The heart beats to several of its own rhythms - within its every beat, between consecutive beats, during breathing and with every thought. For instance, with every breath we take, our heart speeds up with our in-breath (inspiration) and slows down with our out-breath (expiration). The heart also has long, slow swings that span several breaths. These slow (low frequency) swings in heart rate reflect a degree of "flight-or-fight" response, anxiety, or sympathetic activation within our bodies in relation to fears, anger and aggression (which are also forms of fear). Rapid, small (high frequency) variations and "spiking" that show up within the natural variations in heart frequency during breathing, reflect para-sympathetic activity as the heart tries to compensate for the reduced output caused by sympathetic activation. Therefore, we can assess heart rate variability, process its spectral properties and see how much heart activity is normal, sympathetic and parasympathetic. We can see what thoughts, foods and events can trigger unhealthy heart rhythms and we can use HRV feedback to teach ourselves how to relax.
Breathing entrainment (BE) is the measure of how smooth & flowing heart rate variability is with one's breathing (a new form of the word "entrainment"). The breathing rate that is considered to be optimal is based on a 10 second breathing cycle - breathe in for five seconds and breathe out for 5 seconds, making six breathing cycles per minute.There are several HRV systems available. Two systems that I know of are the "Cardio-Pro", by Thought Technology and the "Freezeframer" by Heartmath. The Cardio-Pro consists of an EKG sensor and software as an add-on to the Procomp from Thought Technology. It has advanced analysis software and is meant for the professional. The Freezeframer consists of software and an optical sensor that plugs into the COM port of a computer. The Freezeframer costs under $300.00 US and has reasonably good analysis. It may be used by both professionals and the general public.
Figures 1 - 4 below are from two women with their data taken from the Freezeframer. The Spectral Analysis window is normally viewed from a separate selection, but for the sake of space, we have dropped it into the HRV-heartbeat rate display. Figure 1 has two large sections (pre AVE & post AVE) within it. Each of these sections contains four smaller sections. BE is shown on three bar graphs, where green is the best BE, blue-intermediate and red – poor. The upper left side of each profile (in green) shows the actual heart rate in beats per minute. It would normally span across the entire top area, but we stuck the spectral results (blue "mountains") over top of some of it so we could see everything on one page. The spectral results show a peak at the breathing frequency of 0.1 Hz (ten-second breathing cycles). "Mountains" that are on the left represent sympathetic activity while the smaller "hills" to the right represent para-sympathetic activity. These ten second breathing cycles are paced from a synthesized "babump" heartbeat sound from a Paradise XL through a set of headphones. The user hears these sounds and inhales for two beats and exhales for two beats, and - you got it - they listen to 24 beats per minute, which when divided by 4 beats per breath cycle = 6 breaths per minute (brpm). We've seen many anxious people on the Freezeframer and the results are always the same. When their breathing is paced at 6 brpm, their anxiety shows itself after about three minutes. Their heart rate becomes erratic ("jaggely" green lines with red sections in it) and their performance score begins to erode (small window below). The lady in Figures 1 and 2 was crying in the end. Her average heart rate was 77 and her score (green, blue and red bars) was quite poor.