The Relationship between Cardiovascular Function and Decreased Intra-Abdominal Pressure Following Stool Evacuation

Abstract

Abdominal organs, though less than one-tenth of body mass, receive about 30% of cardiac output, with two-thirds passing through the descending aorta. The abdominal cavity contents—including organs, adipose tissue, and stool—affect peripheral vascular resistance. This study evaluated the impact of stool evacuation exceeding routine daily volume on intra-abdominal vascular resistance and systemic blood pressure. We retrospectively reviewed records of 56 patients who underwent tap water enemas for bloating and constipation. Episodes with >400 g body weight reduction after evacuation were analyzed. Blood pressure, body weight, BMI, mean arterial pressure (MAP), and pulse pressure (PP) were measured before and after evacuation. In hypertensive patients (systolic BP ≥140 mmHg), MAP decreased significantly, with notable PP differences between groups (p<.05). Comparisons among normotensive (≤119 mmHg), prehypertensive (120-139 mmHg), and hypertensive (≥140 mmHg) groups revealed significant MAP changes (p<.001). These findings suggest that stool evacuation beyond routine volume is associated with changes in intra-abdominal vascular resistance and correlates with systemic circulation, particularly showing a reduction in blood pressure among hypertensive individuals.

INTRODUCTION

Anatomically, one-third of the blood ejected from the heart flows through the subclavian arteries to the upper extremities and head, while the remaining two-thirds passes through the aorta, supplying the abdominal cavity and lower extremities via the iliac, superior mesenteric, and inferior mesenteric arteries. The abdominal organs exert pressure on this blood flow, and fecal matter and gas within the colon can further distend the bowel, acting as mechanical factors that impede adjacent organ perfusion.1 Such factors are known to be associated with changes in blood pressure.

Although many individuals do not meet the diagnostic criteria for constipation, they experience various defecation-related discomforts, which have been linked to multiple diseases, particularly cardiovascular disorders.2 However, direct evidence of the impact of defecation on cardiovascular function remains limited. Recent studies on laparoscopic surgery have reported that elevated intra-abdominal pressure during anesthesia affects cardiovascular function.3,4,5 Given that routine defecation is also closely related to intra-abdominal pressure, we aimed to investigate the effects of evacuating more than the usual daily stool volume—specifically, over 400 g—on cardiovascular parameters.

This study aimed to evaluate the effect of stool evacuation exceeding the usual daily defecation volume on intra-abdominal vascular resistance and systemic blood pressure, thereby suggesting factors that may be helpful in the postoperative monitoring of patients undergoing laparoscopic surgery under general anesthesia.

MATERIALS AND METHODS

From May 2006 to July 2007, we retrospectively analyzed cases of patients who visited our clinic for defecation discomfort and underwent enemas, resulting in a body weight reduction of at least 400g. These patients had persistent bowel movement issues despite various treatments, including medications, dietary changes, and exercise.

We focused on cases using a self-colon irrigation system (NaeClear S1.0, NaeClear Ltd, Seoul, Korea), a type of tap water enema.6 The procedure involved instilling 250 mL of water to relieve rectal pressure, followed by 500 mL to stimulate peristalsis with concurrent abdominal massage and leg exercises, and finally another 250 mL for completion. Blood pressure was measured before and after evacuation using an automated sphygmomanometer (FT-500R, Jawon Medical Ltd, Seoul, Korea). To ensure data reliability and consistency, measurements were strictly standardized in accordance with the NICE guidelines,7 requiring patients to remain in a consistent, relaxed resting posture for a designated period before each reading to minimize external physiological variability.

We conducted this study in compliance with the principles of the Declaration of Helsinki. The study’s protocol was approved by the Institutional Review Board of Chonnam National University Hospital (CNUH-2025-347) and written informed consent was waived due to its retrospective nature.

