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Anal Sphincter Pressure Characteristics
Vol. 52, No.3 Printed in U.S.A.
GASTROENTEROLOGY
Copyright © 1967 by The Williams & Wilkins Co.
ANAL SPHINCTER PRESSURE CHARACTERISTICS LEONARD A. KATZ, M.D., HERBERT J. KAUFMANN, M.D., AND HOWARD M. SPIRO, M.D.
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
Recently, Harris and Popel have suggested that sphincter competence in the gastrointestinal tract depends upon the ability of the sphincter to resist distention rather than to maintain a state of tonic contraction. This concept has been employed by Harris et a1. 2 in a study of anal sphincter competence in normal subjects and in patients with fecal incontinence. Regardless of theoretical considerations, the technique of distending the anal sphincter to measure its ability to resist distention provides a useful method to study the components of the anal sphincter in normal subjects and in patients with fecal incontinence. Therefore, we have studied the anal sphincter, using a modification of the Harris technique. Our results confirm the findil}g of a "resting yield pressure"; however, :certain important differences are obtained! both in results and in interpretation of sphincter pressures. Methods Forty-eight subjects ranging in age from 7 to 82 years were studied; 15 were normal controls. Of 14 persons who had fecal incontinence, one boy, aged 7, had psychological difficulties and nocturnal incontinence, 4 had diabetes mellitus Received July 8, 1966. Accepted October 12, 1966. Address requests for reprints to: Dr. Howard M. Spiro, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06511. This work was supported in part by Grant AM-04759 from the United States Public Health Service and by a grant from the New Haven Foundation. The authors wish to express their gratitude to Dr. Jonathan Pincus, Department of Neurology, Yale University School of Medicine, who provided several subjects for study. 513
and neuropathy with occasional fecal incontinence, and 9 had fecal incontinence occurring in association with cerebral vascular or other neurological disease. Nineteen subjects had neurological or medical disease but no incontinence. The anal sphincter pressures were recorded using an air-filled, nonelastic plastic balloon made from the finger of a vinyl disposable glove which was attached over a polyethylene catheter (PE260) and secured with ligatures and cement to give an air-tight fit. When the balloon was filled with air, it distended primarily laterally, to give the shape of a cylinder approximately 2.0 cm in length and 1.5 cm in diameter. Initially a water-filled system was used, but this produced technical difficulties which appeared to result from fluid being trapped at the opening of the catheter and hence led to irregular filling of the balloon. Therefore, an air-filled system was employed. The pressure characteristics of the balloon were such that filling did not lead to a pressure rise until the balloon approached complete distention. With 1.0 ml of air injected, there was less than 6 mm Hg pressure rise. The polyethylene tubing, which was 12 inches long, was attached via a three-way stopcock to a Sanborn 267B pressure transducllr, and the electrical output was graphed by a direct writing recorder. With the subject lying on his left side, the uninflated balloon was placed in the anal sphincter so that the ligatures on the outermost part of the balloon were just visible. After opening the system to the atmosphere, the balloon was then distended through the sidearm with OJ-ml increments of air up to a total of 0.8 to 1.2 ml, the pressures produced at each increment being recorded. The balloon was then deflated and the procedure repeated one or more times. With the balloon empty, the subject was asked to tighten the sphincter and to relax it immediately. The balloon was then inflated with OJ-ml increments, and pressures were recorded at rest and with a contraction at each new volume level. This procedure was performed at least two times. Pressure recordings were also made with the subject maintaining
514
KATZ ET AL.
contraction continuously as the balloon was distended. Finally, the subject was instructed to tighten the sphincter and maintain full contraction either until he could not maintain contraction any longer or until he could no longer recognize that he was tightening his sphincter. Results
In each subject, at rest the recorded pressure showed a stepwise increase as the volume in the balloon increased, until a plateau was reached where further increases in volume did not produce pressure changes. This pressure was called the resting yield pressure (RYP) (fig. 1) . When voluntary sphincter tightening was superimposed on the stepwise volume increases, the pressure generated at each
FIG. 1. Resting yield pressure. Arrows indicate increments of 0.1 ml of air. There is a stepwise increase in pressure with each volume increment, until a plateau is reached, after which further increments in volume do not produce pressure cHange. The slight unsustained pressure rises with each injection appear to result from the physical characteristics of the recording system. Resting yield pressure in this subject IS 65 mm Hg . .Paper speed is 2.5 mm per sec.
