Smoking is a crucial factor in causation and worsening of several respiratory illnesses. The major respiratory illnesses associated with smoking includes bronchial asthma, chronic obstructive pulmonary disease, emphysema, interstitial lung disease, lung fibrosis and lung cancer. Almost all types of pneumonias get worsened and are affected by smoking. A large study done in 2021 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8224924/) investigated association between long-term smoking and exercise capacity, gas exchange in lungs, lung volumes and flow rates. The arterial oxygen pressure and alveolar oxygen tension are shown reduce with increased smoking. The alveolar-arterial carbon dioxide gradient increased with >30 pack years smoking. The arterial oxygen saturation at rest and at maximum exercise declined as cigarette smoke exposure increased. The primary adverse effects of long-term cigarette exposure on pulmonary physiology are small airway narrowing and impairment in the alveolar gas diffusion capacity. An overall reduction in oxygen carrying capacity at cellular results in impaired metabolism, dysfunction and disease.
