Effect of Increased Intraabdominal Pressure on Lower Esophageal Sphincter Pressure Wylie J. Dodds, MD, Walter J. Hogan, MD, William N. Miller, MD, John J. Stef, MSME, Ronald C. Arndorfer, and Sean B. Lydon, MD
This study evaluates the effect of intraabdominal pressure increases on lower esophageal sphincter (LES) pressure in normal subjects and in patients with reflux esophagitis. Intraabdominal and intragastric pressure were increased by abdominal compression, the Valsalva maneuver, and leg raising. In normal subjects changes in pressure recorded from the LES equaled the changes in gastric pressure induced by abdominal compression and Valsalva. Consequently the LES-gastric pressure gradient remained unchanged. During leg raising, pressure recorded from the LES increased more than gastric pressure, thereby increasing the LES-gastric pressure gradient. Although statistically significant, the LES pressure increases associated with leg raising were modest, unrelated to initial sphincter pressure, and unaffected by atropine. When individuals demonstrating a "common cavity" phenomenon were excluded, LES pressure changes during abdominal compression were similar in patients with esophagitis and in normal volunteers. Consequently, response of the LES to abdominal compression generally does not separate patients with esophagitis from normal subjects. We believe that the LES responses to increased intra-abdominal pressure observed in this study are better accounted for by mechanical factors than by a physiologic adaptive response of intrinsic LES tone. T h e effect of increased i n t r a a b d o m i n a l pressure on resting l o w e r esophageal sphincter ( L E S ) pressure remains controversial. S o m e studies claim that increases in i n t r a a b d o m i n a l pressure buttress the i n t r a a b d o m i n a l L E S segment without altering intrinsic L E S tone (1-4). O t h e r studies present evidence suggesting that intrinsic L E S tone increases as a physiologic From the Departments of Radiology and Medicine, The Medical College of Wisconsin, Milwaukee, Wisconsin. This work was supported in part by a grant (PR-58) from the Clinical Research Centers Program of the Division of Research Resources, NIH, and by US Public Health Service Research Grants 1 RO1 AM 15540-01 and 1 RO1 GM 19170-01. Abstracted in part in Clin Res 21:825, 1973. Presented at the American Federation of Clinical Research Meeting, Chicago, November 1973. Address for reprint requests: Dr. Wylie J. Dodds, Department of Radiology, Milwaukee County Medical Complex, 8700 West Wisconsin Avenue, Milwaukee, Wisconsin 53226.
298
adaptive response to increased i n t r a a b d o m i n a l pressure (5-8). In this study L E S responses to increased i n t r a a b d o m i n a l pressure w e r e determined in n o r m a l subjects and patients with reflux esophagitis by station and r a p i d pullt h r o u g h techniques, using a catheter system capable of recording L E S pressure radially.
MATERIALS AND METHODS We performed 32 esophageal manometric studies in 20 normal volunteers, ages 18-30 years, mean 22.6 years. Manometric studies were also obtained in 35 patients referred for suspected esophagitis and whose ages ranged from 19 to 68 years, mean 47.3 years. Each patient complained of pyrosis and demonstrated endoscopic evidence of esophagitis. Prior to their referral, a hiatal hernia had been diagnosed by conventional roentgen examination in 30 of the patients. Manometry was performed using a tube assembly of five longitudinally fused polyvinyl catheters (ID 1.6 mm). Sidehole recording orifices, cut at the same axial level in cath-
Digestive Diseases,Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
A. NOTATION LESPr
L E S P r - R e c o r d e d L E S Pressure L E S P c - Calculated L E S P r e s s u r e (LES-Gestric Gradient) GP - Gastric Pressure
LESPc
# GP
B. METHOD I. A CALCULATED LESP 2. A RECORDED LESP rnm Hg
50
50
50
40.
30-
20.