• MAP (mean arterial pressure) was calculated as:

  MAP=Pdias+1/3(Psys-Pdias)

  (Pdias=diastolic blood pressure, Psys=systolic blood pressure)

  PP (pulse pressure) was calculated as:

  PP=Psys-Pdias

  BMI (body mass index) was calculated as:

  BMI=Weight (kg)/Height (m)2

  Blood pressure categories followed the JNC 7 criteria:8

  Normal: systolic ≤119 mmHg

  Prehypertension: 120-139 mmHg

  Hypertension: ≥140 mmHg

Statistical analyses were performed using IBM SPSS/WIN Ver. 20.0, applying paired t-tests, Wilcoxon signed-rank tests, one-way ANOVA, and Fisher’s exact test. A p-value of ≤.05 was considered statistically significant.

RESULTS

1. General characteristics of the participants

A frequency analysis was conducted to examine the general characteristics of the study participants, and the findings are presented in Table 1. A total of 55 participants were included, with 116 measurement cases analyzed. The mean pre-defecation systolic blood pressure (prePsys) was 122.25 mmHg (SD=21.03), and the mean pre-defecation diastolic blood pressure (prePdias) was 74.58 mmHg (SD=12.54). Following defecation, the mean systolic blood pressure (postPsys) decreased slightly to 119.58 mmHg (SD=17.50), while the mean diastolic blood pressure (postPdias) was 74.42 mmHg (SD=11.01). These results indicate a modest reduction in blood pressure after defecation.

TABLE 1. General characteristics of study participants before and after stool evacuation (n=55).

^*preP_sys: systolic pressure before evacuation, ^†preP_dias: diastolic pressure before evacuation, ^‡postP_sys: systolic pressure after evacuation, ^§postP_dias: diastolic pressure after evacuation, ^∥preMAP: mean arterial pressure before evacuation, ^¶postMAP: mean arterial pressure after evacuation, ^#pp difference: pulse pressure difference, ^**preBMI: body mass index before evacuation

No substantial differences were observed in mean arterial pressure or pulse pressure between the pre- and post-defecation measurements. Body weight showed an average reduction of 0.50 kg, and the difference in BMI before and after defecation was 0.19 (SD=.04).

2. Differences in mean arterial pressure according to body weight change ≥0.4 kg

To examine differences in MAP among participants who experienced a body weight reduction of ≥0.4 kg after defecation, a paired t-test was conducted. The results are presented in Table 2, and the corresponding graphical representation is shown in Fig. 1A.

TABLE 2. Mean arterial pressure (MAP) differences in cases with body weight reduction ≥0.4 kg after evacuation and in participants with pre-evacuation systolic BP ≥140 mmHg.

^†preMAP: MAP before evacuation, ^¶postMAP: MAP after evacuation.

FIG. 1. Changes in MAP in participants with (A) body weight reduction ≥0.4 kg, (B) pre-evacuation systolic BP ≥140 mmHg.

The analysis revealed no statistically significant difference in MAP between pre- and post-defecation measurements (t=0.938, p>.05). Similarly, the nonparametric Wilcoxon Signed Ranks test confirmed the absence of a significant difference (Z=-0.336, p>.05). The mean pre-defecation MAP was 90.47 mmHg, while the mean post-defecation MAP was 89.47 mmHg.

3. Differences in mean arterial pressure among participants with pre-defecation systolic blood pressure ≥140 mmHg

To investigate differences in MAP among participants with prePsys ≥140 mmHg, a paired t-test was performed. The results are presented in Table 2, and the corresponding graphical representation is shown in Fig. 1B.

The analysis demonstrated a statistically significant difference in MAP between pre- and post-defecation measurements (t=2.600, p<.05). Consistent with this finding, the nonparametric Wilcoxon Signed Ranks test also indicated a significant difference (Z=-2.678, p<.01). These results suggest that defecation plays a particularly important role in maintaining blood pressure stability among individuals with elevated systolic blood pressure.

4. Differences in mean arterial pressure according to pre-defecation systolic blood pressure categories

PrePsys was classified into three categories: normal (<120 mmHg), pre-hypertension (120-139 mmHg), and hypertension (≥140 mmHg). Differences in MAP before and after defecation were examined across these groups (Table 3). The analysis revealed a statistically significant difference in MAP according to prePsys categories (F=12.987, p<.001). These results indicated that the hypertensive group demonstrated the highest MAP values.

TABLE 3. MAP changes among normal, prehypertensive, and hypertensive groups.

