ventilation in the physiological sense (strictly, pulmonary ventilation) refers to the volume of air breathed in and out of the lungs: typically 5–6 litres per minute for an average-sized person at rest, with the possibility of increasing by up to twenty-fold in exercise. For example, the size of each breath (tidal volume) could vary from 0.5 to 3 litres, and the number of breaths per minute from 10 to 40. When for any reason breathing stops or becomes inadequate, or if natural breathing is prevented by drug-induced muscle relaxation as an adjunct to anaesthesia, mechanical or artificial ventilation (also known as artificial respiration) is necessary. Methods range from mouth-to-mouth breathing to machines which pump gas rhythmically into the lungs

Stuart Judge

ventilation The process by which a continuous exchange of gases is maintained across respiratory surfaces. Often called external respiration, this is achieved by respiratory movements; in air-breathing vertebrates it is movement of air into and out of the lungs (see also air sac; expiration; inspiration; trachea; ventilation centre). The ventilation rate (or respiration rate) of an animal is the volume of air breathed per minute, i.e. tidal volume × number of breaths per minute. It can be measured with the aid of a respirometer.

ventilation In biology, the process by which air or water is taken into and expelled from the body of an animal and passed over a surface across which gas exchange takes place. Ventilation mechanisms include breathing, by which air is drawn into the lungs for gas exchange across the wall of the alveoli, and the movements of the floor of a fish's mouth, coupled with those of its gill covers, which draw water across the gills. See also alveolus

ventilation (ven-ti-lay-shŏn) n.
1. the passage of air into and out of the respiratory tract. In the alveoli of the lungs gas exchange is most efficient when matched by an adequate blood flow (perfusion). Ventilation/perfusion imbalance is an important cause of anoxia and cyanosis.

2. maintenance or support of the breathing movements of patients either by the insertion of an endotracheal tube (see intubation) or by noninvasive means (see noninvasive ventilation). See also ventilator.