Vol. 52, No.3
volume level was progressively greater until a plateau was reached at a constant level above the RYP. This pressure represents the maximal sphincter pressure (MSP) (fig. 2). If the subject maintained a contraction of the sphincter at the MSP, additional volume increments in the balloon produced no further pressure rise (fig. 2). In each of the 15 normal patients, the pattern was the same: a definite RYP was found, as was a definite MSP. The pressures obtained for a given individual were reproducible with only minor variation, the highest recorded values being used for each subject. Occasionally, lowering of pressure occurred when the balloon slipped partially out of the anal sphincter, but this was readily detected. The results of the three measurements are presented in figures 3, 4, and 5. The RYP in normals ranged from 35 to 80 mm Hg and the MSP from 80 to 190 mm Hg. All normals were able to maintain sphincter contraction for at least 35 sec. In general, the recorded pressures confirmed digital impression of sphincter tone and contraction strength. In the incontinent subjects, the RYP did not differ from that in the normals. The boy with functional nocturnal incontinence had normal resting yield and maximal pressures. The 4 diabetic patients were also found to have normal RYP and MSP. Each of the 9 incontinent patients with neurological ailments had normal RYP, but 7 of the 9 had maximal pressures which were
FIG. 2. Maximal sphincter pressure. Arrows indicate increments of 0.1 ml of air. A, voluntary sphincter contraction, and each wave thereafter is also a sphincter contraction. There is a stepwise increase in pressure with each volume increment until the resting yield pressure ; the magnitude of each voluntary contraction increases progressively until the resting yield pressure, after which the pressure achieved with each voluntary contraction no longer increases d espite further volume increments. This is the maximal sphincter pressure. In this subject, resting yield pressure equals 45 mm Hg and maximal sphincter pressure equals 120 mm Hg. At B, voluntary contraction was begun and maintained until C, during which additional volume increments did not produce a sustained pressure rise which exceeded the maximal sphincter pressure achieved with single contractions.
ANAL SPHINCTER PRESSURE CHARACTERISTICS
March 1967
at least 10 mm Hg below the lowest value recorded in the normal subjects. In addition, this incontinent group could not maintain sphincter contraction as long as the normal subjects. Other patients with a variety of conditions without incontinence were studied. (a) Two patients with myasthenia gravis receiving treatment had yield and maximal pressures which were normal but prolonged contraction which was abnormal. In 1 patient, a prolonged contraction could be maintained for 74 sec on the first try, but, with repeated attempts, the fifth contraction could be maintained for only 11 sec and the sixth for 14 sec. After a 3-min rest, the patient once again could maintain sphincteric contraction for 46 sec. The other patient could not maintain contraction for more than 20 sec, and, with repeated attempts, the duration of contraction did not shorten. (b) One patient with scleroderma with roentgen evidence of abnormal colon sacculations showed normal resting and maximal pressures but could not maintain prolonged contraction. (c)
mmHg
mmH19
160 140 120 100
60 40 20
• ••••• •••
•••
0
• •• • • +8 • • ... _-------- _!-.-----• x ••• x •• •• •• • •• •
0
•
20
o FIG. 4. Maximal sphincter pressure in normals, subjects with fecal incontinence, and patients with neurological or medical ailments without incontinence. The dotted line serves as reference for the lowest values obtained in the normal group. Maximal sphincter pressure was low for 7 of 14 patients with incontinence and 9 of 19 patients with medical and neurological disease without incontinence. DURATION OF PROLONGED CONTRACTION Normal Incant. Other ···>180
120
100
80
••
40
160
120
•• (1901
60
sec
lJ,
MAXIMAL PRESSURE Normal Incant. Other
80 -!-!.-----
RESTING YiElD PRESSURE Other Normal Incant.
