Final answer:
CvO2, or venous oxygen content, directly measures the oxygen consumption of tissues, indicating the amount of oxygen used by tissues from the blood. Other measurements like PaO2, PAO2, and CaO2 refer to blood oxygen levels but not to direct consumption by tissues.
Step-by-step explanation:
The measure that reflects oxygen consumption of tissues directly is d- CvO2, which stands for venous oxygen content. This measurement indicates the amount of oxygen being removed from the blood by the tissues and is therefore a marker of oxygen consumption. The other measures mentioned in the question - PaO2 (arterial oxygen pressure), PAO2 (alveolar oxygen pressure), and CaO2 (arterial oxygen content) - are related to oxygen levels in the blood but are not direct measures of tissue oxygen consumption. Measurements such as those performed by pulse oximeters do not directly indicate tissues' metabolic rates as they measure oxygen saturation of hemoglobin rather than consumption. To determine the true oxygen consumption of tissues, one might utilize methods like the Douglas bag method, which involves collecting expired air to analyze oxygen utilization and carbon dioxide production, reflecting the body's metabolic rate.