During a night shift in the Emergency Department, you see George, a 21 year old, who complains of sharp, stabbing left-sided chest pain and shortness of breath, both of which appeared suddenly while he was playing video games. He is a smoker and mentions his younger brother suffered a pneumothorax last year. On examination, the left side of his chest is slightly more expanded than the right side and his breathing is very shallow. The affected side is also hyperresonant on percussion and there’s diminished breath sounds on auscultation. Then there’s Anna, a 58-year-old with progressively worsening dyspnea, pleuritic chest pain, and fever. She has a history of diabetes and cirrhosis. On examination, her blood pressure and heart rate are both increased, and jugular venous pressure is elevated. Also, the base of her left lung field is dull to percussion with decreased breath sounds. Her lower extremities have pitting edema up to the knee. X-rays were performed in both individuals. In George’s case it showed a retracted visceral pleural edge with a decrease in the left lung volume. In Anna, it showed left sided costophrenic angle blurring.
Now, they both seem to present with conditions affecting the pleura. But to understand the pathophysiology, it’s a good idea to review the anatomy and physiology first. Ok, so the pleura covers the lungs and consists of the parietal pleura, which is stuck to the chest wall, and the visceral pleura, which is stuck to the lungs. It extends all the way up to the clavicle and first rib, which is something that will help you understand why neck injuries can cause tension pneumothorax. Also know the inferior limit of the pleura is the 7th rib on the midclavicular line, the 10th rib on the mid axillary line, and the 12th rib on the paravertebral line. Between the layers of the pleura is the pleural space, containing 10 to 20 milliliters of a lubricating fluid that helps reduce friction as the lungs expand and contract. There’s also pressure within the pleural space, established by two main opposing forces. One is the muscle tension of the diaphragm and chest wall, which contract and expand the thoracic cavity outwards. The other is the elastic recoil of the lungs, which is the lungs’ tendency to collapse inward. The two forces pulling in opposite directions creates a slight vacuum in the pleural space with a pressure of -5 centimeters of water, relative to 0 centimeters of water in both the thoracic cavity and the lungs. The difference in pressure aids air exchange during inspiration and expiration to help the lungs keep their shape and not collapse.