Question

1. (a) Explain how CO interacts with the circulatory system, especially the relationship among CO, CO2, and O2 in blood cells and how exposure to CO influences normal oxygenation mechanisms. (b) Why are individuals with heart disease at greater risk when exposed to elevated CO levels?

2. How is particle deposition and removal from the lung influenced by the size of the particles?

Answer 1

1 .It supplies oxygen and nutrients to our bodies by working with the respiratorysystem. At the same time, the circulatory system helps carry waste and carbon dioxide out of the body. Hormones — produced by the endocrine system — are also transported through the blood in the circulatory system.

(B) Higher levels of carbon monoxide were associated with higher risk of hospitalizations for cardiovascular heart disease

(2)

The mechanism of generation influences the particle size of the resultant bioaerosol (Table 1), and these may be biotic (e.g., sneeze or pollen), or abiotic where the aerosol is produced by a non-living system (e.g., water cooling towers). Irrespective, all aerosols will be generated with an initial mass median aerodynamic diameter (MMAD) that will decrease with increased distance from the source due to evaporation and settling dependent on environmental parameters such as relative humidity and turbulence.

All mechanisms of human oro-nasal activity such as breathing, talking, laughing, coughing and sneezing produce particles within the inhalable range for humans of <1 to >100 μm (Table 1). Significant variation occurs between studies regarding number of particles expelled, size range of the particles and the number of pathogens incorporated within the particles, attributable to differences in methodology and human factors where standardization is difficult.21,26,28,36,37,39 Comparatively, coughing and sneezing produce greater quantities of particles28,36,37 that travel further due to the velocity of expulsion from the nose or mouth.40 The majority of these particles reside in the inhalable fraction for humans (i.e., <100 μm) at 78.6–96.0% and 98.9% for coughing and sneezing respectively; while of this inhalable fraction, 7.1–46.7% and 18.8% produced by coughing and sneezing were less than 4 μm, evaporating to droplet nuclei and deposit in the bronchoalveolar region of the lung.28,36,37

The situation in relation to deposition is more complex due to evaporation. Atmospheric relative humidity (RH) and temperature are generally lower than that of the body. Once the particles are in the atmosphere evaporation occurs at rates according to their original size and composition of the particle to reach equilibrium with atmospheric conditions. Hence, the aerosol produced is dynamic, changing with distance from the initial point of generation. Particles produced from sneezing and coughing will contain varying amounts of saliva and mucus comprising inorganic and organic ions plus glycoproteins.33,38 Many aerosol transmission modeling studies are based on assumptions e.g., settling velocities and/or evaporation parameters of pure water droplets within a vacuum and droplet distributions from healthy volunteers.21,22It is probable that irrespective of composition due to the small droplet sizes originating from a cough or sneeze that evaporation will be rapid unless the presence of solutes greatly retards evaporation, for example, a 5 µm water droplet will evaporate within 0.8 s in 97% RH.21 However, extrapolating to natural situations where the droplet composition will be very different and turbulence will exert a large effect on how rapidly particles deposit requires care. Indeed, one recent study demonstrated that infected individuals generated larger aerosol particles than healthy counterparts.41 This could be attributable to differences in mucus (composition, quantity, and viscosity) produced during infection affecting evaporation and the location of the infection.33,42 The closer an individual is situated to an aerosol source then the greater the likelihood of large particles being inhaled prior to complete evaporation.

Similar principles can be extrapolated to any aerosol present in Table 1, simply the mechanism of generation, the solute type and concentrations (organic and inorganic) plus the surrounding environment will differ and therefore the processes of evaporation and dissemination will accordingly vary. Irrespective of whether aerosol particles are generated by abiotic or biotic processes (e.g., Table 1), inhalation of particles into the warm humid respiratory tract will prompt rehydration and affect deposition due to particle growth.43 It is evident that there is significant potential for URT deposition depending on how close an individual is to the source.