What pressure gradient is established during the process of inhalation?

During inhalation, the diaphragm and intercostal muscles contract, expanding the thoracic cavity. This expansion increases the volume of the lungs, which subsequently decreases the pressure within the lung cavities according to Boyle's Law. As the pressure in the lungs becomes lower than the atmospheric pressure, a negative pressure gradient is established, allowing air to flow from the outside environment into the lungs.

This negative pressure is critical for enabling the flow of air, as it creates a suction effect that pulls air into the lungs to equalize the pressure difference. This phenomenon is essential for effective ventilation, as the movement of air is driven by the need to equalize pressure between the atmosphere and the intra-thoracic region. In contrast, a positive external pressure would inhibit airflow into the lungs, and static pressure would not facilitate the movement necessary for inhalation. Variable pressure in the environment does not create the necessary gradient for inhalation, as it remains constant compared to the negative pressure generated inside the lungs. Hence, recognizing the formation of a negative pressure during inhalation is crucial to understanding respiratory mechanics.