Transmission of droplet-conveyed infectious agents such as SARS-CoV-2 by speech and vocal exercises during speech therapy: preliminary experiment concerning airflow velocity

TL;DR

This study measures airflow velocities during speech and vocal exercises to assess droplet spread risk, finding that vocal exercises produce slower airflow than long exhalation, suggesting lower contamination risk in speech therapy.

Contribution

It provides experimental data on airflow velocities during various vocal exercises, comparing them with CFD simulations, and highlights implications for infection control in speech therapy.

Findings

Higher velocities in loud and whispered voices compared to normal speech

Voiced consonants generate higher velocities than vowels

Long exhalation produces the highest airflow velocities

Abstract

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 /3/ 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.