Transmission of droplet-conveyed infectious agents such as SARS-CoV-2 by speech and vocal exercises during speech therapy: preliminary experiment concerning airflow velocity
Résumé
Purpose Infectious agents, such as SARS-CoV-2, can be carried by droplets expelled during breathing. The spatial dissemination
of droplets varies according to their initial velocity. After a short literature review, our goal was to determine the
velocity of the exhaled air during vocal exercises.
Methods A propylene glycol cloud produced by 2 e-cigarettes’ users allowed visualization of the exhaled air emitted during
vocal exercises. Airflow velocities were measured during the first 200 ms of a long exhalation, a sustained vowel /a/ and
varied vocal exercises. For the long exhalation and the sustained vowel /a/, the decrease of airflow velocity was measured
until 3 s. Results were compared with a Computational Fluid Dynamics (CFD) study using boundary conditions consistent
with our experimental study.
Results Regarding the production of vowels, higher velocities were found in loud and whispered voices than in normal voice.
Voiced consonants like /ʒ/ or /v/ generated higher velocities than vowels. Some voiceless consonants, e.g., /t/ generated
high velocities, but long exhalation had the highest velocities. Semi-occluded vocal tract exercises generated faster airflow
velocities than loud speech, with a decreased velocity during voicing. The initial velocity quickly decreased as was shown
during a long exhalation or a sustained vowel /a/. Velocities were consistent with the CFD data.
Conclusion Initial velocity of the exhaled air is a key factor influencing droplets trajectory. Our study revealed that vocal
exercises produce a slower airflow than long exhalation. Speech therapy should, therefore, not be associated with an increased
risk of contamination when implementing standard recommendations.