In this study, they find that subjects most likely to respond show a decrease in their HF (parasympathetic activity) during exposure to the stressor, that then goes back to baseline.  The subjects less likely to respond show a more rigid HF response.  They also monitored Sample Entropy and I will try to follow up on their exact algorithm.
The reason that I’m digging into this is that my hunch is that the response to acupuncture needling itself, my tell us something about the resilience and adaptability of patients.  I realize I’m probably repeating myself, but somehow it’s taking awhile to sink in.  full pdf herebornas2006 sampen in flight phobics MSE
Appl Psychophysiol Biofeedback. 2012 Mar;37(1):53-62. doi: 10.1007/s10484-011-9179-5.
Heart rate variability profiles and exposure therapy treatment outcome in flight phobia.

Author information

  • 1University of the Balearic Islands, University Research Institute on Health Sciences, Palma, Spain. xavier.bornas@gmail.com

Abstract

The goal of this study was to explore why certain patients in a previous study on exposure therapy for flight phobia did not experience an improvement in their conditions. Participants from a treatment study (N = 45) were selected according to post-treatment results and divided into two groups: the unsatisfactory treatment outcome group (UTO, N = 10) and the satisfactory treatment outcome group (STO, N = 10). The differences between these two groups prior to receiving exposure therapy were analyzed at the behavioral, physiological, and cognitive levels. The UTO participants had been avoiding flying longer than the STO phobics. Following Thayer and Lane’s neurovisceral model of emotion regulation, heart rate variability was analyzed at two levels: tonic and phasic. Low frequency and high frequency (HF) power were calculated in the frequency domain and Sample Entropy was computed in the time domain. The tonic HF power of the UTO group was higher than the STO group’s tonic HF power. In the phasic level, while the STO group’s HF power decreased under exposure and subsequently returned to baseline level, the UTO group demonstrated a more rigid pattern. Finally, the STO group reported higher emotional involvement than the UTO group when they were shown a sample of the therapy. Based on these results, the challenge of matching exposure therapy to each patient’s profile is discussed.