This term literally means without breath, and is used to designate the condition which hinders air from entering the cells of the lungs in sufficient quantities to support life. It may occur in the course of many diseases — especially lung troubles. It is also frequent in heart affections, and may likewise be caused by spasmodic closures of the glottis by foreign substances or throat difficulties, or by the atmosphere inhaled being deficient in its proportion of oxygen or containing deleterious gases[1]. All cases of apnoea must be treated in accordance with the cause of the difficulty as directed in the articles devoted to the various difficulties and diseases in which apnoea is likely to occur.[1] Apnea now refers solely to suspension of breathing, not simply oxygen deprivation (which might be better described as hypoxia).
Excerpts from J. H. Greer's "A Physician in the House: for family and individual consultation", published in 1897. Annotations provided throughout. This is not medical advice - if you're sick, see a doctor.