Abstract: Introduction: There are areas of the lung which have differences of ventilation and perfusion and certainly there are different degrees of ventilation and perfusion matches and mismatches, which can contribute to the final outcome of oxygenation (1). The lung functions can change by the position (2). It is a known fact that an individual adapts different positions to sleep (3). This probably may be related to the most well ventilated areas and probably the best matched perfusion as well. Finding this relationship might have importance in clinical practice to improve oxygenation in respiratory compromised patients.