This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
Fowler's method is employed for the measurement of:- 
Select and explain. 
A. Residual volume, B. Alveolar PO2, C. Anatomic dead space, D. Physiologic dead space
C: Anatomic dead space
Answer: C: Anatomic dead space 
Explanation: Methods used for various studies: - 1. Bohr's method: - Physiological dead space 2. Fowler's method: - Anatomic dead space. Based on single breath nitrogen analysis technique. A person is given 100% oxygen in single breaths, that breath enters alveoli Now the person stas exhaling out, the first air that comes out, it had never reached the alveoli, it is coming out of dead space only from the anatomic dead space. The first pa of exhaled air is last pa of inhaled air. So, when the person sta exhaling, he exhales the last pa of inhaled air first, which is air in anatomic dead space. This first exhaled air is analyzed, & this air will contain only O2. This is fowler's method. Used to measure functional residual capacity 3. Residual volume: Helium dilution method Nitrogen washout method.