Skip to main content

Normal values for high-resolution anorectal manometry in healthy young adults: evidence from Vietnam



High-resolution anorectal manometry (HRAM) has been developed to improve measurement of anorectal functions. This study aims to identify normal HRAM values in healthy young Vietnamese adults.


We conducted a cross-sectional study at the National Hospital of Traditional Medicine (Hanoi, Vietnam) from July through December 2014. Healthy young adults were invited to participate in the study. All anorectal measurement values were performed using the ISOLAB high-resolution manometry system. Differences between groups were analyzed using Student’s t-tests.


Thirty healthy young adults, including 15 males and 15 females aged 19–26 years, were recruited. Mean functional anal canal length was 3.4 ± 0.5 cm (range: 2.4–4.8 mm). Mean maximum resting pressure, mean maximum squeezing pressure, mean maximum coughing pressure, and mean maximum strain pressure were 65.5, 168.0, 125.9, and 84.2 mm Hg, respectively. All anal pressure values were significantly different between males and females. For rectal sensation measurements, only the volume at first sensation was significantly higher in males than in females.


This study provides normal HRAM value for healthy young adults in Vietnam. Sex may influence anal pressure and first rectal sensation values in this cohort. Further studies should be conducted in order to improve the quality of HRAM normal values and to confirm the effects of sex.

Peer Review reports


Anorectal manometry (ARM) is considered a leading method for describing anal and rectal functions [1, 2]. ARM measurements include functional anal canal length, anal pressure, defecation index, rectoanal inhibitory reflex (RAIR), and rectal sensation values, which, together, provide a description of comprehensive anorectal functioning [3,4,5]. Conventional ARM was widely used to diagnose and monitor anorectal disorders, although measurements varied in a manner that could affect diagnosis [6, 7]. As such, high-resolution anorectal manometry (HRAM) has been developed over the last ten years as an improved method for measuring anorectal function [2]. HRAM provides a comprehensive topographic and colorimetric mapping of the anorectal area. To accomplish this, the ARM sensor system and computer software were improved in order to record values of ARM over time and across locations by various companies whose HRAM technologies may include varying features, including differing numbers of pressure-sensitive elements, or various analytical software packages [2, 8, 9].

HRAM can aid in the detection of common anorectal disorders including fecal incontinence, constipation, and Hirschsprung’s disease [2]. However, HRAM values are suspected to fluctuate, affecting diagnosis in several anorectal diseases. Therefore, it is necessary to determine baseline HRAM values ​​in healthy people to be used in comparison with values from anorectal patients. Previous studies from various countries have reported related values [8, 10,11,12]. In Vietnam, HRAM technique is relatively common, and a study comparing HRAM values in patients before and after doppler-guided transanal hemorrhoidal dearterialization has previously been published [13]. However, there are no known studies regarding HRAM values ​​in healthy people. Moreover, there are no known studies investigating HRAM values ​​specifically in healthy young adults. As such, the aim of this study is to identify normal HRAM values in healthy young Vietnamese adults.


We conducted a cross-sectional study at the National Hospital of Traditional Medicine (Hanoi, Vietnam). The study was approved by the ethics committee of the Military Medical University, Vietnam by the Decision no. 2858/QD-HVQY dated 23/11/2010. The study was conducted in accordance with relevant guidelines and regulations. Informed consent was obtained from all participants. This study was implemented from July through December 2014 as part of a larger research project investigating the use of doppler-guided transanal hemorrhoidal dearterialization (THD) in treating patients with hemorrhoid disease grades III and IV. A previous study was conducted that reported on anorectal HRAM values among hemorrhoidal patients before and after THD [13]. In the current study, all participants were healthy volunteers recruited from the pool of medical students at Vietnam University of Traditional Medicine in Hanoi. We provided study participants with all information regarding study aims, objectives, and possible anorectal HRAM adverse effects. All participants provided written consent before participating in the study.

