temperature or electrical impulses is indeed questionable. For this reason most physiologists prefer to measure sensation in terms of a func- tionally known variable volume. In the simplest terms, water at body temperature can be infused through the catheter into an intrarectal balloon.
The levels of first sensation, fullness, and maximum tolerable volume (V) are measured.
These same levels of sensation can be used when calculating rectal compliance. Compliance rep- resents the rectal pressure (P) change that results from infusion of a given quantity of intrarectal content, in this case water. Thus the formula (P1 − P2)/(V2 − V1) can be readily calculated.
Despite the simplicity, reproducibility and func- tional correlation with this technique, reported findings in constipated patients vary greatly (Table 10.1). This may partly reflect differences among various institutions in laboratory tech- nique and definition of the compliance value.
Assessment of Compliance
There are several ways to measure and calculate rectal compliance,
10,12,13but there is still no generally accepted gold standard.
14The most common method is to record the response of intrarectal pressure to progressive rectal disten- tion. This generates a pressure–volume curve, and compliance is defined as the quotient of the change in volume and the change in pressure—
the slope of the curve. The interpretations of the findings, however, are controversial.
15The values obtained are of the threshold volume (volume at which sensation first occurred), fullness volume, and maximal tolerable volume, which vary. This There in no single test that provides a complete
picture of the complex mechanisms of defeca- tion. A comprehensive battery of physiologic tests has gradually assumed an important posi- tion in the evaluation of patients with chronic severe constipation. The normal rectum demon- strates a receptive relaxation in response to dis- tention, conferring its function as a reservoir.
This chapter describes the manovolumetric method for rectal compliance measurement and discusses the clinical importance of rectal reser- voir and sensory function in the investigation of patients with severe chronic constipation.
A major objective finding in constipated patients when compared with controls is the reduced sensation of filling of the rectum (Table 10.1).
1–10Larger than normal volumes are required to distend the rectum sufficiently to evoke a sensation of filling and a desire to evac- uate. This lack of sensitivity is suggestive of a primary neuropathy involving the afferent fibers arising from rather than being secondary to con- stipation.
11Others have postulated that an exces- sive supraspinal inhibition of otherwise normal sacral cord function is a learned subconscious response.
9This impaired sensitivity may explain the difficulty of eliciting the rectoanal inhibitory reflex in some patients with constipation who do not have Hirschsprung’s disease. In addition, the sensitivity cannot be examined when the rectum is dilated, as there might be no contact between the balloon and the rectal wall.
Sensitivity is difficult to quantify. However, both thermal and electrical sensory thresholds can be measured. Despite the reproducibility of these elegant techniques, the teleologic ability of the anorectum to discriminate among various
10
Compliance and Manovolumetry
Olof J. Hallböök and Rune I. Sjödahl
99
variation may reflect a learned cortical response, and may result in a misleading comparison of single values of compliance. Therefore, it may be better to compare the pressure–volume curve of the patient with the normal range (Fig. 10.1) or the mean curves among groups of subjects.
Another possibility is to evaluate the pres- sure–volume quotient at defined distention pres- sure intervals, which can be accomplished with the manovolumetric method described below.
Manovolumetry provides a more objective
measurement of the rectal compliance, as it has no association with the subject’s perception of a rectal balloon.
15Manovolumetry
In the manovolumetry system, the rectal volume is recorded as a dynamic response to a graded rectal distention at atmospheric pressure. This resembles the physiologic events in the intestine,
Waldron et al 19887 44 Increased* Increased* Increased* —
De Medici et al 19898 64 NS — Increased** —
Kerrigan et al 19899 16 — Increased* Increased** —
Wald et al 198910 25 NS Increased* — —
* p< .05; ** p < .01; NS, not significant versus controls; —, no data available.
The figures for compliance and volume are omitted in this table owing to difficulties in comparing laboratory techniques used in various institutions.
Figure 10.1. Pressure–volume re- sponse range in normal subjects (n= 45, mean ± SD) measured with the mano- volumetry method. Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88–91, ©1992, with permission from Elsevier.
amount of water flowing into the air reservoir is measured as weight reduction. This reduction is equal to the volume of the plastic bag, that is, the rectal volume. The water-filled reservoir is open to the air, meaning that the pressure in the rectum is kept constant despite variation in volume. An example of a manovolumetric recording is shown in Figure 10.4, which also shows a recording of the anal canal pressure made at the same time.
