FRC equals CC in which of the following scenarios?

The correct answer indicates that functional residual capacity (FRC) equals closing capacity (CC) under certain age-related conditions and body positions. In this case, the answer refers to the mid-40s in a supine position and the mid-60s in an upright position.

As individuals age, various changes occur in lung function and respiratory mechanics. By the mid-40s, lung volumes, particularly FRC, may begin to decline due to a combination of factors such as loss of elastic recoil and increased stiffness of the lung tissue. Closing capacity, which reflects the volume of air in the lungs at which small airways begin to close during exhalation, can increase due to changes in the elastic properties of the lungs and surrounding structures.

In the upright position, it is common for FRC and CC to converge around the mid-60s due to further age-related changes, including weakened respiratory musculature and altered airway dynamics. Therefore, FRC equaling CC in these specific scenarios accurately reflects the physiological changes that take place as individuals progress through their 40s and into their 60s.

Other scenarios provided do not correctly match the physiological timeline or position dynamics associated with FRC and CC. For instance, the upright position by age