New HRV Features
Resonant Frequency Detection
In heart rate variability (HRV), the resonant frequency can be detected by leading a client through a paced breathing exercise during which the respiration rate is progressively decreased from a starting rate of around seven breaths per minute, all the way down to a rate of five breaths per minute. By decreasing the respiration rate by one half breath per minute every two minutes and monitoring the output of a fast Fourier transform (FFT) computation of the inter-beat intervals (IBI) on a frequency spectrum display, the resonant frequency appears as the frequency bin with the highest magnitude during the whole session. This frequency is variable between individuals and many HRV experts propose that breathing at the specific respiration rate which corresponds to ones resonant frequency is a healthy exercise because it can help to increase the overall heart rate variability range.
BioGraph Infiniti version 4.0 introduces a number of new screen instruments and channel set algorithms which were designed to help detect the resonant frequency. These include an adaptive breathing pacer, a method for tracking the peak frequency’s magnitude and remembering the respiration rate associated with the highest magnitude.
Adaptive Breathing Pacer
Although the breathing pacer can be set to automatically detect the client’s respiration rate and start pacing from there, for the purpose of this exercise, it is set to start at seven breaths per minute and decrease its rate every two minutes until it reaches five breaths per minute. The durations for inhalation and exhalation can be adjusted to the client before starting the session.
Channel Set Settings
Within the channel set are defined computations for peak frequency, peak frequency magnitude and a method for keeping track of the respiration rate, heart rate and, if desired, other physiological measures such as skin conductance and temperature, at the precise moment the maximum magnitude is reached.
The whole session runs for ten minutes, two minutes at each breathing rate: 7.0, 6.5, 6.0, 5.5 and 5.0 breaths per minute. The client is instructed to follow the breathing pacer as best as possible without breathing too deeply to avoid feeling dizzy. During the session, the clinician observes the respiration waveform and the corresponding entrainment of the heart rate signal caused by respiratory sinus arrhythmia (RSA) and makes note of the respiration rate when the two signals in phase, are as this is one of the markers of the resonant frequency.
At the end of the ten minutes, the report screen shows signal line graphs for the whole session with the raw EKG signal, the raw respiration waveform (blue) and heart rate channel (pink).
At the bottom of the screen, a 2D frequency spectrum display of the IBI FFT shows the peak frequency shifting as the respiration rate decreases. The graph above the frequency spectrum shows the changes in peak frequency magnitude, in pink, and the maximum amplitude value, in green. On the screen, the time marker (red line) is set on the exact moment when the maximum amplitude was reached. At that time, the respiration rate was 6.64 breaths per minute and the resonant frequency was 0.11 Hertz.