rate meter is expected to be useful for the management of mental stress as well as the prevention of heat stroke. In this study, two small sweating rate meters, one having high resolution and the other having a large dynamic range, were developed and used to measure mental sweating and thermal sweating. These devices determine the sweating rate by the conventional method, which measures the humidity difference between ambient air and air moistened by sweat. Measurement resolution and dynamic range can be adjusted by controlling the air flow rate. The device for measuring mental sweating rate consists of a main body, which has an air pump and two humidity sensors, and a capsule connected to the main body by tubes in which air flows. The device for measuring thermal sweating rate has a pump and two humidity sensors, an aperture instead of a capsule, and a flow channel on a flexible substrate. The mental sweating rates during arithmetic and speech tasks were measured on the plantar aspect of the big toe using the mental sweating rate meter. The present study on part of the sole showed two sweating types ; a reaction type and a low-reaction type. During the mental stress tasks, sweating rate increased by 0.43 mg/min/cm2 compared to that at rest in reaction type subjects, but by less than 0.1 mg/min/cm2 in low-reaction type subjects, showing very low responses to stimulations. The thermal sweating rate during immersion of the lower legs in warm water was measured using the thermal sweating meter worn on the forearm. Sweating rate increased by approximately 0.4 mg/min/cm2 on average due to thermal stress, and was also successfully measured. These results show that the small sweating rate meters developed in this study can be used for measuring mental and thermal sweating rates.
The skeletal muscle pump and the respiratory pump play important adjunctive roles in preventing excessive orthostatic venous pooling by promoting venous return, but the nature of their interactions remains unclear. This study sought to examine the interaction between muscle pump and respiratory pump functions and cardiovascular and autonomic responses to orthostatic stress. Thirteen healthy volunteers (11 males and 2 females, aged 22 ± 0.8 years) participated in the study. After 3 min of sitting (SIT) followed by 3 min of quiet standing (QS), the subject performed repetitive heel up (HUP) maneuvers at 10 cycles/min for 6 min while standing. HUP was initiated either at the onset of inspiration (Insp) or at the onset of expiration (Exp). Respiratory flow, R-R interval (RRI), and beat-to-beat blood pressure (BP) were determined using a hot-wire flowmeter, electrocardiography, and a Finapres device, respectively. From the continuous BP measurement, beat-by-beat stroke volume (SV) was estimated using the pulse-contour method and cardiac output (CO) was calculated as SV multiplied by heart rate. Using spectral analysis, RRI variability was analyzed for the low- (LF) and high-frequency (HF) bands. The following three periods were analyzed separately : 2 min of steady state SIT (0-2 min from the start of recording), 2 min of QS (1-3 min from the start of standing), and the final 2 min of HUP. Reductions in SV and CO during QS were suppressed by HUP (p < 0.01) in both Exp and Insp conditions. Systolic BP was increased during HUP compared with QS under Exp condition (p < 0.01). HUP in the Insp condition led to an increase in HF power (p < 0.01) and a decrease in LF-to-HF ratio (p < 0.01) compared to Exp, indicating a shift of the sympathovagal balance toward parasympathetic activation. In contrast, the sympathovagal balance shifted towards sympathetic predominance in the Exp condition. These results suggest that cardiovascular and autonomic responses are influenced by the timing of HUP with respect to breathing during standing.
Monitoring heart rate (HR) during exercise can be used not only for early detection of a change in physical condition but also as an indication of the exercise training condition. Photoplethysmography (PPG) is a simple and non-invasive method for HR sensing, but its use during exercise is difficult, since the PPG output is contaminated with motion artifact (MA). Especially for vigorous exercise, MA has the same frequency component as that of blood volume pulses (BVPs) in the PPG output, and no linear MA cancellation technique such as band pass filtering (BPF) can work effectively. This paper proposes a PPG-based MA canceling HR sensor. It is equipped with two sensors ; one is a normal PPG sensor with a light emitting diode (LED)/photo detector (PD) that contacts the skin to detect BVPs andMA, andthe other is an MA sensor with a LED/PD that does not contact the skin to detect only MA. Applying the outputs from the two sensors to an adaptive filter, the BVPs can be obtained easily. We evaluated the performance of the proposed HR sensor in ten subjects who performeda series of resting, walking, running andjumping. The results revealedthat the proposedHR sensor, together with an outlier rejection method, achieved root mean square errors (RMSEs) of 7.1 bpm, 6.4 bpm and6.1 bpm for walking, running andjumping, respectively, when using a Holter monitor as the reference. These results imply a reduction of RMSE by a maximum of 83% compared to no MA cancellation.