160I
515
••••
•••
•••••
•••
••••
•• ••••• ••
I
•• •• •••• ••• X •• x
0
o FIG. 3. Resting yield pressures in normals, subjects with fecal incontinence, and other patients with neurological and medical ailments without incontinence. ., Pressure recorded from 1 patient; 0, diabetics; +, a 7-year-old boy with functional incontinence; X, patients who had undergone hemorrhoidectomy. The values obtained are similar for the three groups.
80
••• • •
0 0
• ••
8 • ••••• •,,--------• -,--------.-------• x •• ••• •• x • • o ••••• ••
40
FIG. 5. Duration of prolonged contraction. The time in seconds of prolonged contraction from the beginning of pressure rise to return to base line was recorded for normals, patients with fecal incontinence, and patients with medicalor neurological diseases. Of the group with fecal incontinence, all but the diabetic patients (0) had short duration of prolonged contraction.
516
KATZ ET AL.
Two patients had had previous operations for hemorrhoids: 1, a hemorrhoidectomy, and the other, a sclerosing injection of hemorrhoids. The RYP was normal in both, but the MSP and duration of contraction were low in both. (d) Three otherwi"e normal persons with an irritable colon syndrome were able to maintain a prolonged contraction for more than 80 sec. Three other patients with irritable colon syndromes, however, did not have this unusual ability. (e) Seven patients with neurological diseases, including 1 with paraplegia secondary to trauma, 1 with paraparesis caused by multiple sclerosis, 3 with hemiparesis, 1 with Huntington's chorea, and 1 with myotonia dystrophica, demonstrated abnormalities of the voluntary component of the anal sphincter which consisted either of subnormal MSPs or of shortened duration of prolonged contraction. The impaired voluntary contraction was usually noted by prior digital examination. None of these patients was incontinent and several were troubled with constipation. Discussion
Measurement of anal sphincter resistance to distention provides an approach to the study of physiological pressure characteristics of the anal sphincter. At rest, the sphincter resists distention until a critical volume is reached (RYP) , after which further distention is no longer resisted; instead, the sphincter accommodates to the increase in volume so that there is no further pressure rise. Voluntary contraction leads to MSP only when the balloon within the sphincter has been distended to the volume required to reach the RYP. The MSP was also achieved when contraction was sustained and the empty balloon was distended progressively. The increase in pressure recorded during voluntary contraction must be the result of external voluntary sphincter activity. The interpretation of the source of the resting pressure is more difficult; presumably, in large part, it reflects the characteristics of the internal or involuntary component of the sphincter, but this need not be completely so because the striated muscle of the external sphincter overlies smooth
Vol. 52, No.3
muscle of the internal sphincter. In addition, local factors such as hemorrhoids or inflammation may playa role. Resistance to distention may serve as the mechanism of sphincter competence at rest. With voluntary contraction, however, the pressure within the distended balloon rises, thereby measuring the pressure which can be used to close the sphincter forcibly. Thus, upon partial distention of the anal sphincter by rectal contents, voluntary sphincter contraction would close the sphincter to maintain continence. The MSP is a measure of sphincter strength. A test of the physiological significance of the MSP might be obtained by actual measurement of the intraluminal pressures required to overcome the sphincter. In their study of the anal sphincter, Harris et a1. 2 employed an open-tipped, water-filled catheter through which 2-ftliter increments of fluid were added. They found that, with the sphincter at rest, each minute increment of water caused a pressure rise until a plateau was reached, after which further increments produced no pressure rise. This plateau was named the "resting yield pressure." With voluntary tightening of the anal sphincter, no pressure change was observed to occur until additional fluid was introduced, and, again, a stepwise increase in pressure occurred until a new plateau was reached, and this was called the "augmented yield pressure." With relaxation of the sphincter, the pressure fell to approximately the RYP. It was presumed that, at the yield pressures, any additional fluid injected seeped out, leaving a tiny bubble intact at the catheter opening. They found that RYPs in a group of normal subjects ranged from 55 to 90 mm Hg and the augmented yield pressure from 130 to 300 mm Hg. The 5 incontinent patients studied had subnormal resting and augmented yield pressures. Our results for normal subjects are somewhat lower and may, in part, reflect the pressure damping which occurs in an airfilled system. Also, we did not find a difference in the RYPs between patients with incontinence and normals; however, most subjects with incontinence did have low MSP. The MSP recorded by our technique dif-
