Airway Surface Liquid and Respiratory Mucus - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 775

Table 12.5. Duration and percentage of beat cycle of respiratory cilium beat stages assuming a
beat frequency of 20 Hz (Source: [ 1531 ]). Estimated speed of a cilium tip during effective stroke
is 1 mm/s.

Duration Percentage

Stage (ms) of beat cycle

Effective stroke 10 20

Rest 13 26

Recovery stroke 27 54

exists during which cilia do not beat [ 1571 ]. 27 At rest, the cilium lies parallel to the
cell surface pointing in the direction of mucus flow. The resting period separates
effective stroke that is mostly planar with an arc of about 110 degrees and recovery
stroke during which cilia sweep backward remaining close to the epithelium and
immersed in the periciliary fluid (without contact with the mucus layer).
Two beating stages result from the sliding of axonemal microtubules and permit
unidirectional propulsion of the mucus layer (Table 12.5 ): (1) a preparatory phase
with a backward motion and, after maximizing its height to interact with the mucus
gel, (2) a propulsion phase that provide impulse to the mucus. During effective
stroke, the bending cilium region passes progressively from the base to the tip to
become fully extended. During recovery stroke, the cilium curls backward in the
same plane. Cilia are more rigid in the forward power stroke and more flexible in
recovery stroke in preparation for the next effective stroke. The ciliary motion speed
differs between the 2 stages, with a quick rising phase and a slow sagging phase.
Elevation in ciliary beat frequency can be achieved by shortening a single or, most
often, several phases.

12.6.2.2 Ciliary Beat Frequency

Ex vivo, cilia of the nose, trachea, and large bronchi beat at a similar frequency
(10-20 Hz). The ciliary beat frequency of samples of human respiratory epithelium
ranges from 9.1 to 16.8 Hz [ 1572 ]. In patients examined by bronchoscopy, the
ciliary beat frequency is similar in nasal, tracheal, and lower lobe bronchial epithelia
(14 Hz), whereas it is slower in peripheral bronchi (10 Hz) [ 1573 ]. Ciliary beat
frequency in human nose in vivo is equal to 11.5 ± 1.6 Hz [ 1574 ] and that of

maxillary sinus mucosa in vitro to 16.6 3.0 Hz [ 1575 ]. Ciliary beat frequency

hence slightly differs between in vivo and in vitro condition.

±

27 Contact with a particle (size 50-75 m) stimulates ciliary beat. Only cilia surrounding the
particle in a patch about 10 times larger are beating at one time. Beat frequency is the highest in the
patch center, close to the particle, and decays toward patch edge. The moving patch of beating cilia
corresponds to a mucus plaque that is produced upon particle impact and surrounds the particle to
be removed. Contact on mucus-depleted epithelium produces a lower ciliary beat frequency.