Introduction
Brad is 45 years old and has been working as a coal cutter in a mine for the last 25 years. He likes the job because it pays well and the same mine had employed his father. Like many of his colleagues, Brad has had problems with a chronic cough. He has avoided his annual checkups for fear that he will be told he has “black lung,” or coal worker’s pneumoconiosis. The disease causes fibrosis, decreased diffusing capacity, and permanent small airway dilation. In later stages, pulmonary capillaries, alveoli, and airways are destroyed.
How can the disease described above create a mismatch between ventilation and perfusion? Use your understanding of alveolar dead space and physiologic shunt to explain your answer
Ventilation and perfusion are the main mechanisms that ensure the implementation of the primary function of the lungs – gas exchange. Each alveolus has its own characteristics of ventilation and blood flow, so in different parts of the lung, the ratio of ventilation and blood flow is different. With the pathology of the respiratory system, the degree of uneven ventilation of different alveoli increases.
It happens due to both deteriorations of the patency of the bronchi and a change in the extensibility of the lung tissue. To ensure effective gas exchange, in addition to uniform ventilation of the lungs, a good blood supply to the ventilated alveoli is necessary. Normally, the anatomical structure of the vessels of the lung, distribution of pulmonary blood flow, and regulatory and adaptive mechanisms for controlling pulmonary circulation are aimed at maintaining an adequate ratio of ventilation and perfusion.
Coal worker’s pneumoconiosis is one of the most common and severe diseases in the mining industry. Perret et al. (2017) state, “coal dust accumulates in the terminal bronchovascular bundle and is engulfed by alveolar and interstitial macrophages” (p. 664). It causes the forming of pulmonic macules and nodules and a deposit of thick collagen fibers. Thus, “lung parenchyma architecture is altered leading to the formation of air-filled spaces, a reduced surface area available for gas exchange and reduced distensibility” (Craig, 2019, p. 694).
It results in a mismatch between ventilation and perfusion as the accumulated dust leads to an obstructed airway. In the lungs, the mentioned air-filled spaces create an additional volume of so-called physiological dead space. The increase of dead space means that the body is spending energy on ventilation for nothing; therefore, the amount of necessary energy for breathing increases. Furthermore, in the case when alveoli are not ventilated, a physiological shunt occurs (because the blood flowing into this zone is not enriched with oxygen).
It should also be mentioned that dead space and physiological shunt must be taken into account when characterizing the ventilation-perfusion ratio. The physiological shunt is the volume of blood flow along the unventilated alveoli, and the physiological dead space is the volume of ventilation of alveoli that do not obtain enough blood. These indicators allow measuring the mismatch between ventilation and perfusion in the lung parenchyma.
Individuals with the chronic obstructive pulmonary disease have more difficulty exhaling than inhaling. Why is this so?
Chronic obstructive pulmonary disease (COPD) is a slowly progressing disease characterized by inflammation of the lower respiratory tract and obstruction (edema) of the bronchi. It includes symptoms of chronic bronchitis and emphysema, which results in a number of severe consequences. Chronic bronchitis may be defined as a condition when a person has a wet cough for three months or more that is not a result of any other illnesses. Then, emphysema may be defined as a long-standing lung disease that “primarily causes shortness of breath due to over-inflation of the alveoli” (“Facts you should know about emphysema,” n.d., para 1).
During emphysema, the alveoli are disrupted because of the loss of cell wall elastin (Craig, 2019). It should also be noticed that the surface area where the process of gas exchange takes place becomes smaller, and the reduction of radial traction leads to the narrowed airways (Craig, 2019). The most harmful substance for the lungs is dust containing cadmium and silicon. Professions related to these substances are builders, workers in the metallurgical and cement industries, and others.
Thus, dust is a crucial element that leads to COPD. Then, due to damage caused to the lungs or the narrowed airways inside them, the air is exhaled with more difficulty than normal (“Obstructive and restrictive lung disease,” n.d.). After complete exhalation, a sustainable amount of air might still be in the lungs. The disease requires a long and careful treatment as well as an absolute rejection from smoking.
In general, terms, what mechanisms in lung disease can affect diffusing capacity across alveolar membranes? Use the Fick law to explain your answer
The efficiency of gas exchange reflects the state of diffusion of the lungs as an integral indicator of pulmonary ventilation and blood flow. Fick’s law of diffusion might exhaustively describe the process above. Powers and Dhamoon (2019) state, “diffusion of a gas across the alveolar membrane increases with an increased surface area of the membrane, increased alveolar pressure difference…, increased solubility of the gas, decreased membrane thickness” (para. 4).
The thickness of the alveolocapillary membrane can vary with physiological and especially with pathological changes in cytoplasmic metabolism. Membrane thickness is influenced by the configuration of alveolar epithelial cells and capillary endothelium. An extension of the diffusion path of oxygen occurs due to the thickening of the liquid layer on the surface of the alveoli. The other factors are swelling of the alveolar membrane and an increase in the volume of interstitial fluid, and the plasma fraction of blood.
Gas diffusion naturally decreases with pneumoconiosis, a chronic lung disease caused by prolonged inhalation of various types of dust and characterized by the development of pulmonary fibrosis (silicosis, asbestosis, berylliosis). The most straightforward functional test to detect impaired diffusion capacity of the lungs is the arbitrary hyperventilation of the lungs. COPD leads to a decrease in the area of the diffusion surface that takes place due to emphysema and has an organic character.
References
Craig, S. K. (2019). Pathophysiology of respiratory disease and its significance to anaesthesia. Anaesthesia & Intensive Care Medicine, 20(12), 693–699.
Facts you should know about emphysema. (n.d.). Web.
Obstructive and restrictive lung disease. (n.d.). Web.
Perret, J. L., Plush, B., Lachapelle, P., Hinks, T. S. C., Walter, C., Clarke, P., … Stewart, A. (2017). Coal mine dust lung disease in the modern era. Respirology, 22(4), 662–670.
Powers, K. A., & Dhamoon, A. S. (2019). Physiology, pulmonary, ventilation and perfusion. Web.