We calculated the study sample size according to the formula for estimating a population mean proposed by the World Health Organization [14]. We assumed a maximum resting pressure of 69.1 mm Hg, according to the results of a previous study [11]. In addition, we assumed a population standard deviation of the maximum resting pressure of 12.5 mm Hg. With a significance level of 0.05 and a relative precision of 10 %, we calculated that the minimum sample size was 13 people. Since we intended to compare anorectal HRAM values between males and females, we doubled the sample size and included a 15% non-response rate, suggesting a selection of 30 healthy volunteers, including 15 males and 15 females. Inclusion criteria for participants included normal defecation for at least three months prior to enrollment and normal physical abdominal and digital anorectal examinations. We excluded participants who had constipation, fecal incontinence, obstructed defecation, hematochezia, hemorrhoid, rectal mucus discharge, or any history of anorectal disease. We conducted digital rectal examinations for all participants to ensure that participants were free from any anorectal disorders or diseases.

We used an ISOLAB high-resolution manometry system (Standard Instruments GmbH, Karlsruhe, Germany) with a 6 mm diameter catheter probe and eight-channel sensors to measure anorectal HRAM values. We recorded HRAM values based on pressure and an electromyographical signal from the digestive tract. To extract anorectal HRAM values after measurement, we used ViMeDat software (Visible Medical Data; Standard Instruments GmbH, Karlsruhe, Germany), which integrates with the ISOLAB system. All participants underwent an enema (Fleet enema, C.B. Fleet Company, Inc., Lynchburg, VA, USA) approximately one hour before measurement. We measured maximum anorectal HRAM pressure values of participants during periods of resting, squeezing, pushing/straining, and coughing, and defined a defecation index as the ratio of the maximum rectal strain pressure to the minimum anal strain pressure. We requested the participant relaxed by lying without speaking for about 5 min to measure the pressure in the resting period. To measure the pressure in the squeezing period, the participant was asked to squeeze the anal canal tightly for 20 s. Then, the participant was instructed to bear down (as if to defecate) for 10–20 s to measure the pressure of the pushing period. Wes asked the participant to cough five to seven times to measure the pressure in the coughing period. In this study, the RAIR was assessed if anal relaxation was greater than 25%. Rectal sensation was measured using a rectal balloon filled with air in 10 mL increments up to a total of 300 mL, and was recorded at three volumes corresponding to participant reporting of first sensation, the desire to defecate, and the urge to defecate. All measurements of the HRAM values in this study were performed by the guidelines proposed by Rao et al. and Lee et al. [2, 15].

Analytical results of quantitative variables were presented as means, standard deviation, and range (minimum and maximum). Differences between males and females were analyzed using Student’s t-test. We conducted all data analyses using STATA version 14.0 (Stata Corp, College Station, TX, USA). Statistical differences were considered significant at p values < 0.05.


A total of 30 healthy young adults were recruited to participate in the study, including 15 males and 15 females. Participants ranged from 19 to 26 years old, and 27/30 (90 %) of participants were aged 23 or 24 years old. Table 1 shows study participant HRAM values. Mean functional anal canal length was 3.4 ± 0.5 cm (range: 2.4–4.8 mm). Anal pressure values included mean maximum squeezing pressure at 168.0 ± 61.0 mm Hg and mean maximum resting pressure at 65.5 ± 13.9 mm Hg. Mean defecation index was 2.2 ± 0.9 (range: 1.3–4.8). Mean threshold volume to elicit RAIR was 17.0 ± 5.3 mL. Values for rectal sensation measurements were 19.7 mL, 46.7 mL, and 221.0 mL at the first sensation, desire to defecate, and urge to defecate, respectively.

Table 1 Anorectal HRAM parameters in 30 healthy study participants

Table 2 presents HRAM values according to sex. The functional anal canal was significantly longer in males than in females (p < 0.01). In addition, all anal pressure values, including mean maximum anal squeeze pressure, mean maximum anal cough pressure, mean maximum anal strain pressure, mean maximum rectal cough pressure, and mean maximum rectal strain pressure, were also significantly higher in males than in females (all values < 0.05). There were no significant differences in defecation index or threshold volume to elicit RAIR between males and females. For rectal sensation values, only the volume at first sensation was significantly higher in males than in females.