The manovolumetric method has the follow- ing properties:
1. Rectal distention with defined pressures allows dynamic registration of volume changes; thus compliance can be calculated in relation to defined pressure intervals.
2. The noncompliant plastic bag is sensitive to bowel wall contractions, making it suitable for motility studies.
3. Anal pressure is recorded simultaneously with rectal volume and motility, which allows assessment of the rectosphincteric reflexes.
Electronic Barostat System
A polyethylene bag in the rectum is fixed to a multilumen tube, which is connected to a baro- stat device. The pressure in the bag is measured via a separate lumen of the tube. The barostat is connected to a computer, where the pressure, volume, and compliance (mL/mm Hg) are constantly monitored and recorded as the pressure–volume curve.
The bag can be distended in steps to either a fixed pressure (isobaric) or a fixed volume (iso- volumetric). It is also able to keep the pressure in the rectal beg at a preselected level, which means that when the rectum relaxes, the system injects air, and when it contracts, the barostat which allow wide changes of volume with
minimal corresponding changes in pressure. It differs from conventional systems where com- pliance is calculated by registration of pressure in response to distention with air or fluid.
The manovolumetry method was designed for investigation of reservoir organs.
16,17It was described and evaluated for studies of anorectal function by Akervall et al
18and Öresland et al.
19The design is shown in Figure 10.2 and the dis- posable part of the system in Figure 10.3. As depicted in Figure 10.2, a water-filled reservoir (a) is open to air and suspended on a weight transducer. This vessel is in continuity via a tube to a closed-air reservoir (b), which is connected to a large, noncompliant plastic bag. This plastic bag is placed in the rectum (c). When the water reservoir is raised, pressure is generated in the air reservoir and consequently in the plastic bag.
This pressure is equal to the difference between the levels of water in the two reservoirs. The
Figure 10.2. Design of the manovol- umetry system.Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88–91, ©1992, with permission from Elsevier.
Figure 10.3. The disposable part of the manovolumetry system. A poly- ethylene bag (length 12 cm, volume 600 mL) hermetically tied to a tube, is placed in the rectum. An endotracheal tube (outer diameter 10 mm) is laced on the tube and used for anal canal pressure registration.Reprinted from Hallbook O, Sjodahl R. Techniques of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88–91, ©1992, with permission from Elsevier.
aspirates air. Thus, the barostat can measure rectal motor activity as changes in the intrarec- tal volume at a constant intrarectal pressure.
20,21Clinical Implications
Preoperative physiologic investigation is manda- tory to select the very small subset of patients with chronic idiopathic constipation who will benefit from colectomy and ileorectal anasto- mosis.
22With respect to rectal reservoir and sensory function in this category of patients, Akervall et al,
23using the manovolumetric method, considered that rectal sensitivity is an important predictive variable for a favorable outcome after colectomy and ileorectal anasto- mosis. They also concluded that sensory abnormalities, which can be demonstrated by manovolumetry, might be overlooked if only the distending volume is recorded.
Preoperatively manovolumetry is more important with normal rectal compliance than with normal sphincter function. A stiff, poorly compliant rectum in combination with the loose
bowel motions in the postoperative period puts considerable stress on the anal sphincters.
The presence of the rectoanal inhibitory reflex should exclude Hirschsprung’s disease. In the absence of a megarectum, the finding of large distending volumes with little sensory awareness should raise the suspicion of spinal disease with the concomitant risk of incontinence if an ileo- rectal anastomosis is performed.
24Conclusion
Owing to the surrounding structures of the rectum and to neurohormonal influence, it is difficult to assess the mechanical properties of the rectal wall in vivo. Thus rectal compliance should be considered as a functional measurement.
The clinical relevance of rectal compliance in the management of constipation is not fully established. Measuring the rectal compliance has not been as important as was expected regarding the decision to operate but is still valuable. The trend is that surgery for constipation is per-
Figure 10.4. Manovolumetry. An example of rectal volume and anal pres- sure response to rectal distention with a preset distention pressure. A steady rate is accomplished within 60 seconds.
(Modified from Akervall et al,23with permis- sion of Springer.)
12. Roe AM, Bartolo DCC, Mortensen NJM. Diagnosis and surgical management of intractable constipation. Br J Surg 1986;73:854–861.
