Small intestinal obstruction is a frequently encountered clinical problem. To understand the mechanisms behind obstruction and the clinical consequences, data are needed on the relation between the morphologic and biomechanical remodeling that takes place in the intestinal wall during chronic obstruction. We sought to determine the effect of partial obstruction on mechanical and morphologic properties of the guinea pig small intestine. Partial obstruction was created surgically in 2 groups of animals living for 2 and 4 weeks. Controls were sham operated and lived for 4 weeks. A combined impedance planimetry-high-frequency ultrasound system was designed to measure the luminal cross-sectional area and wall thickness. These measures were used to compute the circumferential stress and strain of the excised intestinal segments. The incremental elastic modulus was obtained by using nonlinear fitting of the stress-strain curve. Histologic analysis and the measurements of total wall collagen were also performed. The luminal cross-sectional area, wall thickness, and elastic modulus in circumferential direction increased in a time-dependent manner proximal to the obstruction site (P < 0.01), whereas no differences in these parameters were found distal to the obstruction site (P > 0.25). The circumferential stress-strain curves of the proximal segments in 2- and 4-week groups shifted to the left, indicating the intestinal wall became stiffer. Histologic examination revealed a massive increase in the thickness of the muscle layer especially the circular smooth muscle layer (P < 0.05). The collagen content proximal to the obstruction site was significantly larger in the partially obstructed animals compared to controls (P < 0.05). No difference was found distal to the obstruction site. Strong correlation was found between the collagen content and the elastic modulus at stress levels of 70 kPa stress (P < 0.01) and 10 kPa (P < 0.05) proximal to the obstruction site suggesting that the alteration of collagen has great impact on the mechanical remodeling. The morphologic and biomechanical remodeling likely influence the function of the intestine affected by partial obstructed intestine.
The aim of the present study was to correlate the severity of oesophageal motor dysfunction with the severity of cutaneous disease in systemic sclerosis (SS). Patients were divided into three groups based on the degree of skin involvement: type I, acrosclerosis distal to the wrist; type II, scleroderma extending above the wrist in proximal direction; type III, diffuse cutaneous systemic sclerosis. Impedance planimetry employing distensions with pressures up to 5 kPa with the concomitant measurement of oesophageal cross-sectional area (CSA) was used in combination with standard oesophageal manometry. Measurements were made at 7 and 15 cm above the lower oesophageal sphincter (LOS). Thirty patients (16 type I, six type II and eight type III patients) and 23 normal controls were included. LOS pressure was lower in SS patients than in normal patients, with the lowest values in type III. The CSAs were higher in SS patients than in controls at both sites (P < 0.001). The CSAs at the distal site were highest in type III, as compared to type I and II (P < 0.03). The CSA at the highest induced pressure (5.0 kPa) was 613 +/- 45, 719 +/- 79, and 808 +/- 115 mm2 in types I, II and III, respectively. No differences in CSA were found at the proximal site between the three types of SS. The distensibility did not differ between SS and normal patients at the distal site. The distensibility was lowest in SS patients (P < 0.001) at the proximal distension site. The distensibility did not vary with the type of SS at either site. Significant differences in contraction frequency of the secondary peristalsis as function of wall tension were demonstrated between the SS patients and controls at the distal site (P < 0.05). No differences were found at the proximal site. The contraction frequency and amplitude at the distal and proximal sites did not differ among the three types. In conclusion for most parameters studied, SS patients differed from normal patients. Among SS types, the most pronounced changes were found in type III.
Partial obstruction of the small intestine results in dysmotility and morphometric changes proximal to the site of obstruction. However, our understanding of the relation between the morphometric remodeling and change in the motility pattern during chronic obstruction is sparse. The aim of this study was to investigate the effect of partial chronic intestinal obstruction on motility, morphology, and collagen content proximal and distal to the site of obstruction. Twenty guinea-pigs with partial intestinal obstruction and eight sham-operated controls lived for four weeks. Spontaneous and bolus-induced motility was recorded in isolated intestinal segments proximal and distal to the site of obstruction using a perfused low-compliance pressure-measuring system in vitro. After the motility experiments, the specimens were fixed at 2 kPa luminal distension pressure and sampled for histomorphometric determination of luminal radius, layer thickness, and wall thickness. Total wall collagen was also determined. The area under the curve (AUC) of spontaneous contractions and the amplitude, frequency, and AUC for the bolus-induced motility were higher in the proximal segments of the banded animals compared to distal segments and to the intestinal segments in the control animals (P < 0.05). The radius-to-thickness ratio was lowest in the proximal segments of the obstructed animals (P < 0.01). The collagen content was three times higher proximal to the site of obstruction when compared to distal locations and to the controls (P < 0.01). The AUC at 2 ml bolus injections plotted against the radius-to-thickness ratio showed a strong association (r = 0.97 for control, and r = 0.99 for obstruction, P < 0.01). No correlation was found between the collagen content and AUC. In conclusion, partial intestinal obstruction in guinea pigs caused pronounced changes in morphology and motility. An association was found between the radius-to-thickness ratio and bolus-induced motility.
