How is partial pressure of oxygen expressed?

The partial pressure of oxygen is expressed in millimeters of mercury (mmHg) because this unit quantifies the pressure exerted by a specific gas in a mixture of gases. In the context of respiration and anesthesia, understanding the partial pressure of oxygen is crucial, as it reflects the concentration of oxygen available for exchange in the lungs and ultimately influences its uptake in the bloodstream.

Using mmHg allows for a standard measurement that can be compared across different conditions and environments. This unit originates from barometric pressure measurements, where atmospheric pressure can be divided into the pressures contributed by each gas present. In clinical settings, partial pressures are often used alongside total pressures to assess respiratory function and the effectiveness of oxygen delivery to tissues.

The other options refer to different units of measurement not specific to partial pressures. For instance, liters per minute measures flow rates, percentages express ratios without providing a direct measurement of pressure, and grams per liter pertains to concentration rather than pressure. Thus, mmHg is the appropriate unit for describing partial pressure, particularly in the context of gas exchange in respiratory physiology.