The medical acronym WOB stands for Work of Breathing, a physiological measurement that quantifies the energy expenditure required for a person to inhale and exhale air. This measurement reflects the effort the respiratory muscles must exert to move air into and out of the lungs. Although breathing is usually unconscious and low-effort, WOB serves as an important clinical marker for assessing the severity of respiratory distress. Understanding WOB helps medical professionals determine how hard a patient is struggling to maintain adequate oxygen and carbon dioxide levels.
What “WOB” Represents
Work of Breathing is fundamentally defined by physics as the product of pressure multiplied by the change in lung volume. The total WOB is the sum of energy needed to overcome two main types of resistance within the respiratory system. The first component is elastic work, which involves the energy spent to stretch the lung tissue and chest wall, overcoming their natural tendency to recoil. This elastic work accounts for approximately two-thirds of the total effort in a healthy person at rest.
The second component is resistive work, which is the energy required to overcome the frictional forces of air moving through the airways and the friction between tissue layers. Resistive work is significantly influenced by the diameter of the airways and the speed of airflow. When a disease state causes airways to narrow or lung tissue to stiffen, the pressure needed to move air increases dramatically, leading to a pathological rise in the required Work of Breathing.
Recognizing Increased Breathing Effort
Clinicians and caregivers rely on observable physical signs to recognize when a patient’s Work of Breathing has become abnormally high. An increase in the respiratory rate, known as tachypnea, is often the first indicator that the body is attempting to compensate for difficulty. The patient may also start using muscles not typically involved in quiet breathing, referred to as accessory muscle use, such as those in the neck and shoulders, to lift the rib cage.
Another visible sign is retractions, where the skin sinks inward between the ribs, below the rib cage, or above the collarbone during inspiration. Nasal flaring, the widening of the nostrils with each breath, is another attempt to decrease resistance by increasing the diameter of the upper airway. A patient with severely increased WOB may also exhibit paradoxical breathing, where the abdomen moves inward during inspiration instead of outward, indicating extreme diaphragm fatigue.
Conditions That Affect Breathing Effort
Pathological increases in WOB are caused by conditions that affect the two main components of resistance: elastic and resistive.
Increased Resistive Work
Diseases that increase airway resistance make it harder for air to flow freely through the respiratory tubes. Examples include asthma, chronic obstructive pulmonary disease (COPD), and bronchiolitis, all of which cause the airways to narrow due to inflammation or bronchospasm. This narrowing forces the patient to generate much higher pressures to maintain adequate airflow, drastically increasing the resistive WOB.
Increased Elastic Work
Conditions that increase elastic resistance cause the lungs to become stiff and difficult to inflate, a state known as reduced compliance. This requires more energy to stretch the lung and chest wall, boosting the elastic WOB. Specific conditions include pneumonia, which fills lung tissue with fluid, and acute respiratory distress syndrome (ARDS), which causes widespread lung injury and fluid accumulation. Pulmonary edema similarly stiffens the lung tissue and increases the effort needed for expansion.
Clinical Intervention for Abnormal WOB
The primary goal of medical intervention for abnormal WOB is to decrease the patient’s energy expenditure and prevent respiratory muscle fatigue. Initial treatments often include supplemental oxygen therapy to increase the oxygen content of the air, making each breath more efficient. Pharmacological management, such as administering bronchodilators, helps decrease resistive work by widening the airways.
If WOB remains dangerously high, mechanical support is necessary to rest the respiratory muscles. Non-invasive ventilation (NIV), using devices like BiPAP, provides external pressure support to help push air into the lungs, reducing the patient’s effort. In the most severe cases, mechanical ventilation through intubation fully takes over the WOB, allowing the lungs and muscles to recover while the underlying condition is treated.