Adenocarcinoma arising in a Ghon complex and presenting with massive pericardial effusion.

relatively small drop in intrapleural pressure or change in the configuration of the hilum associated with a deep breath can have on perfusion, and second, the implication that this has on the assumption that inspired lS3xenon in the lung is necessarily in the alveoli rather than in the conducting airways. The xenon that diffused from the pulmonary capillaries in the left lung had no significant clearance from the lung so one must assume a block in the small airways. There was no evidence on xray examination of collapse of the left lung, so it may be assumed that the alveoli were air containing. The xenon in the left lung was not secondary to trapped, inhaled xenon because studies done after inhaling xenon from a spirometer at breathholds of FRC + TV and TLC failed to show any residual radioactivity in the left lung after washout. The discrepancy be.tween volume of thoracic gas and residual volume by the helium dilution method accounts for almost 1.25 liters of trapped gas assumed to be in the alveoli of the left lung. The presence of perfusion of the left lung without alveolar ventilation means that significant shunts can come and go with physiologic changes in the thorax possibly related to decreased cornpression of the pulmonary artery or increased negativity of intrathoracic pressure associated with exercise. If shunting varies between resting and exercise states as between resting inspiration and maximal inspiration as noted in this patient, there may be a significant increase in A-a gradient with exercise on the basis of large regional "V/Q abnormalities.