Quantifying Exhaled Particles in Healthy Humans During Various Respiratory Activities Under Realistic Conditions

Background: Quantitatively collecting and characterizing exhaled aerosols is vital for infection risk assessment, but the entire droplet size spectrum has often been neglected. We analyzed particle number and size distribution of healthy participants in various respiratory activities, considering inter-individual variability, and deployed a simplified far-field model to inform on infection risks. Methods: Participants repeated the same respiratory activities on two visits. Particles were collected using an airtight extraction helmet supplied with High Efficiency Particulate Air (HEPA) filtered air. The sampling volume flow was transported to two particle counters covering the small and large particle spectrum. The applied simple mass balance model included respiratory activity, viral load, room size, and air exchange rates. Results: Thirty participants completed the study. The major fraction of the number-based size distribution was <5 μm in all respiratory activities. In contrast, the major fraction of the volume-based size distribution was 2-12 μm in tidal breathing, but >60 μm in all other activities. Aerosol volume flow was lowest in tidal breathing, 10-fold higher in quiet/normal speaking, deep breathing, coughing, and 100-fold higher in loud speaking/singing. Intra-individual reproducibility was high. Between participants, aerosol volume flow varied by two orders of magnitude in droplets <80 μm, and three orders of magnitude in droplets >80 μm. Simple model calculations not accounting for potential particle size-dependent differences in viral load and infection-related differences were used to model airborne pathogen concentrations. Conclusions: Quantitative analysis of exhaled aerosols for the entire droplet size spectrum as well as the variability in aerosol emission between individuals provides information that can support infection research. Clinical Trial Registration number: NCT04771585.

Exhaled particles as markers of small airway inflammation in subjects with asthma

Exhaled breath contains suspended particles of respiratory tract lining fluid from the small airways. The particles are formed when closed airways open during inhalation. We have developed a method called Particles in Exhaled air (PExA^® ) to measure and sample these particles in the exhaled aerosol. Here, we use the PExA^® method to study the effects of birch pollen exposure on the small airways of individuals with asthma and birch pollen allergy. We hypothesized that birch pollen-induced inflammation could change the concentrations of surfactant protein A and albumin in the respiratory tract lining fluid of the small airways and influence the amount of exhaled particles. The amount of exhaled particles was reduced after birch pollen exposure in subjects with asthma and birch pollen allergy, but no significant effect on the concentrations of surfactant protein A and albumin in exhaled particles was found. The reduction in the number of exhaled particles may be due to inflammation in the small airways, which would reduce their diameter and potentially reduce the number of small airways that open and close during inhalation and exhalation.

Characterization of exhaled particles from the human lungs in airway obstruction

BACKGROUND

Human breath contains small particles that might be useful for the noninvasive diagnosis of lung disease. In this study, the impact of airway obstruction on particle emission was investigated.

METHODS

Particle number flux and particle size distribution were measured for healthy nonsmokers (n=16), healthy smokers (n=13), patients with chronic obstructive pulmonary disease (n=28, GOLD stage I-IV), and patients with asthma before and after methacholine challenge (n=10). The measurements were carried out using a condensation nucleus counter (TSI 3760) and a laser spectrometer (PMT LASAIR II-110).

RESULTS

Particle number per breath showed high intrasubject reproducibility. However, there was a large intersubject variability in the number of emitted particles on the order of two magnitudes, with no influence of airway obstruction on emission level. Methacholine-induced airway obstruction, in subjects with allergic asthma, did not change the number of exhaled particles, when compared with prechallenge values. For the droplet size distribution averaged per breath, there was no difference between healthy subjects and subjects with airway obstruction.

CONCLUSIONS

Airway obstruction does not change the number flux or size distribution of particles in exhaled breath. The high intersubject variability of particle emission supports the concept of online determination of aerosol properties (primarily number flux, during exhaled breath) during breath condensate sampling to properly normalize the results of biochemical analysis. As high dilution and variable dilution are the main challenges of biomarker assessment in exhaled breath condensate, this normalization procedure would significantly add to the value of the technique.