Heart rate variability (HRV) refers to the beat-to-beat variation in the time intervals between heart contractions. This phenomenon reflects physiological processes that are trained in many biofeedback applications. HRV is routinely monitored using an electrocardiograph (ECG) or photoplethysmograph (PPG), supplemented by a respirometer. This article explains the importance of inspecting raw signals, describes the effects of prescription medications and social drugs, identifies common sources of signal contamination, and recommends practical precautions to increase recording fidelity.

Valid electrodermal measurements ensure the integrity of client assessment and biofeedback training. Accurate measurements require understanding of the signal and potential artifacts (sources of contamination) and developing “bulletproof procedures.” Peper, Shaffer, and Lin have recommended the following guidelines for ensuring accurate psychophysiological monitoring: (a) understand the physiological mechanisms that generate the signal, (b) always record and inspect the raw signal because this will allow you to identify artifact, (c) question whether displayed values make sense (e.g., skin conductance levels that rapidly fluctuate, exceed 40 μS/cm2, or fall below 1 μS/cm2 should be suspect in a client who is sitting quietly), (d) recognize the appearance of common artifacts and how they alter derived measurements, and (e) intentionally create artifacts so that you can better recognize them (e.g., rhythmically move the fingers attached to a skin sensor, loosening or tightening the sensors if they are attached with the Velcro® finger straps, and review both the raw signal and calculated skin conductance values). This article reviews the anatomy and physiology, measurement procedures, sources of common artifacts and their control, tracking test for recording electrodermal activity, and common response patterns.

Valid peripheral temperature measurements ensure the integrity of client assessment and biofeedback training. Accurate measurements require understanding of the signal and potential influences on measurement fidelity, and developing bulletproof monitoring procedures. In addition to their use in temperature biofeedback, thermistors can assist heart rate variability biofeedback practice and monitor breathing when a respirometer is not available.

Hagedorn (2014) has highlighted the infection risks in biofeedback and neurofeedback practice and identified broad strategies for mitigating infection risk. In the age of Clostridum difficile, Methicillin-resistant Staphylococcus aureus, and human immunodeficiency virus, infection risk cannot be ignored in any health discipline that attaches sensors to patients' skin in most treatments. The present article discusses specific guidelines for care and hygiene of biofeedback and neurofeedback instruments, encoders, cables, and sensors. Attention to practice standards can greatly reduce the risk to practitioner and client alike.