  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.