March 1967
ANAL SPHINCTER PRESSURE CHARACTERISTICS
fers from the augmented yield pressure of Harris. With the Harris method, voluntary tightening of the sphincter produced no pressure change until further increments of fluid were added. This suggested that all pressure changes were the result of resistance to distention of the sphincter. In our system, however, pressure rises were observed with each sphincter contraction regardless of the volume in the balloon, with the maximal pressure rise being achieved only after the balloon had been distended to the volume required to reach the RYP. The explanation for the difference in results lies in technique. The open tipped catheter, when inserted into the sphincter, behaved as if it were "sealed" and hence unable to reflect pressure changes, whereas our nonelastic balloon can reflect these changes. The observed values for the augmented yield pressure and the MSP are comparable; the important distinction is that consideration of the MSP leads one to the conclusion that the voluntary component of the sphincter can act to increase intrasphincteric pressure when the sphincter is distended. Finding some normal pressures in incontinent persons should occasion no surprise; there are different mechanisms of incontinence.! The young boy with functional incontinence certainly would be expected to have normal sphincter pressures. In the diabetic patients, absence of demonstrable weakness of voluntary contraction, together with the history of unrecognized nocturnal incontinence, might suggest a deficit in afferent impulses from the sphincter. Rectal distention has been shown to produce reflex contraction of the external sphincter,3. 4 which may serve to oppose defecation. Incontinent patients with weakness of voluntary contraction, as evidenced by the low MSP, presumably cannot achieve a high enough pressure to oppose the force of peristaltic contraction. If the opposing force is not great, even a weak sphincter may suffice to maintain continence; this may be the explanation for continence in patients with abnormal sphincter pressures, such as 2 patients with paraplegia who also had atonic colons and chronic constipation. One need
517
only consider patients with permanent colostomies and total absence of sphincter to recognize that a weak sphincter need not regularly be accompanied by incontinence. In 2 patients with incontinence despite normal MSP, the duration of voluntary contraction was less than normal. One of these 2 patients had had encephalitis, and the other a brain tumor; the role of cortical factors in sphincter activity in these cases is unknown. This method of study of the anal sphincter may have practical application in the evaluation of resting sphincter tone and sphincter strength. Incontinence which results from weakness of the voluntary sphincter can be identified and separated from incontinence of other etiology. Thus the method has potential clinical usefulness. Summary
A simple method for recording pressures in the anal sphincter during distention at rest and during voluntary contraction is presented. The resting sphincter resists distention until a resting yield pressure is reached, after which further distention of the sphincter produces no further pressure rise. Maximal sphincter pressure is reached by voluntary contraction only after the recording balloon has been distended to the volume needed to reach the resting yield pressure. The ability of the sphincter to resist distention appears to be the mechanism for maintaining continence at rest; however, contraction of the voluntary component of the anal sphincter can forcibly close the sphincter when distended and thereby maintain continence. Of 48 subjects studied, all 14 with incontinence were found to have normal resting yield pressures, but maximal sphincter pressures varied depending upon the cause of incontinence. Most patients with incontinence had low maximal sphincter pressure, but incontinence was not invariable with low maximal sphincter pressure. It is possible to differentiate patients with incontinence as the result of abnormalities of the voluntary component of the anal sphincter from those patients with incontinence of other cause.
518
KATZ ET AL.
REFERENCES 1. Harris, L. D., and C. E. Pope II. 1964. "Squeeze" vs. resistance: an evaluation of the mechanism of sphincter competence. J. Clin. Invest. 43: 2272-2278. 2. Harris, L. D., C. S. Winans, and C. E. Pope II. 1966. Determination of yield pressures: a method for measuring sphincter competence. Gastroenterology 50: 754-760.
Vol. 62, No.3
3. Gaston, E. A. 1958. The physiology of fecal incontinence. Surg. Gynec. Obstet. 87: 280290.
4. Schuster, M. M., P. Hookman, T. R. Hendrix, and A. I. Mendeloff. 1965. Simultaneous manometric recording of internal and external anal sphincter reflexes. Bull. Hopkins Hosp. 116: 79-88.
