**5.2.1 Heart rate variability biofeedback training**

As mentioned in previous sections, hyper-arousal is one of the symptoms found in those with posttraumatic stress disorder. Persistent hyperarousal has been linked to physiological abnormalities such as increased blood pressure, exaggerated heart rate response to stressors, and an elevated resting heart rate (Cohen et al. 1997; Pitman et al. 1987). This has led researchers to speculate that posttraumatic stress disorder may alter sympathetic nervous system reactivity. In addition, researcher found that between 80% to 100% of individuals with posttraumatic stress disorder can be distinguished from those without by looking solely at their physiological reactivity (Orr & Roth 2000), which can be indicative of autonomic nervous system dysfunction. Heart rate variability can be used as an indicator of how the autonomic nervous system is functioning (Appelhans & Luecken 2006). Those with posttraumatic stress disorder typically have low heart rate variability (Tan et. al. 2011). Heart rate variability is the mean value of heart rate fluctuations over a period of time and is reflective of the interplay between the sympathetic and parasympathetic nervous system (Akselrod et al. 1981; Cohen et al. 1999). Research has established that by breathing at an ideal resonance frequency (approximately 5.5 breaths per minute), an individual can increase their heart rate variability (Vaschillo et al. 2002). Ideal resonance frequency varies by person.

Clients undergoing *heart rate variability training* are asked to first meet with the therapist to determine what breathing rate will produce their greatest heart rate variability (Lehrer et. al., 2000; Tan et. al., 2011). Clients are then instructed to practice breathing at this rate at home. They may either practice with a CD that guides them through the breathing techniques or they may be given a machine that notifies them when they are not breathing at their ideal rate. In a pilot study by Tan and colleagues (2011), participants who underwent eight, 30 minute training sessions experienced a significant reduction in posttraumatic stress disorder symptoms from pretest to posttest.
