Heart Rate Variability (HRV) Training:
Heart rate variability refers to the constantly oscillating variations in heart rate that are observed in healthy individuals. These variations may be measured in terms of their frequencies, amplitudes, the range of heart rate changes in each cycle, and the standard deviations of the interbeat intervals (IBI). The standard deviation of these interbeat intervals (IBI), computed after all artifacts have been removed, is called SDNN. We are concerned when SDNN falls below 50 mille-seconds (ms) and prefer to see it above 80 to 100 ms (Gevirtz, 2010). Heart rate changes are being measured using a plethysmograph which measures red light reflected from blood vessels in a finger or thumb.
Measuring pulse to pulse in the thumb gives the same figures at rest (though may not do so during tasks) for SDNN as do electrocardiogram (EKG) sensors on the chest (Giardino, 2002). SDNN is calculated using the Cardiopro program from Thought Technology, which was developed to meet research criteria and provides the statistics used internationally for heart rate variability measures.
There are now studies that show that HRV training can have a positive effect on depression. Katsamanis et al reported significant improvements after HRV TRAINING in the Hamilton Depression Scale (HAM-D) and the Beck Depression Inventory (BDI-II) with concurrent increases in SDNN. They noted that SDNN decreased to baseline levels at the end of treatment and at follow-up, but clinical statistically significant improvement in depression persisted (Katsamanis et al, 2007). Hassett et al found that, in addition to relief of pain in patients who have fibromyalgia, HRV biofeedback significantly improved overall functioning and depression (Hassett, 2007).