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Biomedical subjects

H M Spiro

Publications and source records attributed to H M Spiro.

At least 109 records · Page 6Linked to original sources
PubMed1973

Mechanics of sphincter action. Studies on the lower esophageal sphincter.

The purpose of this study was to evaluate the mechanical factors involved in the genesis of lower esophageal sphincter pressure. We determined the relationship between intraluminal pressure and inside diameter, estimated the ratio between the wall thickness to inside radius, and calculated the tension in the wall of the lower esophageal sphincter as a function of the inside diameter. Various degrees of circumferential stretch were applied by introducing probes of different diameters in the rat lower esophageal sphincter in vivo. The intraluminal pressure produced by the lower esophageal sphincter around each probe was measured and pressure-diameter curves were constructed during (a) resting state, (b) contraction produced by electrical stimulation, and (c) relaxation produced by esophageal distension. The intraluminal pressure at an inside diameter of 0.5 mm was similar to that at inside diameter of 3.2 mm. This was true for the sphincter at rest as well as upon electrical stimulation. The pressure diameter curve, however, was sigmoid in shape; at first it showed a decline and then an increase followed by decline in pressure again with increasing diameters. The ratio of wall thickness to inside radius or the magnification factor varied with inside diameters as expected and this ratio increased steeply at small inside diameters. The tension diameter curves of the sphincter muscle showed that optimal tension development occurred not near sphincter closure but at a much wider diameter of 3.2 mm and that this muscle developed tension even at small luminal diameters. This behavior of the sphincter muscle ensures effective intraluminal pressure over a wide range of luminal diameters.

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PubMed1973

Alien travelers.

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Connecticut↗
PubMed1971

Mechanical properties of the esophageal wall.

Pressure-diameter curves of the esophagus were obtained to define its mechanical properties. The mucosal contribution to the strength of the esophagus was negligible until the outer diameter almost doubled, suggesting that small intraluminal pressures are held by the muscle layer alone. For larger deformations mucosal contribution increased and at failure the mucosa held over one-half of the failure pressure of the esophagus. The paths followed during loading and unloading are different and exhibit hysteresis. They are influenced by the rate of pressure change, being more compliant for low rates of pressure change. They are influenced by the history of loading, being different for successive loading-unloading cycles. If enough loading-unloading cycles are repeated a stable loop is reached, which does not change thereafter. Both the mucosa and the whole esophagus show increasing stiffness with increasing pressure. This behavior can be represented by a simple exponential relationship. However, at rapid rates of pressure increases, the esophageal muscles produce sigmoid loading curves, which gradually become exponential when repeating loading.

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