Neurogenic adaptation contributes to the afferent response to mechanical stimulation.

This study aimed to characterize the effect of mechanical stimuli on mesenteric afferent nerve signaling in the isolated rat jejunum in vitro. This was done to determine the effect of mechanical stresses and strains relative to nonmechanical parameters (neurogenic adaptation). Mechanical stimulations were applied to a segment of jejunum from 15 rats using ramp distension with water at three rates of distension, a relaxation test (volume maintained constant from initial pressure of 20 or 40 mmHg), and a creep test (pressure maintained constant). Circumferential stress and strain and the spike rate increase ratio were calculated for evaluation of afferent nerve activity during the mechanical stimulations. Ramp distension evoked two distinct phases of afferent nerve signaling as a function of circumferential stress or strain. Changing the volume distension rate did not change the stress-strain relationship, but faster distension rate increased the afferent firing rate (P < 0.05). In the stress relaxation test, the spike rate declined faster and to a greater extent than the stress. In the creep test, the spike rate declined, despite a small increase in the strain. Three classes of mechanosensitive single-afferent units (low, wide dynamic range, and high threshold units) showed different response profiles against stress and strain. Low-threshold units exhibited a near linear relationship against the strain (R(2) = 0.8095), whereas high-threshold units exhibited a linear profile against the stress (R(2) = 0.9642). The afferent response is sensitive to the distension speed and to the stress and strain level during distension. However, the afferent nerve response is not a simple function of either stress or strain. Nonmechanical time-dependent adaptive responses other than those related to viscoelasticity also play a role.

A new distensibility technique to measure sphincter of Oddi function.

BACKGROUND: Evaluation of the biliary tract is important in physiological, pathophysiological, and clinical studies. Although the sphincter of Oddi (SO) can be evaluated with manometry, this technique has several limitations. This may explain the difficulties in identifying pathophysiological mechanisms for dysfunction of the SO and in identifying patients who may benefit from certain therapies. To encompass problems with manometry, methods such as the functional lumen imaging probe (FLIP) technique have been developed to study GI sphincters. This study set about miniaturising the FLIP probe and validating it for measurements in the SO. In order to get a better physiological understanding of the SO the aims were to show the sphincter profile in vivo and motility patterns of SO in pilot studies using volunteers that were experiencing biliary type pain but had normal SO manometry. METHODS: The SO probe was constructed to measure eight cross-sectional areas (CSA) along a length of 25 mm inside a saline-filled bag. To validate the technique for profiling the SO, six perspex cylinders with different CSAs were measured nine times to assess reproducibility and accuracy. KEY RESULTS: Reproducibility and accuracy for these measurements were good. The probe performed well in bench tests and was therefore tested in four humans. The data indicated that it was possible to make distensions in the human SO and that a geometric sphincter profile could be obtained. CONCLUSIONS & INFERENCES: The probe will in future studies be tested for diagnostic purposes related to sphincter of Oddi diseases.

A new technique for evaluating sphincter function in visceral organs: application of the functional lumen imaging probe (FLIP) for the evaluation of the oesophago-gastric junction.

No quantitative method has been implemented routinely in clinical practice to assess the oesophago-gastric junction (OGJ). Using impedance planimetry a functional lumen imaging probe (FLIP) was constructed to measure eight cross-sectional areas (CSA) at 4 mm intervals inside a saline-filled bag. To validate the FLIP technique for profiling the OGJ, polymethylmethacrylate (Perspex) cylinders with different CSAs were measured ten times by the FLIP to assess reproducibility and accuracy. A geometric sphincter phantom was constructed and its geometry was measured with a 360 degrees radial ultrasound (US) mini-probe pulled through it at a rate of 1 mm s(-1). The measurements were compared with FLIP measurements. Safety and technique reproducibility were tested on a volunteer. Reproducibility and accuracy between the ten samples were good. The probe performed well with and without a balloon mounted on it except for the smallest CSA (38.5 mm(2)) where there was a difference of 22% from the actual value at one CSA measurement point. The FLIP imaged the phantom geometry as well as the radial scanning US mini-probe. Pilot studies on a volunteer showed that the probe could be placed in the OGJ and the balloon distensions revealed the geometry of the sphincter at various levels of distension. The technique may be useful in accessing the role of the OGJ in diseases such as gastroesophageal reflux disease (GORD) and achalasia and their treatments with surgical and endoscopic therapies.