Dr. Motoyama was not the first person to measure energy flow in the body beyond the electrical energies of the heart and brain. In the 1950s, a German physician named Reinhold Voll merged his understanding of acupuncture and electricity to create an electroacupuncture system. His original instrument was later modified and simplified by his student Helmut Schimmel. The system was called the “EAV.”  Later generations were called “VEGA.” Since then dozens of variations from many companies have appeared. A more generic term has been adopted, electrodermal testing. Sometimes you will find another label applied: MSA or Meridian Stress Assessment.
All these devices, like Dr. Motoyama’s AMI, measure the galvanic response of the skin. Skeptics believe that, since these devices are just simple galvanometers that measure the resistivity of the skin surface, they have no diagnostic value. Proponents argue that the body’s meridians are low resistance pathways along which Chi (i.e., electromagnetic fields) flow. When a pathway is no longer showing low resistance, the meridian has become blocked and the Chi is no longer flowing properly.
These concerns include variations in results depending upon the operator and variations in interpretation by operators who have different levels of experience. In the EAV and VEGA devices, the degree of pressure being applied to the probe affects the strength of the signal received. If one operator pushes a little harder than another operator, the results will be very different. The Prognos avoids this problem by incorporating a feedback sound indicating when the right amount of pressure has been applied. The probe’s spring-loaded tip ensures that a constant pressure is applied. 
The Prognos software also interprets the readings directly, rather than leaving it up to the operator. Within its database the Prognos stores standard meridian readings that are used to calibrate the results and determine if the subject is being stressed due to a wide variety of causes: bacterial infection, parasite infection, toxicity due to metals, hormone or vitamin deficiencies, etc. 
The whole area of measuring energy along meridians has engendered strong opinions by both proponents and skeptics. The interested reader may wish to investigate both sides of this debate further. For the skeptics’ view, visit Quackwatch, which has compiled a good report on Quack Electrodiagnostic Devices.  From the other side, the CIHS has presented research it has been involved with and other’s findings that support the case for these devices.
- — Electro-Acupuncture, according to Voll.
- — This question of variability and reliability of the Prognos was the subject of a study in 2004 by the University of Portland’s Kaiser-Permanente Center for Health Research. The first objective of the study was “to characterize and calibrate an electrodermal screening device.” The team concluded “Prognos performs accurately, against known resistors over the reported range of electrical skin resistance.”
- — Unlike the AMI the Prognos is being offered to anyone so there is a good chance that the reader may be able to find a naturopath who uses the Prognos. The earlier VEGA devices are even more widely used but do suffer from the dual drawbacks of variability in results and interpretation.
- — www.quackwatch.org/01QuackeryRelatedTopics/electro.html.
Our exploration of the energy body, the second kosha, has revealed benefits of the Yin Yoga practice beyond those we discovered in the physical body. The Eastern understanding of energy was developed through centuries of experience: trials and errors. The maps written by the ancient yogis show within the body pathways of communication along which healing energies spread out and help maintain or heal the body. We discovered that recent investigations in the West have uncovered similar pathways for communication, and multiple energetic media that also nurture the body. The exercises and massages incorporated into our yoga practice stimulate these energies and open the pathways, allowing healing information to flow unimpeded throughout our systems. With this understanding in mind, our journey now takes us to the deeper koshas, where we will discover how Yin Yoga can assist in promoting our mental and emotional health.