GASTROENTEROLOGY
Copyright © 1967 by The Williams & Wilkins Co.
ANAL SPHINCTER PRESSURE CHARACTERISTICS LEONARD A. KATZ, M.D., HERBERT J. KAUFMANN, M.D., AND HOWARD M. SPIRO, M.D.
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
Recently, Harris and Popel have suggested that sphincter competence in the gastrointestinal tract depends upon the ability of the sphincter to resist distention rather than to maintain a state of tonic contraction. This concept has been employed by Harris et a1. 2 in a study of anal sphincter competence in normal subjects and in patients with fecal incontinence. Regardless of theoretical considerations, the technique of distending the anal sphincter to measure its ability to resist distention provides a useful method to study the components of the anal sphincter in normal subjects and in patients with fecal incontinence. Therefore, we have studied the anal sphincter, using a modification of the Harris technique. Our results confirm the findil}g of a "resting yield pressure"; however, :certain important differences are obtained! both in results and in interpretation of sphincter pressures. Methods Forty-eight subjects ranging in age from 7 to 82 years were studied; 15 were normal controls. Of 14 persons who had fecal incontinence, one boy, aged 7, had psychological difficulties and nocturnal incontinence, 4 had diabetes mellitus Received July 8, 1966. Accepted October 12, 1966. Address requests for reprints to: Dr. Howard M. Spiro, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06511. This work was supported in part by Grant AM-04759 from the United States Public Health Service and by a grant from the New Haven Foundation. The authors wish to express their gratitude to Dr. Jonathan Pincus, Department of Neurology, Yale University School of Medicine, who provided several subjects for study. 513
and neuropathy with occasional fecal incontinence, and 9 had fecal incontinence occurring in association with cerebral vascular or other neurological disease. Nineteen subjects had neurological or medical disease but no incontinence. The anal sphincter pressures were recorded using an air-filled, nonelastic plastic balloon made from the finger of a vinyl disposable glove which was attached over a polyethylene catheter (PE260) and secured with ligatures and cement to give an air-tight fit. When the balloon was filled with air, it distended primarily laterally, to give the shape of a cylinder approximately 2.0 cm in length and 1.5 cm in diameter. Initially a water-filled system was used, but this produced technical difficulties which appeared to result from fluid being trapped at the opening of the catheter and hence led to irregular filling of the balloon. Therefore, an air-filled system was employed. The pressure characteristics of the balloon were such that filling did not lead to a pressure rise until the balloon approached complete distention. With 1.0 ml of air injected, there was less than 6 mm Hg pressure rise. The polyethylene tubing, which was 12 inches long, was attached via a three-way stopcock to a Sanborn 267B pressure transducllr, and the electrical output was graphed by a direct writing recorder. With the subject lying on his left side, the uninflated balloon was placed in the anal sphincter so that the ligatures on the outermost part of the balloon were just visible. After opening the system to the atmosphere, the balloon was then distended through the sidearm with OJ-ml increments of air up to a total of 0.8 to 1.2 ml, the pressures produced at each increment being recorded. The balloon was then deflated and the procedure repeated one or more times. With the balloon empty, the subject was asked to tighten the sphincter and to relax it immediately. The balloon was then inflated with OJ-ml increments, and pressures were recorded at rest and with a contraction at each new volume level. This procedure was performed at least two times. Pressure recordings were also made with the subject maintaining
514
KATZ ET AL.
contraction continuously as the balloon was distended. Finally, the subject was instructed to tighten the sphincter and maintain full contraction either until he could not maintain contraction any longer or until he could no longer recognize that he was tightening his sphincter. Results
In each subject, at rest the recorded pressure showed a stepwise increase as the volume in the balloon increased, until a plateau was reached where further increases in volume did not produce pressure changes. This pressure was called the resting yield pressure (RYP) (fig. 1) . When voluntary sphincter tightening was superimposed on the stepwise volume increases, the pressure generated at each
FIG. 1. Resting yield pressure. Arrows indicate increments of 0.1 ml of air. There is a stepwise increase in pressure with each volume increment, until a plateau is reached, after which further increments in volume do not produce pressure cHange. The slight unsustained pressure rises with each injection appear to result from the physical characteristics of the recording system. Resting yield pressure in this subject IS 65 mm Hg . .Paper speed is 2.5 mm per sec.