Table 2 Anorectal HRAM parameters in 30 healthy participants according to participant sex


This is the first study in Vietnam to explore typical HRAM values among healthy young adults and thus sets standard baseline values against which to compare in future studies. We show that males tended to have higher HRAM values than did females. Furthermore, we suggest that the availability of normal HRAM values will improve future diagnosis and treatment for patients with anorectal diseases.

Functional anal canal length was one indicator measured and allows comparison to various previous studies. Measured functional anal canal length was similar in our study to results reported by Carrington et al. [8], but much higher than those reported by Jorge et al. [16]. These differences may relate to measurement protocol or to sample size. Furthermore, functional anal canal length values as measured by HRAM may be affected by rectal pressure. When rectal pressure is low, functional anal canal length measurements may be inaccurate due to external artifacts. Vollebregt et al. demonstrated that a rectal pressure of 20 mm Hg or higher is optimal for measuring functional anal canal length [17]. As there is no current specific guideline for controlling rectal pressure during functional anal canal length measurement, it is possible that results from various studies cannot be meaningfully compared. However, all previous studies indicated significant differences in functional anal canal length between men and women; specifically, it was often higher in men than that in women [8, 16, 17]. Although functional anal canal length measurement may not be expected to have much diagnostic value in patients with fecal incontinence or constipation, it may still be useful for detecting anomalies in those patients. We suggest that studies that include a larger sample size should be conducted in order to learn more about functional anal canal length association with various anorectal disorders or diseases.

In this study, we measured baseline anorectal pressure values in healthy young adults, something which reflects the function of the anorectal muscles, including maximum resting pressure, maximum squeezing pressure, maximum coughing pressure, and maximum strain pressure values. Although previous studies have often reported these parameters, previously-reported values may not be as complete as those in our study, or may include other pressure values [8,9,10,11,12, 18, 19]. Although absolute anal pressure values in our study differ from those reported in previous studies, our results maintain previously-reported patterns. Specifically, mean maximum squeezing pressure was the highest pressure value, while mean maximum resting pressure was the lowest. We also found wide variability between minimum and maximum values for each parameter [8,9,10,11,12, 18, 19]. Whereas our study participants were of a similar age, and age did not affect our study results, we did find a statistically significant difference in anal pressure parameters between male and female study participants. This result is consistent with previous studies indicating that mean anal pressure values tended to be higher in males than in females [2, 8, 10, 19, 20]. As anal pressure is induced by the internal anal sphincter, external anal sphincter, and soft tissue of the anal canal [21,22,23], anatomical and physiological differences between males and females likely induce significant differences in measured anal pressure values [24]. Although there was wide variability and overlap between sexes of anal pressure measurements, understanding sex-related differences of anal pressure parameters may help improve anorectal disorder diagnosis and research. As there are currently no guidelines regarding the limits of these indicators, using standard protocols [2, 15, 25] and measuring values in healthy people may improve interpretation of study results and diagnosis in specific anorectal medical disorders [8, 12, 20, 26, 27].

The defecation index is defined as the ratio between the intrarectal pressure and anal sphincter residual pressure. Rectal pressure should thus generally exceed anal pressure in healthy adults [2]. In this study, we found that all defecation index values were greater than 1.3. In addition, we found no statistically significant difference in defecation index between males and females. Both of these results were consistent with previous studies [10, 19], although the defecation index was less commonly reported in studies of healthy people, regardless of its potential to indicate functional defecation disorder [28, 29]. Several studies indicated that some healthy people displayed dyssynergic defecation during HRAM measurement [28, 29].

RAIR indicates the anal reflex response and as such has been used to rule out a number of diseases, including megacolon and Hirschsprung’s disease [30, 31]. In our study, RAIR occurred in all study participants, indicating that all participants had the anal reflex response, although the threshold to elicit RAIR varied among participants. We found that the mean volume to elicit RAIR was 17 mL and was not significantly different between males and females. This result is similar to that of Coss-Adam et al., although those authors used high-definition anorectal manometry (HDAM-3D) [19]. Although no previous studies used HRAM to report on the threshold to elicit RAIR [8, 12, 20, 26, 27], we believe that it is an important parameter to aid research and disease diagnosis.

