Page 255 - Industrial Ventilation Design Guidebook

2 S 6 CHAPTER 5 PHYSIOLOGICAL AND TOXICOLOGICAL. CONSIDERATIONS

FIGURE 5.24 Components of ciliary movement, (a) Power and recovery phases of ciliary move-
ment. Arrows indicate the direction of ciliary travel, (b) Net mucociliary transport Dotted arrows show
the direction of cilia while the solid arrows show mucus transport. Note that net gel movement is for-
ward in I and III while no gel movement occurs in II during the cilia recovery phase. Modified from Ful-
29
ford and Blake.

parallel to the cell surface significantly reduce retrograde momentum ex-
erted on the surrounding fluid during the ciliary recovery phase because
periciliary fluid viscosity is much lower than that of mucus gel. In addi-
tion, the no-slip condition along the epithelial surface also retards retro-
grade movement. Mucus viscosity and the presence of surrounding cilia
further retard any retrograde mucus movement such that gravity has little
effect on tracheobronchial mucociliary transport.
Derangement of metachronal motion impedes mucosal movement and
increases the risk of disease or injury. Slowing mucosal velocity increases
residence times in the affected airway region, permitting greater diffusion
of deposited pathogens and toxins through periciliary fluid and increasing
the risk of direct injury to airway epithelium and systemic injury via the
bloodstream. Reducing the number, activity, or coordination of adjacent
cilia or ciliary fields, hypersecretion of serous fluid or mucus gel, increased
periciliary or mucus viscosity, and excessive periciliary fluid evaporation
can each adversely affect mucociliary transport. Inspiring dry or cold air or
cigarette smoke decreases periciliary fluid depth (altering cilia penetration
into mucus gel) and cilia beat frequencies, which slows mucociliary trans-
port. In addition, changes in periciliary fluid pH, ion concentration, or vis-
cosity due to deposited chemicals, microorganisms (e.g., influenza,
mycoplasmas), or systemic disease (e.g., asthma, cystic fibrosis) also in-
hibit ciliary beat frequency.