2.5. Physiological measures
Prior research has introduced that salivary cortisol is an effective
measure of hypothalamic-pituitary-adrenal (HPA) axis activity (Arafah et
al., 2007; Dorn et al., 2007). In this study, Salivettes® (Sarstedt
51.1534.500, Germany) were used to collect saliva samples, and the
salivary cortisol in these samples was assessed by enzyme-linked
immunosorbent assay (Zhuocai, China). Upon arrival at the laboratory,
participants were instructed to rinse their mouth with clear water and
discard the first saliva sample. The experimenter then inserted a cotton
swab from the sampling device into the participant’s mouth using
tweezers, instructing he/she to hold it in the mouth for one minute
before spitting it back into the sampling device. All saliva samples
were stored in a freezer at -20℃ until assay, with intra- and
inter-assay variability both below 10%.
The heart rate data in this study were measured using the Spirit-10
wireless telemetry biofeedback system. This system was connected to a
computer in a control room, which amplified the collected physiological
signals and displayed them on the computer. Electrocardiogram (ECG)
electrodes were placed on the participant’s chest, and ECG data were
analyzed using BioTrace+ (Mind Media, BV Netherlands) at a sampling rate
of 2048 Hz. Heart rate recordings were time-matched with salivary
cortisol sampling, with each sample collected over a period of 5
minutes.