Ventilation

What is ventilation? How does a mechanical ventilator work?

Mechanical ventilators help with breathing.

In breathing, air is inhaled through the mouth and/or nose, pharynx, larynx, trachea and bronchial tree into tiny alveoli sacs in the lungs, where air mixes with the carbon dioxide-rich gas from the blood. The air is then exhaled.

Normally this cycle repeats at a breathing rate, or frequency, for adults of about 12 breaths per minute. Babies and children breathe at a faster rate.

Gas exchange in the lungs supplies oxygen to the blood and removes carbon dioxide collected from the cells.

Ventilation is the tidal volume of gas entering or leaving the lungs in a given amount of time, and determines if the gas exchange is sufficient.

For mechanical ventilator to work, it must produce the right tidal volume and breathing rate for the body.

Conventional ventilators produce the normal breathing patterns of children and adults, about 12-25 breaths per minute.

Two forces expand the lungs and chest wall during breathing: the contraction of the muscles (including the diaphragm) and the contrasting pressure at the airway opening (mouth and nose) and on the outer surface of the chest wall.

Normally, the respiratory muscles expand the chest wall. This decreases the pressure on the outside of the lungs, so they expand. This enlarges the air space in the lungs and draws air into the lungs.

When respiratory muscles are unable to do the work for breathing, either one or both of these forces can be manipulated with a mechanical ventilator.