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We develop tidal-ventilation pulmonary gas-exchange equations that allow pulmonary shunt to have different values during expiration and inspiration, in accordance with lung collapse and recruitment during lung dysfunction (Am. J. Respir. Crit. Care Med. 158 (1998) 1636). Their solutions are tested against published animal data from intravascular oxygen tension and saturation sensors. These equations provide one explanation for (i) observed physiological phenomena, such as within-breath fluctuations in arterial oxygen saturation and blood-gas tension; and (ii) conventional (time averaged) blood-gas sample oxygen tensions. We suggest that tidal-ventilation models are needed to describe within-breath fluctuations in arterial oxygen saturation and blood-gas tension in acute respiratory distress syndrome (ARDS) subjects. Both the amplitude of these oxygen saturation and tension fluctuations, and the mean oxygen blood-gas values, are affected by physiological variables such as inspired oxygen concentration, lung volume, and the inspiratory:expiratory (I:E) ratio, as well as by changes in pulmonary shunt during the respiratory cycle.


Journal article


Respir Physiol Neurobiol

Publication Date





77 - 88


Animals, Computer Simulation, Dogs, Humans, Lung Volume Measurements, Models, Biological, Oxygen, Pulmonary Alveoli, Pulmonary Artery, Pulmonary Gas Exchange, Pulmonary Ventilation, Respiratory Function Tests, Respiratory Mechanics, Stress Disorders, Traumatic, Acute, Tidal Volume, Time Factors