Influence of pulmonary ventilation rate and breathing cycle period on the risk of cross-infection.

This study examined the characteristics of the exhaled airflow pattern and breathing cycle period of human subjects and evaluated the influence of pulmonary ventilation rate and breathing cycle period on the risk of cross-infection. Measurements with five human subjects and a breathing thermal manikin were performed, and the peak exhaled airflow velocity from the mouth and the breathing cycle period were measured. Experiments on cross-infection between two breathing thermal manikins were then conducted in a full-scale test room, in which the pulmonary ventilation rate and breathing cycle period were varied systematically. Both peak flow velocity and breathing cycle length varied considerably between different subjects. The breathing cycle period in a standing posture was 18.9% lower than in a sitting posture. The influence of pulmonary ventilation rate and breathing cycle period extended up to a separation distance of 1.0 m between the two manikins. Increasing the pulmonary ventilation rate of the exposed person greatly increased the risk of cross-infection. Decreasing the breathing cycle period from the widely used "6 second" value led to a considerable increase in the risk of cross-infection. Standing posture resulted in a higher risk of cross-infection than sitting posture.