When designing medical equipment, engineers can often feel like Goldilocks when it comes to humidity: there’s too much or too little—and their challenge is to make it just right.
Too Much Humidity is a Frequent Problem
The air (or a gas) can only hold so much water vapor. Depending on external factors like temperature and pressure, water vapor can condense and create lot of problems. Condensation fogs sensors, cause premature equipment wear or rain-out into sample lines or breathing circuits.
So, often the challenge is to prevent condensation. When you try to remove water vapor from a gas sample, it needs a place to go. If the ambient air outside of the system has a lower humidity than the gas sample, then you could design it to get transferred there, or you could have a trap to collect water when water vapor condenses. Keep in mind that water trapped in water traps are considered biological waste that needs to be treated in a certain way by healthcare professionals, adding to their immense workload. The problem with water traps however is that it can trap valuable analytes along with water and you run the risk of poor quality analysis. If you are trying to transfer water vapor to ambient air, a unique problem arises when ambient air has very high humidity. In such cases, a dry purge gas can be used to remove water vapor from the wet gas you want to analyse.
Low Humidity is also a Challenge
In some applications, such as when administering therapeutic gasses, the humidity levels can be too low. After all, the human lung (Body temperature, ambient pressure and gas saturation or BTPS) functions at 100% relative humidity and 37C. So, then the challenge becomes how to add water vapor to the gases or how to exchange it with another gas stream with a higher level of humidity.
Being aware of both of these humidity challenges is the first step toward designing medical devices that can keep the humidity levels just right.
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