Tim Hideaki Tanaka, Ph.D.
Paper presented at the 34th Annual Meeting of Association for Applied Psychophysiology and Biofeedback, Jacksonville, Florida March 27-30, 2003.
Respiratory sinus arrhythmia (RSA) is the natural variation in heart rate that occurs through the influence of breathing. One of the main goals of RSA biofeedback is to maximize high RSA oscillation . RSA biofeedback has been utilized in a variety of clinical situations such as for the treatment of asthma , panic disorder , irritable bowel syndrome , and cardiac rehabilitation . The training is typically done by monitoring the patient’s heart rate and respiration and providing real-time feedback which aids to produce large RSA in synchronization with breathing. Ten sessions of RSA biofeedback session are generally recommended and the importance of patients’ self training between sessions has been indicated . A few heart rate variability (HRV) home trainer units are currently available however; they may not be suitable for every patient due to their cost and the need for access to a PC. In addition, there are some patients who find following graphic tracing on a monitor stressful and have difficulty relaxing in front of a computer.
The HRV-Autonomic Trainer CD has been created to assist in RSA biofeedback sessions and to be used as an inexpensive home trainer for patients. The CD contains a series of voice commands, ocean wave sounds, and music. The voice command prompts and the pitch of ocean wave sound is designed to produce a respiration rate of 6 breaths per minute (0.1 Hz.) which has been shown to cause the greatest amplitude of heart rate oscillation in most individuals.
This preliminary study was carried out to monitor the heart rate variability of subjects listening to the CD and to test the naïve subjects’ compliance to CD guided breathing training.
Four young healthy adults participated in the experiment. All participants had no prior experience in breathing techniques or biofeedback.
Subjects were seated with their backs supported. The ECG signals were obtained through the electrodes using a standard lead II configuration. In addition, strain gauge was attached to the subjects’ chests to monitor their respiration. Subjects were instructed to minimize any physical movement and were asked to refrain from falling asleep. After 5 minutes resting period, subjects were asked to breathe at the rate of 12 breathes per minute paced by visual cues on the computer screen for 5 minutes. Then the computer screen was masked and the HRV-Autonomic Trainer CD was played (see Table 1). After 35 minutes, the CD was turned off and the computer screen was again shown to the subjects for 12 breaths per minute paced breathing.
Apparatus and signal analysis:
EKG signals were recorded continuously during the entire procedure using Biopac MP 150 with ECG amplifiers with a sampling rate of 1000 Hz. The power spectral analysis was conducted by means of Fast Fourier Transform based on the stored R-R interval data of the ECG signals. The power spectra was divided into two frequency bands of interest: LF (low frequency band, 0.04 to 0.15 Hz), and HF (high frequency band, 0.15 to 0.4 Hz).
Results and Discussion
Figures 1-4 show each subject’s (A-D) average respiration rate per minute, HF and LF power and LF/HF ratio in each of the 5 minute segments.
The power of the HF component is considered to reflect the efferent vagal activity and the LF component is considered to be a marker of sympathetic and vagal modulation . In this study, HF respiratory-linked variations in heart rate did overlap with low-frequency heart rate fluctuations due to the slow respiration rate during the CD session. Thus, the subjects HF components during the CD session are relatively low (Figure 2).
In order to avoid respiratory-linked heart rate oscillation overlapping with LF, the subjects were asked to pace their respiration at 12 breaths per minute for the duration of 5 minutes in the beginning and at the end of this experiment. There was a tendency for slight increase of sympathetic tone at the end of the experimental sessions. Although, it may also be associated with relatively low LF/HF ratio seen among all subjects at the baseline, it is conceivable that HRV training creates a different type of autonomic status compared to various relaxation training methods.
The subjects’ compliance following the voice commands and ocean wave sounds was very good. Most subjects maintained peak oscillation at 0.1 Hz with ocean wave sounds only (no voice cues). Subjects generally were able to maintain the same respiration rate even after both voice and wave sound cues diminished with music only remaining. This suggests that subjects were generally able to “self train” to breathe at the 0.1 Hz frequency. However, the HRV-Autonomic Trainer CD should be considered complementary to a complete HRV biofeedback session since observing synchronicity with respiration and monitoring other physiological indexes are important.
Previous studies on acupuncture have demonstrated the important relationship between superficial acupuncture and patients’ respiratory phases during stimulation in creating the most desirable autonomic response [7-9]. In addition to use of the CD as a home training tool in between biofeedback sessions, the CD has also been utilized during acupuncture treatments (patients breathe upon the CD’s command during treatment) at the author’s clinical facility. Although it is subject to formal investigation to be conclusive, based on series of clinical observations, the procedure induced very promising results in a variety of conditions.
The author wishes to thank Gordon Gibson and Brad Rogers of Somerset Entertainment (Toronto, Ontario) for help in developing the HRV-Autonomic Trainer CD.