With regards to rectal sensation, our results differed from those of previous studies [12, 20]. Noelting et al. did not report any difference in rectal sensation between males and females [12], whereas Kritasampan et al. reported that the threshold volume to elicit the urge to defecate was significantly higher in males than in females [20]. Using HDAM-3D, Li et al. reported no significant differences between males and females [11], although Coss-Adam showed significant differences between males and females at the threshold volumes of desire to defecate and urgency to defecate [19]. These differences in reporting could be due to measurement protocols or the use of different measuring equipment. In addition, previous studies had a small sample size, so results may diverge from, and not reflect, actual population values. Studies with a larger sample size may thus be needed to improving knowledge about factors related to rectal sensation.

We are aware of some limitations of this study. The sample size was relatively small, something that may affect statistical interpretation. In addition, this was a single-center study, and our results may not be generalizable to the entire population. Beyond this, several other HRAM measurements that are important in assessing anorectal functions were not included in this study, and, although we realize that there are many other factors associated with anorectal function, we did not include those factors here. We conducted this study before the time of London classification for disorders of anorectal function published [32], so we could not apply some recommendations suggested by this protocol, which might limit comparison with other studies. Moreover, this is a cross-sectional study, so interpreting results to indicate causal relationships may not be recommended.


This study establishes normal values of HRAM in young healthy adults in Vietnam. Sex influenced HRAM parameters, including functional anal canal length and the threshold volume of first sensation. We recommend implementing a study with a larger sample size to further confirm HRAM values in the Vietnamese population. In addition, a multicenter study may be needed in order to develop a standard set of normal HRAM values which could indicate baseline values for comparisons useful in the diagnosis and treatment for patients with anorectal medical disorders.

Availability of data and materials

The datasets generated during and/or analyzed during the current study are available in the Figshare repository:


  1. 1.

    Azpiroz F, Enck P, Whitehead WE. Anorectal functional testing: review of collective experience. Am J Gastroenterol. 2002;97(2):232–40.

    PubMed  Google Scholar 

  2. 2.

    Lee TH, Bharucha AE. How to perform and interpret a high-resolution anorectal manometry test. J Neurogastroenterol Motil. 2016;22(1):46–59.

    Article  Google Scholar 

  3. 3.

    Rao SS. Pathophysiology of adult fecal incontinence. Gastroenterology. 2004;126(1 Suppl 1):S14-22.

    PubMed  Google Scholar 

  4. 4.

    Lunniss PJ, Gladman MA, Hetzer FH, Williams NS, Scott SM. Risk factors in acquired faecal incontinence. J R Soc Med. 2004;97(3):111–6.

    Article  Google Scholar 

  5. 5.

    Diamant NE, Kamm MA, Wald A, Whitehead WE. AGA technical review on anorectal testing techniques. Gastroenterology. 1999;116(3):735–60.

    CAS  Article  Google Scholar 

  6. 6.

    Scott SM, Gladman MA. Manometric, sensorimotor, and neurophysiologic evaluation of anorectal function. Gastroenterol Clin North Am. 2008;37(3):511–38 vii.

    Article  Google Scholar 

  7. 7.

    Carrington EV, Scott SM, Bharucha A, Mion F, Remes-Troche JM, Malcolm A, Heinrich H, Fox M, Rao SS, International Anorectal Physiology Working G, et al. Expert consensus document: advances in the evaluation of anorectal function. Nat Rev Gastroenterol Hepatol. 2018;15(5):309–23.

    Article  Google Scholar 

  8. 8.

    Carrington EV, Brokjaer A, Craven H, Zarate N, Horrocks EJ, Palit S, Jackson W, Duthie GS, Knowles CH, Lunniss PJ, et al. Traditional measures of normal anal sphincter function using high-resolution anorectal manometry (HRAM) in 115 healthy volunteers. Neurogastroenterol Motil. 2014;26(5):625–35.

    CAS  Article  Google Scholar 

  9. 9.

