• Elizabeth A Yoder, Kenneth Klann, and Kingman P Strohl.
• Louis Stokes Cleveland DVA Medical Center, Medical Service, Center for Sleep Disorders Research, Case Western Reserve University, Cleveland, Ohio, USA. Beth.Yoder@att.net
• Sleep Breath. 2004 Mar 1; 8 (1): 1-5.

ObjectivesThis study examined the effects of various factors that might influence the fraction of oxygen in inspired air (FiO (2)) in a human and in a model system during nasal positive pressure treatments.Design And MethodsA healthy male volunteer and a mannequin head were each outfitted with a nasal continuous positive air pressure mask and pressure source (BiPAP S, Respironics, Murrysville, PA). Oxygen was added through either a side port in the mask or a port near the machine. Flow and FiO (2) were measured while varying inspiratory and expiratory pressures. Measurements were repeated with a leak added to the system and using different sites of oxygen administration.ResultsIn both the human and in the model system, increasing inspiratory pressure, thereby increasing flow, decreased FiO (2) inside the mask. In the model system, addition of a fixed leak caused an increase in flow and decrease in FiO (2) at any given level of inspiratory and expiratory pressure.ConclusionIn patients using nasal positive pressure therapy, variables of pressure, leak around the mask, and the site of oxygen delivery determine the inspired oxygen concentration when giving oxygen supplementation.

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