Which component of oxygen content is accurately measured by the system described?

The total oxygen available to the tissues is a crucial aspect of assessing oxygen content in the body. This measurement takes into account both the oxygen that is bound to hemoglobin within red blood cells as well as the amount of oxygen dissolved in the plasma. By accurately measuring this total oxygen content, healthcare providers can determine how well the body is oxygenating its tissues, which is vital for diagnosing and managing various conditions related to respiratory and cardiovascular health.

This measurement is essential because it reflects the capacity of the blood to deliver oxygen to cells throughout the body, which is the ultimate goal of respiratory function. The body's tissues require sufficient oxygen for metabolic activities, and any deficiency can lead to significant cellular and organ dysfunction. Therefore, understanding and measuring the total oxygen available is fundamental for effective clinical assessment and intervention.

Other choices would not encompass the comprehensive measurement of oxygen content available to tissues. For example, focusing only on inhaled oxygen would ignore how much is actually utilized and retained in the body, while measuring expired air provides limited information about the oxygen levels actively available for tissue perfusion. Oxygen retention during hypoxia, although clinically relevant, does not define the total oxygen content, making it less comprehensive in this context.