    Jung KW, Joo S, Yang DH, Yoon IJ, Seo SY, Kim SO, Lee J, Lee HJ, Kim KJ, Ye BD. A novel high-resolution anorectal manometry parameter based on a three‐dimensional integrated pressurized volume of a spatiotemporal plot, for predicting balloon expulsion in asymptomatic normal individuals. Neurogastroenterol Motility. 2014;26(7):937–49.

    Article  Google Scholar 

  10. 10.

    Lee HJ, Jung KW, Han S, Kim JW, Park SK, Yoon IJ, Koo HS, Seo SY, Yang DH, Kim KJ, et al. Normal values for high-resolution anorectal manometry/topography in a healthy Korean population and the effects of gender and body mass index. Neurogastroenterol Motil. 2014;26(4):529–37.

    CAS  Article  Google Scholar 

  11. 11.

    Li Y, Yang X, Xu C, Zhang Y, Zhang X. Normal values and pressure morphology for three-dimensional high-resolution anorectal manometry of asymptomatic adults: a study in 110 subjects. Int J Colorectal Dis. 2013;28(8):1161–8.

    Article  Google Scholar 

  12. 12.

    Noelting J, Ratuapli SK, Bharucha AE, Harvey DM, Ravi K, Zinsmeister AR. Normal values for high-resolution anorectal manometry in healthy women: effects of age and significance of rectoanal gradient. Am J Gastroenterol. 2012;107(10):1530–6.

    Article  Google Scholar 

  13. 13.

    Cuong LM, Nam V, Ha TT, Ha TT, Hung TQ, Van Loi D, Hung TM, Van Son N, Kien VD. Anorectal functional outcomes following Doppler-guided transanal hemorrhoidal dearterialization: evidence from Vietnam. Adv Ther. 2020;37(3):1136–44.

    CAS  Article  Google Scholar 

  14. 14.

    Lwanga SK, Lemeshow S, Organization WH. Sample size determination in health studies: a practical manual. Geneva: World Health Organization; 1991.

    Google Scholar 

  15. 15.

    Rao SS, Azpiroz F, Diamant N, Enck P, Tougas G, Wald A. Minimum standards of anorectal manometry. Neurogastroenterol Motil. 2002;14(5):553–9.

    CAS  Article  Google Scholar 

  16. 16.

    Jorge JM, Habr-Gama A. The value of sphincter asymmetry index in anal incontinence. Int J Colorectal Dis. 2000;15(5–6):303–10.

    CAS  Article  Google Scholar 

  17. 17.

    Vollebregt PF, Rasijeff AM, Pares D, Grossi U, Carrington EV, Knowles CH, Scott SM. Functional anal canal length measurement using high-resolution anorectal manometry to investigate anal sphincter dysfunction in patients with fecal incontinence or constipation. Neurogastroenterol Motility. 2019;31(3):e13532.

    Article  Google Scholar 

  18. 18.

    Jones MP, Post J, Crowell MD. High-resolution manometry in the evaluation of anorectal disorders: a simultaneous comparison with water-perfused manometry. Am J Gastroenterol. 2007;102(4):850–5.

    Article  Google Scholar 

  19. 19.

    Coss-Adame E, Rao SS, Valestin J, Ali-Azamar A, Remes-Troche JM: Accuracy and reproducibility of high-definition anorectal manometry and pressure topography analyses in healthy subjects. Clin Gastroenterol Hepatol. 2015;13(6):1143–50 e1141.

    Article  Google Scholar 

  20. 20.

    Kritasampan P, Lohsiriwat S, Leelakusolvong S: Manometric tests of anorectal function in healthy adult Thai subjects. J Med Assoc Thai. 2004;87(5):536–42.

    PubMed  Google Scholar 

  21. 21.

    Lestar B, Penninckx F, Kerremans R: The composition of anal basal pressure. Int J Colorectal Dis. 1989;4(2):118–22.

    CAS  Article  Google Scholar 

  22. 22.

    Lestar B, Penninckx F, Rigauts H, Kerremans R: The internal anal sphincter can not close the anal canal completely. Int J Colorectal Disease. 1992;7(3):159–161.

    CAS  Article  Google Scholar 

  23. 23.

