Abdominal painNice study that looks at Heart Rate Variability (an indicator of the stress response) and acupuncture for constipation.  They found that electroacupuncture at traditional points for constipation (once a week for 8 weeks) not only improved constipation, but increased their HRV over the period (decreased stress response) over the experimental period and continued after treatment was done.

Am J Chin Med. 2013;41(2):301-13.
The influence of electro-acupuncture stimulation to female constipation patients.
Chen CY, Ke MD, Kuo CD, Huang CH, Hsueh YH, Chen JR.
Source

Institute of Electronic Engineering, National Yunlin University of Science and Technology, Taiwan.
Abstract

This study aims to examine electro-acupuncture stimulation (EA) assisted therapy with analysis of heart rate variability to understand autonomic nervous activity variability (ANAV) and to track the changes in female patients with constipation. .. The participants were divided by a single-blind and randomized trial into two groups: the electro-acupuncture-point group, and the non-electro-acupuncture-point group. Both of the groups had eight treatments, once a week. For the electro-acupuncture (EA) group, needles were inserted into their Zusunli (ST36), Shangiuxu (ST37), Tiensu (ST25), Shueidao (ST28), Guanyuan (CV4) and Qihai (CV6) points. For the sham electro-acupuncture (SA) group, needles were inserted into acu-points that were not the ones mentioned for the EA group. While inserting needles, needles were inserted lightly into the participants’ skin and removed quickly (mock Transcutaneous Electrical Nerve Stimulation, TENTS). After an eight-week treatment period, the autonomic nervous system activities of the SA group did not show significant differences in their heart rate variability. However, the autonomic nervous system activities of the EA group had continuously increased after each session. The normalized high frequency powers (nHFP) of their autonomic nervous system activities were 26.79 in the first week, and they increased to 32.28 in the fourth week. In the eighth week, their nHFP had increased to 37.60 (p < 0.05). The normalized low frequency power (nLFP) was 30.81 in the first week. However, it decreased to 25.98 after three weeks of treatment. After the eight-week treatment period, the nLFP decreased to 24.84 (p < 0.05). After the eight-week treatment, the control group did not appear to undergo any physiological change, while the constipation had been improved for the experimental group. It was found that the activation of parasympathetic nervous system in the experimental group increased after the eight-week treatment. The effects of such a result on the enhancement of the activation of parasympathetic nervous system and the improvement of constipation should be further discussed.