I0-
0
LESPzc = 5 0 - 2 0 = : 5 0 LESP~ c = 4 0 - 1 0
=30
LESpC= 0
z~ L E S P ~ 5 0 - 4 0 = I O A G P = 2 0 - I0 =10 zx LESP r _ I0 _ I Z~ GP
I0
Fig 1. Characterization of changes in lower-esophageal sphincter pressure associated with increases in intraabdominal pressure. (A) Notation. Recorded loweresophageal sphincter pressure, LESP r, refers to the actual pressure recorded from the LES and is generally referenced to atmospheric pressure as O. Calculated loweresophageal pressure, LESP c, is obtained by subtracting gastric pressure, GP, from LESP r. The LESP c value corresponds to the LES to Gastric pressure gradient. (B) Methods: 1. Change in calculated LESP, and 2. Change in recorded LESP. Numerical values are provided for each method to serve as examples. Comparison of the mathematical computations beneath each method reveals that a A LESpC of 0 corresponds to a zx LESpr/zx GP ratio of 1.
eters No. 1 to 4, provided four radial recording orifices oriented equidistantly at 90 ~ angles. Radial recording sites were used to minimize the effect of radial asymmetry of resting lower esophageal sphincter pressure (LESP) (9) as a source in variability of LESP measurement. The fifth
Digestive Diseases, Vol. 20, No. 4 (April 1975)
recording orifice was located 5 cm proximally. A lead marker indicated the position of each recording site. During manometry, each catheter was infused with water by greased S0-ml glass syringes driven by Harvard infusion pumps (Model No. 975) set at a rate of 1.6 ml/min. The
299
D O D D S ET AL
A. Calculated
LESP
mm Hg 30-
LEspC
2oI0
0 I0 GP
,)
7~
LI
u
Z~C-O
AC-50
zo 30
AC-IO0
B. Recorded LESP mm Hg
1!1
40
LESPr
30.
&
20.
GP
tO-
~ O
o
zxp
20
iiiiii
AC-O
z~LESPr= AGp
~.C-50
AC-IO0
0.9
0.9
Fig 2. Effect of abdominal compression on loweresophageal sphincter pressure obtained by station pull-through technique. The bars are drawn from mean values; the black keys represent 1 SE, (A) Calculated LESP. Increases in GP caused by AC caused negligible changes in LESPC. (B) Recorded LESP. Increases in GP caused by AC were associated with nearly equal increases in ,LESP r, resulting in • L E S p r / ~ G P ratios of about 1.
performance characteristics of the recording system were such that occlusion of the manometric tube orifices caused pressure rise rates in the five respective catheters which ranged from 80 to 100 mmHg/sec (10, 11). Respiration and deglutition were monitored by pneumographic belts placed around the thorax and neck (12). Three methods were used to increase intraabdominal pressure: Ca) abdominal compression (AC), (b)the Valsalva 300
(Val) maneuver, and (c) straight leg raising (LR). For AC, a pneumatic pressure cuff wrapped around the abdomen was inflated to 50 (AC-50) and 100 mm Hg (AC-100). During the Val or LR maneuvers, each volunteer subject was able to sustain steady increases in gastric pressure (GP) for 20 to 40 see. After the manometric catheter assembly was passed through the nose, each subject was positioned supine. Because the LES moves proximally during abdominal compression (5, 13), LESP was recorded by pull-through technique. Two types of pull-through were used: Ca) the conventional station technique (SPT) and (b) a rapid technique (RPT) (14). The station pull-through technique featured withdrawal of the four radial recording tips through the LES at 0.5 cm increments, pausing 15 seconds or longer at each station. This method takes several minutes to perform and results in a stepped LES pressure tracing, with oscillations caused by respiratory LES motion (15, 16). The rapid pull-through technique features continuous withdrawal of the radial recording sensors through the LES at a rate of 0.5 to 1.0 cm/sec during a 10- to 15-second interval of suspended respiration. The pressure tracing obtained by RPT is a smooth curve, without steps or oscillations (14). In normal subjects, gastric, LES, and esophageal body pressure were recorded during three types of manometric