Prior to my RNY gastric bypass surgery 5 years ago I had sleep apnea but I also had severe asthma. The sleep apnea problem went into remission within a couple months. The asthma disappeared after around 3-4 years.
There was recent research performed in South Korea that showed a direct correlation between weight loss in men and improved lung function.
A group of researchers led by Dr. Eun Kyung Choe from Seoul National University Hospital Healthcare System Gangnam Center, Seoul, South Korea, studied the association between abdominal obesity and lung function โ their study published in PLOS One. These investigators used clinical records from about 1100 adult Korean people โ 428 men โ assessing them at baseline and following them for about 3 years. All were healthy at the beginning of the study, and all were non-smokers who had never smoked.
As the amount of VAT (visceral adipose tissue - fat tissue located deep in the abdomen and around internal organs.) decreased in men so did both FVC (forced vital capacity) and FEV1 (1 second forced expiratory volume). These measures are used, as well as their ratio (FEV1: FVC) to help diagnose lung diseases like emphysema and chronic bronchitis. The authors suggested that the changes in lung function associated with decreases in VAT might be due to mechanical differences, e.g. less pressure on the diaphragm, and/or due to the greater propensity of the VAT to release inflammatory cytokines which could trigger systemic inflammation.
https://www.acsh.org/news/2018/02/28/losing-fat-might-mean-better-breathing-12629