    Gold D, Bartram C, Halligan S, Humphries K, Kamm M, Kmiot W: Three-dimensional endoanal sonography in assessing anal canal injury. Br J Surg. 1999;86(3):365–70.

    CAS  Article  Google Scholar 

  24. 24.

    Williams AB, Cheetham MJ, Bartram CI, Halligan S, Kamm MA, Nicholls RJ, Kmiot WA: Gender differences in the longitudinal pressure profile of the anal canal related to anatomical structure as demonstrated on three-dimensional anal endosonography. Br J Surg. 2000;87(12):1674–9.

    CAS  Article  Google Scholar 

  25. 25.

    Kim J-H: How to interpret conventional anorectal manometry. J Neurogastroenterol Motility 2010;16(4):437–9.

    CAS  Article  Google Scholar 

  26. 26.

    Ratuapli SK, Bharucha AE, Noelting J, Harvey DM, Zinsmeister AR: Phenotypic identification and classification of functional defecatory disorders using high-resolution anorectal manometry. Gastroenterology 2013;144(2):314–22.e312.

    Article  Google Scholar 

  27. 27.

    Ratuapli S, Bharucha AE, Harvey D, Zinsmeister AR: Comparison of rectal balloon expulsion test in seated and left lateral positions. Neurogastroenterol Motility: Offi J Eur Gastroint Motility Soc. 2013;25(12):e813-e820.

    Article  Google Scholar 

  28. 28.

    Seong M-K: Assessment of functional defecation disorders using anorectal manometry. Ann Surg Treat Res. 2018;94(6):330–6.

    Article  Google Scholar 

  29. 29.

    Seo M, Joo S, Jung KW, Lee J, Lee HJ, Soh JS, Yoon IJ, Koo HS, Seo SY, Kim D et al. A high-resolution anorectal manometry parameter based on integrated pressurized volume: a study based on 204 male patients with constipation and 26 controls. Neurogastroenterol Motil. 2018;30(9):e13376.

    CAS  Article  Google Scholar 

  30. 30.

    de Lorijn F, Kremer LC, Reitsma JB, Benninga MA. Diagnostic tests in Hirschsprung disease: a systematic review. J Pediatr Gastroenterol Nutr. 2006;42(5):496–505.

    Article  Google Scholar 

  31. 31.

    Cheeney G, Nguyen M, Valestin J, Rao SSC: Topographic and manometric characterization of the recto-anal inhibitory reflex. Neurogastroenterol Motility: Offi J Eur Gastroint Motility Soc. 2012;24(3):e147–e154.

    Article  Google Scholar 

  32. 32.

    Carrington EV, Heinrich H, Knowles CH, Fox M, Rao S, Altomare DF, Bharucha AE, Burgell R, Chey WD, Chiarioni G. The international anorectal physiology working group (IAPWG) recommendations: standardized testing protocol and the London classification for disorders of anorectal function. Neurogastroenterol Motility. 2020;32(1):e13679.

    Article  Google Scholar 

Download references


The authors thank participants who participated in this study. The views expressed in this article are solely those of the authors and do not represent the official positions of the organizations the authors are affiliated with.


The authors received no funding.

Author information




LMC and VDK developed the study concept and design, wrote the main manuscript text. LMC, HVQ, TMH, NNA, TTH, VDK contributed to the data collection and analysis. HVQ, VVD, DVL, HHHK contributed to the study design. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Le Manh Cuong.

Ethics declarations

Ethics approval and consent to participate

The study was approved by the ethics committee of the Military Medical University, Vietnam by the Decision no. 2858/QD-HVQY dated 23/11/2010. The study was conducted in accordance with relevant guidelines and regulations. Informed consent was obtained from all participants.

Consent for publication

Not applicable.

Competing interest

The authors declare that they have no competing interests.

Additional information

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Cuong, L.M., Van Quyet, H., Hung, T.M. et al. Normal values for high-resolution anorectal manometry in healthy young adults: evidence from Vietnam. BMC Gastroenterol 21, 295 (2021).

Download citation


  • High-resolution anorectal manometry
  • Anorectal manometry
  • Normal values
  • Healthy young people
  • Vietnam