studies: (a) LESP during AC-0, AC-50, and AC-100 was recorded by SPT in 15 subjects; (b) LESP during AC-0, AC-50, AC-100, Val, and LR was recorded by RPT in 11 subjects; and (c) LESP during AC-0, AC-50, AC-100, and LR was recorded by RPT in 6 subjects before and after atropinization (0.025 mg/kg IV). Three LES pull-throughs were obtained as controls at AC-0 and, subsequently, during each of the respective maneuvers used to increase intraabdominal pressure. In patients with esophagitis, LESP was recorded by RPT at AC-0, AC-50, and AC-100. Three RPT's were obtained at each AC. After manometry, the distal esophagus was fluoroscoped with the patient supine; spot films of barium swallows were taken at AC-0 and AC100. Several methods exist for scoring resting LESP recorded by conventional station pull-through technique (15). We calculated LESP on the SPT tracings by subtracting mean GP from the highest mean pressure recorded at any LES station. Such subtraction is equivalent to referencing GP as zero and yields the LES-gastric pressure gradient. Maximal LESP recorded by RPT was determined by subtracting the steady state GP during suspended respiration from the LES pressure profile peak (14). Two methods exist for characterizing the LESP changes that occur during increases in intraabdominal pressure (Figure 1). The first method (5), features subtracting GP, existing during resting conditions or during abdominal pressure increases, from the actual pressure recorded from the LES lumen (Figure 1, B1). Presumably, this method yields LESP values that cannot be accounted for by any butDigestive Diseases, Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
A. Colculoted LESP mm Hg 4030
LESP c
20 lO 0 tO III
GP
20
: Ill
50 40-
AC-O
AC-50
AC-IO0
VAL
LR
B. Recorded LESP mm Hg 7060-
LESP r 5o, Fig 3. Effect of abdominal compression, Valsalva, and leg raising on lower-esophageal sphincter pressure obtained by rapid pull-through technique. The bars are drawn from mean values; the black keys represent 1 SE. (A) Calculated LESP. LESP c did not change significantly during AC or Val, but increased significantly (about 35%) during LR. (B) Recorded LESP. During AC and Val, changes in LESP r did not differ significantly from changes in GP, yielding ,~ LESpr/_4, GP ratios close to 1. With leg raising however, the increase in LESP r was significantly greater than the change in GP, resulting in an average A LESPr/z~ GP ratio of 1.35.
a
40.
:,:.:.:,~.
.ii
30 20
GP io
z:::.:.: :+::::::
o o
AC-O
AC-50
AC-IOO
VAL
LR
ro
zxp
2o, 30 ........,
40
tressing effect intraabdominal pressure has on an intraabdominal LES segment. Such calculated values are believed to reflect intrinsic LES tone or the LES-gastric pressure gradient, and are noted as LESP c in the manu-
Digestive Diseases, Vol. 20, No. 4 (April 1975)
ALESP r AGP
I.I
0.8
1.0
I.:55
script. Because this method yields ALESpC/AGp ratios which are generally less than 1 and frequently negative, such ratios are meaningless. A second method (6) compares changes in recorded LESP, noted LESP r, against changes
301
DODDS ET AL mm Hg
40 30-
I
LESP c
|
20 t
%M
I0
kN O
I0 ..im J l l J
20
GP
I
3O
4O
AC-O
AC-50
AC-IO0
LR
Fig 4. Effect of atropine on lower-esophageal sphincter pressure changes associated with abdominal compression and leg raising. Sphincter pressures were obtained by rapid pull-through technique. The bars are drawn from mean values and the black keys represent 1 SE. All-postatropine values have diagonal cross hatches. Prior to atropinization, LESP c did not change appreciably during AC, but showed a significant rise of about 20 mm Hg during LR. Atropinization reduced LESP c at AC-0 from 30.7 to 16.9 rnm Hg. Starting from the postatropine baseline value, a negligible change in LESP c occurred during AC, but a significant increase in LESP c occurred during LR. When analyzed as either absolute or percent increase, pre- and postatropine LESP c responses to LR did not differ significantly.
