**Core Concept**
Transthoracic compliance refers to the ease with which the thoracic cavity can expand during inspiration, which is essential for maintaining adequate ventilation. The transthoracic compliance formula is a mathematical representation of this concept, allowing clinicians to quantify the relationship between lung volume and pressure changes.

**Why the Correct Answer is Right**
The transthoracic compliance formula is expressed as: C = ΔV / ΔP, where C is transthoracic compliance, ΔV is the change in lung volume, and ΔP is the change in intrapleural pressure. This formula highlights the inverse relationship between transthoracic compliance and the pressure required to achieve a given volume change. In other words, a higher compliance value indicates that the thoracic cavity can expand more easily, resulting in improved lung volumes with minimal pressure changes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the relationship between lung volume and pressure changes.
**Option B:** This option is incorrect because it introduces an extraneous variable, such as lung resistance, which is not a component of the transthoracic compliance formula.
**Option C:** This option is incorrect because it suggests a different mathematical relationship between lung volume and pressure changes, which is not supported by the transthoracic compliance formula.

**Clinical Pearl / High-Yield Fact**
A key clinical application of the transthoracic compliance formula is in the assessment of patients with restrictive lung disease, where decreased compliance values can indicate impaired lung expansion and reduced lung volumes.

**Correct Answer: C. ΔV / ΔP**