Fourier Transform – The specific mathematical transformation of time domain data into frequency domain data. This results in a type of histogram that measures the relative amplitudes for the different frequency components (rhythmic patterns) in the time domain waveform. Fast real-time rhythms map into peaks in the high-frequency portion (right side) of the spectrum, whereas slow rhythms appear on the left, or low-frequency, side. A given peak may be caused by a single rhythmic process or a mixture of rhythms with similar frequencies. The latter will contribute to the height of a peak and increase its width. In the case of heart rate analysis, different frequencies (peaks) present in the power spectrum are caused by cyclic fluctuations in autonomic (sympathetic and parasympathetic) activity.
Power Spectral Density (PSD) – The power spectrum of a waveform is a plot of the wave amplitude for each component squared, as a function of frequency of that component. This plot, expressed in units of energy per hertz, we have the PSD which is the wave power present in a small frequency range, delta f, as a function of frequency, f.
Freeze-Frame® – A tool used in the HeartMath system of self-management that consists of consciously disengaging the mental and emotional reactions to either external or internal events and then shifting the center of attention from the mind and emotions to the physical area around the heart while focusing on a positive emotion such as love or appreciation. This tool thus allows the individual to shift from the mind to the heart. Such a shift results in a wider and more objective perception while stress is occurring, as opposed to after the event has taken place.
Appreciation – The state in which the subject has clear perception or recognition of the feelings of sincere or active appreciation for someone or something. It is this heart-felt feeling that is associated with the HRV changes reported on in this article, as contrasted with the mental concept of appreciation, which does not appear to produce such HRV changes.
Amplified Peace – Used to distinguish an inner state of experience in which a deeper than normal state of peace and centeredness is felt. One also has a sense of standing on the threshold of a new dimension of awareness in this state, with a sense of inner equilibrium and an awareness that one has accessed a new domain of intuition. As with any experiential state, words do not adequately describe it; also, one enters this state for relativity short periods. However, with practice at staying focused in the heart, the ratios of time in this state can be increased. It may be similar to moments at the beach or in the forest when one feels an especially deep contact with nature or with oneself that is beyond one’s normal experience. In such moments one may find answers to life’s deeper issues or problems.
Biological Oscillators – When the instantaneous systemic arterial pressure is continuously recorded, fluctuations with each heart beat and with each breath are always seen. This rhythmic activity in the autonomic nervous system appears to be supported by at least three biological oscillator systems: 1) centrogenic rhythms in brainstem networks with facultative coupling (entrainment) with the respiratory oscillator, 2) the baroreceptor feedback network, and 3) the autorhythmicity of the vascular smooth muscle [31]. The fact that each of the oscillators can develop different frequencies and that the phase-lags between the oscillations are variable, easily explains the general experience that blood pressure waves are quite variable and can appear or disappear in an unpredictable manner. The existence of several oscillators with similar basic frequencies
enables synchronization and entrainment between oscillators. Thus, we can assume that states of regular and steady blood pressure waves are the expression of the entrained action of the complex multi-oscillatory system [31, 58, 59].
Arterial Pulse Transit Time – Measure of the speed of travel of the arterial pulse wave from the heart to a peripheral recording site. It is used as a noninvasive method to monitor the elasticity of artery walls and to indicate beat-to-beat changes in blood pressure. The arterial pressure pulse is a wave of pressure that passes rapidly along the arterial system. The pulse wave velocity (4-5 m/s) is much faster than the velocity of blood flow (<0.5 m/s). The pulse wave velocity varies directly with pressure-related changes in the elasticity of the arterial wall. [64] The more rigid or contracted the arterial wall, the faster the wave velocity. Therefore, it follows that pulse transit time should vary inversely with blood pressure. Common estimates of the magnitude of this effect indicate that pulse transit time varies by about 1 ms/mm Hg change in pressure. [65]