in GP (Figure 1, B2). The ratio ALESpr/AGP is used to characterize sphincter response to abdominal pressure increases, values less than 1 being considered abnormal (8). In this study, both methods for analyzing LESP response to abdominal pressure increases were used. For each SPT or RPT, a mean value of maximal LESP c and LESP r was determined from the four radial catheter tracings. The mean values of three SPTs or three RPTs, respectively, obtained during AC-0 and during each maneuver that produced increased intraabdominal pressure, were averaged. LES position and length recorded by SPT were determined at AC-0, AC-50, and AC-100 by measuring the distance in centimeters from the nares to the proximal and distal LES margins. LES position and length could not be measured accurately from the R P T tracings because the manual withdrawal rate was not uniform, and event marks
302
indicating catheter position were imprecise due to the rapidity of the pull-through. Nevertheless, estimates were made. Statistical comparison between LES pressures as well as LES position and length under different conditions were made using the paired Student's t test.
RESULTS Normal Subjects The effect of abdominal compression on LESP measured by SPT is shown in Figure 2. At AC-0 gastric pressure averaged 11 mm Hg; AC-50 caused an 8.1-mm Hg increase, whereas AC-100 caused a 13.7 m m H g increase. The mean calculated LESP at AC-0, 23.1 mm Hg, Digestive Diseases, Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
did not change significantly during AC-50 or AC-100 (Figure 2A). Changes in recorded LESP during AC-50 and AC-100 were about equal to the changes in gastric pressure, yielding A L E S p r / ~ G P ratios close to 1 (Figure 2B). Pressure rise in the esophageal body during AC was negligible (1 to 2 mm Hg). Significant proximal LES movement (0.5 to 1.0 cm) o c c u r r e d d u r i n g AC-50 and A C - 1 0 0 (P_
This study evaluates the effect of intraabdominal pressure increases on lower esophageal sphincter (LES) pressure in normal subjects and in patients with reflux esophagitis. Intraabdominal and intragastric pressure were increased by abdominal compression, the Valsalva maneuver, and leg raising. In normal subjects changes in pressure recorded from the LES equaled the changes in gastric pressure induced by abdominal compression and Valsalva. Consequently the LES-gastric pressure gradient remained unchanged. During leg raising, pressure recorded from the LES increased more than gastric pressure, thereby increasing the LES-gastric pressure gradient. Although statistically significant, the LES pressure increases associated with leg raising were modest, unrelated to initial sphincter pressure, and unaffected by atropine. When individuals demonstrating a "common cavity" phenomenon were excluded, LES pressure changes during abdominal compression were similar in patients with esophagitis and in normal volunteers. Consequently, response of the LES to abdominal compression generally does not separate patients with esophagitis from normal subjects. We believe that the LES responses to increased intra-abdominal pressure observed in this study are better accounted for by mechanical factors than by a physiologic adaptive response of intrinsic LES tone. T h e effect of increased i n t r a a b d o m i n a l pressure on resting l o w e r esophageal sphincter ( L E S ) pressure remains controversial. S o m e studies claim that increases in i n t r a a b d o m i n a l pressure buttress the i n t r a a b d o m i n a l L E S segment without altering intrinsic L E S tone (1-4). O t h e r studies present evidence suggesting that intrinsic L E S tone increases as a physiologic From the Departments of Radiology and Medicine, The Medical College of Wisconsin, Milwaukee, Wisconsin. This work was supported in part by a grant (PR-58) from the Clinical Research Centers Program of the Division of Research Resources, NIH, and by US Public Health Service Research Grants 1 RO1 AM 15540-01 and 1 RO1 GM 19170-01. Abstracted in part in Clin Res 21:825, 1973. Presented at the American Federation of Clinical Research Meeting, Chicago, November 1973. Address for reprint requests: Dr. Wylie J. Dodds, Department of Radiology, Milwaukee County Medical Complex, 8700 West Wisconsin Avenue, Milwaukee, Wisconsin 53226.
