Table 1.

Processes involved in different pathologies.

Process	Description	Biomarker	References
Marker of oxidative stress	Inflammation process in lung cells; eosinophils, neutrophils, and macrophages produce reactive oxygen species	H2O2	[19,22,23]
	Increase of free radicals, which react to cell membrane phospholipid, generating 8-isoprostane	8-isoprostane	[19,20]
	Oxidation of cell membrane phospholipids produces a chain reaction, the targets of which are polyunsaturated fatty acids, resulting in the formation of unstable lipid hydroperoxides and secondary carbonyl compounds, such as aldehydic products	Malondialdehyde	[19]
	CO, a marker of oxidative stress, is produced by the stress protein hemoglobin oxygenase	CO	[21]
Inflammation of airways	Immune response against infection produces an inflammation process in cells, which generate more NO than in a healthy person	Alveolar NO	[19]
	Cytokines * and chemokines are involved in many aspects of the disease process in chronic obstructive pulmonary disease (COPD), including recruitment of neutrophils, macrophages, T cells, and B cells	Cytokines * and chemokines	[19]
	Leukotrienes are muscle constrictors, such as in lung muscle	Leukotriene B4 and prostaglandins	[19]
	CO is a marker of inflammation	CO	[21]

* Cytokines are agents responsible for cellular communication.