Final answer:
Randall's doctor recommends measuring his lung capacity as part of monitoring respiratory health, which can decline with age. Techniques like spirometry can measure lung volumes and capacities, important for detecting conditions such as asthma or fibrosis.
Step-by-step explanation:
Randall's doctor's recommendation to start measuring his lung capacity is likely due to the common decrease in respiratory system efficiency as age increases. Around the age of 55, it is possible that Randall's lungs have become less compliant or there is increased resistance within the lungs, making it more difficult to breathe, thus warranting the measurements.
Lung volumes are usually measured using a technique called spirometry, which can check the amount of air the lungs are able to hold and how quickly air can be expelled. The Forced Expiratory Volume (FEV) and the Forced Vital Capacity (FVC) are important markers in spirometry. A low FEV1/FVC ratio might indicate increased resistance, characteristic of conditions like asthma, whereas a high ratio could suggest less compliant lungs, often seen in fibrosis.
The total lung capacity of an average adult male is about six liters. It is reasonable for Randall to have his lung volumes, including tidal volume and residual volume, measured regularly as he ages to monitor for any potential respiratory issues.