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Department of Anesthesiology, Hospital of the University of PennsylvaniaIt is commonly believed that the anesthetic actions of thiopental are terminated, not by metabolism of the drug, but by its concentration in body fat.2 Thiopental t is highly fat soluble, 3 but it has not been shown that its uptake by adipose tissue occurs rapidly enough to account for the speed with which consciousness is regained after intravenous injection of the drug. We have attempted to study this point. 9 Our conclusion is that fat does not play the role which has been ascribed to it. Fat concentrates thiopental so slowly that the rate of recovery from anesthesia ordinarily depends to a far greater extent upon the mass of the body than upon its fat content. Reasons for these statements, together with a quantita-

In 1946, Rahn, Otis, Chadwick, and Fenn (1, 2) described a method for obtaining relaxation pressure-volume data for conscious subjects. Essentially the method requires that the subject inspire a measured volume, then close his mouth and nose and relax his respiratory muscles. During the period of relaxation, the pressure in the airway is measured by a manometer connected to a nasal tube; this pressure is assumed to equal alveolar pressure if the glottis is open and there is no airflow. Similar pressure measurements are made at the end of inspirations of different volume, and a relaxation pressure-volume curve plotted. Muscular relaxation is essential for this measurement if it is intended to give information about the balance between the elastic forces of the lungs and those of the remainder of the thorax, uninfluenced by active or reflex contraction or tonus of the respiratory muscles.The method of Rahn, Otis, Chadwick, and Fenn (1) appeared to be a simple technique for determining the elastic properties of the thorax of patients with cardiopulmonary disease and accordingly we applied it to a group of normal subjects and patients. However, we had considerable difficulty in obtaining reproducible curves in many of these (Figure 1). Occasionally, this was due to the subject's inability to keep his glottis open but more often it appeared to be related to his inability to relax his respiratory muscles at endinspiration. This led us to speculate whether even a cooperative and well trained subject, having inspired to certain volumes, could voluntarily relax all of his inspiratory and expiratory muscles and relax these completely at all lung volumes.

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