Vol. 52, No.3
volume level was progressively greater until a plateau was reached at a constant level above the RYP. This pressure represents the maximal sphincter pressure (MSP) (fig. 2). If the subject maintained a contraction of the sphincter at the MSP, additional volume increments in the balloon produced no further pressure rise (fig. 2). In each of the 15 normal patients, the pattern was the same: a definite RYP was found, as was a definite MSP. The pressures obtained for a given individual were reproducible with only minor variation, the highest recorded values being used for each subject. Occasionally, lowering of pressure occurred when the balloon slipped partially out of the anal sphincter, but this was readily detected. The results of the three measurements are presented in figures 3, 4, and 5. The RYP in normals ranged from 35 to 80 mm Hg and the MSP from 80 to 190 mm Hg. All normals were able to maintain sphincter contraction for at least 35 sec. In general, the recorded pressures confirmed digital impression of sphincter tone and contraction strength. In the incontinent subjects, the RYP did not differ from that in the normals. The boy with functional nocturnal incontinence had normal resting yield and maximal pressures. The 4 diabetic patients were also found to have normal RYP and MSP. Each of the 9 incontinent patients with neurological ailments had normal RYP, but 7 of the 9 had maximal pressures which were
FIG. 2. Maximal sphincter pressure. Arrows indicate increments of 0.1 ml of air. A, voluntary sphincter contraction, and each wave thereafter is also a sphincter contraction. There is a stepwise increase in pressure with each volume increment until the resting yield pressure ; the magnitude of each voluntary contraction increases progressively until the resting yield pressure, after which the pressure achieved with each voluntary contraction no longer increases d espite further volume increments. This is the maximal sphincter pressure. In this subject, resting yield pressure equals 45 mm Hg and maximal sphincter pressure equals 120 mm Hg. At B, voluntary contraction was begun and maintained until C, during which additional volume increments did not produce a sustained pressure rise which exceeded the maximal sphincter pressure achieved with single contractions.
ANAL SPHINCTER PRESSURE CHARACTERISTICS
March 1967
at least 10 mm Hg below the lowest value recorded in the normal subjects. In addition, this incontinent group could not maintain sphincter contraction as long as the normal subjects. Other patients with a variety of conditions without incontinence were studied. (a) Two patients with myasthenia gravis receiving treatment had yield and maximal pressures which were normal but prolonged contraction which was abnormal. In 1 patient, a prolonged contraction could be maintained for 74 sec on the first try, but, with repeated attempts, the fifth contraction could be maintained for only 11 sec and the sixth for 14 sec. After a 3-min rest, the patient once again could maintain sphincteric contraction for 46 sec. The other patient could not maintain contraction for more than 20 sec, and, with repeated attempts, the duration of contraction did not shorten. (b) One patient with scleroderma with roentgen evidence of abnormal colon sacculations showed normal resting and maximal pressures but could not maintain prolonged contraction. (c)
mmHg
mmH19
160 140 120 100
60 40 20
• ••••• •••
•••
0
• •• • • +8 • • ... _-------- _!-.-----• x ••• x •• •• •• • •• •
0
•
20
o FIG. 4. Maximal sphincter pressure in normals, subjects with fecal incontinence, and patients with neurological or medical ailments without incontinence. The dotted line serves as reference for the lowest values obtained in the normal group. Maximal sphincter pressure was low for 7 of 14 patients with incontinence and 9 of 19 patients with medical and neurological disease without incontinence. DURATION OF PROLONGED CONTRACTION Normal Incant. Other ···>180
120
100
80
••
40
160
120
•• (1901
60
sec
lJ,
MAXIMAL PRESSURE Normal Incant. Other
80 -!-!.-----
RESTING YiElD PRESSURE Other Normal Incant.
