**Core Concept**
Dunda's grant apparatus is a device used in physiological experiments to study the regulation of breathing and the response of the respiratory system to changes in blood carbon dioxide (CO2) levels. It is a type of respiratory chamber that allows for the measurement of ventilation and gas exchange in the lungs.

**Why the Correct Answer is Right**
Dunda's grant apparatus is specifically designed to measure the respiratory response to hypercapnia, or elevated CO2 levels, in the blood. The apparatus is typically used to study the regulation of breathing in response to changes in CO2 levels, and to measure the sensitivity of the respiratory system to CO2. The device works by allowing the subject to breathe into a chamber, where the CO2 levels can be controlled and measured.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Dunda's grant apparatus is not primarily used to study the regulation of heart rate or blood pressure.
**Option B:** This option is incorrect because Dunda's grant apparatus is not typically used to study the regulation of blood glucose levels.
**Option C:** This option is incorrect because Dunda's grant apparatus is not specifically designed to measure the effects of hypoxia, or low oxygen levels, on the respiratory system.

**Clinical Pearl / High-Yield Fact**
It's worth noting that Dunda's grant apparatus is a classic example of a device used in physiological research to study the regulation of breathing. Understanding how the respiratory system responds to changes in CO2 levels is critical in the diagnosis and management of various respiratory and neurological disorders.

**Correct Answer: A. Respiratory physiology**