Emergency Medical Technician (EMT) Intermediate Practice Exam

Which of the following factors is most likely to affect the delivery of oxygen to tissues?

1. Heart rate

2. Blood volume

3. Ventilation-perfusion mismatch

4. Caloric intake

The correct answer is: Ventilation-perfusion mismatch

The delivery of oxygen to tissues is highly dependent on the balance between ventilation (the movement of air in and out of the lungs) and perfusion (the flow of blood to the capillaries). A ventilation-perfusion mismatch occurs when the lungs are not adequately ventilated for the amount of blood flowing through the pulmonary capillaries, or vice versa. This can lead to areas of the lung that are not being adequately oxygenated, resulting in lower oxygen levels being delivered to the bloodstream and subsequently to the body's tissues. When there is a mismatch, certain regions of the lungs may receive oxygen but are not being perfused with blood, or there may be blood flow to alveoli that are not receiving enough oxygen. This imbalance has a direct impact on the efficiency of gas exchange, leading to insufficient oxygen being transported to tissues, thereby affecting cellular metabolism and function. While factors such as heart rate and blood volume do play significant roles in oxygen delivery, they are not as directly linked to the immediate mechanism of gas exchange as ventilation-perfusion relationships. Caloric intake, while important for overall metabolism and energy, does not have a direct impact on the oxygenation process itself. Thus, ventilation-perfusion mismatch is the most critical factor that directly influences the delivery of