Reliability of the Prognos Electrodermal Device for Measurements of Electrical Skin Resistance at Acupuncture Points

Abstract

Objectives: (1) To characterize and calibrate an electrodermal screening device, Prognos. (2) To replicate a previous test–retest reliability study of this device with measurements of electrical skin resistance (ESR) at 24 Jing-well acupuncture points (APs). (3) To determine measurement precision in three successively more exacting trial protocols on the same set of subjects. Settings: Oregon College of Oriental Medicine and Portland State University, Portland, OR. Instruments: The Prognos device was electrically characterized by a team of research engineers at the Biomedical Signal Processing Laboratory of Portland State University. They determined that Prognos measures the average direct-current (DC) resistance between a metallic wrist strap and an electrode probe tip. The probe tip is connected to a linear spring set to trigger with an optically generated signal at a deflection of 2.62 mm, which corresponds to an average applied force of 2.68 ± 0.04 N (mean ± standard deviation [SD], n = 6). They also determined that the device quantifies resistance by applying a 1.1 µA current for an average of 223 ± 3 ms (n = 7). When calibrated against a series of known resistors, Prognos measures accurately in the range of 150 kΩ to 14.3 MΩ with an error of less than 0.4%. Subjects: Thirty-one (31) healthy volunteers, 17 females and 14 males, 23–63 years of age. Results of reliability test–retest: The mean reliability of a single measurement was; 0.758 for a standard measurement protocol of four sequential sweeps of 24 Jing-well (Ting) APs; 0.851 for four sequential sweeps after ink-marking the APs; and 0.961 for four rapid repeat measurements at each inked AP. Mean absolute values of ESR decreased between the standard and marked protocols, but not between the marked and rapid repeat protocols. Conclusions: Prognos performs accurately, against known resistors over the reported range of ESR. The reliability in the standard protocol (r = 0.758) is comparable to the reliability of 0.721 demonstrated under similar conditions by other investigators. Marking APs, and performing measurements in a rapid sequence, increases reliability of ESR measurements. Increased reliability in the second and third protocols is associated with decreased mean ESR values which may be related to increased accuracy of Prognos probe placement and/or inking the APs.