Question

Define functional residual capacity (FRC). Enumerate the factors that affect FRC with their clinical implications.

Hint:

When considering FRC, it's important to remember that it plays a crucial role in preventing atelectasis. Factors like position, obesity, and age can have a significant impact on lung function, particularly during anaesthesia.

Answer 1

Step 1: Definition of FRC.
Functional Residual Capacity (FRC) is the volume of air remaining in the lungs after a normal tidal exhalation. It is the sum of the Expiratory Reserve Volume (ERV) and the Residual Volume (RV). The FRC is essential as it ensures that the lungs are not empty at the end of exhalation, maintaining a constant exchange of gases during the breathing cycle.

Step 2: Factors affecting FRC.
Several factors can affect the FRC, and these include:
- Body position: FRC is larger when in the upright position compared to the supine position due to gravitational effects on the diaphragm and chest wall.
- Age: FRC increases with age due to loss of lung elasticity and reduced chest wall compliance.
- Obesity: Excess weight can reduce the FRC by compressing the diaphragm and reducing lung expansion.
- Pulmonary diseases: Conditions like Chronic Obstructive Pulmonary Disease (COPD) lead to an increase in FRC due to hyperinflation of the lungs.
- Pregnancy: As the uterus expands, it can push upward on the diaphragm, reducing the FRC.

Step 3: Clinical implications.
The factors affecting FRC are important in the clinical setting, as they influence gas exchange and ventilation strategies, especially in mechanical ventilation and anaesthesia management. FRC reduction can lead to atelectasis (lung collapse) and impaired oxygenation during general anaesthesia.