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 This study concerns a method named impedance planimetry by which it is possible to obtain segmental information on biomechanical properties at one specific circumference of the rectal wall. The aim was to describe these properties by measuring rectal cross sectional area (CSA) at the site ofdistension upon graded isobaric distension in healthy volunteers. We have used the technique in human and animal studies of intestinal wall properties." Methods SUBJECTSWe studied 17 healthy volunteers without any history of bowel disease. The volunteers were nine men (age 28 (27-29) years, height 185 (179-187) cm, weight 80 (75-85) kg) and eight women (26 (23-29) years, 169 (166-172) cm, 58 (53-63) kg). Before the study we obtained informed consent from all subjects. The study was performed according to the second declaration of Helsinki and approved by the Ethical Committee of Aarhus county.The study was conducted between 8 00 am and 1 00 pm. There was a period of at least 12 hours of fasting before the investigations. No laxative was used and subjects were asked to empty the rectum and bladder. Before the investigation a digital examination confirmed an empty rectum. TECHNIQUE AND EXPERIMENTAL PROBE DESIGNWe used a specially constructed four electrode impedance measuring system located inside a balloon on a 20 cm long probe with an 8 mm external diameter (Fig 1). Two outer ring electrodes for excitation were placed with an interelectrode distance of 6 cm. A generator delivered a constant alternating current of 100 microamperes at 5 kHz for excitation.9 5 Midway between the excitation electrodes we placed two ring electrodes with an interelectrode distance of 0-2 cm for measurement of impedance. We used copper electrodes wound around the probe in 0 5 mm wide grooves to ensure a smooth surface. The distance between the excitation and detection electrodes was chosen on the basis that the CSA can be measured up to a diameter of 4 to 5 times the interelectrode distance. 3We measured CSA according to the field gradient principle from the measurement of impedance of the fluid inside the balloon.'3'I_8Rise time for measurement of CSA was 0-02

The propagation speed (C) of surface acoustic waves (SAW), e.g. Rayleigh (R-waves) and longitudinal lateral waves (L-waves), the latter being the surface manifestation ofthe longitudinal waves, strongly reflect mechanical properties of materials. In view of an increasing interest in ultrasonic methodology in the field of bone biomechanics, we tested the hypothesis that both R-and L-waves can be excited in trabecular bone using an acoustic microscope at 1 GHz and that their speeds ( C , and C,) can be extracted from V(z)-curves, i.e. plots of lens output voltage as a function of the lens focal point position with respect to the specimen surface. In accordance with V(z)-curves theoretically synthesized on the basis of incident field theory, experimental curves for canine femoral trabecular bone showed evidence of both R-and L-waves in almost all regions of recording. The measured CR ranged between I .93 and 2.07 km/s (mean & SD.: 2.00 i 0.06 kmls) and the CL ranged between 2.33 and 4.33 km/s (3.37 & 0.61 km/s). Knowledge of both speeds allowed computation of a number of material constants by means of simple theory of elasticity and assumptions of the material density. We found values of Poisson ratio ( u ) ranging from 0.14 to 0.32 (0.23 & 0.07). Young's modulus ( E ) from I5 to 22.8 GPa (19.9 I 2.5 GPa) and the shear modulus (C) from 7.6 to 8.9 GPa (8.4 k 0.5 GPa). Anisotropy in the trabecular bone material was clearly detected at the micrometer level. In conclusion, the V(z)-curve method was successfully used to determine the distribution of material elastic constants of trabecular bone with micrometer resolution.

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.

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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 H₂0 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.