30. Ventilation

Total ventilation (VT, minute ventilation) is the total gas flow into the lungs per minute. It is equal to the tidal volume (VT) x the respiratory rate (n). Total ventilation is the sum of dead space ventilation and alveolar ventilation.

Anatomic dead space is equivalent to the volume of the conducting airways (150 mL in normal individuals), i. e., the trachea and bronchi up to and including the terminal bronchioles. Gas exchange does not occur here. Physiologic dead space is the volume of the respiratory tract that does not participate in gas exchange. It includes the anatomic dead space and partially functional or nonfunctional alveoli (e. g., because of a pulmonan embolus preventing blood supply to a region of alveoli). In normal individuals, anatomic and physiologic dead space are approximately equal. Physiologic dead space can greatly exceed anatomic dead space in individuals with lung disease.

Dead space ventilation is the gas flow into dead space per minute. Alveolar ventilation is the gas flow entering functional alveoli per minute.

Alveolar ventilation: It is the single most important parameter of lung function. It cannot be measured directly. It must be adequate for removal of the CO ₂ produced by tissue metabolism whereas the partial pressure of inspired O ₂ is 150 mmHg, the partial pressure of O ₂ in the alveoli is typically 100 mmHg because of the displacement of O ₂ with CO ₂. PAo2 cannot be measured directly.

New words

total – общее количество

ventilation – вентиляция

flow – поток

per minute – в минуту

equal – равный

the conducting – проведение

airways – воздушные пути

exchange – обмен

tract – трактат

to be measured – быть измеренным

directly – непосредственно

displacement – смещение