13. Varma JS, Smith AN, Busuttil A. Correlation of clinical and manometric abnormalities of rectal function fol- lowing chronic radiation injury. Br J Surg 1985;72:
875–878.
14. Madoff RD, Orrom WJ, Rothenberger DA, et al. Rectal compliance: a critical reappraisal. Int J Colorectal Dis 1990;5:37–40.
15. Hallböök O, Sjödahl R. Technique of rectal compliance measurement. Semin Colon Rectal Surg 1992;3:88–91.
16. Martinson J. Studies on the efferent vagal control of the stomach. Acta Physiol Scand Suppl 1965;255:1–24.
17. Sundin T, Carlsson CA. Reconstruction of severed dorsal roots innervating the urinary bladder. An exper- imental study in cats. I. Studies on the normal afferent pathways in the pelvic and pudendal nerves. Scand J Urol Nephrol 1972;6:176–184.
18. Akervall S, Fasth S, Nordgren S, et al. Manovolumetry:
a new method for investigation of anorectal function.
Gut 1988;29:614–623.
19. Öresland T, Fasth S, Åkervall S, et al. Manovolumetric and sensory characteristics of the ileoanal J pouch compared with healthy rectum. Br J Surg 1990;77:
803–806.
20. Penning C, Steens J, van der Schaar PJ, et al. Motor and sensory function of the rectum in different subtypes of constipation. Scand J Gastroenterol 2001;36:32–38.
21. Steens J, Penning C, Brussee J. Prospective evaluation of ileoanal pouch characteristics measured by barostat.
Dis Colon Rectum 2002;45:1295–1303.
22. Wexner SD, Daniel N, Jagelman DG. Colectomy for constipation: physiologic investigation is the key to success. Dis Colon Rectum 1991;34:851–856.
23. Akervall S, Fasth S, Nordgren S, et al. The functional results after colectomy and ileorectal anastomosis for severe constipation (Arbuthnot Lane’s disease) as related to rectal sensory function. Int J Colorectal Dis 1988;3:96–101.
24. Bartolo DCC. Diagnostic procedures for incon- tinence, constipation. In: Philips SF, Pemberton JH, Shorter RG, eds. The Large Intestine: Physiology, Pathophysiology and Disease. New York: Raven Press, 1991:727–745.
formed less often today. The role of the rectum in the pathophysiology of chronic idiopathic con- stipation is still poorly understood; further studies of rectal reservoir and sensory function are needed.
References
1. Read NW, Abouzekry L, Read MG, et al. Anorectal func- tion in elderly patients with fecal impaction. Gastroen- terology 1985;89:959–966.
2. Bannister JJ, Timms JM, Barfield LJ, et al. Physiological studies in young women with chronic constipation. Int J Colorectal Dis 1986;1:175–82.
3. Read NW, Timms JM, Barfield LJ, et al. Impairment of defecation in young women with severe constipation.
Gastroenterology 1986;90:53–60.
4. Shouler P, Keighley MRB. Changes in colorectal func- tion in severe idiopathic chronic constipation. Gas- troenterology 1986;90:414–420.
5. Roe AM, Bartolo DCc, Mortensen NJM. Slow transit constipation. Comparison between patients with or without previous hysterectomy. Dig Dis Sci 1988;33:
1159–1163.
6. Varma JS, Smith AN. Neurophysiological dysfunction in young women with intractable constipation. Gut 1988;29:963–968.
7. Waldron D, Bowes KL, Kingma YJ, et al. Colonic and anorectal motility in young women with severe idiopathic constipation. Gastroenterology 1988;95:
1388–1394.
8. De Medici A, Badiali D, Corazziari E, et al. Rectal sensi- tivity in chronic constipation. Dig Dis Sci 1989;34:747–
753.
9. Kerrigan DD, Lucas MG, Sun WM. Idiopathic constipa- tion associated with impaired urethrovesical and sacral reflex function. Br J Surg 1989;76:748–751.
10. Wald A, Hinds JP, Caruana BJ. Psychological and phys- iological characteristics of patients with severe idio- pathic constipation. Gastroenterology 1989;97:932–937.
11. Waldron DJ. Constipation. In: Kumar D, Waldron DJ, Williams NS, eds. Clinical Measurement in Coloproc- tology. London: Springer, 1991:97–108.
