Boyle’s Law is a law describing the relationship between a gas’s pressure and volume. According to Kenny and Ponichtera (2021), algebraically, this law is written as PV = K, where P stands for pressure, V – for volume and K – for a constant. In other words, the pressure and the volume are in reverse ratio. When it comes to the human body, one system by which Boyle’s Law mechanism can be traced is the respiratory system. Air is brought into one’s lungs by negative pressure. Kenny and Ponichtera (2021) state that, at the base level, the thoracic cavity is in static equilibrium, and its intrapleural pressure is approximately at -5 cmH2O. When inspiration occurs, inspiratory muscles contract, which increases intrathoracic volume. The combined motion of the chest wall and the lungs causes the lungs to start to expand during inspiration just as the thorax does. In accordance with Boyle’s Law, with the increase of the volume comes the decrease in the pressure; therefore, with the increase of the intrapleural volume comes the decrease in the intrapleural pressure.
In terms of pathophysiology, in the case of such conditions as pneumothorax or hemothorax, the pressure within the intrapleural space increases. Because of that, the dormancy state of approximately -5 cmH2O is moved to a higher value which depends on the complexity of the disease. When this happens, much greater expansion of the thoracic cavity is required to generate a negative pressure for air to be brought in from the atmosphere. According to Kenny and Ponichtera (2021), with tension pneumothorax, the pressure within the pleural space constantly increases the intrapleural pressure, thereby decreasing the lung volume. This condition can create enough pressure to induce a mediastinal shift that ultimately prevents the venous return to the heart’s right side and leads to cardiovascular demise.
Reference
Kenny, B. J., & Ponichtera, K. (2021). Physiology, Boyle’s Law. In StatPearls [Internet]. StatPearls Publishing.