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Revista Latino-Americana de Enfermagem

On-line version ISSN 1518-8345

Rev. Latino-Am. Enfermagem vol.20 no.6 Ribeirão Preto Nov./Dec. 2012 



Analysis of biomechanical parameters extracted from anorectal manometry of fecally-continent and incontinent patients



Bianca EspindolaI; Chris Mayara dos Santos TibesII; Huei Diana LeeIII; Renato Bobsin MachadoIV; André Gustavo MaletzkeV; Wu Feng ChungVI

IMaster's Student, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Brazil
IIIPhD, Professor, Universidade Estadual do Oeste do Paraná, Brazil
IVDoctoral Student, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Brazil. Professor, Universidade Estadual do Oeste do Paraná, Brazil
VMSc, Professor, Universidade Estadual do Oeste do Paraná, Brazil
VIPhD, Professor, Universidade Estadual do Oeste do Paraná, Brasil. Researcher and Professor, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Brazil

Corresponding Author




OBJECTIVE: to evaluate the average resulting area from the Pressure x Time curves resulting from the manometric anorectal exam and compare it with the support capacity of voluntary squeeze. Materials and
METHODS: the data set was represented by data from 11 exams from continent patients and eight exams from patients with grade III fecal incontinence. The manometric curves were delineated, and the areas and support capacity of voluntary squeeze calculated, by means of the R computer language and the algorithm developed. 
RESULTS: the resulting averages for  support capacity of voluntary squeeze in continent patients and patients with grade III fecal incontinence were 33.07 seconds and 30.76 seconds (p>0.05) and the averages for area were 2362.04 mmHg x second and 947.92 mmHg x second (p<0.05), respectively.
CONCLUSION: the average resulting area is able to differentiate continent patients from incontinent and is shown to be a possible parameter in the analysis of biomechanical behavior related to the mechanisms of anorectal continence.

Descriptors: Biomechanics; Colorectal Surgery; Physiology.




Fecal incontinence (FI) is one of the coloproctological disorders which most contributes to an individual's social alienation, because it interferes in his or her physical and psychological conditions.  This is characterized by the loss of control of the physiological mechanisms of defecation, resulting in the unexpected escape of gas and liquid or solid feces via the anal canal(1).

Although the actual incidence of this disorder is not precisely known, it is estimated that it may affect up to 5% of the general population, with high prevalence among the elderly and women(2-5). It is noteworthy that in young patients, the prevalence of FI is higher in women than in men, and that this factor is related to trauma resulting from obstetric procedures(4,6).

The physiology of control of fecal continence (FC) is complex and depends on the integrated action of various factors, such as the musculature of the sphincter and the pelvic floor muscles, the presence of the rectoanal inhibitory reflex, the rectoanal angle, the rectal capacity and compliance, the integrity of the sensory-motor function of the anorectal anatomical region, the patient's neurological state, the consistency of the feces and the bowel transit time(1,7-8). In situations which entail the loss of control of these physiological mechanisms of defecation, as a result of the fact, the scenario of fecal incontinency may arise. This being so, this etiopathogenic condition may be present in old age or be associated with infirmities of clinical or surgical areas such as diabetes mellitus, multiple sclerosis, inflammatory bowel disease, and the post-operative of hemorrhoid disease, and resection of the colon and the rectum(4,9-10).

Various complementary exams are currently used to help in understanding the etiology, detection and classification of FI, such as endoanal ultrasound, pudendal nerve latency time, perineometry and anorectal manometry (AM), this last test being one of the most used(3,11-14). The physical parameters related to the mechanism of defecation, such as presence or absence of the inhibitory rectoanal reflex, resting pressure, maximum voluntary contraction pressure (MVCP) and support capacity of voluntary squeeze (CS) are analyzed through the use of this diagnostic method. The last two attributes are the most requested in the evaluations(1,15). However, according to the studies undertaken, patients diagnosed as incontinent using the MVCP and CS magnitudes are found within the range of normality(1,16-19). This fact indicates that these parameters may evaluate the patient's actual situation incompletely.

For this reason, with the aim of contributing to the broadening of knowledge in the field of anorectal biomechanics, in this work a comparative analysis was performed between the behavior of the physical parameter represented by the average resulting area (ARA) and one of the attributes most requested in routine clinical practice, CS, to promote the differentiation of continent patients and those with grade III (GIII) FI.



This work was carried out in accordance with the Research Ethics Committee's precepts (Protocol number 0481.0.146.000-09/Approval 602/09).

The data set analyzed was represented by data from 19 AM exams belonging to 19 patients, of which 11 were from patients in a condition of fecal continence (FC) and 8 from patients with FI GIII. These tests were performed under the supervision of a single evaluator, in the Anorectal Physiology Laboratory of a Public Institution in the state of São Paulo between September 1995 and August 1996. Exams of patients submitted to AM who did not present sufficient data for classification by the specialist were excluded.

