Effects of Spoken Phones and Patient Characteristics on Respiratory Aerosol Emission

Objectives: This study investigates how the production of three different phones ([a], [o], [r]), as well as breathing, coughing, and individual characteristics, influences respiratory particle emission. Design: Experimental study. Methods: Particle size distribution and sound pressure levels (SPL) were measured in 41 infection-free participants under controlled conditions. The measurement instruments, condensation particle counter (3775, TSI Inc.), and aerodynamic particle sizer (APS 3321, TSI Inc.), covered the size range of 0.004-10 µm. Exhaled flow rates were calculated from CO₂ concentrations measured with LI-840A NDIR gas analyzer (LI-COR Environmental). Results: Production of [o] generated more particles than production of [a] across all size fractions. The alveolar trill [r] generated more small particles than did the vowels. SPL had a consistent positive effect on particle generation but did not fully explain the differences. Exhaled flow rates showed no statistical differences between the phones. Higher age was associated with elevated particle emission in breathing. Higher exhaled flow rate and higher body mass index (BMI) were associated with higher particle emission in coughing. No systematic connection between peak expiratory flow (PEF) or sex and particle emission was observed. Conclusions: Understanding respiratory aerosol generation, in different situations and individuals, is critical for advancing knowledge of airborne transmission of diseases. Our findings corroborate prior evidence of an association between SPL and particle emission in voiced activities. Particle production also varies systematically across different phones, irrespective of SPL. The predominance of small particles in the phonation of [r] suggests the production of satellite particles from the tongue vibration. The higher particle generation in the phonation of [o] compared with [a] suggests the oral opening may contribute to the number of emitted particles. None of the individual characteristics—age, sex, BMI, or PEF—was a systematic predictor of particle production across all respiratory activities.