160I
515
••••
•••
•••••
•••
••••
•• ••••• ••
I
•• •• •••• ••• X •• x
0
o FIG. 3. Resting yield pressures in normals, subjects with fecal incontinence, and other patients with neurological and medical ailments without incontinence. ., Pressure recorded from 1 patient; 0, diabetics; +, a 7-year-old boy with functional incontinence; X, patients who had undergone hemorrhoidectomy. The values obtained are similar for the three groups.
80
••• • •
0 0
• ••
8 • ••••• •,,--------• -,--------.-------• x •• ••• •• x • • o ••••• ••
40
FIG. 5. Duration of prolonged contraction. The time in seconds of prolonged contraction from the beginning of pressure rise to return to base line was recorded for normals, patients with fecal incontinence, and patients with medicalor neurological diseases. Of the group with fecal incontinence, all but the diabetic patients (0) had short duration of prolonged contraction.
516
KATZ ET AL.
Two patients had had previous operations for hemorrhoids: 1, a hemorrhoidectomy, and the other, a sclerosing injection of hemorrhoids. The RYP was normal in both, but the MSP and duration of contraction were low in both. (d) Three otherwi"e normal persons with an irritable colon syndrome were able to maintain a prolonged contraction for more than 80 sec. Three other patients with irritable colon syndromes, however, did not have this unusual ability. (e) Seven patients with neurological diseases, including 1 with paraplegia secondary to trauma, 1 with paraparesis caused by multiple sclerosis, 3 with hemiparesis, 1 with Huntington's chorea, and 1 with myotonia dystrophica, demonstrated abnormalities of the voluntary component of the anal sphincter which consisted either of subnormal MSPs or of shortened duration of prolonged contraction. The impaired voluntary contraction was usually noted by prior digital examination. None of these patients was incontinent and several were troubled with constipation. Discussion
Measurement of anal sphincter resistance to distention provides an approach to the study of physiological pressure characteristics of the anal sphincter. At rest, the sphincter resists distention until a critical volume is reached (RYP) , after which further distention is no longer resisted; instead, the sphincter accommodates to the increase in volume so that there is no further pressure rise. Voluntary contraction leads to MSP only when the balloon within the sphincter has been distended to the volume required to reach the RYP. The MSP was also achieved when contraction was sustained and the empty balloon was distended progressively. The increase in pressure recorded during voluntary contraction must be the result of external voluntary sphincter activity. The interpretation of the source of the resting pressure is more difficult; presumably, in large part, it reflects the characteristics of the internal or involuntary component of the sphincter, but this need not be completely so because the striated muscle of the external sphincter overlies smooth
Vol. 52, No.3
muscle of the internal sphincter. In addition, local factors such as hemorrhoids or inflammation may playa role. Resistance to distention may serve as the mechanism of sphincter competence at rest. With voluntary contraction, however, the pressure within the distended balloon rises, thereby measuring the pressure which can be used to close the sphincter forcibly. Thus, upon partial distention of the anal sphincter by rectal contents, voluntary sphincter contraction would close the sphincter to maintain continence. The MSP is a measure of sphincter strength. A test of the physiological significance of the MSP might be obtained by actual measurement of the intraluminal pressures required to overcome the sphincter. In their study of the anal sphincter, Harris et a1. 2 employed an open-tipped, water-filled catheter through which 2-ftliter increments of fluid were added. They found that, with the sphincter at rest, each minute increment of water caused a pressure rise until a plateau was reached, after which further increments produced no pressure rise. This plateau was named the "resting yield pressure." With voluntary tightening of the anal sphincter, no pressure change was observed to occur until additional fluid was introduced, and, again, a stepwise increase in pressure occurred until a new plateau was reached, and this was called the "augmented yield pressure." With relaxation of the sphincter, the pressure fell to approximately the RYP. It was presumed that, at the yield pressures, any additional fluid injected seeped out, leaving a tiny bubble intact at the catheter opening. They found that RYPs in a group of normal subjects ranged from 55 to 90 mm Hg and the augmented yield pressure from 130 to 300 mm Hg. The 5 incontinent patients studied had subnormal resting and augmented yield pressures. Our results for normal subjects are somewhat lower and may, in part, reflect the pressure damping which occurs in an airfilled system. Also, we did not find a difference in the RYPs between patients with incontinence and normals; however, most subjects with incontinence did have low MSP. The MSP recorded by our technique dif-