The materials used for the analyses were:

- Computer Intel® Pentium 4 CPU 2.80 GHz, 2.79 GHz, 1 GB of RAM and Microsoft Windows XP Professional operating system, Version 2002, Service Pack 2;

- R version 2.9.1® programming language (LR);

- Java Development Kit 1.6® programming language;

- Tinn R software version 1.19® for assistance in developing algorithms in the LR;

- Data referent to the 19 patients' AM tests, stored in ¾ diskettes in the plaintext.

With the aim of analyzing the ARA of the periods of voluntary squeeze from the Pressure x Time curves, and the resultant average of the support capacity (RCS) for each AM exam, the following stages were undertaken: (1) Classification of the exams; (2) Acquisition of the data and calculation of the parameters; and (3) Analysis of the data.

In Stage (1) tables were devised with information such as the identification of the patient by means of a letter, age, sex, clinical history, date of the exam and results of the exam. Afterwards, the AM tests were classified and grouped by the specialist according to the protocol described below(1):

- Continent: no fecal urgency, easy hygiene, no use of clothing protectors and social and professional activities maintained as normal;

- Grade I (GI): occasional loss of gases, defecation urgency in the event of diarrhea, and preservation of social and professional activities;

- Grade II (GII): frequent escape of gases and liquid feces, defecation urgency of solid feces and partial compromising of the individual's social and professional activities;

- Grade III: incontinence of solid feces, daily escape of feces, fecal urgency, obligatory use of clothing protectors and social and professional activities rendered impossible.

In Stage (2), by means of the software developed based on the LR(20), eight graphs of Pressure x Time were delineated, derived from the acquisition of the pressure values of the eight channels of the catheter for AM. Each graph records three periods of voluntary squeeze of the anal sphincter, thus resulting in 24 pressure periods. Afterwards, the specialist analyzed the 24 moments of voluntary squeeze originated by the eight sensors of the AM test and selected three periods derived from one channel for the demarcation of the CS. In this context the starting and finishing points of the voluntary squeeze were defined and, in the remaining 21 moments, the CS was defined automatically by the software developed (Figure 1).

After these actions, the areas under the Pressure x Time curves (APT) of the AM exams were determined, using the method of Numerical Integration Trapezoidal Rule and were represented by the interval between the initial and final points of the voluntary squeeze (Figure 2).



In Stage (3), the averages and the standard deviations (SD) of the CS and APT were calculated by the software developed. Following that, the values arising from the exams of the patients in conditions of FC were compared with the results of the tests of individuals with FI GIII, fixing the level of rejection of the null hypothesis at the value of p ≤ 0.05.



The result of the voluntary support of each patient with condition of continence and FI GIII, and the parameters such as the averages and standard deviations, are presented in Table 1.



The ARA values derived from the Pressure x Time curves for each patient in a condition of continence or FI GIII, and the parameters such as averages and standard deviations, are presented in Table 2.



The result of the statistical comparisons performed between the continent patients and those with FI GIII, and their respective ARA and RCS is described in Table 3.




The mechanisms involved in FI are complex. Currently, various supplementary exams are used in clinical practice to help in the investigation, evaluation, quantification and determination of this etiopathogenic condition, and they may be represented by radiological and ultrassonographic investigations and biomechanical tests such as the AM(1,14,21).

Since it was introduced in 1965, anorectal manometry has become one of the most important methods for evaluating FC, due to its efficacy, ease of use and relatively low cost(22). Since this date, various studies have been done using AM, and, considering this, this method has become one of the most requested for understanding the physiology of defecation and for monitoring infirmities related to FI(3,11-12). Through this exam, various physical parameters of anorectal biomechanical behavior may be analyzed, such as resting pressure, rectoanal inhibitory reflex, MVCP and CS, the last two attributes being the most used by the specialists(1,15). It is worth emphasizing that, despite the two attributes mentioned being widely requested in the investigation of FI, doubts still remain regarding these physical parameters' relationship to the actual clinical situation presented by the incontinent patient, as measurements of MVCP and CS found in these patients may have values similar to those found in continent persons(1,16,23-25).

Within this ambit, researchers have shown in a previous work that 39% of the 36 incontinent patients had MVCP within normal limits(24). In a separate study related to AM, other investigators reported that 54% of the incontinent patients had normal MVCP in line with the following distribution: GI, 62%, GII, 60% and GIII, 7%. The same study observed that 78% of the patients with FI did not have adequate CS and that in 75% of these patients, the MVCP was below the normal(1).

Considering these aspects, there is the possibility that the physical parameters derived from the AM may contribute in the study of the physiology of continence and in the act of defecation, but these demand better analysis of the same and of other methods which may contribute to a more complete understanding of this complex mechanism.

In this way, in the present work, two physical magnitudes derived from the anorectal manometry test were analyzed. These parameters were represented by the average resulting of the CS and by the average resulting area derived from the Pressure x Time curves of the patients' AM exams, with this last magnitude being original to the studies of the manometric dynamic of defecation.