298
adaptive response to increased i n t r a a b d o m i n a l pressure (5-8). In this study L E S responses to increased i n t r a a b d o m i n a l pressure w e r e determined in n o r m a l subjects and patients with reflux esophagitis by station and r a p i d pullt h r o u g h techniques, using a catheter system capable of recording L E S pressure radially.
MATERIALS AND METHODS We performed 32 esophageal manometric studies in 20 normal volunteers, ages 18-30 years, mean 22.6 years. Manometric studies were also obtained in 35 patients referred for suspected esophagitis and whose ages ranged from 19 to 68 years, mean 47.3 years. Each patient complained of pyrosis and demonstrated endoscopic evidence of esophagitis. Prior to their referral, a hiatal hernia had been diagnosed by conventional roentgen examination in 30 of the patients. Manometry was performed using a tube assembly of five longitudinally fused polyvinyl catheters (ID 1.6 mm). Sidehole recording orifices, cut at the same axial level in cath-
Digestive Diseases,Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
A. NOTATION LESPr
L E S P r - R e c o r d e d L E S Pressure L E S P c - Calculated L E S P r e s s u r e (LES-Gestric Gradient) GP - Gastric Pressure
LESPc
# GP
B. METHOD I. A CALCULATED LESP 2. A RECORDED LESP rnm Hg
50
50
50
40.
30-
20.
I0-
0
LESPzc = 5 0 - 2 0 = : 5 0 LESP~ c = 4 0 - 1 0
=30
LESpC= 0
z~ L E S P ~ 5 0 - 4 0 = I O A G P = 2 0 - I0 =10 zx LESP r _ I0 _ I Z~ GP
I0
Fig 1. Characterization of changes in lower-esophageal sphincter pressure associated with increases in intraabdominal pressure. (A) Notation. Recorded loweresophageal sphincter pressure, LESP r, refers to the actual pressure recorded from the LES and is generally referenced to atmospheric pressure as O. Calculated loweresophageal pressure, LESP c, is obtained by subtracting gastric pressure, GP, from LESP r. The LESP c value corresponds to the LES to Gastric pressure gradient. (B) Methods: 1. Change in calculated LESP, and 2. Change in recorded LESP. Numerical values are provided for each method to serve as examples. Comparison of the mathematical computations beneath each method reveals that a A LESpC of 0 corresponds to a zx LESpr/zx GP ratio of 1.
eters No. 1 to 4, provided four radial recording orifices oriented equidistantly at 90 ~ angles. Radial recording sites were used to minimize the effect of radial asymmetry of resting lower esophageal sphincter pressure (LESP) (9) as a source in variability of LESP measurement. The fifth
Digestive Diseases, Vol. 20, No. 4 (April 1975)
recording orifice was located 5 cm proximally. A lead marker indicated the position of each recording site. During manometry, each catheter was infused with water by greased S0-ml glass syringes driven by Harvard infusion pumps (Model No. 975) set at a rate of 1.6 ml/min. The
299
D O D D S ET AL
A. Calculated
LESP
mm Hg 30-
LEspC
2oI0
0 I0 GP
,)
7~
LI
u
Z~C-O
AC-50
zo 30
AC-IO0
B. Recorded LESP mm Hg
1!1
40
LESPr
30.
&
20.
