Effect of Heart Rate on Aerosol Recovery and Dispersion in Human Conducting Airways After Periods of Breathholding

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Abstract
With a newly developed aerosol inhalation device, small volumes of aerosols ("boluses") can be inspired predominantly into the conducting airways of the human lungs. The aerosol is injected by a fast-operating valve system using preselected volumes near the end of a clean air inhalation of 1000 cm3. Particle behavior in upper human airways was investigated by measuring particle recovery and bolus dispersion in exhaled air with a laser photometer positioned directly in front of the mouth after various periods of breathholding. The effect of physical motion of the heart on these measurements has been investigated by increasing the heart rate of a subject by more than a factor of 2. Monodisperse sebacate aerosols were used with droplets in the aerodynamic size (dac) range between 0.8 and 1.1 micron to minimize particle losses by diffusion and by inertial forces. It was shown that motion of the heart considerably influences both particle recovery and dispersion of such boluses during postinhalation periods of breathholding. For a twofold enhancement in heart frequency the standard deviation of the expired aerosol bolus was increased by up to 60% after certain breathholding periods. Particle recovery from shallow volumetric lung depths was significantly decreased.