Analysis of autonomic function during natural defecation in patients with irritable bowel syndrome using real-time recording with a wearable device

Abstract

Background: Autonomic dysfunction is a factor in irritable bowel syndrome (IBS). However, there are no reports of autonomic nervous system (ANS) activity during natural defecation in patients with IBS. We aimed to clarify the relationship between ANS activity and life events, such as defecation and abdominal symptoms, using real-time recording.

Methods: Six patients with IBS and 14 healthy controls were enrolled in this prospective multicenter study. ANS activity was recorded for 24 h using a T-shirt wearable device, and life events were recorded simultaneously in real time using a smartphone application software. Low frequency/high frequency (LF/HF) and HF calculated by power spectrum analysis were defined as activity indicators of the sympathetic and parasympathetic nerves, respectively.

Results: The means of LF/HF and HF in the period with positive symptoms were comparable between the groups; however, the sum of LF/HF, sum of ΔLF/HF, and the maximum variation in ΔLF/HF were significantly higher in the IBS group. In the IBS group, the sum of ΔLF/HF and LF/HF increased significantly from 2 min before defecation, and the sum of LF/HF remained significantly higher until 9 min after defecation. The sum of ΔLF/HF at 2 min before defecation was significantly positively correlated with the intensity of abdominal pain and diarrhea and constipation scores. In contrast, it was significantly negatively correlated with defecation satisfaction and health-related quality of life.

Conclusions: In patients with IBS, sympathetic nerve activity was activated 2 min before defecation, which was correlated with abdominal symptoms and lower QOL.

Fig 1. T-shirt-type wearable device and smartphone application software.

Heart rate variability (HRV) was measured using a T-shirt wearable device attached to a transmitter in front of the T-shirt. The HRV data were transferred and recorded on a smartphone using Bluetooth. At the same time, life events, such as abdominal symptoms, defecation, eating, and awakening or sleep, were recorded in real time using a smartphone application software during HRV recording.

Fig 2. The graph of obtained data and measuring method of ANS activity.

(a) The real graph of obtained data about autonomic nervous system (ANS) activity and life events. The results of low frequency (LF) (yellow line) and high frequency (HF) (green line) represented in a graph. Life events, such as defecation and eating (the enclosed area with orange line) and period with positive symptoms (the enclosed area with pink line), were recorded. (b) Measuring method of ANS activity. The baseline LF/HF was defined as the value included in the range of the mean ± 2 standard deviations (dashed line) of LF/HF measured in the period with no symptoms. The sum of LF/HF was the area under the curve of LF/HF measured in the period with positive symptoms (upward diagonal). The sum of ΔLF/HF was the sum of variation from the mean value of baseline measured in the period with positive symptoms (dots). The maximum variation of ΔLF/HF indicated the maximum variation from the mean value of baseline measured in the period with positive symptoms (arrow). HF was analyzed in the same way.

Fig 3. Autonomic nervous activities before and after defecation.

(a, b) Changes in sympathetic nerve activities before and after defecation were evaluated by the sum of Δlow frequency/high frequency (LF/HF) and the sum of LF/HF, respectively. (c, d) Changes in parasympathetic nerve activities before and after defecation were evaluated by the sum of ΔHF and the sum of HF, respectively. Data represents the median. Statistical significance was calculated by Mann–Whitney test (*p < 0.05).

Fig 4. Relationship among sympathetic nerve activity at 2 min before defecation, symptoms, and quality of life.

Sympathetic nerve activity was evaluated by the sum of Δlow frequency/high frequency (LF/HF). (a) Intensity of abdominal pain, (b) satisfaction levels of defecation, (c) gastrointestinal symptom rating scale (GSRS) diarrhea score, (d) GSRS constipation score, (e) the Japanese version of the 8-item Short-Form Health Survey (SF-8) role physical, and (f) the SF-8 role emotional score were significantly correlated with the sum of ΔLF/HF at 2 min before defecation. Data were analyzed by Spearman test.

Fig 5. Hypothesized mechanism of exacerbated symptoms and increased sympathetic nerve activity before defecation.

The stress of abdominal pain activates the amygdala to release corticotrophin-releasing hormone (CRH), resulting in further exacerbation of abdominal pain by increasing colonic motility. These cascades “exacerbate the circle of pain.” Two minutes before defecation, the stress also activates sympathetic nerves as a stress response against abdominal pain. Increased sympathetic nerve activity can decrease colonic motility, which may have a protective role to hold back the defecation. This situation may be under competition between the accelerator of colonic motility caused by CRH and the brake caused by sympathetic nerve activation.