On the Dynamics of the Aerosol Plume in Common Bottlenose Dolphin Respiratory Events

Abstract

This study examines the trajectories, size, and spatial distribution of aerosols during breathing events of common bottlenose dolphins (Tursiops truncatus) in the National Aquarium in Baltimore, MD. Accounting for the aerodynamic drag and inertia of the small droplets, the trajectories are used for estimating the volumes and flow rates of the exhaled and inhaled air. Data are acquired by training two male and four female dolphins to breathe at the side of the pool within the field-of-view of a high-speed holography system. Droplet-tracking and size measurements are performed for twenty-six datasets involving normal, chuff, and post-exercise breaths, some repeated to assess repeatability. The exhaled liquid originates either from the respiratory system or from the water trapped above the blowhole. The 150-400 ms exhalations have multiple velocity peaks, with the maximum air speed occurring during the first peak for post-exercise breaths. The droplet concentrations and sizes peak at the time of maximum velocity and then gradually decrease. The exhaled liquid volumes vary between 0.1-16 mL, peaking for post-exercise breaths. About 0.5% of the exhaled aerosol travels 2-5 times faster than the surrounding air and droplets, presumably due to ejection from deep within the respiratory tract. A fraction of the airborne liquid (0.02-1.0 mL) is subsequently inhaled during the more than 550 ms long inhalation phase, characterized by low speeds and small droplets. The exhaled and inhaled tidal volumes estimated from the trajectories are consistent with prior measurements of dolphins in the wild and other facilities. To the best of our knowledge, the droplet concentrations, size distributions, and total liquid volumes ejected and aspirated have never been reported for common bottlenose dolphins. Such data are vital for assessing the aerosols generated and inhaled by surface breathing mammals, a critical first step in characterizing health risks to cetaceans in adverse environments.