Biomechanical wall properties of the human rectum. A study with impedance planimetry

Biomechanical properties of the rectal wall were studied in 17 healthy adult volunteers (nine men and eight women). With impedance planimetry it is possible to obtain simultaneous measurements of pressure and rectal cross sectional area (CSA) during balloon inflations. Rectal distensions were done with an intraluminal balloon using specified pressures up to 40 cmH2O above baseline rectal pressure. Balloon inflation elicited a phase of rapid increase in rectal CSA followed by a phase of slow increase until a steady state was reached. Steady state occurred within 67 to 140 seconds with the shortest period at the highest distension pressures. Steady state rectal CSA values had a non-linear relation to increasing distension pressure. Rectal CSA values in women showed a tendency of being slightly higher than male values at all pressure steps with a significant difference at 3 and 5 cm H2O. Biomechanical parameters were calculated from rectal CSA pressure relations. Circumferential wall tension increased in a linear way. Rectal compliance decreased in a non-linear way with no further decline between 30 and 40 cmH2O. The pressure elastic modulus increased steeply until a distension pressure of 35 cmH2O with no further increase to 40 cmH2O. This suggests that rectal tone is reduced as the muscle fails to resist further distension at 35 cmH2O and higher pressures. Impedance planimetry offers new possibilities for investigation of anorectal physiology through the study of segmental biomechanical wall properties of the human rectum.

A new combined high-frequency ultrasound-impedance planimetry measuring system for the quantification of organ wall biomechanics in vivo

The aim was to develop a method for the quantification of the stress-strain distribution of tubular organs in vivo using the porcine duodenum as an experimental model. We placed four electrodes for impedance planimetry and a 20 MHz ultrasound transducer inside an inflatable balloon mounted on a 6 mm-diameter probe for intraluminal use. By means of the ultrasound transducer and the impedance planimetric system, we measured the wall thickness and luminal cross-sectional area of the duodenum. We calculated the luminal radius on the basis of the latter. We validated ultrasonic measurements of wall thicknesses by comparing the former to microscopic measurements of the wall thickness of unstrained duodenal specimens in vitro. Also, we tested whether the magnitude of the applied balloon pressure affected ultrasonic measurements in vitro. The luminal and the outer radius increased non-linearly by a factor of three, rising steeply at low balloon pressures, moderately at higher pressures. The wall thickness decreased as an almost linear function of the applied balloon pressure, resulting in a 50% decrease. The stress-strain distribution calculated on the basis of the balloon pressures, the wall thicknesses and the luminal radii were non-linear. The wall reached a maximum circumferential strain of 1.71 at 6 kPa, corresponding to a stress of 64.8 kPa. Our system enabled us to quantify the stress-strain distribution of the porcine duodenum in vivo, and it may become a valuable tool for future biomechanical investigations of tubular organs in health and disease.

Characteristics of spontaneous and evoked motility in the isolated perfused porcine duodenum

The aims of the study were to evaluate characteristics of spontaneous motility and of the ascending excitatory peristaltic reflex (AEPR) and intraluminal cross-sectional area in the isolated perfused porcine duodenum. The parameters were measured by an intraluminal catheter by use of the perfused side-hole technique and impedance planimetry. Respiratory parameters such as pH and oxygen consumption and the arterial perfusion pressure were monitored and did not vary significantly throughout the study time. Spontaneous motility was intense at the beginning but declined and disappeared within 45-90 min. It was abolished by atropine, epinephrine, and UK-14,304 (an alpha 2-adrenoceptor agonist). Secondary motility was evoked by intraluminal balloon distensions by raising the balloon pressure to 1.5 kPa for 1-min periods. Reproducible results regarding the AEPR, external balloon diameters to elicit the AEPR, and intraluminal cross-sectional area were obtained. The order of potency (pD2 values) for inhibition of the AEPR was the selective M3-receptor antagonist 4-DAMP greater than atropine greater than the selective M2-receptor antagonist AFDX-116 greater than the selective M1-receptor antagonist pirenzepine greater than hexamethonium. 4-DAMP was 16 and 29 times more potent than AFDX-116 (P less than 0.02) and pirenzepine (P less than 0.02). None of the drugs altered the intraluminal cross-sectional area during the balloon distensions. The model provides the opportunity for physiological and pharmacological studies of duodenal motility and duodenal cross-sectional area devoid of extrinsic neural and endocrine effects. The abolishment of the AEPR by atropine is caused by blockade of the M3-receptor in the porcine duodenum.

