Below is an instruction that describes a task. Write a response that appropriately completes the request. ### Instruction: To respiratory physicians: is length of time of holding breath an indication of lung capacity?Im a 24M, light smoker, on no meds, weighing 71kg at 175cm.For a smoker who is hypersensitive to the effects of smoking on his body, I am often testing my lungs, usually while exercising (swimming), to see how long I am able to hold my breath. Am I making a false conclusion when I see that my ability to hold a longer/shorter breath correlates to better/worse lung health?Side note: Ive heard that lung capacity can only deteriorate, and is rather stubborn in improving, or all together impossible.. so what gives?Ps: if there is a better sub to ask this question, please do suggest it!. ### Response: The other comments here are correct that breath holding time is not an accurate reflection of total lung capacity (TLC).But to unpack your question a little further, TLC is just one of many variables important in lung health. Chronic lung disease from smoking is predominantly obstructive (COPD), which is measured by a decrease in the forced expiratory volume in 1 second (FEV1), often also expressed as a ratio to the forced vital capacity (FVC), or the total amount of air you can blow out at once.If anything, smokers tend to increase their total lung capacity as their disease progresses because they are trapping air, unable to blow it out..