Reliability of prognos, an acupoint electrodermal measuring device
Colbert AP 1//Hammerschlag R 2//Aickin M 3//McNames J 4
Research Fellow, Kaiser-Permanente Center for Health Research, Portland, OR [1]//research Director, Oregon College of Oriental Medicine, Portland, OR [2]//Senior Investigator, Kaiser-Permanente Center for Health Research, Portland, OR [3]//Director, Biomedical Signal Processing Laboratory, Portland State University. Portland, OR [4]
Background: Despite a paucity of literature documenting instrument calibration and measurement reliability studies, electrodermal screening systems employing various devices and techniques are widely used by clinicians to calculate electrical skin resistance/conductance (ESR) at acupuncture points (APs). Some researchers propose that ESR at APs may be used to indicate the body's biological energy, in much the same way that electrocardiograms and electro-encephalograms are used to measure the electrical fields of the heart and brain. Prior to establishing ESR recordings at APs as conventional biomarkers, however, the fundamental issue of determining whether commercially available instruments provide reproducible results must be addressed. The Prognosdevice, developed by Russian engineers for use by cosmonauts, is one of the few devices to have undergone rigorous reliability testing (Treugut et al. Forsch Komple-mentarmed 1998;5:284-289). In the present study we attempted to replicate Treugut et al's findings, as the first step in a program of research directed at standardizing ESR measurements at APs for use in diagnosing, screening and monitoring the course of illness.
Objectives: 1) Characterize the Prognos device electronically to compare performance with the manufacturer's technical specifications; 2) Determine test-retest reliability of Prognos for measuring ESR at the 24 Jing-well APs. Design: 1) Device characterization of the Prognos by a team of research engineers; 2) Test-retest reliability assessment at the Jing-well APs on 31 subjects in, three consecutive trials designed to progressively minimize measurement error. Trial 1: Four consecutive sweeps of all 24 APs. Trial 2: Four consecutive sweeps of all 24 APs after marking each AP with non-toxic ink. Trial 3: Fourrepeat measures at each successive marked AP. Participants (clinical study): Thirty-one healthy volunteers, 17 females and 14 males, aged 23-65 years (mean 32.7). Inclusion criteria: ³18 years of age. Exclusion criteria: acute or chronic health problems; visually observable aberrant skin conditions at or near the Jing-well APs.
Results: Device characterization: Prognos measures the average DC resistance between an electrode probe tip and a metallic wrist strap. The 4.7 mm diameter probe tip used to measure impedance is connected to a linear spring that triggers at a deflection of 2.62 mm and an averageforce of 2.68 ± 0.04 N (mean ± SD, n=6). The device quantifies resistance by applying a 1.1 A current for 223±3 msec (N=7) and measures the resulting voltage. Accuracy of measurements was tested with a series of linear resistors and compared to the resistance recorded by a Fluke 187 digital multimeter. Prognos accurately measures in the range of 150 k to 14.3 M with an error of less than 0.4%. Clinical reliability testing: Mean reliability for a single measurement was: 0.757 (Trial 1), 0.851 (Trial 2), and 0.961 (Trial 3). Mean absolute values of ESR at all but 2 Aps decreased significantly between Trials 1 and 2 with no significant decrease in mean ESR between Trials 2 & 3.
Conclusions: The Prognos device performed accurately and in accordance with the manufacturer's technical specifications. The test-retest reliability obtained in Trial 1 (r= 0.757) compares favorably to that found by Treugut et al, 1998 (r= 0.721). This level of reliability is commensurate with that of blood pressure measurements performed in research settings. Marking APs with non-toxic ink appears to increase reliability of ESR measurements at Jing-well APs. However, associated with the increased reliability over the 3 trials was a decrease in mean ESR from Trial 1 to Trial 2. This may be due to a -treatment' effect associated with repetitive measurement stimulation of the APs and/or a result of the constituents and properties of the ink used for marking the points. These two possibilities are under further investigation. Additional issues to be explored in our program of research will be: within-subject variability over time and the reliability of Prognos measurements on APs other than Jing-well points.
Sponsors: Oregon Center for Complementary and Alternative Medicine, supported by the National Center for Complementary and Alternative Medicine/National Institutes of Health. } 7
