Clinical biofeedback therapy is one of the many new approaches in health care aimed at helping individuals take responsibility for their well-being, including responsibility for the cognitive, emotional, and behavioral changes needed to effect healthy physiologic change. This article provides a brief survey of biofeedback therapy by defining what biofeedback involves, reviewing the various modalities that it can serve to monitor, discussing major models of biofeedback therapy, and outlining criteria for evaluating the efficacy of biofeedback interventions.
BIOFEEDBACK: BOTH PROCESS AND INSTRUMENTATION
Biofeedback refers to both a process and the instrumentation used in that process.
The process is one of learning to use physiologic information that is monitored and “fed back” through biofeedback instruments. The term dates from 1969, when it was coined to describe laboratory procedures that had been developed in the 1940s in which research subjects learned to modify heart rate, blood flow, and other physiologic functions that were not normally thought of as being subject to conscious control. Feedback itself has been present through much of human history, particularly through the use of mirrored surfaces to practice the expression of emotion.1
Biofeedback instruments monitor one or more physiologic processes, measure what is monitored and transform that measurement into auditory and/or visual signals, and present what is monitored and measured in a simple, direct, and immediate way. Biofeedback equipment typically is noninvasive. The instruments provide continuous monitoring and transformation of physiologic data into understandable feedback for the patient being monitored. Current computerized instruments can provide simultaneous displays and recording of multiple channels of physiologic information. The goal is to enable the individual being monitored to change some physiologic process, guided by the information provided by the biofeedback equipment. How many training sessions are necessary varies with the individual and the disorder, ranging from a few to 50 or more. Our experience is that the great majority of patients obtain benefit in 8 to 12 sessions.
MULTIPLE MODALITIES FOR MONITORING
Multiple modalities can be monitored via biofeedback. Surface electromyography is perhaps the most commonly used instrumentation. Other commonly used measures in a psychophysiologic/biofeedback assessment are respiration rate and depth, skin surface temperature (particularly at the fingertips), cardiovascular reactivity (particularly heart rate and blood pressure), and electrodermal response.2
Feedback of real-time physiologic data is limited only by one’s creativity and technological capabilities. Most of the early noncomputerized equipment provided feedback through the onset and offset of sounds, the changing of tones and volume, the turning on and off of lights, and digital numeric displays indicating both the direction of change and absolute values (such as digital peripheral temperature). Current computerized equipment uses such feedback features as computer games, which the patient “wins” by reaching a goal (such as a systolic blood pressure level below 130 mm Hg), mandalas that can be filled in with colors of the patient’s choosing as he or she progresses in the desired direction, and complex computer-generated figures and graphs.
Electroencephalographic biofeedback (neurofeedback) has become a separate area of study and application, with particular use in the treatment of attention deficit disorder. A baseline electroencephalogram is used in neurofeedback assessment to identify abnormal patterns, and follow-up training is provided to teach the patient to change these patterns in a healthy direction.3
More recently, heart rate variability has come into use as a measure of adaptability or autonomic balance. Soviet scientists were the first to study heart rate variability biofeedback, working with cosmonauts in measuring autonomic function. They found that the low-frequency (0.1-Hz) bands produced the highest frequency-specific oscillations in heart rate variability, and training typically proceeds in increasing amplitude of the low-frequency band (also called the baroreceptor band). Because diminished heart rate variability is a predictor of increased risk for cardiac mortality, teaching patients to increase heart rate variability made sense. The training involves instruction in breathing at an identified resonant frequency that is related to optimal low-frequency band power.4