Anesthesiology
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Simultaneous measurement of tracheal and esophageal pressures during occluded inspiratory efforts (occlusion test) was used to assess the validity of the esophageal balloon technique in anesthetized supine subjects. Ten ASA 1 patients undergoing general anesthesia (halothane 1 MAC, nitrous oxide 70%, and oxygen) for minor surgery were studied. Esophageal pressure (Pes) was measured using a 5-cm-long balloon and was plotted against tracheal pressure (Pt). ⋯ In the remaining three, however, the difference between delta Pes and delta Pt ranged between +20% and -40%. By repositioning the balloon to 5 or 15 cm above the cardia, a locus was found in all subjects where the difference is less than 10%. We conclude that the esophageal balloon technique can be used in anesthetized supine subjects to give reliable measurements of changes in pleural pressure, provided that it is validated with the occlusion test.
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The differential susceptibility of large and small axons to lidocaine was studied on units in the rabbit vagus nerve. The results classified the units into three groups: 1) myelinated, conduction velocity 37.5-5 m/s, which were blocked by lidocaine 0.4-0.8 mM; 2) slow, unmyelinated axons, conduction velocity 1.2-0.5 m/s, and these axons were not blocked by 0.2, 0.4, or 0.6 mM lidocaine but usually were blocked by 0.8 mM lidocaine; and 3) Axons of intermediate conduction velocity, between 1.2 and 4 m/s. The last group of axons was the most sensitive: some were blocked by as little as 0.2 mM lidocaine. No size-related trend was detected within the groups.