GP
tO-
~ O
o
zxp
20
iiiiii
AC-O
z~LESPr= AGp
~.C-50
AC-IO0
0.9
0.9
Fig 2. Effect of abdominal compression on loweresophageal sphincter pressure obtained by station pull-through technique. The bars are drawn from mean values; the black keys represent 1 SE, (A) Calculated LESP. Increases in GP caused by AC caused negligible changes in LESPC. (B) Recorded LESP. Increases in GP caused by AC were associated with nearly equal increases in ,LESP r, resulting in • L E S p r / ~ G P ratios of about 1.
performance characteristics of the recording system were such that occlusion of the manometric tube orifices caused pressure rise rates in the five respective catheters which ranged from 80 to 100 mmHg/sec (10, 11). Respiration and deglutition were monitored by pneumographic belts placed around the thorax and neck (12). Three methods were used to increase intraabdominal pressure: Ca) abdominal compression (AC), (b)the Valsalva 300
(Val) maneuver, and (c) straight leg raising (LR). For AC, a pneumatic pressure cuff wrapped around the abdomen was inflated to 50 (AC-50) and 100 mm Hg (AC-100). During the Val or LR maneuvers, each volunteer subject was able to sustain steady increases in gastric pressure (GP) for 20 to 40 see. After the manometric catheter assembly was passed through the nose, each subject was positioned supine. Because the LES moves proximally during abdominal compression (5, 13), LESP was recorded by pull-through technique. Two types of pull-through were used: Ca) the conventional station technique (SPT) and (b) a rapid technique (RPT) (14). The station pull-through technique featured withdrawal of the four radial recording tips through the LES at 0.5 cm increments, pausing 15 seconds or longer at each station. This method takes several minutes to perform and results in a stepped LES pressure tracing, with oscillations caused by respiratory LES motion (15, 16). The rapid pull-through technique features continuous withdrawal of the radial recording sensors through the LES at a rate of 0.5 to 1.0 cm/sec during a 10- to 15-second interval of suspended respiration. The pressure tracing obtained by RPT is a smooth curve, without steps or oscillations (14). In normal subjects, gastric, LES, and esophageal body pressure were recorded during three types of manometric studies: (a) LESP during AC-0, AC-50, and AC-100 was recorded by SPT in 15 subjects; (b) LESP during AC-0, AC-50, AC-100, Val, and LR was recorded by RPT in 11 subjects; and (c) LESP during AC-0, AC-50, AC-100, and LR was recorded by RPT in 6 subjects before and after atropinization (0.025 mg/kg IV). Three LES pull-throughs were obtained as controls at AC-0 and, subsequently, during each of the respective maneuvers used to increase intraabdominal pressure. In patients with esophagitis, LESP was recorded by RPT at AC-0, AC-50, and AC-100. Three RPT's were obtained at each AC. After manometry, the distal esophagus was fluoroscoped with the patient supine; spot films of barium swallows were taken at AC-0 and AC100. Several methods exist for scoring resting LESP recorded by conventional station pull-through technique (15). We calculated LESP on the SPT tracings by subtracting mean GP from the highest mean pressure recorded at any LES station. Such subtraction is equivalent to referencing GP as zero and yields the LES-gastric pressure gradient. Maximal LESP recorded by RPT was determined by subtracting the steady state GP during suspended respiration from the LES pressure profile peak (14). Two methods exist for characterizing the LESP changes that occur during increases in intraabdominal pressure (Figure 1). The first method (5), features subtracting GP, existing during resting conditions or during abdominal pressure increases, from the actual pressure recorded from the LES lumen (Figure 1, B1). Presumably, this method yields LESP values that cannot be accounted for by any butDigestive Diseases, Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
A. Colculoted LESP mm Hg 4030
LESP c
20 lO 0 tO III
GP
20
: Ill
50 40-
AC-O
AC-50
AC-IO0
VAL
LR
B. Recorded LESP mm Hg 7060-
LESP r 5o, Fig 3. Effect of abdominal compression, Valsalva, and leg raising on lower-esophageal sphincter pressure obtained by rapid pull-through technique. The bars are drawn from mean values; the black keys represent 1 SE. (A) Calculated LESP. LESP c did not change significantly during AC or Val, but increased significantly (about 35%) during LR. (B) Recorded LESP. During AC and Val, changes in LESP r did not differ significantly from changes in GP, yielding ,~ LESpr/_4, GP ratios close to 1. With leg raising however, the increase in LESP r was significantly greater than the change in GP, resulting in an average A LESPr/z~ GP ratio of 1.35.
a
40.