March 1967
ANAL SPHINCTER PRESSURE CHARACTERISTICS
fers from the augmented yield pressure of Harris. With the Harris method, voluntary tightening of the sphincter produced no pressure change until further increments of fluid were added. This suggested that all pressure changes were the result of resistance to distention of the sphincter. In our system, however, pressure rises were observed with each sphincter contraction regardless of the volume in the balloon, with the maximal pressure rise being achieved only after the balloon had been distended to the volume required to reach the RYP. The explanation for the difference in results lies in technique. The open tipped catheter, when inserted into the sphincter, behaved as if it were "sealed" and hence unable to reflect pressure changes, whereas our nonelastic balloon can reflect these changes. The observed values for the augmented yield pressure and the MSP are comparable; the important distinction is that consideration of the MSP leads one to the conclusion that the voluntary component of the sphincter can act to increase intrasphincteric pressure when the sphincter is distended. Finding some normal pressures in incontinent persons should occasion no surprise; there are different mechanisms of incontinence.! The young boy with functional incontinence certainly would be expected to have normal sphincter pressures. In the diabetic patients, absence of demonstrable weakness of voluntary contraction, together with the history of unrecognized nocturnal incontinence, might suggest a deficit in afferent impulses from the sphincter. Rectal distention has been shown to produce reflex contraction of the external sphincter,3. 4 which may serve to oppose defecation. Incontinent patients with weakness of voluntary contraction, as evidenced by the low MSP, presumably cannot achieve a high enough pressure to oppose the force of peristaltic contraction. If the opposing force is not great, even a weak sphincter may suffice to maintain continence; this may be the explanation for continence in patients with abnormal sphincter pressures, such as 2 patients with paraplegia who also had atonic colons and chronic constipation. One need
517
only consider patients with permanent colostomies and total absence of sphincter to recognize that a weak sphincter need not regularly be accompanied by incontinence. In 2 patients with incontinence despite normal MSP, the duration of voluntary contraction was less than normal. One of these 2 patients had had encephalitis, and the other a brain tumor; the role of cortical factors in sphincter activity in these cases is unknown. This method of study of the anal sphincter may have practical application in the evaluation of resting sphincter tone and sphincter strength. Incontinence which results from weakness of the voluntary sphincter can be identified and separated from incontinence of other etiology. Thus the method has potential clinical usefulness. Summary
A simple method for recording pressures in the anal sphincter during distention at rest and during voluntary contraction is presented. The resting sphincter resists distention until a resting yield pressure is reached, after which further distention of the sphincter produces no further pressure rise. Maximal sphincter pressure is reached by voluntary contraction only after the recording balloon has been distended to the volume needed to reach the resting yield pressure. The ability of the sphincter to resist distention appears to be the mechanism for maintaining continence at rest; however, contraction of the voluntary component of the anal sphincter can forcibly close the sphincter when distended and thereby maintain continence. Of 48 subjects studied, all 14 with incontinence were found to have normal resting yield pressures, but maximal sphincter pressures varied depending upon the cause of incontinence. Most patients with incontinence had low maximal sphincter pressure, but incontinence was not invariable with low maximal sphincter pressure. It is possible to differentiate patients with incontinence as the result of abnormalities of the voluntary component of the anal sphincter from those patients with incontinence of other cause.
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REFERENCES 1. Harris, L. D., and C. E. Pope II. 1964. "Squeeze" vs. resistance: an evaluation of the mechanism of sphincter competence. J. Clin. Invest. 43: 2272-2278. 2. Harris, L. D., C. S. Winans, and C. E. Pope II. 1966. Determination of yield pressures: a method for measuring sphincter competence. Gastroenterology 50: 754-760.
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3. Gaston, E. A. 1958. The physiology of fecal incontinence. Surg. Gynec. Obstet. 87: 280290.
4. Schuster, M. M., P. Hookman, T. R. Hendrix, and A. I. Mendeloff. 1965. Simultaneous manometric recording of internal and external anal sphincter reflexes. Bull. Hopkins Hosp. 116: 79-88.