What drives the movement of air in and out of the lungs?

The movement of air in and out of the lungs is primarily driven by pressure differences, specifically the changes in atmospheric pressure and intrathoracic pressure during the respiratory cycle. While carbon dioxide levels do play a role in the regulation of breathing, they do not directly drive the physical movement of air.

During inhalation, the diaphragm and intercostal muscles contract, creating negative pressure within the thoracic cavity. This negative pressure draws air into the lungs from the atmosphere, where the atmospheric pressure is higher than the pressure inside the lung cavities. Therefore, the mechanism of air movement is largely dependent on these pressure gradients rather than the levels of carbon dioxide or other parameters listed in the options provided.

Thus, choice D, atmospheric pressure, is the correct factor influencing airflow, as it establishes the necessary pressure gradient that allows air to flow into the lungs during inhalation and out during exhalation.