Why Work of Breathing Increases in EMPHYSEMA (COPD) - 1st Year MBBS
Channel: Cool Concepts in Physiology, Anatomy (& Life)
Date: 2021-06-29

he work of breathing increases in emphysema, a type of Chronic Obstructive Pulmonary Disease (COPD), due to several key factors related to changes in lung mechanics and airway function. Here's an explanation:

1. Loss of Elastic Recoil
In emphysema, the destruction of alveolar walls leads to the loss of elastic tissue in the lungs. Normally, the elastic recoil of the lungs helps push air out during exhalation with minimal effort. In emphysema, the lungs become "floppy" and cannot easily return to their normal size after expansion, which means patients must actively work to exhale, increasing the energy required for breathing.
2. Airway Collapse
During exhalation, particularly in emphysema, there is a collapse of small airways (bronchioles) due to reduced elastic support. This airway collapse increases airway resistance, making it harder for air to flow out of the lungs. To overcome this increased resistance, patients must generate higher pressures by using more muscular effort, further increasing the work of breathing.
3. Hyperinflation
In emphysema, because of the loss of elastic recoil and the collapse of small airways, air gets trapped in the lungs, causing lung hyperinflation. This increases the lung volume at the end of exhalation (increased functional residual capacity - FRC). Hyperinflation stretches the respiratory muscles, especially the diaphragm, reducing their efficiency and making them work harder to initiate the next breath.
4. Increased Compliance but Decreased Efficiency
Although lung compliance (the ease of lung expansion) is increased in emphysema due to the loss of elastic tissue, this paradoxically increases the work of breathing. While it’s easier to expand the lungs, they expand to abnormally large volumes, which makes it more difficult to exhale. Patients must recruit additional respiratory muscles to generate the pressures required for both inhalation and exhalation.
5. Use of Accessory Muscles
As the diaphragm becomes less effective due to hyperinflation, patients with emphysema begin to rely on accessory muscles (such as the neck and shoulder muscles) to assist with breathing. This recruitment of additional muscles increases the overall energy expenditure and oxygen consumption, contributing to increased work of breathing.
Clinical Relevance:
Patients with emphysema often feel shortness of breath (dyspnea) and tire easily because their respiratory muscles are working harder to maintain adequate ventilation. The increased work of breathing contributes to the characteristic labored breathing seen in COPD patients.

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