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When anesthetized dogs were allowed to breathe spontaneously or were paralyzed and ventilated in the resting tidal range by means of a pump, pulmonary compliance fell progressively. These changes were immediately reversed following forced inflations of the lungs, while forced deflations caused further compliance reductions. The appearance of the lungs post mortem suggested that closure of air-spaces was at least in part responsible for the compliance reductions. Evidence from measurements of total and ventilatory lung gas volumes indicated that the closed spaces were essentially atelectatic. These findings have been related to other observations made in experimental animals and in man. Submitted on December 29, 1958

To investigate whether adaptation which modifies some acute effects of ozone (O3) exposure can develop in humans, six male volunteers with respiratory hyperreactivity were exposed in a controlled environment chamber to 0.5 ppm O3 2h/day for 4 successive days under conditions stimulating ambient pollution exposures. One subject showed little measurable response, while five showed function decrement on exposure days 1-3 which was largely reversed by day 4. Symptom responses generally paralleled the physiological responses. These results suggest that at least some humans adapt to O3 exposure at concentrations occurring in severe community air pollution episodes, to the extent that obvious acute respiratory effects are prevented. Other adverse effects of O3 may not be prevented by this adaptation.

Since the experiments of von Basch (1) it has been recognized that pulmonary vascular congestion influences the mechanical behavior of the lungs. A number of studies in patients with chronic congestive failure have demonstrated marked changes in pulmonary elasticity (2-6). It has not been possible to determine in such patients the relative contributions of pulmonary edema, other parenchymal changes, and vascular congestion per se to the observed changes. Experiments with acute congestion in man or living animals (7-10) and isolated lungs (11) have yielded conflicting results.The purpose of the present study was to examine in the living animal the effects of acute changes in pulmonary arterial and venous pressures and blood flow on the mechanical behavior of the lungs. The left atrial pressure and the pulmonary blood flow were varied independently. In one set of experiments, volume-pressure curves were obtained during stepwise inflation and deflation of the lung over a wide range of volume starting from the passively collapsed state. In another group, pulmonary compliance and flow-resistance were studied during continuous cycling of the lungs in the normal tidal range of lung volume. Nembutal@ (25 to 45 mg. per Kg. body weight, intravenously). The chest was opened by splitting the sternum, and the chest wall was retracted to minimize crowding of the intrathoracic viscera during inflation of the lungs. The right ventricle was replaced by a pump without interruption of the circulation as in an experimental preparation previously described (12). Systemic venous blood was diverted into a reservoir from which it was pumped into either the main pulmonary artery or into the two pulmonary artery branches separately.When both pulmonary arteries were cannulated, the blood flow in the lung to be studied was varied by changing distribution of flow. In addition, pulmonary flow could be varied by changing pump output. Left atrial pressure was varied by mechanically altering the systemic arterial resistance (constriction of the ascending aorta, inflation of balloon in ascending aorta, systemic A-V shunt). Sometimes additional adjustment of left atrial pressure was obtained with an overflow system between the left atrium and the venous reservoir. In this way changes could be made in pulmonary flow or left atrial pressure independent of each other.Pulmonary blood flows were measured with rotameters. Pressures in the pulmonary arteries distal to the respective cannulae, in the left atrium, and in the femoral or carotid arteries were measured with electromanometers. These values were recorded on a direct-writing Sanborn oscillograph.Two methods were used to measure the mechanical characteristics of the lung.