The aim was to study and compare the passive biomechanical wall properties in the isolated duodenum and distal ileum of the guinea pig in vitro. The organ bath contained a Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. Stepwise inflation of an intraluminal balloon, in which the cross-sectional area (CSA) was measured, provided the distension stimulus. The circumferential wall tension-strain distributions and wall stiffness-strain relations were computed from steady-state values of these measurements in order to evaluate the passive elastic properties. The CSA always reached equilibrium within the 2-min distension period. The CSAs obtained in the distal ileum were higher than those in the duodenum (P < 0.001). The basal CSA was 17.31 +/- 1.14 mm2 and 12.96 +/- 0.42 mm2 for the distal ileum and the duodenum, respectively (P < 0.01). At a maximum pressure of 6 kPa, the CSA of the ileum was 56.63 +/- 1.81 mm2 and 36.86 +/- 1.76 mm2 for the duodenum (P < 0.01). The circumferential wall tension-strain distributions showed an exponential behavior that accorded well with the equation Y = exp(a+bX) with determination coefficients of 0.96 +/- 0.01 and 0.99 +/- 0.00 in the duodenal segments in the distal ileal segments, respectively. The values of a (intercept with the y-axis) were 0.54 +/- 0.11 and -0.35 +/- 0.19 for the duodenal and ileal segments, respectively (P < 0.001). The slope of the curves (b values) were 4.34 +/- 0.35 in the duodenal and 5.23 +/- 0.37 in the ileal segments (0.1 > P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
The aim of the study is to devise a method for direct measurements of pressure, cross-sectional area (CSA) and wall thickness of a vessel when pressurised. Segments of porcine descending thoracic aorta from 22 and 35 kg pigs (in groups 1 and 2, respectively) and of abdominal aorta from 35 kg pigs are studied in vitro. Impedance planimetry provides measurements of the luminal pressure and CSA of the aorta. The wall thickness is measured simultaneously by means of 20 MHz A-mode ultrasound. The pressure, CSA and wall thickness are registered at different pressure at steady state. At maximum pressure, the CSAs are 107 +/- 10, 215 +/- 19 and 257 +/- 17 mm2 in the abdominal, group 1 and 2 segments, respectively. There is a difference between the abdominal group and groups 1 and 2 (p < 0.05), but not between group 1 and 2 segments (p > 0.2). At maximum pressure, the wall thickness is 0.52 +/- 0.04, 0.79 +/- 0.07 and 1.07 +/- 0.02 mm, in the abdominal group 1 and 2 segments, respectively (p < 0.05). The circumferential stress-strain relationship accorded well with stress = a x exp(b x strain). The stress-strain curve of the abdominal aortas is shifted to the left, indicating an increase (p < 0.05).
We compared the stress-strain distributions obtained from isolated segments of the guinea pig duodenum, jejunum, and distal ileum, and the relation between the elastic properties and the collagen content. The segments were immersed in Krebs-Ringer solution containing 10(-2) M MgCl2 to abolish contractile activity. Stepwise inflation of an intraluminal balloon in which the cross-sectional area (CSA) was measured provided the luminal pressure-loading stimulus. The wall thickness was measured by means of 20-MHz A-mode ultrasound. The stress-strain and the incremental elastic modulus-strain distributions were derived from the steady-state values of wall thickness, internal radius, and applied pressure. The CSA-pressure relations and the wall thickness-pressure relations were nonlinear and both differed between the segments (P < 0.01). The stress-strain distributions showed an exponential behavior that fitted well to the equation Y = a x Exp(b x X) (r2 = 0.97 +/- 0.01). The intercept with they axis (a) and the slope of the curves (b) differed between the segments (P < 0.01 and P < 0.05). The collagen contents were 3.99 +/- 0.18 microg/mg, 2.51 +/- 0.13 microg/mg, and 2.10 +/- 0.11 microg/mg in the duodenum, jejunum, and distal ileum, respectively. This difference was significant among all three locations (P > 0.05). An association was found between the collagen content and the incremental elastic modulus (stiffness) at a stress level of 70 kPa (P < 0.05).
The aim was to investigate elastic wall properties of the isolated perfused porcine duodenum using manometry and impedance planimetry. Distension of an intraluminal balloon with definite pressure steps of 0.5, 1.0, 2.0, 3.0 and 5.0 kPa was done with simultaneous recording of balloon pressure and balloon cross-sectional area (Bcsa). Wall thickness of the relaxed intestine was estimated from measurement of tissue density. The elastic wall parameters were calculated from these measurements. Balloon inflation elicited a phase of rapid Bcsa increase followed by an accommodation phase of slow Bcsa increase. At steady state, the circumferential and the radial wall stress increased as linear functions of the applied balloon pressure, while the circumferential and the radial wall strain increased nonlinearly. The incremental elastic moduli increased exponentially. Our model allows the study of passive biomechanical wall properties of the intact duodenum. The duodenal wall showed qualitatively and also quantitatively an elastic nature.
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