RLO: Ventilation

School of Nursing and Academic Division of Midwifery

Mechanical concepts of ventilation

So, how is air forced in and out of the lungs? It is basic mechanics carried out by a few muscles, plus a bit of physics. In simple terms, for inhalation to take place, the lower walls of the lungs are pulled downwards (in a similar way to the plunger in a bike-pump or a syringe). In addition, the outer walls for the lungs are pulled outwards and upwards (in a similar way to the bellows of a concertina). This makes the space inside the thorax bigger and causes air to be sucked-in, down the airways.

Fortunately, we don’t need these devices to draw air into our lungs - the external intercostal muscles and the diaphragm do the job instead. But how can muscles that are not attached to the lung tissue manage to pull air into the lungs? They do it indirectly by causing a “sucking” effect.