Apneic diffusion oxygenation and continuous flow apneic ventilation. A review.
Evolution of life coincides with the most rapid rate of rise in atmospheric oxygen concentration during Devonian time. Oxygen is essential for life, but at the same time is a cellular poison if present in tensions considerably higher than those the particular cellular milieu has become adapted to. Animals exposed to low oxygen tensions breathe continuously, e.g. most species of fish obtain their oxygen from a continuous flow of water at low oxygen tensions. Evolution from water to land breathing generally is associated with intermittent breathing, mass movement of gas in one direction, i.e. inhalation and exhalation. Intermittent breathing is part of this evolutionary process and reduces the inspired oxygen tension from 150 mmHg (19.95 kPa) to approximately 100 mmHg (13.3 kPa) at the alveolar blood interface. Perhaps evolution from continuous ventilation to intermittent breathing may be protecting the body against the high atmospheric oxygen tension. Therefore, it is not surprising that mammals can have adequate oxygen uptake with apneic diffusion oxygenation (ADO) and continuous flow apneic ventilation (CFAV). Mechanical ventilation classic techniques, i.e. intermittent positive-pressure ventilation and continuous positive-pressure ventilation, employ ventilatory frequencies close to the resting breathing rate of the adult. Utilizing low-compression patient circuits has made mechanical ventilation with higher frequencies possible. 60 to 400 breaths per min is used for high-frequency positive-pressure ventilation and high-frequency jet ventilation, and up to 40 Hz is used for high-frequency oscillation (HFO). The two extremes of artificial ventilation - ADO, i.e. supply of O2 by continuous flow, and HFO, i.e. supply of O2 by oscillatory changes - both primarily involve diffusion, even though convection (also secondary to cardiac oscillations) obviously is important in the process of gas exchange. Some recent experimental findings favor continued development and evaluation of CFAV as an additional alternative to artificial ventilation.
D000818:Animals; D006801:Humans; D007385:Intermittent Positive-Pressure Ventilation; D010100:Oxygen / Q000502:physiology / Q000506:poisoning; D011175:Positive-Pressure Respiration; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000379:methods*
D010100:Oxygen