^†Normal: systolic pressure ≤119 mmHg, ^‡Prehypertension: systolic pressure between 120-139 mmHg, ^§Stage I hypertension: systolic pressure ≥140 mmHg.

5. Changes in mean arterial pressure according to body mass index (BMI)

To examine differences in MAP according to BMI, participants were classified based on the general obesity criterion of 25 kg/m². The results are presented in Table 4.

TABLE 4. MAP changes according to BMI category (<25 vs. ≥25 kg/m²).

^aFisher’s Exact test p-value, ^†BMI(kg/m²): body mass index.

The analysis showed no statistically significant differences in MAP changes between participants with BMI <25 kg/m² and those with BMI ≥25 kg/m² (p>.05). Specifically, the chi-square test yielded a value of 3.778 (df=1, p=.052), and Fisher’s Exact test also indicated no significant difference (p=.060). Among participants with BMI <25 kg/m², 67.3% exhibited a decrease in MAP, while 32.7% of those with BMI ≥25 kg/m² showed a decrease. Overall, no significant association was observed between BMI category and changes in MAP.

DISCUSSION

Constipation is a common condition, with prevalence rates ranging from 1.9% to 27% in Western populations9,10 and approximately 9.2% in Korea.11 Many individuals seek relief through dietary fiber, exercise, laxatives, or enemas,12 and some use self-colon irrigation under medical supervision.6 While chronic constipation is associated with cardiovascular disease,2 few studies have examined the direct hemodynamic effects of defecation.13

This study is significant as the first to confirm the correlation between intra-abdominal pressure and stool evaluation performed at our tertiary medical institution. However, because a statistically significant difference in MAP was observed only within the small hypertensive subgroup (n=21) and not in the overall cohort, these findings must be interpreted as exploratory and hypothesis-generating. However, relying on subgroup results carries a risk of Type I error, and these data should be validated in larger, prospective trials.

These findings provide scientific evidence to support nursing practice related to bowel management in hypertensive patients within clinical settings. To reflect diverse clinical environments, further studies are recommended that vary in stool characteristics, participant populations, and research designs. Furthermore, our study population represents a highly specific clinical group undergoing tap water enemas for severe bloating and constipation. This inherent selection bias limits the external validity of our findings; the observed hemodynamic parameters may not be generalizable to the broader population with healthy, routine bowel habits, but rather specifically to patients experiencing significant fecal loading.

These results support the potential benefit of promoting regular and sufficient bowel evacuation, particularly in hypertensive individuals, as part of cardiovascular risk management. Nevertheless, it is critical to distinguish between statistical significance and clinical relevance. Although the MAP reduction in the hypertensive group reached statistical significance (p<.05), the absolute change is modest. While maintaining regular defecation may act as a supportive adjunct for blood pressure stability, it should not be considered a substitute for standard, guideline-based antihypertensive therapy.

Limitations of this study include the small number of validation patients, the fact that it was performed as a single study, long ago at a single tertiary medical institution, and the potential data bias. Importantly, a primary mechanistic limitation is the absence of direct intra-abdominal pressure (IAP) measurements; we utilized stool weight reduction (≥0.4 kg) as a surrogate marker. While colonic distension is known to impede adjacent organ perfusion, the lack of direct manometry means the proposed physiological pathway remains exploratory rather than definitive.

Additional standardized, large-scale, multicenter randomized controlled trials are needed for high-risk groups, such as patients with cardiovascular disease and the elderly, who face increased physiological burdens of pneumoperitoneum.

A multidisciplinary approach, including thorough and personalized consultation with anesthesiologists regarding anesthesia, ventilator control, and pharmacotherapy during laparoscopic surgery, followed by postoperative hemodynamic monitoring with nurses and early walking exercises, could help maximize patient recovery and stability before and after surgery.

In conclusion, among patients with hypertension, stool evacuation exceeding the usual daily volume showed a significant association with a reduction in MAP and PP within the hypertensive subgroup, suggesting a potential correlation with decreased intra-abdominal pressure. Encouraging regular, complete bowel movements may be correlated with the stabilization of cardiovascular function.