Features | REMstar^® Humidifiers

Temperature

The air temperature plays a key role when discussing humidification. At any given temperature air can hold a specific amount of water vapor. Basically the higher the temperature the more capacity the air has to hold water vapor.

Relative Humidity

Relative humidity is the ratio of actual water vapor in the air compared to how much water vapor the air is capable of holding (its capacity). Relative humidity's unit of measure is %.

Absolute Humidity

Absolute humidity is a measurement of actual water vapor content per volume of air, measured in milligrams of water vapor per liter of air {mg H20/L}.

Dew Point

The temperature level where a fully saturated gas begins to condense. (This is often referred to as rain out in a patient circuit.)

In the example below, the water vapor content per liter of air (absolute humidity) is identical in both cases @ 44mg H20 / L. However, the 37 degree C cube must have a relative humidity level of 100% to enable 44 mg H20 to be present when compared to a 67% relative humidity level at the higher temperature level of 45 degrees C. The warmer the temperature the greater its capacity for holding water vapor.

Difference between Cool Pass-over & Heated Humidification

Cool pass-over style humidifiers allow the air flow to pass over a pool of water and subsequently pick up water vapor by free evaporation. Typically the larger the surface area of the pool of water the more water vapor the air stream can pick up. This is why Respironics' LX Humidifier and the new REMstar Pass-over Humidifier provide additional humidification capabilities vs. a non-heated canister-type water chamber with minimal surface area.

The REMstar Heated Humidifier is also a pass-over style humidifier but it is heated. Heated pass-over style humidifiers are much more efficient at providing humidification simply by increasing the water temperature, which increases water vapor production vs. free humidification (see picture below). By increasing the water temperature, additional energy is added to the individual molecules, allowing more of them to transform from the liquid state. As a result, the heated humidifier has the capability to provide additional water vapor to the air stream vs. a typical cool pass-over design.

Bacteria and the Chamber

Heated humidification produces molecular water vapor (.0001 microns in size) that is too small to transport bacteria into the air stream that is delivered to the patient. If small amounts of bacteria are present in the chamber there is little risk to the patient. Bacteria requires a carrier and molecular water vapor cannot provide this mechanism.

Note: The humidifier chamber does offer good conditions for colonization by micro-organisms such as bacteria. This has been demonstrated over the years with other respiratory devices. This fact highlights the importance of proper and frequent cleaning of the humidifier chambers.

Distilled water vs. tap water

Most tap water contains various minerals. When a pool of water is heated and evaporated, these minerals are left behind and may cause discoloration to the aluminum plate and plastic housing of the humidifier chamber. It may adversely affect the longevity of the chamber. Distilled water has been purified and will not generate mineral residue upon evaporation and may extend the usable life of the chamber.