Oxygen window

In diving and decompression, the oxygen window is the difference between the partial pressure of oxygen (PO2) in arterial blood and the PO2 in body tissues. It is caused by metabolic consumption of oxygen. The term "oxygen window" was first used by Albert R. Behnke in 1967. Behnke refers to early work by Momsen on "partial pressure vacancy" (PPV) where he used partial pressures of oxygen and helium as high as 2–3 ATA to create a maximal PPV. Behnke then goes on to describe "isobaric inert gas transport" or "inherent unsaturation" as termed by LeMessurier and Hills and separately by Hills, who made their independent observations at the same time. Van Liew et al. also made a similar observation that they did not name at the time. The clinical significance of their work was later shown by Sass. The oxygen window effect in decompression is described in diving medical texts and the limits reviewed by Van Liew et al. in 1993. Van Liew et al. describe the measurements important to evaluating the oxygen window as well as simplify the "assumptions available for the existing complex anatomical and physiological situation to provide calculations, over a wide range of exposures, of the oxygen window". Oxygen is used to decrease the time needed for safe decompression in diving, but the practical consequences and benefits need further research. Decompression is still far from being an exact science, and divers when diving deep must make many decisions based on personal experience rather than scientific knowledge. In technical diving, applying the oxygen window effect by using decompression gases with high PO2 increases decompression efficiency and allows shorter decompression stops. Reducing decompression time can be important to reduce time spent at shallow depths in open water (avoiding dangers such as water currents and boat traffic), and to reduce the physical stress imposed on the diver. The oxygen window does not increase the rate of offgassing for a given concentration gradient of inert gas, but it reduces the risk of bubble formation and growth which depends on the total dissolved gas tension.