Median Displacement Research Articles

Blood volume distribution in the Trendelenburg position

The Trendelenburg position is used frequently in treating hypotensive patients. It is believed that placing patients in the Trendelenburg position causes an autotransfusion of blood to the central circulation. No published studies document the volume of blood displaced centrally. In our study ten volunteers were placed in the Trendelenburg position. Blood volumes were determined from body surface area, and radionuclide scanning was used to determine blood volume distribution. Placing normovolemic volunteers in the Trendelenburg resulted in a 1.8% (median) displacement of the total volume centrally. The autotransfusion of blood produced by the Trendelenburg position is small and is unlikely to have an important clinical effect.

Clearance of mucus by simulated cough

We examined the relationship between mucus rheology, depth of mucus layer, and clearance by simulated cough. A model trachea was constructed of rigid Plexiglas of rectangular cross section (1 X 2 X 35 cm). The bottom of the trachea was lined with mucus simulants, gels prepared from locust bean gum cross-linked with sodium borate. Cough was simulated by opening a solenoid valve connecting the model trachea to a pressurized tank. An upstream flow-constrictive element was used to shape the flow profile of the simulated cough to approximate the pattern seen in a normal adult. Clearance of mucus was quantitated by observing the movement of contrasting marker particles floating in the mucus layer. The median particle displacement per cough maneuver was defined as the clearance index (CI). We found that CI for any initial depth of mucus increased with the driving pressure in the tank. For a given driving pressure, CI increased linearly with increasing mucus depth. For a given driving pressure and depth, CI decreased with increasing mucus cross-link density. For mucus samples with comparable levels of dynamic viscosity, samples with higher elasticity cleared less well. Mucus clearance was associated with transient wave formation in the lining layer.

The Clinical Value of Laryngeal Tomographies in Unilateral Recurrent Laryngeal Nerve Paralysis

As compared to conventional indirect laryngoscopy and the lately developed endonasal fiberscopy, laryngeal tomographies may prove more useful in terms of a precise understanding of the contour of the ventricle, level difference of bilateral vocal cords, the thickness and also the direction of a paralyzed cord and finally, the subglottic angle formed by either the adduction or fixation of the vocal cord during phonation. The results of a laryngeal tomographic analysis on 47 cases with unilateral recurrent laryngeal nerve paralysis were summarized as follows. Every analysis was made on tomograms taken during phonation and also compared with hemilarynx of the healthy side as well as indirect laryngoscopic findings.1) An apparent enlargement of the paralyzed ventricle appears to be related to the paralyzed vocal cord fixed at the intermediate position in 61 per cent of the cases.2) A higher level for the paralyzed vocal cord was observed in 23 cases (49 per cent). The paralyzed vocal cord showing fixation at the intermediate position, as well as bowing in the mirror, tends to be located at a higher level in the tomograms than the fixed vocal cord at the paramedian position and of straight appearance. The consistency of these findings as to the level of a paralyzed vocal cord may be only 50 per cent when comparing indirect laryngoscopic views with the tomographic studies.3) Twenty nine cases (62 per cent) showed a significantly thinner vocal cord on the paralyzed side and also an upward direction for the median edge of the paralyzed vocal cord.4) A significantly greater angle of the subglottis on the paralyzed side was demonstrated in 45 cases (95 per cent).These results stress the medical and/or surgical aspects of not only the median displacement but also the sagittal correction of a paralyzed vocal cord to achieve vocal improvement.

The accuracy of track location in triggered spark counters

Studies have been made of the accuracy with which the spark in an air-filled triggered spark counter reproduces the trajectory of the triggering particle. For a single counter the r.m.s. displacement is found to be 1.54 mm and the median displacement 0.4 mm. With a 6-layer counter and a large displacement cut-off technique, the r.m.s. error of track location is reduced to 0.38 mm and the median displacement to 0.2 mm.