Inhaling to mitigate exhaled bioaerosols

Abstract

Humans commonly exhale aerosols comprised of small droplets of airway-lining fluid during normal breathing. These "exhaled bioaerosols" may carry airborne pathogens and thereby magnify the spread of certain infectious diseases, such as influenza, tuberculosis, and severe acute respiratory syndrome. We hypothesize that, by altering lung airway surface properties through an inhaled nontoxic aerosol, we might substantially diminish the number of exhaled bioaerosol droplets and thereby provide a simple means to potentially mitigate the spread of airborne infectious disease independently of the identity of the airborne pathogen or the nature of any specific therapy. We find that some normal human subjects expire many more bioaerosol particles than other individuals during quiet breathing and therefore bear the burden of production of exhaled bioaerosols. Administering nebulized isotonic saline to these "high-producer" individuals diminishes the number of exhaled bioaerosol particles expired by 72.10 +/- 8.19% for up to 6 h. In vitro and in vivo experiments with saline and surfactants suggest that the mechanism of action of the nebulized saline relates to modification of the physical properties of the airway-lining fluid, notably surface tension.

Fig. 1.

Exhaled bioaerosol particles during normal breathing of 11 healthy human subjects. (A) Exhaled bioaerosol particles per liter vs. time for 11 healthy human subjects. Particles of >150 nm were counted in these measurements, after a period of 2-min expiration at each represented time point. (B) Average exhaled bioaerosol particles per liter vs. human subject over the 6-h measurement interval. The average exhaled particle per liter number was obtained by summing the measured particle numbers for every time point during the 6-h period and dividing by the number of time points. High producers are defined as those subjects who expire on average >500 particles per liter. (C) Cumulative expired particles per liter vs. time for the high- (n = 6 subjects) and low-producer (n = 5 subjects) groups. Cumulative expired particles were determined by summing up the expired particles per liter for all individuals of a group at each time point.

Fig. 2.

Exhaled bioaerosol particles after delivery of isotonic saline during normal breathing in 11 healthy human subjects. (A) Exhaled bioaerosol particles per liter vs. time for 11 healthy human subjects after inhalation of isotonic saline at t = 0. Particles of >150 nm were counted in these measurements, after a period of 2-min expiration at each represented time point. (B) Average exhaled bioaerosol particles per liter vs. human subject over the 6-h measurement interval for the cases of baseline and saline delivery. The average exhaled particle per liter number was obtained by summing the measured particle numbers for every time point during the 6-h period and dividing by the number of time points. (C) Cumulative expired particles per liter vs. time for all human subjects after inspiration of saline (n = 11 subjects) and of air (i.e., baseline) (n = 11 subjects). Cumulative expired particles were determined by summing up the expired particles per liter for all individuals of a group at each time point.

Fig. 3.

Aerosol concentration of particles produced in the in vitro cough machine after delivery of isotonic saline or surfactant as a consequence of a burst of air over the simulated mucus. (A) The effect of saline delivery on density distribution of aerosol particles formed after exposure of mucus simulant surface to a burst of air in the in vitro cough machine. Four cases are shown: (i) mucus simulant (solid grey line), (ii) mucus simulant immediately after application of nebulized isotonic saline (dotted green line), (iii) mucus simulant 30 min after application of nebulized isotonic saline (dashed-dotted red line), and (iv) mucus simulant 60 min after application of nebulized isotonic saline (dashed blue line). (B) The effect of surfactant delivery on density distribution of aerosol particles formed after exposure of mucus simulant surface to a burst of air in the in vitro cough machine. Four cases are shown: (i) mucus simulant (solid grey line), (ii) mucus simulant immediately after application of nebulized isotonic saline (dotted green line), (iii) mucus simulant 30 min after application of nebulized isotonic saline (dashed-dotted red line), and (iv) mucus simulant 60 min after application of nebulized isotonic saline (dotted blue line).

Fig. 4.

Cumulative expired particles per liter vs. time for all human subjects after inspiration of saline (n = 11 subjects) and of surfactant (n = 11 subjects). Cumulative expired particles were determined by summing up the expired particles per liter for all individuals of a group at each time point.