Characterizing respiratory aerosol emissions during sustained phonation

Abstract

Objective To elucidate the role of phonation frequency (i.e., pitch) and intensity of speech on respiratory aerosol emissions during sustained phonations. Methods Respiratory aerosol emissions are measured in 40 (24 males and 16 females) healthy, non-trained singers phonating the phoneme /a/ at seven specific frequencies at varying vocal intensity levels. Results Increasing frequency of phonation was positively correlated with particle production ( r = 0.28, p < 0.001). Particle production rate was also positively correlated ( r = 0.37, p < 0.001) with the vocal intensity of phonation, confirming previously reported findings. The primary mode (particle diameter ~0.6 μm) and width of the particle number size distribution were independent of frequency and vocal intensity. Regression models of the particle production rate using frequency, vocal intensity, and the individual subject as predictor variables only produced goodness of fit of adjusted R 2 = 40% ( p < 0.001). Finally, it is proposed that superemitters be defined as statistical outliers, which resulted in the identification of one superemitter in the sample of 40 participants. Significance The results suggest there remain unexplored effects (e.g., biomechanical, environmental, behavioral, etc.) that contribute to the high variability in respiratory particle production rates, which ranged from 0.2 particles/s to 142 particles/s across all trials. This is evidenced as well by changes in the distribution of participant particle production that transitions to a more bimodal distribution (second mode at particle diameter ~2 μm) at higher frequencies and vocal intensity levels.

Respiratory particle emission rates from children during speaking

“…However, an accurate comparison of the measured concentrations between our study and previous studies cannot be easily achieved because of the different methodologies applied in the experimental studies in terms of experimental apparatus, respiratory activity, and type of volunteers. Nonetheless, a rough comparison with previous studies reveals that the particle concentrations we measured for children were within the ranges measured for similar speaking activities performed by adolescents and adults 24 , 25 , 27 , 31 – 33 as shown in Table 3 .…”

“…Nonetheless, these challenges in measuring the respiratory particles and the difficulty of recruiting and working with human participants have resulted in a limited number of studies reporting on respiratory particle emission characteristics with a limited number of subjects (generally fewer than 20) and a range of different methodologies. The experimental apparatus has varied; in some studies volunteers were asked to speak into a sampling funnel directly connected to the particle counter (the experiments were conducted in a HEPA filtered laminar flow hood, in a cleanroom, or in ambient air) 17 , 24 , 25 , 33 . In other studies the subjects had to speak into a large duct, where a constant airflow was generated by suction of a filter fan unit, and the measurement probe was placed at a certain distance from the volunteer 22 , 23 .…”

“…There have also been major differences in the testing protocols. For example, respiratory activities (breathing, speaking, singing, coughing, and shouting) were performed by pronouncing specific phonemes 25 , 26 or multiphonetic text (e.g., “Rainbow passage”) 26 with or without sound pressure level control 27 . Finally, volunteers involved in the studies have mainly included adolescents 22 and adults 26 , 32 , 34 , whereas little information on children aged 12 years and younger is currently available 17 , 23 , 35 .…”

Impact of respiratory aerosol size and number distribution on the relative importance of different routes in SARS‐CoV‐2 transmission

“…Singing has been associated with increased emission of respiratory aerosol relative to breathing (Lelieveld et al., 2020; Sommerstein et al., 2020). And respiratory particle production increases with both vocal intensity and phonation frequency (Ahmed et al., 2022), showing that the difference between singing and talking in respiratory aerosol emissions may lead to a higher risk of infection for choruses. Such information is consistent with the finding in this study that infection risk increases with the total number of respiratory aerosol particles emitted (Figure A8).…”

Resuspension of Seeded Particles Containing Live Influenza A Virus in a Full-Scale Laboratory

“…Therefore, the transport, deposition, and resuspension dynamics of viruses are governed by the properties of the carrier particles. The size distribution and composition of respiratory viral aerosol emissions have been well characterized [5,[20][21][22][23], but characterization of the carrier particles for resuspended viruses has not been reported in the literature.…”