Capillary Replacement in a Tube Prefilled with a Viscous Fluid.

Capillary invasion of a liquid into an empty tube, which is called capillary rise when the tube axis is in the vertical direction, is one of the fundamental phenomena representing capillary effects. Usually, the tube is filled with another pre-existing fluid, air, whose viscosity and inertia can be practically neglected. In this study, we considered the effect of the pre-existing fluid, when its viscosity is non-negligible, in a horizontal geometry. We observed the dynamics when a capillary tube that is submerged horizontally in a liquid gets in contact with a second liquid. An appropriate combination of liquids allowed us to observe that the second liquid replaces the first without any prewetting process, thanks to a careful cleaning of capillary tubes. As a result, we experimentally observed three distinct viscous dynamics: (i) the conventional slowing-down dynamics, (ii) an unusual accelerating dynamics, and (iii) another unusual dynamics, which is linear in time. We derived a simple unified expression describing the three distinct dynamics, which accounts well for the observations. We also demonstrated a thorough experimental confirmation on the initial velocity of the replacement and the replacement time, the time required for the invading fluid to completely replace the pre-existing fluid in the horizontal geometry.

Abnormal predefecatory colonic motor patterns define constipation in obstructed defecation.

BACKGROUND & AIMS: The pathophysiology of constipation in the syndrome of obstructed defecation is unknown. Using 24-hour pancolonic manometric recordings of the unprepared colon to record basal pressures and spontaneous defecation episodes, we tested the hypothesis that the frequency, timing, or spatial distribution of propagating colonic pressure waves is abnormal in patients with obstructed defecation. METHODS: In 11 patients with obstructed defecation and 16 healthy controls, pressures were recorded using a nasocolonic catheter that was positioned such that 16 recording sites spanned the unprepared colon at 7.5-cm intervals. RESULTS: The overall frequency of propagating sequences (PS) in the colon did not differ between patients and controls. When compared with controls, patients had a significant increase in the frequency of retrograde and antegrade PS (P < 0.05) in the left colon and a significant reduction in the amplitude of propagating pressure waves throughout the entire colon (P < 0.03). Defecation occurred in 6 of 11 patients and 9 of 16 controls. In the 15 minutes before defecation, controls showed a highly significant increase in frequency (P = 0.001) and amplitude (P = 0.01) of PS. In contrast, patients did not demonstrate this or the typical spatiotemporal organization of PS normally observed before expulsion of stool. CONCLUSIONS: Patients with obstructed defecation lack the normal predefecatory augmentation in frequency and amplitude of propagating pressure waves and lack the normal stereotypic spatiotemporal patterning of colonic pressure waves that would normally culminate in effective expulsion of stool.