Biofeedback therapy in cardiovascular disease: Rationale and research overview
ABSTRACT
Biofeedback has much therapeutic potential in cardiovascular diseases, since many of these diseases involve dysregulation of the autonomic nervous system. Studies have clearly demonstrated that patients can use biofeedback techniques to regulate the input of the autonomic nervous system to the heart, but the clinical utility of these techniques has not been well explored in systematic trials. Much biofeedback research to date has focused on patients with hypertension, but outcomes have been inconclusive. Preliminary studies suggest that heart rate variability biofeedback may be useful in improving symptoms and quality of life in patients with cardiac disease, and early studies suggest a possible effect of biofeedback on remodeling of the failing heart. Both of these areas require further research, however. Biofeedback is increasingly used as an adjunct to stress management in cardiac rehabilitation programs, providing the impetus for a large-scale, systematic study of self-regulation in cardiac disease.
BIOFEEDBACK STUDIES OF SPECIFIC CARDIOVASCULAR PARAMETERS AND DISEASES
A host of parameters for assessment
Many cardiovascular parameters can be used for biofeedback. Commonly these include heart rate, blood pressure, skin temperature, and, more recently, heart rate variability. In each case, the parameter is measured and displayed for the subject, and the subject is taught to make it change in a positive direction through relaxation, thought patterns, imagery, or some combination of techniques. Many times the display of the physiologic parameter and the demonstration that it can be controlled are quite surprising to the subject and lead to an enhanced desire to participate in the therapy.
Heart rate variability: A focus of recent interest
The newest parameter in use, and one that has gained considerable interest in the field of cardiovascular biofeedback, is heart rate variability.4 Heart rate variability refers to the variation within the R-R interval of the electrocardiogram during a fixed cycle. It is associated with adaptiveness of the cardiovascular system, and high variability is believed to be a sign of health. Low variability is associated with a number of disease states. Heart rate variability reflects the balance between sympathetic and parasympathetic input to the heart, and many cardiac disease states have been shown to be associated with low variability. Therapies that increase heart rate variability have been shown to improve prognosis.
On the basis of these observations, heart rate variability biofeedback is used to train patients to increase the variability in their heart rate, using feedback from equipment that records the R-R interval from the electrocardiogram or from blood pulse volume sensors. Patients learn to make the variability greater, primarily by breathing at a resonant frequency, as described by Lehrer et al.5
Several preliminary studies have been conducted with heart rate variability in cardiac patients, but much remains to be understood about its use. In 63 patients with established coronary artery disease, Del Pozo et al showed that six biofeedback sessions coupled with daily practice resulted in significantly increased heart rate variability.6 Similarly, Nolan and colleagues found that five sessions of biofeedback improved symptoms and quality of life in 46 patients with coronary artery disease.7 In 14 patients with heart failure, Luskin et al demonstrated that eight sessions of heart rate variability biofeedback produced reductions in perceived stress and improved function on the 6-minute walk test.8
It remains unclear whether heart rate variability biofeedback has more or less potential than other types of biofeedback in patients with cardiovascular disease, but these preliminary observations suggest that it may be useful in improving symptoms and quality of life.
Biofeedback in hypertension: Despite decades of study, conclusions elusive
Among diseases of the cardiovascular system, biofeedback has been used most frequently in hypertension, where it has been under investigation for more than 30 years, since the early days of biofeedback study.9 The field of biofeedback in hypertension is fraught with difficulties, rendering conclusions about its efficacy difficult.
Biofeedback has been assessed in many different types of hypertension, often within the same study. Essential hypertension and “white coat” hypertension, now known as excessive cardiovascular reactivity, have been most commonly investigated, but with no apparent consensus. The biofeedback techniques used in these studies have ranged from blood pressure biofeedback to electromyography, finger temperature, and skin conductance. More recently, heart rate variability biofeedback has also been used in this population.
In general, biofeedback has been more successful in the treatment of hypertension when respiratory training has been a component of the biofeedback. McGrady has established that certain types of patients with hypertension fare better with biofeedback than others.10 These include patients with higher baseline blood pressure, higher heart rate, cool hands, high electromyographic response, and high plasma renin activity.in short, patients who can be seen to have a high degree of sympathetic arousal.
Blood pressure can be lowered by 6 to 10 mm Hg when biofeedback is effective, which is less of an effect than that observed with most drug therapy for hypertension. Biofeedback does have the advantage, however, of improving overall cardiovascular reactivity and giving the patient a greater sense of control over his or her physical well-being, which may prove valuable in the setting of hypertension. Typically, the most effective interventions for hypertension (and perhaps for cardiovascular disease in general) are individualized for the patient and not protocol-driven. Thus, although biofeedback has potential in hypertension, its efficacy is not proven and systematic trials are lacking.
Biofeedback in heart failure: Targeting sympathetic overactivation
In patients with heart failure, the sympathetic nervous system is overactivated, as noted previously. High levels of plasma norepinephrine correlate with worse prognosis. Decreasing activation of the sympathetic nervous system improves both symptoms and prognosis, as demonstrated in patients taking beta-adrenergic blocking agents or those treated with a left ventricular assist device.
Several studies have suggested that biofeedback may be able to provide a similar reduction in sympathetic nervous system activation in patients with heart failure. Moser and colleagues showed that a single session of skin temperature biofeedback plus relaxation training increased cardiac output in patients with heart failure,11 while studies by Weiner et al,12 Bernardi et al,13 and Mangin et al14 showed that training heart failure patients to breathe more slowly increased their exercise tolerance. Although these studies are preliminary, they support the speculation that if biofeedback can decrease activation of the sympathetic nervous system in patients with heart failure, it may actually cause some degree of remodeling of the failing heart, such as that observed with beta-blockers or left ventricular assist device therapy.