It should be stressed that the exams used in this work were always administered by a single specialist and in the same service. This characteristic is fundamental, as it demonstrates the concern over the homogeneity of the undertaking of the exam and the precision of the results achieved. On the other hand, it significantly reduces the quantity of samples, principally when this data is from a hospital or teaching institution. For this reason, training must be carried out with the students, residents and teams as a whole with the aim of achieving greater homogeneity in the data arising from the AM exams, so as to achieve maximum precision in the results.

The attributes such as age, sex and type of surgery undertaken may also affect the results' accuracy, however,  it was decided to analyze all the patients selected randomly during September 1995 to August 1996, who met the criteria proposed in the exclusion protocol(1). In this way, it was possible to investigate the population of patients who were submitted to the anorectal manometric test in the Coloproctological department of a public institution in the state of São Paulo during the period of the study.

For the calculation of the RCS and of the ARA, software using the computer language R was developed. The choice of LR in the development of the software for assisting the studies of AM was based in the fact it is open source and robust, making it ideal in the academic setting, bearing in mind that it facilitates in resolving the problem of paid-for software licenses(20,25).

The averages resulting from the CS found in the groups of continent patients and in the patients with FI GIII were 33.07 seconds and 30.76 seconds, respectively. Through statistical analysis, it was observed that there was no significant difference for p-value < 0.05 (p=0.3872). This characteristic demonstrates that this physical attribute was unable to distinguish, in the data set analyzed, the presence or not of FC.

This result, when compared to another study carried out, did not demonstrate significant similarity considering the CS parameter in determining the conditions of fecal continence and incontinence. It is believed that this difference may be explained by the combination of parameters such as the specificity and sensitivity  found by this author, that is, the values of 93% and 78% respectively(1). In this context, through this relationship, there is the inference that studies of greater depth - such as prospective studies with analysis of this physical attribute - may contribute to a better understanding of this issue.

Another parameter analyzed in the present work is the ARA. This physical magnitude is obtained through calculating the result of the areas of the 24 moments of voluntary squeeze and support derived from the graphs for Pressure x Time of each AM exam. This value corresponds to the result of the energy accumulated by the group of muscles responsible for continence and is based in the inter-relation of the physiological actions of these anatomical structures(25).

In this work, the results obtained from the ARA of the control group and the group of patients with FI GIII were 2362.04 mmHg x second and 947.92 mmHg x second, respectively. Through the statistical analysis, it could be observed that there was a significant difference for p-value < 0.05 (p=0.001).

The dispersions of the RCS found in the groups of continent and incontinent patients were 12.18% and 16.32%, while in the ARA, these were 38.86% and 50.06%, respectively. Although the dispersions of the data of the ARA are higher, it is important to take into account that the RCS evaluates only one physical attribute, time, while the ARA analyzes two physical magnitudes fundamental for the biomechanical behavior of defecation, pressure and time, pressure being directly related to the result of the forces exercised by the muscles per unit of area.

In biomechanics, physical attributes of muscular action are characterized most completely through the energy spent for the completion of a task, this being equivalent to the product of the force of the muscle by the amplitude of the contraction of the same. The muscle's force is directly related to the number of muscle fibers, and the amplitude of contraction depends on the degree of shortening of these structures(25).

In this way, the muscles which make up the pelvic floor work together for maintaining control of continence, and this condition depends on various factors such as the patient's neurological state, the volume and consistency of the feces, the rectal compliance and sensitivity, the function of the sphincters of the anus and the recto-anal inhibitory reflex. All these attributes are correlated and the response is directed and attributed principally by the action of the musculature of this anatomical region. This being so, in accordance with these characteristics, one may say that the work done by the muscles is represented by the result of the forces exercised by the whole set of muscles responsible for the maintenance of continence.

Currently, various works have as their scope the study of other methods and parameters for the evaluation of the biomechanics of defecation. The use of these tools can help in new fields of research, contributing to the understanding and elucidation of doubts regarding anorectal physiology, and, contribute in the diagnosis, treatment and prevention of this serious etiopathogenic condition.



The analyses accomplished in this work permit the following conclusions:

The average result of the support capacity of the pressure of voluntary squeeze was not shown to be adequate for the differentiation of continent patients and patients with grade III fecal incontinence;

The average resulting area derived from the Pressure x Time curves of the anorectal manometry exams were shown to be adequate for differentiating patients with the characteristic of continence and patients with grade III fecal incontinence and are shown to be a possible parameter in the analysis of the biomechanical behavior related to the mechanisms of anorectal continence.



We would like to express our gratitude to professors Cláudio Saddy Rodrigues Coy and João José Fagundes for their support in all phases of the study.



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Corresponding Author:
Bianca Espindola
Rua Goslar, 139
Bairro FrankFurt
CEP: 85960-000, Marechal Cândido Rondon, Brasil

Received: May 17th 2012
Accepted: Nov. 6th 2012

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