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1. Replacement of air or other gas in a space by fresh air or gas. 2. Movement of gas(es) into and out of the lungs. SYN: oxidative metabolism, respiration (2). 3. (V) In physiology, the tidal exchange of air between the lungs and the atmosphere that occurs in breathing. SEE ALSO: respiration. [see ventilate]

- airway pressure release v. mechanical v. in which patients being treated with continuous positive airway pressure have intermittent decreases rather than increases in airway pressure and volume.

- alveolar v. (V_A) the volume of gas expired from the alveoli to the outside of the body per minute; calculated as the respiratory frequency (f) multiplied by the difference between tidal volume and the dead space (V_T − V_D); units: ml/min BTPS.

- artificial v. any means of producing gas exchange mechanically or manually between the lungs and the surrounding air, which is not performed entirely by the person's own respiratory system. SYN: artificial respiration.

- assist-control v. artificial positive-pressure v. by machine in which a full breath is produced automatically, following a patient's natural inspiratory effort. In the event that the patient does not initiate such an effort, the machine will provide a baseline, or “backup” respiratory rate.

- assisted v. application of mechanically or manually generated positive pressure to gas(es) in or about the airway during inhalation as a means of augmenting movement of gases into the lungs. SYN: assisted respiration.

- bag v. SYN: manual v..

- continuous positive pressure v. (CPPV) SYN: controlled mechanical v..

- controlled v. intermittent application of mechanically or manually generated positive pressure to gas(es) in or about the airway as a means of forcing gases into the lungs in the absence of spontaneous ventilatory efforts. SYN: controlled respiration.

- controlled mechanical v. (CMV) artificial v. in which all inspirations are provided by positive pressure applied to the airway, regardless of the patient's own efforts at breathing. In current clinical practice, this mode is almost never used. SYN: continuous positive pressure v., intermittent positive pressure v..

- high-frequency v. mechanical v. using “jet” administration of breaths at frequencies anywhere from 300–3000 breaths per minute to avoid some complications of more conventional v..

- intermittent mandatory v. (IMV) mechanical application of positive pressure volume at a predetermined frequency to the airway, interspersed between the patient's own natural breathing through the ventilator circuit. No attempt is made to time the machine's breaths with the patient's own.

- intermittent positive pressure v. (IPPV) SYN: controlled mechanical v..

- inverse-ratio v. mechanical v. in which the time allowed by the machine for inspiration exceeds that allowed for expiration, which is opposite the situation in more standard modes of v..

- liquid v. an experimental means of ventilating lungs suffering from severe injury, through use of O₂ and CO₂ dissolved in perfluorocarbons in a liquid, thus (theoretically) decreasing the incidence of atelectasis and other problems.

- mandatory minute v. mechanical v. in which the ventilator is configured to ensure a certain minute volume, but only if needed.

- manual v. intermittent manual compression of a gas-filled reservoir bag to force gases into a patient's lungs and thus maintain oxygenation and carbon dioxide elimination during apnea or hypoventilation. SYN: bag v..

- maximum voluntary v. (MVV) the volume of air breathed when an individual breathes as deeply and as quickly as possible for a given time ( e.g., 15 s.). Usually extrapolated to what could be breathed over 1 minute. SYN: maximum breathing capacity.

- mechanical v. any mechanically assisted breathing, employing either positive or negative pressure devices. Some positive-pressure devices require intubation of the trachea and some require only a mask applied to the mouth or nose. For the past several decades, the standard way of mechanicaly ventilating a patient with respiratory failure has involved intubation of the trachea and either pressure- or volume-limited application of positive pressure to the lungs through the endotracheal tube; currently, the need for intubation in all cases is coming into question and many chronic respiratory failure patients can be adequately ventilated by noninvasive devices.

- negative pressure v. mechanical v. in which various devices that surround the thorax are used in such a way that the development of negative or subatmospheric pressure causes thoracic expansion and thus inhalation; the release of the negative pressure allows the thorax to relax and thus the lungs to exhale. This is the type of v. made famous by the “iron lung,” used in so many patients with poliomyelitis. Other such ventilators include the cuirass and the body suit.

- noninvasive positive pressure v. the application of positive pressure through a nasal or full-face mask encompassing the nose and mouth, which is cycled in a similar way to modes of v. in which more direct control of the patient's airway or trachea has been achieved. This type of v. is often used to temporize while treating the patient to avoid endotracheal intubation.

- permissive hypercapnic v. mechanical v. in which the level of carbon dioxide in the blood is allowed to rise well above normal values, to minimize the amount of mechanical support given to the patient, and thus minimize complications of that support, such as barotrauma. This mode of v. is used commonly in severe asthmatic patients, who, if ventilated more traditionally, would generate huge pressures in their airways, with resultant pneumothorax.

- pressure-controlled v. mechanical v. that is achieved regardless of the patient's spontaneous breathing, but that uses pressure as the major determining variable, along with rate and time, of how much air the patient receives.

- pressure-support v. mechanical ventilatory assistance in which each breath triggers a pressure-limited amount of support. The ventilator only provides support of each breath to a preset amount of pressure, thus the volume breathed can differ from breath to breath taken.

- proportional assist v. mechanical v. in which the ventilator, in synchrony with the patient's own breathing, gives support in proportion to the effort generated by the patient. This mode allows the patient to determine completely how much support is given by the machine.

- pulmonary v. respiratory minute volume, i.e., the total volume of gas per minute inspired (V_I) or expired (V_E) expressed in liters per minute; differs from alveolar v. by including the exchange of dead space gas.

- synchronized intermittent mandatory v. (SIMV) intermittent mandatory v. spontaneously initiated by the patient to increase tidal volume to a preset volume, and subsequently synchronized with the patient's respiratory cycle; if the patient makes no respiratory effort, the machine automatically delivers a preset number of breaths by itself.

- wasted v. that part of the pulmonary v. which is ineffective in exchanging oxygen and carbon dioxide with pulmonary capillary blood; calculated as physiologic dead space multiplied by respiratory frequency.

ven·ti·la·tion .vent-əl-'ā-shən n

1) the act or process of ventilating

2) the circulation and exchange of gases in the lungs or gills that is basic to respiration

the passage of air into and out of the respiratory tract. The air that reaches only as far as the conducting airways cannot take part in gas exchange and is known as dead space ventilation - this may be reduced by performing a tracheostomy. In the air sacs of the lungs (alveoli) gas exchange is most efficient when matched by adequate blood flow (perfusion). Ventilation/perfusion imbalance (ventilation of underperfused alveoli or perfusion of underventilated alveoli) is an important cause of anoxia and cyanosis.