Pleural Space [HD]

Summary

Dr. Ricardo Gonzalez Rafi and Jody Chapman explore the pleura and pleural space in this informative video. They explain the pleura's role in regulating lung pressure and the function of pleural fluid, which normally contains 8-10 mL per side in an adult, providing lubrication during breathing. The script delves into the mechanics of pleural fluid absorption and the consequences of pleural effusion, such as lung compression and shortness of breath, caused by disruptions in the pleural space. Clinical examples include effusions due to heart failure, tumors, and pneumonia, highlighting the impact of various diseases on pleural fluid dynamics.

Takeaways

• 📚 The pleura is a continuous membrane of cells that folds over itself at the apex and base of each lung.
• 🌐 The pleural space is a potential space between the parietal pleura (lining the chest wall) and the visceral pleura (lining the lungs).
• 🛠 The pleural space helps regulate pressure during breathing and provides lubrication for the lungs and chest wall as they move against each other.
• 💧 The pleural space typically contains 8-10 milliliters of fluid per side in an average-sized adult, serving as a lubricant for the pleural surfaces.
• 🧬 Pleural fluid is a clear plasma filtrate originating from small capillaries in the chest wall, containing solutes like sodium chloride, bicarbonate, glucose, and small amounts of protein.
• 🔬 Pleural fluid has equivalent glucose concentrations to serum but slightly higher concentrations of albumin and bicarbonate, resulting in an alkaline pH of about 7.6.
• 🔄 The pleural fluid provides mechanical coupling between the pleural surfaces, allowing for the transmission of forces and sliding during the breathing cycle.
• 💉 Pleural fluid is absorbed primarily through the mesothelial cells of the visceral pleura and exits via microscopic uni-directional valves known as lymphatic stoma in the parietal pleura.
• 🚫 A pleural effusion occurs when there is too much fluid in the pleural space, disrupting the mechanical coupling and causing the lung to pull away from the chest wall.
• 🏥 Clinical examples of pleural effusions include conditions that increase hydrostatic pressure (like heart failure), tumors obstructing lymphatic drainage, and inflammation from pneumonia.
• 🛑 A trapped lung occurs when the lung physically pulls away from the chest wall due to conditions like inflammatory, infectious, or neoplastic changes, leading to pleural effusion.

Q & A

What is the pleura and what is its function?

The pleura is a continuous membrane of cells that folds over onto itself at the apex and base of each lung. It functions to help regulate the pressure inside and outside the lungs during breathing and provides lubrication for the pleural surfaces as they slide against each other during the breathing cycle.

What is the pleural space and where is it located?

The pleural space is a potential space between the parietal pleura, which lines the inside of the chest wall, and the visceral pleura that lines the lungs. It is where the two pleural membranes fold upon themselves.

How much fluid is normally present in the pleural space?

The pleural space is estimated to hold between eight and ten milliliters of fluid per side in an average-sized adult man.

What is pleural fluid and what substances does it normally contain?

Pleural fluid is a clear plasma filtrate that originates from small capillaries in the chest wall and contains small solutes like sodium chloride, bicarbonate, glucose, and small amounts of protein including albumin. It also contains macrophages, lymphocytes, and mesothelial cells.

What is the normal pH of pleural fluid and why is it alkaline?

The normal pH of pleural fluid is approximately 7.6, which is alkaline due to the increased bicarbonate concentration compared to serum.

How does the pleural space provide mechanical coupling during breathing?

The fluid in the pleural space provides mechanical coupling between the two pleural surfaces, allowing instantaneous transmission of perpendicular forces between them, similar to how a damp glass coaster sticks to the bottom of a glass.

Where does pleural fluid come from and how is it absorbed?

Pleural fluid originates from plasma filtrate drawn by a pressure gradient from the subpleural capillaries in the chest wall. It is primarily absorbed through the mesothelial cells of the visceral pleura and exits the space through microscopic unidirectional valves known as lymphatic stoma found in the parietal pleura.

What happens when there is too much fluid in the pleural space, causing a pleural effusion?

When there is too much fluid, it disrupts the mechanical coupling between the chest wall and the lung, causing the lung to pull away from the chest wall. This can lead to shortness of breath and a feeling of fullness in the chest, as the lung tissue becomes compressed and alveoli are electively reduced.

What are some clinical examples of conditions that can cause a pleural effusion?

Conditions such as heart failure, which increases hydrostatic pressure leading to fluid accumulation; tumors in the lung or chest wall obstructing lymphatic drainage; and pneumonia, which increases capillary permeability, can all cause pleural effusions.

What is a trapped lung and how does it relate to pleural effusion?

A trapped lung occurs when certain conditions cause the lung to become unexpanded, physically pulling away from the chest wall and creating an imbalance of pressure that favors increased filtration of fluid into the pleural space, leading to pathologic pleural effusion.

Can pleural effusions occur even when pleural mechanics are normal?

Yes, pleural effusions can occur when fluid formation within the thorax and absorption are intact, but excess fluid entry occurs via non-physiologic routes, such as peritoneal dialysis fluid entering the pleural space via diaphragmatic defects in liver disease.