Increased airway resistance is/are caused bya) Forced expirationb) Denser airc) Low lung volumed) High lung volue
## **Core Concept**
Airway resistance is influenced by several factors including lung volume, airflow rate, and the physical properties of the air. Understanding how these factors affect airway resistance is crucial in respiratory physiology.
## **Why the Correct Answer is Right**
The correct answer involves understanding how different conditions affect airway resistance.
- **Forced expiration (a)**: During forced expiration, the intrathoracic airways are compressed due to the increased intrapleural pressure. This compression increases the resistance to airflow.
- **Denser air (b)**: Air density affects airway resistance; however, under normal physiological conditions, the effect of air density on airway resistance is minimal compared to other factors like lung volume and airflow rate.
- **Low lung volume (c)**: At low lung volumes, the airways are smaller and more collapsible, which increases airway resistance.
- **High lung volume (d)**: At high lung volumes, the airways are larger and less collapsible, which generally decreases airway resistance.
## **Why Each Wrong Option is Incorrect**
- **Option B:** This option is incorrect because while increased density of air can increase airway resistance according to Poiseuille's law, the effect is generally minimal under normal conditions and not as directly impactful as dynamic changes like those during forced expiration or changes in lung volume.
- **Option D:** This option might seem plausible because high lung volumes can affect airway diameter; however, the relationship is not as straightforward. High lung volumes generally decrease airway resistance because the larger lung volume helps to keep the airways open.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that airway resistance is significantly affected by lung volume and the rate of airflow. During forced expiration, as seen in conditions like asthma or COPD, airway resistance increases substantially due to both the increased flow rate and the dynamic compression of airways.
## **Correct Answer:** C. a, c.