Biomechanical wall properties of the porcine rectum: a study using impedance planimetry

The aim was to investigate biomechanical wall properties of the porcine rectum by way of manometry and impedance planimetry. Distension of a balloon inserted into the rectum with definite pressure steps up to 80 cm H2O was done for simultaneous recording of pressure and the balloon cross-sectional area (Bcsa). Viscoelastic wall properties were derived in terms of compliance. Besides eliciting the ascending peristaltic reflex and relaxation of the internal anal sphincter, the balloon inflation elicited a phase of rapid Bcsa increase followed by an accommodation phase of slow Bcsa increase to a steady-state Bcsa, reached within 3 min. The Bcsa increased in a nonlinear way with increasing balloon pressures with only a minimal increase from 70 to 80 cm H2O. Rectal compliance decreased in a nonlinear way with increasing distension pressure.

Elastic properties of the isolated perfused porcine duodenum

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.

Effects of noradrenaline and galanin on duodenal motility in the isolated perfused porcine pancreatico-duodenal block

The influence of neurotransmitters on gastrointestinal motility is different in different segments of the gastrointestinal tract. To clarify the regulation of duodenal motility, the aim of the present study was to investigate the effects of alpha-adrenoceptor agonism and blockade and of galanin on duodenal motility. The study was undertaken in the isolated perfused porcine pancreatico-duodenal block. The agents under investigation were administered arterially. Duodenal motility was measured by means of a low-compliance perfusion system using an intraluminal catheter. In addition the concentration of galanin was measured in the portal effluent. We found that spontaneous motility was abolished by noradrenaline by an effect that was counteracted by the alpha 2-adrenoceptor antagonist idazoxan. In contrast, the selective alpha 1-adrenoceptor antagonist prazosin did not influence the effect of noradrenaline. Galanin, like noradrenaline, abolished duodenal motility. Furthermore, the concentration of galanin in the portal effluent was decreased by noradrenaline by an alpha 2-adrenoceptor mediated mechanism. We conclude that alpha 2-adrenoceptor activation and galanin inhibit duodenal motility and that the release of galanin from the pancreatico-duodenal preparation is reduced by alpha 2-adrenoceptors.

Effect of vasoactive intestinal peptide on duodenal motility in the isolated perfused porcine pancreaticoduodenal block

The peptidergic regulation of duodenal motility has not been clarified in detail. The aim of the present study was to investigate the effect of vasoactive intestinal polypeptide (VIP) on duodenal motility in the isolated perfused porcine pancreaticoduodenal block. VIP was administered arterially at 10(-7) M and motility was measured by means of the perfused side-hole technique using an intraluminal catheter. It was found that spontaneous duodenal motility was intense at the beginning of each experiment. However, the spontaneous motility diminished by time to cease after 45-90 min. VIP inhibited the duodenal motility. Thus, the frequency of duodenal contraction was decreased from 11 (8-16) to 3 (0-10) contractions per minute by VIP (p less than 0.01) and VIP also decreased the arterial perfusion pressure from 7.5 (3.5-23.2) to 5.8 (2.6-17.3) kPa (p less than 0.01). Since the same inhibitory effect has previously been demonstrated after alpha 2-adrenoceptor activation, we also examined whether alpha 1- and alpha 2-adrenoceptor agonism stimulated the release of VIP from this preparation. We then found that alpha 1-adrenoceptor agonism (phenylephrine or noradrenaline plus idazoxan) given intra-arterially stimulated VIP release (p less than 0.01). In contrast, alpha 2-adrenoceptor agonism (UK-14,304 or noradrenaline plus prazosin) had no effect. Therefore, we conclude that VIP inhibits duodenal motility in the pig but that this effect does not mediate the sympathetically induced inhibition of motility.