:,:.:.:,~.
.ii
30 20
GP io
z:::.:.: :+::::::
o o
AC-O
AC-50
AC-IOO
VAL
LR
ro
zxp
2o, 30 ........,
40
tressing effect intraabdominal pressure has on an intraabdominal LES segment. Such calculated values are believed to reflect intrinsic LES tone or the LES-gastric pressure gradient, and are noted as LESP c in the manu-
Digestive Diseases, Vol. 20, No. 4 (April 1975)
ALESP r AGP
I.I
0.8
1.0
I.:55
script. Because this method yields ALESpC/AGp ratios which are generally less than 1 and frequently negative, such ratios are meaningless. A second method (6) compares changes in recorded LESP, noted LESP r, against changes
301
DODDS ET AL mm Hg
40 30-
I
LESP c
|
20 t
%M
I0
kN O
I0 ..im J l l J
20
GP
I
3O
4O
AC-O
AC-50
AC-IO0
LR
Fig 4. Effect of atropine on lower-esophageal sphincter pressure changes associated with abdominal compression and leg raising. Sphincter pressures were obtained by rapid pull-through technique. The bars are drawn from mean values and the black keys represent 1 SE. All-postatropine values have diagonal cross hatches. Prior to atropinization, LESP c did not change appreciably during AC, but showed a significant rise of about 20 mm Hg during LR. Atropinization reduced LESP c at AC-0 from 30.7 to 16.9 rnm Hg. Starting from the postatropine baseline value, a negligible change in LESP c occurred during AC, but a significant increase in LESP c occurred during LR. When analyzed as either absolute or percent increase, pre- and postatropine LESP c responses to LR did not differ significantly.
in GP (Figure 1, B2). The ratio ALESpr/AGP is used to characterize sphincter response to abdominal pressure increases, values less than 1 being considered abnormal (8). In this study, both methods for analyzing LESP response to abdominal pressure increases were used. For each SPT or RPT, a mean value of maximal LESP c and LESP r was determined from the four radial catheter tracings. The mean values of three SPTs or three RPTs, respectively, obtained during AC-0 and during each maneuver that produced increased intraabdominal pressure, were averaged. LES position and length recorded by SPT were determined at AC-0, AC-50, and AC-100 by measuring the distance in centimeters from the nares to the proximal and distal LES margins. LES position and length could not be measured accurately from the R P T tracings because the manual withdrawal rate was not uniform, and event marks
302
indicating catheter position were imprecise due to the rapidity of the pull-through. Nevertheless, estimates were made. Statistical comparison between LES pressures as well as LES position and length under different conditions were made using the paired Student's t test.
RESULTS Normal Subjects The effect of abdominal compression on LESP measured by SPT is shown in Figure 2. At AC-0 gastric pressure averaged 11 mm Hg; AC-50 caused an 8.1-mm Hg increase, whereas AC-100 caused a 13.7 m m H g increase. The mean calculated LESP at AC-0, 23.1 mm Hg, Digestive Diseases, Vol. 20, No. 4 (April 1975)
INTRAABDOMINAL AND LES PRESSURE
did not change significantly during AC-50 or AC-100 (Figure 2A). Changes in recorded LESP during AC-50 and AC-100 were about equal to the changes in gastric pressure, yielding A L E S p r / ~ G P ratios close to 1 (Figure 2B). Pressure rise in the esophageal body during AC was negligible (1 to 2 mm Hg). Significant proximal LES movement (0.5 to 1.0 cm) o c c u r r e d d u r i n g AC-50 and A C - 1 0 0 (P_
