In a healthy human, 75% of respiratory gas conditioning occurs in the upper respiratory tract and the remaining 25% are taken over by the trachea. The upper respiratory tract humidifies, warms and cleanses 1,000 to 21,000 liters of respiratory gas every day in accordance with body size.

The warming of breathed-in air is directly impacted by many small blood vessels, with blood flow being regulated by nerve impulses. When cold air is being breathed in, more blood is supplied.

Mucous membranes inside the nose and mouth release moisture to gas as it is breathed in, this results in a healthy adult evaporating between 200 to 300 ml of water per day. When travelling to the lower respiratory tract, the respiratory gas, which has already been humidified in the nasopharynx, is conditioned further until the isothermal saturation limit is reached. Isothermal saturation limit refers to the maximum possible humidity at a specific temperature, which amounts to 100% relative humidity and 44 mg absolute humidity at 37°C. That equilibrium is reached during nasal breathing in a healthy person at the bifurcation of the trachea. This means only water vapor-satiated and body-warm air reaches the alveoli.

Gas humidifiers are used during mechanical ventilation as natural respiratory gas conditioning can be significantly impacted. In non-invasive respiratory treatment such as oxygen masks, a continuous positive flow is administered. This can cause upper respiratory tracts to dry out and result in blockages of air passages and congestion. Gas humidifiers can help avoid this by ensuring that the gas is well saturated and warm.

When invasive respiration is necessary, such as via intubation or tracheotomy, upper respiratory tracts are bypassed and thus do not exercise their usual function. The trachea is unable to offer the required humidifying, warming and clearing alone. This is why gas humidifiers are critical for treating the gas prior to it entering the human body.

Replicating Human Breath with Gas Humidifiers

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