Transfer of respiratory pathogens: Equilibrium size of respiratory aerosols

TL;DR

Respiratory droplets, containing solutes and bound water, have different equilibrium sizes depending on the relative humidity, with mucus fragments being the more common source of infectious aerosols.

Transcript

PROFESSOR: So let's look at a little more detail at the equilibrium size of respiratory droplets that are emitted during breathing, or coughing, or speaking. And the key idea is that these droplets are not pure liquid. As explained in the wells curve, pure droplets that are small enough will shrink completely and evaporate. However, these droplets ... Read More

Key Insights

• 💦 Respiratory droplets emitted during breathing, coughing, or speaking contain solutes and bound water, which affect their equilibrium size.
• 💦 Mucus fragments have a higher solute content and are more likely to result in larger droplets that can remain infectious in the air.
• 💦 The presence of solutes helps retain water and provides a stable environment for viruses, increasing their viability and transmissibility.
• 🎴 Relative humidity plays a vital role in determining the size and behavior of respiratory droplets, with low humidity causing shrinkage and high humidity leading to growth.

Questions & Answers

Q: What determines the equilibrium size of respiratory droplets?

The equilibrium size of respiratory droplets is determined by the presence of solutes and bound water, as well as the relative humidity. Higher solute content and higher relative humidity result in larger droplets.

Q: How do respiratory droplets with high solute content affect transmission?

Respiratory droplets with high solute content, such as mucus fragments, are more likely to remain infectious in the air. The solutes help retain water, providing a stable environment for viruses, making them more viable and easily transmittable.

Q: Can respiratory droplets evaporate completely?

Respiratory droplets can shrink and evaporate, but the solutes, such as proteins and macromolecules, do not evaporate. This means that despite water evaporation, the solutes remain in the droplets.

Q: What is the significance of relative humidity in respiratory droplet equilibrium?

Relative humidity plays a crucial role in respiratory droplet equilibrium. It determines the size and behavior of the droplets, with low humidity causing shrinkage and high humidity leading to growth and absorption of more water.

Summary & Key Takeaways

• Respiratory droplets emitted during breathing, coughing, or speaking are not pure liquid, but contain solutes such as proteins, macromolecules, and dissolved salts.

• The presence of solutes and bound water in these droplets affects their equilibrium size, with higher relative humidity leading to growth and lower relative humidity causing shrinkage.

• Mucus fragments, due to their high solute content, are more likely to result in larger droplets that can remain infectious in the air.