Table 4.
Results and conclusions of the studies included in the review. Comparison of the size of effects for primary and secondary variables.
| Primary and Secondary Variables | Methods for Assessing Variables | Effect Sizes a | Significance Level | Conclusions |
|---|---|---|---|---|
| Shi et al. [51] | ||||
| IBS symptoms | IBS-SSS | d = 1.30 | p = 0.001 | taVNS improved HRV parameters—increased the vagal activity (HF-norm). taVNS reduced IBS symptoms, pain, anxiety, and depression, and improved quality of life. |
| HRV | HF-norm | d = −0.66 | p = 0.04 | |
| LF-norm | n/d | n/d | ||
| Pain | VAS | d = 1.17 | p = 0.001 | |
| Anxiety | SAS | d = 1.24 | p < 0.001 | |
| Depression | SDS | d = 0.84 | p = 0.011 | |
| Stress | not measured | |||
| Go and Park [50] | ||||
| IBS symptoms | BSSS-AD-F | d = 0.81 | n/d | Auricular acupressure effectively reduced IBS symptoms. The severity of loose stools, diarrhea, abdominal pain, and abdominal discomfort were lower. In the experimental group, HRV parameters significantly improved, indicating increased parasympathetic activity (increase in HFNorm), increased resistance to stress (increase in SDRR), and decreased LH/HF balance. The level of experienced stress in the experimental group decreased significantly. |
| BSSS-AD-DS. | d = 1.16 | n/d | ||
| BSSS-AD-DB | d = 1.52 | n/d | ||
| HRV | HF-norm | d = −1.1 | n/d | |
| LF-norm | d = 0.88 | n/d | ||
| LF/HF | d = 0.88 | n/d | ||
| PSI | d = 0.29 | n/d | ||
| SDRR | d = −0.59 | n/d | ||
| Pain | BSSS-AP-F | d = 0.42 | n/d | |
| BSSS-AP-DS. | d = −0.70 | n/d | ||
| BSSS-AP-DB | d = 0.97 | n/d | ||
| Anxiety | SCL-90R-K-A | d = 0.24 | n/d | |
| Depression | SCL-90R-K-D | d = 0.13 | n/d | |
| Stress | PSS | d = 1.07 | n/d | |
| Park and Cha [49] | ||||
| IBS symptoms | BSSS-AD-F | d = 0 | n/d | Some of the symptoms of IBS have improved—especially those related to abdominal pain: frequency of loose stools and abdominal pain, reduction of anxiety and perceived disability caused by abdominal pain, flatulence, and discomfort in the abdominal cavity. KHA was not effective in reducing stress and promoting mental health. There was no change in HRV. |
| BSSS-AD-DS. | d = −0.32 | n/d | ||
| BSSS-AD-DB | d = −0.24 | n/d | ||
| HRV | HF-norm | d = 0.18 | n/d | |
| HF | d = −0.39 | n/d | ||
| LF-norm | d = −0.18 | n/d | ||
| LF | d = −0.24 | n/d | ||
| LF/HF | d = −0.20 | n/d | ||
| PSI | d = 0.48 | n/d | ||
| SDRR | d = −0.42 | n/d | ||
| Pain | BSSS-AP-F | d = 0.19 | n/d | |
| BSSS-AP-DS. | d = 0.15 | n/d | ||
| BSSS-AP-DB | d = −0.32 | n/d | ||
| Anxiety | SCL-90R-K-A | d = −0.11 | n/d | |
| Depression | SCL-90R-K-D | d = −0.05 | n/d | |
| Stress | GARS | d = −0.51 | n/d | |
| Jurek et al. [47] | ||||
| IBS symptoms | IBS-SSS | d = −0.19 | n/d | There were no changes in the functioning of the autonomic system (no significant differences in HRV). The severity of IBS symptoms has not changed. |
| HRV | HF | d = 0 | n/d | |
| LF/HF | d = 0.16 eta2 = 0.47 | n/d | ||
| PNS index | d = 0.80 | n/d | ||
| SNS index | d = 0.18 | n/d | ||
| Pain | not measured | |||
| Anxiety | ||||
| Depression | ||||
| Stress | ||||
| Jang et al. [46] | ||||
| IBS symptoms | GSRS-IBS | n/d | p < 0.001 | Significant changes in the functioning of ANS were observed—CBT resulted in a significant increase in HF and a significant decrease in the LF/HF ratio. These changes coexisted with significant reductions in IBS symptoms, anxiety, depression, and stress. Differences in HF and the LF/HF ratio were significantly associated with changes in symptoms of IBS, anxiety, depression, and stress. |
| HRV | HF | n/d | p = 0.017 | |
| LF/HF | n/d | p = 0.003 | ||
| Pain | not measured | |||
| Anxiety | HADS-A | n/d | p < 0.001 | |
| Depression | HADS-D | n/d | p < 0.001 | |
| Stress | GARS | n/d | p < 0.001 | |
| Kavuri, Selvan, Malamud et al. [48] | ||||
| IBS symptoms | IBS-SSS | Y vs. WL: d = 4.03 | p < 0.001 | The remedial yoga module (RYM) reduces symptoms of IBS, anxiety, and depression (in both groups: (Y), yoga with limited conventional treatment; and (CB), combination—yoga with conventional treatment). Only in the combination group (yoga with conventional treatment) were there significantly favourable changes in HRV parameters (indicating increased parasympathetic activity). |
| CB vs. WL: d = 3.12 | p < 0.001 | |||
| Y vs. CB d = 0.52 | p > 0.05 | |||
| HRV | HF | n/d | CB vs. WL: p < 0.01 | |
| LF | n/d | CB vs. WL: p < 0.05 | ||
| LF/HF | n/d | CB vs. WL: p < 0.01 | ||
| Pain | not measured | |||
| Anxiety | HADS-A | n/d | Y vs. WL *** | |
| n/d | CB vs. WL *** | |||
| n/d | Y vs. CB | |||
| Depression | HADS-D | n/d | Y vs. WL *** | |
| n/d | CB vs. WL *** | |||
| n/d | Y vs. CB | |||
| Stress | not measured | |||
IBS-SSS, IBS Symptom Severity Scale; BSSS-AD, Bowel Symptom Severity Scale; AD, abdominal discomfort: F = frequency, DS = distress, DB = disability; AP = abdominal pain; GARS, Global Assessment of Recent Stress; GSRS-IBS, GI Symptom Rating Scale; HADS, Hospital Anxiety and Depression Scale; HF, high frequency; HF-norm, normalized high frequency (HF/LF + HF); HRV = heart rate variability; KHA, Korean hand acupuncture; LF, low frequency; LF/HF, low frequency/high frequency ratio; LF-norm, normalized low frequency LF (LF/LF + HF); n/d = no data; PNS index, parasympathetic nervous system index; PSI, physical stress index; PSS, Perceived Stress Scale; SAS, Self-rating Anxiety Scale; SCL-90R-K-A/D, Symptom Checklist–90–Revision, Korean version; A = anxiety, D = depression; SDRR, standard deviation of RR intervals; SDS, self-rating depression scale; SNS index, sympathetic nervous system index; taVNS, transcutaneous auricular vagus nerve stimulation; VAS, Visual Analogue Scale. a The effect sizes were calculated based on the mean differences between the groups in the post-test. d = Cohen’s d effect size (When the effect sizes were not available, they have been calculated from means and standard deviations.). *** = p < 0.001.