Restrictive lung diseases are just as they sound, restrictive.
There are two types of restrictive lung diseases, interstitial and extra-pulmonary.
For the interstitial type, it refers to the lung tissue itself being damaged.
Imagine a lung being hard and stiff like tough rubber, that lung tissue won’t easily allow air to enter during inhalation, thereby reducing the lung volume.
In the extra-pulmonary type, the structures around the lung are damaged and that prevents chest expansion.
Think about how hard it would be to take a breath when you have someone sitting on your chest.
During inhalation, both the diaphragm and intercostal muscles located in between your ribs contract to pull the ribs up and out and expand the chest cavity. This creates a vacuum which pulls the lungs open.
The air reaches the alveoli and this is where the majority of gas exchange occurs in the lungs.
Between the alveoli, there’s connective tissue made up of proteins like elastin fibers, which give the lungs their rubber-band like properties, and collagen, which gives the lungs their firmness and their overall shape.
During exhalation, both the diaphragm and the intercostal muscles relax to allow the chest wall to fall and return the chest cavity back to normal.
At the same time, the elastin and collagen fibers in the interstitium allow the lung to spring back and push the air back out.
There are a number of ways to measure the volume of air as it is inhaled and exhaled from the lungs.
For example, total lung capacity is the total amount of air that the lungs can hold.
Tidal volume is the volume of air inhaled during normal inhalation and the functional residual capacity is the total amount of air left in the lungs after a normal exhalation.
There’s also the forced vital capacity, or FVC, which is the maximum amount of air exhaled after a full inhalation, and the forced expiratory volume in one second, or FEV1, which is the amount of air forcibly breathed out in one second after a maximum inhalation.
The normal ratio of FEV1 to FVC is 0.8, meaning that 80% of the air should be able to get forced out in the first second.
In interstitial restrictive lung diseases, the lung tissue gets damaged in various ways.
The first large category of these diseases is called pneumoconiosis, which is a broad category that includes the diseases that result from occupational exposures.
Coal workers’ pneumoconiosis occurs in coal miners who inhale tiny particles of coal or carbon dust which mainly settle in small airways in the upper lobes of the lung.
Silicosis is another type of pneumoconiosis which occurs in silica miners and sandblasters who inhale silica particles which also settle in the upper lobes of the lung.
A third type of pneumoconiosis is asbestosis and that typically occurs in construction workers and shipyard workers because asbestos has been used in building materials for many years.
Often, asbestos fibers settle in the lower lobes and on the pleural membrane which surrounds the lung, forming white thick patches called pleural plaques.
All of these different particles - carbon dust, silica particles, and asbestos fibers - can cause an immune reaction to develop.
When macrophages pick up these particles, they release chemokines like interleukin-1 and interleukin-18, which cause a large immune response.
As more immune cells are recruited, cytokines released by these immune cells damage the alveolar epithelium.
Fibroblasts then arrive on scene to try and repair the damage by depositing extracellular matrix composed of collagen.
A second type of interstitial restrictive lung disease is sarcoidosis which is a systemic disease with an underlying mechanism that’s not well understood.
