The potential of biofeedback therapies in cardiovascular disease is only recently beginning to be explored in a systematic way. This article reviews the rationale for the use of biofeedback therapy in cardiovascular disease and briefly surveys research on the usefulness of biofeedback for several specific cardiovascular parameters and conditions.
RECOGNIZING THE POTENTIAL OF BIOFEEDBACK IN CARDIOVASCULAR DISEASE
Biofeedback is part of a group of modalities known as “self-regulation therapies,” in which a subject is taught to control the activities of his or her autonomic nervous system. The autonomic nervous system has also been called the “visceral,” “involuntary,” and “automatic” nervous system, which suggests that the physiologic processes governed by this branch of the nervous system are largely beyond conscious control. Until the 1950s, this was largely believed to be true. Physicians and scientists had been convinced that the functions regulated by the sympathetic and parasympathetic branches of the autonomic nervous system, such as digestion, blood pressure, and body temperature, were not amenable to self-regulation.
During the 1950s, however, it became clear that functions of the autonomic nervous system could be controlled by conscious thought and training. Subjects could be taught to correctly perceive and also to control heart rate, blood pressure, skin temperature, and other seemingly involuntary functions. The field of biofeedback and applied psychophysiology became possible with these discoveries and with the advent of technologies capable of measuring physiologic variables with enough sensitivity to detect small changes.
Key role of sympathetic/parasympathetic balance
In cardiovascular medicine, biofeedback has a great deal of therapeutic potential because many diseases of the heart and vasculature involve inappropriate regulation of the autonomic nervous system.
Under normal conditions, the sympathetic branch of the autonomic nervous system serves to augment cardiac function in times of stress, increasing heart rate, contractility, and blood pressure, as well as favoring clotting processes that would be mainly adaptive during the “fight or flight” response. The parasympathetic branch of the autonomic nervous system plays the opposite role during health, exerting a calming influence on cardiovascular function.
Normal cardiovascular function is regulated by a balance between sympathetic and parasympathetic inputs to the heart and blood vessels. Heart rate, for example, is governed by the parasympathetic nervous system under resting conditions, when the intrinsic firing rate of the sinus node is decreased by vagal input. Under stressful conditions, this inhibition is released and sympathetic excitation can increase the heart rate even further. In many pathological cardiac conditions, such as arrhythmias, an imbalance between the two branches of the autonomic nervous system causes at least some of the disease manifestations and often contributes to progression.
Biofeedback as a ‘physiologic beta-blocker’
Another good example is heart failure, where over-activation of the sympathetic nervous system results in many of the phenotypic changes in the myocardium and contributes to the downward spiral from compensatory cardiac hypertrophy to end-stage decompensated failure. The role of sympathetic overactivation in heart failure is clearly evident by the success of beta-adrenergic blocking agents in ameliorating symptoms and delaying disease progression. Given the role of autonomic nervous system dysregulation in cardiovascular diseases, biofeedback therapy has the potential to teach patients a skill that may allow them to decrease activation of their autonomic nervous system, theoretically acting as a “physiologic beta-blocker.”
An adjunct to stress management
The potential of biofeedback to have an impact in the arena of cardiovascular disease has not been well explored. Clinically, biofeedback is often used in the context of stress management programs, but biofeedback is not synonymous with stress management. Stress management programs most commonly involve some type of relaxation training and perhaps cognitive behavioral therapy. Biofeedback can be used to augment relaxation, helping the subject to be more aware of physiologic responses and thus be better able to elicit the relaxation response. Biofeedback can also be used to train subjects to control particular physiologic responses that contribute to symptoms or to disease progression. In cardiovascular disease, although stress management is frequently a component of cardiac rehabilitation programs, the question of whether stress management is more effective with or without biofeedback has not been systematically investigated.
PIONEERING STUDIES OF BIOFEEDBACK IN CARDIOVASCULAR DISEASE
Some of the earliest studies of physiologic regulation using biofeedback were attempted in patients with cardiovascular abnormalities. In 1971, Weiss and Engel reported success in using operant conditioning of heart rate in eight patients with premature ventricular contractions.1 All eight patients were able to achieve some degree of control, and five of the patients were able to decrease the frequency of premature beats, demonstrating increased success over a 21-month follow-up period. Interestingly, use of pharmacologic agents to understand the mechanisms of control suggested that one patient was able to decrease sympathetic control of his heart rate while another increased the parasympathetic influence.
Several years later, Pickering and Gorham reported their work with a single subject, a 31-year-old woman who had a ventricular parasystolic rhythm.2 Using a biofeedback technique, they were able to teach the woman to voluntarily control her heart rate, demonstrating that she could both increase and decrease the rate, avoiding the ranges in which the arrhythmia occurred. In the same year, Benson et al demonstrated that they could teach patients the relaxation response and decrease the incidence of premature ventricular contractions.3 Using Holter monitors for validation, these investigators showed that 4 weeks of relaxation training resulted in 8 of 11 patients being able to control their heart rates sufficiently to have therapeutic impact.
These pioneering studies were very early in the development of the field of biofeedback, but they showed what has been clearly established since—that the input of the autonomic nervous system to the heart can be regulated by biofeedback techniques.