Certified Respiratory Therapist Practice Exam

To assess gas exchange at the tissues, blood should be sampled from which part of the circulatory system?

1. Pulmonary vein

2. Aorta

3. Pulmonary artery

4. Capillary bed

The correct answer is: Pulmonary artery

To assess gas exchange at the tissues effectively, blood should ideally be sampled from the capillary bed. This area is where the exchange of oxygen and carbon dioxide occurs between the blood and the tissues. In the lungs, oxygen is absorbed from the air into the blood, while carbon dioxide is removed from the blood to be expelled from the body. Sampling from the capillary bed allows for the most accurate measurement of the gaseous contents of blood, reflecting the actual functional state of gas exchange at the tissues. Here, you would assess the partial pressures of oxygen and carbon dioxide after they have been utilized or produced by the cells of the body. This provides critical insight into how well the body's tissues are being oxygenated and how effectively carbon dioxide is being removed. In contrast, sampling from the pulmonary vein would give a reading of oxygenated blood right before it enters the left atrium, which would not provide information on the tissues' gas exchange as it reflects what has just been oxygenated in the lungs. Blood taken from the aorta represents blood that has already been distributed throughout the body, but it does not give direct insight into the tissue exchange process itself. The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the