Final answer:
The superior chest tube inserted into the pleural cavity after an open cardiovascular procedure evacuates air. This is important for maintaining normal respiratory function by preventing any impediment to lung expansion.
Step-by-step explanation:
When two chest tubes are inserted into the pleural cavity after an open cardiovascular procedure, the superior tube is typically responsible for evacuating air that may have entered the pleural space. This is because air rises to the upper part of the thoracic cavity due to its lower density compared to other fluids. The secondary, or inferior, chest tube is generally placed to drain blood and other fluids that collect at the lower part of the cavity due to gravity. These chest tubes ensure that the pleural space remains free of substances that could impair lung expansion and normal respiratory function.