**Core Concept**
The pulmonary changes in lateral position in an anaesthetized patient are related to the distribution of blood flow and ventilation in the lungs. When a patient is placed in the lateral position, the weight of the mediastinum and the heart causes the lungs to be compressed, leading to a decrease in lung volume and ventilation in the dependent lung.

**Why the Correct Answer is Right**
When a patient is in the lateral position, the dependent lung (the lung that is on the bottom) receives a decrease in ventilation and perfusion due to the compression of the lung tissue. This is because the weight of the mediastinum and the heart causes the dependent lung to be compressed, leading to a decrease in lung volume and ventilation. Additionally, the dependent lung receives less blood flow due to the effects of gravity on blood distribution. This results in a ventilation-perfusion mismatch, which can lead to hypoxemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the pulmonary changes in lateral position are not solely due to the effects of gravity on blood distribution. While gravity does play a role, the compression of the lung tissue by the mediastinum and heart is a more significant factor.
* **Option B:** This option is incorrect because the pulmonary changes in lateral position are not limited to the dependent lung. The non-dependent lung (the lung that is on top) also experiences changes in ventilation and perfusion, although to a lesser extent.

**Clinical Pearl / High-Yield Fact**
When positioning an anaesthetized patient, it's essential to consider the effects of gravity on blood distribution and lung compression. This can help prevent complications such as hypoxemia and atelectasis.

**Correct Answer: C. The dependent lung receives a decrease in ventilation and perfusion due to compression of the lung tissue.**